Abstract 6718: Evaluating toxicity and efficacy of bispecific EGFRXCD3 T cell engager in solid tumor-bearing humanized animal model

Abstract Background: Cancer immunotherapy has currently become a highly active research area of oncology and a common treatment strategy for several cancer types. One prominent reason is that the utilized animal models could not accurately predict the of toxic response of human immune system to anti-cancer drug. For improving the safety of immune drug development, it is urgent to establish a predictive nonclinical animal platform that can accurately predict human immune response to the drugs and detect potential unwanted toxicity to human patient will be critical. We have demonstrated a disseminated tumor-bearing humanized mouse model that can evaluate the toxicity and efficacy of bispecific T cell engager (BiTE). In this study, we co-engrafted disseminated and solid tumor cells to the same mice and compared with mice engrafted with disseminated tumor or solid tumor. The purpose is to develop a novel tumor-bearing mouse model that can simultaneously evaluate the long-term efficacy against solid tumors in addition to cytokine level assessment. Method: Epidermal growth factor receptor (EGFR) expressing human triple negative breast cancer MDA-MB-231/Luciferase-2A-GFP (MDA) cell line was utilized to establish solid tumors in mice. The cells were implanted into PBMC humanized NSG-MHC class I/II double knock out (DKO) mice via orthotopic injection into mammary fat pad (MFP). Disseminated MDA cells were injected intravenously (IV) and tumor cells normally colonize in mouse lungs. Following EGFRxCD3 BiTE dosing initiation, tumor burden in MFP and lungs were evaluated via in vivo Xenogen imaging system, and solid tumor volume in MFP was measured 2 to 3 times a week by a digital caliper. To evaluate the toxicity in response to EGFRxCD3 BiTE treatment, human inflammatory cytokine levels was analyzed by BD cytometric bead. Clinical observations and body weight change, and human immune cell activation were evaluated. Result: EGFRxCD3 BiTE treatments significantly inhibited MFP solid tumor growth regardless the presence of IV implanted with MDA cells. EGFRxCD3 BiTE treatment induced elevated human inflammatory cytokines from humanized mice implanted with combined MFP and IV tumors. By comparison, the serum cytokine levels were low in mice implanted with MDA cells via MFP alone, suggesting that disseminated tumor cells are required for cytokine production induced by EGFRxCD3 BiTE. Conclusion: Without disseminated tumor, MFP solid tumor-bearing mice can be served as a model for drug efficacy but did not induce inflammatory cytokines by EGFRxCD3 BiTE treatment. Combination of solid and disseminated tumor models in the same mice provide a new approach for simultaneously evaluating the toxic cytokine release and efficacy of immunotherapy drugs. Citation Format: Guoxiang Yang, Li-Chin Yao, James G. Keck, Mingshan Cheng. Evaluating toxicity and efficacy of bispecific EGFRXCD3 T cell engager in solid tumor-bearing humanized animal model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6718.