Purpose

Prostate cancer (PCa), characterized by tumor heterogeneity, may exhibit low or absent prostate-specific membrane antigen (PSMA) expression in cancerous lesions, limiting the detection sensitivity of monospecific probes. Given that fibroblast activation protein (FAP) is frequently overexpressed in the tumor microenvironment (TME), we developed a PSMA/FAP dual-targeting tracer to address this limitation.

Methods

The binding affinities of precursors and their corresponding non-radioactive standards were assessed using recombinant PSMA and FAP proteins. PET/CT imaging was performed in 22Rv1 (PSMA-positive) and U87MG (FAP-positive) xenograft models. Clinical evaluation of [¹⁸F]AlF-NOTA-PSFA-1 was conducted in two PCa patients, directly compared with [⁶⁸Ga]Ga-PSMA-11.

Results

All precursors and their corresponding non-radioactive standards exhibited high affinity for both PSMA (Ki = 0.13–4.86 nM) and FAP (Ki = 0.012–0.40 nM). Among them, [¹⁸F]AlF-NOTA-PSFA-1, demonstrated the highest tumor uptake in both 22RV1 (SUVmax = 4.64) and U87MG (SUVmax = 7.23) models, along with favorable tumor retention over time. Compared to [⁶⁸Ga]Ga-PSMA-11, [¹⁸F]AlF-NOTA-PSFA-1 showed higher lesion uptake, reduced background accumulation in off-target organs, and improved imaging quality in metastatic PCa patient.

Conclusions

The biphenyl-based bispecific tracers developed in this study achieved high tumor affinity, prolonged retention, and notably reduced renal uptake in mouse models. [¹⁸F]AlF-NOTA-PSFA-1 emerged as the most promising candidate, demonstrating superior imaging performance over [⁶⁸Ga]Ga-PSMA-11 in both preclinical and first-in-human evaluation.