99mTc-Alafosfalin: an antibiotic peptide infection imaging agent

Abstract

The radiolabeled antibiotic peptide 99mTc-alafosfalin was assessed as an infection imaging agent in a rat model by comparison with 99mTc-DTPA and 99mTc-leukocytes. 99mTc-alafosfalin was prepared via an instant cold kit and 99mTc-leukocytes were prepared using 99mTc-stannous fluoride colloid in an ex vivo labeling procedure of whole blood. In separate experiments, the three radiotracers were administered to rats infected with staphylococcus aureus. Quantitative biodistribution studies were performed as well as scintigraphic images and histopathology. 99mTc-alafosfalin is a stable product, obtained in high radiochemical purity (>95%). This agent was mainly renally excreted, with low liver, spleen and bone uptake, and resulted in a mean ratio of infected/non-infected thighs of 4.3/1.0 at 4 hr post radiotracer injection. 99mTc-DTPA gave a corresponding ratio of 1.9/1.0 and 99mTc-leukocytes gave 20.0/1.0 at the same time point. An in vitro assay found the level of 99mTc-alafosfalin binding to staphylococcus aureas higher than 99mTc-DTPA (10% versus 1% respectively). 99mTc-alafosfalin accumulates at sites of infection in a rat model better than the perfusion molecule 99mTc-DTPA, yet less than 99mTc-leukocytes. The distribution characteristics of this 99mTc-antibiotic peptide would be an advantage in imaging abdominal and soft tissue infection.