Cancer-selective cytotoxic Ca(2+) overload in acute myeloid leukemia cells and attenuation of disease progression in mice by synergistically acting polyphenols curcumin and carnosic acid

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy characterized by extremely heterogeneous molecular and biologic abnormalities that hamper the development of effective targeted treatment modalities. While AML cells are highly sensitive to cytotoxic Ca(2+) overload, the feasibility of Ca(2+)- targeted therapy of this disease remains unclear. Here, we show that apoptotic response of AML cells to the synergistically acting polyphenols curcumin (CUR) and carnosic acid (CA), combined at low, non-cytotoxic doses of each compound was mediated solely by disruption of cellular Ca(2+) homeostasis. Specifically, activation of caspase cascade in CUR+CA-treated AML cells resulted from sustained elevation of cytosolic Ca(2+) (Ca(2+)(cyt)) and was not preceded by endoplasmic reticulum stress or mitochondrial damage. The CUR+CA-induced Ca(2+)(cyt) rise did not involve excessive influx of extracellular Ca(2+) but, rather, occurred due to massive Ca(2+) release from intracellular stores concomitant with inhibition of Ca(2+)(cyt) extrusion through the plasma membrane. Notably, the CUR+CA combination did not alter Ca(2+) homeostasis and viability in non-neoplastic hematopoietic cells, suggesting its cancer-selective action. Most importantly, co-administration of CUR and CA to AML-bearing mice markedly attenuated disease progression in two animal models. Collectively, our results provide the mechanistic and translational basis for further characterization of this combination as a prototype of novel Ca(2+)-targeted pharmacological tools for the treatment of AML.