A new combined cancer chemotherapy regimen of mitomycin C (MMC) and cisplatin (DDP) showed synergistic antitumor activity against human gastric cancer xenografts St‐40 and SC‐1‐NU in BALB/c nu/nu mice. The drugs were administered intraperitoneally at doses of 2 or 4 mg/kg for MMC and 3 or 6 mg/kg for DDP, respectively. To clarify the schedule‐dependent antitumor activity of MMC and DDP against St‐40 and SC‐1‐NU, different sequential therapies were conducted. Simultaneous administration of these agents showed the highest antitumor activity against SC1‐NU among the three regimens used, whereas the sequence of MMC followed by DDP showed higher antitumor activity than the reverse sequence against St‐40. The intratumoral concentration of platinum was significantly increased in St‐40 treated with the sequence MMC to DDP, in comparison with the sequence DDP to MMC. The maximum tolerated dose (MTD) of this combination was 4 mg MMC plus 6 mg DDP per kg in all the combinations, and these MTDs were 2/3 of the corresponding values for their single use. Since this combination increased the antitumor activity of each single agent without any increase in their toxicity, it would appear to be useful clinically. © 1994 Wiley‐Liss, Inc.
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