Abstract 2184: The roles of intracellular calcium and ER stress in the synergistic apoptotic effect of the plant polyphenols curcumin and carnosic acid in acute myeloid leukemia cells.

Abstract

Abstract Failure to cure acute myeloid leukemia (AML) by conventional chemotherapy still represents a challenge for hematological oncology. Small molecule plant-derived agents and their derivatives (e.g., vinblastine, paclitaxel, etoposide, topotecan) have been widely employed for the treatment of several types of malignancies. However, it is still unclear whether active phytochemicals can be used for the management of AML. We have recently reported that the combination of the plant polyphenols curcumin (CUR) and carnosic acid (CA) at low, bioavailable concentrations synergistically arrests cell growth and induces robust apoptotic response in KG-1a and HL60 human AML cell lines [Pesakhov et al. Nutr. Cancer 2010, 62:811-824], but the underlying mechanisms remain obscure. Here, employing pharmacologic inhibitors of caspases as well as dominant-negative mutants of caspase-8 and -9 and the death receptor adaptor protein FADD, we reveal the involvement of both extrinsic and intrinsic apoptotic pathways as well as their interdependence in CUR/CA-induced cytotoxicity. The activation of both pathways was preceded by upregulation of the expression of endoplasmatic reticulum (ER) stress markers (GRP78 and CHOP) and by the sustained elevation of cytosolic Ca2+ ([Ca2+]cyt). CUR/CA-induced apoptosis was only partially attenuated by the ER stress blocker salubrinal but was fully prevented by lowering [Ca2+]cyt with the membrane-permeable Ca2+ chelator BAPTA-AM. Notably, each polyphenol alone caused modest reduction in ER Ca2+ content, whereas their combination dramatically depleted ER Ca2+ stores thereby triggering cytotoxic [Ca2+]cyt rise. Preincubation of AML cells with 2-aminoethoxydiphenyl borate (2-APB), the ER inositol trisphosphate receptor antagonist, which blocks the main route of Ca2+ release from the ER, also prevented CUR/CA-induced apoptosis. Importantly, the Ca2+ store depletion as well as [Ca2+]cyt accumulation were not observed in CUR/CA-treated peripheral blood mononuclear cells obtained from healthy donors, consistent with the lack of CUR/CA-induced cytotoxicity in these cells. In summary, our findings indicate that the malignant cell-selective synergistic CUR/CA cytotoxicity is mediated by disruption of cellular Ca2+ homeostasis and, partially, through the ER stress response, leading to stimulation of apoptotic pathways. These results suggest that this combination may have potential for the treatment and/or prevention of AML and, possibly, other malignant diseases. (Supported by the American Institute for Cancer Research grant #10A049 to G.P.S. and M.D.) Citation Format: Stella Pesakhov, Nasma Aqaqe, George P. Studzinski, Daniel Fishman, Michael Danilenko. The roles of intracellular calcium and ER stress in the synergistic apoptotic effect of the plant polyphenols curcumin and carnosic acid in acute myeloid leukemia cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2184. doi:10.1158/1538-7445.AM2013-2184