Abstract B089: Development, characterization, and humanization of NCI-N87 human gastric carcinoma xenograft model in NSG mice

Abstract Nearly one million people worldwide are diagnosed with gastric cancer, with approximately 660,000 people succumbing to the disease every year. Sixty-four percent of gastric cancer cases occur in Asia, and approximately 3% in the United States. Primary therapies for the treatment of gastric cancer include surgery, chemotherapy, immunotherapy, and targeted therapies such as blocking antibodies and antibody-drug conjugates (ADCs). Human Epidermal growth factor Receptor 2 (HER2) is a protein overexpressed in a variety of cancer types of epithelial origin, including gastric cancer. The anti-HER2 monoclonal antibody trastuzumab is the standard of care for certain types of HER2+ cancers. Trastuzumab has a multi-faceted mechanism of action, including Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC), which is primarily mediated by Natural Killer (NK) cells in the clinic. However, in the absence of NK cells, neutrophil- and macrophage-dependent ADCC and Antibody Dependent Cellular Phagocytosis (ADCP) may contribute to the mechanism of action of monoclonal antibodies in immunocompromised mice (such as NSG mice). The gastric carcinoma tumor cell line NCI-N87 overexpresses HER2, and thus this model was chosen to evaluate the effect of multiple standard of care agents, including trastuzumab and the ADC trastuzumab-DXd, in the presence and absence of human NK cells. NCI-N87 cells were evaluated for HER2 expression by flow cytometry and were found to be approximately 99% HER2 positive. FcγRI and FcγRIIa-H mediated ADCP and FcγRIIIa mediated ADCC of trastuzumab and ADCs trastuzumab-DXd, trastuzumab-DM1, and trastuzumab-MMAE, were measured in vitro using reporter assays. Similar activity between trastuzumab and ADCs was observed, although it is presumed the antibody-payload linker may be interfering with binding to either the NCI-N87 cells or the Fc receptor, causing some variability in fold induction. For in vivo experiments, NCI-N87 cells were mixed with 50% extracellular matrix, and subcutaneously implanted in female NSG mice. Mice with established tumors were treated with osimertinib mesylate, 5-fluorouracil, lapatinib, trastuzumab, and trastuzumab-DXd to assess anti-tumor response. Additionally, a cohort of mice was humanized with peripheral blood mononuclear cells (PBMC) to evaluate the impact of human immune cells on the efficacy of trastuzumab and trastuzumab-DXd. All standard of care agents had significant anti-tumor activity, with trastuzumab-DXd being highly effective. Humanization did not appear to provide additional efficacy. In summary, a well-characterized HER2+ model of gastric cancer has been established. Future studies include testing the activity of a T-cell-engaging HER2-targeting bispecific antibody in the humanized NCI-N87 xenograft model. Citation Format: Hillary J. Millar Quinn, Kyla Emerson, Sean Shukait, Natalie Czeryba, Lauren Kucharczyk, Anita J. Zaitouna, Sheri Barnes, Scott Wise. Development, characterization, and humanization of NCI-N87 human gastric carcinoma xenograft model in NSG mice [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr B089.