title: Comparison of two peptide radiotracers for prostate carcinoma targeting.
abstract: OBJECTIVE
  Scintigraphy is generally not the first choice treatment for prostate cancer, although successful studies using bombesin analog radiopeptides have been performed. Recently, a novel peptide obtained using a phage display library demonstrated an affinity for prostate tumor cells. The aim of this study was to compare the use of a bombesin analog to that of a phage display library peptide (DUP-1) radiolabeled with technetium-99m for the treatment of prostate carcinoma. The peptides were first conjugated to S-acetyl-MAG3 with a 6-carbon spacer, namely aminohexanoic acid.
  
  
  METHODS
  The technetium-99m labeling required a sodium tartrate buffer. Radiochemical evaluation was performed using ITLC and was confirmed by high-performance liquid chromatography. The coefficient partition was determined, and in vitro studies were performed using human prostate tumor cells. Biodistribution was evaluated in healthy animals at various time points and also in mice bearing tumors.
  
  
  RESULTS
  The radiochemical purity of both radiotracers was greater than 95%. The DUP-1 tracer was more hydrophilic (log P = -2.41) than the bombesin tracer (log P = -0.39). The biodistribution evaluation confirmed this hydrophilicity by revealing the greater kidney uptake of DUP-1. The bombesin concentration in the pancreas was greater than that of DUP-1 due to specific gastrin-releasing peptide receptors. Bombesin internalization occurred for 78.32% of the total binding in tumor cells. The DUP-1 tracer showed very low binding to tumor cells during the in vitro evaluation, although tumor uptake for both tracers was similar. The tumors were primarily blocked by DUP1 and the bombesin radiotracer primarily targeted the pancreas.
  
  
  CONCLUSIONS
  Further studies with the radiolabeled DUP-1 peptide are recommended. With further structural changes, this molecule could become an efficient alternative tracer for prostate tumor diagnosis.
authors.affiliation: Institute of Energy and Nuclear Research, Radiopharmacy Center, São Paulo, Brazil. blfaintuch@hotmail.com
authors.forename: Bluma Linkowski
authors.initials: BL
authors.lastname: Faintuch
authors.forename: Erica A
authors.initials: EA
authors.lastname: Oliveira
authors.forename: Eutimio G F
authors.initials: EG
authors.lastname: Nunez
authors.forename: Ana M
authors.initials: AM
authors.lastname: Moro
authors.forename: P K
authors.initials: PK
authors.lastname: Nanda
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Smith
mesh_terms: D000614:Aminocaproates / Q000737:chemistry* / Q000493:pharmacokinetics; D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism; D001839:Bombesin / Q000031:analogs & derivatives; D003470:Culture Media; D004195:Disease Models, Animal; D006801:Humans; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009842:Oligopeptides / Q000737:chemistry* / Q000493:pharmacokinetics; D010179:Pancreas / Q000000981:diagnostic imaging; D010455:Peptides; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D011897:Random Allocation; D018004:Receptors, Bombesin / Q000032:analysis / Q000378:metabolism; D013667:Technetium
chemical_list: D000614:Aminocaproates; D014408:Biomarkers, Tumor; D003470:Culture Media; C501462:DUP-1 peptide; D009842:Oligopeptides; D010455:Peptides; D019275:Radiopharmaceuticals; D018004:Receptors, Bombesin; C077650:N-(phenylethylphosphonyl)-glycyl-prolyl-aminohexanoic acid; D013667:Technetium; D001839:Bombesin