Labelling of liposomal of Budesonide with ^99mTc for pulmonary targeting studies.

Current methods for radiolabelling (^99mTc) of liposomes involve chelating the radioactivity into appropriate chelators like HYNIC and HMPAO, which are introduced into aqueous interior of the liposomes; or chemical derivatisation of the chelator by incorporating hydrophobic groups, which binds on the surface of liposome; use of ampiphilic polychelating polymers. The main limitation of these methods is stability. An attempt was made to label liposomal aerosols of Budesonide with ^99mTc to determine the drug deposition and distribution pattern of the inhaled drug in the lungs.

Budesonide loaded liposomes were prepared by lipid film hydration technique. The following methods were attempted to label the liposomes: (a) Rehydration of the liposomes during preparation using ^99mTco₄⁻ solution; (b) Feasibility of using lipophilic complexes like ^99mTc-Mebrofenin and ^99mTc-ECD was evaluated, by incubating them with rat esterase enzyme and glutathione followed by extraction in chloroform; (c) Labelling with ^99mTc by using SnCl₂ as a reducing agent. Very low labeling (10%) was observed during rehydration. Labelling efficiency with Mebrofenin and Tc-ECD was very less, as negligible activity was detected in chloroform, whereas with SnCl₂ it was maximum (97%); hence this method was optimised further for pH, incubation time, SnCl₂ concentration, amount of lipids. The labelling stability was confirmed in saline, in human plasma, on nebulisation and in vivo by injecting in rabbits; and was found to be more than 12 hr. In Conclusion, liposomes could be effectively labelled with ^99mTc, using SnCl₂ as a reducing agent, and the technique can serve as a useful tool to study deposition and retention of liposomal systems in the target organ.