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bioRxiv · 10.1101/2023.06.28.546820

Synergistic effects of PARP inhibitors by Schlafen 11 and BRCA2-deficiency through accumulation of single-strand DNA gaps behind a fork

Onji, H.·Tate, S.·Sakaue, T.·Onishi, N.·Matsumoto, T.·Sugiyama, T.·Higashiyama, S.·Murai, J.
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Abstract

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis) induce synthetic lethality in breast cancer gene (BRCA)-deficient tumors. Besides the original model proposed by accumulation of double-strand DNA breaks due to the impaired homologous recombination, accumulation of single-strand DNA (ssDNA) gaps due to impaired BRCA-mediated Okazaki fragment processing has emerged as an alternative mechanism of synthetic lethality. Accordingly, PARPis induce ssDNA gaps behind a replication fork in BRCA-deficient cells. Schlafen 11 (SLFN11), a member of the SLFN family, binds replication protein A (RPA)-coated ssDNA gaps and sensitizes cancer cells to DNA-damaging anticancer agents. These facts motivated us to examine the combinational effects of SLFN11 and BRCA-deficiency on PARPis sensitivity. Here, we show that SLFN11 and BRCA2-deficiency synergistically increased sensitivity to PARPis (talazoparib, niraparib, olaparib, and veliparib) at specific concentrations, where SLFN11 alone showed marginal effects. Using chromatin-bound proteins and alkaline BrdU comet assays in human cancer cells, we revealed that ssDNA gaps induced by PARPis were increased by SLFN11 or BRCA2-deficiency and that the combination of the two had the greatest effect. SLFN11 was recruited to and colocalized with chromatin-bound RPA2 under PARPis. SLFN11 recruited around a fork under DNA damage blocked replication, whereas SLFN11 recruited behind a fork under PARPis did not. Chromatin recruitment of SLFN11 and RPA2 was attenuated by the MRE11 inhibitor mirin. Hence, our studies showed that BRCA2-deficiency increased ssDNA gaps behind a fork under PARPis treatment, where SLFN11 bound and further increased the gaps. Our findings provide a mechanistic understanding of favorable responses to PARPis in SLFN11-proficient and BRCA-deficient tumors. SignificanceThis study reveals how SLFN11 enhances the antitumor effects of PARP inhibitors in BRCA2-deficient cancer cells and highlights the importance of analyzing SLFN11 expression in addition to BRCA analysis in clinical practice.

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Onji, H., Tate, S., Sakaue, T., Onishi, N., Matsumoto, T., Sugiyama, T., Higashiyama, S., Murai, J.. 2023-06-28. Synergistic effects of PARP inhibitors by Schlafen 11 and BRCA2-deficiency through accumulation of single-strand DNA gaps behind a fork. https://doi.org/10.1101/2023.06.28.546820

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