Quantitative dual-isotope preclinical SPECT/CT imaging and biodistribution of the mercury-197m/g theranostic pair with [197m/gHg]HgCl2 and a superior [197m/gHg]Hg-tetrathiol complex as a platform for radiopharmaceutical development

Quantitative dual-isotope preclinical SPECT/CT imaging and biodistribution of the mercury-197m/g theranostic pair with [197m/gHg]HgCl2 and a superior [197m/gHg]Hg-tetrathiol complex as a platform for radiopharmaceutical development | 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 Quantitative dual-isotope preclinical SPECT/CT imaging and biodistribution of the mercury-197m/g theranostic pair with [197m/gHg]HgCl2 and a superior [197m/gHg]Hg-tetrathiol complex as a platform for radiopharmaceutical development Parmissa Randhawa, Cristina Rodríguez-Rodríguez, Helena Koniar, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7216255/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Oct, 2025 Read the published version in EJNMMI Radiopharmacy and Chemistry → Version 1 posted 5 You are reading this latest preprint version Abstract Background Mercury-197m ( 197m Hg, t 1/2 = 23.8 h) and mercury-197g ( 197g Hg, t 1/2 = 64.14 h) possess favorable nuclear properties for imaging and targeted therapy, but the development of suitable chelators for mercury-based radiopharmaceuticals remains underexplored. Additionally, accurate imaging and quantification of mercury isotopes, particularly in dual-isotope formats, require tools that account for their complex decay schemes. Phantom imaging studies are essential for validating spatial resolution, quantitative accuracy, and isotope-specific calibration prior to in vivo application. In this study, we investigated the commercially available ligand H 4 Tetrathiol for chelation of [ 197m/g Hg]Hg 2+ and developed a robust imaging and quantification pipeline to support the use of these nuclear isomers in preclinical imaging. Results Radiolabeling of H 4 Tetrathiol yielded exceptionally efficient complexation, achieving the lowest ligand-to-metal ratio reported for radio-mercury. The resulting [ 197m/g Hg]Hg 2+ -complex demonstrated high in vitro stability in the presence of serum proteins, glutathione, and competing biologically relevant metal ions, though it exhibited kinetic lability when challenged with excess HgCl₂. In vivo biodistribution studies in mice showed a distinct pharmacokinetic profile from unchelated [ 197m/g Hg]HgCl₂, suggesting in vivo complex stability. Phantom imaging studies with a high sensitivity collimator demonstrated submillimeter resolution (≥1.1 mm) for both 197g Hg and 197m Hg, with decay behavior consistent with known half-lives. To facilitate accurate quantification, we developed HgQuant , a Python-based tool for isotope-specific calibration, Bateman decay correction, and automated dual-isotope analysis. This tool enabled reproducible, time-resolved quantification in both phantom and in vivo settings. Conclusions These results establish Tetrathiol as a promising scaffold for mercury-based theranostics, offering efficient radiolabeling and in vivo stability. The integration of high-resolution imaging and HgQuant -based quantification of each isomer establishes a comprehensive framework for advancing [ 197m/g Hg]Hg radiopharmaceutical development. Mercury-197 SPECT theranostics tetrathiol chelators Hg2+ phantom imaging Full Text Supplementary Files TetrathiolSI20250728.pdf Cite Share Download PDF Status: Published Journal Publication published 14 Oct, 2025 Read the published version in EJNMMI Radiopharmacy and Chemistry → Version 1 posted Editorial decision: Major revision 19 Aug, 2025 Reviewers agreed at journal 05 Aug, 2025 Reviewers invited by journal 30 Jul, 2025 Editor assigned by journal 29 Jul, 2025 First submitted to journal 29 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-7216255","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492945815,"identity":"6cc675f9-3876-4422-89be-6306c84e53e1","order_by":0,"name":"Parmissa Randhawa","email":"","orcid":"","institution":"Simon Fraser University","correspondingAuthor":false,"prefix":"","firstName":"Parmissa","middleName":"","lastName":"Randhawa","suffix":""},{"id":492945816,"identity":"b0f20d1d-50d8-403e-a130-3bc22717ba37","order_by":1,"name":"Cristina Rodríguez-Rodríguez","email":"","orcid":"","institution":"The University of British Columbia","correspondingAuthor":false,"prefix":"","firstName":"Cristina","middleName":"","lastName":"Rodríguez-Rodríguez","suffix":""},{"id":492945817,"identity":"97080b3e-dbf9-4c1d-b97c-c00a74d44cd9","order_by":2,"name":"Helena Koniar","email":"","orcid":"","institution":"TRIUMF","correspondingAuthor":false,"prefix":"","firstName":"Helena","middleName":"","lastName":"Koniar","suffix":""},{"id":492945818,"identity":"047e6e52-f4fb-446b-9c8a-070d1744d47a","order_by":3,"name":"Patrick R.W.J. Davey","email":"","orcid":"","institution":"Simon Fraser University","correspondingAuthor":false,"prefix":"","firstName":"Patrick","middleName":"R.W.J.","lastName":"Davey","suffix":""},{"id":492945819,"identity":"41c5dd99-6f27-4664-934b-6e528433fb24","order_by":4,"name":"Shaohuang Chen","email":"","orcid":"","institution":"Simon Fraser University","correspondingAuthor":false,"prefix":"","firstName":"Shaohuang","middleName":"","lastName":"Chen","suffix":""},{"id":492945820,"identity":"da0011cc-d418-4ac1-bfcc-1f09eee35439","order_by":5,"name":"Valery Radchenko","email":"","orcid":"","institution":"TRIUMF","correspondingAuthor":false,"prefix":"","firstName":"Valery","middleName":"","lastName":"Radchenko","suffix":""},{"id":492945821,"identity":"fe2dfd58-bb3a-4826-9428-1ec7a90f85e0","order_by":6,"name":"Caterina F. 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Additionally, accurate imaging and quantification of mercury isotopes, particularly in dual-isotope formats, require tools that account for their complex decay schemes. Phantom imaging studies are essential for validating spatial resolution, quantitative accuracy, and isotope-specific calibration prior to in vivo application. In this study, we investigated the commercially available ligand H\u003csub\u003e4\u003c/sub\u003eTetrathiol for chelation of [\u003csup\u003e197m/g\u003c/sup\u003eHg]Hg\u003csup\u003e2+\u003c/sup\u003e and developed a robust imaging and quantification pipeline to support the use of these nuclear isomers in preclinical imaging.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRadiolabeling of H\u003csub\u003e4\u003c/sub\u003eTetrathiol yielded exceptionally efficient complexation, achieving the lowest ligand-to-metal ratio reported for radio-mercury. The resulting [\u003csup\u003e197m/g\u003c/sup\u003eHg]Hg\u003csup\u003e2+\u003c/sup\u003e-complex demonstrated high in vitro stability in the presence of serum proteins, glutathione, and competing biologically relevant metal ions, though it exhibited kinetic lability when challenged with excess HgCl₂. In vivo biodistribution studies in mice showed a distinct pharmacokinetic profile from unchelated [\u003csup\u003e197m/g\u003c/sup\u003eHg]HgCl₂, suggesting in vivo complex stability.\u003c/p\u003e\n\u003cp\u003ePhantom imaging studies with a high sensitivity collimator demonstrated submillimeter resolution (≥1.1 mm) for both \u003csup\u003e197g\u003c/sup\u003eHg and \u003csup\u003e197m\u003c/sup\u003eHg, with decay behavior consistent with known half-lives. To facilitate accurate quantification, we developed \u003cem\u003e\u003cstrong\u003eHgQuant\u003c/strong\u003e\u003c/em\u003e, a Python-based tool for isotope-specific calibration, Bateman decay correction, and automated dual-isotope analysis. This tool enabled reproducible, time-resolved quantification in both phantom and in vivo settings.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThese results establish Tetrathiol as a promising scaffold for mercury-based theranostics, offering efficient radiolabeling and in vivo stability. The integration of high-resolution imaging and \u003cem\u003eHgQuant\u003c/em\u003e-based quantification of each isomer establishes a comprehensive framework for advancing \u0026nbsp;[\u003csup\u003e197m/g\u003c/sup\u003eHg]Hg radiopharmaceutical development.\u003c/p\u003e","manuscriptTitle":"Quantitative dual-isotope preclinical SPECT/CT imaging and biodistribution of the mercury-197m/g theranostic pair with [197m/gHg]HgCl2 and a superior [197m/gHg]Hg-tetrathiol complex as a platform for radiopharmaceutical development","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-04 18:26:19","doi":"10.21203/rs.3.rs-7216255/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2025-08-19T04:36:52+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-08-05T13:58:47+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-30T05:52:16+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-30T00:13:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"EJNMMI Radiopharmacy and Chemistry","date":"2025-07-29T12:21:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ejnmmi-radiopharmacy-and-chemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"erpc","sideBox":"Learn more about [EJNMMI Radiopharmacy and Chemistry](http://ejnmmipharmchem.springeropen.com)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/erpc/default.aspx","title":"EJNMMI Radiopharmacy and Chemistry","twitterHandle":"@officialEANM","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e14aed1f-5bab-4f82-ae76-d42644944aa0","owner":[],"postedDate":"August 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T16:06:06+00:00","versionOfRecord":{"articleIdentity":"rs-7216255","link":"https://doi.org/10.1186/s41181-025-00391-2","journal":{"identity":"ejnmmi-radiopharmacy-and-chemistry","isVorOnly":false,"title":"EJNMMI Radiopharmacy and Chemistry"},"publishedOn":"2025-10-14 15:57:33","publishedOnDateReadable":"October 14th, 2025"},"versionCreatedAt":"2025-08-04 18:26:19","video":"","vorDoi":"10.1186/s41181-025-00391-2","vorDoiUrl":"https://doi.org/10.1186/s41181-025-00391-2","workflowStages":[]},"version":"v1","identity":"rs-7216255","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7216255","identity":"rs-7216255","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}