Vision restoration using a light-responsive small molecule photoswitch (KIO-301) in advanced retinitis pigmentosa: the ABACUS-1 phase 1/2 clinical trial

Vision restoration using a light-responsive small molecule photoswitch (KIO-301) in advanced retinitis pigmentosa: the ABACUS-1 phase 1/2 clinical trial | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Vision restoration using a light-responsive small molecule photoswitch (KIO-301) in advanced retinitis pigmentosa: the ABACUS-1 phase 1/2 clinical trial Robert Casson, Eric Daniels, Christen Barras, Andrew Dwyer, Brian Strem, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8060107/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Apr, 2026 Read the published version in Nature Medicine → Version 1 posted You are reading this latest preprint version Abstract A small, azobenzene, photoswitch molecule (KIO-301) that renders retinal ganglion cells responsive to light was investigated for safety and activity in a first-in-human, phase 1/2, open-label, dose-escalation clinical trial in individuals with advanced retinitis pigmentosa. KIO-301 was delivered by intravitreal injection to 12 eyes of 6 participants. The primary endpoint was safety. Secondary endpoints included assessment of functional vision, visual acuity, kinetic visual field, functional magnetic resonance imaging (fMRI) and participant reported outcomes. There were no drug-related adverse events. A participant with no light perception at baseline recovered light perception by 2 days post injection. Visual function, including navigational ability, displayed a trend of improvement. By day 2-14 post injection the fMRI signal to visual stimuli in the primary visual cortex was enhanced and decayed over the ensuing 3 weeks. Participant-reported quality of life improved. The excellent safety profile and evidence supporting proof-of-principle has motivated a larger, randomized controlled trial. Health sciences/Health care/Therapeutics/Biological therapy Biological sciences/Neuroscience/Visual system/Retina Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Main Retinitis pigmentosa (RP) comprises a genetically heterogeneous group of inherited retinal dystrophies (IRDs) characterized by gradual rod-cone photoreceptor degeneration associated with night blindness, visual field loss, and progression to profound visual impairment in most affected individuals by middle age. RP is a leading cause of blindness in the working-age population in high-income countries, with an estimated prevalence of approximately 1 in 3,000 - 4,000. 1-3 The number of known causative genes encompassing syndromic and non-syndromic variants continues to grow and currently exceeds 450. 4 The large number of monogenic variants makes gene-agnostic therapeutic strategies clinically attractive. A variety of approaches are being investigated, including optoelectronic prosthetics, cellular replacement approaches, and optogenetics. 5 We have pursued an alternative gene-agnostic approach that exploits properties of a novel small molecule photoisomer (KIO-301), rendering surviving retinal ganglion cells (RGCs) responsive to light. 6 Specialized light-detecting cells are highly phylogenetically conserved, and in all metazoans, the natural photoisomer in the classical photoreceptors is 11-cis-retinal. 7 Light-induced change in its molecular configuration stimulates a biochemical cascade which hyperpolarizes photoreceptors, reducing glutamate release to bipolar cells, which in turn synapse with RGCs, the third-order neurons of the visual pathway. RGCs are analogous to digital converters, receiving graded excitatory input from bipolar cells and inhibitory input from amacrine cells, resulting in transmission of digitized information encoded as action potentials to the occipital cortex in the brain. In RP, rods and cones progressively degenerate, while variable secondary pathological changes in the inner retina have been reported. 8 In a large histopathological series of genetically diverse RP, approximately two-thirds of RGCs were retained in the central retina of affected eyes compared to healthy controls, implying that therapeutic strategies targeting stimulation of RGCs has a rational histopathological foundation. 9 Synthetic molecules that isomerize and alter configuration in response to photon interaction, in a manner analogous to cis -retinal, have been termed “photoswitches”. 10 In preclinical studies, these small molecules were shown to enter RGCs and render endogenous voltage-gated cation channels sensitive to light without requiring genetic manipulation, and thus enabling photocontrol of action potential generation. 6,10,11 In 2014, Tochitsky et al. reported that the azobenzene photoswitch DENAQ restored electrophysiological and behavioural responses in blind rd1 mice (a murine model of severe RP) for several days after a single intraocular injection. 10 Subsequently, Tochitsky et al. developed a longer-acting photoswitch molecule, BENAQ, which restored visual responses in rd1 mice for several weeks after a single intraocular injection. 11 In mice and rabbits, BENAQ was nontoxic at concentrations 10-fold higher than that needed to confer photoresponsiveness. 11 The mechanism of action of this photoswitch is depicted graphically in Figure 1 . Here, we report the first-in-human translation of this photoswitch small molecule. ABACUS-1 was a phase 1/2, single-dose, open-label dose-escalation trial of BENAQ, developed and formulated for ophthalmic therapy as KIO-301 administered by intravitreal injection (IVT) to 12 eyes of 6 individuals legally blind from advanced RP. Results Confirmation of KIO-301 Activity Prior to administration, activity of KIO-301 drug substance was confirmed in vitro using explanted retinas from retinal degeneration type 1 (rd1) mice and a multielectrode array (MEA) recording system. Using this model, after treatment with 100 µM KIO-301, explanted rd1 retinas responded rapidly and reliably to light flashes with spikes elicited quickly (within 100 msec) after light onset and ceasing quickly (within 200 msec) after light termination. Untreated retinas from rd1 mice showed no detectable light responses ( Supplementary Figure 1 ), consistent with loss of functional rods and cones. Participants’ demographic and clinical characteristics After screening and review of inclusion and exclusion criteria, six (6) participants (12 eyes) with a clinical diagnosis of advanced RP and a median age of 68.5 years were enrolled into the study. The demographic and clinical characteristics of the participants are shown in Supplementary Table 1 , with 3 participants (Cohort 1) having baseline vision clinically diagnosed as either no light perception (NLP) or bare light perception (BLP), corresponding to a logarithm of the minimal angle of resolution (logMAR) > 2.9 using the Berkeley Rudimentary Vision Test (BRVT). The other 3 participants (Cohort 2) were clinically diagnosed as hand motion (HM) or count fingers (CF), corresponding to logMAR ≤ 2.9 and > 1.6 using the BRVT. All enrolled participants completed the study and there were no early discontinuations or early withdrawals. Study overview The ABACUS-1 study was registered in ClinicalTrials.gov (NCT05282953) and was conducted at two sites in Adelaide, Australia with approval from the Central Adelaide Local Health Network Human Research Ethics Committee. The study was conducted in full conformity with all applicable laws and regulations, including the International Conference on Harmonisation Guidelines for Good Clinical Practice (CPMP/ICH/135/95) and relevant articles of the Declaration of Helsinki (seventh revision, 2013). Written informed consent was obtained from each study participant. The dosing protocol is shown in Figure 2 . In Part 1 of the study, Cohort 1 received 7.5 µg of KIO-301 and Cohort 2 received 25 µg of KIO-301 to the right eye ( oculus dexter , OD). In Part 2 of the study the contralateral eyes were treated, occurring between 70-100 days after administration of KIO-301 OD; specifically, Cohort 1 participants received 25 µg of KIO-301 and Cohort 2 participants received 50 µg of KIO-301 into the left eye ( oculus sinister , OS). KIO-301 was administered by standard 50 µL IVT injection and participants were followed longitudinally for study assessments on day 1 (pre and post injection) and post-injection days 2, 3, 7, 8, 14, 15, 29 with the final study visit on day 30 (all +/-1) for each part of the study. Systemic and ocular safety were monitored throughout the duration of the trial. Primary outcome: safety There were no serious adverse events (SAEs), nor any systemic or definitive ocular drug-related adverse events (AEs) reported. Vital signs, hematology, biochemistry and electrocardiographic parameters of all participants were normal pre- and post-injection. Reported ocular AEs included mild ocular discomfort and mild swelling in the peri-injection period (deemed unrelated to KIO-301) in one participant (administered 25 µg KIO-301 OS) and mild increased intraocular pressure (IOP) in a second participant (administered 7.5 µg KIO-301 OD). This participant had borderline elevated IOP in both eyes at baseline and slightly increased (27 mmHg) IOP recorded after IVT administration of KIO-301 into the right eye only. The OD event was coded as mild in nature and possibly related to KIO-301 and was managed with a standard single-agent topical ocular hypotensive medication. No participant developed any signs or symptoms of intraocular inflammation. The anterior and vitreous chambers were normal on slit lamp examination at all time points. At no time point was the drug visible in the vitreous. There were no changes to the fundus appearance in any participant, nor any changes noted on optical coherence tomography (OCT). No participant developed macular edema. A complete listing of ocular AEs is shown in Table 1 . Secondary outcomes: visual assessments Light Perception Participants were asked to indicate when they saw a randomly repeating, illuminated image of a letter ‘X’ on a dark background across multiple attempts (see Methods). The mean correct responses with the treated eyes of all 3 participants in Cohort 1 improved from baseline and is shown in Supplementary Figure 2 . One participant who had been without any light perception for over 10 years regained the ability to perceive light 2 days after IVT. His experiences were recorded in a post study interview ( Supplementary Video 1 ). Participants in Cohort 2, the group with better baseline visual acuities, had a higher baseline of light perception with no observed changes in this endpoint post injection. Visual acuity Visual acuity was assessed with the BRVT and recorded as a logMAR score, with a reduction in logMAR corresponding to an improvement in visual acuity (see Methods). Due to the severe stage of RP for participants in Cohort 1, the visual acuity was not measurable on this scale and was recorded as logMAR > 2.9 at all timepoints, including baseline. The mean logMAR of the participants’ treated eye in Cohort 2 improved from 2.1 +/- 0.2 at baseline to 2.0 +/- 0.1 at day 29 (mean +/- SEM, n = 3 treated eyes, 3 eyes dosed at 25 µg OD- Figure 4a ) indicating a slight improvement in acuity. The mean logMAR of Cohort 2 participants treated at the higher dose was observed to have a further reduction in logMAR over the course of the study. Kinetic visual field Manual Goldmann kinetic perimetry with an illuminated light stimulus (440-460 nm range) was used to assess the visual fields of participants (see Methods). As shown in Figure 4b , the extent of the mean field of vision in the treated eye of all participants at all doses of KIO-301 increased from baseline by 15 degrees and plateaued from day 15 through day 30. Functional vision testing Functional vision was assessed during the study via a series of four (4) standardized orientation and mobility assessments at various light levels as described in Methods. Due to the range of profound visual impairment, some participants were unable to perform certain tasks at varying light levels. Walking Direction Test At baseline, participants demonstrated an approximately 50% chance of determining walking direction, as expected by chance alone. However, this increased to 70% by day 15 and had reverted to baseline by day 30. ( Figure 4a , all light levels- 45, 125, & 350 lux, n = 10 treated eyes from 6 participants administered 7.5 µg, 25 µg or 50 µg KIO-301). Window Location Test The Window Location Test was conducted in Cohort 1 patients only (deemed prior to study initiation as this task was not challenging for Cohort 2 participants). The proportion of successes which a participant could successfully locate a window increased from 44% to 56% one day after administration of KIO-301 and peaked at 63% 7 days later. ( Figure 4b , 350 lux, n = 5 treated eyes from 3 participants administered KIO-301 at 7.5 µg OD and 25 µg OS). Room Exit Test The ability to navigate accurately through a room, locating the exit in high contrast, increased from a 37% success rate at baseline to a 67% success rate 14 days after administration of KIO-301 ( Fig. 4c ). This response then trended downward at day 30 across all participants administered the test and at all doses of KIO-301 administered. Door Location Test The Door Location Test was conducted in all Cohort 2 participants and 1 participant in Cohort 1. There was no clear change in the ability to successfully locate and navigate to a door after administration of KIO-301 ( Fig. 4d ). Functional magnetic resonance imaging (fMRI) There was evidence of a qualitative increase in the primary visual cortex and extra-striate visual cortex BOLD signal in response to light stimuli applied to the treated eyes (Figure 6a), with activations of variable intensity and a statistically significant increase in mean voxels ( Figure 6b ) on quantitative analyses at all timepoints compared to baseline (mean +/- SEM; checkerboard stimuli; n = 12 eyes from 6 participants administered KIO-301 at 7.5, 25 or 50 µg; p < 0.05, z threshold = 3.1). This increase peaked on day 3 (2 days after treatment), was reduced at day 14 and then remained stable and significantly above baseline at day 29. Predominant visual stimulus signal contributions were derived from the flickering checkboard and on/off paradigms. Quality of Life The composite QoL score, measured using the National Eye Institute Visual Function Questionnaire-25, across all 6 participants increased by a mean of 4.2 points from baseline to day 29 after administration of KIO-301 ( Supplementary Figure 3 ). pK sampling The concentration of KIO-301 in plasma was below the limit of quantitation (0.2 ng/mL) in all study participants at 4 hours (+/- 15 minutes) and at 14 days after IVT administration except for one participant in Cohort 2 who received 50 µg OS (0.215 ng/mL) at 4 hours post-injection. Discussion There is an urgent unmet need for safe and cost-effective vision restoration approaches for individuals affected by IRDs. KIO-301 is an intravitreal formulation of the photoswitch molecule, BENAQ chloride, which in pre-clinical studies was shown to selectively enter RGCs downstream of degenerated photoreceptors and render endogenous voltage-gated cation channels sensitive to light without requiring genetic manipulation, thus enabling photocontrol of optic nerve action potential generation in response to light. 6,10,11 In this first-in-human clinical trial of any photoswitch molecule, KIO-301 demonstrated an excellent tolerability. There were no serious adverse events nor definite drug-related adverse events. No intraocular inflammation was evident at any time point (a known drawback of viral vector-based gene therapy approaches to IRDs). 12 There was no change in the vitreous or fundus appearance, nor any change to the macula OCT imaging. All adverse events were minor and are well-described features of IVT injections, including transient pain and mild ocular hypertension. The standard IVT injection procedure is usually well tolerated under topical anaesthesia in an office setting and indefinite injections at intervals of 1-3 months are commonly performed to treat neovascular age-related macular degeneration and other retinal disorders. Hence, intravitreal delivery of a therapeutic agent that can potentially recover visual function in RP is clinically feasible. Although safety was the primary endpoint of the ABACUS-1 trial, establishing proof-of-concept effectiveness in a clinical setting was also an objective. Of note, the study also provided valuable information on the challenges and applicability of assessments that can be utilised to explore clinical effectiveness in a population of patients with profound vision loss. In this study, we utilized a panel of visual function assessments, incorporating a simple light perception test, visual acuity testing using the BRVT, visual field testing, a panel of four multi-luminance orientation and mobility tests, functional MRI, and standardized patient-reported outcomes. Although limited by low patient numbers and challenges in adapting these assessments to the ultra-low vision population of ABACUS-1, the most striking clinical observation was the concordance of improvements revealed by these multiple vision endpoints and consistency of response. The general improvement in visual function following intravitreal KIO-301 administration may have several mechanisms. First, the direct conferral of light sensitivity to RGCs is likely to restore light-sensing function to the retina and is the presumptive mechanism responsible for conferral of light perception to the NLP-vision individual in this study. Remarkably, BENAQ and other ‘second generation’ photoswitches appear to selectively target RGCs downstream of degenerating photoreceptors while not affecting the physiology of intact areas of retina in murine models. 10 Such a mechanism would be expected to increase the visual field of individuals with partial retinal degeneration but some intact central vision, as was seen in our subjects with less advanced disease. Finally, in mice, photoswitches appear to suppress the 5-10 Hz rhythmic ‘noise’ in RGC firing that occurs after outer retinal degeneration, 14 which would be expected to improve signal-to-noise and visual acuity in both injected and potentially contralateral eye vision. Such an effect has been noted following unilateral gene therapy for Leber hereditary optic neuropathy. 15 The correlation between objective, subjective and imaging efficacy endpoints aligns with the underlying mechanism of action of KIO-301 and, along with the high level of tolerability demonstrated in this phase 1/2 study is an encouraging early sign which has motivated a larger phase 2 trial of this photoswitch technology. Methods Preclinical Retinal Explant Assessment Ethical approval for the research involving animals was obtained from the UC Berkeley Institutional Animal Care and Use Committee. KIO-301 was prepared as a concentrated 10 mM stock solution in DMSO and stored at -20 o C in darkness. A working solution of 100 µM KIO-301 was prepared by diluting the stock into physiological saline. Retinas obtained from P30-P60 rd1 mice were treated with the working solution for 30 min at 21 o C, followed by thorough washing with drug-free saline for 10 min. Retinas were mounted on a 60-electrode multi-electrode array (Multi Channel Systems, Holliston, MA, USA), inner retina side down, for simultaneous extracellular spike recording from many RGCs. Light responses were elicited with brief (1 s) flashes from a 455 nm LED light source at ~1.5 mW/cm 2 intensity, simulating photopic stimulation. To quantify the strength of the light response in KIO-301-treated retinas, we measured the photoswitch index for each unit in the recording, defined as the mean frequency of spiking during the light flash minus the mean frequency in darkness, divided by the sum of the mean frequencies in light plus darkness. The photoswitch index provides a measure of the change in firing elicited by light, correcting for differences in background firing rate (i.e. in darkness) observed different retinal samples. ABACUS-1 – Details of the Study Protocol Ethical and Regulatory Considerations The ABACUS-1 study was registered in ClinicalTrials.gov (NCT05282953) and was conducted at two sites in Adelaide, Australia with approval from the Central Adelaide Local Health Network Human Research Ethics Committee. The study was conducted in full conformity with all applicable laws and regulations, including the International Conference on Harmonisation Guidelines for Good Clinical Practice (CPMP/ICH/135/95) and relevant articles of the Declaration of Helsinki (seventh revision, 2013). Written informed consent was obtained from each study participant. Study Design ABACUS-1 enrolled 6 participants with legal blindness due to RP into the open label, unmasked, dose escalating phase of the study. The sample size was estimated to provide information about safety. Dose escalation was conducted in two parts with safety data reviewed by a safety monitoring committee before confirming whether escalation to a higher dose level could occur. KIO-301 was administered as a single 50 µL IVT injection OD (Part 1) and OS (Part 2). During Part 1 of the study, 3 participants with RP and NLP or BLP vision received 7.5 µg KIO-301 (Cohort 1) and 3 participants with RP and either LP, CF, or HM vision received 25 µg KIO-301 OD (Cohort 2). All participants were followed longitudinally for 1-month via weekly study visits during which safety and efficacy assessments were carried out. During Part 2 of the study, the same 3 participants with RP and NLP or BLP (Cohort 1) received 25 µg KIO-301 and the same 3 participants with RP and CF or HM (Cohort 2) received 50 µg KIO-301 OS. Study visits and safety and efficacy assessments were as per Part 1. Systemic and ocular safety was followed for each participant throughout the entire study period. Inclusion/Exclusion Criteria Participants were enrolled into the study if they were willing and able to provide informed consent for participation in the study. The following key inclusion criteria for Cohort 1 and 2 of the study were applied: (1) aged between 18 to 80 years (unless otherwise approved by the principal investigator) and able to comply with the study protocol, attend all study visits and adequately perform all study assessments, (2) had a clinical diagnosis of RP, (3) similar VA in both eyes ( 2.9 using the BRVT) or CF or HM for cohort 2 (confirmed with a logMAR 1.6 using the BRVT). Key exclusion criteria were as follows: (1) evidence of material/substantial optic nerve disease, (2) history of retinal detachments, (3) other clinically significant ocular disease or opacities which might interfere with the study assessments, (4) high intraocular pressure (IOP) > 22 mmHg, (5) previous intraocular surgery (excluding phacoemulsification surgery with intraocular lens implant), (6) aphakia, (7) any psychiatric condition, medical condition or co-morbidities which in the view of the Investigator is likely to interfere with the study or put the participant at risk, (8) any routine contraindication to MRI, including MRI-incompatible metal containing implant or object such as pacemakers, intracranial aneurysm clips, cochlear implants, drug infusion devices, prosthetic devices, contraceptive devices, shrapnel, pins, screws or wire mesh. Statistical Analyses This was a first-in-human trial with qualitative safety data as the primary outcome. There were no a priori hypotheses concerning the clinical data; hence, no null hypothesis significant testing was reported. The fMRI data was statistically analysed as described below. Clinical Assessments Safety The primary endpoint of this study was safety assessed by (1) incidence of AEs, serious AEs and deaths; (2) spectral domain OCT of overall retinal thickness and thickness of individual layers; (3) fundus autofluorescence (FA) of the retina; (4) slit lamp assessment of the anterior segment; (5) IOP with Goldmann applanation tonometry; (6) vital signs and electrocardiography; (7) clinical chemistry and hematology; (8) serum pharmacokinetics. Efficacy Assessments Key secondary efficacy endpoints included assessment of (1) light perception as measured by an unprompted, multi-luminance, back-projected letter display; (2) visual acuity using the BRVT; (3) kinetic visual field using a modified Goldmann device; (4) functional vision via a series of standardised multi-luminance orientation and mobility assessments (MLOM); (5) functional magnetic resonance imaging; and (6) National Eye Institute Visual Function Questionnaire-25. Light Perception This assessment involves showing the subject a series of videos and recording whether or not the subject perceived the visual stimulus, which was always an ‘X’ located at various locations on a screen. A strip of tape in front of the screen marked 60 cm where the center of the chair was placed and the patient seated. This assessment is meant to be performed as a monocular test and, therefore, an eyepatch was used to occlude the eye not being tested while assessing the contralateral eye. A unique video file driving the display of Xs on the screen was produced to correspond for each visit. There was also a setting for three different brightness levels (ranging from 3e14 photons/cm 2 /s (low), 1e15 photons/cm2/s (medium) and 5e15 photons/cm2/s (high), wavelength 400-800 nm). For each video, a series of six (6) images are displayed to the subject and the subject is instructed to verbally indicate if they perceive a particular shape or object and the responses are recorded as a success or failure. Vi sual Acuity Visual acuity (VA) was measured prior to pupillary dilation, both monocularly and then binocularly. and testing was performed under normal room illumination (between 250 and 1000 lux). VA assessment was performed using the Berkeley Rudimentary Vision Test (BRVT; Precision Vision, Woodstock, IL), as described by Bailey et al. 13 , which consists of presenting subjects three hinged card-pairs: Single Tumbling E Card-Pair (STE) Grating Acuity Card-Pair (GA) Basic Vision Card-Pair (BV) A testing flow chart, based on the ability of subjects to perform the required task, converts responses to a logMAR score. If the BV card-pair was not seen by the participant, light perception was assessed at 25 cm using a pen torch, and the resultant VA was either LP if seen, or NLP if not seen. Kinetic Visual Field This assessment involves measuring the subject’s visual field using a traditional Goldmann kinetic perimeter outfitted with a custom light source. All perimetric assessments were performed by trained orthoptists and/or optometrists. The subject’s visual field was mapped in both in a horizontal and vertical meridian and measurements were taken in triplicate and averaged. The total change in degrees was obtained by summing the average horizontal and vertical field changes. This was performed as a monocular assessment. Visual Function Tests The Ora-MLOM™ (Multiluminance Orientation & Mobility) installation included a modular lighting system and a series of orientation and mobility test floor layouts of varying difficulty conducted at 3 ambient light levels (45 lux (low), 125 lux (mid), 350 lux (high)) monocularly (OD and OS) and binocularly (OU). The Window Location test is a stationary test that requires the study participant to locate a randomly placed (front, left, centre, right, no window) white “window” approximately three feet by two feet attached to a black opaque screen for contrast. Each test is a sequence of 8 trials conducted at each lux level. The Walking Direction test is a stationary test that requires the participant to identify the direction of motion (to the left, to the right, or no motion) of a person walking between 2 opaque screens located 10 feet in front of them. Each test is a sequence of 6 trials conducted at each lux level. The Door Location test is a straight-line mobility course that requires a participant to locate and navigate to a randomly located (left, right centre) high-contrast door-like object placed on a wall 12 feet in front of them. Each test is a sequence of 6 trials conducted at each lux level. The Exit Room Test is a straight-line mobility test that requires a participant to follow a pathway while avoiding three randomly placed high contrast 2 x 2 feet foam obstacles. Each test is a sequence of 6 trials conducted at each lux level. Success requires the participant to navigate the course from start to end without (i) hitting 2 or more obstacles during a single run, (ii) stepping completely off the white path with both feet or (iii) exceeding 3 minutes. fMRI fMRI was performed using Siemens MAGNETOM 3T Skyra (first 6 eyes) and 3T Cima.X scanners (second 6 eyes) and a 64-channel phased array head coil (Siemens, Erlangen, Germany). Light stimuli were delivered to the participant from an MRI-compatible projector (TeleMed, Istanbul, Turkiye), directed via mirrors to the patient. A unilateral eye patch was positioned over the non-tested eye, alternating left and right to avoid fatigue. Paradigms were presented to the participant using a NNL Aktiva fMRI interface (Nordic NeuroLab, Bergen, Norway). A series of three block design visual paradigms, each lasting approximately 5 minutes, was administered to each participant, testing each eye separately at baseline, and repeated at 2 days, 14 days and 28 days following treatment of each eye. A new baseline scan was established for the eye when treated with an increased dose approximately 3 months following the first treatment. Cohort 1 (NLP/BLP) paradigms consisted of: full visual field on/off, switching hemifield and flickering checkboard presentations. Cohort 2 (HM/CF) paradigms consisted of: E-down, moving line and flickering checkerboard presentations. Qualitative fMRI analysis was performed using Siemens Syngo Via workstation software (Erlangen, Germany) and post-processing using NNL with manual thresholding techniques, image interpretations by a single neuroradiologist. Earplug protection was provided to each patient, and padded head clamps applied to limit head motion. T1-weighted anatomical images were acquired using three-dimensional magnetization-prepared rapid acquisition gradient echo sequence: 1 slab; 176 sagittal slices; FOV, 256 × 256 mm; slice thickness, 1 mm; isotropic voxel size, 1 × 1 × 1 mm; TR, 2300 ms; TE 2.98 ms; TI, 900 ms; and flip angle, 9°. Blood-oxygenation-level-dependent (BOLD) fMRI data were acquired using a gradient-echo, simultaneous multi-slice, accelerated echo-planar imaging (EPI) T2*-weighted sequence: 54 transversal slices angled to avoid the maxillary sinuses; in-plane resolution, 2 × 2 mm; slice thickness, 2.5 mm; field of view (FOV), 192 × 192 mm; repetition time (TR), 3000 ms; echo time (TE), 30 ms; flip angle, 90°; echo spacing, 0.65 ms; bandwidth, 1774 Hz/Px; and total acceleration factor of 4 (SMS 2, GRAPPA 2); 110 measurements were acquired for each paradigm, except for checkboard where 90 measurements were acquired. The field map was acquired using a dual-echo gradient echo pulse sequence: 36 slices with the same position as fMRI; slice thickness, 3 mm without gap; voxel size, 3 × 3 × 3 mm; FOV, 192 × 192 mm; TR, 400 ms; TE1/TE2, 4.92/7.38 ms; and flip angle, 60°. Quantification of fMRI Data For quantitative fMRI analyses, EPI field maps were acquired with the same geometric parameters as the BOLD fMRI sequence, with 20 measurements acquired. DICOM files were converted to NiFTi format and pre-processed with de-meaning, masking and brain extraction techniques. First-level analysis used a general linear model (GLM), motion correction and high-pass temporal filtering with probability set to p < 0.05, z of 3.1 and registration to standard space with 6 degrees of freedom. For each participant, all scans were registered to a single T1 image and second level GLM contrasts were generated between visits, with occipital lobe masking. Post-dose scans were compared to the baseline scan and maps of statically significant voxels were extracted. Quantitative analyses were performed using FSL version 6.7.0.10, Oxford, UK. National Eye Institute Visual Function Questionnaire-25 The NEI VFQ-25, without optional questions, was administered by study personnel and responses recorded accordingly. Declarations Acknowledgements We would like to thank Dr. Stefan Sperl and Lisa Plasser for overseeing the manufacturing of the drug substance and drug product used in the studies described in this manuscript. In addition, we would like to acknowledge Drs. Lynton Graetz and Mark Jenkinson for their contribution to the analysis of the quantitative fMRI data. The authors also acknowledge Angela Walls and the facilities of the National Imaging Facility, a National Collaborative Research Infrastructure Strategy (NCRIS) capability, at the South Australian Health and Medical Research Institute. Finally, we would like to thank Lisa Tuomi for her assistance on this manuscript. Author contributions Study design: R.J.C., E.D, B.M.S., C.D.B, A.D, R.V.G. Patient recruitment and treatment: R.J.C. Data generation, analyses and interpretation: E.D, R.J.C, C.D.B., A.D., R. K., R.V.G. Drafting manuscript: R.J.C, E.D. Reviewing and editing manuscript: E.D, B.M.S, C.D.B, A.D, C.C.W, C.G-K, C.S, R.K, R.V.G. Competing interests E.D. is an employee/Officer and shareholder of Kiora Pharmaceuticals B.M.S. is an employee/Officer and shareholder of Kiora Pharmaceuticals C.G-K is an employee and shareholder of Kiora Pharmaceuticals C.C.W. is a consultant of Kiora C.S. is an employee of Ora R.K is a consultant of Kiora Authorship: inclusion and ethics in global research This was an industry-sponsored trial conducted in a high-income country (Australia). Data Availability This study was sponsored by Kiora Pharmaceuticals, Inc. (Encinitas, CA). Deidentified datasets related to participant demographics, baseline characteristics, safety parameters (adverse events, vital signs, laboratory values), and efficacy outcomes (light perception, visual acuity, kinetic visual field, functional vision testing, fMRI, and quality of life questionnaire results) will be made available upon request. These data will be accessible with the exception of certain proprietary information, which will remain confidential at the discretion of Kiora Pharmaceutical. Non-proprietary data supporting the findings, including the study protocol, statistical analysis plan, and a general description of the fMRI data processing pipeline, are available from the corresponding author upon reasonable request. All data sharing is in accordance with ethical guidelines, patient privacy, and applicable regulations. Access to the available datasets will be considered for researchers who submit a methodologically sound proposal, for purposes of scholarly research that aligns with ethical standards. Data will be available from publication date for at least 5 years. Data will be shared via a secure, password-protected platform, with access granted after a formal data use agreement is signed. Requests for data access should be directed to the corresponding author, Robert J. Casson ( [email protected] ). Code availability Not applicable References Bunker, C.H., Berson, E.L., Bromley, W.C., Hayes, R.P. & Roderick, T.H. Prevalence of retinitis pigmentosa in Maine. Am J Ophthalmol 97 , 357-365 (1984). Heath Jeffery, R.C. , et al. Inherited retinal diseases are the most common cause of blindness in the working-age population in Australia. Ophthalmic Genet 42 , 431-439 (2021). Rahman, F., Zekite, A., Bunce, C., Jayaram, H. & Flanagan, D. Recent trends in vision impairment certifications in England and Wales. Eye (Lond) 34 , 1271-1278 (2020). Quinodoz, M. , et al. RetiGene, a comprehensive gene atlas for inherited retinal diseases (IRDs). bioRxiv (2025). Van Gelder, R.N. , et al. Regenerative and restorative medicine for eye disease. Nat Med 28 , 1149-1156 (2022). Tochitsky, I., Kienzler, M.A., Isacoff, E. & Kramer, R.H. Restoring Vision to the Blind with Chemical Photoswitches. Chem Rev 118 , 10748-10773 (2018). Fain, G.L., Hardie, R. & Laughlin, S.B. Phototransduction and the evolution of photoreceptors. Curr Biol 20 , R114-124 (2010). Milam, A.H., Li, Z.Y. & Fariss, R.N. Histopathology of the human retina in retinitis pigmentosa. Prog Retin Eye Res 17 , 175-205 (1998). Stone, J.L., Barlow, W.E., Humayun, M.S., de Juan, E., Jr. & Milam, A.H. Morphometric analysis of macular photoreceptors and ganglion cells in retinas with retinitis pigmentosa. Arch Ophthalmol 110 , 1634-1639 (1992). Tochitsky, I. , et al. Restoring visual function to blind mice with a photoswitch that exploits electrophysiological remodeling of retinal ganglion cells. Neuron 81 , 800-813 (2014). Tochitsky, I., Trautman, J., Gallerani, N., Malis, J.G. & Kramer, R.H. Restoring visual function to the blind retina with a potent, safe and long-lasting photoswitch. Sci Rep 7 , 45487 (2017). Britten-Jones, A.C. , et al. The safety and efficacy of gene therapy treatment for monogenic retinal and optic nerve diseases: A systematic review. Genet Med 24 , 521-534 (2022). Bailey, I.L., Jackson, A.J., Minto, H., Greer, R.B. & Chu, M.A. The Berkeley Rudimentary Vision Test. Optom Vis Sci 89 , 1257-1264 (2012). Table 1 Table 1. Ocular adverse events for all participants at all doses MedDRA Term* KIO-301 7.5 µg N = 3 (%) KIO-301 25 µg N = 6 (%) KIO-301 50 µg N = 3 (%) Severity Drug Related Total N = 12 (%) Eye Pain 0 (0%) 2 (33%) 0 (0%) Mild Unlikely 2 (17%) Eye Swelling 0 (0%) 1 (17%) 0 (0%) Mild Unlikely 1 (8.3%) Ocular Hypertension 1 (33%) 0 (0%) 0 (0%) Mild Possible 1 (8.3%) Anterior Chamber Cell 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Anterior Chamber Flare 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Vitreous Cells 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Retinitis 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Vasculitis 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Iritis 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Keratic Precipitates 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Photophobia 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Photopsia 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Vitreous Floaters 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Punctate Keratitis 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) Conjunctival Hyperemia 0 (0%) 0 (0%) 0 (0%) N/A N/A 0 (0%) *MedDRA = Medical Dictionary for Regulatory Activities Additional Declarations Yes there is potential Competing Interest. Competing interests E.D. is an employee/Officer and shareholder of Kiora Pharmaceuticals B.M.S. is an employee/Officer and shareholder of Kiora Pharmaceuticals C.G-K is an employee and shareholder of Kiora Pharmaceuticals C.C.W. is a consultant of Kiora C.S. is an employee of Ora R.K is a consultant of Kiora Supplementary Files SupplementalMaterials.docx Supplementary Material SuppVideo.mp4 Restoration of light perception testimony Cite Share Download PDF Status: Published Journal Publication published 14 Apr, 2026 Read the published version in Nature Medicine → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8060107","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":545222338,"identity":"b2444027-23ab-4ffd-8b3b-e2ec9757dd47","order_by":0,"name":"Robert Casson","email":"data:image/png;base64,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","orcid":"","institution":"University of Adelaide","correspondingAuthor":true,"prefix":"","firstName":"Robert","middleName":"","lastName":"Casson","suffix":""},{"id":545222339,"identity":"8f49697c-6add-48d5-8961-a6950b81af48","order_by":1,"name":"Eric Daniels","email":"","orcid":"","institution":"Kiora Pharmaceuticals","correspondingAuthor":false,"prefix":"","firstName":"Eric","middleName":"","lastName":"Daniels","suffix":""},{"id":545222340,"identity":"ca53e358-e971-490b-8ca1-1e9089300658","order_by":2,"name":"Christen Barras","email":"","orcid":"","institution":"South Australian Health and Medical Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Christen","middleName":"","lastName":"Barras","suffix":""},{"id":545222341,"identity":"0e16bb3e-b488-4c73-88d5-76f4e74c67f9","order_by":3,"name":"Andrew Dwyer","email":"","orcid":"","institution":"South Australian Health and Medical Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Andrew","middleName":"","lastName":"Dwyer","suffix":""},{"id":545222342,"identity":"2adf9182-1df2-4a86-96fb-9dee54aaf95c","order_by":4,"name":"Brian Strem","email":"","orcid":"","institution":"Kiora Pharmaceuticals","correspondingAuthor":false,"prefix":"","firstName":"Brian","middleName":"","lastName":"Strem","suffix":""},{"id":545222343,"identity":"cf29f90e-916e-44af-8b1a-b90ab4fc9c2e","order_by":5,"name":"Charles Wykoff","email":"","orcid":"https://orcid.org/0000-0001-7756-5091","institution":"Retina Consultants of Texas, Retina Consultants of America","correspondingAuthor":false,"prefix":"","firstName":"Charles","middleName":"","lastName":"Wykoff","suffix":""},{"id":545222344,"identity":"1bc9faa6-24e9-48cd-8902-ffa876e38ac3","order_by":6,"name":"Claudia Gregorio-King Gregorio-King","email":"","orcid":"","institution":"Kiora Pharmaceuticals","correspondingAuthor":false,"prefix":"","firstName":"Claudia","middleName":"Gregorio-King","lastName":"Gregorio-King","suffix":""},{"id":545222345,"identity":"fdfeed89-7b4b-4194-8018-399cd3e41245","order_by":7,"name":"Cameron Schuh","email":"","orcid":"","institution":"Ora, Inc.","correspondingAuthor":false,"prefix":"","firstName":"Cameron","middleName":"","lastName":"Schuh","suffix":""},{"id":545222346,"identity":"08a2e8ac-8520-45e6-9171-c2663cb1fe63","order_by":8,"name":"Richard Kramer","email":"","orcid":"https://orcid.org/0000-0002-8755-9389","institution":"University of California, Berkeley","correspondingAuthor":false,"prefix":"","firstName":"Richard","middleName":"","lastName":"Kramer","suffix":""},{"id":545222347,"identity":"354b36aa-a1ce-45b2-8179-b2dad6932861","order_by":9,"name":"Russell Van Gelder","email":"","orcid":"https://orcid.org/0000-0001-5368-3659","institution":"University of Washington","correspondingAuthor":false,"prefix":"","firstName":"Russell","middleName":"Van","lastName":"Gelder","suffix":""}],"badges":[],"createdAt":"2025-11-07 21:00:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8060107/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8060107/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41591-026-04317-6","type":"published","date":"2026-04-14T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":96051233,"identity":"80b9ed8c-d23d-4451-ba3e-6608db35d324","added_by":"auto","created_at":"2025-11-17 06:40:03","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":640057,"visible":true,"origin":"","legend":"\u003cp\u003eDepiction of the mechanism of action of KIO-301. (\u003cstrong\u003eA\u003c/strong\u003e) KIO-301 enters retinal ganglion cells (RGCs), in either isomerisation state, through large pore P2X7 channels which are overexpressed in retinas with degenerating photoreceptors 13. The photoswitch non-covalently resides in the intracellular domain of hyperpolarization-activated cyclic nucleotide–gated (HCN) ion channels. In the dark, KIO-301 is in its trans configuration which blocks the influx of Na+ ions. (\u003cstrong\u003eB\u003c/strong\u003e) In the presence of visible spectrum light, KIO-301 reversibly isomerizes to its cis configuration. This conformational change opens the HCN channel to Na+ influx causing RGC depolarization and triggers an action potential.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/cc4f6603a5b5abd8a340bc06.png"},{"id":96051267,"identity":"e2cca904-d529-4509-aec5-d1a73768f344","added_by":"auto","created_at":"2025-11-17 06:40:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":562745,"visible":true,"origin":"","legend":"\u003cp\u003eParticipant flow chart\u003c/p\u003e\n\u003cp\u003eNLP = no light perception; BLP = bare light perception; HM = hand movements; CF = count fingers.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/5b3c66628b57e3322dc6bbb3.png"},{"id":96051269,"identity":"7a0ecab1-8d90-4eaf-922f-5fd63336a413","added_by":"auto","created_at":"2025-11-17 06:40:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":252451,"visible":true,"origin":"","legend":"\u003cp\u003eChange in visual acuity and visual field after delivery of KIO-301. Individual data points for each participant identification number are displayed with grey symbols. (\u003cstrong\u003eA\u003c/strong\u003e) The mean logarithm of the minimum angle of resolution (logMAR) of the participants’ treated eye in Cohort 2 improved from 2.1 +/- 0.2 at baseline to 2.0 +/- 0.1 at day 29 (mean +/- SEM, n = 3 treated eyes, 3 eyes dosed at 25 µg OD) indicating a slight improvement in acuity. The mean logMAR of Cohort 2 participants treated at the higher dose decreased from 2.1 +/- 0.2 at baseline to 1.8 +/- 0.2 at day 29 (mean +/- SEM, n = 3 treated eyes administered 50 µg KIO-301 OS). (\u003cstrong\u003eB\u003c/strong\u003e) The mean degrees of visual field in the treated eye of all participants at all doses of KIO-301 increased from baseline and plateaued from day 15 through day 30 (28 +/- 14 degrees at baseline versus 43 +/- 7 degrees at Day 30; means +/- SEM, 220 lux, n = 12 treated eyes from 6 participants in Cohorts 1 and 2 administered 7.5, 25 or 50 µg KIO-301).\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/5e3df01f2188228b5644f612.png"},{"id":96051257,"identity":"3d4fe861-5c68-4d9c-b28b-934974533807","added_by":"auto","created_at":"2025-11-17 06:40:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":718805,"visible":true,"origin":"","legend":"\u003cp\u003eChange in functional vision after KIO-301 delivery. Due to profound vision loss, some participants were unable to complete all requested tasks. Individual data points corresponding to each participant identification number are displayed with grey symbols (\u003cstrong\u003eA\u003c/strong\u003e) Ability of a participant to successfully determine the walking direction of another individual after administration of KIO-301, peaked on day 8 (all light levels, n = 10 treated eyes from 6 participants administered 7.5, 25 or 50 µg KIO-301). (\u003cstrong\u003eB\u003c/strong\u003e) Ability of a participant from Cohort 1 to successfully locate a window after administration of KIO-301, peaked on day 15, (350 lux, n = 5 treated eyes from 3 participants administered KIO-301 at 7.5 µg OD and 25 µg OS). (\u003cstrong\u003eC\u003c/strong\u003e) The proportion of successful attempts to navigate accurately through a high-contrast room exit text increased from baseline (24.7 +/- 15.2%) after administration of KIO-301, peaking at 65.7 +/- 18.7% on day 15. This response then trended downward at day 30 across all participants administered the test and at all doses of KIO-301 administered (mean +/- SEM, all light levels, n = 10 eyes from 6 participants administered KIO-301 at 7.5, 25 or 50 µg). (\u003cstrong\u003eD\u003c/strong\u003e) The Door Location Test was conducted in all Cohort 2 participants and 1 participant in Cohort 1. There was no change in the ability to successfully locate and navigate to a door after administration of KIO-301 (125 lux, n = 7 treated eyes from 4 participants administered KIO-301 at 7.5, 25 or 50 µg).\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/bdfb2576f485478ebb7e5c8d.png"},{"id":96051280,"identity":"b7ce5a36-d104-4665-921d-a603e51ebf14","added_by":"auto","created_at":"2025-11-17 06:40:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1678264,"visible":true,"origin":"","legend":"\u003cp\u003eChange in functional magnetic resonance imaging after KIO-3-1 delivery. (\u003cstrong\u003eA\u003c/strong\u003e) A participant from Cohort 1 with longstanding (\u0026gt; 10 years) no light perception, reported light perception 2 days after KIO-301 delivery and demonstrated a qualitative increase in blood oxygen level dependent (BOLD) signal centered upon the primary visual cortex within 48 hours after administration of KIO-301 that reduced over the study period (see accompanying supplemental subject testimonial video). (\u003cstrong\u003eB\u003c/strong\u003e) There was a statistically significant increase in mean voxels activated at all timepoints compared to baseline (mean +/- SEM; checkerboard stimuli; n = 12 eyes from 6 participants administered KIO-301 at 7.5, 25 or 50 µg; p \u0026lt; 0.05, z threshold = 3.1).\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/7aa52c9522e6a67ca64b642e.png"},{"id":106949725,"identity":"fa441195-5658-4b4d-8b28-52d0d1692a57","added_by":"auto","created_at":"2026-04-15 07:14:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5765754,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/75a6022d-0f54-4a7d-97d8-1c159bb4b061.pdf"},{"id":96051252,"identity":"e6c8282a-b557-40cf-99ce-2bbf691d2cde","added_by":"auto","created_at":"2025-11-17 06:40:04","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":132486,"visible":true,"origin":"","legend":"Supplementary Material","description":"","filename":"SupplementalMaterials.docx","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/ac213d8ad2155e67dca243b6.docx"},{"id":96051283,"identity":"06ab33c9-5062-41dd-b292-3dab3d8a04b7","added_by":"auto","created_at":"2025-11-17 06:40:07","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":29174384,"visible":true,"origin":"","legend":"Restoration of light perception testimony","description":"","filename":"SuppVideo.mp4","url":"https://assets-eu.researchsquare.com/files/rs-8060107/v1/b7f5182f9278fa51d737328c.mp4"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nCompeting interests\r\nE.D. is an employee/Officer and shareholder of Kiora Pharmaceuticals\r\nB.M.S. is an employee/Officer and shareholder of Kiora Pharmaceuticals\r\nC.G-K is an employee and shareholder of Kiora Pharmaceuticals\r\nC.C.W. is a consultant of Kiora\r\nC.S. is an employee of Ora\r\nR.K is a consultant of Kiora","formattedTitle":"Vision restoration using a light-responsive small molecule photoswitch (KIO-301) in advanced retinitis pigmentosa: the ABACUS-1 phase 1/2 clinical trial","fulltext":[{"header":"Main","content":"\u003cp\u003eRetinitis pigmentosa (RP) comprises a genetically heterogeneous group of inherited retinal dystrophies (IRDs) characterized by gradual rod-cone photoreceptor degeneration associated with night blindness, visual field loss, and progression to profound visual impairment in most affected individuals by middle age. RP is a leading cause of blindness in the working-age population in high-income countries,\u0026nbsp;with an estimated\u0026nbsp;prevalence of approximately 1 in 3,000 - 4,000.\u003csup\u003e1-3\u003c/sup\u003e The number of known causative genes encompassing syndromic and non-syndromic variants continues to grow and currently exceeds 450.\u003csup\u003e4\u003c/sup\u003e The large number of monogenic variants makes gene-agnostic therapeutic strategies clinically attractive. A variety of approaches are being investigated, including optoelectronic prosthetics, cellular replacement approaches, and optogenetics.\u003csup\u003e5\u003c/sup\u003e We have pursued an alternative gene-agnostic approach that exploits properties of a novel small molecule photoisomer (KIO-301), rendering surviving retinal ganglion cells (RGCs) responsive to light.\u003csup\u003e6\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSpecialized light-detecting cells are highly phylogenetically conserved, and in all metazoans, the natural photoisomer in the classical photoreceptors is 11-cis-retinal.\u003csup\u003e7\u003c/sup\u003e Light-induced change in its molecular configuration stimulates a biochemical cascade which hyperpolarizes photoreceptors, reducing glutamate release to bipolar cells,\u0026nbsp;which in turn synapse with RGCs, the third-order neurons of the visual pathway. RGCs are analogous to digital converters, receiving graded excitatory input from bipolar cells and inhibitory input from amacrine cells, resulting in transmission of digitized information encoded as action potentials to the occipital cortex in the brain.\u003c/p\u003e\n\u003cp\u003eIn RP, rods and cones progressively degenerate, while variable secondary pathological changes in the inner retina have been reported.\u003csup\u003e8\u003c/sup\u003e In a large histopathological series of genetically diverse RP, approximately two-thirds of RGCs were retained in the central retina of affected eyes compared to healthy controls, implying that therapeutic strategies targeting stimulation of RGCs has a rational histopathological foundation.\u003csup\u003e9\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSynthetic molecules that isomerize and alter configuration in response to photon interaction, in a manner analogous to \u003cem\u003ecis\u003c/em\u003e-retinal, have been termed \u0026ldquo;photoswitches\u0026rdquo;.\u003csup\u003e10\u003c/sup\u003e In\u0026nbsp;preclinical\u0026nbsp;studies, these small molecules were shown to enter RGCs and render endogenous voltage-gated cation channels sensitive to light without requiring genetic manipulation, and thus enabling photocontrol of action potential generation.\u003csup\u003e6,10,11\u003c/sup\u003e In 2014, Tochitsky \u003cem\u003eet al.\u003c/em\u003e reported that the azobenzene photoswitch DENAQ restored electrophysiological and behavioural responses in blind \u003cem\u003erd1\u003c/em\u003e mice (a murine model of severe RP) for several days after a single intraocular injection.\u003csup\u003e10\u003c/sup\u003e Subsequently, Tochitsky et al. developed a longer-acting photoswitch molecule, BENAQ, which restored visual responses in \u003cem\u003erd1\u003c/em\u003e mice for several weeks after a single intraocular injection.\u003csup\u003e11\u003c/sup\u003e In mice and rabbits,\u0026nbsp;BENAQ was\u0026nbsp;nontoxic\u0026nbsp;at concentrations 10-fold higher than that needed to confer\u0026nbsp;photoresponsiveness.\u003csup\u003e11\u003c/sup\u003e The mechanism of action of this photoswitch is depicted graphically in \u003cstrong\u003eFigure 1\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eHere, we report the first-in-human translation of this photoswitch small molecule. ABACUS-1 was a\u0026nbsp;phase\u0026nbsp;1/2, single-dose, open-label dose-escalation trial of BENAQ, developed and formulated for ophthalmic therapy as KIO-301 administered by intravitreal injection (IVT) to 12 eyes of 6 individuals legally blind from advanced RP.\u0026nbsp;\u003c/p\u003e\n\n"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eConfirmation of KIO-301 Activity\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePrior to administration, activity of KIO-301 drug substance was confirmed \u003cem\u003ein vitro\u003c/em\u003e using explanted retinas from retinal degeneration type 1 (rd1) mice and a multielectrode array (MEA) recording system. Using this model, after treatment with 100 \u0026micro;M KIO-301, explanted rd1 retinas responded rapidly and reliably to light flashes with spikes elicited quickly (within 100 msec) after light onset and ceasing quickly (within 200 msec) after light termination. Untreated retinas from rd1 mice showed no detectable light responses (\u003cstrong\u003eSupplementary Figure 1\u003c/strong\u003e), consistent with loss of functional rods and cones. \u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eParticipants\u0026rsquo; demographic and clinical characteristics\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter screening and review of inclusion and exclusion criteria, six (6) participants (12 eyes) with a clinical diagnosis of advanced RP and a median age of 68.5 years were enrolled into the study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe demographic and clinical characteristics of the participants are shown in \u003cstrong\u003eSupplementary Table 1\u003c/strong\u003e, with 3 participants (Cohort 1) having baseline vision clinically diagnosed as either no light perception (NLP) or bare light perception (BLP), corresponding to a logarithm of the minimal angle of resolution (logMAR) \u0026gt; 2.9 using the Berkeley Rudimentary Vision Test (BRVT). The other 3 participants (Cohort 2) were clinically diagnosed as hand motion (HM) or count fingers (CF), corresponding to logMAR \u0026le; 2.9 and \u0026gt; 1.6 using the BRVT. All enrolled participants completed the study and there were no early discontinuations or early withdrawals.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStudy overview\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe ABACUS-1 study was registered in ClinicalTrials.gov (NCT05282953) and was conducted at two sites in Adelaide, Australia with approval from the Central Adelaide Local Health Network Human Research Ethics Committee. The study was conducted in full conformity with all applicable laws and regulations, including the International Conference on Harmonisation Guidelines for Good Clinical Practice (CPMP/ICH/135/95) and relevant articles of the Declaration of Helsinki (seventh revision, 2013). Written informed consent was obtained from each study participant.\u003c/p\u003e\n\u003cp\u003eThe dosing protocol is shown in \u003cstrong\u003eFigure 2\u003c/strong\u003e. In Part 1 of the study, Cohort 1 received 7.5 \u0026micro;g of KIO-301 and Cohort 2 received 25 \u0026micro;g of KIO-301 to the right eye (\u003cem\u003eoculus dexter\u003c/em\u003e, OD). In Part 2 of the study the contralateral eyes were treated, occurring between 70-100 days after administration of KIO-301 OD; specifically, Cohort 1 participants received 25 \u0026micro;g of KIO-301 and Cohort 2 participants received 50 \u0026micro;g of KIO-301 into the left eye (\u003cem\u003eoculus sinister\u003c/em\u003e, OS). KIO-301 was administered by standard 50 \u0026micro;L IVT injection and participants were followed longitudinally for study assessments on day 1 (pre and post injection) and post-injection days 2, 3, 7, 8, 14, 15, 29 with the final study visit on day 30 (all +/-1) for each part of the study. Systemic and ocular safety were monitored throughout the duration of the trial.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePrimary outcome: safety\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere were no serious adverse events (SAEs), nor any systemic or definitive ocular drug-related adverse events (AEs) reported. Vital signs, hematology, biochemistry and electrocardiographic parameters of all participants were normal pre- and post-injection.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eReported ocular AEs included mild ocular discomfort and mild swelling in the peri-injection period (deemed unrelated to KIO-301) in one participant (administered 25 \u0026micro;g KIO-301 OS) and mild increased intraocular pressure (IOP) in a second participant (administered 7.5 \u0026micro;g KIO-301 OD). This participant had borderline elevated IOP in both eyes at baseline and slightly increased (27 mmHg) IOP recorded after IVT administration of KIO-301 into the right eye only. The OD event was coded as mild in nature and possibly related to KIO-301 and was managed with a standard single-agent topical ocular hypotensive medication.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNo participant developed any signs or symptoms of intraocular inflammation. The anterior and vitreous chambers were normal on slit lamp examination at all time points. At no time point was the drug visible in the vitreous. There were no changes to the fundus appearance in any participant, nor any changes noted on optical coherence tomography (OCT). No participant developed macular edema. A complete listing of ocular AEs is shown in \u003cstrong\u003eTable 1\u003c/strong\u003e.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSecondary outcomes: visual assessments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eLight Perception\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eParticipants were asked to indicate when they saw a randomly repeating, illuminated image of a letter \u0026lsquo;X\u0026rsquo; on a dark background across multiple attempts (see Methods). The mean correct responses with the treated eyes of all 3 participants in Cohort 1 improved from baseline and is shown in \u003cstrong\u003eSupplementary Figure 2\u003c/strong\u003e. One participant who had been without any light perception for over 10 years regained the ability to perceive light 2 days after IVT. His experiences were recorded in a post study interview (\u003cstrong\u003eSupplementary Video 1\u003c/strong\u003e). Participants in Cohort 2, the group with better baseline visual acuities, had a higher baseline of light perception with no observed changes in this endpoint post injection.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eVisual acuity\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eVisual acuity was assessed with the BRVT and recorded as a logMAR score, with a reduction in logMAR corresponding to an improvement in visual acuity (see Methods). Due to the severe stage of RP for participants in Cohort 1, the visual acuity was not measurable on this scale and was recorded as logMAR \u0026gt; 2.9 at all timepoints, including baseline.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe mean logMAR of the participants\u0026rsquo; treated eye in Cohort 2 improved \u0026nbsp;from 2.1 +/- 0.2 at baseline to 2.0 +/- 0.1 at day 29 (mean +/- SEM, n = 3 treated eyes, 3 eyes dosed at 25\u0026nbsp;\u0026micro;g\u0026nbsp;OD-\u003cstrong\u003eFigure 4a\u003c/strong\u003e) indicating a slight improvement in acuity. The mean logMAR of Cohort 2 participants treated at the higher dose was observed to have a further reduction in logMAR over the course of the study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eKinetic visual field\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eManual Goldmann kinetic perimetry with an illuminated light stimulus (440-460 nm range) was used to assess the visual fields of participants (see Methods). As shown in \u003cstrong\u003eFigure 4b\u003c/strong\u003e, the extent of the mean field of vision in the treated eye of all participants at all doses of KIO-301 increased from baseline by 15 degrees and plateaued from day 15 through day 30.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFunctional vision testing\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFunctional vision was assessed during the study via a series of four (4) standardized orientation and mobility assessments at various light levels as described in Methods. Due to the range of profound visual impairment, some participants were unable to perform certain tasks at varying light levels.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eWalking Direction Test\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eAt baseline, participants demonstrated an approximately 50% chance of determining walking direction, as expected by chance alone. However, this increased to 70% by day 15 and had reverted to baseline by day 30. \u0026nbsp;(\u003cstrong\u003eFigure 4a\u003c/strong\u003e, all light levels- 45, 125, \u0026amp; 350 lux, n = 10 treated eyes from 6 participants administered 7.5 \u0026micro;g, 25 \u0026micro;g or 50 \u0026micro;g KIO-301).\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eWindow Location Test\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe Window Location Test was conducted in Cohort 1 patients only (deemed prior to study initiation as this task was not challenging for Cohort 2 participants). The proportion of successes which a participant could successfully locate a window increased from 44% to 56% one day after administration of KIO-301 and peaked at 63% 7 days later. (\u003cstrong\u003eFigure 4b\u003c/strong\u003e, 350 lux, n = 5 treated eyes from 3 participants administered KIO-301 at 7.5 \u0026micro;g OD and 25 \u0026micro;g OS).\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eRoom Exit Test\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe ability to navigate accurately through a room, locating the exit in high contrast, increased from a 37% success rate at baseline to a 67% success rate 14 days after administration of KIO-301 (\u003cstrong\u003eFig. 4c\u003c/strong\u003e). This response then trended downward at day 30 across all participants administered the test and at all doses of KIO-301 administered.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eDoor Location Test\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe Door Location Test was conducted in all Cohort 2 participants and 1 participant in Cohort 1. There was no clear change in the ability to successfully locate and navigate to a door after administration of KIO-301 (\u003cstrong\u003eFig. 4d\u003c/strong\u003e).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFunctional magnetic resonance imaging (fMRI)\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThere was evidence of a qualitative increase in the primary visual cortex and extra-striate visual cortex BOLD signal in response to light stimuli applied to the treated eyes \u003cstrong\u003e(Figure 6a),\u003c/strong\u003e with activations of variable intensity and a statistically significant increase in mean voxels (\u003cstrong\u003eFigure 6b\u003c/strong\u003e) on quantitative analyses at all timepoints compared to baseline (mean +/- SEM; checkerboard stimuli; n = 12 eyes from 6 participants administered KIO-301 at 7.5, 25 or 50\u0026nbsp;\u0026micro;g; p \u0026lt; 0.05, z threshold = 3.1). This increase peaked on day 3 (2 days after treatment), was reduced at day 14 and then remained stable and significantly above baseline at day 29. Predominant visual stimulus signal contributions were derived from the flickering checkboard and on/off paradigms.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eQuality of Life\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe composite QoL score, measured using the\u0026nbsp;National Eye Institute Visual Function Questionnaire-25, across all 6 participants increased by a mean of 4.2 points from baseline to day 29 after administration of KIO-301 (\u003cstrong\u003eSupplementary Figure 3\u003c/strong\u003e). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003epK sampling\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe concentration of KIO-301 in plasma was below the limit of quantitation (0.2 ng/mL) in all study participants at 4 hours (+/- 15 minutes) and at 14 days after IVT administration except for one participant in Cohort 2 who received 50 \u0026micro;g OS (0.215 ng/mL) at 4 hours post-injection.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThere is an urgent unmet need for safe and cost-effective vision restoration approaches for individuals affected by IRDs. \u0026nbsp;KIO-301 is an intravitreal formulation of the photoswitch molecule, BENAQ chloride, which in pre-clinical studies was shown to selectively enter RGCs downstream of degenerated photoreceptors and render endogenous voltage-gated cation channels sensitive to light without requiring genetic manipulation, thus enabling photocontrol of optic nerve action potential generation in response to light.\u003csup\u003e6,10,11\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this first-in-human clinical trial of any photoswitch molecule, KIO-301 demonstrated an excellent tolerability. There were no serious adverse events nor definite drug-related adverse events. No intraocular inflammation was evident at any time point (a known drawback of viral vector-based gene therapy approaches to IRDs).\u003csup\u003e12\u003c/sup\u003e There was no change in the vitreous or fundus appearance, nor any change to the macula OCT imaging. All adverse events were minor and are well-described features of IVT injections, including transient pain and mild ocular hypertension. The standard IVT injection procedure is usually well tolerated under topical anaesthesia in an office setting and indefinite injections at intervals of 1-3 months are commonly performed to treat neovascular age-related macular degeneration and other retinal disorders. Hence, intravitreal delivery of a therapeutic agent that can potentially recover visual function in RP is clinically feasible.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAlthough safety was the primary endpoint of the ABACUS-1 trial, establishing proof-of-concept effectiveness in a clinical setting was also an objective. Of note, the study also provided valuable information on the challenges and applicability of assessments that can be utilised to explore clinical effectiveness in a population of patients with profound vision loss.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this study, we utilized a panel of visual function assessments, incorporating a simple light perception test, visual acuity testing using the BRVT, visual field testing, a panel of four multi-luminance orientation and mobility tests, functional MRI, and standardized patient-reported outcomes. Although limited by low patient numbers and challenges in adapting these assessments to the ultra-low vision population of ABACUS-1, the most striking clinical observation was the concordance of improvements revealed by these multiple vision endpoints and consistency of response.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe general improvement in visual function following intravitreal KIO-301 administration may have several mechanisms. \u0026nbsp;First, the direct conferral of light sensitivity to RGCs is likely to restore light-sensing function to the retina and is the presumptive mechanism responsible for conferral of light perception to the NLP-vision individual in this study. \u0026nbsp;Remarkably, BENAQ and other \u0026lsquo;second generation\u0026rsquo; photoswitches appear to selectively target RGCs downstream of degenerating photoreceptors while not affecting the physiology of intact areas of retina in murine models.\u003csup\u003e10\u003c/sup\u003e Such a mechanism would be expected to increase the visual field of individuals with partial retinal degeneration but some intact central vision, as was seen in our subjects with less advanced disease. \u0026nbsp;Finally, in mice, photoswitches appear to suppress the 5-10 Hz rhythmic \u0026lsquo;noise\u0026rsquo; in RGC firing that occurs after outer retinal degeneration,\u003csup\u003e14\u003c/sup\u003e which would be expected to improve signal-to-noise and visual acuity in both injected and potentially contralateral eye vision. \u0026nbsp; Such an effect has been noted following unilateral gene therapy for Leber hereditary optic neuropathy.\u003csup\u003e15\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eThe correlation between objective, subjective and imaging efficacy endpoints aligns with the underlying mechanism of action of KIO-301 and, along with the high level of tolerability demonstrated in this phase 1/2 study is an encouraging early sign which has motivated a larger phase 2 trial of this photoswitch technology.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cem\u003ePreclinical Retinal Explant Assessment\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eEthical approval for the research involving animals was obtained from the UC Berkeley Institutional Animal Care and Use Committee. KIO-301 was prepared as a concentrated 10 mM stock solution in DMSO and stored at -20 \u003csup\u003eo\u003c/sup\u003eC in darkness. A working solution of 100 \u0026micro;M KIO-301 was prepared by diluting the stock into physiological saline. Retinas obtained from P30-P60 rd1 mice were treated with the working solution for 30 min at 21\u003csup\u003eo\u003c/sup\u003eC, followed by thorough washing with drug-free saline for 10 min. Retinas were mounted on a 60-electrode multi-electrode array (Multi Channel Systems, Holliston, MA, USA), inner retina side down, for simultaneous extracellular spike recording from many RGCs. Light responses were elicited with brief (1 s) flashes from a 455 nm LED light source at ~1.5 mW/cm\u003csup\u003e2\u003c/sup\u003e intensity, simulating photopic stimulation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo quantify the strength of the light response in KIO-301-treated retinas, we measured the photoswitch index for each unit in the recording, defined as the mean frequency of spiking during the light flash minus the mean frequency in darkness, divided by the sum of the mean frequencies in light plus darkness. The photoswitch index provides a measure of the change in firing elicited by light, correcting for differences in background firing rate (i.e. in darkness) observed different retinal samples.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eABACUS-1 \u0026ndash; Details of the Study Protocol\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eEthical and Regulatory Considerations\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe ABACUS-1 study was registered in ClinicalTrials.gov (NCT05282953) and was conducted at two sites in Adelaide, Australia with approval from the Central Adelaide Local Health Network Human Research Ethics Committee. The study was conducted in full conformity with all applicable laws and regulations, including the International Conference on Harmonisation Guidelines for Good Clinical Practice (CPMP/ICH/135/95) and relevant articles of the Declaration of Helsinki (seventh revision, 2013). Written informed consent was obtained from each study participant.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eStudy Design\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eABACUS-1 enrolled 6 participants with legal blindness due to RP into the open label, unmasked, dose escalating phase of the study. The sample size was estimated to provide information about safety. Dose escalation was conducted in two parts with safety data reviewed by a safety monitoring committee before confirming whether escalation to a higher dose level could occur. KIO-301 was administered as a single 50 \u0026micro;L IVT injection OD (Part 1) and OS (Part 2). During Part 1 of the study, 3 participants with RP and NLP or BLP vision received 7.5 \u0026micro;g KIO-301 (Cohort 1) and 3 participants with RP and either LP, CF, or HM vision received 25 \u0026micro;g KIO-301 OD (Cohort 2). All participants were followed longitudinally for 1-month via weekly study visits during which safety and efficacy assessments were carried out. During Part 2 of the study, the same 3 participants with RP and NLP or BLP (Cohort 1) received 25 \u0026micro;g KIO-301 and the same 3 participants with RP and CF or HM (Cohort 2) received 50 \u0026micro;g KIO-301 OS. Study visits and safety and efficacy assessments were as per Part 1. Systemic and ocular safety was followed for each participant throughout the entire study period.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eInclusion/Exclusion Criteria\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Participants were enrolled into the study if they were willing and able to provide informed consent for participation in the study. The following key inclusion criteria for Cohort 1 and 2 of the study were applied: (1) aged between 18 to 80 years (unless otherwise approved by the principal investigator) and able to comply with the study protocol, attend all study visits and adequately perform all study assessments, (2) had a clinical diagnosis of RP, (3) similar VA in both eyes (\u0026lt; 0.05 logMAR difference using the BRVT) of NLP or BLP for cohort 1 (confirmed with a logMAR \u0026gt; 2.9 using the BRVT) or CF or HM for cohort 2 (confirmed with a logMAR \u0026lt; 2.9 and \u0026gt; 1.6 using the BRVT). Key exclusion criteria were as follows: (1) evidence of material/substantial optic nerve disease, (2) history of retinal detachments, (3) other clinically significant ocular disease or opacities which might interfere with the study assessments, (4) high intraocular pressure (IOP) \u0026gt; 22 mmHg, (5) previous intraocular surgery (excluding phacoemulsification surgery with intraocular lens implant), (6) aphakia, (7) any psychiatric condition, \u0026nbsp;medical condition or \u0026nbsp;co-morbidities which in the view of the Investigator is likely to interfere with the study or put the participant at risk, (8) any routine contraindication to MRI, including MRI-incompatible metal containing implant or object such as pacemakers, intracranial aneurysm clips, cochlear implants, drug infusion devices, prosthetic devices, contraceptive devices, shrapnel, pins, screws or wire mesh.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eStatistical Analyses\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThis was a first-in-human trial with qualitative safety data as the primary outcome. There were no \u003cem\u003ea priori\u003c/em\u003e hypotheses concerning the clinical data; hence, no null hypothesis significant testing was reported. The fMRI data was statistically analysed as described below.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eClinical Assessments\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSafety\u003c/em\u003e\u003cu\u003e\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThe primary endpoint of this study was safety assessed by (1) incidence of AEs, serious AEs and deaths; (2) spectral domain OCT of overall retinal thickness and thickness of individual layers; (3) fundus autofluorescence (FA) of the retina; (4) slit lamp assessment of the anterior segment; (5) IOP with Goldmann applanation tonometry; (6) vital signs and electrocardiography; (7) clinical chemistry and hematology; (8) serum pharmacokinetics. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEfficacy Assessments\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eKey secondary efficacy endpoints included assessment of (1)\u0026nbsp;light perception as measured by\u0026nbsp;an unprompted, multi-luminance, \u0026nbsp;back-projected letter display;\u0026nbsp;(2) visual acuity using the BRVT; (3) kinetic visual field using a modified Goldmann device; (4) functional vision via a series of standardised multi-luminance orientation and mobility assessments (MLOM); \u0026nbsp; (5) functional magnetic resonance imaging; and (6) National Eye Institute Visual Function Questionnaire-25.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eLight Perception\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThis assessment involves showing the subject a series of videos and recording whether or not the subject perceived the visual stimulus, which was always an \u0026lsquo;X\u0026rsquo; located at various locations on a screen. A strip of tape in front of the screen marked 60 cm where the center of the chair was placed and the patient seated. This assessment is meant to be performed as a monocular test and, therefore, an eyepatch was used to occlude the eye not being tested while assessing the contralateral eye. A unique video file driving the display of Xs on the screen was produced to correspond for each visit. There was also a setting for three different brightness levels (ranging from 3e14 photons/cm\u003csup\u003e2\u003c/sup\u003e/s (low), 1e15 photons/cm2/s (medium) and 5e15 photons/cm2/s (high), wavelength 400-800 nm). For each video, a series of six (6) images are displayed to the subject and the subject is instructed to verbally indicate if they perceive a particular shape or object and the responses are recorded as a success or failure.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eVi\u003c/em\u003e\u003cem\u003esual Acuity\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eVisual acuity (VA) was measured prior to pupillary dilation, both monocularly and then binocularly. and testing was performed under normal room illumination (between 250 and 1000 lux). VA assessment was performed using the Berkeley Rudimentary Vision Test (BRVT; Precision Vision, Woodstock, IL), as described by Bailey et al.\u003csup\u003e13\u003c/sup\u003e, which consists of presenting subjects three hinged card-pairs:\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eSingle Tumbling E Card-Pair (STE)\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGrating Acuity Card-Pair (GA)\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eBasic Vision Card-Pair (BV)\u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eA testing flow chart, based on the ability of subjects to perform the required task, converts responses to a logMAR score. \u0026nbsp;If the BV card-pair was not seen by the participant, light perception was assessed at 25 cm using a pen torch, and the resultant VA was either LP if seen, or NLP if not seen. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eKinetic Visual Field\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThis assessment involves measuring the subject\u0026rsquo;s visual field using a traditional Goldmann kinetic perimeter outfitted with a custom light source. All perimetric assessments were performed by trained orthoptists and/or optometrists. The subject\u0026rsquo;s visual field was mapped in both in a horizontal and vertical meridian and measurements were taken in triplicate and averaged. The total change in degrees was obtained by summing the average horizontal and vertical field changes. This was performed as a monocular assessment. \u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eVisual Function Tests\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe\u0026nbsp;Ora-MLOM\u0026trade; (Multiluminance Orientation \u0026amp; Mobility) installation included a modular lighting system and a series of orientation and mobility test floor layouts of varying difficulty conducted at 3 ambient light levels (45 lux (low), 125 lux (mid), 350 lux (high)) monocularly (OD and OS) and binocularly (OU).\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eThe Window Location test is a stationary test that requires the study participant to locate a randomly placed (front, left, centre, right, no window) white \u0026ldquo;window\u0026rdquo; approximately three feet by two feet attached to a black opaque screen for contrast. Each test is a sequence of 8 trials conducted at each lux level.\u003c/li\u003e\n \u003cli\u003eThe Walking Direction test is a stationary test that requires the participant to identify the direction of motion (to the left, to the right, or no motion) of a person walking between 2 opaque screens located 10 feet in front of them. Each test is a sequence of 6 trials conducted at each lux level.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eThe Door Location test is a straight-line mobility course that requires a participant to locate and navigate to a randomly located (left, right centre) high-contrast door-like object placed on a wall 12 feet in front of them. Each test is a sequence of 6 trials conducted at each lux level.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eThe Exit Room Test is a straight-line mobility test that requires a participant to follow a pathway while avoiding three randomly placed high contrast 2 x 2 feet foam obstacles. Each test is a sequence of 6 trials conducted at each lux level. \u0026nbsp;Success requires the participant to navigate the course from start to end without (i) hitting 2 or more obstacles during a single run, (ii) stepping completely off the white path with both feet or (iii) exceeding 3 minutes.\u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003efMRI\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003efMRI was performed using Siemens MAGNETOM 3T Skyra (first 6 eyes) and 3T Cima.X scanners (second 6 eyes) and a 64-channel phased array head coil (Siemens, Erlangen, Germany). Light stimuli were delivered to the participant from an MRI-compatible projector (TeleMed, Istanbul, Turkiye), directed via mirrors to the patient. A unilateral eye patch was positioned over the non-tested eye, alternating left and right to avoid fatigue.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eParadigms were presented to the participant using a NNL Aktiva fMRI interface (Nordic NeuroLab, Bergen, Norway). A series of three block design visual paradigms, each lasting approximately 5 minutes, was administered to each participant, testing each eye separately at baseline, and repeated at 2 days, 14 days and 28 days following treatment of each eye. A new baseline scan was established for the eye when treated with an increased dose approximately 3 months following the first treatment. \u0026nbsp;Cohort 1 (NLP/BLP) paradigms consisted of: full visual field on/off, switching hemifield and flickering checkboard presentations. Cohort 2 (HM/CF) paradigms consisted of: E-down, moving line and flickering checkerboard presentations. Qualitative fMRI analysis was performed using Siemens Syngo Via workstation software (Erlangen, Germany) and post-processing using NNL with manual thresholding techniques, image interpretations by a single neuroradiologist.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEarplug protection was provided to each patient, and padded head clamps applied to limit head motion. T1-weighted anatomical images were acquired using three-dimensional magnetization-prepared rapid acquisition gradient echo sequence: 1 slab; 176 sagittal slices; FOV, 256\u0026thinsp;\u0026times;\u0026thinsp;256\u0026thinsp;mm; slice thickness, 1\u0026thinsp;mm; isotropic voxel size, 1\u0026thinsp;\u0026times;\u0026thinsp;1\u0026thinsp;\u0026times;\u0026thinsp;1\u0026thinsp;mm; TR, 2300\u0026thinsp;ms; TE 2.98\u0026thinsp;ms; TI, 900\u0026thinsp;ms; and flip angle, 9\u0026deg;.\u003c/p\u003e\n\u003cp\u003eBlood-oxygenation-level-dependent (BOLD) fMRI data were acquired using a gradient-echo, simultaneous multi-slice, accelerated echo-planar imaging (EPI) T2*-weighted sequence: 54 transversal slices angled to avoid the maxillary sinuses; in-plane resolution, 2\u0026thinsp;\u0026times;\u0026thinsp;2\u0026thinsp;mm; slice thickness, 2.5\u0026thinsp;mm; field of view (FOV), 192\u0026thinsp;\u0026times;\u0026thinsp;192\u0026thinsp;mm; repetition time (TR), 3000\u0026thinsp;ms; echo time (TE), 30\u0026thinsp;ms; flip angle, 90\u0026deg;; echo spacing, 0.65\u0026thinsp;ms; bandwidth, 1774\u0026thinsp;Hz/Px; and total acceleration factor of 4 (SMS 2, GRAPPA 2); 110 measurements were acquired for each paradigm, except for checkboard where 90 measurements were acquired.\u003c/p\u003e\n\u003cp\u003eThe field map was acquired using a dual-echo gradient echo pulse sequence: 36 slices with the same position as fMRI; slice thickness, 3\u0026thinsp;mm without gap; voxel size, 3\u0026thinsp;\u0026times;\u0026thinsp;3\u0026thinsp;\u0026times;\u0026thinsp;3\u0026thinsp;mm; FOV, 192\u0026thinsp;\u0026times;\u0026thinsp;192\u0026thinsp;mm; TR, 400\u0026thinsp;ms; TE1/TE2, 4.92/7.38\u0026thinsp;ms; and flip angle, 60\u0026deg;.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eQuantification of fMRI Data\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFor quantitative fMRI analyses, EPI field maps were acquired with the same geometric parameters as the BOLD fMRI sequence, with 20 measurements acquired. \u0026nbsp;DICOM files were converted to NiFTi format and pre-processed with de-meaning, masking and brain extraction techniques. First-level analysis used a general linear model (GLM), motion correction and high-pass temporal filtering with probability set to p \u0026lt; 0.05, z of 3.1 and registration to standard space with 6 degrees of freedom. For each participant, all scans were registered to a single T1 image and second level GLM contrasts were generated between visits, with occipital lobe masking. Post-dose scans were compared to the baseline scan and maps of statically significant voxels were extracted. Quantitative analyses were performed using FSL version 6.7.0.10, Oxford, UK.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eNational Eye Institute Visual Function Questionnaire-25\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe NEI VFQ-25, without optional questions, was administered by study personnel and responses recorded accordingly.\u0026nbsp;\u003c/p\u003e\n"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to thank Dr. Stefan Sperl and Lisa Plasser for overseeing the manufacturing of the drug substance and drug product used in the studies described in this manuscript. In addition, we would like to acknowledge Drs. Lynton Graetz and Mark Jenkinson for their contribution to the analysis of the quantitative fMRI data. The authors also acknowledge Angela Walls and the facilities of the National Imaging Facility, a National Collaborative Research Infrastructure Strategy (NCRIS) capability, at the South Australian Health and Medical Research Institute. Finally, we would like to thank Lisa Tuomi for her assistance on this manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStudy design: R.J.C., E.D, B.M.S., C.D.B, A.D, R.V.G.\u003c/p\u003e\n\u003cp\u003ePatient recruitment and treatment: R.J.C.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData generation, analyses and interpretation: E.D, R.J.C, C.D.B., A.D., R. K., R.V.G. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDrafting manuscript: R.J.C, E.D.\u003c/p\u003e\n\u003cp\u003eReviewing and editing manuscript: E.D, B.M.S, C.D.B, A.D, C.C.W, C.G-K, C.S, R.K, R.V.G. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eE.D. is an employee/Officer and shareholder of Kiora Pharmaceuticals\u003c/p\u003e\n\u003cp\u003eB.M.S. is an employee/Officer and shareholder of Kiora Pharmaceuticals\u003c/p\u003e\n\u003cp\u003eC.G-K is an employee and shareholder of Kiora Pharmaceuticals\u003c/p\u003e\n\u003cp\u003eC.C.W. is a consultant of Kiora\u003c/p\u003e\n\u003cp\u003eC.S. is an employee of Ora\u003c/p\u003e\n\u003cp\u003eR.K is a consultant of Kiora\u003c/p\u003e\u003cp\u003eAuthorship: inclusion and ethics in global research\u003c/p\u003e\n\u003cp\u003eThis was an industry-sponsored trial conducted in a high-income country (Australia). \u0026nbsp;\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was sponsored by Kiora Pharmaceuticals, Inc. (Encinitas, CA). Deidentified datasets related to participant demographics, baseline characteristics, safety parameters (adverse events, vital signs, laboratory values), and efficacy outcomes (light perception, visual acuity, kinetic visual field, functional vision testing, fMRI, and quality of life questionnaire results) will be made available upon request. These data will be accessible with the exception of certain proprietary information, which will remain confidential at the discretion of Kiora Pharmaceutical. Non-proprietary data supporting the findings, including the study protocol, statistical analysis plan, and a general description of the fMRI data processing pipeline, are available from the corresponding author upon reasonable request. All data sharing is in accordance with ethical guidelines, patient privacy, and applicable regulations. Access to the available datasets will be considered for researchers who submit a methodologically sound proposal, for purposes of scholarly research that aligns with ethical standards. Data will be available from publication date for at least 5 years. Data will be shared via a secure, password-protected platform, with access granted after a formal data use agreement is signed. Requests for data access should be directed to the corresponding author, Robert J. Casson ([email protected]). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBunker, C.H., Berson, E.L., Bromley, W.C., Hayes, R.P. \u0026amp; Roderick, T.H. Prevalence of retinitis pigmentosa in Maine. \u003cem\u003eAm J Ophthalmol\u003c/em\u003e \u003cstrong\u003e97\u003c/strong\u003e, 357-365 (1984).\u003c/li\u003e\n\u003cli\u003eHeath Jeffery, R.C.\u003cem\u003e, et al.\u003c/em\u003e Inherited retinal diseases are the most common cause of blindness in the working-age population in Australia. \u003cem\u003eOphthalmic Genet\u003c/em\u003e \u003cstrong\u003e42\u003c/strong\u003e, 431-439 (2021).\u003c/li\u003e\n\u003cli\u003eRahman, F., Zekite, A., Bunce, C., Jayaram, H. \u0026amp; Flanagan, D. Recent trends in vision impairment certifications in England and Wales. \u003cem\u003eEye (Lond)\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, 1271-1278 (2020).\u003c/li\u003e\n\u003cli\u003eQuinodoz, M.\u003cem\u003e, et al.\u003c/em\u003e RetiGene, a comprehensive gene atlas for inherited retinal diseases (IRDs). \u003cem\u003ebioRxiv\u003c/em\u003e (2025).\u003c/li\u003e\n\u003cli\u003eVan Gelder, R.N.\u003cem\u003e, et al.\u003c/em\u003e Regenerative and restorative medicine for eye disease. \u003cem\u003eNat Med\u003c/em\u003e \u003cstrong\u003e28\u003c/strong\u003e, 1149-1156 (2022).\u003c/li\u003e\n\u003cli\u003eTochitsky, I., Kienzler, M.A., Isacoff, E. \u0026amp; Kramer, R.H. Restoring Vision to the Blind with Chemical Photoswitches. \u003cem\u003eChem Rev\u003c/em\u003e \u003cstrong\u003e118\u003c/strong\u003e, 10748-10773 (2018).\u003c/li\u003e\n\u003cli\u003eFain, G.L., Hardie, R. \u0026amp; Laughlin, S.B. Phototransduction and the evolution of photoreceptors. \u003cem\u003eCurr Biol\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, R114-124 (2010).\u003c/li\u003e\n\u003cli\u003eMilam, A.H., Li, Z.Y. \u0026amp; Fariss, R.N. Histopathology of the human retina in retinitis pigmentosa. \u003cem\u003eProg Retin Eye Res\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 175-205 (1998).\u003c/li\u003e\n\u003cli\u003eStone, J.L., Barlow, W.E., Humayun, M.S., de Juan, E., Jr. \u0026amp; Milam, A.H. Morphometric analysis of macular photoreceptors and ganglion cells in retinas with retinitis pigmentosa. \u003cem\u003eArch Ophthalmol\u003c/em\u003e \u003cstrong\u003e110\u003c/strong\u003e, 1634-1639 (1992).\u003c/li\u003e\n\u003cli\u003eTochitsky, I.\u003cem\u003e, et al.\u003c/em\u003e Restoring visual function to blind mice with a photoswitch that exploits electrophysiological remodeling of retinal ganglion cells. \u003cem\u003eNeuron\u003c/em\u003e \u003cstrong\u003e81\u003c/strong\u003e, 800-813 (2014).\u003c/li\u003e\n\u003cli\u003eTochitsky, I., Trautman, J., Gallerani, N., Malis, J.G. \u0026amp; Kramer, R.H. Restoring visual function to the blind retina with a potent, safe and long-lasting photoswitch. \u003cem\u003eSci Rep\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 45487 (2017).\u003c/li\u003e\n\u003cli\u003eBritten-Jones, A.C.\u003cem\u003e, et al.\u003c/em\u003e The safety and efficacy of gene therapy treatment for monogenic retinal and optic nerve diseases: A systematic review. \u003cem\u003eGenet Med\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, 521-534 (2022).\u003c/li\u003e\n\u003cli\u003eBailey, I.L., Jackson, A.J., Minto, H., Greer, R.B. \u0026amp; Chu, M.A. The Berkeley Rudimentary Vision Test. \u003cem\u003eOptom Vis Sci\u003c/em\u003e \u003cstrong\u003e89\u003c/strong\u003e, 1257-1264 (2012).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table 1","content":"\u003cp\u003eTable 1. Ocular adverse events for all participants at all doses\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"603\" class=\"fr-table-selection-hover\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eMedDRA Term*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eKIO-301\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e7.5 \u0026micro;g\u003cbr\u003e\u0026nbsp;N = 3 (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eKIO-301\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e25 \u0026micro;g\u003cbr\u003e\u0026nbsp;N = 6 (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eKIO-301\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e50 \u0026micro;g\u003cbr\u003e\u0026nbsp;N = 3 (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eSeverity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eDrug Related\u003cbr\u003e\u0026nbsp;Total N = 12 (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eEye Pain\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e2 (33%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eMild\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eUnlikely\u003cbr\u003e\u0026nbsp;2 (17%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eEye Swelling\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e1 (17%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eMild\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eUnlikely\u003cbr\u003e\u0026nbsp;1 (8.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eOcular Hypertension\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e1 (33%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eMild\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003ePossible\u003cbr\u003e\u0026nbsp;1 (8.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eAnterior Chamber Cell\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eAnterior Chamber Flare\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eVitreous Cells\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eRetinitis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eVasculitis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eIritis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eKeratic Precipitates\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003ePhotophobia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003ePhotopsia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eVitreous Floaters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003ePunctate Keratitis\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 17.9104%;\"\u003e\n \u003cp\u003eConjunctival Hyperemia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003e0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.9204%;\"\u003e\n \u003cp\u003eN/A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.408%;\"\u003e\n \u003cp\u003eN/A\u003cbr\u003e\u0026nbsp;0 (0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e*MedDRA = Medical Dictionary for Regulatory Activities\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8060107/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8060107/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"A small, azobenzene, photoswitch molecule (KIO-301) that renders retinal ganglion cells responsive to light was investigated for safety and activity in a first-in-human, phase 1/2, open-label, dose-escalation clinical trial in individuals with advanced retinitis pigmentosa. KIO-301 was delivered by intravitreal injection to 12 eyes of 6 participants. The primary endpoint was safety. Secondary endpoints included assessment of functional vision, visual acuity, kinetic visual field, functional magnetic resonance imaging (fMRI) and participant reported outcomes. There were no drug-related adverse events. A participant with no light perception at baseline recovered light perception by 2 days post injection. Visual function, including navigational ability, displayed a trend of improvement. By day 2-14 post injection the fMRI signal to visual stimuli in the primary visual cortex was enhanced and decayed over the ensuing 3 weeks. Participant-reported quality of life improved. The excellent safety profile and evidence supporting proof-of-principle has motivated a larger, randomized controlled trial.","manuscriptTitle":"Vision restoration using a light-responsive small molecule photoswitch (KIO-301) in advanced retinitis pigmentosa: the ABACUS-1 phase 1/2 clinical trial","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-17 06:39:57","doi":"10.21203/rs.3.rs-8060107/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-medicine","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nm","sideBox":"Learn more about [Nature Medicine](http://www.nature.com/nm/)","snPcode":"","submissionUrl":"","title":"Nature Medicine","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"c35efce4-696d-41a5-b0a2-bccab0824de8","owner":[],"postedDate":"November 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":58010500,"name":"Health sciences/Health care/Therapeutics/Biological therapy"},{"id":58010501,"name":"Biological sciences/Neuroscience/Visual system/Retina"}],"tags":[],"updatedAt":"2026-04-15T07:13:32+00:00","versionOfRecord":{"articleIdentity":"rs-8060107","link":"https://doi.org/10.1038/s41591-026-04317-6","journal":{"identity":"nature-medicine","isVorOnly":false,"title":"Nature Medicine"},"publishedOn":"2026-04-14 04:00:00","publishedOnDateReadable":"April 14th, 2026"},"versionCreatedAt":"2025-11-17 06:39:57","video":"","vorDoi":"10.1038/s41591-026-04317-6","vorDoiUrl":"https://doi.org/10.1038/s41591-026-04317-6","workflowStages":[]},"version":"v1","identity":"rs-8060107","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8060107","identity":"rs-8060107","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}