Evaluation of the antiangiogenic effect of Taxol in a human epithelial ovarian carcinoma cell line

Purpose. Angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) are major ligands for the endothelium-specific tyrosine kinase receptor Tie-2 and are important regulators of endothelial cell survival. In the presence of vascular endothelial growth factor (VEGF), vessel destabilization by Ang-2 has been hypothesized to induce an angiogenic response, but in the absence of VEGF, Ang-2 leads to vessel regression. In the present study, a human ovarian cancer cell line was used to investigate the possibility that Taxol might affect the expression of Ang-1, Ang-2, and VEGF. Materials and methods. KF 28, a single-cell clone of a human ovarian epithelial carcinoma cell line, was used. The expression of Ang-1, Ang-2, and VEGF was assessed by quantitative real-time RT-PCR and Western blot analysis or enzyme-linked immunosorbent assay. Conditioned medium was used in the in vitro angiogenesis assay. Results. The concentration of Taxol that inhibited the growth of cells to the level of 50% of control cell growth was 4.65+/-0.35 nM. Quantitative real-time RT-PCR indicated that Ang-1 gene expression was significantly decreased by exposure to 2 nM Taxol for 168 h (P<0.05 vs control cells). Western blot analysis confirmed that the Ang-1 protein level was decreased by exposure to 2 nM Taxol for 168 h. Ang-2 gene expression did not significantly differ between control cells and those exposed to Taxol for any of the indicated times. The Ang-1/Ang-2 gene expression ratio was significantly decreased by exposure to Taxol for 168 h (P<0.05 vs control cells). VEGF gene expression was significantly decreased by exposure to Taxol for 168 h (P<0.05). The VEGF concentration in the conditioned medium was also significantly reduced by exposure to Taxol for 168 h (P<0.05). Conditioned medium collected following Taxol treatment for 168 h significantly inhibited endothelial tubule formation (P<0.05). Cell growth did not significantly differ between control cells and those exposed to Taxol for any of the indicated times. Conclusions. Our results show that exposure of ovarian cancer cells to a low concentration of Taxol may inhibit the initiating event in angiogenesis, namely, vascular regression. This information might be valuable in the development of new therapeutic interventions for epithelial ovarian cancer.