Effects of Protein Kinase Inhibitors 1(5-isoquinolinesulfonyl)-2-methylpiperazine Dihydrochloride (h-7) and N-[2-guanidinoethyli- 5-isoquinolinesulfonamide Hydrochloride (ha1004) on Calcitriol-induced Differentiation of Hl-60 Cells*

HL-60 promyelocytic leukemia cells were induced to differentiate by 1,25_dihydroxyvitamin D3 (calcitriol) into mature monocytes. Differentiation was assessed by nitro blue tetrazoliuin dye reduction, nonspecific esterase activity, and DNA synthesis. Terminal differentiation of cultures induced by calcitriol (1bnM) was inhibitedby 80% whkn cells were treated simultaneously with protein kinase inhibitors l-(5-isoauinolinesulfonv%2-methvlninerazine dihvdrochloride (H-71 (32 uMI and N-12guanidinoethyll-5-isoquionlinesulfonamid hydroihiohde (HA1064) (320 PM).‘ The ;c,’ for'inhibitibn of calcitriol-induced differentiation was approximately 15 PM for H-7 and 170 PM for HA1004. The lcsO values for H-7 and HA1004 antagonism of calcitriol-induced differentiation are quantitatively and relatively correlated to their known action to inhibit protein kinase C activity. Treatment of cells with concentrations of O-32 PM H-7 or &32OpM HA1004 alone did not affect cell growth, differentiation, or trypan blue exclusion. However, higher concentrations of H7 (> 32 PM) and HA1004 (> 320 PM) were found to be cytotoxic. The data presented suggest that calcitriol-induced differentiation is antagonized by inhibitors of protein kinase and are consistent with the hypothesis that kinase C activity is required for HL-60 cell differentiation. Human HL-60 promyelocytic leukemia cells constitute a useful cell culture system for the study of cellular differentiation. HL-60 cells can be induced to terminally differentiate to morphologically mature myeloid cells by a wide variety of compounds including DMSO$, RA, phorbol diesters and calcitriol [l91. DMSO and RA induce mature neutrophil-like cells, whereas calcitriol and phorbol diesters induce differentiation to a monocyte-macrophage pheno-