Distinct Combinatorial Effects of the Plant Polyphenols Curcumin, Carnosic Acid, and Silibinin on Proliferation and Apoptosis in Acute Myeloid Leukemia Cells

Abstract

Acute myeloid leukemia (AML) is a malignancy without effective treatment for most patients. Here we demonstrate that combinations of the dietary plant polyphenols—curcumin and carnosic acid—at noncytotoxic concentrations of each agent, produced a synergistic antiproliferative effect and a massive apoptotic cell death in HL-60 and KG-1a human AML cells. In contrast, combinations of curcumin and another plant polyphenol silibinin had a predominantly additive cytostatic effect, without pronounced cytotoxicity. Neither polyphenol combination affected viability of normal human fibroblasts or proliferating and nonproliferating blood cells. Early stage of curcumin/carnosic acid-induced apoptosis was associated with cleavage (activation) of caspase-8, caspase-9, and caspase-3 and the proapoptotic protein Bid, but not with oxidative stress or altered levels of other Bcl-2 family proteins (Bcl-2, Bcl-xl, Mcl-1, Bax, and Bak). Inhibitors of caspase-8 and caspase-9 markedly attenuated apoptosis, indicating the involvement of both extrinsic and intrinsic apoptotic pathways. Caspase-8 inhibition abrogated Bid cleavage and strongly reduced caspase-9 activation, suggesting that the cross-talk mechanism mediated by caspase-8-dependent Bid cleavage can contribute to the activation of the intrinsic apoptotic pathway by curcumin + carnosic acid. Collectively, these results suggest a mechanistic basis for the potential use of dietary plant polyphenol combinations in the treatment and prevention of AML.

ACKNOWLEDGMENTS

We thank Rachel Levy (Department of Clinical Biochemistry, Ben Gurion University), Nilli Grossman (Soroka Medical Center), and Eitan Fibach (Department of Hematology, Hadassah University Hospital, Jerusalem) for kindly providing leukemia cell lines. This study was supported by the National Institutes of Health grant number: RO1-CA117942–02 (to G. P. Studzinski. and M. Danilenko) and the Israel Science Foundation grant number 778/07 (to M. Danilenko).

Notes

*P < 0.05.

**P < 0.01.

***P < 0.001. Significant differences between the effects of an agent alone and its combination with another agent.