Arsenic affects homologous recombination and single-strand annealing but not end-joining pathways during DNA double-strand break repair.

Arsenic is a carcinogen that can cause skin, lung, and bladder cancer. While DNA double-strand breaks (DSBs) have been implicated in arsenic-induced carcinogenesis, the exact mechanism remains unclear. In this study, we performed genetic analysis to examine the impact of arsenic trioxide (As O ) on four different DSB repair pathways using the human pre-B cell line Nalm-6. Random integration analysis showed that As O does not negatively affect non-homologous end joining or polymerase theta-mediated end joining. In contrast, chromosomal DSB repair analysis revealed that As O decreases the efficiency of homologous recombination (HR) and, less prominently, single-strand annealing. Consistent with this finding, As O decreased gene-targeting efficiency, owing to a significant reduction in the frequency of HR-mediated targeted integration. To further verify the inhibitory effect of arsenic on HR, we examined cellular sensitivity to olaparib and camptothecin, which induce one-ended DSBs requiring HR for precise repair. Intriguingly, we found that As O significantly enhances sensitivity to those anticancer agents in HR-proficient cells. Our results suggest that arsenic-induced genomic instability is attributed to HR suppression, providing valuable insights into arsenic-associated carcinogenesis and therapeutic options.