Molecular mechanism of paclitaxel on CDDP resistant ovarian cancer

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We analyzed molecular mechanisms of paclitaxel action on CDDP resistant ovarian cancer cells on the basis of bcl-2 expression and phosphorylation, and apoptotic cell death.We measured IC50 by MTT assay when treated with CDDP and paclitaxel using ovarian cancer cell lines TYK, Nakajima, and HRA, and their CDDP-resistant lines TYK-R, Nakajima-R, and HRA-R. Two of the 3 CDDP resistant lines turned out to be sensitive to paclitaxel, however, only HRA-R showed resistance to paclitaxel. When treated with CDDP and paclitaxel, DNA fragmentation was observed on agarose gel electrophoresis, revealing apoptotic cell death. We also analyzed mRNA expression of bcl-2 and p53 by RT-PCR, and protein expression by Western blotting. In the 3 CDDP resistant lines, bcl-2 expression was increased, and p53 expression was decreased both in mRNA and protein level. Although we did riot observe the phosphorylation of bcl-2 by the treatment of CDDP, paclitaxel treatment of the parental cell lines clearly induced the phosphorylation of bcl-2. On the other hand, bcl-2 phosphorylation on paclitaxel sensitive TYK-R, and Nakajima-R was shown by the treatment of paclitaxel, however, on paclitaxel resistant HRA-R, even 10 μM of paclitaxel was unable to induce the phosphorylatisn of bcl-2. These data raise the possibility of the mechanism by which paclitaxel treatment induce the phosphorylation of bcl-2 and lead to apoptolic cell death in CDDP resistant cells.