Pumitepa is a purine derivative patented by All-Union Scientific-Research Chemical-Pharmaceutical Institute as cancerolytic. Although the exact mechanism of action of pumitepa has yet to be fully elucidated, this agent appears to work through alkylation, thereby causing DNA damage and cell cycle arrest. In in vitro studies, Pumitepa prolonged the mitotic cycle in human embryo fibroblasts by 2.5-3 hr, primarily by prolonging the start of phase G1. Pumitepa induced similar types of chromosomal aberrations in cells of all phases of the mitotic cycle. Chromosomes in phase S were the most sensitive for Pumitepa, followed by chromosomes in phases G1 and G2.