title: Characterization and evaluation of DOTA-conjugated Bombesin/RGD-antagonists for prostate cancer tumor imaging and therapy.
abstract: BACKGROUND
  Here we present the metallation, characterization, in vivo and in vitro evaluations of dual-targeting, peptide-based radiopharmaceuticals with utility for imaging and potentially treating prostate tumors by virtue of their ability to target the αVβ3 integrin or the gastrin releasing peptide receptor (GRPr).
  
  
  METHODS
  [RGD-Glu-6Ahx-RM2] (RGD: Arg-Gly-Asp; Glu: glutamic acid; 6-Ahx: 6-amino hexanoic acid; RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2)) was conjugated to a DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) bifunctional chelator (BFCA) purified via reversed-phase high-performance liquid chromatography (RP-HPLC), characterized by electrospray ionization-mass spectrometry (ESI-MS), and radiolabeled with (111)In or (177)Lu. Natural-metallated compounds were assessed for binding affinity for the αVβ3 integrin or GRPr in human glioblastoma U87-MG and prostate PC-3 cell lines and stability prior to in vivo evaluation in normal CF-1 mice and SCID mice xenografted with PC-3 cells.
  
  
  RESULTS
  Competitive displacement binding assays with PC-3 and U87-MG cells revealed high to moderate binding affinity for the GRPr or the αVβ3 integrin (IC50 range of 5.39±1.37 nM to 9.26±0.00 nM in PC-3 cells, and a range of 255±47 nM to 321±85 nM in U87-MG cells). Biodistribution studies indicated high tumor uptake in PC-3 tumor-bearing mice (average of 7.40±0.53% ID/g at 1h post-intravenous injection) and prolonged retention of tracer (mean of 4.41±0.91% ID/g at 24h post-intravenous injection). Blocking assays corroborated the specificity of radioconjugates for each target. Micro-single photon emission computed tomography (microSPECT) confirmed favorable radiouptake profiles in xenografted mice at 20h post-injection.
  
  
  CONCLUSIONS
  [RGD-Glu-[(111)In-DO3A]-6-Ahx-RM2] and [RGD-Glu-[(177)Lu- DO3A]-6-Ahx-RM2] show favorable pharmacokinetic and radiouptake profiles, meriting continued evaluation for molecular imaging in murine U87-MG/PC-3 xenograft models and radiotherapy studies with (177)Lu and (90)Y conjugates.
  
  
  CONCLUSIONS
  These heterovalent, peptide-targeting ligands perform comparably with many mono- and multivalent conjugates with the potential benefit of increased sensitivity for detecting cancer cells exhibiting differential expression of target receptors.
authors.affiliation: Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, United States, 65201; Department of Veterinary Pathobiology, Comparative Medicine Program, University of Missouri College of Veterinary Medicine, Columbia, MO, United States, 65211. Electronic address: stottreynoldst@missouri.edu.
authors.forename: Tamila J
authors.initials: TJ
authors.lastname: Stott Reynolds
authors.affiliation: Veterinary Research Scholars Program, University of Missouri College of Veterinary Medicine, Columbia, MO, United States, 65211.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Schehr
authors.affiliation: Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, United States, 65201; Department of Radiology, University of Missouri School of Medicine, Columbia, MO, United States, 65211.
authors.forename: Dijie
authors.initials: D
authors.lastname: Liu
authors.affiliation: College of Pharmacy, University of New Mexico, Albuquerque, NM, United States, 87131.
authors.forename: Jingli
authors.initials: J
authors.lastname: Xu
authors.affiliation: College of Pharmacy, University of New Mexico, Albuquerque, NM, United States, 87131; Cancer Research and Treatment Center, University of New Mexico, Albuquerque, NM, United States, 87131; Department of Dermatology, University of New Mexico, Albuquerque, NM, United States, 87131.
authors.forename: Yubin
authors.initials: Y
authors.lastname: Miao
authors.affiliation: Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, United States, 65201; Department of Internal Medicine, University of Missouri School of Medicine, Columbia, MO, United States, 65211; Department of Chemistry, University of Missouri, Columbia, MO, United States, 65211.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Hoffman
authors.affiliation: Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, United States, 65201; Department of Internal Medicine, University of Missouri School of Medicine, Columbia, MO, United States, 65211.
authors.forename: Tammy L
authors.initials: TL
authors.lastname: Rold
authors.affiliation: Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, United States, 65201; Department of Radiology, University of Missouri School of Medicine, Columbia, MO, United States, 65211.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Lewis
authors.affiliation: Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, Missouri, United States, 65201; Department of Radiology, University of Missouri School of Medicine, Columbia, MO, United States, 65211; University of Missouri Research Reactor Center, University of Missouri, Columbia, MO, United States, 65211. Electronic address: smithcj@health.missouri.edu.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Smith
mesh_terms: D000818:Animals; D001839:Bombesin / Q000493:pharmacokinetics / Q000494:pharmacology / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes / Q000627:therapeutic use; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000037:antagonists & inhibitors; D008297:Male; D051379:Mice; D009842:Oligopeptides / Q000737:chemistry*; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000473:pathology / Q000532:radiotherapy*; D018004:Receptors, Bombesin / Q000037:antagonists & inhibitors; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon; D055114:X-Ray Microtomography
chemical_list: D003301:Copper Radioisotopes; D006573:Heterocyclic Compounds, 1-Ring; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D018004:Receptors, Bombesin; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; C047981:arginyl-glycyl-aspartic acid; D001839:Bombesin
keywords: Bombesin; Gastrin-releasing peptide; Prostate cancer; RGD; RM2