Gliomas are extremely resistant to anticancer
therapies resulting in poor patient survival, due, in part, to altered expression of
antioxidant enzymes. The primary
antioxidant enzyme,
catalase, is elevated constitutively in
gliomas compared to normal astrocytes. We hypothesized that downregulating
catalase in
glioma cells would sensitize these cells to oxidative stress. To test this hypothesis, we implemented two approaches. The first, a pharmacological approach, used
3-amino-1,2,4-triazole, an irreversible inhibitor that reduced
catalase enzymatic activity by 75%. Pharmacological inhibition of
catalase was not associated with a reduction in rat 36B10
glioma cell viability until the cells were challenged with additional oxidative stress, i.e., ionizing radiation or
hydrogen peroxide (H(2)O(2)). In the second molecular approach, we generated 36B10
glioma cells stably expressing
catalase shRNA; a stable cell line displayed a 75% reduction in
catalase immunoreactive
protein and enzymatic activity. This was accompanied by an increase in intracellular
reactive oxygen species and extracellular H(2)O(2). These cells exhibited increased sensitivity to radiation and H(2)O(2), which was rescued by the
antioxidant,
N-acetylcysteine. These results support the hypothesis that
catalase is a major participant in the defense of 36B10
glioma cells against oxidative stress mediated by
anticancer agents capable of increasing steady-state levels of H(2)O(2).