Development of the Fibronectin–Mimetic Peptide KSSPHSRN(SG)5RGDSP as a Novel Radioprobe for Molecular Imaging of the Cancer Biomarker α5β1 Integrin

• Published in: Biological & pharmaceutical bulletin 2015/11/01, Vol.38(11), pp.1722-1731
• Main Authors: Jin, Zhao-Hui, Furukawa, Takako, Kumata, Katsushi, Xie, Lin, Yui, Joji, Wakizaka, Hidekatsu, Fujibayashi, Yasuhisa, Zhang, Ming-Rong, Saga, Tsuneo
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Biomarkers, Tumor - metabolism; Colorectal Neoplasms - metabolism; Disease Models, Animal; Female; Fibronectins - metabolism; fibronectin–mimetic peptide; fluorine-18; Humans; Integrin alpha5beta1 - metabolism; Melanoma, Experimental - metabolism; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Molecular Imaging - methods; Molecular Probes - chemistry; Neoplasms - diagnosis; Neoplasms - metabolism; Peptides - metabolism; positron emission tomography; Positron-Emission Tomography - methods; radioprobe; Rats; α5β1 integrin
• ISSN: 0918-6158; 1347-5215
• DOI: 10.1248/bpb.b15-00344

α5β1 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 α5β1-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 α5β1 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 α5β1-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 α5β1-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 α5β1-positive tumors than in α5β1-negative tumors and higher α5β1-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 α5β1 expression in tumors.