Antioxidant Enzymes Mediate Survival of Breast Cancer Cells Deprived of Extracellular Matrix

Metastasis by cancer cells relies upon the acquisition of the ability to evade anoikis, a cell death process elicited by detachment from extracellular matrix (ECM). The molecular mechanisms that ECM-detached cancer cells use to survive are not understood. Striking increases in reactive oxygen species (ROS) occur in ECM-detached mammary epithelial cells, threatening cell viability by inhibiting ATP production, suggesting that ROS must be neutralized if cells are to survive ECM-detachment. Here, we report the discovery of a prominent role for antioxidant enzymes, including catalase and superoxide dismutase, in facilitating the survival of breast cancer cells after ECM-detachment. Enhanced expression of antioxidant enzymes in nonmalignant mammary epithelial cells detached from ECM resulted in ATP elevation and survival in the luminal space of mammary acini. Conversely, silencing antioxidant enzyme expression in multiple breast cancer cell lines caused ATP reduction and compromised anchorage-independent growth. Notably, antioxidant enzyme-deficient cancer cells were compromised in their ability to form tumors in mice. In aggregate, our results reveal a vital role for antioxidant enzyme activity in maintaining metabolic activity and anchorage-independent growth in breast cancer cells. Furthermore, these findings imply that eliminating antioxidant enzyme activity may be an effective strategy to enhance susceptibility to cell death in cancer cells that may otherwise survive ECM-detachment.