The Role and Therapeutic Targeting of GPR56 in Colorectal Cancer

ABSTRACT: Colorectal Cancer (CRC) remains the second leading cause of cancer-related deaths as current treatments for advanced disease have been limited by low response rates and adverse side-effects. Failure of treatment is attributed to tumor heterogeneity and the presence of cancer stem-like cells (CSCs). Plasticity of CSCs has been shown to drive therapy resistance and metastasis. Identifying novel targets involved in plasticity and disease progression is important for the development of more effective therapies. GPR56, a member of the adhesion G protein-coupled receptor family, is highly expressed in a large fraction of CRC and is associated with poor prognosis. We showed GPR56 increased resistance to chemotherapies and promoted tumor growth in mouse models of CRC. GPR56 is upregulated with loss of the CSC marker LGR5, suggesting a role in plasticity. Our group has generated unique GPR56 monoclonal antibodies (mAbs) that can be used to investigate GPR56 function and for the development of antibody-drug conjugates (ADCs). The objectives of this project are to identify the role and signaling mechanisms of GPR56 in disease progression and resistance and to develop and evaluate unique GPR56-targeted ADCs and combination therapies for the improved treatment of CRC. In Aim 1, patient-derived organoids will be used to characterize the role and signaling mechanism of GPR56 in colorectal CSCs and metastasis. In Aim 2, we will develop highly potent GPR56 ADCs and evaluate tolerability and efficacy. Phage display and immunoPET will be used to improve GPR56 mAb affinity and select leads for ADC development, respectively. Optimized GPR56 ADCs will be generated with different linker-payloads using site- specific conjugation and evaluated for antitumor efficacy in syngeneic and patient-derived xenograft models. In Aim 3, we will assess an ADC dual-targeted approach to overcome therapy resistance and metastasis. GPR56 ADCs will be tested alone and in combination with other CSC-targeted therapies for the prevention and treatment of metastasis using orthotopic models. The proposed study presents an opportunity to reveal novel functions for GPR56 in CRC and develop unique ADCs and dual-targeted strategies to potentially overcome resistance and metastasis.