Identification of Natural Compound Derivative for Inhibition of XLF and Overcoming Chemoresistance in Colorectal Cancer Cells

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 mu M). 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.