Investigation of technetium-99m labelled infection imaging radiopharmaceutical based on antibacterial peptide

Current nuclear medicine techniques enable visualization of infection and inflammation with the aid of technetium-99m (99mTc) tracers. However, these radiopharmaceuticals cannot distinguish between infections and sterile inflammatory lesions. Improvement in the imaging of the inflammation foci could be achieved either by truly ''infection specific'' agent such as antimicrobial peptide or by ''nonspecific agent'' showing faster pharmacokinetics and less normal tissue radioactivity uptake than that displayed by radiolabelled cells or human imunoglobulin, hIgG. The aim of our work was to perform the experiments on 99mTc labelled antibacterial peptide. UBI (ubiquicidin derivative) could be labelled with 99mTc directly using potassium borohydride and stannous pyrophosphate as reduction environment. The ingredients for 99mTc labelling of UBI were prepared in the form of dry kit. Radiochemical purity of 99mTc-UBI was checked by instant thin layer chromatography (ITLC) and by reverse-pase HPLC and found to exceed 95%. The kits were stable for the period of over six months. 99mTc-UBI was tested in vitro for binding to proteins in human plasma and for binding to human leukocytes. The biodistribution of 99mTc-UBI was evaluated in normal mice. The complex is excreted via kidneys mostly. The scintigrams of experimental thigh muscle infections (Staphylococcus aureus) were made and compared to those obtained using heat killed bacteria. (author)