Abstract 1853: Reduced glucose uptake and inhibition of ATP synthase by mefloquine results in death of glioblastoma multiforme.
Authors: Sharma Natasha , Dong Dezheng , Louie Stan , Cho Heeyeon , Chen Thomas , Hofman Florence , Schonthal Axel 
Published: August 2014

A number of studies have shown that increased expression of glucose transporters (GLUT) facilitates the high level of glycolytic activity found in most cancers. As well, increased expression of GLUT3 has been linked to chemoresistance towards temozolomide (TMZ), the current drug of choice for the treatment of malignant glioma (GBM). This relation between glucose metabolism on one side, and cancer survival and drug resistance on the other, demands further interrogation to more precisely dissect the mechanism(s) driving this cellular adaptation. Insights as to the relation between tumor metabolism and chemoresistance development can provide important information in order to exploit this mechanism as a potential drug target. To this end, we have investigated whether mefloquine (MQ), an FDA-approved antimalarial agent, can be used to inhibit the growth of glioma cells expressing high levels of GLUT3.

We evaluated the effects of MQ on cellular viability and proliferation by MTT assay and colony formation assay. Markers of apoptosis (e.g. cleavage of caspase 7 and PARP) were analyzed by Western blot, and necrosis was quantitated by LDH release. The effect of MQ on GLUT3 levels was studied by Western blot, and the uptake of glucose was analyzed by using fluorescently labeled 2-deoxy-glucose. Mitochondrial respiration and glycolytic flux were measured using the Seahorse Extracellular Flux Analyzer. We also analyzed the effects of MQ on individual complexes of the electron transport chain.

MQ exerted cytotoxic effects on GBM cell lines, including highly TMZ-resistant variants.Cell death was primarily necrosis, with only limited involvement of apoptosis. Treatment with MQ was able to reduce GLUT3 expression, which correlated with reduced glucose uptake in a dose-dependent manner. Methyl pyruvate treatment provided only partial protection from MQ mediated cytotoxicity. MQ also displayed direct inhibition of complex V (ATP synthase) of the mitochondrial electron transport chain. Overall cellular ATP production was severely down-regulated by MQ.

The cytotoxic potency of MQ on GBM cell lines, including highly drug-resistant variants, appears to be caused by drug-induced depletion of cellular energy (ATP), due to decreased glycolytic flux (as a result of reduced glucose uptake) in combination with inhibition of mitochondrial respiration (as a result of potent inhibition of ATP synthase). Exhaustion of cellular ATP precludes apoptosis, which might explain why MQ primarily triggers necrotic cell death. Considering the sugar-craving phenotype of most tumor cells, MQ appears to be well suited to exploit this feature in order to selectively starve malignant cells to death. Thus, our preliminary data suggest that MQ should be further investigated for cancer therapeutic approaches aimed at tumor cell metabolism.

Citation Format: Natasha Sharma, Dezheng Dong, Stan Louie, Heeyeon Cho, Thomas Chen, Florence Hofman, Axel Schonthal. Reduced glucose uptake and inhibition of ATP synthase by mefloquine results in death of glioblastoma multiforme. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1853. doi:10.1158/1538-7445.AM2013-1853