Mechanistic Study Of Apoptosis Induced By Novel Epothilone Derivatives In Breast Cancer Cells

The prototype of microtubule-stablizer paclitaxel has been used world-wide to treat cancers. However, due to its poor resources and easy to develop drug-resistance in patients, the clinical benefit of paclitaxel had been severely limited. Epothilone is a new series of microtubule-stable agents; it exhibits many advantages over paclitaxel and has become a new focus of anti-cancer drug discovery.In this study, the cytotoxicity of Epothilone derivates, UTDs and BG44S, in MCF7 and MCF7/Adr cells were investigated by SRB assay. Compare with other derivates, BG44AH and BG44BH have more viability. The IC50 values were also determined, BG44BH showed the minimum concentration:2.76nmol/L for MCF7 cells and 56.7nmol/L and for MCF7/Adr cells, respectively. Therefore, BG44BH was selected as an example to compare with Paclitaxel, and to study its mechanism of inducing tumor cell apoptosis.The induction of cell apoptosis was detected by morphological observation and flow cytometer detection. Western blot was performed to test the expression of Bcl-2, Bax, Caspase-8, Caspase-9 and phosphorylation of Akt. The results showed that, when BG44BH concentration was increased, cell cycle was blocked at G2/M stage and then the level of Bcl-2 protein decreased, which increased the activities of Caspase-9, and triggered the cascade of apoptosis in MCF7/Adr cells. We also concluded that a potential target:Akt, a protein kinase which can cause drug resistance did not show significant change, neither in cells treated with BG44BH nor Paclitaxel.Results in this thesis show that BG44BH induce MCF7/Adr cell death through the mitochondria pathway. Higher expression level of Bcl-2 is the main way to induce multidrug-resistance. In addition, based on the phosphorylation level of Akt, it can be implied that the effect of Akt phosphorylation may cause some cell reflection, but it is not the main way to help cancer cells gain the ability of multidrug resistance. This study was not only useful for the structure design of epothilone, but also provided a novel insight into the deeper mechanism of drug resistance.