KRN5500, a novel antitumor agent, induces apoptosis or cell differentiation in HL-60 cells

BACKGROUND: KRN5500, a derivative of spicamycin, shows antitumor activity against a variety of tumor cell lines. However, the mechanism of cytotoxic action has remained unclear. METHODS: The viability of HL-60 human leukemic cells treated with KRN5500 was studied by the dye exclusion assay. Induction of apoptosis and effects on the cell cycle were investigated by flow cytometry: We measured cellular DNA content after extraction of fragmented DNA, and apoptosis-induced DNA strand breaks. Cell morphology was observed by light microscopy. DNA strand breaks at a nucleosomal unit were analyzed by electrophoresis. RESULTS: Our data demonstrated that KRN5500 caused inhibition of cell growth, and that apoptosis was the mode of cell death. G(1) phase cells were more susceptible to KRN5500 induced apoptosis. In addition, KRN5500 induced cell differentiation at lower concentration. CONCLUSIONS: It is anticipated that KRN5500 will be used clinically as an anti-leukemic agent. Its mechanism of antitumor action is to induce apoptosis or cell differentiation.