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

Abstract

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 (18)F based on the chelation of (18)F-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. (18)F-PR_b was produced with a labeling yield of 22.3±1.9% based on (18)F-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 (18)F-PR_b PET imaging. Both imaging and biodistribution studies suggested higher uptake of (18)F-PR_b in α5β1-positive tumors than in α5β1-negative tumors and higher α5β1-positive tumor uptake of (18)F-PR_b than the control probe. In contrast, there was no significant difference seen in the contralateral muscle uptake. A PET radioprobe, (18)F-PR_b, was developed de novo and potentially can be used for noninvasive detection of α5β1 expression in tumors.

• Authors: Zhao-Hui Jin, Takako Furukawa, Katsushi Kumata, Lin Xie, Joji Yui, Hidekatsu Wakizaka, Yasuhisa Fujibayashi, Ming-Rong Zhang, Tsuneo Saga
• Journal: Biological & pharmaceutical bulletin (Biol Pharm Bull) Vol. 38 Issue 11 Pg. 1722-31 ( 2015) ISSN: 1347-5215 [Electronic] Japan
• PMID: 26277991 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Biomarkers, Tumor
• Fibronectins
• Integrin alpha5beta1
• Molecular Probes
• Peptides

Topics

• Amino Acid Sequence
• Animals
• Biomarkers, Tumor (metabolism)
• Colorectal Neoplasms (metabolism)
• Disease Models, Animal
• Female
• Fibronectins (metabolism)
• Humans
• Integrin alpha5beta1 (metabolism)
• Melanoma, Experimental (metabolism)
• Mice
• Mice, Inbred BALB C
• Mice, Inbred C57BL
• Molecular Imaging (methods)
• Molecular Probes (chemistry)
• Neoplasms (diagnosis, metabolism)
• Peptides (metabolism)
• Positron-Emission Tomography (methods)
• Rats