Glyoxalase 1 overexpression-associated multi-drug resistance in cancer chemotherapy

Glyoxalase 1 (Glo1) overexpression is found in refractory tumours and this project aims to characterise the resistance to clinical anticancer drugs by Glo1 overexpression in the human HEK-293 tumour cell line in vitro and investigate druginduced increased methylglyoxal and related cytotoxicity as a likely cause. HEK-293 cells had high Glo1 expression and activity that was increased up to 5-fold when stably transfected with a pIRES2-EGFP-GLO1 plasmid with respect to empty vector control using G-418. Dose-response studies determined the median growth inhibitory concentration and showed that Doxorubicin, Mitomycin C, Taxol, Methotrexate and Mechlorethamine had the highest Glo1-linked multi-drug resistance. There was drug-induced increased glycolysis and flux of methylgloxal formation in vitro. Transient transfection of GLO1 siRNA, the cell-permeable Glo1 inhibitor S-p-bromobenzylglutathione cyclopentyl diester, exogenous methylglyoxal and hypoxia potentiated the cytotoxicity of anti-tumour drugs and increased dicarbonyl stress. Stable isotopic LC-MS/MS analysis revealed that Mitomycin C enhanced glutathione (GSH) depletion whereas Mechlorethamine increased GSH levels. There were increased methylglyoxal levels in drug-treated HEK-293 cells in vitro. Overall, decreasing Glo1 expression and activity increased MG toxicity and sensitivity to anti-tumour drugs. Anti-tumours drugs are not direct Glo1 inhibitors and may be influenced by unrecognised downstream signalling mechanisms on glycolysis and MG metabolism