Development of the Fibronectin-Mimetic Peptide KSSPHSRN(SG)5RGDSP as a Novel Radioprobe for Molecular Imaging of the Cancer Biomarker α5β1 Integrin.
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.
Molecular Imaging Center, National Institute of Radiological Sciences.
Zhao-Hui
ZH
Jin
Takako
T
Furukawa
Katsushi
K
Kumata
Lin
L
Xie
Joji
J
Yui
Hidekatsu
H
Wakizaka
Yasuhisa
Y
Fujibayashi
Ming-Rong
MR
Zhang
Tsuneo
T
Saga
D000595:Amino Acid Sequence; D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism*; D015179:Colorectal Neoplasms / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D039081:Integrin alpha5beta1 / Q000378:metabolism*; D008546:Melanoma, Experimental / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D057054:Molecular Imaging / Q000379:methods*; D015335:Molecular Probes / Q000737:chemistry; D009369:Neoplasms / Q000175:diagnosis / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D049268:Positron-Emission Tomography / Q000379:methods; D051381:Rats
D014408:Biomarkers, Tumor; D005353:Fibronectins; D039081:Integrin alpha5beta1; D015335:Molecular Probes; D010455:Peptides