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Background Paclitaxel is an microtubule inhibitors, whose action results in the formation of stable bundles of microtubules within the cell, increasing tubulin polymerization, thus inhibiting the formation of mitotic spindle and cell cycle,finally inducing the cell apoptosis.It has been demonstrated that paclitaxel induced apoptosis in several cancers(such as ovarian and breast cancer as well as leukemic cells).However,it is not clear how paclitaxel induces apoptosis in human osteosarcoma and whether the apoptosis is related to apoptosis-regulated gene Bcl-2 and Bax.The objective of the current study was to investigate the apoptosis in human osteosarcoma cells induced by paclitaxel,and the relationship between this apoptosis and expression of Bcl-2 and Bax. Methods MG63 OS cells were treated with various concentrations of paclitaxel.Proliferation was determined by cell count in a cytometer chamber.Viability was assessed by typan blue dye exclusion.The cell morphologic alterations were visualized using light and transmitting electron microscope. The percentage of apoptosis of osteosarcoma cell MG63 was measured by TdT-mediated dUTP Nick End Labeling technique(TUNEL) staining method and flowcytometry using Annexin V/PI double staining method after 0, 24, 48,72 and 96 hours of culture in the presence or absence of paclitaxel. The expression of apoptosis-regulated gene Bcl-2 and Bax were detected using immunohistochemical staining. Results A time-dependent and dose-dependent cell growth inhibition was shown after exposure to paclitaxel.Paclitaxel induced MG63 cells to undergo apoptosis with typical apoptosis characteristics, including morphological changes of chromatin condensation, chromatin crescent formation,nucleus fragmentation.The DNA-cleavage was detected by using TUNEL assay.The cells treated with paclitaxel showed initially G2/M phase arrest,which was followed by apoptosis.Paclitaxel could reduce the expression of apoptosis-regulated gene Bcl-2 and improved the expression of apoptosis-regulated gene Bax. Conclusions Paclitaxel is able to induce the apoptosis in human osteosarcoma cells through the initiation of G2/M phase arrest and inhibiting mitosis in both a time-dependent and dose-dependent manner.This apoptosis maybe mediated by down-expression of apoptosis-regulated gene Bcl-2 and up-expression of apoptosis-regulated gene Bax.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]