Clinical in vivo and in vitro studies have revealed pronounced gastric cancer activity using the combination of 5-fluorouracil (5-FU) and cisplatin (CDDP). In addition, the combination of 5-fluorouracil plus cisplatin (FP treatment) possesses synergistic cytotoxicity against gastric cancer. Sensitivity of two gastric cancer cell lines to anti-cancer drugs, 5-fluorouracil (5-FU) and/or cisplatinum (CDDP), was evaluated by use of either flow cytometric analysis (FACS) or morphological observation in terms of induction of apoptosis. In morphological observation, a new experimental technique was used in which cancer cells were distributed in thin collagen gel as one or two cell layers, and cultured with anti-cancer drugs. Thereafter, cells were stained with fluorescent Hoechst 33258 (Ho) and photographed, then stained with hematoxylin and eosin (H&E) and photographed again. Cell death patterns were determined by combining observations of Ho- and H&E-stained cells. While combined administration of 5-FU and CDDP did not induce apoptosis of MKN-28 (mutant-type p53), apoptotic cells were markedly observed in the case of MKN45 (wild-type p53). In addition, consecutive administration of CDDP for 3 h and 5-FU for 21 h effectively induced apoptosis of MKN45. These results indicated that the type of p53 expression in cancer cells could be a promising factor in predicting response to FP therapy and the administration of CDDP prior to 5-FU may be more effective in inducing apoptosis of gastric cancer cells with wild-type p53 expression. These data may provide evidence to support the idea that p53 expression is related to multidrug resistance (MDR) in FP therapy of gastric cancer cell lines.

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