Small molecule inhibitors of Slit2/Robo signaling as novel therapeutics for glioblastoma

PROJECT SUMMARY/ABSTRACT: Glioblastoma (GBM), the most prevalent malignant primary brain tumor, is an extremely aggressive form of diffuse glioma originating from astrocytic lineage. Despite recent advancements in multimodal GBM therapy, which incorporates surgery, radiotherapy, chemotherapy, and supportive care, the overall prognosis remains dismal, and long-term survival is rare. Immunotherapy holds promise in leveraging the immune system to target and eliminate brain tumor cells. However, the highly immunosuppressive environment within GBM represents a critical impediment to successful immunotherapy. SLIT2/ROBO signaling is a novel immune evasion mechanism in the tumor microenvironment of GBM. High SLIT2 expression in GBM patients results in the accumulation of immunosuppressive tumor-associated macrophages (TAMs) as well as vascular dysmorphia. This is further supported by the prevention of TAM tumor-supportive polarization and angiogenic gene expression upon systemic SLIT2 inhibition, resulting in improved tumor vessel function and enhanced efficacy of chemotherapy and immunotherapy in GBM mouse models. Therapeutic targeting of SLIT2/ROBO interaction is currently restricted to biologics, and there are no active clinical trials for GBM evaluating SLIT2/ROBO inhibition as a therapeutic strategy. In comparison to biologics, small molecules will minimize the immunogenicity risk, enable better management of adverse events (AEs) based on their amenability for pharmacokinetic optimization, and hold promise for central nervous system (CNS) penetration. In response to PAR-23-264, our three-year proposal aims to establish a novel macrophage-based immunotherapy approach for GBM based on targeting SLIT2/ROBO interaction with small molecules, which may synergize with current FDA-approved therapies for GBM. Our expertise in assay development, high-throughput screening (HTS), discovery of small molecule immunomodulators, hit-to-lead optimization, and immunopharmacology uniquely positions us to achieve this goal. Aim 1 will complete the screening of a CNS-focused chemical library of small molecules for SLIT2 binding, followed by an evaluation of the ability of the hits to inhibit SLIT2/ROBO interaction using fluorescence-based assays. Aim 2A will validate the top hit compounds as SLIT2/ROBO inhibitors using a panel of cell-free and cell-based assays, including an in vitro spheroid invasion assay using patient-derived cells from GBM tissue. Aim 2B will perform exploratory medicinal chemistry and preliminary structural optimization of the top validated hits in order to guide future extensive optimization. The proximal expected outcome of this work is introducing first-in-class small molecule SLIT2/ROBO inhibitors as candidates for preclinical evaluation, particularly within innovative combination therapies for GBM.