Project 3 SUMMARY/ABSTRACT High-grade serous ovarian cancer (HGSC) is the most common and aggressive type of epithelial ovarian cancer, and the mortality rates remain unacceptably high. It is well documented that aberrant angiogenesis occurs in the tumor microenvironment (TME) and angiogenesis inhibitors are important for cancer therapy. However, the clinical benefit of bevacizumab (vascular endothelial growth factor (VEGF) targeted antibody) has been limited due to rapid emergence of resistance in most patients with ovarian cancer. Moreover, therapies targeting the VEGF signaling pathway can also result in adverse events and interfere with wound healing since VEGF is known to be also important for physiological angiogenesis. Thus, new targets and approaches aimed at the TME for improving therapeutic outcomes are needed. We identified epidermal growth factor (EGF)-like domain multiple 6 (EGFL6) as the most differentially expressed gene in tumor endothelial cells compared to endothelial cells from normal ovarian tissues and healing wounds. Our preliminary data suggest that high EGFL6 expression in tumors is associated with an immune suppressive TME with high M2 macrophage infiltration. To develop a therapeutic approach for blocking EGFL6, we developed and tested a large number of candidate antibodies; the final candidates have been humanized. Our in vivo results indicated that these antibodies had robust anti-tumor effects and reduced angiogenesis in ovarian cancer models. Based on our compelling preliminary data, we hypothesize that EGFL6 promotes aberrant angiogenesis, and immune suppression, resulting in ovarian cancer growth and progression. Blocking EGFL6 with a monoclonal antibody provides a novel and effective approach for treatment of ovarian cancer. We will test our hypothesis under three Aims: 1) To delineate the molecular regulation of EGFL6 and identify sources of EGFL6 in the tumor microenvironment; 2) To investigate the biological effects of anti-EGFL6 monoclonal antibody as monotherapy or in combination with chemotherapy, anti- VEGF antibody, or immune checkpoint inhibitor; and 3) To determine the safety and tolerability of an anti-EGFL6 antibody in a first-in-human, first-in-class phase I clinical trial in patients with recurrent ovarian cancer. Collectively, the work proposed in this project will provide scientific rationale for developing new anti-EGFL6 based therapies. The proposed studies will provide fundamental mechanistic insights into the role of EGFL6 in regulating immune responses in the TME. Findings from this proposal could significantly impact the clinical outcomes of patients with ovarian cancer.

Project 3 NARRATIVE Angiogenesis is essential for tumor growth; several anti-angiogenesis drugs including bevacizumab have been approved for clinical use but have shown only modest efficacy. This necessitates development of new anti- angiogenesis therapies. Elevated EGFL6 was reported in ovarian cancer but not in normal adult tissues; our preliminary studies showed that EGFL6 blockade in ovarian cancer models resulted in significant reduction in tumor burden without affecting wound healing. The proposed work could have significant implications for development of new anti-EGFL6 based therapies in ovarian cancer.