Abstract 24: Influence of culture conditions and donor material on phenotypic features of PDX-derived breast cancer tumoroid lines

Abstract Introduction: Breast cancer is one of the most common and deadly cancers among women, highlighting the need for reliable in vitro models to study tumor biology and assess therapeutic strategies. In this project, we established and characterized three breast cancer tumoroid lines (two triple negative and one HER2+), derived from patient-derived xenograft models as a robust in vitro system for cancer research: MAXFHER 2500, MAXFT 583 and MAXFTN 2988. The tumoroids were maintained under various conditions, including long-term culture, cryopreservation, and suspension adaptation, to evaluate their morphological stability and functional fidelity over time. They were characterized by histology, multiplex IHC and QuantiGene analysis. To evaluate predictivity for preclinical in vivo as well as clinical outcomes, four standard of care compounds were evaluated in the HER2 positive breast cancer model MAXFHER 2500 and compared to in vivo data of the corresponding PDX. To be able to determine tumor growth as well as efficacy of test compounds an automated image analysis script was developed to quantify tumoroid growth. Results: The three lines showed very similar expression levels of Ki67, Her2 (both IHC) and histological architecture as compared to the donor PDX and the donor patient. The expression levels of Estrogen as well as Progestogen receptor, EpCAM and Cytokeratin 18 were comparable in the tumoroid lines and the PDX as confirmed by multiplex IHC. The different culture techniques, dome (high Matrigel concentration) vs suspension method (low Matrigel concentration) did not influence the expression of the above-mentioned markers or the histological structure of the tumoroids. It was possible to create tumoroid lines from fresh PDX as well as from viably frozen material. Cisplatin was highly active in all three tested culture conditions with IC50 values ranging from 2.9 - 9.6 µM. In contrast, the sensitivity towards Oxaliplatin was influenced by the culture conditions with IC50s ranging from 8.2 - 94.6 µM. Gemcitabine and Cisplatin efficacy in vitro was predictive for antitumoral activity in vivo. However, Paclitaxel was inactive in vitro but showed some efficacy in vivo. Discussion: Overall, this study demonstrates that tumoroid lines derived from PDX models retain key tumor characteristics, making them a valuable tool for cancer research. Although the breast cancer tumoroid lines preserved morphological and functional features under various conditions there were indications that some culture conditions do influence the sensitivity towards anticancer treatment. The observed variability underscores the importance of carefully selecting and optimizing culture conditions to maintain the predictive value of PDX derived tumoroids for breast cancer drug development. Citation Format: Ellen Klaproth, Julia Thiel, Jannik Scherer, Meng Dong, Kanstantsin Lashuk, Julia B. Schueler. Influence of culture conditions and donor material on phenotypic features of PDX-derived breast cancer tumoroid lines [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 24.