Abstract
Abstract The cytotoxic and differentiating effects of 10-hydroxycamptothecin (HCPT) in the human promyelocytic leukemia cell line HL-60 were examined. By trypan blue dye exclusion, a 24-h exposure of the cells to 0.1 μM of the drug was found to be cytotoxic. Exposure of the cells to lower concentrations (0.001–0.01 μ M) for 3 days reduced cell proliferation and induced cell differentiation. As determined by Wright-Giemsa staining, approximately 25% of promyelocytic cells became metamyelocytes, banded and segmented neutrophils. Electron microscopy demonstrated alterations in the ultrastructure of HCPT-induced HL-60 cells that included the formation of lobulated nuclei and the accumulation of large vesicles and small myelin bodies as well as glycogen-like particles in the cell periphery. Qualitatively similar results were obtained in a subline of HL-60 that is resistant to 4′-(9-acridinylamino)methanesulfon- m-anisidide ( m-AMSA); however, the rate and extent of induced ni-troblue tetrazolium-positive cells by HCPT and several other agents were greater in the resistant cell line. Under conditions that induced cell differentiation, HCPT sharply inhibited [ 3H]thymidine incorporation into DNA and increased the rate of protein synthesis without an effect on the rate of RNA synthesis. The measurement of DNA topoisomerase I activity in nuclear extracts from both HCPT- and DMSO-treated cells demonstrated that the enzyme was decreased in mature cells compared to nondifferentiated controls. The data suggest that progressive reduction of DNA topoisomerase I activity may be associated with cell differentiation, but whether HCPT-induced differentiation is mediated by inhibition of the enzyme is inconclusive.
Published Version
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