Use of DNA repair proteins translated from biomarker screening to predict overall survival in patients with esophageal cancer treated with oxaliplatin chemotherapy.

Abstract

e13587 Background: Oxaliplatin is first-line chemotherapy for colorectal, gastric, and esophageal cancers. Aim was to identify key determinants of oxaliplatin sensitivity and optimise these biomarkers to select patients for chemotherapy. Methods: High-throughput screening of oxaliplatin sensitivity was performed in a Schizosaccharomyces pombe deletion library of 229 DNA repair strains and Chinese Hamster Ovary (CHO) cell lines with mutations in specific proteins. Biopsies were taken from 50 patients with esophageal cancer, who then received two cycles of oxaliplatin and fluorouracil chemotherapy prior to surgery. Levels of DNA repair proteins were quantified by immunohistochemistry and by qRT-PCR. Results: Twelve lead biomarkers were identified from the preclinical models. In CHO cells, XPF and ERCC1 mutants were approximately 30 times more sensitive than the WT cells (p<0.01). In comparison to WT CHO cells, XPF-deficient cells had prolonged delay in mid-late S-phase after oxaliplatin treatment, and persistence of double strand breaks for at least 48 hours. Modified Comet assay confirmed persistence of inter-strand crosslinks created by oxaliplatin. Cells deficient in DNA polymerase eta (pol eta) also accumulated in S-phase and were 3-fold more sensitive (p<0.01) to oxaliplatin treatment than pol eta-complemented cells. Knockdown of XPF, ERCC1 or pol eta sensitised both oxaliplatin-resistant and oxaliplatin-sensitive HCT116 cells to oxaliplatin. In patients with esophageal cancer, low or absent XPF protein expression predicted complete pathological response to chemotherapy with a sensitivity of 58% and specificity of 72%. Cyclin A protein levels (univariate analysis, p<0.005) and pol eta mRNA levels (multivariate analysis, P<0.005) in pre-treatment esophageal biopsies correlated with overall survival. Conclusions: Results suggest that inter-strand DNA cross-links are the principal cytotoxic lesions created by oxaliplatin. Homologous recombination and damage checkpoint proteins are leading biomarkers for patient selection. In patients with esophageal cancer, XPF and pol eta predict response to oxaliplatin chemotherapy.