The aim of this work was to determine the functional activities of four different antioxidative
enzymes (
glutathione reductase,
glutathione-S-transferase,
glutathione peroxidase,
thioredoxin reductase) and the
protein expression of three
ATP-binding cassette transporters (
P-glycoprotein,
multidrug resistance protein 1,
multidrug resistance protein 2) in a panel of 14 human
cancer cell lines.
Enzyme activities and transporter expression were then correlated with the in-vitro cytotoxic activities (GI50 values) of 19 standard
antitumor drugs. Analogous data from the National Cancer Institute were used for comparison. The GI50 values of the
platinum complexes,
alkylating agents,
antimetabolites,
topoisomerase inhibitors and
antimitotic drugs were determined by
crystal violet or 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium
bromide assay. Standard enzymatic assays employed to measure the
glutathione peroxidase,
glutathione-S-transferase,
glutathione reductase and
thioredoxin reductase activities. The
protein expression of the
ATP-binding cassette transporter proteins was investigated by the Western-blot method. The delta method was used to normalize the data before bivariant correlation analysis. Only a few correlations between
enzyme and cytotoxic activities of the
antitumor agents were found. The GI50 values for
melphalan and
camptothecin correlated positively with the activity of
glutathione-S-transferase, whereas GI50 values for
methotrexate correlated positively with the cellular activities of both
glutathione reductase and
thioredoxin reductase. A significant correlation between
glutathione reductase and
thioredoxin reductase activities was found in our panel of cell lines. Neither
P-glycoprotein nor
multidrug resistance protein 2 expression could be detected by Western blot analysis in any cell lines investigated, but
multidrug resistance protein 1 was consistently observed in all but four lines.
Multidrug resistance protein 1 expression correlates positively with the GI50 values of several drugs, e.g.
vinblastine and
etoposide, and negatively with the GI50 values of
5-fluorouracil. The results confirm the complexity of resistance to
antitumor agents and show that the GSH-
thioredoxin system alone is not a good indication of intrinsic resistance for many of these anticancer drugs.