Glutathione S-transferases in normal and cancerous human colon tissue

In order to evaluate the role of the placental form of glutathione S-transferase (GST-Pi) as a tumour marker, activity and composition of GSTs from human colon were investigated. GSTs were purified from normal colon mucosa and from colonic tumours by affinity chromatography on glutathione-agarose. After SDS-PAGE or isoelectric focusing these purified preparations revealed only one band that comigrated with GST-Pi from human placenta. A monoclonal antibody (mAb) very specific for GST-Pi was developed and characterized. On immunoblot this mAb stains purified GST from normal and diseased colon tissue. GST activity was significantly higher in most cancerous (247 +/- 38 nmol/min/mg protein; n = 7), compared with the corresponding normal tissues (171 +/- 18 nmol/min/mg protein; n = 7). In colon from patients without large bowel malignancies GST-Pi is also by far the most prominent isoform detectable. In conclusion, both normal and tumorous colon tissue predominantly express GST-Pi and therefore GST-Pi is not suitable as a tumour marker for colonic carcinomas. However, the increased GST-Pi levels in colonic tumours could possibly contribute to the relatively high resistance to anti-cancer drugs.