Effect of rapamycin on the tumor growth of bearing cancer mice of RM-1 and mechansim

Objective To investigate the effect of rapamycin (RAPA) on the tumor growth of bearing cancer mice of RM-1 and the underlying mechanism. Methods In cellular level, RM-1 cells were treated with different concentrations of RAPA. The expression of p62 and cysteinyl aspartate-specific protease (Caspase)-3 proteins was detected by Western blotting. In Animal level, 30 bearing cancer mice of RM-1 were randomly divided into model group, 5 mg/kg RAPA group, 10 mg/kg RAPA group and 20 mg/kg RAPA group. Mice in 5 mg/kg RAPA, 10 mg/kg RAPA and 20 mg/kg RAPA groups were given intraperitoneal injection of RAPA with the doses of 5, 10 and 20 mg/kg respectively. Mice in mode group were given the same volume of phosphate buffer (PBS). Tumor growth and survival rate of four groups were observed after administration for 30 days. Caspase-3 mRNA and protein levels were analyzed by real-time fluorescent quantitative polymerase chain reaction (FQ-PCR) and Western blotting respectively. Cell apoptosis index in tumor tissue was analyzed by terminal-deoxynucleotidyl transferase mediated nick end labeling (TUNEL) staining method. Results As compared with the control group (1.89±0.17), the levels of p62 in the cells treated with 125 nmol/L, 250 nmol/L and 500 nmol/L (0.91±0.19, 0.68±0.12, 0.31±0.10) decreased significantly (t=2.019, 3.491, 4.910, P<0.05). As compared with the control group (0.21±0.09), the expression levels of Caspase-3 protein in cells treated with 125 nmol/L, 250 nmol/L and 500 nmol/L were significantly increased (0.41±0.14, 0.87±0.18, 2.01±0.21) (t=1.989, 2.582, 5.019, P<0.05). As compared with the model group, RAPA of 5, 10 and 20 mg/kg significantly slowed down the growth of tumors in mice, and the survival rate was significantly higher than that in the model group in a dose-dependent manner. As compared with the model group, the levels of Caspase-3 and p62 proteins in tumor tissues of mice in 5 mg/kg RAPA, 10 mg/kg RAPA and 20 mg/kg RAPA groups increased significantly, and those of p62 protein decreased significantly. Casepase-3 and p62 proteins in 5 mg/kg RAPA, 10 mg/kg RAPA and 20 mg/kg RAPA groups were dose-dependently correlated with RAPA concentrations. As compared the model group (5.01±1.12), the apoptotic levels of tumor cells in 3 mg/kg RAPA, 6 mg/kg RAPA and 9 mg/kg RAPA groups [(20.14±4.12), (51.23±8.99), (78.43±10.32)] increased significantly (t=3.109, 5.192, 7.102, P<0.05). Conclusion RAPA can induce excessive autophagy of tumor cells, and excessive autophagy can result in tumor cell apoptosis to achieve anti-tumor effects. Key words: Rapamycin; Prostate cancer; Autophagy; Apoptosis