Synergistic cytotoxic and antitumor effects of irradiation and taxol on human HeLa cervix carcinoma and mouse B16 melanoma cells.

Several articles have appeared in the scientific literature which report that taxol has the ability to block and/or prolong cells in the G2/Mp phase of the cell cycle by inducing extremely stable microtubules. The G2/M phase is known to be the most radiosensitive phase of the cell cycle. It is the purpose of this study to evaluate the effect of combination taxol and ionizing radiation on tumor cell lines which have not been previously reported in the literature. Decrease in viability and inhibition of proliferation of HeLa and B16 cells induced by irradiation were dose-dependent and significantly enhanced by pretreatment the cells with taxol. Similar antitumor effects of irradiation and taxol were demonstrated by flow cytometric analysis of chromatic fragment formation induced in these cells. The exact mechanism by which taxol enhanced the tumoricidal effect of irradiation is not known. Cell cycle analysis showed that taxol was effective in blocking HeLa and B16 cells at the G2/M stage, at which the tumor cells are believed to be most sensitive to irradiation. This study is in agreement with others who have found that taxol is a powerful radiation sensitizer. Clinical research protocols have been developed and are under way to determine if taxol produces similar synergistic effects in patients undergoing radiation therapy.