Effects of dimaprit on growth and differentiation of human promyelocytic cell line, HL-60

The human promyelocytic cell line HL-60, differentiates in response to a variety of agents including dibutyryl cAMP and agents which increase intracellular cAMP concentrations (phosphodiesterase inhibitors, PGE2, and cholera toxin). HL-60 is also known to be rich in H2 -histamine sensitive adenylate cyclase activity. The present study was therefore designed to test the effects of H2-stimulation on growth and differentiation of HL-60 using the potent H2 agonist dimaprit. Dimaprit markedly increased cAMP production in a dose-dependent manner reaching maximal levels after 30-60 minutes. Intracellular cAMP levels decreased thereafter and by 24 hours were approximately 2-3 fold increased above control. Intracellular cAMP levels were not altered by dimaprit (10(-7)M to 10(-4)M) at 4 days in culture compared to either untreated HL-60 cells or dimethylsulfoxide (DMSO) (1.3%) treated cells. While exponential growth was unaltered by dimaprit (10(-7)M to 10(-4)M) as compared to control, dimaprit induced i) morphologic maturation to the myelocyte and metamyelocyte form with no differentiation seen beyond the metamyelocyte even after 6 days in culture, ii) increased NBT reductase activity and iii) dose-dependent increase in lysozyme activity which could be completely blocked by cimetidine, a specific H2 antagonist. Dimaprit-induced differentiation of HL-60 cells was associated with an initial but transient increase in intracellular cAMP production. Maturation beyond the metamyelocyte stage was not observed. Acquisition of NBT reductase and lysozyme activity correlated with morphologic maturation.