A Novel Redox Based Therapy Targets the Malignant Cellular Redox State

Redox active antioxidants offer a novel method of targeted cancer treatment. The altered redox state between cancer and normal cells provides a means for antioxidant compounds that can redox cycle to target the highthen redox state within malignant tissues via pro-oxidant effects, inducing cell death mechanisms. Conversely, the same treatment activates servival pathways in normal cells. We demonstrate the therapeutic effect of a MnSOD mimetic, Mn(III) mesotetrakis (N-n-butoxyethylpyridinium-2yl) porphyrin, MnBuOE (MnP) in myelodysplastic syndrome (MDS). Quantitation of intracellular glutathione species demonstrates a difference in normal and malignant cellular redox states (Δ-13mV). MnP treatment results in cellular glutathione depletion leading to a change in the 2GSH/GSSG ratio and the cellular reduction potential. MnP treatment (20 μM) induces significant cytotoxicity in MDSL cells (p=2.0 E-6). Similar treatment of healthy cells isolated from human bone marrow increases cell viability in the CD34+CD38- (p=0.016) and CD34+CD38+ (p= 0.001) stem/progenitor cell populations. Transcriptional activity array analysis indicates that MnP activates the transcription factor nuclear factor (erythroid-derived 2)-like 2 (NRF2) in normal Hematopoietic stem/progenitor cells but activates the activator protein 1 (AP-1) in MDSL cells. Biochemical analysis confirms AP-1 pathway activation in MnP treated MDSL cells and identifies JunB as a transcriptional mediator of MnP induced cytotoxicity. Co-immunoprecipitation analysis of JunB with its binding partners reveals a redox-based mechanism of JunB transcriptional activation via Ref-1; a protein specifically involved in the redox-modification of the JunB DNA binding region. The finding that MnP can target malignant cell redox states and exert selective cytotoxicity via differential activation of molecular pathways controlling cell fate will significantly aid development of safe, effective redox-active therapeutics for clinical applications.