281 Therapeutic Monoclonal Antibody-Mediated Inhibition of NOTCH Pathway Prolongs Survival in High Grade Glioma Models

INTRODUCTION: High grade gliomas (HGGs) have poor prognosis partially owing to a glioma-stem cell (GSC) population that escapes most therapeutic modalities. Inhibition of NOTCH signaling, necessary for GSC maintenance, has shown promise, however clinically limited by systemic (on-target, off-tumor) side effects. METHODS: Patient-derived, glioma cell lines were treated with 1H5 to determine therapeutic IC50 and characterize downstream, NOTCH-related effectors. A patient-derived explant system, which best replicates the tumor microenvironment in vitro, was generated and treated. An orthotopic xenograft model (PDX) of HGG was created and treated with convection enhanced delivery (CED) of 1H5 to assess tumor volume and survival. RESULTS: ADAM10 is found in a majority of IDH-wildtype HGGs, but not on IDH-mutant HGGs or low-grade gliomas. 1H5 has nanomolar IC50 against a large library of HGG patient-derived cell lines, achieving cell death via NOTCH-signaling inhibition . In explants, treatment with 1H5 significant delays explant progression (p = 0.01), expansion (4.1-fold decrease, p = 0.007), and reduces the fraction of ADAM10+ cells (from 63.3% to 2.6%, p = 0.004), of replicating cells (from 10.0% to 0.9%, p = 0.006), and of GSCs (SOX2+ cells; from 65.8% to 12.8%, p = 0.06) . In vivo, CED of 1H5 both slows down tumor growth compared to vehicle-treated controls (2.2-fold decrease in tumor volume, p = 0.03), and significantly prolongs survival (p = 0.01), without the development of significant side effects, through a reduction of replicating cells (p = 0.01) and SOX2+ GSCs (p < 0.0001), in a dose-dependent fashion, as determined via 1H5 fluorescent tagging (488-1H5). CONCLUSIONS: 1H5 is efficacious against HGG preclinical models both in vitro and in vivo by targeting NOTCH signaling. This posits 1H5 as a new promising therapeutic worthy of expeditious clinical translation.