Antiangiogenic activity of TPT in vitro.

Proc Amer Assoc Cancer Res, Volume 47, 2006 5542 Protracted administration of topotecan (TPT), a topoisomerase I inhibitor, appears to be more efficacious both in animal models and human cancers. This phenomenon is thought partly mediated through the inhibition of angiogenesis. We found that TPT inhibited EA.hy926 cells proliferation and CAM angiogenesis in a sublethal concentration. The IC50 value of TPT for EA.hy926 cells detected by MTT assay was 0.13 μM, lower than TPT for most of sensitive cancer cell lines (IC50 range, 0.17μM to 5.1μM). TPT (1-10 μM/egg) resulted in a dose-dependent angiogenic inhibition in CAM assay. In AO/EB assay, apoptosis induced by TPT in EA.hy926 cells was observed with a dosed-dependent manner, and the result of flow cytometry was similar to the AO/EB assay with the apoptosis percentage was 2.5% (control), 17.3% (TPT 0.05 μM), 48.9% (TPT 0.5 μM), and 52.3% (TPT 5 μM). By flow cytometry, we also found that various concentrations of TPT induced cell cycle disturbance in EA.hy926 cells. TPT caused G2/M arrest at a dose of 0.05 μM, G1/G0 arrest at a dose of 5 μM, and induced S arrest at a dose of 0.5 μM. The VEGF expression of PC-3 cells was inhibited by TPT under hypoxia. In normoxia, overexpression of p53 and downregulation of ERK were caused by TPT in EA.hy926 cells. In conclusion, TPT exerts tumor suppressing action through interacting with topoisomerase I and inhibiting angiogenesis. The antiangiogenesis mechanism of TPT may correlate with inhibiting proliferation, inducing apoptosis of endothelial cells and down-regulating the expression of VEGF in cancer cells. Further mechanism is under study.