Three different procedures in labeling of Ubiquicidin with technetium 99m: a comparative study

UBI 29-41 (a derivative of antimicrobial peptide ubiquicidin) labelled with 99mTc is reported to discriminate between bacterial infections and sterile inflammatory processes. In this study, three lyophilized kit were performed, one of them based on the direct labelling with only SnCl2 as reducing agent, and other two based on 6- hydrazinopyridine-3-carboxylic acid (HYNIC) and tricine as a coligands with or without ethylenediamine -N,N’-diacetic acid (EDDA). Synthesis of UBI 29-41 was performed on solid phase using a standard Fmoc strategy. BOC-HYNIC was conjugated with peptide in solution. Three lyophilized kits were prepared as follows: kit 1: 40 μg UBI 29-41, 5 μg SnCl2, pH = 9; kit 2: 40 μg UBI 29-41, 40 μg SnCl2, 20 mg tricine, pH = 5.2; kit 3: 40 μg UBI 29- 41, 40 μg SnCl2, 15 mg tricine, 5 mg EDDA, pH = 7. With addition of 99mTcO4- solution, kits were labeled under specific conditions, and the radiochemical purity was evaluated by ITLC and HPLC methods. Stability and protein binding in human serum followed by in vitro binding to bacteria were assessed. Biodistribution of radiopeptides in staphylococcus aureus infected rats muscles were studied using ex vivo counting and scintigraphy. Radiochemical analysis indicated rapid and high labeling yield (>95%) for the three kits. Binding to bacteria for kit 2 was to some extent higher than that was obtained for the two other kits. Specific accumulation in infected thigh muscles, as indicated by T/NT ratios was 3.29, 4.6 and 3.77 for kit 1, 2 and 3, respectively. The HYNIC-UBI 29-41 labeled in presence of tricine as coligands (kit 2) showed the most promising results for further in vivo evaluation.