Development and validation of a PSMA-positive triple-negative breast cancer mouse model for preclinical targeted radionuclide therapies.

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, for which targeted therapies are emerging. Prostate-specific membrane antigen (PSMA), expressed mainly by the endothelial cells of the neovascularization of TNBC, or tumor cells, is an interesting target in TNBC that needs to be studied. However, native TNBC models do not express PSMA on tumor cells, which justifies the need for genetic modification to enable PSMA-targeted imaging and therapy studies. This study aims to validate a reproductible, PSMA-positive murine model for Targeted Radionuclide Therapy (TRT) assessment. Twenty-five syngeneic or xenograft murine models were produced by modifying the TNBC cell line, the implantation site (ectopic and orthotopic), cell numbers and matrix (e.g. Matrigel®) use. Tumor growth and engraftment were recorded. PSMA expression was evaluated histologically using immunohistochemistry (IHC) and PSMA-targeted positron emission tomography (PET)- computed tomography (CT) with [18F]-DCFPyL. The tumor-to-liver ratio (TLR) was used to quantify the uptake of the radiopharmaceutical. To address the absence of PSMA expression in native models, MDA-MB-231 cells were genetically modified via lentiviral transduction to overexpress PSMA for in vivo evaluation. Despite high cellular proliferation and extensive tumor neovascularization, immunohistochemical analyses revealed an absence of PSMA expression in all non-transfected models tested. This finding was further confirmed by [¹⁸F]-DCFPyL PET/CT imaging, which showed a TLR below 1, indicating negligible radiotracer uptake within tumoral tissues. In contrast, the MDA-MB-231psma model achieved 100% tumor engraftment and a tumor volume of 208 ± 61 mm3 at 28 days post-injection (not significantly different from the MDA-MB-231wt model). This model showed a TLR of 10.3 ± 4.3 one hour after intravenous injection of [18F]-DCFPyL. This study emphasizes the challenge of creating a reproducible murine model with PSMA expression. Nevertheless, the initial transfection of MDA-MB-231 cells to express PSMA resulted in the development of an innovative TNBC murine model that expresses PSMA. This model is reproducible and exhibits heterogeneous PSMA expression, and is representative of clinical observations. It is also suitable for evaluating PSMA-targeted TRT in TNBC.