Synergistic suppression of cholangiocarcinoma cells via DNA damage response and cell cycle arrest by dual targeting PARP and ATM in DNA damage repair pathway

This study investigated alterations in DNA damage repair (DDR) genes in cholangiocarcinoma (CCA) influencing cellular vulnerability to DDR inhibitors, notably poly (ADP-ribose) polymerase inhibitors (PARPi) and ataxia-telangiectasia mutated inhibitors (ATMi). Genomic DDR alterations in CCA tumors were identified via cBioPortal. The cytotoxic effect of the inhibitors was determined in 8 CCA cell lines. Cell cycle arrest and apoptosis were determined using flow cytometry. The levels of γ-H2A histone family member X (γ-H2AX) were evaluated using an immunofluorescence assay. Proteins associated with the cell cycle and DDR were evaluated using Western blotting. Among these CCA cells, BRCA-mutated KKU-023 cells exhibited the highest PARPi sensitivity. Co-treatment with ATMi induced a synthetic homologous recombination deficiency (HRD) state in BRCA-proficient CCA cells, thereby sensitizing them to PARPi. This drug combination suppressed CCA cell growth via G2/M phase arrest, downregulated cyclin A and B1 expression, and enhanced apoptosis. Mechanistically, this synergistic cytotoxicity was attributed to increased DNA double-strand breaks, evidenced by elevated γ-H2AX and reduced RAD51 expression, signifying compromised DNA repair. These preclinical findings support the therapeutic potential of DDR inhibitors, individually or in combination, for CCA subsets characterized by DDR gene alterations.