BOK is a pro-apoptotic member of the BCL-2 family frequently repressed in cancer and with emerging roles beyond apoptosis. BOK interacts with and increases uridine monophosphate synthetase (UMPS) activity, thereby promoting uridine monophosphate (UMP) synthesis. We previously showed that BOK protein is downregulated in primary human lung cancer samples, correlating with poorer patient survival. Here, we demonstrate that BOK deficiency increases DNA damage, triggering p53 activation and cell cycle arrest in two independent non-small cell lung cancer (NSCLC) cell models that express either WT or defective p53. In a p53-deficient setting, BOK loss caused elevated baseline DNA damage rendering cells more dependent on alternative DNA repair pathways. We exploited this vulnerability by inhibiting the ATR-mediated DNA damage response pathway with the selective ATR inhibitor ceralasertib (AZD6738). ATR inhibition in BOK/p53 compound-deficient NSCLC cells exacerbated DNA damage and induced cell death, indicating a synthetic lethal interaction. The DNA damage in BOK-deficient cells was rescued by a cell permeable BOK-BH3-derived peptide, confirming the mechanistic link between BOK and UMPS. Taken together, our findings reveal a vulnerability in NSCLC, where combined loss of p53 and BOK sensitises cells to ATR inhibition. This synthetic interaction suggests that p53-deficient tumours with reduced BOK expression may be more reliant on ATR-mediated DNA repair, providing a mechanistic basis for their susceptibility to ATR inhibitors. Given the frequent inactivation of p53 in lung cancer, our study offers a rationale for clinical exploration of ATR inhibitors, in combination with standard chemotherapy, in the context of reduced BOK function. Future investigations into the broader role of BOK in genomic stability and nucleotide metabolism may uncover additional therapeutic strategies for cancers with repressed BOK.
