Characterization of HIO-2, a tumor-produced protein that inhibits therapeutic antibody-mediated cellular cytotoxicity via Fc Receptor (CD16a) blockade

About This Grant

The field involving antibody-dependent cellular cytotoxicity (ADCC) and complement-mediate cytotoxicity (CDC) activities mediated by therapeutic antibodies is referred to as humoral immuno-oncology (HIO). Tumor-produced factors that may have immunosuppressive effects on ADCC and CDC activities are called HIO factors. We screened several HIO factor candidates (HIO-Xs) based on their production/secretion by various tumor types. HIO-Xs can be serum biomarkers representing proteins shed by the tumor. Using a set of optimized HIO assays which we developed, two new HIO factors were found to be immunosuppressive and were named HIO-2 and HIO-3. The focus of this proposal is on the characterization of HIO-2. HIO-2 is a mucin protein produced and over-expressed in breast, lung, ovarian, endometrial, bladder, and gastrointestinal cancers. HIO-2 is present in a membrane-bound form as well as a soluble/shed form. Preliminary data suggest that soluble HIO-2 binds to CD16a/Fc gamma receptor, blocking antibody binding, and ultimately inhibiting ADCC activity of trastuzumab and pertuzumab due to reduced antibody/Fc receptor engagement. HIO-2 blockade of CD16a function creates an immunosuppressed tumor microenvironment potentially impacting therapeutic antibodies activity. In fact, elevated serum levels of HIO-2 correlate with worse progression-free survival after treatment with trastuzumab. The goal of our program is to generate and test compounds that can overcome immunosuppression mediated by HIO-2. This proposal focuses on the initial tasks of an overarching approach aimed at bringing HIO-2 antagonists into clinical testing after appropriate discovery and preclinical validation. In Year 1, we will be answering the question: Can a pharmaceutically viable HIO-2 antagonist candidate be developed? In Aim 1, effort will be allocated to defining the HIO-2/CD16a binding interface which will guide future structure-activity relationship analyses of HIO-2 antagonists. In Aim 2, an expanded natural compound library will be screened to identify additional HIO-2 antagonist candidates having improved activity profile. Lead candidates and their analogs will be tested in vitro for potential toxicity and metabolic stability. In Year 2, we will be answering the question: Can HIO-2 antagonist enhance the anti-tumor effect mediated by therapeutic antibodies in vivo? In Aim 3, the current lead HIO-2 antagonist, or any better lead(s) identified in Aim 2, will be assessed for oral availability in mice and compared to intravenous administration. The maximum tolerated dose of the lead antagonist will be assessed for the selected route (PO or i.v.). Finally, the lead HIO-2 antagonist will be tested alone and in combination with trastuzumab using a patient-derived xenograft (PDX) model of breast cancer, wherein this PDX has high levels of HER2 expression, high levels of HIO-2, and is somewhat resistant to trastuzumab anti-tumor effect. The benefit of a HIO-2 antagonist strategy extends to current and future therapeutic antibodies with immune effector function, including rituximab, daratumumab, cetuximab, and others.