The effect of topotecan on lung cancer cell cycle and the mechanism of topotecan-induced apoptosis

AIM To study the effect of Topotecan(TPT) on cell cycle and apoptosis of hunman lung cancer SPC A 1 cells and the role of Caspase 3 and bcl 2 involved in TPT induced apoptosis. METHODS Cells were incubated with TPT(5,10,15 and 20 mg·L -1 ) for 24 h. Apoptosis was detected by TUNEL staining, electronic microscope and DNA agarose gel electropheresis. Flow cytometer was used to analyse cell cycle changes and to detect apoptotic rates and bcl 2 expression of cells treated with TPT or TPT and 50 μmol·L -1 Ac DEVD CHO(specific Caspase 3 inhibitor). RESULTS Apoptosis of cells treated with TPT(5 mg·L -1 ) was not detected, but apoptosis rates increased with the increase of TPT concentration and there was significant difference between each concentration group( P 0 01).After treated with TPT(20 mg·L -1 ) for 24 h, typical morphological features of apoptotic cells were detected by TUNEL staining and electronic microscope.DNA ladder was also viewed on agarose gel. Cell cycle changes were detected by flow cytometer with G 1 phase significantly more than control ( P 0 01) and S phase significantly less than control ( P 0 01).Apoptotic rate of cells with TPT(20 mg·L -1 ) was 11 9%±2 6%, higher than control cells ( P 0 01). bcl 2 expression rate of cells with TPT was 7 9%±1 2%,much lower than control cells (44 7%±7 1%, P 0 01). Apoptosis rate of cells with TPT(20 mg·L -1 ) and Ac DEVD CHO(50 μmol·L -1 ) for 24 h was 6 1%±1 8%,lower than cells with TPT only ( P 0 01). bcl 2 expression rate of cells with TPT and Ac DEVD CHO was 33 4%±5 2%, higher than cells with TPT only ( P 0 01). CONCLUSION TPT can act on hunman lung cancer SPC A 1 cells at phase G 1 and effectively induce apoptosis in the way of dose dependent.The possible mechanism was through Caspase 3 activation and its cleavage to inhibit bcl 2.