Abstract 1718: Schlafen 11 (SLFN11) is a critical determinant of cellular sensitivity to PARP inhibitors

Abstract Poly(ADP-ribose)polymerases (PARP) are DNA damage sensors and major repair factors for DNA single-strand breaks. Since the discovery of the synthetic lethality of PARP inhibitors in homologous recombination-deficient cells, the mechanism by which PARP inhibitors exert their cytotoxicity has been dominantly interpreted as an accumulation of unrepaired single-strand breaks resulting from catalytic PARP inhibition. We recently reported that several PARP inhibitors have an additional cytotoxic mechanism by trapping PARP-DNA complexes (1). BMN 673 is the most potent PARP inhibitor to date in terms of cytotoxicity and PARP trapping potency (2). Nevertheless, the NCI60 data show that half of the 60 cell lines are tolerant to BMN 673. To elucidate the mechanisms of tolerance, we searched for genes with expression levels correlated to BMN 673 sensitivity, and found that Schlafen 11 (SLFN11) is one of the most positively correlated genes. Most cells without SLFN11 expression were tolerant to BMN 673. To examine the involvement of SLFN11 in BMN 673 sensitivity, we disrupted the SLFN11 gene in DU145 prostate cancer cells and EW8 Ewing's sarcoma cells where SLFN11 expression levels and BMN 673 sensitivities are high. Knocking out SLFN11 in DU145 and EW8 did not affect their cell growth or cell cycle progression under normal conditions, but diminished their hypersensitivity to BMN 673 and another PARP inhibitor, olaparib. Cell cycle analyses revealed that SLFN11-proficient cells arrested at S phase while SLFN11 deficient cells were able to progress to G2 phase in the presence of BMN 673. Interestingly, arresting points at S phase in SLFN11 proficient cells were earlier when more PARP-DNA complexes were induced, suggesting that SLFN11 inhibits DNA replication under DNA damage. Differential kinetics of DNA repair and PARP-DNA complex formation were observed between SLFN11 proficient versus deficient cells. Our data suggest that the expression of SLFN11 may be a novel genomic biomarker for PARP inhibitor sensitivity. 1. Murai J, Huang S-yN, Das BB, Renaud A, Zhang Y, Doroshow JH, et al. Trapping of PARP1 and PARP2 by Clinical PARP Inhibitors. Cancer Research. 2012;72:5588-99. 2. Murai J, Huang SN, Renaud A, Zhang Y, Ji J, Takeda S, et al. Stereospecific PARP trapping by BMN 673 and comparison with olaparib and rucaparib. Mol Cancer Ther. 2014; Submitted. Citation Format: Junko Murai, Rozenn Josse, James H. Doroshow, Yves Pommier. Schlafen 11 (SLFN11) is a critical determinant of cellular sensitivity to PARP inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1718. doi:10.1158/1538-7445.AM2014-1718