Chemical inhibition of RPA gap protection sensitizes BRCA1-deficient cancers to PARP inhibition

VanderVere-Carozza, P. S.; Jordan, M. R.; Garrett, J. E.; Pollok, K. E.; Hinshaw, H. D.; Sulaiman, X.; Liu, S.; Wan, J.; Pawelczak, K. S.; Turchi, J. J.

doi:10.1101/2025.04.09.647957

bioRxiv · 10.1101/2025.04.09.647957

Chemical inhibition of RPA gap protection sensitizes BRCA1-deficient cancers to PARP inhibition

VanderVere-Carozza, P. S.·Jordan, M. R.·Garrett, J. E.·Pollok, K. E.·Hinshaw, H. D.·Sulaiman, X.·Liu, S.·Wan, J.·Pawelczak, K. S.·Turchi, J. J.

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Abstract

Poly (ADP-ribose) polymerase inhibitors (PARPi) are standard of care for many BRCA1 deficient cancers, though few cures are achieved. We sought to determine if targeting the protection of the single-strand DNA gaps induced by PARPi in BRCA-deficient cancers could increase efficacy. Replication protein A (RPA) participates in critical protein-protein and protein-DNA interactions to protect single-stranded DNA (ssDNA) and support DNA metabolism. We have reported the optimization of small molecule RPA inhibitors (RPAi) that target protein-ssDNA interactions to chemically exhaust RPA and elicit single-agent anticancer activity. RPAi sensitizes cells to PARPi in BRCA1-deficient non-cancerous cells, where ssDNA gap formation drives therapeutic efficacy. We show that RPAi treatment abolishes PARPi-induced replication gap protection, resulting in genomic instability via replication fork degradation and chromosomal integrity, and that, in vivo, the RPA and PARP targeted combination abrogates cancer growth in a BRCA1-mutant breast cancer model. We find that genetic predispositions to ssDNA gap accumulation correlate with RPAi sensitivity, and BRCA1-proficient cells remain sensitive to combination treatment but require more PARP inhibition to increase ssDNA gaps. RPAi-PARPi combination activity in patient-derived ovarian cancer models demonstrates the utility of targeting gap protection to increase PARPi sensitivity and circumvent resistance. Collectively, this work provides a unifying mechanism of chemical RPA exhaustion as a cancer therapeutic strategy. One Sentence SummaryInhibition of single-strand DNA gap protection potentiates PARP targeted treatment of BRCA1 deficient cancers.

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VanderVere-Carozza, P. S., Jordan, M. R., Garrett, J. E., Pollok, K. E., Hinshaw, H. D., Sulaiman, X., Liu, S., Wan, J., Pawelczak, K. S., Turchi, J. J.. 2025-04-15. Chemical inhibition of RPA gap protection sensitizes BRCA1-deficient cancers to PARP inhibition. https://doi.org/10.1101/2025.04.09.647957

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