GLUTATHIONE-ASSOCIATED ENZYMES IN THE HUMAN CELL-LINES OF THE NATIONAL-CANCER-INSTITUTE DRUG SCREENING-PROGRAM

The steady state expression of glutathione S-transferases (GSTs) at bo th the protein and mRNA level is reported for the 60 tumor cell lines that are used for the National Cancer Institute Drug Screening Program . Individual GST isozymes were separated, identified, and quantified ( with reverse-phase calibration curves) through a novel high performanc e liquid chromatographic procedure. GSTP1 was the predominant isozyme and was found at quantifiable levels in all but two of the cell lines. This isozyme ranged from 0.03% to 2.7% of the total cytosolic protein . For the mu family, 90% of the lines had GSTM2, 68% had GSTM3, but on ly 28% were positive for the M1 phenotype. The M1 proportion is lower than would be expected from the standard M1 null phenotype for human p opulations. Isozymes of the a:family were detected only at very low le vels in 35% of the lines. Significant quantitative correlations among enzyme activity, total enzyme protein, and mRNA were shown for GSTP1. However, such relationships were not apparent for the mu or alpha fami lies. Levels of glutathione (GSH), and the transcript levels of other enzymes involved in GSH homeostasis were determined. gamma-Glutamyl cy steine synthetase (gamma-GCS) was present in ail cell lines, but did n ot correlate with levels of intracellular GSH. Glyoxalase-1 and gamma- glutamyl transpeptidase, both involved in GSH salvage, were found in 1 00% and 70% of the cell lines, respectively. Using a pattern-matching computer program, COMPARE, we compared and correlated the arrays of mR NA and protein levels with the pattern of chemosensitivity or chemores istance of the 60 cell lines with 175 agents constituting a standard a gent database. This database is composed of compounds to which a putat ive mechanism of action has been assigned. Although Pearson correlatio n coefficients relating the target and drug patterns were generally mo dest, when the patterns for the enzyme protein and mRNA levels for GST pi were correlated to drug sensitivity patterns, the list of 30 agent s most closely matching (for which p < 0.05) was enriched with alkylat ing agents, gamma-GCS also showed an enrichment of alkylating agents i n the COMPARE correlations, indicating that high levels of gamma-GCS m ay be an important determinant of resistance. In contrast, none of the other enzymes or GSH had patterns of expression that resulted in an o bvious correlation to the sensitivity or resistance of alkylating agen ts.