LAUSR

Purpose A previous study has identified that XRCC4-like factor (XLF) is a potential target to overcome resistance to 5-fluorouracil (5-Fu) and oxaliplatin (OXA) in colorectal cancer (CRC). The purpose of this study is to develop potent XLF inhibitors to chemoresistance in CRC. Methods Virtual screening was adopted to identify novel XLF-binding compounds by initially testing 6800 molecules in Chemical Entities of Biological Interest library. Hit compounds were further validated by Western blot assay. Cell sensitivity to 5-Fu and OXA was measured using sulforhodamine B assay. The effect of XLF inhibitor on DNA repair efficiency was evaluated by comet assay, fluorescent-based nonhomologous end joining (NHEJ) and homologous recombination (HR) reporter assays. DNA-binding activity of NHEJ key factors was examined by chromatin fractionation assay. Results We identified G3, a novel and potent XLF inhibitor (IC50 0.47±0.02 µM). G3 induced XLF protein degradation in CRC cells. Significantly, G3 improved cell sensitivity to 5-Fu and OXA in chemoresistant CRC cell lines. Mechanistically, G3 depleted XLF expression, severely compromised NHEJ efficiency by up to 65% and inhibited NHEJ key factor assembly on DNA. G3 also inhibited HR efficiency in a time-dependent manner. Conclusion These results suggest that G3 overcomes 5-Fu and OXA resistance in CRC cells by inhibiting XLF expression. Thus, XLF is a promising target and its inhibitor G3 is a potential candidate for treatment of chemoresistant CRC patients.