In vivo Antitumor Activity of Hexamethylmelamine against Human Breast, Stomach and Colon Carcinoma Xenografts

We have evaluated the antitumor activity of Altretamine (hexamethylmelamine, HMM) on human carcinoma xenografts serially transplanted in nude mice. Five human breast carcinoma xenografts, MX‐1, T‐61, MCF‐7, R‐27 and Br‐10, were inoculated subcutaneously into female nude mice. Two human stomach carcinoma xenografts, SC‐1‐NU and St‐4, and three human colon carcinoma xenografts, Co‐3, Co‐4 and Co‐6, were inoculated subcutaneously into male nude mice. One pellet of 17β‐estradiol (0.1 mg/mouse) was inoculated subcutaneously in the mice transplanted with MCF‐7 when the tumors were inoculated. HMM was administered per os daily for 4 weeks. MX‐1 and T‐61 tumors regressed completely after treatment with HMM at a dose of 75 mg/kg (the maximum tolerated dose: MTD) for MX‐1 and 25 mg/kg for T‐61. Br‐10 was sensitive, whereas MCF‐7 and R‐27 were resistant to HMM at its MTD. HMM exerted the most potent antitumor effect against T‐61. Against MX‐1, it exerted an antitumor effect equivalent to that of cisplatin or cyclophosphamide. In addition, this agent was effective against all stomach and colon carcinoma xenografts, in particular St‐4 (T/C%= 10.7: the mean tumor weight of treated group/the mean tumor weight of control group) and Co‐3 (T/C%=31.5%) which are insensitive to presently available agents. HMM seems worthy of further clinical investigation as a candidate agent to treat breast, stomach, colon and other carcinomas.