title: Synthesis and biological evaluation of copper-64 radiolabeled [DUPA-6-Ahx-(NODAGA)-5-Ava-BBN(7-14)NH2], a novel bivalent targeting vector having affinity for two distinct biomarkers (GRPr/PSMA) of prostate cancer.
abstract: Gastrin-releasing peptide receptors (GRPr) and prostate-specific membrane antigen (PSMA) are two identifying biomarkers expressed in very high numbers on prostate cancer cells and could serve as a useful tool for molecular targeting and diagnosis of disease via positron-emission tomography (PET). The aim of this study was to produce the multipurpose, bivalent [DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] radioligand for prostate cancer imaging, where DUPA = (2-[3-(1,3-dicarboxypropyl)-ureido]pentanedioic acid), a small-molecule, PSMA-targeting probe, 6Ahx = 6-aminohexanoic acid, 5-Ava = 5-aminovaleric acid, NODAGA = [2-(4,7-biscarboxymethyl)-1,4,7-(triazonan-1-yl)pentanedioic acid] (a derivative of NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid)), and BBN(7-14)NH2 = bombesin, a GRPr-specific peptide targeting probe.
  
  
  METHODS
  The PSMA/GRPr dual targeting ligand precursor [DUPA-6-Ahx-K-5-Ava-BBN(7-14)NH2], was synthesized by solid-phase and manual peptide synthesis, after which NODAGA was added via manual conjugation to the ε-amine of lysine (K). The new bivalent GRPr/PSMA targeting vector was purified by reversed-phase high performance liquid chromatography (RP-HPLC), characterized by electrospray-ionization mass spectrometry (ESI-MS), and metallated with (64)CuCl2 and (nat)CuCl2. The receptor binding affinity was evaluated in human, prostate, PC-3 (GRPr-positive) and LNCaP (PSMA-positive) cells and the tumor-targeting efficacy determined in severe combined immunodeficient (SCID) and athymic nude mice bearing PC-3 and LNCaP tumors. Whole-body maximum intensity microPET/CT images of PC-3/LNCaP tumor-bearing mice were obtained 18 h post-injection (p.i.).
  
  
  RESULTS
  Competitive binding assays in PC-3 and LNCaP cells indicated high receptor binding affinity for the [DUPA-6-Ahx-((nat)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] conjugate. MicroPET scintigraphy in PC-3/LNCaP tumor-bearing mice indicated that xenografted tumors were visible at 18h p.i. with collateral, background radiation also being observed in non-target tissue.
  
  
  CONCLUSIONS
  DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] targeting vector, as described herein, is the first example of a dual GRPr-/PSMA-targeting radioligand for molecular of imaging prostate tumors. Detailed in vitro studies and microPET molecular imaging investigations of [DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2 in tumor-bearing mice indicate that further studies are necessary to optimize uptake and retention of tracer in GRPr- and PSMA-positive tissues.
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
authors: Rajendra Prasad
authors: RP
authors: Bandari
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Chemistry, University of Missouri, Columbia, MO 65211, USA.
authors: Zongrun
authors: Z
authors: Jiang
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Veterinary Pathobiology, University of Missouri College of Veterinary Medicine, Columbia, MO 65211, USA.
authors: Tamila Stott
authors: TS
authors: Reynolds
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
authors: Nicole E
authors: NE
authors: Bernskoetter
authors: Research Service, Truman VA, Columbia, MO 65201, USA.
authors: Ashley F
authors: AF
authors: Szczodroski
authors: Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
authors: Kurt J
authors: KJ
authors: Bassuner
authors: Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
authors: Daniel L
authors: DL
authors: Kirkpatrick
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Internal Medicine, University of Missouri School of Medicine, Columbia, MO 65211, USA.
authors: Tammy L
authors: TL
authors: Rold
authors: Research Service, Truman VA, Columbia, MO 65201, USA.
authors: Gary L
authors: GL
authors: Sieckman
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Internal Medicine, University of Missouri School of Medicine, Columbia, MO 65211, USA; Department of Chemistry, University of Missouri, Columbia, MO 65211, USA.
authors: Timothy J
authors: TJ
authors: Hoffman
authors: Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
authors: James P
authors: JP
authors: Connors
authors: Research Service, Truman VA, Columbia, MO 65201, USA; Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA; University of Missouri Research Reactor Center, University of Missouri, Columbia, MO 65211, USA. Electronic address: smithcj@health.missouri.edu.
authors: Charles J
authors: CJ
authors: Smith
mesh_terms: D000085:Acetates / Q000737:chemistry; D021542:Amino Acids, Neutral / Q000737:chemistry; D015119:Aminocaproic Acid / Q000737:chemistry; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D001692:Biological Transport; D014408:Biomarkers, Tumor / Q000378:metabolism*; D001839:Bombesin / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D045744:Cell Line, Tumor; D060326:Chemistry Techniques, Synthetic; D003301:Copper Radioisotopes; D005260:Female; D043425:Glutamate Carboxypeptidase II / Q000378:metabolism*; D005977:Glutarates / Q000737:chemistry; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D008297:Male; D051379:Mice; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D011854:Radiochemistry; D018004:Receptors, Bombesin / Q000378:metabolism*; D014508:Urea / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: C572723:1-(1,3-carboxypropyl)-4,7-carboxymethyl-1,4,7-triazacyclononane; C544380:2-(3-(1,3-dicarboxypropyl)ureido)pentanedioic acid; D000085:Acetates; D021542:Amino Acids, Neutral; D000954:Antigens, Surface; D014408:Biomarkers, Tumor; D003301:Copper Radioisotopes; D005977:Glutarates; D006573:Heterocyclic Compounds, 1-Ring; D018004:Receptors, Bombesin; C013809:5-aminovaleric acid; D014508:Urea; C473848:FOLH1 protein, human; D043425:Glutamate Carboxypeptidase II; D001839:Bombesin; D015119:Aminocaproic Acid
keywords: Bombesin; Copper-64; Gastrin-releasing peptide; Prostate cancer; Prostate-specific membrane antigen