The synergistic antitumor activity of mitomycin C (MMC) and cisplatin (DDP) against the gastric cancer cell lines MKN‐28 and MKN‐45 was assessed in vitro using the MTT assay. The synergism of the two agents was evaluated in terms of the interaction index (I.I.). The sequence of MMC followed by DDP showed higher antitumor activity than the reverse sequence against MKN‐28 and MKN‐45, and the intracellular concentration of platinum was significantly increased in MKN‐45 by preincubation with MMC, suggesting that MMC modulates cellular permeability to DDP or the ability of DDP to intercalate DNA. Since these two antitumor agents show different types of toxicity clinically, i.e., myelotoxicity by MMC and nephrotoxicity by DDP, this combination chemotherapy could be advantageous by providing synergistic antitumor activity without increased toxicity. © 1993 Wiley‐Liss, Inc.
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