Chelerythrine and dihydrochelerythrine induce G1 phase arrest and bimodal cell death in human leukemia HL-60 cells

A quaternary benzo[c]phenanthridine alkaloid chelerythrine displays a wide range of biological activities including cytotoxicity to normal and cancer cells. In contrast, less is known about the biological activity of dihydrochelerythrine, a product of chelerythrine reduction. We examined the cytotoxicity of chelerythrine and dihydrochelerythrine in human promyelocytic leukemia HL-60 cells. After 4 h of treatment, chelerythrine induced a dose-dependent decrease in the cell viability with IC50 of 2.6 mu M as shown by MTT reduction assay. Dihydrochelerythrine appeared to be less cytotoxic since the viability of cells exposed to 20 mu M dihydrochelerythrine for 24 h was reduced only to 53%. Decrease in the viability induced by both alkaloids was accompanied by apoptotic events including the dissipation of mitochondrial membrane potential, activation of caspase-9 and -3, and appearance of cells with sub-G1 DNA. Moreover, chelerythrine, but not dihydrochelerythrine, elevated the activity of caspase-8. A dose-dependent induction of apoptosis and necrosis by chelerythrine and dihydrochelerythrine was confirmed by annexin. V/propidium iodide dual staining flow cytometry. Besides, both alkaloids were found to induce accumulation of HL-60 cells in G1 phase of the cell cycle. We conclude that both chelerythrine and dihydrochelerythrine affect cell cycle distribution, activate mitochondrial apoptotic pathway, and induce apoptosis and necrosis in HL-60 cells. (c) 2008 Elsevier Ltd. All rights reserved.