Topical latanoprost acid for female androgenetic alopecia: a pilot proof-of-concept trial with mechanistic evidence of FP-receptor activation

Topical latanoprost acid for female androgenetic alopecia: a pilot proof-of-concept trial with mechanistic evidence of FP-receptor activation | 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 Research Article Topical latanoprost acid for female androgenetic alopecia: a pilot proof-of-concept trial with mechanistic evidence of FP-receptor activation Adriana Rakowska, Małgorzata Dutkiewicz, Oliwia Zegrocka-Stendel, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8949172/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 9 You are reading this latest preprint version Abstract Background Prostaglandin F2α (FP) receptor signaling is a plausible target for promoting hair growth, but clinical data on topical latanoprost acid (the active free-acid FP agonist) in hair loss are lacking. Methods In an investigator-initiated, randomized, double-blind, single-center, dose-ranging pilot trial, adult women with hair loss predominantly consistent with female androgenetic alopecia applied once-daily topical latanoprost acid 0.01%, 0.05%, or 0.1% for 6 months; a small vehicle group was included to support masking. The primary endpoint was within-participant change in target-area hair count (TAHC, hairs/cm²) from baseline to Month 6; trichoscopic activity markers (yellow dots) and follicular-unit (FU) remodeling were secondary/exploratory outcomes. Human hair dermal papilla cells were assessed for FP-linked signaling (intracellular Ca²⁺ flux) and proliferation (EdU) after exposure to latanoprost acid versus equimolar latanoprost. Results TAHC increased across active arms, with the most consistent multi-endpoint signal in the 0.05% group (mean ± SD ΔTAHC 23.5 ± 21.2 hairs/cm²), accompanied by reduced yellow dots and a shift from single-hair to multi-hair FUs; between-dose comparisons were not powered. Safety was favorable with no serious adverse events. In mechanistic assays, latanoprost acid triggered rapid, concentration-dependent Ca²⁺ flux, whereas equimolar latanoprost produced delayed signals; neither compound increased EdU incorporation. Conclusions Topical latanoprost acid showed a coherent clinical-trichoscopic bioactivity signal with supportive FP-linked signaling in human hair dermal papilla cells, warranting larger PK/PD-integrated trials centered on 0.05%. Trial registration: ClinicalTrials.gov, NCT07412587; registered on February 2, 2026. androgenetic alopecia latanoprost acid FP receptor dermal papilla calcium signaling hair growth Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Hair loss is common in both men and women and is frequently associated with distress, reduced self-esteem, and diminished quality of life [ 1 , 2 ]. In women, female androgenetic alopecia is the most common cause of the female pattern hair loss phenotype and manifests as diffuse thinning over the vertex and mid-scalp, whereas chronic telogen effluvium (TE) presents with persistent diffuse shedding [ 1 , 3 ]. Existing therapies, including topical or oral minoxidil and oral anti-androgens (e.g., finasteride, spironolactone or dutasteride), can benefit many patients; however, responses are variable and long-term use may be limited by tolerability, contraindications, or patient preference, underscoring the need for additional safe and effective options [ 4 – 6 ]. Since the initial observation of eyelash hypertrichosis in glaucoma patients treated with latanoprost, prostaglandin analogues have been recognized as promising hair-growth modulators [ 7 ]. Prostaglandin signaling provides a biologically plausible route to hair growth promotion [ 8 ]. In the follicle, FP (PGF₂α) receptor is expressed in anagen human hair follicles, including dermal papilla and perifollicular compartments [ 8 ] and couples via Gq to phosphoinositide/PLC signaling with intracellular Ca²⁺ mobilization [ 9 ]. Clinically, FP-pathway agonism has been associated with increased hair growth and pigmentation in clinical dermatologic contexts [ 7 , 10 ]. Despite this receptor-level rationale, clinical work to date has centered on marketed glaucoma prostaglandin analogues, including topical latanoprost. Latanoprost is an isopropyl-ester prodrug that requires hydrolysis to latanoprost acid, the active FP-receptor agonist, and, to a more limited extent, bimatoprost/prostamide analogues, rather than on the corresponding active moieties (e.g., the free acids), leaving direct evaluation of these active forms largely unexplored [ 11 ]. Given that prostaglandin analogue activation depends on tissue hydrolases (e.g., esterases for latanoprost; amidases generating the carboxylic acid from bimatoprost) [ 12 , 13 ] and that cutaneous drug-metabolizing enzyme activity can vary by anatomical site and between individuals [ 14 , 15 ], direct testing of active moieties could yield more predictable pharmacodynamics in target engagement. Moreover, as a charged free acid, latanoprost acid is expected to have lower trans-barrier flux, which may limit systemic exposure with topical scalp application [ 16 , 17 ]. Latanoprost was explicitly designed as an isopropyl-ester prodrug to enhance tissue penetration, followed by hydrolysis to latanoprost acid after barrier crossing [ 12 , 16 ]. Consistent with this principle, ocular dosing with latanoprost has been associated with detectable systemic exposure to latanoprost acid [ 16 ]. These considerations support evaluating latanoprost acid itself as a topical scalp treatment. Here, we report the first, to our knowledge, investigator-initiated clinical evaluation of topical latanoprost acid in women with hair loss. We assessed changes in target-area hair count and trichoscopic outcomes, and we complemented clinical findings with mechanistic experiments in human hair dermal papilla cells (HHDPCs), including FP-receptor engagement (Ca²⁺ flux) and cell-proliferation assays following exposure to latanoprost acid versus latanoprost. Material and Methods Study design, participants, and ethics This investigator-initiated, randomized, double-blind, single-center, dose-ranging pilot trial was conducted at the Department of Dermatology, Medical University of Warsaw. Participants received once-daily topical treatment for 6 months, with evaluations at baseline, Month 3, and Month 6. The study protocol was approved by the Ethics Committee of the Medical University of Warsaw (KB/148/2015; approved on July 7, 2015). The privacy rights of participants were observed. All participants provided written informed consent prior to enrollment. The study was conducted in accordance with the Declaration of Helsinki and ICH-GCP. The study was registered at ClinicalTrials.gov (Identifier: NCT07412587; first posted on February 2, 2026). Women aged 18–60 years with patterned scalp hair loss consistent with female androgenetic alopecia (Ludwig I–III) or chronic telogen effluvium were eligible. For participants with female androgenetic alopecia, the diagnosis was confirmed by trichoscopy [ 18 ]. Exclusion criteria included recent use of hair-growth treatments, active scalp dermatoses, or significant uncontrolled medical conditions. Forty patients were screened; 29 were enrolled. Randomization, masking, and interventions Participants were randomized to vehicle or latanoprost acid 0.01%, 0.05%, or 0.1% in identical, coded dropper bottles. Allocation was computer-generated, and masking was maintained for participants and investigators through Month 6. The assigned study product was applied once daily to the androgen-dependent scalp region (i.e., the clinically affected area). Participants were instructed to apply 2–3 mL as needed to cover the area, distribute it evenly, avoid runoff, and refrain from washing the area for ≥ 8 h. The tested product was formulated as an oil-in-water (o/w) emulsion. Major excipients included water, phosphate buffer, EDTA, xanthan gum, paraffin, an emulsifying system based on a mixture of fatty alcohols and their ethers, propylene glycol, and phenoxyethanol. The placebo vehicle was identical, without latanoprost acid. Hair-care routines were kept constant; concomitant hair-loss therapies were prohibited. Clinical and trichoscopic outcome assessments were performed at standardized assessment sites/fields at fixed scalp locations within the treated region, using the same locations consistently across visits. Outcomes The primary endpoint was the within-subject absolute change in target-area hair count (ΔTAHC, hairs/cm²) from baseline to Month 6 (Month 3 change supportive). Trichoscopic assessments (TAHC and secondary trichoscopic features) were performed in standardized assessment fields/sites at fixed scalp locations within the treated androgen-dependent region (including points located 1 cm beyond the hairline), using the same locations consistently across visits. Percent change TAHC (%TAHC) from baseline was summarized as a supportive analysis. Secondary endpoints included trichoscopic features such as hair-shaft thickness (grade 0–3), follicular-unit arrangement, number of yellow dots, and patient-reported outcomes. Safety/tolerability endpoints comprised adverse events, local scalp findings (erythema/irritation), and vital signs. Assessments Standardized clinical macrophotographs of the androgen-dependent scalp region and trichoscopy were obtained at each visit using a consistent acquisition protocol. Trichoscopy images were acquired at fixed scalp locations within the treated region (20× and 70× magnification). For target-area hair count (TAHC), a 1 cm² area was delineated on the 20× trichoscopy image and all visible hairs within this area were counted manually (hairs/cm²). Trichoscopy also captured follicular-unit arrangement (percentage of follicular units with single hair [%FU1], and with two or three hairs [%FU2 and %FU3]) and the number of yellow dots, assessed from images obtained at the same standardized locations. Patient self-assessments (shedding, thickness, overall growth) were collected at Months 3 and 6 using a structured questionnaire. Safety was assessed at each visit via systematic adverse-event queries, targeted scalp examination, and vital signs. Cell-based functional assays in HHDPCs Functional effects of latanoprost acid and latanoprost on HHDPCs were evaluated using complementary assays addressing receptor signaling and cell proliferation. Ca²⁺-flux assays measured intracellular calcium dynamics as a direct marker of FP-receptor activation, while EdU incorporation assays assessed whether receptor activation translated into proliferative responses. Intracellular Ca²⁺ flux Primary HHDPCs (Innoprot, Spain) were cultured in Mesenchymal Stem Cell Medium with growth supplement and penicillin/streptomycin on poly-L-lysine-coated plastic (0.01% for 30 min). Cells were seeded on glass coverslips, grown for 48 h to confluence, and loaded with Fura-2 AM (4 µM, 30 min, 37°C). Ratiometric cytosolic [Ca²⁺] signals (F340/F380) were recorded at RT in physiological buffer (with 2 mM CaCl₂) using a spectrofluorimeter (Hitachi F-7000 or equivalent). Latanoprost acid and latanoprost were applied at concentrations ranging from 31.25–500 nM; vehicle controls were included. DNA synthesis assay DNA synthesis was quantified using the 5-Ethynyl-2'-deoxyuridine (EdU) Proliferation Kit (Lumiprobe) according to the manufacturer’s instructions. Cells were seeded in poly-L-lysine-coated 96-well optical-bottom plates (Greiner) at a density of 1,600 cells per well. HHDPCs were exposed to latanoprost acid or latanoprost (31.25–1000 nM) in complete medium and assessed after 24, 48 or 72 h. Cells were pulsed with EdU (10 µM, 1 h), fixed with 4% paraformaldehyde, permeabilized (0.5% Triton X-100), and stained via copper(I)-catalyzed azide–alkyne click chemistry with sulfo-Cy3–conjugated azide. Nuclei were counterstained with Hoechst 33342. Images were acquired with 20× objective on Operetta CLS imaging system under identical settings. At least 13 random fields per condition per experiment were analyzed with Harmony 4.9 software. The EdU index was calculated as the fraction of EdU-positive nuclei (Cy3-positive) among total Hoechst-positive nuclei and averaged across three independent experiments. PrestoBlue metabolic activity assay Metabolic activity of HHDPCs was assessed using the PrestoBlue™ (Thermo Fisher Scientific/Invitrogen) resazurin-based assay according to the manufacturer’s instructions. Cells were exposed to vehicle or the indicated concentrations of latanoprost acid or latanoprost, followed by incubation with PrestoBlue reagent and measurement of fluorescence. Signals were background-subtracted and normalized to vehicle controls. Statistical analysis All analyses were exploratory. Continuous outcomes are summarized as mean ± SEM unless stated otherwise. Repeated-measures clinical endpoints, including TAHC and trichoscopic/follicular-unit arrangement measures, were analyzed using a mixed-effects model for repeated measures (REML), with time and treatment concentration, and their interaction as fixed effects, and participant as a random effect. For outcomes expressed as change from baseline (e.g., ΔTAHC and %TAHC), the dependent variables were the change scores at Month 3 and Month 6. This approach uses all available observations without imputing missing values. Post-hoc comparisons were performed using Tukey’s multiple comparisons test. Results are reported as model-estimated (least-squares) mean differences with 95% confidence intervals and Tukey-adjusted p values. The investigator-rated hair-shaft thickness improvement grade (ordinal scale 0–3) assessed at Month 6 was compared across concentrations using the Kruskal–Wallis test (exact p value). For in vitro EdU incorporation experiments, percent EdU-positive cells were analyzed by two-way ANOVA with factors compound (latanoprost acid vs latanoprost) and concentration, including their interaction; where applicable, multiplicity-adjusted post-hoc comparisons were applied. All tests were two-sided; p < 0.05 was considered statistically significant. Analyses were performed in GraphPad Prism (version 10.2; GraphPad Software, San Diego, CA, USA). Results Participant Disposition and Baseline Characteristics Twenty-nine women were randomized: vehicle ( n = 2), latanoprost acid 0.01% ( n = 7), 0.05% ( n = 13), and 0.1% ( n = 7). Enrollment stopped early (target 40) for practical reasons, yielding unequal group sizes. Overall, 25/29 (86%) completed Month 6. Four discontinued: one in group 0.01% at Month 3 due to headache; in group 0.05% one lost at ~ 4 weeks for increased shedding, one lost to follow-up after baseline, and one for non-compliance. Efficacy analyses used a modified intent-to-treat set, defined as all randomized participants with ≥ 1 post-baseline efficacy assessment; safety analyses included all treated participants. Baseline characteristics were broadly comparable. The mean age was in the mid-30s (range 24–60), and all participants were female. Most (27/29) had female androgenetic alopecia (predominantly Ludwig I-II), with two cases of chronic telogen effluvium. Baseline TAHC varied; by chance, the 0.05% group started lower than 0.01% and 0.1% (138.0 ± 34.1 vs 175.5 ± 65.4 and 165.0 ± 62.3 hairs/cm²). Baseline trichoscopic features (%FU1, %FU2, %FU3, number of yellow dots) did not differ significantly. All efficacy analyses were conducted as within-subject changes from baseline. Primary efficacy outcome: absolute change in target-area hair count (ΔTAHC) From baseline to Month 6, ΔTAHC increased across concentration arms (Fig. 1 A). Descriptively, mean (± SD) ΔTAHC at Month 6 was 17.8 ± 10.7 (0.01%), 23.5 ± 21.2 (0.05%), and 16.5 ± 15.6 hairs/cm² (0.1%). A significant main effect of time was observed (p = 0.0058), with no evidence of a concentration effect (p = 0.95) or time×concentration interaction (p = 0.17). In supportive analyses of trajectory, we examined the incremental change from Month 3 to Month 6 (i.e., additional gain after Month 3): the incremental change between Month 3 and Month 6 was significant only in the 0.05% arm (model-estimated mean difference 11.36 hairs/cm²; 95% CI 5.02–17.71; Tukey-adjusted p = 0.0014), whereas changes were not significant in the 0.01% (8.37; 95% CI − 0.96 to 17.71; p = 0.0759) or 0.1% arms (1.33; 95% CI − 7.25 to 9.92; p = 0.7487). Between-arm differences at Month 3 and Month 6 were not significant (all Tukey-adjusted p > 0.69). Supportive analysis: percent change in target-area hair count (%TAHC) Results were consistent when expressed as percent change from baseline (Fig. 1 B). Model-estimated %TAHC increased from Month 3 to Month 6 across all arms (0.01%: 6.93% to 11.96%; 0.05%: 9.81% to 18.99%; 0.1%: 10.37% to 13.94%). The Month 3 - Month 6 increment was significant only in the 0.05% arm (+ 9.18 percentage points; 95% CI 3.08–15.28; Tukey-adjusted p = 0.0053) and was not significant in the 0.01% (+ 5.02 pp; 95% CI − 3.94 to 13.98; p = 0.2553) or 0.1% arms (+ 3.57 pp; 95% CI − 4.70 to 11.82; p = 0.3776). Between-arm differences at Month 3 and Month 6 were not significant (Tukey-adjusted p ≥ 0.61). Together, these analyses support a treatment-associated increase in hair density over 6 months with topical latanoprost acid, with the most consistent progressive signal observed at 0.05%. Responder analysis When applying a liberal responder definition (any increase > 0% from baseline), responder rates at Month 6 were 100% (5/5), 90.9% (10/11), and 83.3% (5/6) for the 0.01%, 0.05%, and 0.1% groups, respectively. A more conservative definition (≥ 10% increase in TAHC) yielded proportionally lower responder rates (80.0%, 72.7%, and 66.7%, respectively), but the same ranking across concentrations. These findings are consistent with the mixed-model results showing the greatest mean improvement in the 0.05% group. Secondary and Exploratory Outcomes (Trichoscopy) Yellow dots Yellow dot counts decreased over time (time effect p < 0.0001), with no evidence of concentration effects or a time×concentration interaction (Fig. 2 ). Tukey-adjusted post-hoc comparisons showed a significant reduction in the 0.05% arm at Month 3 (p = 0.0011) and Month 6 (p = 0.0001), and a smaller reduction in the 0.01% arm at Month 3 (p = 0.0317); no significant change was observed in the 0.1% arm. Follicular unit (FU) arrangement Complementary changes were observed in follicular-unit arrangement (Fig. 3 ). Because some observations were missing, FU outcomes were analyzed using a mixed-effects model (REML) with Tukey-adjusted multiple comparisons. In the 0.05% arm, %FU1 decreased significantly versus baseline at Month 3 and Month 6 (both p < 0.0001), accompanied by a reciprocal increase in %FU3 (baseline vs Month 3, p = 0.0149; baseline vs Month 6, p = 0.0004), consistent with a shift toward multi-hair follicular units. No significant within-arm changes in %FU1 or %FU3 were detected in the 0.01% arm, and changes in the 0.1% arm did not reach significance (baseline vs Month 6 for %FU3, p = 0.0528). At baseline, %FU1 was higher in the 0.05% arm than in the 0.01% and 0.1% arms (p = 0.0015 and p = 0.0296, respectively), and %FU3 was lower in the 0.05% arm than in the 0.1% arm (p = 0.0241). Between-arm differences were not significant by Month 6 (all p > 0.05), although %FU3 remained borderline between 0.05% and 0.1% (p = 0.0593). Hair-shaft thickness improvement grade (0–3) At Month 6, investigator-rated improvement in hair-shaft thickness (0 = no improvement; higher scores indicate greater improvement) did not differ significantly across dose arms (Kruskal-Wallis test, exact p = 0.188). Median [IQR] improvement grades were 1 [ 1 – 1 ] for 0.01% (n = 5), 2 [ 1 – 2 ] for 0.05% (n = 11), and 2 [ 1 – 2 ] for 0.1% (n = 6), consistent with modest clinician-rated improvement without evidence of a dose-dependent difference (Fig. 4 ). Representative trichoscopic images Representative 70× trichoscopic images from participants in the 0.05% and 0.1% arms at baseline and Month 6 are shown in Fig. 5 . Patient-Reported Outcomes By Month 3, approximately half of participants across treatment arms reported reduced shedding and perceived improvement in hair quality, most often in the 0.05% and 0.1% arms. By Month 6, participants in these arms more frequently reported visible gains in hair volume and density, whereas responses in the 0.01% arm were more variable. Overall, patient-reported outcomes were directionally consistent with changes in TAHC and trichoscopic measures. Safety Topical latanoprost acid was generally well tolerated. No serious adverse events or hospitalizations occurred. Targeted scalp examinations revealed no clinically relevant irritation or inflammation, and vital signs remained within normal limits. Causes for discontinuation included headache in the 0.01% arm (by Month 3) and three discontinuations in the 0.05% arm (increased shedding at ~ 4–6 weeks, loss to follow-up, and non-compliance). Mechanistic assessment in HHDPCs To explore whether the clinical pattern of improvement is consistent with FP-receptor-mediated signaling, we compared latanoprost acid and latanoprost in cultured HHDPCs, assessing Ca²⁺ flux and proliferation-related readouts. FP-receptor engagement in HHDPCs (Ca²⁺ flux) Latanoprost acid elicited a rapid, transient, concentration-dependent Ca²⁺ response, whereas equimolar latanoprost produced a delayed, gradually rising response without a distinct peak (Fig. 6 ). A clear Ca²⁺ signal was detectable for latanoprost acid at concentrations as low as 31.25 nM, while latanoprost at the same concentration did not elicit a discernible Ca²⁺ response above baseline. These findings are consistent with more immediate FP-receptor-linked signaling by the free-acid form compared with the ester prodrug under the conditions tested. Cell proliferation and metabolic activity in HHDPCs Neither latanoprost acid nor latanoprost altered the proportion of EdU-positive nuclei compared with vehicle across the tested concentration range at any time point (24, 48, or 72 h). Representative data at 48 h are shown in Fig. 7 , indicating no detectable effect on DNA synthesis. Consistently, neither compound increased PrestoBlue signal compared with vehicle across the tested concentration range (data not shown). Discussion In this investigator-initiated, randomized, double-blind pilot study, topical latanoprost acid was associated with clinically interpretable improvements over 6 months in women with female androgenetic alopecia, with a small number of participants with chronic telogen effluvium included. Across the doses tested, the 0.05% arm showed the most consistent, multi-endpoint pattern of objective change: higher target-area hair count (TAHC), a reduction in the proportion of single-hair follicular units (%FU1) accompanied by a reciprocal rise in the proportion of three-hair units (%FU3), and a reduced number of yellow dots, a trichoscopic feature linked to inactive/kenogen-phase follicles [ 18 , 19 ]. Baseline imbalances in FU arrangement were present (higher %FU1 and lower %FU3 in the 0.05% arm vs comparators), and between-arm comparisons of change scores were under-powered due to unequal group sizes and attrition; accordingly, dose-related inferences should be interpreted cautiously. Patient-reported outcomes were directionally consistent with these signals, with perceived gains in volume/density reported more frequently at 0.05% and 0.1%. Beyond mean changes, the categorical emergence of multi-hair follicular units supports a biologically interpretable shift in follicular output. In the 0.05% arm, the proportion of evaluable participants with any FU3 present in the target area rose from 27.3% at baseline to 54.5% at Month 3 and 81.8% at Month 6, with 6/8 participants who had no FU3 at baseline exhibiting FU3 by Month 6. By contrast, the 0.1% arm showed high, stable prevalence of FU3 (~ 83%) across visits, consistent with a possible ceiling effect, and the 0.01% arm also remained near-saturated (rising from 86% to 100% among evaluable participants). This categorical emergence in the 0.05% arm complements the reduction in yellow dots and the within-arm remodeling in FU arrangement (decreasing %FU1 with increasing %FU3), collectively supporting treatment-associated follicular reactivation and/or enhanced output from previously low-output follicles. Importantly, the dermoscopic/trichoscopic pattern (fewer yellow dots and a shift from single- to multi-hair follicular units) is compatible with reactivation of follicles in kenogen phase [ 20 , 21 ], although confirmatory studies with larger cohorts and prespecified imaging/assessment procedures are needed to define the biological substrate with greater certainty. An interpretable dose pattern emerged in which 0.05% yielded the most consistent improvements across endpoints, whereas 0.1% did not clearly outperform the mid dose. Several non-exclusive explanations are plausible: (i) a pharmacodynamic ceiling or inverted-U dose–response, in which FP-receptor/effector systems may be near-maximally engaged at 0.05%; (ii) subtle local effects at higher concentrations (insufficient to register as adverse events yet potentially capable of attenuating growth signals); (iii) baseline imbalances (e.g., lower baseline TAHC in 0.05% and higher in 0.1%, potentially influencing the magnitude of observable change); and (iv) limited statistical power. These hypotheses require confirmation. Collectively, the present data nominate 0.05% as a candidate dose to be evaluated in larger, prospectively dose-ranging trials with prespecified between-group contrasts and standardized assessment procedures. The mechanistic bridge from receptor to clinic is supported on two complementary levels. First, Ca²⁺-flux assays in HHDPCs demonstrated rapid, concentration-dependent responses to latanoprost acid with a clear transient peak, while equimolar latanoprost (an ester prodrug) produced delayed, slowly rising signals without a distinct peak. This pattern is consistent with more immediate FP-receptor-linked signaling by the free acid and conversion-limited activity of the prodrug under the conditions tested. Second, the trichoscopic profile. i.e., fewer yellow dots and a shift toward multi-hair follicular units, is compatible with follicular reactivation and/or increased output from follicles transitioning out of kenogen [ 20 , 21 ]. Prior studies have linked prostaglandin-pathway activation to changes in hair-shaft pigmentation; however, pigmentation was not assessed here and warrants future evaluation [ 7 , 11 ]. Taken together, these observations support a mechanistically distinct FP-receptor-targeted approach that delivers the active free acid (bypassing potential variability in prodrug activation) and provides a coherent biological rationale for clinical translation. In parallel, cell-proliferation assays using EdU incorporation demonstrated that neither latanoprost acid nor latanoprost increased DNA synthesis in HHDPCs after 24–72 h of exposure across nanomolar concentrations. These findings suggest that FP-receptor-linked signaling (as reflected by Ca²⁺ flux) is not accompanied by detectable cell-cycle progression under these conditions, which is consistent with a signal-modulatory/paracrine role of dermal papilla cells in follicular regeneration rather than direct expansion of the dermal papilla cell population. Accordingly, the clinical and trichoscopic signals observed may reflect enhanced follicular activation and intercellular communication within the follicular niche rather than a primary proliferative mechanism in dermal papilla cells. Despite long-standing clinical signals that prostaglandin analogues can stimulate hair growth, no prostaglandin-pathway drug is approved for scalp hair loss. To date, bimatoprost 0.03% (LATISSE®) remains the only FDA-approved prostaglandin analogue for a hair indication (eyelash hypotrichosis) [ 22 , 23 ]. A pragmatic contributor to the historical gap in scalp indications may be the prolonged “cosmetic route” in which prostaglandin analogues appeared in over-the-counter eyelash/brow serums in Europe [ 24 , 25 ], blurring boundaries between cosmetic and medicinal use and dampening incentives for formal drug development. Regulatory scrutiny has tightened only recently. In 2022, the European Union Scientific Committee on Consumer Safety (SCCS) raised explicit safety concerns about prostaglandin analogues in cosmetics [ 25 ], and in 2025 the SCCS concluded that specific prostaglandin analogues cannot be considered safe for cosmetic products intended to promote eyelash/eyebrow growth [ 26 ]. In parallel, the European Union has advanced updates strengthening prohibitions on unsafe cosmetic substances [ 27 ]. Together, these developments have narrowed the cosmetic route and may help re-align incentives toward indication-specific medicinal development for scalp hair loss. Importantly, most clinical work on prostaglandin analogues in scalp hair loss has focused on ester prodrugs rather than free acids, leaving direct delivery of the active moiety underexplored. Addressing this gap, our study is, to our knowledge, the first investigator-initiated clinical evaluation of topically administered latanoprost acid, the active moiety of latanoprost, for scalp hair loss. In this proof-of-concept work, topically applied latanoprost acid exhibited consistent bioactivity signals in human scalp hair, as evidenced by concordant improvements in TAHC and trichoscopic markers over 6 months, alongside a favorable safety profile. The magnitude and consistency of these effects were most evident at 0.05%, supporting its prioritization for confirmation in larger, prospectively dose-ranging studies. Given the potential for long-term use, assessing the safety and tolerability of topical latanoprost acid is particularly important. In this study, safety was favorable across concentrations, with no serious adverse events, no ocular or pigmentary concerns detected, and no unwanted hair growth (ectopic hypertrichosis). The absence of systemic clinical signals is consistent with the limited permeability expected for the free-acid form on the scalp and aligns with our a priori safety hypothesis [ 5 , 17 ]. Nonetheless, longer exposure, larger cohorts, and pharmacokinetic assessment will be necessary to characterize uncommon events and to confirm minimal systemic exposure, particularly if higher concentrations are pursued. Limitations. This pilot study was small, single-center, and ended early due to funding constraints, resulting in unequal group sizes and a particularly small vehicle arm, limiting between-arm inference. The 6-month follow-up may not capture maximal response or long-term durability. Although follicular-unit metrics were collected at each visit, denominators varied due to attrition, and analyses were sensitive to missingness across time points. Patient-reported outcomes were collected via structured interview rather than a fully validated instrument. Finally, inclusion of two participants with chronic telogen effluvium may have contributed to response heterogeneity. Taken together, the convergence of cellular (Ca²⁺ flux), trichoscopic, and clinical signals indicates bioactivity of latanoprost acid in human scalp hair. These proof-of-concept data support an adequately powered, randomized, dose-ranging trial centered on 0.05%, with PK/PD integration to relate scalp exposure to FP-receptor-linked signaling and clinical endpoints. Future studies should extend follow-up to ≥ 12 months to define trajectory and durability; incorporate validated patient-reported outcomes; implement standardized global photography and trichoscopy; evaluate combination therapy (e.g., with minoxidil and/or anti-androgens); and explicitly contrast prodrug versus free-acid strategies to clarify class effects and optimize translational approaches. In summary, topical latanoprost acid was associated with consistent improvements in objective and subjective measures over 6 months, with 0.05% showing the most consistent multi-endpoint signal and a favorable safety profile. These findings support continued clinical development of latanoprost acid and related FP-receptor modulators as targeted treatments for hair loss. Declarations Funding statement This work was supported in part by the Ministry of Science and Higher Education (Innovation Incubator 2.0 programme; grant no. MNISW/2017/DIR/71/II+) implemented within the Smart Growth Operational Programme 2014–2020 (POIR) and co-financed by the European Regional Development Fund (ERDF). Selected in vitro experiments were supported by BioResearch Pharma S.A. Conflict of interest statement A.R., L.R., and K.K. are inventors on a patent related to the use of latanoprost acid for promoting hair growth. K.K. is a co-founder of BioResearch Pharma S.A. and serves as its Chief Scientific Officer. M.W. is an employee of BioResearch Pharma S.A. (R&D Project Manager). BioResearch Pharma S.A. was incorporated several years after completion of the human study and therefore had no involvement in its design or conduct. The company provided partial financial support for selected in vitro analyses reported in this manuscript. The funders had no role in data analysis, interpretation, or the decision to submit the manuscript. All other authors declare no competing interests. Author contributions K.K., A.R., L.R., and J.W. contributed to the conceptualization of the study. A.R., M.D., O.Z.-S., J.W., D.D., G.H., M.W., L.R., and K.K. contributed to the methodology. A.R., M.D., O.Z.-S., D.D., J.W., and G.H. conducted the investigation. A.R., J.W., D.D., and K.K. curated the data. K.K. and L.R. performed the formal analysis. K.K. wrote the original draft of the manuscript. A.R., M.D., O.Z.-S., G.H., D.D., J.W., M.W., and L.R. reviewed and edited the manuscript. K.K. performed validation and supervised the study. A.R. and K.K. prepared the visualizations. K.K. acquired funding. All authors reviewed and approved the final manuscript. Data availability statement The data that support the findings of this study are available from the corresponding author upon reasonable request. References Muller Ramos P, Melo DF, Radwanski H, de Almeida RFC, Miot HA. Female-pattern hair loss: therapeutic update. An Bras Dermatol. 2023;98(4):506-19. Mohamed NE, Soltan MR, Galal SA, El Sayed HS, Hassan HM, Khatery BH. Female Pattern Hair Loss and Negative Psychological Impact: Possible Role of Brain-derived Neurotrophic Factor (BDNF). Dermatol Pract Concept. 2023;13(3). Chien Yin GO, Siong-See JL, Wang ECE. Telogen Effluvium - a review of the science and current obstacles. J Dermatol Sci. 2021;101(3):156-63. Lucky AW, Piacquadio DJ, Ditre CM, Dunlap F, Kantor I, Pandya AG, et al. A randomized, placebo-controlled trial of 5% and 2% topical minoxidil solutions in the treatment of female pattern hair loss. J Am Acad Dermatol. 2004;50(4):541-53. Kanti V, Messenger A, Dobos G, Reygagne P, Finner A, Blumeyer A, et al. Evidence-based (S3) guideline for the treatment of androgenetic alopecia in women and in men - short version. J Eur Acad Dermatol Venereol. 2018;32(1):11-22. Ong MM, Avram M, McMichael A, Tosti A, Lipner SR. Antiandrogen therapy for the treatment of female pattern hair loss: A clinical review of current and emerging therapies. J Am Acad Dermatol. 2025;93(3):749-60. Johnstone MA. Hypertrichosis and increased pigmentation of eyelashes and adjacent hair in the region of the ipsilateral eyelids of patients treated with unilateral topical latanoprost. Am J Ophthalmol. 1997;124(4):544-7. Colombe L, Michelet JF, Bernard BA. Prostanoid receptors in anagen human hair follicles. Exp Dermatol. 2008;17(1):63-72. Ito S, Sakamoto K, Mochizuki-Oda N, Ezashi T, Miwa K, Okuda-Ashitaka E, et al. Prostaglandin F2 alpha receptor is coupled to Gq in cDNA-transfected Chinese hamster ovary cells. Biochem Biophys Res Commun. 1994;200(2):756-62. Carruthers J, Beer K, Carruthers A, Coleman WP, 3rd, Draelos ZD, Jones D, et al. Bimatoprost 0.03% for the Treatment of Eyebrow Hypotrichosis. Dermatol Surg. 2016;42(5):608-17. Blume-Peytavi U, Lonnfors S, Hillmann K, Garcia Bartels N. A randomized double-blind placebo-controlled pilot study to assess the efficacy of a 24-week topical treatment by latanoprost 0.1% on hair growth and pigmentation in healthy volunteers with androgenetic alopecia. J Am Acad Dermatol. 2012;66(5):794-800. Stjernschantz JW. From PGF(2alpha)-isopropyl ester to latanoprost: a review of the development of xalatan: the Proctor Lecture. Invest Ophthalmol Vis Sci. 2001;42(6):1134-45. Maxey KM, Johnson JL, LaBrecque J. The hydrolysis of bimatoprost in corneal tissue generates a potent prostanoid FP receptor agonist. Surv Ophthalmol. 2002;47 Suppl 1:S34-40. Pyo SM, Maibach HI. Skin Metabolism: Relevance of Skin Enzymes for Rational Drug Design. Skin Pharmacol Physiol. 2019;32(5):283-94. Telaprolu KC, Grice JE, Mohammed YH, Roberts MS. Human Skin Drug Metabolism: Relationships between Methyl Salicylate Metabolism and Esterase Activities in IVPT Skin Membranes. Metabolites. 2023;13(8). Sjoquist B, Stjernschantz J. Ocular and systemic pharmacokinetics of latanoprost in humans. Surv Ophthalmol. 2002;47 Suppl 1:S6-12. N'Da DD. Prodrug strategies for enhancing the percutaneous absorption of drugs. Molecules. 2014;19(12):20780-807. Rakowska A, Slowinska M, Kowalska-Oledzka E, Olszewska M, Rudnicka L. Dermoscopy in female androgenic alopecia: method standardization and diagnostic criteria. Int J Trichology. 2009;1(2):123-30. Lima CDS, Lemes LR, Melo DF. Yellow dots in trichoscopy: relevance, clinical significance and peculiarities. An Bras Dermatol. 2017;92(5):724-6. Rebora A, Guarrera M. Kenogen. A new phase of the hair cycle? Dermatology. 2002;205(2):108-10. Kuczara A, Waskiel-Burnat A, Rakowska A, Olszewska M, Rudnicka L. Trichoscopy of Androgenetic Alopecia: A Systematic Review. J Clin Med. 2024;13(7). Law SK. Bimatoprost in the treatment of eyelash hypotrichosis. Clin Ophthalmol. 2010;4:349-58. U.S. Food and Drug Administration. Medical Review(s): Latisse (bimatoprost ophthalmic solution) 0.03% (NDA 022369). Center for Drug Evaluation and Research (CDER), U.S. Food and Drug Administration; 2008. Report No.: NDA 022369. Hopley C CS, Webster W, Bird G, Dillon E, Axford I. Prostaglandin analogues in cosmetics. 2024. Report No.: BEIS/OPSS: RE21425 SCCS (Scientific Committee on Consumer Safety). Opinion on Prostaglandins and prostaglandin-analogues used in cosmetic products. European Commission, Directorate-General for Health and Food Safety (DG SANTE); 2022. Report No.: SCCS/1635/21. Safety) SSCoC. Opinion on prostaglandin analogues used in cosmetic products. 2025. Report No.: SCCS/1680/25. EC. Commission Regulation (EU) 2025/877 of 12 May 2025 amending Regulation (EC) No 1223/2009 of the European Parliament and of the Council as regards the use in cosmetic products of certain substances classified as carcinogenic, mutagenic or toxic for reproduction. 2025. Additional Declarations Competing interest reported. A.Rudnicka, L.Rudnicka, and K.Koziak are inventors on a patent related to the use of latanoprost acid for promoting hair growth. K.Koziak is a co-founder of BioResearch Pharma S.A. and serves as its Chief Scientific Officer. M.Wierzbicki is an employee of BioResearch Pharma S.A. (R&D Project Manager). BioResearch Pharma S.A. was incorporated several years after completion of the human study and therefore had no involvement in its design or conduct. The company provided partial financial support for selected in vitro analyses reported in this manuscript. The funders had no role in data analysis, interpretation, or the decision to submit the manuscript. All other authors declare no competing interests. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 14 Apr, 2026 Reviews received at journal 11 Mar, 2026 Reviewers agreed at journal 10 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers agreed at journal 04 Mar, 2026 Reviewers invited by journal 04 Mar, 2026 Editor assigned by journal 26 Feb, 2026 Submission checks completed at journal 26 Feb, 2026 First submitted to journal 23 Feb, 2026 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. 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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-8949172","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":602554439,"identity":"06d4eb86-a92c-4aff-826f-9a5bc5f231a8","order_by":0,"name":"Adriana Rakowska","email":"","orcid":"","institution":"Medical University of Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Adriana","middleName":"","lastName":"Rakowska","suffix":""},{"id":602554440,"identity":"bd563f57-adb8-488c-a920-81070afa9a34","order_by":1,"name":"Małgorzata Dutkiewicz","email":"","orcid":"","institution":"Medical University of Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Małgorzata","middleName":"","lastName":"Dutkiewicz","suffix":""},{"id":602554441,"identity":"e9731560-6ecf-4373-a657-88e151b4d504","order_by":2,"name":"Oliwia Zegrocka-Stendel","email":"","orcid":"","institution":"Medical University of Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Oliwia","middleName":"","lastName":"Zegrocka-Stendel","suffix":""},{"id":602554442,"identity":"2de464f1-f401-446f-9bcf-10c850aff65f","order_by":3,"name":"Dorota Dymkowska","email":"","orcid":"","institution":"Instytut Biologii Doświadczalnej im. Marcelego Nenckiego","correspondingAuthor":false,"prefix":"","firstName":"Dorota","middleName":"","lastName":"Dymkowska","suffix":""},{"id":602554443,"identity":"ab805e43-7709-495a-a1c7-0845f85bf184","order_by":4,"name":"Grzegorz Huszcza","email":"","orcid":"","institution":"Pharmaceutical Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Grzegorz","middleName":"","lastName":"Huszcza","suffix":""},{"id":602554444,"identity":"2fc92937-ef7c-4ae9-8882-626ae6ee9af4","order_by":5,"name":"Maciej Wierzbicki","email":"","orcid":"","institution":"BioResearch Pharma S.A.","correspondingAuthor":false,"prefix":"","firstName":"Maciej","middleName":"","lastName":"Wierzbicki","suffix":""},{"id":602554445,"identity":"197fbb18-5bcd-4656-aadf-35959522bd39","order_by":6,"name":"Jarosław Walczak","email":"","orcid":"","institution":"Institute of Fundamental Technological Research","correspondingAuthor":false,"prefix":"","firstName":"Jarosław","middleName":"","lastName":"Walczak","suffix":""},{"id":602554446,"identity":"5bed6dba-9c8e-48f6-8a6b-b4bf7ac158bf","order_by":7,"name":"Lidia Rudnicka","email":"","orcid":"","institution":"Medical University of Warsaw","correspondingAuthor":false,"prefix":"","firstName":"Lidia","middleName":"","lastName":"Rudnicka","suffix":""},{"id":602554447,"identity":"e2f1f0fa-2323-4700-bd8f-41dd3f69ff44","order_by":8,"name":"Katarzyna Koziak","email":"data:image/png;base64,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","orcid":"","institution":"Medical University of Warsaw","correspondingAuthor":true,"prefix":"","firstName":"Katarzyna","middleName":"","lastName":"Koziak","suffix":""}],"badges":[],"createdAt":"2026-02-23 16:38:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8949172/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8949172/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104405766,"identity":"bfee2e94-4367-4ad4-9049-7910d2669c4a","added_by":"auto","created_at":"2026-03-11 12:23:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":27371,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eChange in target-area hair count (TAHC) from baseline at Months 3 and 6 after topical latanoprost acid. (A) Absolute change from baseline (ΔTAHC, hairs/cm²). (B) Percent change from baseline (%TAHC). Bars show mean ± SEM. Brackets indicate Month 3 vs Month 6 within-arm comparisons; ** Tukey-adjusted p\u0026lt;0.01 (post-hoc following mixed-effects [REML] analysis).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/4b57c0c7139a25b438e3c700.png"},{"id":104344739,"identity":"98546e17-646c-479f-9221-80cfb386912e","added_by":"auto","created_at":"2026-03-10 17:26:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":15797,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of topical latanoprost acid on yellow-dot counts. Bars show mean ± SEM at baseline, Month 3, and Month 6 for 0.01%, 0.05%, and 0.1% arms. Brackets indicate within-arm comparisons versus baseline; *p\u0026lt;0.05, **p\u0026lt;0.01, ***p\u0026lt;0.001 (Tukey-adjusted post-hoc following mixed-effects [REML] analysis). A main effect of time was observed (p\u0026lt;0.0001).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/c0ce10cb0353274162887afa.png"},{"id":104406150,"identity":"bcc81a93-b0c3-4d6c-b238-c4b749bc9b5e","added_by":"auto","created_at":"2026-03-11 12:24:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":23917,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFollicular-unit (FU) arrangement during topical latanoprost acid treatment. (A) Percentage of single-hair FUs (%FU1) and (B) percentage of triple-hair FUs (%FU3) at baseline, Month 3, and Month 6 in participants treated with 0.01%, 0.05%, or 0.1% latanoprost acid. Bars show mean ± SEM. Brackets indicate within-arm comparisons versus baseline; *p\u0026lt;0.05, **p\u0026lt;0.01, ***p\u0026lt;0.001, ****p\u0026lt;0.0001 (Tukey-adjusted post-hoc following mixed-effects [REML] analysis). In the 0.05% arm, %FU1 decreased and %FU3 increased over time, consistent with a shift toward multi-hair follicular units.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/794c2fe388fc3efacb32a23b.png"},{"id":104344745,"identity":"bbbc829e-b146-4d63-881e-3215c85cc4dc","added_by":"auto","created_at":"2026-03-10 17:26:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":22304,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eInvestigator-rated hair-shaft thickness improvement at Month 6. \u003c/strong\u003eStacked bars show the percentage of participants in each arm assigned to each grade on the ordinal scale (0=no improvement; 3=highest improvement). Arms: 0.01% (n=5), 0.05% (n=11), and 0.1% (n=6). Between-arm differences were assessed using the Kruskal–Wallis test (exact p=0.188).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/2b1ce34ea00c33ae0b0b4682.png"},{"id":104344743,"identity":"d7dea30a-e2e0-4227-ade0-6ef8b31e37be","added_by":"auto","created_at":"2026-03-10 17:26:09","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":640590,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRepresentative 70× trichoscopic images at baseline and Month 6. (A) Two participants treated with 0.05% latanoprost acid and (B) two participants treated with 0.1% latanoprost acid. For each participant, baseline and Month 6 images are shown side-by-side (left to right). Images were obtained from the androgen-dependent scalp region following the study’s standardized imaging protocol.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/9356fe886c26c224e0b22613.png"},{"id":104344741,"identity":"7e65fb57-0486-47af-851b-abd3d14ce940","added_by":"auto","created_at":"2026-03-10 17:26:09","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":46199,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCa²⁺ flux responses to latanoprost acid and latanoprost in human hair dermal papilla cells (HHDPCs). Representative ratiometric traces (F340/F380) recorded following exposure to latanoprost acid (A) or latanoprost (B) at increasing concentrations (31.25-500 nM). Arrows indicate compound addition. Traces are representative of three independent experiments with comparable results.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/4443cfa23682f6c6edbc6672.png"},{"id":104344744,"identity":"aa0a3d1b-8a8a-4617-9647-296865a027c7","added_by":"auto","created_at":"2026-03-10 17:26:09","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":15008,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEdU incorporation in human hair dermal papilla cells (HHDPCs) following 48 h exposure to latanoprost acid or latanoprost. Percentage of EdU-positive nuclei is shown as mean ± SEM across the indicated concentration range (vehicle to 1000 nM). LA, latanoprost acid; LAT, latanoprost.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/9060b5422d8400a1aa54ecbc.png"},{"id":104409523,"identity":"00f20640-db4a-45c5-ad2a-40548fb9e707","added_by":"auto","created_at":"2026-03-11 12:45:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2750033,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8949172/v1/ac189dc2-ef97-42c2-aaec-cae888d0c9ef.pdf"}],"financialInterests":"Competing interest reported. A.Rudnicka, L.Rudnicka, and K.Koziak are inventors on a patent related to the use of latanoprost acid for promoting hair growth. K.Koziak is a co-founder of BioResearch Pharma S.A. and serves as its Chief Scientific Officer. M.Wierzbicki is an employee of BioResearch Pharma S.A. (R\u0026D Project Manager). BioResearch Pharma S.A. was incorporated several years after completion of the human study and therefore had no involvement in its design or conduct. The company provided partial financial support for selected in vitro analyses reported in this manuscript. The funders had no role in data analysis, interpretation, or the decision to submit the manuscript. All other authors declare no competing interests.","formattedTitle":"Topical latanoprost acid for female androgenetic alopecia: a pilot proof-of-concept trial with mechanistic evidence of FP-receptor activation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHair loss is common in both men and women and is frequently associated with distress, reduced self-esteem, and diminished quality of life [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In women, female androgenetic alopecia is the most common cause of the female pattern hair loss phenotype and manifests as diffuse thinning over the vertex and mid-scalp, whereas chronic telogen effluvium (TE) presents with persistent diffuse shedding [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Existing therapies, including topical or oral minoxidil and oral anti-androgens (e.g., finasteride, spironolactone or dutasteride), can benefit many patients; however, responses are variable and long-term use may be limited by tolerability, contraindications, or patient preference, underscoring the need for additional safe and effective options [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSince the initial observation of eyelash hypertrichosis in glaucoma patients treated with latanoprost, prostaglandin analogues have been recognized as promising hair-growth modulators [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Prostaglandin signaling provides a biologically plausible route to hair growth promotion [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In the follicle, FP (PGF₂α) receptor is expressed in anagen human hair follicles, including dermal papilla and perifollicular compartments [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and couples via Gq to phosphoinositide/PLC signaling with intracellular Ca\u0026sup2;⁺ mobilization [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Clinically, FP-pathway agonism has been associated with increased hair growth and pigmentation in clinical dermatologic contexts [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Despite this receptor-level rationale, clinical work to date has centered on marketed glaucoma prostaglandin analogues, including topical latanoprost. Latanoprost is an isopropyl-ester prodrug that requires hydrolysis to latanoprost acid, the active FP-receptor agonist, and, to a more limited extent, bimatoprost/prostamide analogues, rather than on the corresponding active moieties (e.g., the free acids), leaving direct evaluation of these active forms largely unexplored [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGiven that prostaglandin analogue activation depends on tissue hydrolases (e.g., esterases for latanoprost; amidases generating the carboxylic acid from bimatoprost) [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] and that cutaneous drug-metabolizing enzyme activity can vary by anatomical site and between individuals [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], direct testing of active moieties could yield more predictable pharmacodynamics in target engagement. Moreover, as a charged free acid, latanoprost acid is expected to have lower trans-barrier flux, which may limit systemic exposure with topical scalp application [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Latanoprost was explicitly designed as an isopropyl-ester prodrug to enhance tissue penetration, followed by hydrolysis to latanoprost acid after barrier crossing [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Consistent with this principle, ocular dosing with latanoprost has been associated with detectable systemic exposure to latanoprost acid [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. These considerations support evaluating latanoprost acid itself as a topical scalp treatment.\u003c/p\u003e \u003cp\u003eHere, we report the first, to our knowledge, investigator-initiated clinical evaluation of topical latanoprost acid in women with hair loss. We assessed changes in target-area hair count and trichoscopic outcomes, and we complemented clinical findings with mechanistic experiments in human hair dermal papilla cells (HHDPCs), including FP-receptor engagement (Ca\u0026sup2;⁺ flux) and cell-proliferation assays following exposure to latanoprost acid versus latanoprost.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design, participants, and ethics\u003c/h2\u003e \u003cp\u003eThis investigator-initiated, randomized, double-blind, single-center, dose-ranging pilot trial was conducted at the Department of Dermatology, Medical University of Warsaw. Participants received once-daily topical treatment for 6 months, with evaluations at baseline, Month 3, and Month 6. The study protocol was approved by the Ethics Committee of the Medical University of Warsaw (KB/148/2015; approved on July 7, 2015). The privacy rights of participants were observed. All participants provided written informed consent prior to enrollment. The study was conducted in accordance with the Declaration of Helsinki and ICH-GCP. The study was registered at ClinicalTrials.gov (Identifier: NCT07412587; first posted on February 2, 2026).\u003c/p\u003e \u003cp\u003eWomen aged 18\u0026ndash;60 years with patterned scalp hair loss consistent with female androgenetic alopecia (Ludwig I\u0026ndash;III) or chronic telogen effluvium were eligible. For participants with female androgenetic alopecia, the diagnosis was confirmed by trichoscopy [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Exclusion criteria included recent use of hair-growth treatments, active scalp dermatoses, or significant uncontrolled medical conditions. Forty patients were screened; 29 were enrolled.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eRandomization, masking, and interventions\u003c/h3\u003e\n\u003cp\u003eParticipants were randomized to vehicle or latanoprost acid 0.01%, 0.05%, or 0.1% in identical, coded dropper bottles. Allocation was computer-generated, and masking was maintained for participants and investigators through Month 6. The assigned study product was applied once daily to the androgen-dependent scalp region (i.e., the clinically affected area). Participants were instructed to apply 2\u0026ndash;3 mL as needed to cover the area, distribute it evenly, avoid runoff, and refrain from washing the area for \u0026ge;\u0026thinsp;8 h. The tested product was formulated as an oil-in-water (o/w) emulsion. Major excipients included water, phosphate buffer, EDTA, xanthan gum, paraffin, an emulsifying system based on a mixture of fatty alcohols and their ethers, propylene glycol, and phenoxyethanol. The placebo vehicle was identical, without latanoprost acid. Hair-care routines were kept constant; concomitant hair-loss therapies were prohibited. Clinical and trichoscopic outcome assessments were performed at standardized assessment sites/fields at fixed scalp locations within the treated region, using the same locations consistently across visits.\u003c/p\u003e\n\u003ch3\u003eOutcomes\u003c/h3\u003e\n\u003cp\u003eThe primary endpoint was the within-subject absolute change in target-area hair count (ΔTAHC, hairs/cm\u0026sup2;) from baseline to Month 6 (Month 3 change supportive). Trichoscopic assessments (TAHC and secondary trichoscopic features) were performed in standardized assessment fields/sites at fixed scalp locations within the treated androgen-dependent region (including points located 1 cm beyond the hairline), using the same locations consistently across visits. Percent change TAHC (%TAHC) from baseline was summarized as a supportive analysis. Secondary endpoints included trichoscopic features such as hair-shaft thickness (grade 0\u0026ndash;3), follicular-unit arrangement, number of yellow dots, and patient-reported outcomes. Safety/tolerability endpoints comprised adverse events, local scalp findings (erythema/irritation), and vital signs.\u003c/p\u003e\n\u003ch3\u003eAssessments\u003c/h3\u003e\n\u003cp\u003eStandardized clinical macrophotographs of the androgen-dependent scalp region and trichoscopy were obtained at each visit using a consistent acquisition protocol. Trichoscopy images were acquired at fixed scalp locations within the treated region (20\u0026times; and 70\u0026times; magnification). For target-area hair count (TAHC), a 1 cm\u0026sup2; area was delineated on the 20\u0026times; trichoscopy image and all visible hairs within this area were counted manually (hairs/cm\u0026sup2;). Trichoscopy also captured follicular-unit arrangement (percentage of follicular units with single hair [%FU1], and with two or three hairs [%FU2 and %FU3]) and the number of yellow dots, assessed from images obtained at the same standardized locations. Patient self-assessments (shedding, thickness, overall growth) were collected at Months 3 and 6 using a structured questionnaire. Safety was assessed at each visit via systematic adverse-event queries, targeted scalp examination, and vital signs.\u003c/p\u003e\n\u003ch3\u003eCell-based functional assays in HHDPCs\u003c/h3\u003e\n\u003cp\u003eFunctional effects of latanoprost acid and latanoprost on HHDPCs were evaluated using complementary assays addressing receptor signaling and cell proliferation. Ca\u0026sup2;⁺-flux assays measured intracellular calcium dynamics as a direct marker of FP-receptor activation, while EdU incorporation assays assessed whether receptor activation translated into proliferative responses.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eIntracellular Ca\u0026sup2;⁺ flux\u003c/h2\u003e \u003cp\u003ePrimary HHDPCs (Innoprot, Spain) were cultured in Mesenchymal Stem Cell Medium with growth supplement and penicillin/streptomycin on poly-L-lysine-coated plastic (0.01% for 30 min). Cells were seeded on glass coverslips, grown for 48 h to confluence, and loaded with Fura-2 AM (4 \u0026micro;M, 30 min, 37\u0026deg;C). Ratiometric cytosolic [Ca\u0026sup2;⁺] signals (F340/F380) were recorded at RT in physiological buffer (with 2 mM CaCl₂) using a spectrofluorimeter (Hitachi F-7000 or equivalent). Latanoprost acid and latanoprost were applied at concentrations ranging from 31.25\u0026ndash;500 nM; vehicle controls were included.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDNA synthesis assay\u003c/h3\u003e\n\u003cp\u003eDNA synthesis was quantified using the 5-Ethynyl-2'-deoxyuridine (EdU) Proliferation Kit (Lumiprobe) according to the manufacturer\u0026rsquo;s instructions. Cells were seeded in poly-L-lysine-coated 96-well optical-bottom plates (Greiner) at a density of 1,600 cells per well. HHDPCs were exposed to latanoprost acid or latanoprost (31.25\u0026ndash;1000 nM) in complete medium and assessed after 24, 48 or 72 h. Cells were pulsed with EdU (10 \u0026micro;M, 1 h), fixed with 4% paraformaldehyde, permeabilized (0.5% Triton X-100), and stained via copper(I)-catalyzed azide\u0026ndash;alkyne click chemistry with sulfo-Cy3\u0026ndash;conjugated azide. Nuclei were counterstained with Hoechst 33342. Images were acquired with 20\u0026times; objective on Operetta CLS imaging system under identical settings. At least 13 random fields per condition per experiment were analyzed with Harmony 4.9 software. The EdU index was calculated as the fraction of EdU-positive nuclei (Cy3-positive) among total Hoechst-positive nuclei and averaged across three independent experiments.\u003c/p\u003e\n\u003ch3\u003ePrestoBlue metabolic activity assay\u003c/h3\u003e\n\u003cp\u003eMetabolic activity of HHDPCs was assessed using the PrestoBlue\u0026trade; (Thermo Fisher Scientific/Invitrogen) resazurin-based assay according to the manufacturer\u0026rsquo;s instructions. Cells were exposed to vehicle or the indicated concentrations of latanoprost acid or latanoprost, followed by incubation with PrestoBlue reagent and measurement of fluorescence. Signals were background-subtracted and normalized to vehicle controls.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll analyses were exploratory. Continuous outcomes are summarized as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM unless stated otherwise. Repeated-measures clinical endpoints, including TAHC and trichoscopic/follicular-unit arrangement measures, were analyzed using a mixed-effects model for repeated measures (REML), with time and treatment concentration, and their interaction as fixed effects, and participant as a random effect. For outcomes expressed as change from baseline (e.g., ΔTAHC and %TAHC), the dependent variables were the change scores at Month 3 and Month 6. This approach uses all available observations without imputing missing values. Post-hoc comparisons were performed using Tukey\u0026rsquo;s multiple comparisons test. Results are reported as model-estimated (least-squares) mean differences with 95% confidence intervals and Tukey-adjusted p values. The investigator-rated hair-shaft thickness improvement grade (ordinal scale 0\u0026ndash;3) assessed at Month 6 was compared across concentrations using the Kruskal\u0026ndash;Wallis test (exact p value). For in vitro EdU incorporation experiments, percent EdU-positive cells were analyzed by two-way ANOVA with factors compound (latanoprost acid vs latanoprost) and concentration, including their interaction; where applicable, multiplicity-adjusted post-hoc comparisons were applied. All tests were two-sided; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant. Analyses were performed in GraphPad Prism (version 10.2; GraphPad Software, San Diego, CA, USA).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eParticipant Disposition and Baseline Characteristics\u003c/h2\u003e \u003cp\u003eTwenty-nine women were randomized: vehicle (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2), latanoprost acid 0.01% (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7), 0.05% (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;13), and 0.1% (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7). Enrollment stopped early (target 40) for practical reasons, yielding unequal group sizes. Overall, 25/29 (86%) completed Month 6. Four discontinued: one in group 0.01% at Month 3 due to headache; in group 0.05% one lost at ~\u0026thinsp;4 weeks for increased shedding, one lost to follow-up after baseline, and one for non-compliance. Efficacy analyses used a modified intent-to-treat set, defined as all randomized participants with \u0026ge;\u0026thinsp;1 post-baseline efficacy assessment; safety analyses included all treated participants.\u003c/p\u003e \u003cp\u003eBaseline characteristics were broadly comparable. The mean age was in the mid-30s (range 24\u0026ndash;60), and all participants were female. Most (27/29) had female androgenetic alopecia (predominantly Ludwig I-II), with two cases of chronic telogen effluvium. Baseline TAHC varied; by chance, the 0.05% group started lower than 0.01% and 0.1% (138.0\u0026thinsp;\u0026plusmn;\u0026thinsp;34.1 vs 175.5\u0026thinsp;\u0026plusmn;\u0026thinsp;65.4 and 165.0\u0026thinsp;\u0026plusmn;\u0026thinsp;62.3 hairs/cm\u0026sup2;). Baseline trichoscopic features (%FU1, %FU2, %FU3, number of yellow dots) did not differ significantly. All efficacy analyses were conducted as within-subject changes from baseline.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003ePrimary efficacy outcome: absolute change in target-area hair count (ΔTAHC)\u003c/h2\u003e \u003cp\u003eFrom baseline to Month 6, ΔTAHC increased across concentration arms (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Descriptively, mean (\u0026plusmn;\u0026thinsp;SD) ΔTAHC at Month 6 was 17.8\u0026thinsp;\u0026plusmn;\u0026thinsp;10.7 (0.01%), 23.5\u0026thinsp;\u0026plusmn;\u0026thinsp;21.2 (0.05%), and 16.5\u0026thinsp;\u0026plusmn;\u0026thinsp;15.6 hairs/cm\u0026sup2; (0.1%). A significant main effect of time was observed (p\u0026thinsp;=\u0026thinsp;0.0058), with no evidence of a concentration effect (p\u0026thinsp;=\u0026thinsp;0.95) or time\u0026times;concentration interaction (p\u0026thinsp;=\u0026thinsp;0.17). In supportive analyses of trajectory, we examined the incremental change from Month 3 to Month 6 (i.e., additional gain after Month 3): the incremental change between Month 3 and Month 6 was significant only in the 0.05% arm (model-estimated mean difference 11.36 hairs/cm\u0026sup2;; 95% CI 5.02\u0026ndash;17.71; Tukey-adjusted p\u0026thinsp;=\u0026thinsp;0.0014), whereas changes were not significant in the 0.01% (8.37; 95% CI\u0026thinsp;\u0026minus;\u0026thinsp;0.96 to 17.71; p\u0026thinsp;=\u0026thinsp;0.0759) or 0.1% arms (1.33; 95% CI\u0026thinsp;\u0026minus;\u0026thinsp;7.25 to 9.92; p\u0026thinsp;=\u0026thinsp;0.7487). Between-arm differences at Month 3 and Month 6 were not significant (all Tukey-adjusted p\u0026thinsp;\u0026gt;\u0026thinsp;0.69).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSupportive analysis: percent change in target-area hair count (%TAHC)\u003c/h2\u003e \u003cp\u003eResults were consistent when expressed as percent change from baseline (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Model-estimated %TAHC increased from Month 3 to Month 6 across all arms (0.01%: 6.93% to 11.96%; 0.05%: 9.81% to 18.99%; 0.1%: 10.37% to 13.94%). The Month 3 - Month 6 increment was significant only in the 0.05% arm (+\u0026thinsp;9.18 percentage points; 95% CI 3.08\u0026ndash;15.28; Tukey-adjusted p\u0026thinsp;=\u0026thinsp;0.0053) and was not significant in the 0.01% (+\u0026thinsp;5.02 pp; 95% CI\u0026thinsp;\u0026minus;\u0026thinsp;3.94 to 13.98; p\u0026thinsp;=\u0026thinsp;0.2553) or 0.1% arms (+\u0026thinsp;3.57 pp; 95% CI\u0026thinsp;\u0026minus;\u0026thinsp;4.70 to 11.82; p\u0026thinsp;=\u0026thinsp;0.3776). Between-arm differences at Month 3 and Month 6 were not significant (Tukey-adjusted p\u0026thinsp;\u0026ge;\u0026thinsp;0.61).\u003c/p\u003e \u003cp\u003eTogether, these analyses support a treatment-associated increase in hair density over 6 months with topical latanoprost acid, with the most consistent progressive signal observed at 0.05%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eResponder analysis\u003c/h2\u003e \u003cp\u003eWhen applying a liberal responder definition (any increase\u0026thinsp;\u0026gt;\u0026thinsp;0% from baseline), responder rates at Month 6 were 100% (5/5), 90.9% (10/11), and 83.3% (5/6) for the 0.01%, 0.05%, and 0.1% groups, respectively. A more conservative definition (\u0026ge;\u0026thinsp;10% increase in TAHC) yielded proportionally lower responder rates (80.0%, 72.7%, and 66.7%, respectively), but the same ranking across concentrations.\u003c/p\u003e \u003cp\u003eThese findings are consistent with the mixed-model results showing the greatest mean improvement in the 0.05% group.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSecondary and Exploratory Outcomes\u003c/b\u003e (Trichoscopy)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eYellow dots\u003c/h2\u003e \u003cp\u003eYellow dot counts decreased over time (time effect p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), with no evidence of concentration effects or a time\u0026times;concentration interaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Tukey-adjusted post-hoc comparisons showed a significant reduction in the 0.05% arm at Month 3 (p\u0026thinsp;=\u0026thinsp;0.0011) and Month 6 (p\u0026thinsp;=\u0026thinsp;0.0001), and a smaller reduction in the 0.01% arm at Month 3 (p\u0026thinsp;=\u0026thinsp;0.0317); no significant change was observed in the 0.1% arm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eFollicular unit (FU) arrangement\u003c/h2\u003e \u003cp\u003eComplementary changes were observed in follicular-unit arrangement (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Because some observations were missing, FU outcomes were analyzed using a mixed-effects model (REML) with Tukey-adjusted multiple comparisons. In the 0.05% arm, %FU1 decreased significantly versus baseline at Month 3 and Month 6 (both p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), accompanied by a reciprocal increase in %FU3 (baseline vs Month 3, p\u0026thinsp;=\u0026thinsp;0.0149; baseline vs Month 6, p\u0026thinsp;=\u0026thinsp;0.0004), consistent with a shift toward multi-hair follicular units. No significant within-arm changes in %FU1 or %FU3 were detected in the 0.01% arm, and changes in the 0.1% arm did not reach significance (baseline vs Month 6 for %FU3, p\u0026thinsp;=\u0026thinsp;0.0528). At baseline, %FU1 was higher in the 0.05% arm than in the 0.01% and 0.1% arms (p\u0026thinsp;=\u0026thinsp;0.0015 and p\u0026thinsp;=\u0026thinsp;0.0296, respectively), and %FU3 was lower in the 0.05% arm than in the 0.1% arm (p\u0026thinsp;=\u0026thinsp;0.0241). Between-arm differences were not significant by Month 6 (all p\u0026thinsp;\u0026gt;\u0026thinsp;0.05), although %FU3 remained borderline between 0.05% and 0.1% (p\u0026thinsp;=\u0026thinsp;0.0593).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eHair-shaft thickness improvement grade (0\u0026ndash;3)\u003c/h2\u003e \u003cp\u003eAt Month 6, investigator-rated improvement in hair-shaft thickness (0\u0026thinsp;=\u0026thinsp;no improvement; higher scores indicate greater improvement) did not differ significantly across dose arms (Kruskal-Wallis test, exact p\u0026thinsp;=\u0026thinsp;0.188). Median [IQR] improvement grades were 1 [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] for 0.01% (n\u0026thinsp;=\u0026thinsp;5), 2 [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] for 0.05% (n\u0026thinsp;=\u0026thinsp;11), and 2 [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] for 0.1% (n\u0026thinsp;=\u0026thinsp;6), consistent with modest clinician-rated improvement without evidence of a dose-dependent difference (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eRepresentative trichoscopic images\u003c/h2\u003e \u003cp\u003eRepresentative 70\u0026times; trichoscopic images from participants in the 0.05% and 0.1% arms at baseline and Month 6 are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003ePatient-Reported Outcomes\u003c/h2\u003e \u003cp\u003eBy Month 3, approximately half of participants across treatment arms reported reduced shedding and perceived improvement in hair quality, most often in the 0.05% and 0.1% arms. By Month 6, participants in these arms more frequently reported visible gains in hair volume and density, whereas responses in the 0.01% arm were more variable. Overall, patient-reported outcomes were directionally consistent with changes in TAHC and trichoscopic measures.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eSafety\u003c/h2\u003e \u003cp\u003eTopical latanoprost acid was generally well tolerated. No serious adverse events or hospitalizations occurred. Targeted scalp examinations revealed no clinically relevant irritation or inflammation, and vital signs remained within normal limits. Causes for discontinuation included headache in the 0.01% arm (by Month 3) and three discontinuations in the 0.05% arm (increased shedding at ~\u0026thinsp;4\u0026ndash;6 weeks, loss to follow-up, and non-compliance).\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eMechanistic assessment in HHDPCs\u003c/h2\u003e \u003cp\u003eTo explore whether the clinical pattern of improvement is consistent with FP-receptor-mediated signaling, we compared latanoprost acid and latanoprost in cultured HHDPCs, assessing Ca\u0026sup2;⁺ flux and proliferation-related readouts.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eFP-receptor engagement in HHDPCs (Ca\u0026sup2;⁺ flux)\u003c/h2\u003e \u003cp\u003eLatanoprost acid elicited a rapid, transient, concentration-dependent Ca\u0026sup2;⁺ response, whereas equimolar latanoprost produced a delayed, gradually rising response without a distinct peak (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). A clear Ca\u0026sup2;⁺ signal was detectable for latanoprost acid at concentrations as low as 31.25 nM, while latanoprost at the same concentration did not elicit a discernible Ca\u0026sup2;⁺ response above baseline. These findings are consistent with more immediate FP-receptor-linked signaling by the free-acid form compared with the ester prodrug under the conditions tested.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003eCell proliferation and metabolic activity in HHDPCs\u003c/h2\u003e \u003cp\u003eNeither latanoprost acid nor latanoprost altered the proportion of EdU-positive nuclei compared with vehicle across the tested concentration range at any time point (24, 48, or 72 h). Representative data at 48 h are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, indicating no detectable effect on DNA synthesis. Consistently, neither compound increased PrestoBlue signal compared with vehicle across the tested concentration range (data not shown).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this investigator-initiated, randomized, double-blind pilot study, topical latanoprost acid was associated with clinically interpretable improvements over 6 months in women with female androgenetic alopecia, with a small number of participants with chronic telogen effluvium included. Across the doses tested, the 0.05% arm showed the most consistent, multi-endpoint pattern of objective change: higher target-area hair count (TAHC), a reduction in the proportion of single-hair follicular units (%FU1) accompanied by a reciprocal rise in the proportion of three-hair units (%FU3), and a reduced number of yellow dots, a trichoscopic feature linked to inactive/kenogen-phase follicles [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Baseline imbalances in FU arrangement were present (higher %FU1 and lower %FU3 in the 0.05% arm vs comparators), and between-arm comparisons of change scores were under-powered due to unequal group sizes and attrition; accordingly, dose-related inferences should be interpreted cautiously. Patient-reported outcomes were directionally consistent with these signals, with perceived gains in volume/density reported more frequently at 0.05% and 0.1%.\u003c/p\u003e \u003cp\u003eBeyond mean changes, the categorical emergence of multi-hair follicular units supports a biologically interpretable shift in follicular output. In the 0.05% arm, the proportion of evaluable participants with any FU3 present in the target area rose from 27.3% at baseline to 54.5% at Month 3 and 81.8% at Month 6, with 6/8 participants who had no FU3 at baseline exhibiting FU3 by Month 6. By contrast, the 0.1% arm showed high, stable prevalence of FU3 (~\u0026thinsp;83%) across visits, consistent with a possible ceiling effect, and the 0.01% arm also remained near-saturated (rising from 86% to 100% among evaluable participants). This categorical emergence in the 0.05% arm complements the reduction in yellow dots and the within-arm remodeling in FU arrangement (decreasing %FU1 with increasing %FU3), collectively supporting treatment-associated follicular reactivation and/or enhanced output from previously low-output follicles. Importantly, the dermoscopic/trichoscopic pattern (fewer yellow dots and a shift from single- to multi-hair follicular units) is compatible with reactivation of follicles in kenogen phase [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], although confirmatory studies with larger cohorts and prespecified imaging/assessment procedures are needed to define the biological substrate with greater certainty.\u003c/p\u003e \u003cp\u003eAn interpretable dose pattern emerged in which 0.05% yielded the most consistent improvements across endpoints, whereas 0.1% did not clearly outperform the mid dose. Several non-exclusive explanations are plausible: (i) a pharmacodynamic ceiling or inverted-U dose\u0026ndash;response, in which FP-receptor/effector systems may be near-maximally engaged at 0.05%; (ii) subtle local effects at higher concentrations (insufficient to register as adverse events yet potentially capable of attenuating growth signals); (iii) baseline imbalances (e.g., lower baseline TAHC in 0.05% and higher in 0.1%, potentially influencing the magnitude of observable change); and (iv) limited statistical power. These hypotheses require confirmation. Collectively, the present data nominate 0.05% as a candidate dose to be evaluated in larger, prospectively dose-ranging trials with prespecified between-group contrasts and standardized assessment procedures.\u003c/p\u003e \u003cp\u003eThe mechanistic bridge from receptor to clinic is supported on two complementary levels. First, Ca\u0026sup2;⁺-flux assays in HHDPCs demonstrated rapid, concentration-dependent responses to latanoprost acid with a clear transient peak, while equimolar latanoprost (an ester prodrug) produced delayed, slowly rising signals without a distinct peak. This pattern is consistent with more immediate FP-receptor-linked signaling by the free acid and conversion-limited activity of the prodrug under the conditions tested. Second, the trichoscopic profile. i.e., fewer yellow dots and a shift toward multi-hair follicular units, is compatible with follicular reactivation and/or increased output from follicles transitioning out of kenogen [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Prior studies have linked prostaglandin-pathway activation to changes in hair-shaft pigmentation; however, pigmentation was not assessed here and warrants future evaluation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Taken together, these observations support a mechanistically distinct FP-receptor-targeted approach that delivers the active free acid (bypassing potential variability in prodrug activation) and provides a coherent biological rationale for clinical translation.\u003c/p\u003e \u003cp\u003eIn parallel, cell-proliferation assays using EdU incorporation demonstrated that neither latanoprost acid nor latanoprost increased DNA synthesis in HHDPCs after 24\u0026ndash;72 h of exposure across nanomolar concentrations. These findings suggest that FP-receptor-linked signaling (as reflected by Ca\u0026sup2;⁺ flux) is not accompanied by detectable cell-cycle progression under these conditions, which is consistent with a signal-modulatory/paracrine role of dermal papilla cells in follicular regeneration rather than direct expansion of the dermal papilla cell population. Accordingly, the clinical and trichoscopic signals observed may reflect enhanced follicular activation and intercellular communication within the follicular niche rather than a primary proliferative mechanism in dermal papilla cells.\u003c/p\u003e \u003cp\u003eDespite long-standing clinical signals that prostaglandin analogues can stimulate hair growth, no prostaglandin-pathway drug is approved for scalp hair loss. To date, bimatoprost 0.03% (LATISSE\u0026reg;) remains the only FDA-approved prostaglandin analogue for a hair indication (eyelash hypotrichosis) [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. A pragmatic contributor to the historical gap in scalp indications may be the prolonged \u0026ldquo;cosmetic route\u0026rdquo; in which prostaglandin analogues appeared in over-the-counter eyelash/brow serums in Europe [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], blurring boundaries between cosmetic and medicinal use and dampening incentives for formal drug development. Regulatory scrutiny has tightened only recently. In 2022, the European Union Scientific Committee on Consumer Safety (SCCS) raised explicit safety concerns about prostaglandin analogues in cosmetics [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], and in 2025 the SCCS concluded that specific prostaglandin analogues cannot be considered safe for cosmetic products intended to promote eyelash/eyebrow growth [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In parallel, the European Union has advanced updates strengthening prohibitions on unsafe cosmetic substances [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Together, these developments have narrowed the cosmetic route and may help re-align incentives toward indication-specific medicinal development for scalp hair loss.\u003c/p\u003e \u003cp\u003eImportantly, most clinical work on prostaglandin analogues in scalp hair loss has focused on ester prodrugs rather than free acids, leaving direct delivery of the active moiety underexplored. Addressing this gap, our study is, to our knowledge, the first investigator-initiated clinical evaluation of topically administered latanoprost acid, the active moiety of latanoprost, for scalp hair loss. In this proof-of-concept work, topically applied latanoprost acid exhibited consistent bioactivity signals in human scalp hair, as evidenced by concordant improvements in TAHC and trichoscopic markers over 6 months, alongside a favorable safety profile. The magnitude and consistency of these effects were most evident at 0.05%, supporting its prioritization for confirmation in larger, prospectively dose-ranging studies.\u003c/p\u003e \u003cp\u003eGiven the potential for long-term use, assessing the safety and tolerability of topical latanoprost acid is particularly important. In this study, safety was favorable across concentrations, with no serious adverse events, no ocular or pigmentary concerns detected, and no unwanted hair growth (ectopic hypertrichosis). The absence of systemic clinical signals is consistent with the limited permeability expected for the free-acid form on the scalp and aligns with our a priori safety hypothesis [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Nonetheless, longer exposure, larger cohorts, and pharmacokinetic assessment will be necessary to characterize uncommon events and to confirm minimal systemic exposure, particularly if higher concentrations are pursued.\u003c/p\u003e \u003cp\u003eLimitations. This pilot study was small, single-center, and ended early due to funding constraints, resulting in unequal group sizes and a particularly small vehicle arm, limiting between-arm inference. The 6-month follow-up may not capture maximal response or long-term durability. Although follicular-unit metrics were collected at each visit, denominators varied due to attrition, and analyses were sensitive to missingness across time points. Patient-reported outcomes were collected via structured interview rather than a fully validated instrument. Finally, inclusion of two participants with chronic telogen effluvium may have contributed to response heterogeneity.\u003c/p\u003e \u003cp\u003eTaken together, the convergence of cellular (Ca\u0026sup2;⁺ flux), trichoscopic, and clinical signals indicates bioactivity of latanoprost acid in human scalp hair. These proof-of-concept data support an adequately powered, randomized, dose-ranging trial centered on 0.05%, with PK/PD integration to relate scalp exposure to FP-receptor-linked signaling and clinical endpoints. Future studies should extend follow-up to \u0026ge;\u0026thinsp;12 months to define trajectory and durability; incorporate validated patient-reported outcomes; implement standardized global photography and trichoscopy; evaluate combination therapy (e.g., with minoxidil and/or anti-androgens); and explicitly contrast prodrug versus free-acid strategies to clarify class effects and optimize translational approaches.\u003c/p\u003e \u003cp\u003eIn summary, topical latanoprost acid was associated with consistent improvements in objective and subjective measures over 6 months, with 0.05% showing the most consistent multi-endpoint signal and a favorable safety profile. These findings support continued clinical development of latanoprost acid and related FP-receptor modulators as targeted treatments for hair loss.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported in part by the Ministry of Science and Higher Education (Innovation Incubator 2.0 programme; grant no. MNISW/2017/DIR/71/II+) implemented within the Smart Growth Operational Programme 2014\u0026ndash;2020 (POIR) and co-financed by the European Regional Development Fund (ERDF). Selected in vitro experiments were supported by BioResearch Pharma S.A.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA.R., L.R., and K.K. are inventors on a patent related to the use of latanoprost acid for promoting hair growth. K.K. is a co-founder of BioResearch Pharma S.A. and serves as its Chief Scientific Officer. M.W. is an employee of BioResearch Pharma S.A. (R\u0026amp;D Project Manager). BioResearch Pharma S.A. was incorporated several years after completion of the human study and therefore had no involvement in its design or conduct. The company provided partial financial support for selected in vitro analyses reported in this manuscript. The funders had no role in data analysis, interpretation, or the decision to submit the manuscript. All other authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eK.K., A.R., L.R., and J.W. contributed to the conceptualization of the study. A.R., M.D., O.Z.-S., J.W., D.D., G.H., M.W., L.R., and K.K. contributed to the methodology. A.R., M.D., O.Z.-S., D.D., J.W., and G.H. conducted the investigation. A.R., J.W., D.D., and K.K. curated the data. K.K. and L.R. performed the formal analysis. K.K. wrote the original draft of the manuscript. A.R., M.D., O.Z.-S., G.H., D.D., J.W., M.W., and L.R. reviewed and edited the manuscript. K.K. performed validation and supervised the study. A.R. and K.K. prepared the visualizations. K.K. acquired funding. All authors reviewed and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eMuller Ramos P, Melo DF, Radwanski H, de Almeida RFC, Miot HA. Female-pattern hair loss: therapeutic update. An Bras Dermatol. 2023;98(4):506-19.\u003c/li\u003e\n \u003cli\u003eMohamed NE, Soltan MR, Galal SA, El Sayed HS, Hassan HM, Khatery BH. Female Pattern Hair Loss and Negative Psychological Impact: Possible Role of Brain-derived Neurotrophic Factor (BDNF). Dermatol Pract Concept. 2023;13(3).\u003c/li\u003e\n \u003cli\u003eChien Yin GO, Siong-See JL, Wang ECE. Telogen Effluvium - a review of the science and current obstacles. J Dermatol Sci. 2021;101(3):156-63.\u003c/li\u003e\n \u003cli\u003eLucky AW, Piacquadio DJ, Ditre CM, Dunlap F, Kantor I, Pandya AG, et al. A randomized, placebo-controlled trial of 5% and 2% topical minoxidil solutions in the treatment of female pattern hair loss. J Am Acad Dermatol. 2004;50(4):541-53.\u003c/li\u003e\n \u003cli\u003eKanti V, Messenger A, Dobos G, Reygagne P, Finner A, Blumeyer A, et al. Evidence-based (S3) guideline for the treatment of androgenetic alopecia in women and in men - short version. J Eur Acad Dermatol Venereol. 2018;32(1):11-22.\u003c/li\u003e\n \u003cli\u003eOng MM, Avram M, McMichael A, Tosti A, Lipner SR. Antiandrogen therapy for the treatment of female pattern hair loss: A clinical review of current and emerging therapies. J Am Acad Dermatol. 2025;93(3):749-60.\u003c/li\u003e\n \u003cli\u003eJohnstone MA. Hypertrichosis and increased pigmentation of eyelashes and adjacent hair in the region of the ipsilateral eyelids of patients treated with unilateral topical latanoprost. Am J Ophthalmol. 1997;124(4):544-7.\u003c/li\u003e\n \u003cli\u003eColombe L, Michelet JF, Bernard BA. Prostanoid receptors in anagen human hair follicles. Exp Dermatol. 2008;17(1):63-72.\u003c/li\u003e\n \u003cli\u003eIto S, Sakamoto K, Mochizuki-Oda N, Ezashi T, Miwa K, Okuda-Ashitaka E, et al. Prostaglandin F2 alpha receptor is coupled to Gq in cDNA-transfected Chinese hamster ovary cells. Biochem Biophys Res Commun. 1994;200(2):756-62.\u003c/li\u003e\n \u003cli\u003eCarruthers J, Beer K, Carruthers A, Coleman WP, 3rd, Draelos ZD, Jones D, et al. Bimatoprost 0.03% for the Treatment of Eyebrow Hypotrichosis. Dermatol Surg. 2016;42(5):608-17.\u003c/li\u003e\n \u003cli\u003eBlume-Peytavi U, Lonnfors S, Hillmann K, Garcia Bartels N. A randomized double-blind placebo-controlled pilot study to assess the efficacy of a 24-week topical treatment by latanoprost 0.1% on hair growth and pigmentation in healthy volunteers with androgenetic alopecia. J Am Acad Dermatol. 2012;66(5):794-800.\u003c/li\u003e\n \u003cli\u003eStjernschantz JW. From PGF(2alpha)-isopropyl ester to latanoprost: a review of the development of xalatan: the Proctor Lecture. Invest Ophthalmol Vis Sci. 2001;42(6):1134-45.\u003c/li\u003e\n \u003cli\u003eMaxey KM, Johnson JL, LaBrecque J. The hydrolysis of bimatoprost in corneal tissue generates a potent prostanoid FP receptor agonist. Surv Ophthalmol. 2002;47 Suppl 1:S34-40.\u003c/li\u003e\n \u003cli\u003ePyo SM, Maibach HI. Skin Metabolism: Relevance of Skin Enzymes for Rational Drug Design. Skin Pharmacol Physiol. 2019;32(5):283-94.\u003c/li\u003e\n \u003cli\u003eTelaprolu KC, Grice JE, Mohammed YH, Roberts MS. Human Skin Drug Metabolism: Relationships between Methyl Salicylate Metabolism and Esterase Activities in IVPT Skin Membranes. Metabolites. 2023;13(8).\u003c/li\u003e\n \u003cli\u003eSjoquist B, Stjernschantz J. Ocular and systemic pharmacokinetics of latanoprost in humans. Surv Ophthalmol. 2002;47 Suppl 1:S6-12.\u003c/li\u003e\n \u003cli\u003eN\u0026apos;Da DD. Prodrug strategies for enhancing the percutaneous absorption of drugs. Molecules. 2014;19(12):20780-807.\u003c/li\u003e\n \u003cli\u003eRakowska A, Slowinska M, Kowalska-Oledzka E, Olszewska M, Rudnicka L. Dermoscopy in female androgenic alopecia: method standardization and diagnostic criteria. Int J Trichology. 2009;1(2):123-30.\u003c/li\u003e\n \u003cli\u003eLima CDS, Lemes LR, Melo DF. Yellow dots in trichoscopy: relevance, clinical significance and peculiarities. An Bras Dermatol. 2017;92(5):724-6.\u003c/li\u003e\n \u003cli\u003eRebora A, Guarrera M. Kenogen. A new phase of the hair cycle? Dermatology. 2002;205(2):108-10.\u003c/li\u003e\n \u003cli\u003eKuczara A, Waskiel-Burnat A, Rakowska A, Olszewska M, Rudnicka L. Trichoscopy of Androgenetic Alopecia: A Systematic Review. J Clin Med. 2024;13(7).\u003c/li\u003e\n \u003cli\u003eLaw SK. Bimatoprost in the treatment of eyelash hypotrichosis. Clin Ophthalmol. 2010;4:349-58.\u003c/li\u003e\n \u003cli\u003eU.S. Food and Drug Administration. Medical Review(s): Latisse (bimatoprost ophthalmic solution) 0.03% (NDA 022369). Center for Drug Evaluation and Research (CDER), U.S. Food and Drug Administration; 2008. Report No.: NDA 022369.\u003c/li\u003e\n \u003cli\u003eHopley C CS, Webster W, Bird G, Dillon E, Axford I. Prostaglandin analogues in cosmetics. 2024. Report No.: BEIS/OPSS: RE21425\u003c/li\u003e\n \u003cli\u003eSCCS (Scientific Committee on Consumer Safety). Opinion on Prostaglandins and prostaglandin-analogues used in cosmetic products. European Commission, Directorate-General for Health and Food Safety (DG SANTE); 2022. Report No.: SCCS/1635/21.\u003c/li\u003e\n \u003cli\u003eSafety) SSCoC. Opinion on prostaglandin analogues used in cosmetic products. 2025. Report No.: SCCS/1680/25.\u003c/li\u003e\n \u003cli\u003eEC. Commission Regulation (EU) 2025/877 of 12 May 2025 amending Regulation (EC) No 1223/2009 of the European Parliament and of the Council as regards the use in cosmetic products of certain substances classified as carcinogenic, mutagenic or toxic for reproduction. 2025.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"pharmacological-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prep","sideBox":"Learn more about [Pharmacological Reports](https://link.springer.com/journal/43440)","snPcode":"43440","submissionUrl":"https://submission.springernature.com/new-submission/43440/3","title":"Pharmacological Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"androgenetic alopecia, latanoprost acid, FP receptor, dermal papilla, calcium signaling, hair growth","lastPublishedDoi":"10.21203/rs.3.rs-8949172/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8949172/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eProstaglandin F2α (FP) receptor signaling is a plausible target for promoting hair growth, but clinical data on topical latanoprost acid (the active free-acid FP agonist) in hair loss are lacking.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eIn an investigator-initiated, randomized, double-blind, single-center, dose-ranging pilot trial, adult women with hair loss predominantly consistent with female androgenetic alopecia applied once-daily topical latanoprost acid 0.01%, 0.05%, or 0.1% for 6 months; a small vehicle group was included to support masking. The primary endpoint was within-participant change in target-area hair count (TAHC, hairs/cm\u0026sup2;) from baseline to Month 6; trichoscopic activity markers (yellow dots) and follicular-unit (FU) remodeling were secondary/exploratory outcomes. Human hair dermal papilla cells were assessed for FP-linked signaling (intracellular Ca\u0026sup2;⁺ flux) and proliferation (EdU) after exposure to latanoprost acid versus equimolar latanoprost.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eTAHC increased across active arms, with the most consistent multi-endpoint signal in the 0.05% group (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD ΔTAHC 23.5\u0026thinsp;\u0026plusmn;\u0026thinsp;21.2 hairs/cm\u0026sup2;), accompanied by reduced yellow dots and a shift from single-hair to multi-hair FUs; between-dose comparisons were not powered. Safety was favorable with no serious adverse events. In mechanistic assays, latanoprost acid triggered rapid, concentration-dependent Ca\u0026sup2;⁺ flux, whereas equimolar latanoprost produced delayed signals; neither compound increased EdU incorporation.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eTopical latanoprost acid showed a coherent clinical-trichoscopic bioactivity signal with supportive FP-linked signaling in human hair dermal papilla cells, warranting larger PK/PD-integrated trials centered on 0.05%.\u003c/p\u003e\u003ch2\u003eTrial registration:\u003c/h2\u003e \u003cp\u003eClinicalTrials.gov, NCT07412587; registered on February 2, 2026.\u003c/p\u003e","manuscriptTitle":"Topical latanoprost acid for female androgenetic alopecia: a pilot proof-of-concept trial with mechanistic evidence of FP-receptor activation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-10 17:26:04","doi":"10.21203/rs.3.rs-8949172/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-14T13:22:48+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-11T19:29:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"203513526970606896024962247079210136818","date":"2026-03-10T10:42:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"85626268036626501738367036320497206926","date":"2026-03-05T12:44:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"52277662183616889340318573118411668713","date":"2026-03-05T01:03:32+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-05T01:01:07+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-26T12:24:34+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-26T11:59:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"Pharmacological Reports","date":"2026-02-23T16:29:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"pharmacological-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prep","sideBox":"Learn more about [Pharmacological Reports](https://link.springer.com/journal/43440)","snPcode":"43440","submissionUrl":"https://submission.springernature.com/new-submission/43440/3","title":"Pharmacological Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"adcbc617-98cb-4053-ac43-624799c20337","owner":[],"postedDate":"March 10th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-05-14T17:24:15+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-10 17:26:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8949172","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8949172","identity":"rs-8949172","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}