Development and Characterization of the PSMA-Expressing CT26-PSMA Cell Line as a Rapid Preclinical Platform for 68Ga-Labeled PSMA-Targeted Radioconjugates

Preclinical models play a critical role in the development of PSMA-targeted radiopharmaceuticals for prostate cancer. However, many existing models have practical limitations, including slow tumor growth, low engraftment rates, and restricted availability, and all human PSMA-positive lines are confined to immunodeficient hosts. We developed and characterized a novel PSMA-expressing transgenic cell line, CT26-PSMA, as a practical tool for preclinical screening of PSMA-targeting agents. The CT26-PSMA cell line was established by stable transfection of the murine colon carcinoma CT26 cell line with human PSMA using the Sleeping Beauty transposon system. PSMA expression was confirmed by RT-qPCR (reverse transcription quantitative polymerase chain reaction), flow cytometry, and radioligand saturation binding on intact cells. Two [68Ga]Ga-labeled radioconjugates—the well-established PSMA-617 and a newly synthesized conjugate (Conjugate-1)—were used to validate the functionality of the model through in vitro binding, uptake and internalization studies, and through ex vivo biodistribution in CT26-PSMA tumor-bearing athymic male nu/nu mice. The CT26-PSMA cell line demonstrated high and stable PSMA expression, with approximately 95% of cells expressing the biomarker and no measurable loss over 16 passages in antibiotic-free medium. Saturation binding gave a receptor density of ∼3.5 × 106 sites per cell, approximately four-fold higher than that of LNCaP cells (∼0.8 × 106), with dissociation constants that were indistinguishable between the two radioconjugates and between the two cell lines (Kd 9.0–11.6 nM). Subcutaneous tumors reached ~300 mm3 within 8–10 days of inoculation, with a take rate of 10/10 versus 1/10 for LNCaP (Fisher’s exact test, p = 1.2 × 10−4). Both radiotracers showed saturable, 2-PMPA-blockable binding and uptake in CT26-PSMA cells, confirming the functional activity of the recombinant receptor. Biodistribution studies revealed accumulation of both conjugates in CT26-PSMA tumors, with generally comparable tumor-to-background profiles. The CT26-PSMA cell line represents a robust, rapid, and reproducible platform for preclinical evaluation of PSMA-targeting radiopharmaceuticals, and its murine BALB/c origin permits engraftment in immunocompetent or minimally immunosuppressed hosts, whereas existing human PSMA-positive lines do not. It is intended as a screening platform rather than as a model of prostate cancer biology. The validation data obtained with [68Ga]Ga-labelled conjugates confirm the suitability of this cell line for future studies of PSMA-directed compounds.