5,10-Dideazatetrahydrofolic acid (
DDATHF) is an inhibitor of
glycinamide ribonucleotide transformylase, the first of two
tetrahydrofolate requiring
enzymes in the de novo
purine nucleotide biosynthetic pathway, and is a potent inducer of the maturation of HL-60 promyelocytic
leukemia cells. The inhibition of cellular growth by
DDATHF was effectively prevented by
adenosine or
deoxyadenosine, whereas
guanosine or
deoxyguanosine only partially prevented the growth inhibition produced by this
folate antimetabolite, implying that the depletion of both
ATP and
GTP, which occurs with this agent, was responsible for its growth inhibitory effects. In contrast, the induction of differentiation by
DDATHF was completely abolished by the presence of
guanosine or
deoxyguanosine, suggesting that the depletion of intracellular
guanine nucleotides by
DDATHF represents the event that is essential to the induction of differentiation by this
folate analog. This possibility was supported by the observation that the concentration of
dGTP was not decreased in cells treated with
DDATHF under the conditions employed. Both
guanine nucleosides selectively restored intracellular
GTP pools depleted by the treatment with
DDATHF to their normal level, whereas only
adenine nucleosides completely restored the levels of both
ATP and
GTP to their normal intracellular concentrations. The relationship between
guanine nucleotide pools and the induction of HL-60 differentiation by
DDATHF was further supported by the finding that maturation and the depletion of intracellular
GTP by
DDATHF were not reversed by
guanine nucleosides in HL-60 cells deficient in
hypoxanthine-guanine phosphoribosyltransferase activity. The findings provide support for the hypothesis that the terminal differentiation of these leukemic cells by
DDATHF is the result of the depletion of intracellular
GTP pools.