A Novel 68Ga-Labeled 2-Azabicyclo[3.1.0]Hexane-3-Carbonitrile-Based Fibroblast Activation Protein-Targeted Tracer for Cancer Imaging With Positron Emission Tomography

Abstract

Most of the reported small molecule-based fibroblast activation protein (FAP)-targeted radioligands are derived from UAMC1110 and contain a 4-difluoro-2-cyanopyrrolidine moiety. In this study, we investigated the effect of replacing the 4-difluoro-2-cyanopyrrolidine moiety of [⁶⁸Ga]Ga-FAPI-04 with 2-azabicyclo[3.1.0]hexane-3-carbonitrile on the in vitro/vivo FAP-targeting capability. The newly derived ⁶⁸Ga-labeled FAP-targeted tracer, [⁶⁸Ga]Ga-JC02076, was obtained in 43.5 ± 10.4% decay-corrected radiochemical yield within 33.5 ± 5.8 min (n = 4). The radiochemical purity and molar activity were 97.2 ± 3.4% and 411.6 ± 232.5 GBq/μmol, respectively. Ga-JC02076 showed good binding affinity for FAP (IC₅₀ = 29.7 ± 3.5 nM). Most importantly, [⁶⁸Ga]Ga-JC02076 enabled clear visualization of HEK293T:hFAP tumor xenografts in PET images and had good tumor uptake (7.17 ± 2.19 %ID/g) and excellent tumor-to-bone (17.3 ± 6.99) and tumor-to-muscle (32.3 ± 12.5) uptake ratios at 1 h post-injection. Our data suggest that N-(4-quinolinoyl)-Gly-(2-azabicyclo[3.1.0]hexane-3-carbonitrile) is a promising pharmacophore for the design of FAP-targeted tracers.