ATR and esophageal squamous cell carcinoma: POLQ-depleted and control ESCC cells were treated with different genotoxic agents including conventional platinum-based chemotherapy drug cisplatin, replication stress inducer hydroxyurea, environmental toxin formaldehyde, topoisomerase inhibitors camptothecin and etoposide and ATR inhibitor VE822 before being subjected to the MTT assay.