Activity of mitozolomide (NSC 353451), a new imidazotetrazine, against xenografts from human melanomas, sarcomas, and lung and colon carcinomas.

The chemosensitivity of human tumor xenografts to mitozolomide, 8-carbamoyl-3-(2-chloroethyl)imidazo[5-1-d]-1,2,3,5-tetrazin-4(3H) -one, was studied in 3 different assay systems. In concentrations of 1 to 500 micrograms/ml, mitozolomide completely inhibited the colony-forming ability in soft agar of cell suspensions from sarcomas, melanomas, lung and colon cancers, and a mammary carcinoma. When a panel of tumors of the different histological types was tested for its sensitivity to mitozolomide in vitro, in the 6-day subrenal capsule assay in conventional mice, and, in some cases, as s.c. growing tumors in nude mice, good agreement between the different assay systems was seen. In most cases, a very pronounced antitumor effect was observed. The efficacy of mitozolomide was as good or better than that of the drugs clinically used against the tumor types tested. Tumor size measurements and histological examinations indicated that nude mice carrying a melanoma, a small cell lung cancer, and an osteosarcoma were cured of their tumors. The approach here used for evaluating the effect of a new drug on human cancers may be useful for selecting the tumor types which primarily should be studied in clinical trials. The results indicate that clinical responses to mitozolomide may be anticipated in sarcoma, melanoma, small cell lung cancer, and possibly in colon cancer.