Abstract 3491: Differential antileukemic activity of plant polyphenol combinations in acute myeloid leukemia (AML) cells

Abstract

Abstract AML is the most common acute leukemia in adults with high mortality rate. This malignancy results from the block of terminal differentiation of the multipotent hematopoietic progenitors at early stages of myelopoiesis. The standard approach for AML treatment is cytotoxic chemotherapy with cytarabine and anthracyclines which has low efficiency and is accompanied by severe side effects. Therefore, AML represents a largely unsolved challenge for chemotherapy of malignant disease. Plant polyphenols, which are abundant in diet rich in vegetables and fruits, have been shown to act as chemopreventive and anticancer agents. In this study we demonstrate the in-vitro antileukemic activity of curcumin (CUR), carnosic acid (CA) and silibinin (SIL), alone and in combination, in several human AML cell lines representing different stages of myeloid differentiation: KG-1a (FAB: M1; WHO: AML with minimal differentiation), HL60 (FAB: M2; WHO: AML with maturation), and U937 (FAB: M4; WHO: acute myelomonocytic leukemia). All polyphenols tested inhibited cell proliferation in a concentration-dependent manner. Remarkably, when administered together even at non-cytotoxic concentrations, CUR (2.5-5 µM) and CA (5-10 µM) induced robust cell death in all cell lines tested. This effect was due to the induction of apoptosis concomitant with activation of caspase −8, −9 and −3, and was associated with cell cycle arrest in the S-phase. Interestingly, the induction of cell death was not accompanied either by generation of the intracellular reactive oxygen species or by a decrease in the glutathione content. In addition, the combined treatment induced caspase-8-dependent cleavage of the BH3-only protein Bid, but had no effect on the other Bcl-2 family pro- and anti- apoptotic proteins tested, including Bcl-2, Bcl-xL, Mcl-1, Bax and Bak. In contrast to the CUR/CA combination, cell treatment with SIL (30-60 µM) combined with either CUR or CA resulted in an enhanced inhibition of proliferation with a minor decrease in cell viability. This antiproliferative effect was accompanied by a marked G0/G1 cell cycle arrest with a concomitant decrease in the protein levels of cyclin E and cyclin-dependent kinase-4, and elevation of the cyclin-dependent kinase inhibitor p27Kip1 levels. Importantly, the polyphenol combinations tested here did not affect the viability of human normal skin fibroblasts as well as of both proliferating and non-proliferating peripheral blood mononuclear cells. Our findings indicate that distinct combinations of plant polyphenols exert strong but differential in vitro antileukemic effects by selectively inducing synergistic growth arrest and/or apoptotic cell death. These results suggest that such combinations may have potential for the treatment of AML. Supported by RO1-CA117942-02 grant from the NIH-NCI (to both G.P.S. and M.D.) and by Israel Science Foundation grant 778/07 (to M.D.). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3491.