Development of a new class of BLVRB-targeted redox therapeutics in breast cancer

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SUMMARY Enhanced metabolic and mitochondrial activity inherent in actively proliferating cancer cells generates an excessive amount of reactive oxygen species (ROS), associated with intracellular redox imbalance that impacts cellular viability.To survive chronic oxidative stress, cancer cells evolve to activate scavenging/anti-oxidant enzymes to restore redox balance. This differential activation of antioxidant pathways compared to normal cells provides a therapeutic window for novel cellular targets. Moreover, the effects of chemo- and radiotherapy (in part) are attributed to oxidative stress that causes irreversible oxidative damage and cell death, and activation of redox-regulating pathways is thought to promote resistance to such therapies. The obligatory dependence of cancer cells on antioxidant defense pathways as a fundamental pro-survival mechanism suggests the broad translational utility of their targeting in breast cancer. Modulation of redox-adaptation mechanisms represents a feasible strategy to eradicate cancer cells and/or restore chemosensitivity to conventional therapies. For the first time, we identified the heme (Fe2+-protoporphyrin IX) catabolic enzyme BLVRB (biliverdin IXβ reductase) as a new cellular target in breast cancer. We demonstrated the requisite and non-redundant pro- survival antioxidant function of BLVRB in breast cancer cells, coupled with therapy resistance and poor outcomes in breast cancer patients. The primary hypothesis of this application is that BLVRB functions in a redox- regulated pathway of antioxidant handling and cytoprotection in breast cancer cells. The secondary hypothesis is that BLVRB-selective inhibitor(s) may be developed as a novel and potentially non-toxic strategy for breast cancer treatment with minimal predicted off-target effects in normal cells. Using (1) BLVRB/inhibitor co-crystal structures, (2) computational RMSD matrices for SARs, and (3) extensive ADME/T and PK studies, we identified two lead compounds with excellent bioavailability and oral PK characteristics that selectively block BLVRB redox coupling. The objectives of this proposal are (1) to extend initial proof-of-principle studies for BLVRB pre-clinical target validation using in vivo breast cancer models, and (2) to characterize first-in-class BLVRB-selective inhibitors for in vitro and in vivo efficacy. Study Design: We will apply in vivo genetic models for target validation, simultaneously addressing redox-dependent mechanisms by gene complementation studies using BLVRB+/+ and BLVRB-/- breast cancer isogenic lines: (1) to confirm requisite functions in tumor growth and metastatic burden; (2) to establish redox-dependent phenotype (Aim 1). Aim 2 will validate the pre-clinical efficacy of lead compounds using well-established phenotypic read-outs in vitro and in orthotopic breast cancer implantation models. We will also address synthetic lethality BLVRB inhibitors with standard-of-care chemotherapy in vivo. Impact: If successful, the proposed work would be first-in-class pre-clinical validation of redox inhibitors in breast cancer, representing a potential paradigm shift for cancer therapeutics.