ATR and cancer: Moreover, PARP inhibition in cancer cells may upregulate the homologous recombination (HR) repair pathway to maintain cell survival [10]; thus, ongoing research has uncovered promising synergies between PARPi and other DNA damage response (DDR) inhibitors, especially ataxia telangiectasia and Rad3-related (ATR) and checkpoint kinase 1 (CHK1) inhibitors [11].