Role of alpha class glutathione transferases (GSTs) in chemoprevention: GSTA1 and A4 overexpressing human leukemia (HL60) cells resist sulforaphane and curcumin induced toxicity.

Alpha-class glutathione transferases (α-GSTs) have been shown to protect cells from the harmful effects of reactive oxygen species (ROS) induced lipid peroxidation (LPO) during oxidative stress caused by various physico-chemical agents. While GSTA1-1/A2-2 isozymes exhibit high activity towards lipid and fatty acid hydroperoxides through their selenium independent glutathione peroxidase (GPx) activity, the GSTA4-4 isozyme efficiently metabolizes the LPO product 4-hydroxynonenal (4-HNE) by conjugating it with glutathione (GSH). Because of the fact that ROS generated by the chemopreventive agents, sulforaphane (SFN) and curcumin (Cur), are implicated in the mechanisms of cancer cell killing, the present studies were designed to investigate the contribution of ROS induced LPO in the cytotoxic effects of these agents and the role of α-class GSTs in modulating their toxicity. Human erythroleukemic (HL60) cells were stably transfected with the cDNA encoding the hGSTA1-1 and mGsta4-4 isozymes. After analysing the expression and activities of the respective GST isozymes, the effects of SFN and Cur on the extent of LPO, cytotoxicity and apoptosis were compared in empty vector (VT), hGSTA1-1 and mGsta4-4 expressing HL60 cells. These studies demonstrate that when compared with SFN, Cur was relatively more cytotoxic to HL60 cells. The ectopic expression of hGSTA1-1 and mGsta4-4 isozymes provided resistance to SFN and Cur induced cytotoxicity and apoptosis through a significant suppression of LPO in these cells. Overall, the results suggest that the expression of α-class GSTs in cancer cells can modulate the therapeutic efficacy of chemopreventive agents.