BLM helicase inhibition synergizes with PARP inhibition to improve the radiosensitivity of olaparib resistant non-small cell lung cancer cells by inhibiting homologous recombination repair

摘要

Objective:We aimed to investigate the radiosensitizing efficacy of the poly-ADP-ribose polymerase(PARP)inhibitor,olaparib,and the Bloom syndrome protein(BLM)helicase inhibitor,ML216,in non-small cell lung cancer(NSCLC)cells.Methods:Radiosensitization of NSCLC cells was assessed by colony formation and tumor growth assays.Mechanistically,the effects of ML216,olaparib,and radiation on cell and tumor proliferation,DNA damage,cell cycle,apoptosis,homologous recombination(HR)repair,and non-homologous end joining(NHEJ)repair activity were determined.Results:Both olaparib and ML216 enhanced the radiosensitivities of olaparib-sensitive H460 and H1299 cells,which was seen as decreased surviving fractions and Rad51 foci,increased total DNA damage,andγH2AX and 53BP1 foci(P<0.05).The expressions of HR repair proteins were remarkably decreased in olaparib-treated H460 and H1299 cells after irradiation(P<0.05),while olaparib combined with ML216 exerted a synergistic radiosensitization effect on olaparib-resistant A549 cells.In addition to increases of double strand break(DSB)damage and decreases of Rad51 foci,olaparib combined with ML216 also increased pDNA-PKcs(S2056)foci,abrogated G2 cell cycle arrest,and induced apoptosis in A549 lung cancer after irradiation in vitro and in vivo(P<0.05).Moreover,Western blot showed that olaparib combined with ML216 and irradiation inhibited HR repair,promoted NHEJ repair,and inactivated cell cycle checkpoint signals both in vitro and in vivo(P<0.05).Conclusions:Taken together,these results showed the efficacy of PARP and BLM helicase inhibitors for radiosensitizing NSCLC cells,and supported the model that BLM inhibition sensitizes cells to PARP inhibitor-mediated radiosensitization,as well as providing the basis for the potential clinical development of this combination for tumors intrinsically resistant to PARP inhibitors and radiotherapy.