The Study Of Anti-proliferation Effect Of Rapamycin On Human Breast Cancer MCF-7 Cells Under Hypoxia And Its Related Mechanism

Objective Hypoxia is a basic characteristic of micro-enviroment of solid tumors and also leads to drug resistance.The key factor regulating cellular O₂ homeostastis is hypoxia-inducible factor-1α(HIF-1α).This study was to determine the anti-proliferation effects of using rapamycin, a novel anti-tumor drug,on human breast cancer MCF-7 cells exposed to normal oxygen concentration or hypoxic enviroment and its related mechanism in vitro and to investigate the possibility of anti-hypoxia of this drug and the synergistic possibility of using rapamycin combined with adriamycin.Methods Hypoxic enviroment is acquired by a modular incubator chamber flushed with an atmosphere saturated with 1%O₂,5%CO₂ and 94%N₂.MTT assay and flow cytometry were used to examine the influence of the drugs on cell proliferation and cell cycle of MCF-7 cells. MCF-7 cells were exposed to normal or hypoxic enviroment and treated with rapamycin or adriamycin alone or co-treated with rapamycin and adriamycin.Western blot analysis was used to assess the expression level of HIF-1αand pAkt,which expression can enhance the sensitivity of rapamycin.Results Opposite to adriamycin,the effect of rapamycin at 5ng/ml to 40ng/ml on inhibiting cell proliferation of MCF-7 cells was enhanced when exposed to hypoxia compared with the effect under normal oxygen environment.Regardless of oxygen concentrations,no synergistic interaction was observed when rapamycin at clinical normal drug level (10ng/ml)combined with adriamycin at 0.25μg/ml to 2.0μg/ml on MCF-7 cells.The MCF-7 cells treated with rapamycin alone were arrested at G1,while co-treated with rapamycin and adriamycin were arrested at G2.Hypoxia enhanced the expression levels of HIF-1αand pAkt,while rapamycin at 10ng/ml had no influence on the expression levels of HIF- 1αand pAkt.Conclusions Hypoxia increase the sensitivity of rapamycin at clinical normal drug level on MCF-7 cells and may be caused by increasing pAkt expression subsequent to hypoxia.