Abstract 3355: Inhibiting glyoxylase 1 as a strategy to target highly glycolytic cancer cells
Authors: Gruenewald Sylvia , Steckel Michael , Timmermann Andreas , Rehwinkel Hartmut , Steigemann Patrick , Zacharias Sylvia , Walter Alexander , Bauser Marcus , Haegebarth Andrea 
Published: May 2015

Abstract
Cancer cells typically display altered glucose metabolism characterized by a preference of aerobic glycolysis (Warburg effect) resulting in higher levels of glycolytic waste including methylglyoxal (MG). GLO1 (Glyoxalase 1) functions in the detoxification of MG: MG reacts with glutathione to form hemithioacetal, which is converted into S-D-Lactoylglutathione by GLO1 and further metabolised into D-lactate by GLO2. When not detoxified, MG acts as a cytotoxic reagent by forming DNA- and protein-adducts (advanced glycation end products = AGEs) that subsequently lead to cell death. Therefore, GLO1 has been discussed as a potential anti-tumor target for highly glycolytic cancers.
We confirmed previous reports that GLO1 expression is elevated in several tumor entities as compared to normal tissue. Tumor cells with high GLO1 expression levels are proposed to be highly dependent on GLO1 for removal of toxic MG. Therefore sensitivity to GLO1 inhibition was probed in a panel of cell lines covering lung, colon, breast, prostate and skin cancer with varying GLO1 amplification and expression levels. siRNA-mediated knock down of GLO1 did neither cause significant reduction of cellular proliferation nor significant induction of apoptosis in any of the tested tumor cells. Furthermore, treatment of these cells with a potent GLO1 inhibitor (Chiba et al. Bioorg Med Chem Lett. 2012, IC50=11 nM) did not affect proliferation or induce apoptosis at sub-µM concentrations. In addition, no increase in AGEs upon GLO1 inhibition could be detected by western blot. Activity of the GLO1 inhibitor was further tested under conditions expected to increase endogenous MG levels such as hypoxia and elevated glucotriose (via GAPDH inhibition). Furthermore, a spheroid assay was developed to test the GLO1 inhibitor in a 3D assay system, better reflecting in vivo tumor growth. Even under hypoxic or spheroidal assay conditions, proliferation of cancer cells could not be reduced upon GLO1 inhibition. We could demonstrate however that GLO1 inhibition in A375 melanoma and SW620 colon adenocarcinoma cells sensitized the cells to exogenous MG.
Taken together we could not confirm earlier published data that GLO1 inhibition leads to reduced proliferation and induction of apoptosis in cancer cells that have elevated GLO1 expression levels. Being aware that cellular systems may not reflect the situation in vivo, we speculate that GLO1 function alone may be redundant in detoxifying MG. Other possible enzymes which have been linked to MG removal include aldose reductase. Simultaneous inhibition of both enzymes might be a strategy to target highly glycolytic cancers in the future.
Citation Format: Sylvia Gruenewald, Michael Steckel, Andreas Timmermann, Hartmut Rehwinkel, Patrick Steigemann, Sylvia Zacharias, Alexander Walter, Marcus Bauser, Andrea Haegebarth. Inhibiting glyoxylase 1 as a strategy to target highly glycolytic cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3355. doi:10.1158/1538-7445.AM2014-3355