RELATIONSHIP BETWEEN CYTOTOXICITY AND CONVERSION OF THIOSANGIVAMYCIN ANALOGS TO TOYOCAMYCIN ANALOGS IN CELL-CULTURE MEDIUM

Non-nucleoside analogs of the pyrrolopyrimidine nucleosides toyocamyci n, sangivamycin and thiosangivamycin have been synthesized and their c ytotoxicity in mammalian cells determined. While studying the effects of 5-thioamide-substituted analogs on cell growth, we observed an inte resting phenomenon in which cells recovered spontaneously from growth inhibition during extended incubations. HPLC studies demonstrated that the 5-thioamide moiety of several structurally dissimilar 7-substitut ed 4-aminopyrrolo[2,3-d]pyrimidines, including thiosangivamycin, is un stable in cell culture medium and is converted to the corresponding 5- nitrile with a half-life of approximately 48 hr. In contrast, differen t substituents at the 4-position of the heterocycle significantly affe cted the stability of the 5-thioamide moiety. Conversion of the thioam ide to the nitrile was caused by components in the cell culture medium , not components of serum. The above observations demonstrate that cau tion should be exercised in interpreting biological data obtained in v itro for 5-thioamide pyrrolo[2,3-d]pyrimidines.