title: In vitro and in vivo evaluation of a 64Cu-labeled NOTA-Bn-SCN-Aoc-bombesin analogue in gastrin-releasing peptide receptor expressing prostate cancer.
abstract: BACKGROUND
  Bombesin (BN) is an amphibian peptide that binds to the gastrin-releasing peptide receptor (GRPR). It has been demonstrated that BN analogues can be radiolabeled for potential diagnosis and treatment of GRPR-expressing malignancies. Previous studies have conjugated various chelators to the eight C-terminal amino acids of BN [BN(7-14)] for radiolabeling with 64Cu. Recently, (1,4,7-triazacyclononane-1,4,7-triacetic acid) (NOTA) has been evaluated as the five-coordinate 64Cu complex, with results indicating GRPR-specific tumor uptake. This study aimed to conjugate S-2-(4-isothiocyanatobenzyl)-NOTA (p-SCN-Bn-NOTA) to BN(7-14) such that it could form a six-coordinate complex with 64Cu and to evaluate the resulting peptide.
  
  
  METHODS
  p-SCN-NOTA was conjugated to 8-aminooctanoic acid (Aoc)-BN(7-14) in solution to yield NOTA-Bn-SCN-Aoc-BN(7-14). The unlabeled peptide was evaluated in a cell binding assay using PC-3 prostate cancer cells and 125I-Tyr4-BN to determine the IC50 value. The peptide was radiolabeled with 64Cu and evaluated for internalization into PC-3 cells and for tumor uptake in mice bearing PC-3 xenografts using biodistribution and micro-positron emission tomography imaging studies.
  
  
  RESULTS
  The binding assay demonstrated that NOTA-Bn-SCN-Aoc-BN(7-14) bound with high affinity to GRPR with an IC50 of 1.4 nM. The radiolabeled peptide demonstrated time-dependent internalization into PC-3 cells. In vivo, the peptide demonstrated tumor-specific uptake and imaging that were comparable to those of previously reported 64Cu-labeled BN analogues.
  
  
  CONCLUSIONS
  These studies demonstrate that 64Cu-NOTA-Bn-SCN-Aoc-BN(7-14) binds to GRPR-expressing cells and that it can be used for imaging of GRPR-expressing prostate cancer.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO 63108, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Craft
authors.forename: Ravindra A
authors.initials: RA
authors.lastname: De Silva
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Lears
authors.forename: Rebecca
authors.initials: R
authors.lastname: Andrews
authors.forename: Kexian
authors.initials: K
authors.lastname: Liang
authors.forename: Samuel
authors.initials: S
authors.lastname: Achilefu
authors.forename: Buck E
authors.initials: BE
authors.lastname: Rogers
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D001839:Bombesin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000493:pharmacokinetics; D002210:Caprylates / Q000737:chemistry*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D003301:Copper Radioisotopes; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006801:Humans; D017879:Isothiocyanates / Q000737:chemistry*; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology*; D018004:Receptors, Bombesin / Q000378:metabolism*; D014057:Tomography, X-Ray Computed
chemical_list: D002210:Caprylates; D003301:Copper Radioisotopes; D006571:Heterocyclic Compounds; D017879:Isothiocyanates; D018004:Receptors, Bombesin; C046323:omega-aminocaprylic acid; C082060:2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid; D001839:Bombesin