Abstract 70: Novel PSMA+ and FAP+ mouse models to support the development of novel molecular radiotherapy agents

To evaluate novel molecular radiotherapies preclinically, non-radiosensitive mouse models with optimal target expression levels that recapitulate the human tumor microenvironment are required. Within the past year Oncodesign Services has developed and validated such models for two targets: fibroblast activated protein (FAP) and prostate specific membrane antigen (PSMA), which are of high interest to the oncological and nuclear medicine community. To assess novel FAP inhibitor (FAPi) tracers, we developed two FAP-overexpressing cell lines. First, HT-1080 human sarcoma (FAP-negative; 0.0% FAP+) and U87-MG human glioblastoma cells (low FAP-positive; 15.0% FAP+) were transduced using a lentiviral vector overexpressing FAP and ZsGreen (VectorBuilder, Neu-Isenburg, Germany). Immunohistochemistry and flow cytometry confirmed the expression of both markers in the transduced cells, with up to 63.4% and 96.0% of FAP-positive cells in the HT-1080-FAP and U87-MG-FAP cells, respectively. Next, Swiss Nude mice (Charles River, Ecully, France) were subcutaneous engrafted with either the FAP-overexpressing HT-1080 or U87-MG cell line. A slow homogeneous tumor growth (humane endpoint of 1500 mm3 reached after 33-36 days) was noted with U87-MG-FAP tumors, while a faster and more heterogeneous tumor development was observed in mice bearing HT-1080-FAP tumors (humane endpoint reached after 14-18 days). Flow cytometry of the tumors ex vivo showed a higher expression of FAP in the U87-MG-FAP tumors (up to 81.5% FAP+ tumor cells) compared to HT-1080-FAP tumors (up to 61.5% FAP+ cells), as previously noted in vitro. In parallel, our team also focused on developing additional models for the assessment of novel molecular radiotherapies targeting PSMA. Male BRGSF mice (GenOway, Lyon, France) were subcutaneously engrafted with either LnCaP C4.2 cells (50%/50% Matrigel) or 22RV1-Luc-mCherry cells. A special enrichment was put in place to allow group housing of the male mice. The growth of LnCaP C4.2 tumors was relatively quick but heterogenous (humane endpoint reached after 19-32 days) and accompanied by a body weight loss that reached 23.6% despite the use of an enriched diet. 22RV1-Luc-mCherry tumor growth was relatively homogeneous and tumor size surpassed the human endpoint of 1500 mm3 after 29 days. Castration of the BRGSF mice before tumor cell engraftment delayed tumor growth by 3 to 11 days, depending on individual mice. Confirmation of PSMA expression or evaluation of PSMA tracers/molecular radiotherapy is foreseen in future projects. In conclusion, we designed several new mouse models, which could aid in the development of novel imaging or molecular radiotherapy agents for both FAP and PSMA, two “hot” biomarkers in the field of oncology. Citation Format: Sarah Belderbos, Peggy Provent, Solène Fernandez, Maëva Albanese, Marie Grunenwald, Florent Potvain, Kenny Herry, Didier Grillot, Nicolas Ancellin, Eftychia Koumarianou. Novel PSMA+ and FAP+ mouse models to support the development of novel molecular radiotherapy agents [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 70.