⁶⁸Ga-labeled ubiquicidin for monitoring of mouse infected with Staphylococcus aureus

Ubiquicidin is a cationic, antimicrobial peptide found in the innate hose defence against pathogens. The peptide selectively interacts with the surface of microorganism. This work aimed to develop the radiopharmaceutical for infection imaging using antimicrobial peptide. Optimum labelling condition to obtain radiopharmaceutical purity (RCP) of ⁶⁸Ga-DOTA-ubiquicidin (29-41) more than 90% was evaluated. The RCP more than 95% was achievable with 30 micrograms peptide at solution reaction pH 4. Stability testing of the labelled peptide was also studied by resembling to in vitro condition using fresh frozen human plasma. The radiolabelled peptide retained its RCP >90% after 4 hours of incubation. Animal study was performed in infected and sterile inflamed mice groups with Staphylococcus aureus or sterilized S. aureus at the left thigh 24 hours prior administration of ⁶⁸Ga-DOTA-UBI. Radioactivity count rate at the infected or sterilized inflamed site of the left thigh of each mouse was compared and normalized with radioactivity count accumulated in normal muscle of its right thigh. Accumulation of ⁶⁸Ga-DOTA-UBI in muscle of infected mice was significantly greater than the sterile inflamed mice; 4.62 ± 3.44 and 1.53 ± 1.73, respectively, at 1 hour post injection. These results showed the efficacy of ⁶⁸Ga-DOTA-UBI as a radiopharmaceutical for monitoring of bacterial infection.