Radiolabeled Cationic Peptides for Targeted Imaging of Infection

Abstract

Molecular probes targeting bacteria provide opportunities to target bacterial infections in vivo for both imaging and therapy. In the current study, we report the development of positron emission tomography (PET) probes for imaging of live bacterial infection based on the small molecules HLys-DOTA, a polycationic peptide synthesized as the D-isomer (RYWVAWRNRG) conjugated to 1, 4, 7, 10-tetraazacyclododecane-N′,N″,N‴,N-tetraacetic acid (DOTA) and AB1-HLys-DOTA, which includes an unnatural amino acid AB1 that preferentially binds to bacteria membrane lipids with amine groups via formation of iminoboronates. HLys-DOTA and AB1-HLys-DOTA peptides were radiolabeled with 64Cu and investigated as PET imaging agents to track bacterial infection in vitro and in intramuscularly infected (IM) mice models. Cell uptake studies at 37°C in Staphylococcus aureus (SA) show higher uptake of 64Cu-AB1-HLys-DOTA; 98.47 ± 3.54% vs 64Cu-HLys-DOTA; 39.12 ± 3.27% at 24 h. Standard uptake values (SUV) analysis of the PET images resulted in mean SUV of 0.70 ± 0.08, 0.49 ± 0.04, and 0.31 ± 0.01 for 64Cu-AB1-HLys-DOTA and 0.17 ± 0.06, 0.16 ± 0.02, and 0.13 ± 0.01 for 64Cu-HLys-DOTA at 1, 4, and 24 h post injection, respectively, in the infected muscles. Similarly, in the biodistribution studies, dose uptake in the infected muscles was 4 times higher in the targeted 64Cu-AB1-HLys-DOTA group than in the 64Cu-HLys-DOTA group and 2‐3 times higher than in the PBS control group at 1, 4, and 24 h post injection. 64Cu-AB1-HLys-DOTA was able to distinguish between SA-infected muscle and Pseudomonas aeruginosa (PA) infected muscle with lower mean SUV of 0.28 ± 0.10 at 1 h post injection. This illustrates the utility of the AB1 covalently targeting group in synergy with the HLys peptide, which noncovalently binds to bacterial membranes. These results suggest that 64Cu-labeled AB1-HLys-DOTA peptide could be used as an imaging probe for detection of bacterial infection in vivo with specificity for Gram-positive bacteria.

Integrating a covalent probe with ubiquicidin fragment enables effective bacterial infection imaging

“…14 2-APBA probe incorporated AMPs have been established to improve binding to bacterial membrane due to the synergistic action of 2-APBA and the peptides. 15,16 Lysylation of PG is a well-known strategy employed by S. aureus to evade the binding of cationic antibiotics. 17 But covalent amine recognition strategy implies that lysyl-PG based detection can even help diagnose certain antimicrobial resistant strains.…”

Highlights of the Latest Developments in Radiopharmaceuticals for Infection Imaging and Future Perspectives

“…It has been labeled with 99m Tc via hydrazinonicotinamide (HYNIC) or other chelating agents to enable SPECT imaging (31,32) but relatively recent availability of PET-enabling 68 Ga has made the labeling with the latter supplanting other radionuclides due to the good match between short physical half-life of 68 Ga (68 min) and short plasma half-life of ubiquicidin and other AMPs (33,34). Other recently described AMPs-radionuclide combinations include [ 99m Tc-HYNIC/EDDA]-MccJ25 (35); 99m Tc-human beta-defensin 3 (HBD-3) (36); 64 Cu-labeled cationic peptides HLys-DOTA, synthesized as the D-isomer and AB1-HLys-DOTA, synthesized with an unnatural aminoacid to slow down the blood clearance (37); and 68 Ga-DOTA-CF-17 (38).…”

“…The advantage of AMPs over radiolabeled antibiotics is that AMP are larger molecules which should allow attachment of radiolabels without loss of the ability to bind bacteria in a specific manner; the disadvantage is their fast blood clearance due to enzymatic destruction and also high kidney uptake. Evaluation of AMPs in murine models of S. aureus (34,(36)(37)(38), mice with E. coli infection (35), P. aeruginosa (38) demonstrated the highest target to non-target ratios of 2-6 reached from 45 to 120 min post administration of radiolabeled peptides, showing their ability to distinguish the infected tissues from sterile inflammation. Auletta et al performed side by side comparison of 99m Tc-Ubiquicidin 29-41, 99m Tc-ciprofloxacin and 99m Tc-ciprofloxacin dithiocarbamate (CS2) in vitro and in mice with S. aureus and E.coli infections (32).…”

Peptide Multimerization as Leads for Therapeutic Development

“…For example, Khoshbakht et al developed a 18 F-FDG-Aoe-LIKKP-Pyr-F peptide with higher affinity for apoptotic cells and further hypothesised its potential in the diagnosis and therapy monitoring of apoptosisrelated pathologies [173]. Aweda et al [174] used a polycationic peptide conjugated with positron emission tomography (PET) probes, namely 1, 4, 7, 10-tetraazacyclododecane-N ,N ,N ,N-tetraacetic acid (DOTA) and AB1-HLys-DOTA, to target bacterial membrane lipids. These PET peptides can provide fascinating insights into the imaging of live bacterial infections, of which the 64 Cu-AB1-HLys-DOTA analogue can even distinguish infected muscle caused Staphylococcus aureus and Pseudomonas aeruginosa in vivo.…”