Abstract 1123: AML cells have low reserve capacity in their respiratory chain complexes leading to increased sensitivity to palmitate-induced cell death
Authors: Sriskanthadevan Shrivani , Skrtic Marko , Jhas Bozhena , Jitkova Yulia , Hurren Rose , Gronda Marcela , Wang Xiaoming , Sukhai Mahadeo A. , Minden Mark , Schimmer Aaron 
Published: August 2012

Abstract
Mitochondria contain their own DNA that encodes 13 proteins that comprise the respiratory chain. Recently we demonstrated that inhibiting mitochondrial protein synthesis is preferentially cytotoxic to AML cells and stem cells over normal hematopoietic stem cells due to dysregulated mitochondrial biogenesis in AML. Given the dysregulated mitochondrial biogenesis in primary AML cells, we examined the activity of the respiratory chain complexes in primary AML and normal PBSCs. The enzymatic activity of the respiratory chain complexes were equivalent between primary AML cell and normal hematopoietic cells. We then evaluated the reserve capacity of the respiratory chain complexes. Primary AML cells (n=11) and PBSCs (n =5) were treated with increasing concentrations of chemical respiratory complex inhibitors and the effects on oxygen consumption were measured using the 96-well Seahorse XF Extracellular Flux (XF) Analyzer. AML cells with increased mitochondrial mass displayed heightened sensitivity to the complex inhibitors and less reserve capacity in the respiratory complex compared to normal hematopoietic cells. For example, the mean concentration of the complex III inhibitor antimycin required to reduce oxygen consumption by 50% in primary AML cells was 13.7 ± 1.6 nM vs 29.0 ± 2.4 nM (p=0.0007) for normal hematopoietic cells. Thus, small reductions in the enzyme activity of the respiratory complexes produced greater reductions in oxygen consumption in AML cells compared to normal hematopoietic cells. The reduced capacity of the respiratory chain in primary AML cells highlighted a potential therapeutic approach. We speculated that increasing electron flux through the respiratory chain would preferentially overwhelm the capacity of the complexes in AML cells. To test this strategy, AML cell lines and primary AML samples were treated with increasing concentrations of the fatty acid substrate palmitate to increase the production of Acetyl-CoA and increase flux of electrons through the respiratory chain. Treatment of AML cells with palmitate transiently increased oxygen consumption. However, by 4 hours after treatment, reactive oxygen species increased, oxygen consumption decreased and cell death ensued. In contrast, cell lines with greater reserve capacity including normal hematopoietic cells displayed no change in oxygen consumption, reactive oxygen species or cell viability after palmitate treatment. Thus, we have demonstrated that AML cells have reduced reserve capacity in their respiratory chain leading to heightened sensitivity to reductions in respiratory complexes by inhibiting mitochondrial protein synthesis. The reduced reserve capacity also heightens their sensitivity to increased electron flux through the respiratory chain. As such, targeting the aberrant metabolism of AML may be a novel therapeutic strategy.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1123. doi:1538-7445.AM2012-1123