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

Abstract

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, and γH2AX 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.

Blocking PARP activity with the inhibitor veliparib enhances radiotherapy sensitivity in endometrial carcinoma

“…Olaparib has been revealed to exert a radiosensitization effect on ovarian cancer H460 and H1299 cell lines, and olaparib combined with RT significantly upregulates the expression of γH2AX. 38 This result is consistent with those of the current study.…”

“…The current study assessed the extent of DNA damage via western blotting, and the results revealed that Ishikawa cells significantly increased the formation of DSBs when treated with a low dose of veliparib in combination with RT in vitro. Olaparib has been revealed to exert a radiosensitization effect on ovarian cancer H460 and H1299 cell lines, and olaparib combined with RT significantly upregulates the expression of γH2AX 38 …”

BMN673 Is a PARP Inhibitor with Unique Radiosensitizing Properties: Mechanisms and Potential in Radiation Therapy

“…Another study also reported increase in RPA foci numbers in irradiated cells treated with BMN673 [ 129 ]. Notably, in contrast to BMN673, a study reported that olaparib decreased RPA70 foci formation and promoted c-NHEJ by facilitating DNA-PKcs phosphorylation [ 130 ]. This result was confirmed in a more recent study [ 81 ].…”

Elevated BTG2 improves the radiosensitivity of non‐small cell lung cancer (NSCLC) through apoptosis

“…Several studies have shown that various factors affect the response of NCSLC to IR, including endogenous RNAs molecules (mRNA, miRNA and lncRNA) and exogenous molecules (small molecule inhibitors). [6][7][8][9][10] IR also leads to a variety of changes in cancer, especially at the transcription level, providing the new thoughts for the study of molecular mechanism. 11,12 For example, Yang et al found that IR reduced COMMD10 expression, which increased the radioresistance of hepatocellular carcinoma through inhibiting the HIF1α/CP loop.…”

“…Several studies have shown that various factors affect the response of NCSLC to IR, including endogenous RNAs molecules (mRNA, miRNA and lncRNA) and exogenous molecules (small molecule inhibitors) 6–10 . IR also leads to a variety of changes in cancer, especially at the transcription level, providing the new thoughts for the study of molecular mechanism 11,12 .…”