Characteristics of antitumor activity of KW-2189, a novel water-soluble derivative of duocarmycin, against murine and human tumors.

Methyl(1S)-1-bromomethyl-7-methyl-5-[(4-methylpiperazinyl)-carb onyloxy]- 3-[(5,6,7-trimethoxy-2-indolyl)-carbonyl]-1,2-dihydro-3H-pyrolo[3, 2-e] indole-8-carboxylate hydrobromide (KW-2189), a novel derivative of duocarmycin B2, was selected for extensive evaluation based on its improved antitumor activity, water solubility, and stability in the culture medium, as compared with duocarmycin B2. Although the in vitro cell growth-inhibitory activity of KW-2189 was less potent than that of duocarmycin B2, it significantly inhibited the growth of five murine solid tumors including Colon 26 adenocarcinoma, Colon 38 adenocarcinoma, and B16 melanoma in vivo. KW-2189 was also effective against murine P388 leukemia and L1210 leukemia not only by local administration (i.p.-i.p. system), but also by systemic administration (i.p.-i.v. or i.v.-i.v. system). The most remarkable feature of KW-2189 was its efficacy against various human xenografts, which was observed in 14 tumors among 16 tested tumors including drug-insensitive tumors by single i.v. administration. Tumor regression was observed in mice bearing LC-6 lung, St-4 and St-40 stomach, Li-7 liver, PAN-2 pancreas, and MX-1 breast carcinomas. In many cases, the activities of KW-2189 were more than those of clinically active agents, mitomycin C, Adriamycin, cisplatin, and cyclophosphamide. Delayed lethal toxicity, which was reported in mice treated with CC-1065 whose structure was similar to KW-2189, was not observed in mice treated with KW-2189. KW-2189 inhibited DNA synthesis more significantly than RNA or protein synthesis, although DNA strand breaks were not observed. KW-2189 was activated by porcine liver esterase, mouse liver homogenate or Hep G2 homogenate, and DU-86-DNA adducts were detected in KW-2189-treated HeLa S3 cells, suggesting that KW-2189 was converted to DU-86 in the cells. These results indicate that KW-2189 is an interesting candidate for further development as a novel antitumor agent.