Grant: CIHR - ICR / Cancer Research Society Partnership - Research Grants

Background: Nectin-4 is a cell adhesion molecule that is expressed during embryonic development and is absent in normal adult tissues. However, high expression of Nectin-4 is seen in several cancers including ~62% of triple-negative breast cancers (TNBC). Nectin-4 expression is tumorigenic and it plays in important role in cell proliferation, angiogenesis, migration, and metastasis through PI3K/Akt signaling pathway. Therefore Nectin-4 is an excellent target for anticancer therapy. In this proposal, our goal is to develop molecular imaging probes targeting Nectin-4, for non-invasive imaging of TNBC. Monoclonal antibodies that bind to cancer cell-surface markers are traditionally used for both therapy and non-invasive imaging of tumors, in a “theranostics” approach. However, long half-life of monoclonal antibodies in patient serum, is not ideal for molecular imaging applications. Recent advances have led to the development of alternative binding proteins that are ~20 times smaller than antibodies. The small size (~20 times smaller than antibodies) enables better tumor penetration and rapid clearance from the bloodstream. High contrast PET/CT images can be generated in a much shorter time frame when compared to full-length antibodies. Hypothesis and Objectives: We hypothesize that small protein-based imaging probes will be more effective in tumor penetration due to small size and monomeric binding capacity compared to bivalent monoclonal antibodies. Our goal for this proposal is to develop and evaluate small protein-based imaging probes targeting Nectin-4 and compare their efficacy with antibody-based imaging probes for molecular imaging of TNBC. Research Methodology: We have recently developed human origin antibodies (N4mAb) and alternative scaffold based binders (N4bp) to proximal IgV domain of Nectin-4. In this proposal, our plan is to further develop and compare antibody and small protein-based imaging probes; Our specific aims are: 1. Optimize site-specific labeling of lead small protein binder, N4bp, to minimize loss of affinity 2. Develop and optimize genetically fused dimers of N4bp for studying the effect of bivalent binding 3. Develop 89Zr derivatives of N4bp, N4bp-dimer and N4mAb and evaluate their potential as non-invasive PET/CT imaging agents in TNBC cell xenograft models. Expected Outcomes: The imaging probes developed from this study will be useful for diagnosis, stratification personalized treatment and monitoring progression of TNBC. This study will enable the pre-clinical development of optimal probes that can be translated for non-invasive imaging of primary and metastatic tumors in TNBC patients.