Abstract PO001: Preclinical activity of glypican-3 (GPC3) and NKp46 directed FLEX-NK™ engager antibody (CYT-303) in combination with iPSC derived natural killer cells (iNKs) or peripheral blood (PB) NK cells in hepatocellular carcinoma (HCC)

Abstract

Abstract BACKGROUND: GPC3 is highly expressed in HCC while it is hardly expressed in adult normal tissues except placenta. Given the presence of dysfunctional NK cells in the HCC tumor microenvironment that contribute to poor anti-tumor immune responses, we sought to develop an iNK cell therapy in combination with GPC3 targeted NK cell engagers (NKE). FLEX-NK™ is a proprietary tetravalent IgG1-like multifunctional antibody NKE platform with a novel FLEX-linker to allow for simultaneous binding to different antigens on different cells. CYT-303 was constructed to engage NK cells via the activation receptor NKp46 and to target cancer cells via GPC3. We hypothesized that CYT-303 may be active in the tumor microenvironment where there are sufficient number and function of endogenous NK cells, but that this activity may be augmented by fresh functional NK cells. iNK cells derived from iPSC, a uniform starting material with unlimited self-renewal capabilities, can be expanded to produce a universal off-the-shelf allogeneic therapy. We investigated the combination of CYT-303 to enhance tumor specificity and potency of iNKs. METHODS: CYT-303 was expressed in CHOZEN cells and purified by step column chromatography. iNK’s were differentiated from iPSC’s and expanded using irradiated feeder cells. PB-NK cells were purified from healthy donor blood. iNK and PB-NK cytotoxicity against Hep3B tumors was evaluated in the presence of CYT-303 or isotype control antibodies at a fixed E/T ratio. CYT-303 pharmacokinetics in mice was evaluated following a single intravenous injection. Anti-tumor efficacy of the iNK combination with CYT-303 was evaluated in NSG-IL15 mice bearing subcutaneous Hep3B tumors following intra-tumoral injection of iNKs and intravenous dosing with CYT-303. Blood alpha-fetoprotein (AFP) levels were assessed by immunoassay. Cytokine release assessments for CYT-303 was evaluated in an in-vitro PBMC activation assay. RESULTS: iNK cells express high levels of multiple activation receptors including NKp46, but low levels of CD16. Despite low expression of CD16, natural cytotoxicity of iNK’s against Hep3B tumors was higher than with fresh PB-NK and CYT-303 redirected killing of Hep3B tumors was comparable to PB-NK’s. The CYT-303 pharmacokinetics study in mice showed a terminal half-life of 17 hrs. In a Hep3B tumor model in NSG-hIL-15 mice, the combination of CYT-303 and iNK’s showed significantly greater tumor growth inhibition compared to iNK’s alone plus an IgG1 isotype control. Blood AFP levels decreased in the CYT-303 plus iNK combination compared to iNK’s alone. Cytokine release assessment of CYT-303 in the human PBMC assay showed no evidence of cytokine release while high levels of cytokine release was observed with anti-CD28 (TGN1412) and CD3 antibody controls. CONCLUSIONS: The combination of NK cell engager CYT-303 and iNK cells is active in preclinical models of HCC with low levels of cytokine release. These data support further development of CYT-303 and iNKs to engage and empower NK cells as an off the shelf therapeutic approach in HCC. Citation Format: Antonio Arulanandam, Liang Lin, Hao-Ming Chang, Harish Potu, Vishal Khairnar, David Zou, Melissa Triggiano, Nejmi Dilmac, Yinan Yang, Shira Kahlon, Stanley Frankel, Jean Kadouche, Daniel Teper, Ofer Mandelboim, Yoav Hershkovitz, Yaron Ilan, Wei Li. Preclinical activity of glypican-3 (GPC3) and NKp46 directed FLEX-NK™ engager antibody (CYT-303) in combination with iPSC derived natural killer cells (iNKs) or peripheral blood (PB) NK cells in hepatocellular carcinoma (HCC) [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PO001.