title: 18F-labeled mini-PEG spacered RGD dimer (18F-FPRGD2): synthesis and microPET imaging of alphavbeta3 integrin expression.
abstract: OBJECTIVE
  We have previously reported that (18)F-FB-E[c(RGDyK)](2) ((18)F-FRGD2) allows quantitative PET imaging of integrin alpha(v)beta(3) expression. However, the potential clinical translation was hampered by the relatively low radiochemical yield. The goal of this study was to improve the radiolabeling yield, without compromising the tumor targeting efficiency and in vivo kinetics, by incorporating a hydrophilic bifunctional mini-PEG spacer.
  
  
  METHODS
  (18)F-FB-mini-PEG-E[c(RGDyK)](2) ((18)F-FPRGD2) was synthesized by coupling N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) with NH(2)-mini-PEG-E[c(RGDyK)](2) (denoted as PRGD2). In vitro receptor binding affinity, metabolic stability, and integrin alpha(v)beta(3) specificity of the new tracer (18)F-FPRGD2 were assessed. The diagnostic value of (18)F-FPRGD2 was evaluated in subcutaneous U87MG glioblastoma xenografted mice and in c-neu transgenic mice by quantitative microPET imaging studies.
  
  
  RESULTS
  The decay-corrected radiochemical yield based on (18)F-SFB was more than 60% with radiochemical purity of >99%. (18)F-FPRGD2 had high receptor binding affinity, metabolic stability, and integrin alpha(v)beta(3)-specific tumor uptake in the U87MG glioma xenograft model comparable to those of (18)F-FRGD2. The kidney uptake was appreciably lower for (18)F-FPRGD2 compared with (18)F-FRGD2 [2.0 +/- 0.2%ID/g for (18)F-FPRGD2 vs 3.0 +/- 0.2%ID/g for (18)F-FRGD2 at 1 h post injection (p.i.)]. The uptake in all the other organs except the urinary bladder was at background level. (18)F-FPRGD2 also exhibited excellent tumor uptake in c-neu oncomice (3.6 +/- 0.1%ID/g at 30 min p.i.).
  
  
  CONCLUSIONS
  Incorporation of a mini-PEG spacer significantly improved the overall radiolabeling yield of (18)F-FPRGD2. (18)F-FPRGD2 also had reduced renal uptake and similar tumor targeting efficacy as compared with (18)F-FRGD2. Further testing and clinical translation of (18)F-FPRGD2 are warranted.
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Stanford University School of Medicine, 1201 Welch Rd, P095, Stanford, CA 94305-5484, USA.
authors.forename: Zhanhong
authors.initials: Z
authors.lastname: Wu
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Stanford University School of Medicine, 1201 Welch Rd, P095, Stanford, CA 94305-5484, USA.
authors.forename: Zi-Bo
authors.initials: ZB
authors.lastname: Li
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Stanford University School of Medicine, 1201 Welch Rd, P095, Stanford, CA 94305-5484, USA.
authors.forename: Weibo
authors.initials: W
authors.lastname: Cai
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Stanford University School of Medicine, 1201 Welch Rd, P095, Stanford, CA 94305-5484, USA.
authors.forename: Lina
authors.initials: L
authors.lastname: He
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Stanford University School of Medicine, 1201 Welch Rd, P095, Stanford, CA 94305-5484, USA.
authors.forename: Frederick T
authors.initials: FT
authors.lastname: Chin
authors.affiliation: Department of Nuclear Medicine, Peking Union Medical College Hospital, Beijing, People's Republic of China.
authors.forename: Fang
authors.initials: F
authors.lastname: Li
authors.affiliation: The Molecular Imaging Program at Stanford (MIPS), Department of Radiology and Bio-X Program, Stanford University School of Medicine, 1201 Welch Rd, P095, Stanford, CA 94305-5484, USA.
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Chen
mesh_terms: D000818:Animals; D019281:Dimerization; D005260:Female; D005462:Fluorine Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics*; D020869:Gene Expression Profiling / Q000379:methods; D005909:Glioblastoma / Q000000981:diagnostic imaging* / Q000378:metabolism*; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009842:Oligopeptides / Q000737:chemistry / Q000493:pharmacokinetics*; D009928:Organ Specificity; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution
chemical_list: D005462:Fluorine Radioisotopes; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D019275:Radiopharmaceuticals; C047981:arginyl-glycyl-aspartic acid