Targeting Sulfiredoxin in Colorectal Cancer

The poor outcome of patients with advanced CRC due to metastasis urges further understanding of CRC pathogenesis and development of reagents targeting specifically to block molecular drivers of metastasis. Sulfiredoxin (Srx) is an oxidoreductase that restores the peroxidase activity of peroxiredoxins (Prxs) to maintain cellular redox balance. Our published data demonstrate that Srx has a novel oncogenic function in human cancer development, and knockout of Srx in mice renders resistant to chemical carcinogens induced skin as well as colon tumorigenesis. Our preliminary data indicate that Srx is preferentially expressed in patient specimens of advanced CRC as well as poorly-differentiated CRC cell lines. Knockdown of Srx in CRC cells not only leads to the inhibition of colony formation and cell invasion in culture, but also abolishes their ability to form metastases in distant organs in immunodeficient mice. Notably, exactly opposite effects are observed when Srx is ectopically expressed in well-differentiated CRC cells. Therefore, we hypothesize that targeted inhibition of Srx is an effective strategy to control CRC development. Our objective is to test this central hypothesis through the completion of the following specific aims: Aim 1. To determine the mechanism by which Srx promotes CRC cell invasion and metastasis. We demonstrate that expression of Srx enhances, whereas knockdown of Srx inhibits mitogen activated protein kinase (MAPK) signaling. We will investigate (a) the mechanism by which Srx enhances oncogenic MAPK signaling through the activation of epithelial growth factor receptor (EGFR); (b) the mechanism by which Srx promotes the epithelial-mesenchymal transition (EMT) of CRC cells; (c) the significance of the Srx-Prx4 interaction in mediating the EGFR-MAPK signaling and EMT. Aim 2. To determine the efficacy of a novel small molecule inhibitor of Srx (or its derivatives) in the treatment of CRC in mouse xenograft models. ISO-1 (Inhibitor of Sulfiredoxin Oxidoreductase-1) is a novel small molecule that we recently identified from a structure-based virtual screening using strategies of computer aided drug designing. We have demonstrated that ISO-1 binds to Srx and inhibits its oxidoreductase activity in CRC cells. We will determine (a) the anti-tumor effect of ISO-1 in cell culture, including its effect to inhibit Srx-mediated MAPK activation, cell growth & proliferation, colony formation, cell invasion and EMT; (b) chemical modifications of ISO-1 to generate derivatives that have higher binding affinity and potency to inhibit Srx; (c) the efficacy of ISO-1 or its derivatives to inhibit CRC xenograft growth in a mouse subcutaneous injection model and to reduce tumor metastasis in an orthotopic implantation model. In summary, Srx is a unique oxidoreductase that has oncogenic function and preferentially expressed in cancer, and targeting Srx has advantages of disrupting redox homeostasis and simultaneously reducing oncogenic signaling only in cancer cells. Our long-term goal is to understand mechanisms of CRC metastasis to develop target-directed, mechanism-based, efficient therapeutics for patients.