title: (68)Ga-labeled cyclic RGD dimers with Gly3 and PEG4 linkers: promising agents for tumor integrin alphavbeta3 PET imaging.
abstract: OBJECTIVE
  Radiolabeled cyclic RGD (Arg-Gly-Asp) peptides have great potential for the early tumor detection and noninvasive monitoring of tumor metastasis and therapeutic response. (18)F-labeled RGD analogs ([(18)F]-AH111585 and [(18)F]Galacto-RGD) have been investigated in clinical trials for positron emission tomography (PET) imaging of integrin expression in cancer patients. To develop new RGD radiotracers with higher tumor accumulation, improved in vivo kinetics, easy availability and low cost, we developed two new RGD peptides and labeled them with generator-eluted (68)Ga (t(1/2) = 68 min) for PET imaging of integrin alpha(v)beta(3) expression in tumor xenograft models.
  
  
  METHODS
  The two new cyclic RGD dimers, E[PEG(4)-c(RGDfK)](2) (P(4)-RGD2, PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and E[Gly(3)-c(RGDfK)](2) (G(3)-RGD2, G(3) = Gly-Gly-Gly) were designed, synthesized and conjugated with 1,4,7-triazacyclononanetriacetic acid (NOTA) for (68)Ga labeling. The microPET imaging and biodistribution of the (68)Ga labeled RGD tracers were investigated in integrin alpha(v)beta(3)-positive tumor xenografts.
  
  
  RESULTS
  The new RGD dimers with the Gly(3) and PEG(4) linkers showed higher integrin alpha(v)beta(3) binding affinity than no-linker RGD dimer (RGD2). NOTA-G(3)-RGD2 and NOTA-P(4)-RGD2 could be labeled with (68)Ga within 30 min with higher purity (>98%) and specific activity (8.88-11.84 MBq/nmol). Both (68)Ga-NOTA-P(4)-RGD2 and (68)Ga-NOTA-G(3)-RGD2 exhibited significantly higher tumor uptake and tumor-to-normal tissue ratios than (68)Ga-NOTA-RGD2.
  
  
  CONCLUSIONS
  Because of their high affinity, high specificity and excellent pharmacokinetic properties, further investigation of the two novel RGD dimers for clinical PET imaging of integrin alpha(v)beta(3) expression in cancer patients is warranted.
authors.affiliation: Department of Radiology, Biophysics & Bio-X, Stanford University, Stanford, CA 94305, USA.
authors.forename: Zhaofei
authors.initials: Z
authors.lastname: Liu
authors.forename: Gang
authors.initials: G
authors.lastname: Niu
authors.forename: Jiyun
authors.initials: J
authors.lastname: Shi
authors.forename: Shuanglong
authors.initials: S
authors.lastname: Liu
authors.forename: Fan
authors.initials: F
authors.lastname: Wang
authors.forename: Shuang
authors.initials: S
authors.lastname: Liu
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Chen
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D019281:Dimerization; D005260:Female; D005710:Gallium Radioisotopes / Q000737:chemistry; D005998:Glycine / Q000737:chemistry*; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000032:analysis / Q000378:metabolism*; D051379:Mice; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D011092:Polyethylene Glycols / Q000737:chemistry*; D049268:Positron-Emission Tomography; D011854:Radiochemistry; D013194:Staining and Labeling; D014018:Tissue Distribution
chemical_list: C516050:15-amino-4,7,10,13-tetraoxapentadecanoic acid; D005710:Gallium Radioisotopes; D039302:Integrin alphaVbeta3; D010456:Peptides, Cyclic; C507169:cyclic arginine-glycine-aspartic acid peptide; D011092:Polyethylene Glycols; D005998:Glycine