Toxicological study on a new nitrosourea derivative, 1-(2-chloroethyl)-3-isobutyl-3-(beta-maltosyl)-1-nitrosourea

TA-077, 1-(2-chloroethyl)-3-isobutyl-3-(beta-maltosyl)-1-nitrosourea, is a new water-soluble nitrosourea derivative which is disubstituted at the N-3 position of the structure, and is activated by a unique mechanism whereby organic isocyanates can never be produced. In order to clarify the biological functions of the organic isocyanates which common nitrosourea derivatives generate, TA-077 was tested in BDF1 mice for lethality, weight loss and hematological toxicity. TA-077 showed qualitatively and quantitatively similar toxicity to other nitrosourea derivatives which generate organic isocyanates, such as 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitrosour ea (ACNU), methyl 6-[3-(2-chloroethyl)-3-nitrosoureido ]-6-deoxy-alpha-D-glucopyranoside (MCNU), and 1-(2-chloroethyl)-3-(beta-D-glucopyranosyl)-1-nitrosourea (GANU), indicating that the organic isocyanates do not play an important role in the biological activity of the nitrosourea derivatives. Furthermore, the toxicity of TA-077 did not increase significantly (except for weight loss) when the drug was administered daily for five days, and TA-077 given according to this schedule showed far more effective antitumor activity than when given as a single treatment. These results suggested that TA-077 is an analog suitable for consecutive administration in cancer treatment.