62: When Origins Fail: Pre-RC Loss and PARP Inhibitor Resistance

Pappas K et al., PNAS - A genome-wide CRISPR screen in Brca2‑deficient murine prostate organoids identifies loss-of-function in DNA prereplication complex genes (CDT1, CDC6, DBF4) as a reversion‑independent mechanism of resistance to PARP inhibitors; pharmacologic disruption of the Geminin–CDT1 interaction can restore sensitivity. Key terms: PARP inhibitors, BRCA2, prereplication complex, prostate cancer, organoids. Study Highlights:Using primary mouse prostate organoids with engineered Brca2 loss and genome-wide CRISPR screening, the authors found multiple independent sgRNAs targeting pre‑RC genes (Cdt1, Cdc6, Dbf4) that confer resistance to olaparib and the PARP1-selective inhibitor AZD5305. Pre‑RC loss promoted rapid resolution of PARPi‑induced DNA damage and rescued replication fork protection in Brca2‑deficient cells. Copy number loss of CDT1 is frequent in CRPC and overlaps with BRCA2 loss, suggesting potential biomarker relevance. Pharmacologic disruption of the Geminin–CDT1 interaction (AF615) restored PARPi sensitivity in selected pre‑RC deficient models. Conclusion:Impaired DNA prereplication complex function provides a reversion‑mutation‑independent route to PARP inhibitor resistance in BRCA2‑deficient prostate cancer models, and targeting the Geminin–CDT1 axis may reverse resistance in specific contexts. Music:Enjoy the music based on this article at the end of the episode. Article title:BRCA2 reversion mutation–independent resistance to PARP inhibition through impaired DNA prereplication complex function First author:Pappas K Journal:PNAS DOI:10.1073/pnas.2426743122 Reference:Pappas K., Ferrari M., Smith P., et al. BRCA2 reversion mutation–independent resistance to PARP inhibition through impaired DNA prereplication complex function. PNAS. 2025;122(23):e2426743122. doi:10.1073/pnas.2426743122 License:This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support:Base by Base – Stripe donations: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 Official website https://basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/pre-rc-loss-parpi-resistance QC:This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-07-01. QC Scope:- article metadata and core scientific claims from the narration- excludes analogies, intro/outro, and music- transcript coverage: Audited sections describing BRCA2-deficient PARPi resistance, the DNA prereplication complex (CDT1, CDC6, DBF4), replication fork protection and γH2AX dynamics, Geminin regulation and AF615/Geminin–CDT1 axis as a therapeutic angle, and clinical biomarker implications (CDT1 copy-number loss in CRPC).- transcript topics: BRCA2-deficient PARP inhibitor resistance in prostate organoids; DNA prereplication complex (CDT1, CDC6, DBF4) and PARPi resistance; Replication fork protection and γH2AX dynamics under PARPi; Geminin regulation of pre-RC and CDT1 sequestration; AF615 and AZD5305 combination therapy to reverse resistance; CDT1 copy-number loss as a CRPC biomarker QC Summary:- factual score: 10/10- metadata score: 10/10- supported core claims: 6- claims flagged for review: 0- metadata checks passed: 4- metadata issues found: 0 Metadata Audited:- article_doi- article_title- article_journal- license Factual Items Audited:- Upfront PARP inhibitor resistance is common in BRCA-mutant CRPC (~50%).- Genome-wide CRISPR screens repeatedly identified CDT1, CDC...