{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,8,4]],"date-time":"2026-08-04T16:21:04Z","timestamp":1785860464956,"version":"3.56.0"},"posted":{"date-parts":[[2026,8,3]]},"group-title":"Cancer Biology","reference-count":50,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T00:00:00Z","timestamp":1785715200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/www.biorxiv.org\/about\/FAQ#license"}],"funder":[{"award":["U54CA224081"],"award-info":[{"award-number":["U54CA224081"]}],"id":[{"id":"https:\/\/ror.org\/01cwqze88","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,8,3]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                <jats:p>\n                  APOBEC3A and APOBEC3B are antiviral cytidine deaminases found to drive cancer-associated mutagenesis, contributing to tumor evolution and therapeutic resistance across multiple cancer types. Inhibiting these enzymes holds promise for prolonging response to a wide range of cancer therapies by delaying development of resistance. However, APOBEC3A and APOBEC3B remain challenging drug targets, with no potent and selective small molecule inhibitors reported. Here, we use a fluorescence polarization-based assay to identify small molecules inhibitors of the APOBEC3A-single-stranded DNA interaction. From a library of 2,400 disulfide compounds, we identified 64 hits (mean polarization +\/- 3 sigma, hit rate of 2.7%). Intact protein mass spectrometry revealed that a subset of compounds covalently engages A3A at cysteine 64, including Compounds 1 and 2. Compounds 1 and 2 disrupt APOBEC3A\/APOBEC3B-single-stranded DNA interactions and inhibit APOBEC3A\/APOBEC3B deaminase activity in a dose-dependent manner, with micromolar IC\n                  <jats:sub>50<\/jats:sub>\n                  . Surprisingly, inhibition of APOBEC3A\/APOBEC3B by Compounds 1 and 2 is independent of covalent tethering to cysteine, suggesting a predominantly non-covalent mode of binding. Together, these studies establish an integrated workflow for APOBEC ligand discovery and identify Compounds 1 and 2 as starting points for developing chemical probes to investigate APOBEC-driven mutagenesis and therapeutic resistance.\n                <\/jats:p>","DOI":"10.64898\/2026.07.31.742089","type":"posted-content","created":{"date-parts":[[2026,8,3]],"date-time":"2026-08-03T13:20:28Z","timestamp":1785763228000},"source":"Crossref","is-referenced-by-count":0,"title":["Fluorescence polarization-based fragment screen identifies inhibitors of APOBEC3A and APOBEC3B"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0009-0008-3846-1458","authenticated-orcid":false,"given":"Julianna S.","family":"Brunello","sequence":"first","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94143, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7021-0703","authenticated-orcid":false,"given":"Hannah R.","family":"Allegakoen","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94143, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6356-2674","authenticated-orcid":false,"given":"Weicheng","family":"Li","sequence":"additional","affiliation":[{"name":"Department of Medicine, University of California, San Francisco, San Francisco, California 94158, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8794-6784","authenticated-orcid":false,"given":"Jezrael L.","family":"Revalde","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94143, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7090-9664","authenticated-orcid":false,"given":"Rohit","family":"Bhadoria","sequence":"additional","affiliation":[{"name":"Department of Medicine, University of California, San Francisco, San Francisco, California 94158, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1631-5122","authenticated-orcid":false,"given":"Colton M.","family":"Sanders","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94143, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9366-6770","authenticated-orcid":false,"given":"Michelle R.","family":"Arkin","sequence":"additional","affiliation":[{"name":"Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California 94143, United States"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9085-1615","authenticated-orcid":false,"given":"Jonathan M. 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