Abstract B17: Ceramide-antiestrogen regimen targets bioenergetic elements in acute myelogenous leukemia

Abstract

Abstract Acute myelogenous leukemia (AML), the most common type of leukemia in adults, is heterogeneous in nature and aggressive and only about 25% of patients that experience remission with cytotoxic chemotherapy remain disease-free. The present work demonstrates the therapeutic efficacy of a novel antiestrogen-ceramide regimen in AML. Herein we show that the antiestrogen tamoxifen (tam) magnifies the cytotoxic impact of ceramide, a tumor-suppressor sphingolipid, inducing apoptosis through mitochondrial-bioenergetic targeting, an expedient, practicable avenue for disrupting the energy-producing systems of cancer cells and a potentially fruitful therapeutic direction. C6-ceramide (C6-cer), a short-chain, hydrophilic analog of ceramide was used in these studies. Nanoliposomal formulations of C6-cer and tam were also utilized and found equally effective. In human AML cell lines and in patient-derived AML cells, the C6-cer-tam combination was far more active than single agents in depressing viability and in inducing apoptosis (Annexin V binding; DNA fragmentation). Interestingly, the major tam metabolite in humans, and the one with the longest serum half-life, N-desmethyltamoxifen (DMT), was equally effective in combination with C6-cer. As an example, in KG-1 cells, whereas C6-cer (5 μM) and DMT (5 μM) reduced viability to only 95 and 90% of control, respectively, the combination resulted in 10% viability after 72 hr exposure. In-depth investigations revealed that cytotoxic responses to the C6-cer-antiestrogen regimen were accompanied by i) time- and dose-dependent loss of mitochondrial membrane potential, ii) inhibition of mitochondrial Complex I respiration, iii) mitochondrial cytochrome c release, a key initiative step in the apoptotic process, iv) decreases in cellular ATP levels as marked by robust increases the ratio of ADP to ATP, and v) a >50% reduction in cellular glycolytic capacity, a demonstration of commitment to energy severance. As loss of mitochondrial membrane potential constitutes a critical event in cell death and depletion of ATP in conjunction with targeting the “Warburg effect” represent potent metabolic “hits”, we conclude that the C6-cer-tamoxifen regimen could be a potentially effective targeted therapy for AML, independent of the multidrug resistant phenotype, as shown by efficacy in vincristine-resistant AML cells. Although a two-drug combination, this regimen could be classified as a mitocan, an agent that targets mitochondria and exhibits anti-cancer activity. Support: NCI CA171983 Citation Format: Samy A.F. Morad, Terence E. Ryan, Brian M. Barth, David F. Claxton, Mark Kester, Thomas P. Loughran, Jr., Myles C. Cabot. Ceramide-antiestrogen regimen targets bioenergetic elements in acute myelogenous leukemia. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B17.