Detection of sites of infection in mice using 99mTc-labeled PN2S-PEG conjugated to UBI and 99mTc-UBI: a comparative biodistribution study

Meléndez-Alafort, Laura; Nadali, Anna; Pasut, Gianfranco; Zangoni, Elena; De Caro, Raffaele; Cariolato, Luca; Giron, Maria Cecilia; Castagliuolo, Ignazio; Veronese, Francesco M.; Mazzi, Ulderico

doi:10.1016/j.nucmedbio.2008.10.011

« Previous Next »Nuclear Medicine and Biology
Volume 36, Issue 1 , Pages 57-64, January 2009

Detection of sites of infection in mice using ^99mTc-labeled PN₂S-PEG conjugated to UBI and ^99mTc-UBI: a comparative biodistribution study

Laura Meléndez-Alafort
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
- Corresponding author. Tel.: +39 049 827 5342; fax: +39 049 827 5366.
Anna Nadali
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Gianfranco Pasut
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Elena Zangoni
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Raffaele De Caro
- Department of Anatomy and Physiology, University of Padua, 35131 Padova, Italy
Luca Cariolato
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Maria Cecilia Giron
- Department of Pharmacology and Anesthesiology, University of Padua, 35131 Padova, Italy
Ignazio Castagliuolo
- Department of Histology, Microbiology and Medical Biotechnologies, University of Padua, 35131 Padova, Italy
Francesco M. Veronese
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy
Ulderico Mazzi
- Department of Pharmaceutical Sciences, University of Padua, 35131 Padova, Italy

Received 9 July 2008; received in revised form 15 October 2008; accepted 25 October 2008.

Abstract

The antimicrobial peptide ubiquicidin (UBI) directly labeled with technetium-99m (^99mTc) 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-PN₂S) in order to compare its ability to detect infection sites with that of ^99mTc-UBI.

Methods

The PN₂S-PEG-UBI conjugate was prepared and labeled with ^99mTc, 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 ^99mTc-PN₂S-PEG-UBI and its precursor ^99mTc-PN₂S-PEG and in infected mice to compare the uptakes of ^99mTc-UBI and ^99mTc-PN₂S-PEG-UBI at the site of infection using scintigraphic imaging and ex vivo tissue counting.

Results

^99mTc-PN₂S-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 ^99mTc-UBI and ^99mTc-PN₂S-PEG-UBI uptake in infected mouse thigh, and the site of infection was clearly visualized using scintigraphic imaging.

Conclusions

^99mTc-PN₂S-PEG-UBI proved to be as effective as ^99mTc-UBI in detecting sites of infection; however, the well-defined chemical structure of ^99mTc-PN₂S-PEG-UBI makes it a better candidate for clinical imaging of infection.

Keywords: Ubiquicidin, Infection detection, Labeled peptides, PN₂S, PEG, Technetium-99m