756P Glypican-3 (GPC3) and NKp46 directed FLEX-NK engager antibody (CYT-303) recruits natural killer (NK) cells to tumors in a preclinical hepatocellular carcinoma (HCC) mouse model

Abstract

GPC3 is an oncofetal antigen that is highly expressed in HCC while minimally expressed in adult normal tissues except placenta. CYT-303 is a multifunctional bispecific NK engager targeting NK cell activating receptor NKp46 and GPC3 expressed on tumor cells constructed with Cytovia’s Flex-NK scaffold with a fully functional Fc. Previously, we reported CYT-303 in vitro treatment of Hep3B tumor cells demonstrated cytolysis and cytokine production as well as in vivo tumor growth inhibition when combined with both PBNK and iNK cells. Here we further characterized the CYT-303 dose-response for tumor growth inhibition in vivo and its influence on NK cell distribution. CYT -303 pharmacokinetics was evaluated in tumor-bearing mice. Anti-tumor efficacy and dose response of CYT-303 in the presence of human PBNKs or iNKs was evaluated in NSG-IL15 mice bearing subcutaneous Hep3B tumors. Biodistribution of the NK cells were analyzed by flow cytometry. CYT-303 pharmacokinetics in tumor bearing mice was similar to normal mice suggesting no target mediated clearance. In the Hep3B tumor model in PBNK or iNK injected NSG-hIL-15 mice, CYT-303 showed dose dependent tumor growth inhibition compared to control hIgG1 treated mice. Consistent with CYT-303 tumor growth inhibition, increased NK cells were detected in the tumor compared to control animals. Blood NK cells in CYT-303 treated animals were significantly lower compared to IgG1 isotype control treated mice suggesting CYT-303 could facilitate NK cell trafficking from blood into the tumor. Blood AFP (alpha fetoprotein), a biomarker in HCC, decreased with CYT-303 tumor growth inhibition. Pharmacologically active CYT-303 doses were identified. CYT-303 can help recruit NK cells to the tumor site to achieve tumor growth inhibition.