Purpose: Investigate the impact of various halogens on pharmacokinetics, biodistribution, and micro positron emission tomography/computed tomography (PET/CT) imaging of Glu-urea-Lys-based prostate-specific membrane antigen (PSMA) inhibitors.
Procedures: Based on the modification of SC691, a small molecule inhibitor of PSMA previously developed by our group, we synthesized 68Ga-labeled compounds by modifying the lysine terminal amino with different halogenated phenyl substituents. After complete characterization, in vitro and in vivo properties were studied.
Results: The [68Ga]Ga-DOTA-SC691-R possesses a high radiochemical yield (98-99%). The internalization values of [68Ga]Ga-DOTA-SC691-H, [68Ga]Ga-DOTA-SC691-Cl, and [68Ga]Ga-DOTA-SC691-Br in LNCaP cells all displayed time-dependent pattern enhanced with time. The results of in vitro competitive inhibition assay showed that the affinity of natGa-DOTA-SC691-R for PSMA had a trend of H < F < Cl < Br < I. The blocking imaging and dynamic imaging on micro-PET/CT of male non-obese diabetic/severe combined immunodeficiency mice with LNCaP tumors showed the rapid tumor targeting properties of [68Ga]Ga-DOTA-SC691-R with specificity for PSMA. Static imaging of micro-PEC/CT of these compounds could rapidly localize LNCaP tumors with decent image quality (except for [68Ga]Ga-DOTA-SC691-H). Biodistribution data showed that [68Ga]Ga-DOTA-SC691-R were metabolized via the kidney and tumor accumulation followed the order of H ≈ F ≈ Cl < I < Br uptake values at 1 h. [68Ga]Ga-DOTA-SC691-Br showed the highest tumor accumulation and retention (15.21 ± 5.57%ID/g at 30 min, 20.39 ± 4.38%ID/g at 60 min, and 13.30 ± 4.39%ID/g at 120 min), which is consistent with the results of the competitive inhibition assay and cell binding assay.
Conclusions: It was demonstrated that the halogen substituent on the lysine terminal amino group on the Glu-urea-Lys backbone did positively affect the binding of [68Ga]Ga-DOTA-SC691-R to PSMA. The bulkier and less electronegative Br (or I) elements are preferred for structural modifications here.
Keywords: Halogen; Positron emission tomography; Prostate cancer; Prostate-specific membrane antigen; Radiopharmaceutical.
© 2023. The Author(s), under exclusive licence to World Molecular Imaging Society.