Col-6 is a compound found in certain edible plants. Col-6 has been synthesized, and structurely-characterized. This study investigated its effects on the growth of human promyelocytic leukemic cell line, HL-60.

Exposure of HL-60 cells to Col-6 at high concentrations (≥40 μM) resulted in cytolysis in 90% cells within 72 hours. At lower concentrations (<20 μM) the cell density and viability were reduced as compared to untreated cells. A 30% reduction in cell growth rate was seen at 10 μM within 48 hours. A reduction of the proliferating cells in S and G2M phases along with an increase of G1 were detected, indicating a G1 arrest. Multiple assays were used to characterize apoptosis, including DNA strand breaks by TUNEL assay, and the presence of sub-G1 peak by flow cytometry. Col-6 induced apoptosis of HL-60 cells regularly at a concentration as low as 0.1 μM. The degree of apoptosis was proportional to the concentrations and the length of exposure. Mononuclear cells isolated from normal peripheral blood (PBMC) and bone marrow (BMMC) were similarly exposed to Col-6. At a concentration as high as 40 μM, Col-6 did not cause apoptosis of PBMC nor BMMC, suggesting that Col-6 does not have the apoptotic effects on normal non-dividing cells. Apoptosis was further correlated with the increase of caspase 9, and the cleavage of PARP (substrate of caspases), as defined by Western blot analyses. The expression of bcl-2 was markedly decreased in the treated cells.

Conclusion: Col-6, a compound found in edible plants, induced apoptosis of HL-60 cells and down-regulation of bcl-2. Col-6 may be a potential novel anti-leukemia agent. Further in vivo study is indicated.

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