Induction of differentiation in the human promyelocytic leukemia cell line HL-60 by the cyclopentenyl analogue of cytidine

Abstract

The effects of the cyclopentenyl (cCyd) and cyclopentyl (carbodine) analogues of cytidine on differentiation, and nucleic acid and nucleotide biosynthesis, were examined in the human promyelocytic leukemia cell line HL-60. Continuous exposure for 5 days to 10 −8 to 10 −6 M cCyd or 10 −6 to 10 −5 M carbodine produced progressive inhibition of cell growth. During this exposure interval, pronounced differentiation to mature myeloid cells occurred wherein 95% of the cell population reduced nitroblue tetrazolium 4 days after exposure to 10 −7 M cCyd or 10 −5 M carbodine. Preceding differentiation was the inhibition of DNA synthesis which reached 10% of control levels 24 hr after exposure to 10 −7 M cCyd or 10 −5 M carbodine, while RNA synthesis was inhibited to a lesser extent. The induction of mature myeloid cells by cCyd was preceded by the inhibition of c- myc mRNA levels which was more pronounced than the reduction in total cellular RNA synthesis. During the interval of cCyd treatment, there was a rapid and pronounced inhibition in the level of CTP, but not of UTP, ATP or GTP, where the half-life for the disappearance of CTP was 1.5 to 2hr. Following drug removal, cells treated with cCyd showed a sustained reduction in CTP levels, whereas cells treated with carbodine showed almost complete recovery of CTP levels within 48 hr. These results indicate that the reduction in CTP levels leads to rapid inhibition of DNA synthesis and reduction in c- myc mRNA levels which precede the appearance of differentiated cells.