Half maximal concentrations of baccatin III in contrast, varied between a narrow range of 2 5 uM for figure 2 all these cells. These results indicate that although taxol induces apoptosis in all the cells tested, there are sensitivity differ ences between the cell lines towards fungal taxol and bac catin III treatment. Fungal taxol and baccatin III induced apoptosis was demonstrated by morphological criteria after staining with Hoechst or AO EB staining. A significant loss in the mitochondrial membrane potential was obtained upon treatment of JR4 Jurkat cells with fungal taxol and baccatin III reaching up to 80% after 36 h at the given concentration. Convincing genetic evidence has been provided to show that taxol mediated apoptosis solely relies on the mitochondrial pathway.

Baccatin III has been shown to induce apoptosis in human breast cancer and epidermal carcinoma cell lines, but the mechanism is not fully understood. Fur thermore, JR4 Jurkat and HeLa cells treated with 0. 1 uM fungal taxol or 3. 5 and 3 uM of baccatin III respectively showed a considerable increase in the percentage of apoptotic nuclei after 12 h incubation. DNA fragmentation in a ladder like fashion, one of the main hallmarks of apoptosis, was observed upon treat ment of the cell lines with fungal taxol and baccatin III and it occurs at 6 nM and fungal taxol, and 3. 5 uM 3 uM fungal baccatin III. The requirement of caspase 10 activation downstream of mitochondria in taxol induced apoptosis has been re ported earlier.

Earlier it was shown that caspase 10 is involved in etiposide induced apoptosis in U937 human leukemic cell line and flunarizine channel blocker induced apoptosis in Jurkat cells. In this study, Specific involvement of caspase 10 has been demonstrated in apoptosis of JR4 Jurkat cells in duced by fungal taxol and baccatin III, employing the in hibitors of caspase 9, 3, 2 and 10. Baccatin III is known to be the precursor of taxol. But the experiments with respective growth over a period of time did not show the expected precursor product rela tionship. The presence of high concentration of bacca tin III during the growth period may therefore indicate that this molecule by itself is active and may even have other roles. Further, the ester bond at C13 position of taxol is likely to be hydrolyzed during transport into the cell and thereby yield a higher intracellular concentration of bacca tin III. Substantiating this hypothesis would explain the higher efficacy of taxol. These studies suggest Anacetrapib to us that baccatin III is probably the main active molecule inside the cell and calls for investigation into its intracellular actions.