99m Tc-labeled teicoplanin and its biological evaluation in experimental animals for detection of bacterial infection

Labeling of teicoplanin with ^99m Tc using SnCl₂·2H₂O as reducing agent was performed. The dependence of the ^99m Tc-teicoplanin yield on the concentrations of teicoplanin and reducing agent, pH of the reaction mixture, reaction time, and reaction temperature was studied. Under optimum conditions (2 mg of teicoplanin, 5 μg of SnCl₂·2H₂O, pH 9, 30 min, 25°C), the labeling yield of ^99m Tc-teicoplanin of 87.7 ± 1.3% was achieved. ^99m Tc-teicoplanin is stable for 4 h after labeling; then its relative content decreased gradually to reach 81.7 ± 1.1% in 8 h. Biodistribution studies in mice with infection induced in the left thigh by Staphylococcus aureus were carried out. The bacterial infected thigh/contralateral thigh uptake ratio (T/NT) was evaluated. The time for the maximum accumulation of ^99mTc-teicoplanin in the infection site was 2 h after administration of the labeled compound. The abscess-to-muscle ratio for ^99m Tc-teicoplanin was 4.33 ± 0.3, while that for commercially available ^99m Tc-ciprofloxacin was 3.8 ± 0.5 under similar conditions. Thus, ^99m Tc-teicoplanin can be used for infection imaging.