Antitumor activity and toxicity in animals of RR-150 (7-cysteaminomitosane), a new mitomycin derivative.

The experimental antitumor activity of a new mitomycin derivative, 7-cysteaminomitosane (RR-150), was evaluated in mice. When administered i.p. to mice bearing i.p.-implanted tumors, RR-150 was superior to mitomycin C (MMC) in increasing the life span of animals bearing P388 leukemia, B16 melanoma, and a line of L1210 leukemia partially resistant to MMC. RR-150 appeared comparable to MMC in increasing life span of mice bearing Madison 109 lung carcinoma, Colon 26 carcinoma, or parental (nonresistant) L1210 leukemia. Mice immunosuppressed with 550 rads whole-body irradiation prior to i.p. implantation of B16 still benefited (e.g., 40% cure rate) following optimal RR-150 therapy when compared to nonirradiated, B16-implanted mice given RR-150 (e.g., 70% cure rate). RR-150 had inconsistent activity in the treatment of s.c.-implanted tumors. In toxicity evaluations, RR-150 was comparable to MMC in suppression of total while blood cell counts but appeared to be less neutropenic. RR-150 also caused less cumulative leukopenia than did MMC in a weekly chronic dose experiment. Based on serum chemistries, RR-150 did not have significant nephrotoxicity, but there was evidence of possible liver toxicity at doses near the 50% lethal dose. Because of the balance of favorable antitumor and toxicity properties of RR-150, work is under way to prepare a more bioavailable form for advanced evaluation.