One-step (18)F labeling of non-peptidic bivalent integrin αvβ3 antagonist for cancer imaging

Abstract

A rapid one-step (18)F labeling reaction with fluoridealuminum complex, which is based on chelation chemistry, has received a surge of interest for (18)F radiolabeling of peptides. In this study, a non-peptidic bivalent integrin αvβ3 antagonist (bivalent-IA) was conjugated with 1,4,7-triazacyclononane-1,4-diiacetic acid (NODA). A novel (18)F labeled radiotracer, (18)F-bivalent-IA, was developed via one step (18)F-AlF/NODA chelation reaction in aqueous phase with high radiochemical yield (65-75%, decay corrected) and good specific activity (750-850 mCi/μmol). The tumor integrin targeting efficiency and in vivo pharmacokinetic profile of (18)F-bivalent-IA were evaluated in U-87 MG (integrin positive) and MDA-MB-231 (integrin negative) models by small-animal PET/CT scan followed by a biodistribution study. The PET/CT and ROI results showed high tumor uptake of (18)F-bivalent-IA in U-87 MG tumor-bearing mice from 5 to 120 min p.i. with good contrast, and the U-87 MG tumor uptake values (6.35 ± 0.67%ID/g, at 1 h p.i.) were 6 times higher than those of MDA-MB-231 tumor (1.05 ± 0.12%ID/g, at 1 h p.i.) (P < 0.0001) which correlated with the integrin αvβ3 expression in tumor tissues confirmed by immunohistochemistry. Co-injection of the (18)F-bivalent-IA with 6 nmol (6 μg) of nonradioactive bivalent-IA effectively blocked tumor uptake demonstrating the integrin αvβ3-specificity. In conclusion, the first (18)F labeled non-peptidic bivalent integrin αvβ3 targeting radiotracer, (18)F-bivalent-IA, was developed and proved to be a highly potent and specific PET radiopharmaceutical for noninvasive imaging of integrin αvβ3, which plays a critical role in tumor angiogenesis and metastasis.

Figure 1

Chemical structures of IA and ¹⁸F-bivalent-IA.

Figure 2

(A) PET/CT images of U-87 MG tumor-bearing mice injected intravenously with approximately 100 μCi of ¹⁸F-bivalent-IA. (B) Time–activity curves of tumor and major organs of U-87 MG tumor-bearing mice from 60 min dynamic scans after intravenous injection of ¹⁸F-bivalent-IA (n = 5). (Tumors are indicated by arrowheads.)

Figure 3

(A) PET/CT images of U-87 MG tumor-bearing mice injected intravenously with¹⁸F-bivalent-IA, and (B) PET/CT images of U-87 MG tumor-bearing mice injected intravenously with ¹⁸F-bivalent-IA and 6 nmol (6 μg) of bivalent-IA. (C) PET/CT images of MDA-MB-231 breast tumor-bearing mice injected intravenously with ¹⁸F-bivalent-IA. (Tumors are indicated by arrowheads.) (D) Quantitative analysis of small-animal PET/CT images. Comparison of decay-corrected ROI analysis of ¹⁸F-bivalent-IA (U-87 MG tumor-bearing mice) (n = 5), ¹⁸F-bivalent-IA (MDA-MB-231 breast tumor-bearing mice) (n = 3), and ¹⁸F-bivalent-IA coinjected with 6 nmol (6 μg) of bivalent-IA (U-87 MG tumor-bearing mice) (n = 4) in tumor. (E) Comparison of tumor-to-muscle uptake ratios after injection of ¹⁸F-bivalent-IA (U-87 MG tumor-bearing mice) (n = 5), ¹⁸F-bivalent-IA (MDA-MB-231 breast tumor-bearing mice) (n = 3), and ¹⁸F-bivalent-IA coinjected with 6 nmol (6 μg) of bivalent-IA (U-87 MG tumor-bearing mice) (n = 4). (F) Cell uptake and competition assay. Binding of ¹⁸F-bivalent-IA to U-87 MG and MDA-MB-231 cells with varying levels of integrin α_vβ₃.

Figure 4

Biodistribution at 3 h postinjection ¹⁸F-NODA-bivalent-IA (U-87 MG tumor-bearing mice) (n = 5), ¹⁸F-NODA-bivalent-IA (MDA-MB-231 breast tumor-bearing mice) (n = 3), and ¹⁸F-NODA-bivalent-IA coinjected with blocking dose of bivalent-IA (U-87 MG tumor-bearing mice) (n = 4).