α
5β
1 Integrin, a fibronectin receptor, is becoming a pertinent therapeutic target and a promising prognostic biomarker for cancer patients. The aim of this study was to functionalize an α
5β
1-specific fibronectin–mimetic peptide sequence KSSPHSRN(SG)
5RGDSP (called PR_b) as a positron emission tomography (PET) probe. PR_b was modified by addition of a β-alanine residue, conjugated with 2-
S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (
p-SCN-Bn-NOTA), and radiolabeled with
18F based on the chelation of
18F-aluminum fluoride. A control probe was produced by glycine to alanine substitution in the RGD motif of PR_b. Cell binding and blocking assays, autoradiographic evaluation of tissue binding and blocking, dynamic PET scans, and a biodistribution study were conducted using cell lines and murine tumor models with determined expression levels of α
5β
1 and other related integrins.
18F-PR_b was produced with a labeling yield of 22.3±1.9% based on
18F-F
−, a radiochemical purity of >99%, and a specific activity of 30–70 GBq/µmol; it exhibited α
5β
1-binding activity and specificity
in vitro,
ex vivo, and
in vivo, and had a rapid blood clearance and a predominant renal excretion pathway.
In vivo α
5β
1-positive tumors could be clearly visualized by
18F-PR_b PET imaging. Both imaging and biodistribution studies suggested higher uptake of
18F-PR_b in α
5β
1-positive tumors than in α
5β
1-negative tumors and higher α
5β
1-positive tumor uptake of
18F-PR_b than the control probe. In contrast, there was no significant difference seen in the contralateral muscle uptake. A PET radioprobe,
18F-PR_b, was developed
de novo and potentially can be used for noninvasive detection of α
5β
1 expression in tumors.
抄録全体を表示