Caerin 1.1/1.9 peptides cooperate with 5-fluorouracil to suppress melanoma by reprogramming myeloid suppressor cells and regulatory T cells

Caerin 1.1/1.9 peptides cooperate with 5-fluorouracil to suppress melanoma by reprogramming myeloid suppressor cells and regulatory T cells | 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 Caerin 1.1/1.9 peptides cooperate with 5-fluorouracil to suppress melanoma by reprogramming myeloid suppressor cells and regulatory T cells Xinyi Song, Jiawei Fu, Quanlan Fu, Junjie Li, Yuandong Luo, Hejie Li, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8780310/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose Myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) are major barriers to effective anti-tumour immunity in melanoma. While 5-fluorouracil (5-FU) can partially modulate tumour immunity, its effects are often incomplete. We investigated whether combining host-defence peptides caerin 1.1/1.9 (F1/F3) with 5-FU enhances antitumour efficacy by reprogramming immunosuppressive compartments within the tumour microenvironment (TME). Experimental Design: Antitumour activity of F1/F3 and 5-FU was assessed in the B16 melanoma model using survival, tumour burden, and immune profiling analyses. Cytotoxic interactions were evaluated in vitro . Flow cytometry, single-cell RNA sequencing, T-cell receptor repertoire analysis, cytokine assays, and bioinformatic approaches characterised immune composition, functional states, and intercellular communication under different treatments. Results F1/F3 and 5-FU did not exhibit synergistic cytotoxicity in vitro but produced marked therapeutic synergy in vivo . Dual therapy (DT) significantly prolonged survival and enhanced intratumoural CD8⁺ T-cell infiltration while reducing immunosuppressive MDSCs and Tregs. scRNA-seq revealed that DT selectively impaired metabolically active neutrophil-like PMN-MDSCs and reprogrammed monocytic M-MDSCs toward an IL-1/NF-κB–driven inflammatory, immune-interactive state. Tregs under DT showed destabilisation of canonical suppressive programs and acquisition of effector-like features. These changes were accompanied by enhanced myeloid–lymphoid communication and pronounced clonal focusing of tumour-infiltrating T cells, indicating antigen-driven immune activation. Conclusions F1/F3 peptides convert 5-FU from a partially immunomodulatory chemotherapy into a potent immune-reprogramming regimen by dismantling myeloid and Treg-mediated suppression. This coordinated remodelling of the TME promotes effective adaptive immunity and provides a mechanistic rationale for integrating host-defence peptides with chemotherapy to overcome immune resistance in melanoma. Melanoma 5-Fluorouracil Caerin peptide B16 cell Regulatory T cell Myeloid-derived suppressor cell Single-cell RNA sequencing Full Text Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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-8780310","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":585325023,"identity":"ab75b634-6824-4ae3-801a-39874935fb36","order_by":0,"name":"Xinyi Song","email":"","orcid":"","institution":"The First Affiliated Hospital/School of Clinical Medicine of Guangdong Pharmaceutical University","correspondingAuthor":false,"prefix":"","firstName":"Xinyi","middleName":"","lastName":"Song","suffix":""},{"id":585325024,"identity":"2bcaf280-7e8e-41cf-af34-c63d9e76d0c3","order_by":1,"name":"Jiawei Fu","email":"","orcid":"","institution":"The 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interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eCaerin 1.1/1.9 peptides cooperate with 5-fluorouracil to suppress melanoma by reprogramming myeloid suppressor cells and regulatory T cells\u003c/strong\u003e\u003c/p\u003e","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"First Affiliated Hospital of Guangdong Pharmaceutical University","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Melanoma, 5-Fluorouracil, Caerin peptide, B16 cell, Regulatory T cell, Myeloid-derived suppressor cell, Single-cell RNA sequencing","lastPublishedDoi":"10.21203/rs.3.rs-8780310/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8780310/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eMyeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) are major barriers to effective anti-tumour immunity in melanoma. While 5-fluorouracil (5-FU) can partially modulate tumour immunity, its effects are often incomplete. We investigated whether combining host-defence peptides caerin 1.1/1.9 (F1/F3) with 5-FU enhances antitumour efficacy by reprogramming immunosuppressive compartments within the tumour microenvironment (TME).\u003c/p\u003e\u003ch2\u003eExperimental Design:\u003c/h2\u003e \u003cp\u003eAntitumour activity of F1/F3 and 5-FU was assessed in the B16 melanoma model using survival, tumour burden, and immune profiling analyses. Cytotoxic interactions were evaluated \u003cem\u003ein vitro\u003c/em\u003e. Flow cytometry, single-cell RNA sequencing, T-cell receptor repertoire analysis, cytokine assays, and bioinformatic approaches characterised immune composition, functional states, and intercellular communication under different treatments.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eF1/F3 and 5-FU did not exhibit synergistic cytotoxicity \u003cem\u003ein vitro\u003c/em\u003e but produced marked therapeutic synergy \u003cem\u003ein vivo\u003c/em\u003e. Dual therapy (DT) significantly prolonged survival and enhanced intratumoural CD8⁺ T-cell infiltration while reducing immunosuppressive MDSCs and Tregs. scRNA-seq revealed that DT selectively impaired metabolically active neutrophil-like PMN-MDSCs and reprogrammed monocytic M-MDSCs toward an IL-1/NF-κB\u0026ndash;driven inflammatory, immune-interactive state. Tregs under DT showed destabilisation of canonical suppressive programs and acquisition of effector-like features. These changes were accompanied by enhanced myeloid\u0026ndash;lymphoid communication and pronounced clonal focusing of tumour-infiltrating T cells, indicating antigen-driven immune activation.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eF1/F3 peptides convert 5-FU from a partially immunomodulatory chemotherapy into a potent immune-reprogramming regimen by dismantling myeloid and Treg-mediated suppression. This coordinated remodelling of the TME promotes effective adaptive immunity and provides a mechanistic rationale for integrating host-defence peptides with chemotherapy to overcome immune resistance in melanoma.\u003c/p\u003e","manuscriptTitle":"Caerin 1.1/1.9 peptides cooperate with 5-fluorouracil to suppress melanoma by reprogramming myeloid suppressor cells and regulatory T cells","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-05 06:05:10","doi":"10.21203/rs.3.rs-8780310/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9b0f7fd6-3105-4707-908c-7ea770f104b5","owner":[],"postedDate":"February 5th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-02-05T06:05:10+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-05 06:05:10","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8780310","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8780310","identity":"rs-8780310","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}