Abstract B17: Ceramide-antiestrogen regimen targets bioenergetic elements in acute myelogenous leukemia
Authors: Morad Samy A.F. , Ryan Terence E. , Barth Brian M. , Claxton David F. , Kester Mark , Loughran Thomas P. , Cabot Myles C. 
Published: May 2016

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 &gt;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.