Tumour metabolism of methylglyoxal as a target for treatment of glyoxalase1-linked multidrug resistance in cancer chemotherapy

The glyoxalase system is the major pathway for metabolism of the reactive dicarbonyl metabolites, methylglyoxal (MG) in human cells. It is comprised of two enzymes, glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2). These enzymes catalyse the metabolism of MG into D-lactate via intermediate called S-D-lactoylglutathione. MG is produced in glycolysis as a by-product by the trace-level degradation of triosephosphate glycolytic intermediates. The main physiological function of Glo1 is cytoprotective, suppressing the steady-state concentration of MG to low tolerable levels. Cytotoxicity of MG is linked to its reaction with cell protein and DNA, leading to activation of apoptosis. Overexpression of Glo1 in tumour cells is a mediator of multidrug resistance in cancer chemotherapy and cell permeable inhibitors of Glo1 have anticancer activity, suggesting that cytotoxicity of MG may have a key role in cancer chemotherapy. The host research suggested that increased Glo1 expression is permissive of high glycolytic rate and growth of many tumours. My project emerged from this to study evidence of Glo1 expression as a negative survival factor in cancer therapy and the proteomic mechanism of cytotoxicity of MG to human tumour cells. I accessed databases of gene expression in the public domain: KM Plotter – gene expression with links to breast cancer patient survival; and Cancer Cell Line Encyclopaedia (CCLE) – gene expression of human tumour cell lines. assessement between the association of Glo1 expression in cancer patients to effectiveness of treatment (progression free survival) and in human tumour cell lines to other gene expression were performed. Also investigated proteomic changes during MG-induced cytotoxicity in human HEK293 in vitro. Key findings were: Glo1 is a negative survival factor in breast cancer – hazard ratio 1.37 (1.22 – 1.53), logrank P = 2.8 x 10-8 (n = 3951); applicable for all treatments, genotypes, intrinsic subtypes and stages of breast cancers. In human tumour cell lines, Glo1 expression correlated positively with GLO1 copy number and with genes enriched in spliceosome, RNA transport, and cell cycle and DNA replication pathways, and negatively with apoptosis adaptor TRADD. In proteomics analysis of MG-induced cytotoxicity, the mitochondrial apoptosis pathway was activated and proteins of the ribosome, spliceosome, RNA transport, proteasome, respiratory electron transport, ATP formation by chemiosmotic coupling and gluconeogenesis were decreased. It is conclude that Glo1 impacts negatively on breast cancer survival and is a potential target for improved cancer therapy with Glo1 inhibitors where associated MG-induced cytotoxicity involves impairment of multiple processes, including spliceosome function

Studies of glyoxalase 1-linked multidrug resistance reveal glycolysis-derived reactive metabolite, methylglyoxal, is a common contributor in cancer chemotherapy targeting the spliceosome

Background: Tumor glycolysis is a target for cancer chemotherapy. Methylglyoxal (MG) is a reactive metabolite formed mainly as a by-product in anaerobic glycolysis, metabolized by glyoxalase 1 (Glo1) of the glyoxalase system. We investigated the role of MG and Glo1 in cancer chemotherapy related in multidrug resistance (MDR). Methods: Human Glo1 was overexpressed in HEK293 cells and the effect on anticancer drug potency, drug-induced increase in MG and mechanism of cytotoxicity characterized. Drug-induced increased MG and the mechanisms driving it were investigated and the proteomic response to MG-induced cytotoxicity explored by high mass resolution proteomics of cytoplasmic and other subcellular protein extracts. Glo1 expression data of 1,040 human tumor cell lines and 7,489 tumors were examined for functional correlates and impact of cancer patient survival. Results: Overexpression of Glo1 decreased cytotoxicity of antitumor drugs, impairing antiproliferative activity of alkylating agents, topoisomerase inhibitors, antitubulins, and antimetabolites. Antitumor drugs increased MG to cytotoxic levels which contributed to the cytotoxic, antiproliferative mechanism of action, consistent with Glo1-mediated MDR. This was linked to off-target effects of drugs on glycolysis and was potentiated in hypoxia. MG activated the intrinsic pathway of apoptosis, with decrease of mitochondrial and spliceosomal proteins. Spliceosomal proteins were targets of MG modification. Spliceosomal gene expression correlated positively with Glo1 in human tumor cell lines and tumors. In clinical chemotherapy of breast cancer, increased expression of Glo1 was associated with decreased patient survival, with hazard ratio (HR) = 1.82 (logrank p < 0.001, n = 683) where upper quartile survival of patients was decreased by 64% with high Glo1 expression. Conclusions: We conclude that MG-mediated cytotoxicity contributes to the cancer chemotherapeutic response and targets the spliceosome. High expression of Glo1 contributes to multidrug resistance by shielding the spliceosome from MG modification and decreasing survival in the chemotherapy of breast cancer. Adjunct chemotherapy with Glo1 inhibitor may improve treatment outcomes