Humanized anti-DEspR monoclonal antibody to improve overall survival in xenograft pancreatic peritoneal carcinomatosis nude rat model.

e16262 Background: Pancreatic adenocarcinoma (PDAC) with peritoneal carcinomatosis (PPC) has the worst median overall survival (mOS) among all PDAC metastasis. Novel therapeutic approaches are needed for PPC. The Dual Endothelin-1/VEGF-signal-peptide Receptor (DEspR) is a cell surface receptor which regulates PDAC tumor cell and cancer stem-like cell (CSC) anoikis resistance, tumorigenicity, and tumoral angiogenesis. To translate these findings into a novel anti-cancer therapy, we evaluated the efficacy, empirical safety, pharmacokinetics, and pharmacodynamics of a recombinant, humanized, anti-DEspR hinge-stabilized IgG4S228P monoclonal antibody, hu-6g8, in a PPC xenograft tumor nude rat model. Methods: We used a Panc1 CSC-derived xenograft tumor model of PPC developed via intraperitoneal injection of two million Panc1 CSCs functionally isolated for anoikis resistance. Isolated CSCs had variable DEspR expression, thus modeling CSC-heterogeneity. For efficacy studies, PPC-rats were randomized to receive a single intravenous injection of either 3mg/kg or 15mg/kg hu-6g8, 100mg/kg gemcitabine, or saline, given 3 weeks after CSC injection with palpable PPC tumors. Blood samples were collected to monitor for hematological adverse events (AEs) and vital organs were collected to evaluate for hu-6g8-induced apoptosis. Pharmacokinetics was assessed in a separate study cohort by sequential blood draws after rats received a single dose of 3 mg/kg or 15 mg/kg hu-6g8. In a 3rd cohort, pharmacodynamics were assessed by vital organ collection and immunohistochemistry after rats received either a single-iv injection of 3mg/kg hu-6g8 or IgG4 isotype control. Results: Single dose 15 mg/kg hu-6g8 treatment significantly improved median overall survival (189 days, n = 0.0007) with 3 mg/kg hu-6g8 being comparable to 100 mg/kg gemcitabine (92 vs 115 days, n = 0.62). No hematological AEs were observed in hu-6g8 treated rats, and there was no evidence of increased apoptosis by hu-6g8 in normal tissues by immunohistochemistry of activated Caspase-3. Hu-6g8 demonstrated an average elimination half-life of 46.1 hrs in a two-compartment model. Biodistribution of the antibody showed predominant uptake, albeit heterogenous, and induction of activated caspase 3+ apoptosis in the peritoneal tumors by 24-hours with minimal off-target binding. Conclusions: Treatment with monoclonal hu-6g8 significantly improved survival in a model of PCC with excellent tumor specificity and minimal off-target effect.