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

Biol Pharm Bull. 2015;38(11):1722-31. doi: 10.1248/bpb.b15-00344. Epub 2015 Aug 15.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 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
  • Neoplasms / metabolism*
  • Peptides / metabolism*
  • Positron-Emission Tomography / methods
  • Rats

Substances

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