title: Ursolic acid sensitizes radioresistant NSCLC cells expressing HIF-1α through reducing endogenous GSH and inhibiting HIF-1α.
abstract: In previous studies, the present authors demonstrated that effective sensitization of ionizing radiation-induced death of tumor cells, including non-small cell lung cancer (NSCLC) cells, could be produced by oleanolic acid (OA), a pentacyclic triterpenoid present in plants. In the present study, it was investigated whether ursolic acid (UA), an isomer of OA, had also the capacity of sensitizing radioresistant NSCLC cells. The radioresistant cell line H1299/M-hypoxia inducible factor-1α (HIF-1α) was established by transfection with a recombinant plasmid expressing mutant HIF-1α (M-HIF-1α). Compared with parental H1299 cells and H1299 cells transfected with empty plasmid, H1299/M-HIF-1α cells had lower radiosensitivity. Following the use of UA to treat NSCLC cells, elevation of the radiosensitivity of cells was observed by MTT assay. The irradiated H1299/M-HIF-1α cells were more sensitive to UA pretreatment than the irradiated cells with empty plasmid and control. The alteration of DNA damage in the irradiated cells was further measured using micronucleus (MN) assay. The combination of UA treatment with radiation could induce the increase of cellular MN frequencies, in agreement with the change in the tendency observed in the cell viability assay. It was further shown that the endogenous glutathione (GSH) contents were markedly attenuated in the differently irradiated NSCLC cells with UA (80 µmol/l) pretreatment through glutathione reductase/5,5'-dithiobis-(2-nitrob-enzoic acid) (DTNB) recycling assay. The results revealed that UA treatment alone could effectively decrease the GSH content in H1299/M-HIF-1α cells. In addition, the inhibition of HIF-1α expression in radioresistant cells was confirmed by western blotting. It was then concluded that UA could upregulate the radiosensitivity of NSCLC cells, and in particular reduce the refractory response of cells expressing HIF-1α to ionizing radiation. The primary mechanism is associated with reduction of endogenous GSH and inhibition of high expression of intracellular HIF-1α. UA should therefore be deeply studied as a potential radiosensitizing reagent for NSCLC radiotherapy.
authors.affiliation: Department of Cardiology, First Affiliated Hospital, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Bing
authors.initials: B
authors.lastname: Song
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Maohu
authors.initials: M
authors.lastname: Yu
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Xinrong
authors.initials: X
authors.lastname: Qi
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Gang
authors.initials: G
authors.lastname: Wang
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Linlin
authors.initials: L
authors.lastname: Xiao
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Qiyi
authors.initials: Q
authors.lastname: Yi
authors.affiliation: Teaching and Research Section of Nuclear Medicine, Anhui Medical University, Hefei, Anhui 230032, P.R. China.
authors.forename: Wensen
authors.initials: W
authors.lastname: Jin
keywords: glutathione; hypoxia inducible factor-1α; non-small cell lung cancer; radiosensitization; ursolic acid