SLFN11 and ATR as targets for overcoming cisplatin resistance in ovarian cancer cells.

The levels and activities of the DNA/RNA helicase schlafen11 (SLFN11) and the serine/threonine-protein kinase ataxia telangiectasia and Rad3-related protein (ATR) may determine cancer cell sensitivity to DNA damaging agents, including platinum drugs. Here, we studied the roles of SLFN11 and ATR in cisplatin resistance of ovarian cancer using cell lines displaying acquired or intrinsic cisplatin resistance. W1CR, the cisplatin-resistant subline of W1 ovarian cancer cells, displayed reduced SLFN11 levels. HDAC inhibition using entinostat returned an epigenetic downregulation of SLFN11 in W1CR cells, caused SLFN11 re-expression and re-sensitized these cells to cisplatin. Moreover, entinostat also sensitized intrinsically resistant EFO21 ovarian cancer cells to cisplatin by upregulating SLFN11. However, SLFN11 was not involved in cisplatin resistance in all other cell models. Thus, SLFN11 expression is not a general cisplatin resistance marker in ovarian cancer. In contrast, inhibition of the DNA damage repair master regulator ATR using sub-toxic concentrations of elimusertib sensitized parental cell lines as well as intrinsically resistant EFO21 cells to cisplatin, and fully reversed acquired cisplatin resistance in cisplatin-adapted sublines W1CR, A2780cis, and KuramochiCDDP. Mechanisms underlying ATR-mediated cisplatin resistance differed between the cell lines and included CHK1/WEE1 signaling and induction of homologous recombination. In conclusion, SLFN11 and ATR are involved in ovarian cancer cisplatin resistance. Although our data identify ATR as key target for tackling cisplatin resistance in ovarian cancer, future studies are needed to identify biomarkers that indicate, which individual ovarian cancers benefit from SLFN11 re-activation and/or ATR inhibition.