Cisplatin (CDDP) exerts significant activity against a wide variety of human malignancies. However, sensitivity to CDDP differs among cancer cells. CDDP induces apoptosis in cancer cells. In the present study, to evaluate good markers of chemo-sensitivity or chemo-resistance of cancer cells, the correlation between occurrence of apoptosis and the changes in expression levels of messenger RNA (mRNA) of three genes (bax, bcl-2, and survivin) in cancer cell lines during CDDP treatment were investigated. Cells (MKN-45, LoVo, and PANC-1) were incubated with CDDP (10 μg/ml). The percentage of cells in sub-G1 fraction was measured by flow cytometry. The changes in expression levels of three genes (bax, bcl-2, and survivin) during CDDP treatment were evaluated by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). The percentage of cells in sub-G1 fraction increased after a shorter incubation with CDDP in LoVo cells and also increased between 12 and 24 h CDDP treatment in MKN-45 cells. On the other hand, even with a 24 h incubation with CDDP, the percentage of cells in sub-G1 fraction did not change in PANC-1 cells. The expression level of bax mRNA significantly increased after 24 h treatment with CDDP in MKN-45 cells and it significantly increased after 12 h treatment with CDDP in LoVo cells. Also, in LoVo cells, the expression level of bcl-2 mRNA decreased after 24 h treatment with CDDP. On the other hand, during CDDP treatment, the expression levels of bcl-2 and survivin mRNA significantly increased in PANC-1 cells. These findings indicate that during chemotherapy, changes in expression levels of bax, bcl-2, and survivin may provide information about chemo-sensitivity or the chemo-resistance of tumors.

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