BIBR1532,a Telomerase Inhibitor,Enhances Radiosensitivity Of Non-Small Cell Lung Cancer Through Increasing Telomere Dysfunction And ATM/CHK1 Inhibition

Background: Lung cancer is one of the malignant tumors with the highest morbidity and mortality,among which non-small cell lung cancer accounts for about 80% of the total lung cancer.NSCLC is one of the core areas of tumor research worldwide.Radiotherapy is involved in the treatment of nearly 70% of NSCLC and plays a central role in the treatment of non-small cell lung cancer.However,radioresistance is still the main cause of treatment failure.BIBR1532 is a non-nucleoside small molecule compound that inhibits telomerase activity by non-competitive binding to the active site of h TERT.Preclinical studies have shown that BIBR1532 can inhibit tumor cell growth in vivo and in vitro,and improve the chemotherapeutic sensitivity of tumor cells.However,little is known about the effects of BIBR1532 in combination with radiotherapy on tumors and the toxic side effects of combination therapy.Objective: The purpose of this study is to investigate the effect of the highly selective telomerase inhibitor BIBR1532 on sensitivity of radiotherapy in non-small cell lung cancer and its underlying mechanism.Methods: CCK-8 assays,TRAP(Telomeric Repeat Amplification Protocol)assays and terminal restriction fragment(TRF)analysis were performed to examine the effects of BIBR1532 on cell proliferation,telomerase activity and telomerase length.The effects of BIBR1532 on the radiosensitivity in non-small cell lung cancer and the corresponding molecular mechanism were investigated by clonogenic survival assays,flow cytometry,Western blotting,immunofluorescence and senescence-associated ?-galactosidase detection.Finally,the radiosensitization of BIBR1532 to non-small cell lung cancer was further verified by xenograft tumor assays and immunohistochemical experiments in nude mice.Results: We observed dose-dependent direct cytotoxicity of BIBR1532 at relatively high concentrations in NSCLC cells.Low concentrations of BIBR1532 did not appear toxic to NSCLC cells;however,they substantially increased the therapeutic efficacy of IR in vitro by enhancing IR-induced apoptosis,senescence,and mitotic catastrophe.Moreover,in a mouse xenograft model,BIBR1532 treatment synergized with IR at nontoxic dose levels promoted the antitumor efficacy of IR without toxicity to hema-tologic and internal organs.Mechanistically,lower concentrations of BIBR1532 effectively inhibited telomerase activity and increased IR-induced telomere dysfunction,resulting in disruption of chromosomal stability and inhibition of the ATM/CHK1(ataxia-telangiectasia-mutated/Checkpoint kinase 1)pathway,which impaired DNA damage repair.Conclusions: Our findings demonstrate that disturbances in telomerase function by nontoxic dose levels of BIBR1532 effectively enhance the radiosensitivity of NSCLC cells.This finding provides a rationale for the clinical assessment of BIBR1532 as a radiosensitizer.