Differentiation of human promyelocytic leukemia cells in vitro by 6-thioguanine

The antineoplastic agent, 6-thioguanine, was found to be a highly potent inducer of differentiation of HL60 human leukemia cells in vitro, producing cells with predominantly myeloid characteristics, as judged by morphological, functional, and cytochemical criteria. Maturation of HL60 was attainable without significant cytotoxicity as measured by cell number; moreover, maximal differentiation occurred at a level of the purine antimetabolite below that producing 50% growth inhibition. The 6-thioguanine-induced differentiated cells had distinctive granulocytic morphology, and were capable of generating superoxide anion during the respiratory burst typical of mature phagocytic cells.