Glutathione-related Enzymes Contribute to Resistance of Tumor Cells and Low Toxicity in Normal Organs to Artesunate

Abstract

The anti-malarial artesunate (ART) also inhibits the growth of cancer cells. The active moiety is an endoperoxide bridge whose cleavage generates reactive oxygen species and free radicals. We analyzed whether glutathione-related enzymes contribute to tumor resistance to ART and to the low toxicity of ART towards normal organs. The microarray-based mRNA expression of dihydrodiol dehydrogenase, γ-glutamylcysteine synthase (γ-GCS), glutathione S-transferases GSTM4, GSTT2, GSTZ1, and microsomal glutathione S-transferase MGST3 showed significant relationships (p<0.05) to cellular response to ART in 55 cell lines of the National Cancer Institute, USA. A tendency for correlation (0.05<p<0.1) was observed for GSTA1, GSTA2, GSTP1 and MGST1. A further 12 glutathione-related genes were not linked to ART resistance. MSC-HL13 cells transfected with cDNAs for heavy and light subunits of γ-GCS were more resistant to ART than mock control vector-transfected MSV-PC4 cells. L-buthionine sulfoximine, a γ-GCS inhibitor that depletes cellular glutathione pools, completely reversed ART resistance in MSV-HL13 cells, while a partial reversion was obtained by ethacrynic acid, an inhibitor of GST. The expression of GST-P was analyzed immunohistochemically in normal rat organs. GST-P immunostaining was found in all organs analyzed, albeit with varying staining intensities and in different histological structures of the organs. GST expression in normal organs may, therefore, contribute to the good tolerability and minimal toxicity of ART in normal organs.