Biochemical and antitumor activity of tiazofurin and its selenium analog (2-beta-D-ribofuranosyl-4-selenazolecarboxamide).

2-beta-D-Ribofuranosyl-4-selenazolecarboxamide (selenazofurin, CI-935), the selenium analog of tiazofurin (CI-909), was 3- to 10-fold more cytotoxic to murine or human tumor cells in vitro than tiazofurin and was also more active against P388 mouse leukemia in vivo. In vitro cytotoxicity could be reversed by guanosine or guanine but not by other purine nucleosides or bases. Three human tumor cell lines selected for selenazofurin or tiazofurin resistance showed cross resistance between selenazofurin and tiazofurin. Treatment with tiazofurin, selenazofurin, or mycophenolic acid decreased guanylate pools and caused an accumulation of IMP in WIL2 human lymphoma cells. The decrease in guanylate pools was accompanied by inhibition of RNA and DNA synthesis. The NAD analogs of tiazofurin and selenazofurin were inhibitors of L1210 IMP dehydrogenase (IMP:NAD oxidoreductase, EC 1.2.1.14), and both showed uncompetitive inhibition with respect to NAD having Kii values of 5.7 X 10(-8)M and 3.3 X 10(-8)M respectively.