A simple method for producing a technetium-99m-labeled liposome which is stable in vivo

A new method for labelling preformed liposomes with technetium-99m (99mTc) has been developed which is simple to perform and stable in vivo. Previous 99mTc-liposome labels have had variable labeling efficiencies and stability. This method consistently achieves high labeling efficiencies (greater than 90%) with excellent stability. A commercially available radiopharmaceutical kit--hexamethylpropyleneamine oxime (HM-PAO)--is reconstituted with 99mTcO4- and then incubated with preformed liposomes that encapsulate glutathione. The incubation takes only 30 min at room temperature. Liposomes that co-encapsulate other proteins such as hemoglobin or albumin, in addition to glutathione, also label with high efficiency. Both in vitro and in vivo studies indicate good stability of this label. Rabbit images show significant spleen and liver uptake at 2 and 20 h after liposome infusion without visualization of thyroid, stomach or bladder activity. This labeling method can be used to study the biodistribution of a wide variety of liposome preparations that are being tested as novel drug delivery systems. This method of labeling liposomes with 99mTc may also have applications in diagnostic imaging.