Abstract 2028A: Glutamine deprivation-elicited sensitization of multiple myeloma to venetoclax is associated with electron transport chain inhibition
Authors: Bajpai Richa , Wei Changyong , Shanmugam Mala 
Published: July 2017

Abstract
Cancer cells exhibit altered glucose and glutamine metabolism to sustain survival and proliferation. Altered nutrient utilization also contributes to the development of resistance to apoptosis via regulation of pro and anti-apoptotic BCL-2 family members. We previously reported that glutamine deprivation enhanced binding of BIM to BCL-2 thereby sensitizing myeloma cell lines and patient samples to Venetoclax (ABT-199). In this study we investigated the metabolites regulated by glutamine withdrawal that contribute to enhanced BIM-BCL-2 association and ABT-199 sensitivity. Metabolite profiling and isotope tracing flux analyses of glutamine deprived myeloma cell lines revealed specific reduction of TCA cycle metabolites including succinate, that were not maintained by glucose present in the medium. Cellular bioenergetics end points i.e. OCR and ATP were also suppressed upon glutamine withdrawal correlating with a suppression of the TCA cycle and oxidative phosphorylation. Supplementation of cell permeant dimethyl-α-ketoglutarate (DMK), a TCA cycle metabolite derived from glutaminolysis, to glutamine deprived cells reversed sensitivity to ABT-199. This ability of DMK to reverse ABT-199 sensitization in glutamine deprived cells was associated with a replenishment of TCA cycle intermediates without restoration of ATP levels. Therefore, we sought to further interrogate the TCA cycle and electron transport chain (ETC) in facilitating glutamine withdrawal-associated ABT-199 sensitization. TCA cycle metabolites are linked to mitochondrial respiration through ETC complexes. Inhibition of ETC complexes I, II, III or V in myeloma cell lines enforced similar effects as glutamine deprivation and sensitized cells to ABT-199. Among all five complexes, complex II is more explicitly linked with the TCA cycle through succinate dehydrogenase (SDH). SDH facilitates the oxidation of succinate to fumarate in the TCA cycle through its subunit SDHA, and transfers the released electrons to ubiquinone via its SDHB, C and D subunits supporting the ETC activity of complex II. Competitive inhibition of succinate dehydrogenase by 3-nitro propionic acid (3NPA) induced BIM expression and sensitized myeloma cells to ABT-199, similar to that detected upon glutamine deprivation. Our observations thus narrow down a role for ETC inhibition in facilitating ABT-199 sensitivity and underscore the importance of further interrogation of ways to metabolically perturb and sensitize cancer cells to the highly potent BH3 mimetic ABT-199.
Citation Format: Richa Bajpai, Changyong Wei, Mala Shanmugam. Glutamine deprivation-elicited sensitization of multiple myeloma to venetoclax is associated with electron transport chain inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2028A. doi:10.1158/1538-7445.AM2017-2028A