Defect of MLH1 expression sensitized esophageal squamous cell carcinoma cells to Polθ inhibitor

Background: A large scale detection of MLH1 methylation is lacking in esophageal Cancer. MLH1 is a well-known mismatch repair gene. The mechanism of MLH1 in DNA double strand break (DSB) repair remains unclear.

Methods: Esophageal Cancer cell lines and 1018 cases of primary Cancer samples were employed. Methylation specific PCR, Western Blot, and CRISPR/Cas9 knockout technique were utilized.

Results: Methylation of MLH1 was detected in 3.93%. MLH1 methylation was significantly associated with tumor differentiation, male gender, smoking, and tumor size (all p < 0.05). The median overall survival (OS) was 24.7 months (95% CI 13.4-36.0) and 51.5 months (95% CI 40.4-62.5) in MLH1 methylated and unmethylated groups, respectively. OS was shorter in MLH1 methylated compared to unmethylated group patients (p < 0.01). Multivariate factor analysis indicated that MLH1 methylation is an independent poor prognosis marker (p < 0.05). MLH1 promotes ataxia telangiectasia mutated (ATM), ataxia telangiectasia and RAD3-related (ATR), and non-homologous end-joining repair (NHEJ), while inhibiting microhomology-mediated end joining (MMEJ) repair signaling pathways. Deletion of MLH1 sensitized esophageal Cancer cells to novobiocin.

Conclusions: MLH1 plays important roles in DSB repair and deletion of MLH1 sensitizes ESCC cells to Polθ inhibitor.

DNA damage repair; DNA methylation; MLH1; Polθ; esophageal cancer; synthetic lethality.