Technetium-99m labelled antimicrobial peptides discriminate between bacterial infections and sterile inflammations

Abstract

The aim of this study was to select technetium-99m labelled peptides that can discriminate between bacterial infections and sterile inflammations. For this purpose, we first assessed the binding of various 99mTc-labelled natural or synthetic peptides, which are based on the sequence of the human antimicrobial peptide ubiquicidin (UBI) or human lactoferrin (hLF), to bacteria and to leucocytes in vitro. In order to select peptides that preferentially bind to bacteria over host cells, radiolabelled peptides were injected into mice intraperitoneally infected with Klebsiella pneumoniae (K. pneumoniae) and the amount of radioactivity associated with the bacteria and with the leucocytes was quantitated. The next phase focussed on discrimination between bacterial infections and sterile inflammatory processes using 99mTc-labelled peptides in mice intramuscularly infected with various bacteria (e.g. multi-drug-resistant Staphylococcus aureus) and in animals that had been injected with lipopolysaccharides (LPS) of bacterial origin to create a sterile inflammatory process. Also, we studied the distribution of 99mTc-labelled UBI 29-41 and UBI 18-35 in rabbits having an experimental thigh muscle infection with K. pneumoniae and in rabbits injected with LPS. Based on the results of our in vitro and in vivo binding assays, two peptides, i.e. UBI 29-41 and UBI 18-35, were selected as possible candidates for infection imaging. The radiolabelled peptides can detect infections with both gram-positive and gram-negative bacteria in mice as early as 5-30 min after injection, with a target-to-non-target (T/NT) ratio between 2 and 3; maximum T/NT ratios were seen within 1 h after injection. In rabbits, high T/NT ratios (>5) for 99mTc-labelled UBI 29-41 were observed from 1 h after injection. No accumulation of the selected 99mTc-labelled UBI-derived peptides was observed in thighs of mice and rabbits previously injected with LPS. Scintigraphic investigation into the biodistribution of 99mTc-labelled UBI peptides revealed that these peptides were rapidly removed from the circulation by renal excretion. Similar data were observed for 99mTc-labelled defensin 1-3. Our data for 99mTc-labelled hLF and related peptides indicate that these compounds are less favourable for infection detection. Taken together, 99mTc-labelled UBI 18-35 and UBI 29-41 enable discrimination between bacterial infections and sterile inflammatory processes in both mice and rabbits. Based on their characteristics, we consider these peptides the candidates of preference for detection of bacterial infections in man.

Investigation of four 99mTc-labeled bacteriophages for infection-specific imaging

“…Binding of the 99m Tc-labeled phages P22 and E79 to host bacteria were reduced in the presence of the non-ionic detergent Tween-80, a detergent that disrupts lipid-lipid and lipid-protein interactions (4). As shown in Figure 2 the addition of Tween-80 to the incubation buffer reduced the binding of 99m Tc-P22 to its host S. enterica to levels observed for the non host bacteria, P. aeruginosa and E. coli, while having no influence on binding to the non host bacteria.…”

Diagnostic value of 99mTc-ubiquicidin scintigraphy for osteomyelitis and comparisons with 99mTc-methylene diphosphonate scintigraphy and magnetic resonance imaging

“…In all radiopharmaceuticals, antimicrobial peptides that attach directly to bacteria are preferred over pharmaceuticals that have an indirect approach (such as binding to leukocytes or antigranulocyte antibodies) [22]. Among the peptides, 99m Tc-UBI 29-41 scans have shown the most promising results for differentiation between infection and inflammation in animal models [11,12,30] and also in limited human studies [22].…”

“…The most promising ones among them are 99m Tc-labeled cationic antimicrobial peptides originating from ubiquicidin (UBI), which remarkably bind to microorganisms [10,11]. These radiolabeled antimicrobial peptides result in the rapid visualization of Gram-positive and Gram-negative bacterial infections [12] and fungi [10], with the least accumulation at sites of sterile inflammation [11]. Furthermore, 99m Tc-UBI 29-41 has been used to monitor the effectiveness of treatment of experimental infections in animals [13].…”

Molecular imaging in musculoskeletal infections with 99mTc-UBI 29-41 SPECT/CT

“…The Coordinated Research Project (CRP) established by the IAEA over the past decade has encouraged the evaluation of UBI as an effective tracer. Studies under the CRP and others have reported UBI to exhibit a high labelling efficiency > 90%, good stability, rapid uptake and clearance via the kidneys, excellent ability to detect infection focus and its differentiation from sterile inflammation as well as therapy response assessment [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Tc-UBI 29-41 scintigraphy of a 38-year-old man in whom posttraumatic osteomyelitis of the right tibia was suspected.…”