Increased Manganese Superoxide Dismutase Expression or Treatment with Manganese Porphyrin Potentiates Dexamethasone-Induced Apoptosis in Lymphoma Cells

Glucocorticoid-induced apoptosis is exploited for the treatment of hematologic malignancies. Innate and acquired resistance limits treatment efficacy; however, resistance mechanisms are not well understood. Previously, using WEHI7.2 murine thymic lymphoma cells, we found that increasing the resistance to hydrogen peroxide (11202) by catalase transfection or selection for H2O2 resistance caused glucocorticoid resistance. This suggests the possibility that increasing H2O2 sensitivity could sensitize the cells to glucocorticoids. In other cell types, increasing manganese superoxide dismutase (MnSOD) can increase intracellular H2O2. The current study showed that increased expression of MnSOD sensitized WERI7.2 cells to glucocorticoid-induced apoptosis and H2O2. Treatment of WEHI7.2 cells with the catalytic antioxidant Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP5+), a manganoporphyrin, mimicked the effects of increased MnSOD expression. MnTE-2-PyP5+ also sensitized WEHI7.2 cells to cyclophosphamide and inhibited cell growth; it had no effect on the WEHI7.2 cell response to doxorubicin or vincristine. In primary follicular lymphoma cells, MnTE-2-PyP5+ increased cell death due to dexamethasone. Treatment of H9c2 cardiomyocytes with MnTE-2-PyP5+ inhibited doxorubicin cytotoxicity. The profile of MnTE-2-PyP5+ effects suggests MnTE-2-PyP5+ has potential for use in hematologic malignancies that are treated with glucocorticoids, cyclophosphamide, and doxorubicin. [Cancer Res 2009;69(13):5450-7]