Smith Pameeka S, Zhao Weiling, Spitz Douglas R, Robbins Mike E
Section of Radiation Biology, Department of Radiation Oncology, and Brain Tumor Center of Excellence, Comprehensive Cancer Center, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
Free Radic Biol Med. 2007 Mar 15;42(6):787-97. doi: 10.1016/j.freeradbiomed.2006.11.032. Epub 2006 Dec 15.
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).
胶质瘤对抗癌治疗极具抗性，导致患者生存率低下，部分原因是抗氧化酶的表达发生了改变。与正常星形胶质细胞相比，胶质瘤中主要的抗氧化酶过氧化氢酶的组成性表达升高。我们假设下调胶质瘤细胞中的过氧化氢酶会使这些细胞对氧化应激敏感。为了验证这一假设，我们采用了两种方法。第一种是药理学方法，使用3-氨基-1,2,4-三唑，一种不可逆抑制剂，可使过氧化氢酶的酶活性降低75%。在细胞受到额外的氧化应激，即电离辐射或过氧化氢（H₂O₂）攻击之前，过氧化氢酶的药理学抑制与大鼠36B10胶质瘤细胞活力的降低无关。在第二种分子方法中，我们构建了稳定表达过氧化氢酶短发夹RNA的36B10胶质瘤细胞；一个稳定的细胞系显示过氧化氢酶免疫反应性蛋白和酶活性降低了75%。这伴随着细胞内活性氧和细胞外H₂O₂的增加。这些细胞对辐射和H₂O₂的敏感性增加，而抗氧化剂N-乙酰半胱氨酸可挽救这种情况。这些结果支持了这样的假设，即过氧化氢酶是36B10胶质瘤细胞抵御由能够增加H₂O₂稳态水平的抗癌药物介导的氧化应激的主要参与者。
