Synthesis and validation of cFLFLF-PEG76-99mTc, a neutrophil-targeting gamma imaging probe, with a bacteria-infected rabbit model

Objectives Peptide cinnamoyl-F-(D)L-F-(D)L-F (cFLFLF) was reported as a high-affinity binding ligand to formyl peptide receptors (FPRs) on neutrophil without alteration to neutrophil propensity. We aim to develop a novel neutrophil-targeting gamma imaging probe for detection of inflammatory and infectious diseases.

Methods A formyl peptide receptor binding peptide cFLFLF was sequentially conjugated with polyethylene glycol moiety and a bifunctional radiometal chelator hydrazinonictinamide (HYNIC), followed by 99mTc conjugation with tricine/nicotinic acid as co-ligands. The resulting probe, cFLFLF-PEG76-99mTc was evaluated by in vitro binding affinity studies with human neutrophils. SPECT scans (Infinia VC Hawkeye SPECT/CT) and biodistribution studies in rabbit infectious models were also performed to evaluate the in vivo performance of the probe.

Results cFLFLF-PEG76-99mTc could bind neutrophils specifically. The half-life time of blood clearance was 86 min. Biodistribution studies showed that cFLFLF-PEG76-99mTc was mainly concentrated in kidney and spleen at 3h post injection. The uptake ratio of infected/contralateral muscles was 3.31±0.54 at the same time point. The SPECT scans showed that infection sites were most clearly visualized at 3h after injection with cFLFLF-PEG76-99mTc and infectious/contralateral limbs muscle ratio was 3.27±0.22. Excess amount of neutrophils were confirmed in the infected sites by Hematoxylin and Eosin Staining.

Conclusions The 99mTc labeled peptide, cFLFLF-PEG76-99mTc, which targeting FPR of neutrophils, is a promising gamma imaging probe for infection and inflammation.

Research Support This work was financially supported by the Natural Science Foundation of Hubei Province, China (Grant No. 2011CDB551), National Nature Science Foundation of(Grant No.86271600).