Mechanism Of Killing Effect Of Thioridazine On Human Lung Cancer PC9 Cells

Background and Objective Epidemiological study shows that lung cancer has become the malignant tumor with the highest incidence in China, most of which is non-small cell lung cancer. Due to its insidious onset, lung cancer is likely to be diagnosed when it has already reached a late stage. Traditional treatments of advanced lung cancer can not yet meet the patients’ expectations because of its easiness of relapse, acquired drug resistance and poor prognosis, new strategies for cancer drugs development in treating NSCLC have become the urgent problems to be solved. Recent research shows thioridazine, a kind of phenothiazine antipsychotic drugs, can inhibit the proliferation of tumor cells in vitro, but the role of thioridazine on lung cancer has not been reported. In this study, PC9 cell lines were selected as the research object by observing the killing effect of thioridazine and the possible mechanism involved.Methods After treated with different concentrations of thioridazine, the proliferation of PC9 cells was determined by methyl thiazolyltetrazolium(MTT) assay. Flow cytometry was used to measure the cell cycle distribution and apoptosis. The expressions of cell cycle protein Cyclin D1 and apoptosis-related proteins Caspase-3, Caspase-8, Caspase-9,Bcl-2, Bax and Bcl-x L were detected by Western blotting.Results The proliferation of PC9 cells was significantly inhibited by thioridazine in a dose- and time-dependent manner. The IC50 value of thioridazine for PC9 cells after 12 h,24 h,48 h was(45.851±2.59) μmol/L,(37.726±1.96) μmol/L and(32.594±1.73)μmol/L respectively. Flow cytometry analysis showed that cell cycle was arrested in G0/G1 phase and the apoptotic rates were remarkably up-regulated with the increasing concentration of thioridazine. Compared with the control group, the differences were statistically significant(P<0.05 or P<0.01). Western blot analysis showed, compared with the control group, thioridazine reduced the expression of Cyclin D1, Bcl-2 and Bcl-x L(P<0.01) and increased Bax expression(P<0.01). Meanwhile, thioridazine promoted the activities of Caspase-3, Caspase-8 and Caspase-9(P<0.01).Conclusion The mechanism of thioridazine inhibiting the proliferation of PC9 cells may be related to activation of caspase cascade in a sequential manner, down-regulation of Cyclin D1, Bcl-2, Bcl-x L and up-regulation of Bax.