title: Detection of sites of infection in mice using 99mTc-labeled PN(2)S-PEG conjugated to UBI and 99mTc-UBI: a comparative biodistribution study.
abstract: The antimicrobial peptide ubiquicidin (UBI) directly labeled with technetium-99m ((99m)Tc) has recently been shown to be specifically taken up at sites of infection; however, its chemical structure is not well defined. To address this problem, the aim of the present study was to label UBI using poly(ethyleneglycol)-N-(N-(3-diphenylphosphinopropionyl)glycyl)-S-tritylcysteine ligand (PEG-PN(2)S) in order to compare its ability to detect infection sites with that of (99m)Tc-UBI.
  
  
  METHODS
  The PN(2)S-PEG-UBI conjugate was prepared and labeled with (99m)Tc, and its radiochemical purity was subsequently assessed. The stability of the conjugate to cysteine challenge and dilution with both saline solution and phosphate buffer was determined and serum stability and protein binding were also assessed. In vivo studies were carried out in healthy mice to study the biodistribution of (99m)Tc-PN(2)S-PEG-UBI and its precursor (99m)Tc-PN(2)S-PEG and in infected mice to compare the uptakes of (99m)Tc-UBI and (99m)Tc-PN(2)S-PEG-UBI at the site of infection using scintigraphic imaging and ex vivo tissue counting.
  
  
  RESULTS
  (99m)Tc-PN(2)S-PEG-UBI was obtained with high radiochemical purity (98+/-1%) and high stability. The amphiphilic nature of the conjugate leads to a tendency to form micellar aggregates that explain the high protein binding values obtained. Biodistribution studies in mice showed low renal clearance followed by a predominant reticuloendothelial system clearance that limits its application in the abdominal area. Statistical analysis revealed no significant difference between (99m)Tc-UBI and (99m)Tc-PN(2)S-PEG-UBI uptake in infected mouse thigh, and the site of infection was clearly visualized using scintigraphic imaging.
  
  
  CONCLUSIONS
  (99m)Tc-PN(2)S-PEG-UBI proved to be as effective as (99m)Tc-UBI in detecting sites of infection; however, the well-defined chemical structure of (99m)Tc-PN(2)S-PEG-UBI makes it a better candidate for clinical imaging of infection.
authors.affiliation: Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy. lmalafort@yahoo.com
authors.forename: Laura
authors.initials: L
authors.lastname: Meléndez-Alafort
authors.forename: Anna
authors.initials: A
authors.lastname: Nadali
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Pasut
authors.forename: Elena
authors.initials: E
authors.lastname: Zangoni
authors.forename: Raffaele
authors.initials: R
authors.lastname: De Caro
authors.forename: Luca
authors.initials: L
authors.lastname: Cariolato
authors.forename: Maria Cecilia
authors.initials: MC
authors.lastname: Giron
authors.forename: Ignazio
authors.initials: I
authors.lastname: Castagliuolo
authors.forename: Francesco M
authors.initials: FM
authors.lastname: Veronese
authors.forename: Ulderico
authors.initials: U
authors.lastname: Mazzi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics*; D003545:Cysteine / Q000031:analogs & derivatives* / Q000737:chemistry; D051379:Mice; D015609:Organotechnetium Compounds / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D012269:Ribosomal Proteins / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics*; D013194:Staining and Labeling; D013203:Staphylococcal Infections / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D023181:Antimicrobial Cationic Peptides; D015609:Organotechnetium Compounds; D012269:Ribosomal Proteins; C539758:poly(ethyleneglycol)-N-(N-(3-diphenylphosphinopropionyl)glycyl)-S-tritylcysteine; C040469:ribosomal protein S30; D011092:Polyethylene Glycols; D003545:Cysteine