Abstract 4006: HER2-positive patient-derived xenograft organoids (PDXOs) as a novel preclinical tool to evaluate new therapies against HER2-driven cancers

Abstract The human epidermal growth factor 2 receptor (HER2) is a key member of the receptor tyrosine kinase superfamily. Alterations in HER2 have been identified in various malignancies, including approximately 20% of non-small-cell lung cancer (NSCLC) and about 30% of breast cancer (BRCA). These HER2 alterations encompass gene mutations, gene amplification, and protein overexpression, all of which are associated with tumorigenesis and contribute to enhanced cancer cell proliferation. Cancers with HER2 alterations often exhibit more aggressive behavior, a higher recurrence rate, and a poorer prognosis. The introduction of HER2-directed therapies has significantly improved therapeutic outcomes. FDA-approved therapeutic options for HER2-positive cancers can be categorized into three major groups: tyrosine kinase inhibitors (TKIs), antibodies, and antibody-drug conjugates (ADCs). These treatments specifically target the HER2 receptor or its downstream signaling pathways. However, many studies show that nonselective TKIs and HER2 naked antibodies demonstrate limited therapeutic effectiveness in HER2-positive cancers. In contrast, HER2-directed ADCs selectively deliver cytotoxic compounds to HER2-positive tumor cells, resulting in better responses and fewer adverse effects, as evidenced by numerous preclinical and clinical studies. In our current work, to showcase our well-characterized PDX-O platform BRCA and NSCLC models were selected and assessed to be HER2 positive as evidenced by complete and intense membrane staining identified in patient-derived xenograft organoids (PDXOs) tissue blocks. Furthermore, from early low passages, assay-ready cells were seeded in a 96-well plate high throughput format at a density of 5000 cells per well. Well-defined 3D structures formed after 3 days, and the models were evaluated for morphology and proliferation assessment. Cytotoxicity controls: 10 µM Staurosporine and 0.1% DMSO were added to each plate to serve as plate controls and used in determining the Z factor of the assay. The models were tested for efficacy of Lapatinib (TKI); and Enhertu and Kadcyla (ADC) and their corresponding Isotypes. All models demonstrated a classic 3D morphology with > 150 µm diameter formed 72 hrs. after seeding; and were then dosed. The duration of drug incubation was 6 days after which Cell-Titer-Glo® reagent was added to all wells to determine half-maximal inhibitory concentration (IC50). The assay was robust with a Z factor > 0 and a high Signal: Noise ratio. Specifically for one model, the IC50 of Lapatinib was 69.15 µM. Both ADCs: Kadcyla and Enhertu, exhibited greater specificity and efficacy compared to their isotype controls. The ex vivo HER2-positive CTG3D platform represents a reliable and powerful tool for screening newly designed HER2 treatment regimens. Citation Format: Fu-Ju Chou, Yamini Nallana, Hsiu-Wen Tsai, Mara Gilardi, Stefano Cairo, BanuPriya Sridharan. HER2-positive patient-derived xenograft organoids (PDXOs) as a novel preclinical tool to evaluate new therapies against HER2-driven cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4006.