Assays and screens; imaging; drug properties

A cell-based imaging method could identify targets that promote resistance to PARP inhibitors and identify synergistic combinations of PARP and other inhibitors. The method uses fluorescent microscopy in cancer cells treated with a PARP inhibitor and siRNAs to measure changes in levels of S139-phosphorylated H2A histone family member X (H2AFX; H2AX), a marker of DNA damage response; decreases in levels of phosphorylated H2AFX indicate the siRNA-targeted gene could contribute to PARP inhibitor resistance, and increases in phosphorylated H2AFX indicate a potential synergy between gene knockdown and PARP inhibition. When applied to a human osteosarcoma cell line treated with the PARP inhibitor Lynparza olaparib, siRNA targeting poly(ADP-ribose) glycohydrolase (PARG) decreased levels of serine139-phosphorylated H2AFX compared with non-specific control siRNA, suggesting PARG contributes to PARP inhibitor resistance. Also in the Lynparza-treated cell line, siRNAs targeting genes in the stem cell factor (SCF; c-Kit ligand; KITLG) complex increased serine139-phosphorylated histone H2AFX, and Lynparza plus the SCF pathway inhibitor pevonedistat decreased viability compared with either agent alone. Next steps could include using the method to identify other PARP inhibitor combinations that have synergistic effects or overcome drug resistance in cancer.

Merck & Co. Inc. markets Lynparza for ovarian cancer and has the compound approved for breast cancer...