Glutathione S-transferase isoenzymes and glutathione peroxidase activity in normal and tumour samples from human lung

An increasing body of evidence suggests that glutathione-dependent enzymes are an important factor in determining the sensitivity of tumours to cytotoxic drugs. Ten randomized normal and tumour samples from individuals with lung cancer were analysed for glutathione S-transferase isoenzyme (GST) content and glutathione peroxidase (Gpx) activity. The normal tissue samples exhibited a 5.1- and 7.0-fold variation in GST and Gpx activity respectively. High levels of the pi class, acidic Yf, GST subunit were found in all the samples, with little variation between individuals. The concentration of alpha and mu class subunits was 5- to 10-fold lower and were subject to significant individual variability. The mu class subunit identified had a faster mobility on SDS-PAGE than the hepatic GST mu standard and did not appear subject to the genetic polymorphism associated with certain members of this gene family. This suggests the presence of a novel pulmonary protein which may correspond to the rat Yn Yn protein. The normal to tumour ratio for GST activity varied significantly between the samples and tended to follow the relative expression of the mu class subunit, and to a lesser extent the alpha class GST subunit. The pi subunit was present in the normal and tumour cells in very similar concentration. The expression of the mu class GST appeared to follow the differences in GST enzymic activity and although the numbers were small appeared to segregate according to tumour type. Gpx activity was also elevated in certain tumours. Of particular interest were the two adenocarcinomas which had a 20- to 30-fold higher tumour Gpx activity.