MnTE-2-PyP modulates thiol oxidation in a hydrogen peroxide-mediated manner in a human prostate cancer cell

To improve the treatment of advanced prostate cancer, the development of effective and innovative antitumor agents is needed. Our previous work demonstrated that the ROS (reactive oxygen species) scavenger, MnTE-2-PyP, inhibited human prostate cancer growth and also inhibited prostate cancer migration and invasion. We showed that MnTE-2-PyP treatment altered the affinity of the histone acetyltransferase enzyme, p300, to bind to DNA. We speculate that this may be one mechanism by which MnTE-2-PyP inhibits prostate cancer progression. Specifically, MnTE-2-PyP decreased p300/HIF-1/CREB complex (p300/hypoxia-inducible factor-1/cAMP response element-binding protein) binding to a specific hypoxia-response element (HRE) motif within the plasminogen activator inhibitor-1 (PAI-1) gene promoter region, and consequently, repressed PAI-1 expression. However, it remains unclear how MnTE-2-PyP reduces p300 complex binding affinity to the promoter region of specific genes. In this study, we found that overexpression of Cu/ZnSOD (superoxide dismutase 1, SOD1) significantly suppressed PAI-1 gene expression and p300 complex binding to the promoter region of PAI-1 gene, just as was observed in cells treated with MnTE-2-PyP. Furthermore, catalase (CAT) overexpression rescued the inhibition of PAI-1 expression and p300 binding by MnTE-2-PyP. Taken together, the above findings suggest that hydrogen peroxide (H₂O₂) is likely the mediator through which MnTE-2-PyP inhibits the PAI-1 expression and p300 complex binding in PC3 cells. To confirm this, we measured the production of H₂O₂ following overexpression of SOD1 or catalase with MnTE-2-PyP treatment in the presence or absence of radiation. We found that MnTE-2-PyP increased the intracellular steady-state levels of H₂O₂ and increased nuclear H₂O₂ levels. As expected, catalase overexpression significantly decreased the levels of intracellular H₂O₂ induced by MnTE-2-PyP. We then determined if this increased H₂O₂ production could result in oxidized protein thiol groups. In the presence of MnTE-2-PyP, there was a significant increase in oxidized thiols in PC3 cell lysates and this was reversed with catalase overexpression. Specifically, we showed that p300 was oxidized after MnTE-2-PyP treatment, indicating that MnTE-2-PyP is creating a more oxidizing environment and this is altering the oxidation state of p300 thiol residues. Our data provide an in depth mechanism by which MnTE-2-PyP regulates gene transcription through induced H₂O₂ mediated oxidation of particular proteins, supporting an important role for MnTE-2-PyP as an effective and innovative antitumor agent to enhance treatment outcomes in prostate cancer radiotherapy.