Design, preclinical evaluation, and first-in-human PET study of [⁶⁸Ga]Ga-PSFA-01: a PSMA/FAP heterobivalent tracer

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 precursor (PSFA-01) was synthesized by coupling a quinolone-based FAP-targeting scaffold and EuK with HBED-CC via amide bonds. The dual-receptor-binding affinity and cell uptake of PSFA-01 and [^natGa]Ga-PSFA-01 was evaluated in vitro. Micro-PET/CT imaging was performed on 22Rv1 and U87MG tumor-bearing mice. The feasibility of [⁶⁸Ga]Ga-PSFA-01 PET/CT in a clinical setting was evaluated in a metastatic prostate cancer patient, and the results were compared with those of [⁶⁸Ga]Ga-FAPI-04 and [⁶⁸Ga]Ga-PSMA-11 PET/CT.

Results

PSFA-01 and [^natGa]Ga-PSFA-01 showed high affinity for both FAP and PSMA proteins (Ki = 0.14–1.02 nM). On micro-PET/CT imaging, the 22Rv1 tumor uptake of [⁶⁸Ga]Ga-PSFA-01 (SUVmax = 3.89 ± 0.47) was higher than that of [⁶⁸Ga]Ga-PSMA-11 (SUVmax = 2.96 ± 0.48). The U87MG tumor uptake of [⁶⁸Ga]Ga-PSFA-01 was significantly higher (SUVmax = 7.29 ± 1.13) than [⁶⁸Ga]Ga-FAPI-04 (SUVmax = 0.28 ± 0.12), showing tumor to muscle ratio as 12.68 ± 1.93 at 1 h p.i. On clinical trial, the primary tumor and metastatic lesions were distinctly identified by [⁶⁸Ga]Ga-PSFA-01 (21 lesions), demonstrating superior performance compared to [⁶⁸Ga]Ga-FAPI-04 (3 lesions) and [⁶⁸Ga]Ga-PSMA-11 (13 lesions) in terms of lesion count and specificity.

Conclusions

[⁶⁸Ga]Ga-PSFA-01 exhibited satisfactory PSMA and FAP dual-receptor-targeting properties both in vitro and in vivo. This study highlights the clinical feasibility of [⁶⁸Ga]Ga-PSFA-01 PET/CT for detecting metastatic tumors of prostate cancer more sensitively compared to monomeric [⁶⁸Ga]Ga-PSMA-11 and [⁶⁸Ga]Ga-FAPI-04, which also suggests that a PSMA/FAP dual-targeted radionuclide therapy could potentially overcome challenges related to tumor heterogeneity and insufficient PSMA expression in PCa.