Enhancing Radiosensitivity Of NSCLC Cells By Ursolic Acid

ObjectiveNon-small cell lung cancer (nonsmall cell lung cancer, NSCLC) accounted forabout80%of total lung cancer and is the main indications of radiation therapy. Due tothe internal heterogeneity of tumor tissues, some lung cancer cells could producetolerance to radiation therapy. In this study, we investigated whether ursolic acid (UA),a natural drug, could influence the radiosensitivity of NSCLC cells.MethodsThree NSCLC cell lines were used in the present study, including A549cells,H1299cells and radioresistant H1299/M-HIF-1α cells with high expression of HIF-1α,to observe the influence of the radiosensitivity of different cells by UA pretreatment.MTT colorimetric method was used to detect half inhibitory concentration (IC50) ofdifferent cells. To colony forming experiment, the survival fractions (SFs) of A549cellswere calculated. Furthermore, according to single hit multi-target model, thedose-response curves were fitted in order to calculate D0of A549cells and thesensitivity enhancement ratios (SERs) of the different concentrations of UA. On theother hand, after X-ray irradiated in2Gy and5Gy, MTT method was used to detect thesurvival rates (SRs) of H1299and H1299/M-HIF-1α cells with different concentrationsof UA treatment at different time, followed by all SERs being calculated. Subsequently,intracellular reduced GSH content was assayed by GSH-GSSG detection kit.ResultsMTT results showed that the IC50values of UA to A549cells, H1299cells andH1299/M-HIF-1α cells were50.82μmol/L,62.8μmol/L and34μmol/L respectively.The result from clonogenic assay displayed that the SER of A549cells was1.27withUA at30%IC50. Meanwhile, it was observed that the SR of H1299/M-HIF-1α cellexposure to irradiation in2Gy and5Gy was statistically decreased with different concentrations of UA pretreatment at various time (P<0.01). The SER value ranges ofUA to H1299/M-HIF-1α cells were1.91-4.46and2.28-5.76at50μmol/L and80μmol/Lof concentrations each. Moreover, the SR of parent H1299cells was reduced by80μmol/L UA pretreatment at12h and24h. The results showed that there was a obviousreduction in GSH contents of H1299/M-HIF-1α cell and irradiated H1299cell with UAtreatment.ConclusionIt is concluded that UA could significantly down-regulate the redioresistance ofNSCLC cells and produce radiosensitizing effect on radiosensitive NSCLC cells. Themechanism is correlation with the reduction of intracellular GSH contents andanti-oxidant capability.