CONTRIBUTION OF GLUTATHIONE TRANSFERASE M3-3 TO 1,3-BIS(2-CHLOROETHYL)-1-NITROSOUREA RESISTANCE IN A HUMAN NONSMALL CELL LUNG-CANCER CELL-LINE

The glutathione transferase (GST) isoenzyme profile was determined in two human tumor cell lines, U1690 derived from a small cell lung cance r and U1810 derived from a non-small cell lung cancer. U1810 cells are 3.2-fold more resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU ) than are U1690 cells, a finding ascribable in part to the expression of O6-alkylguanine-DNA alkyltransferase activity in the U1810 cells. GST P1-1 and GST A1-1 were determined quantitatively by enzyme-linked immunoassay and were found to be 1.3- and 15-fold higher in the cytoso l fraction of U1690 cells as compared to U1810 cells, respectively. Th e higher BCNU resistance in U1810 cells can, therefore, not be correla ted with the expression of these isoenzymes. However, sodium dodecyl s ulfate/polyacrylamide gel electrophoresis in combination with immunobl ot analysis demonstrated a class Mu GST, which was identified as GST M 3-3 on the basis of electrophoretic mobility and cross-reaction with a nti-rat GST 3-3 antibodies. This isoenzyme was detectable in U1810 cel ls but not in U1690 cells. Studies with purified human GST A1-1, GST M 1-1, GST M3-3, and GST P1-1 demonstrated that GST M3-3, but not the ot her isoenzymes, catalyzed the denitrosation of BCNU. Such inactivation of BCNU has previously been demonstrated with rat class Mu GSTs (M. T . Smith et al., Cancer Res., 49: 2621-2625, 1989) but not with any hum an GST. These findings suggest that GST M3-3 contributes to BCNU resis tance in the U1810 cells.