Bone marrow-targeted liposomal carriers: A feasibility study in nonhuman primates

Background & aims: Recently, we described a novel surface-modified lipid vesicle formulation (liposome) that had very high targeting to bone marrow in normal rabbits. Because the bone marrow is the site of hematopoiesis, bone marrow-targeted drug-delivery systems have many potential applications. In this study we investigated whether these bone marrow-targeted vesicles are also similarly effective for bone marrow targeting in rhesus monkeys, a primate animal model that is more relevant to humans. Materials & methods: The preformed vesicles encapsulating 30mM glutathione were labeled with technetium-99m (^99mTc) for scintigraphic imaging. The vesicles were 216 ± 21 nm in diameter with a negative surface charge composed of DPPC, cholesterol, anionic amphiphile and poly(ethylene glycol)-DSPE (1:1:0.2:0.013 molar ratio). Results: The whole-body images of rhesus monkeys receiving intravenous ^99mTc vesicles revealed high uptake of the ^99mTc vesicles in bone marrow. Based on image analysis, we estimated that approximately 70% of the injected dose of the ^99mTc vesicles was taken up by the bone marrow. Conclusion: This finding increases the feasibility of using this bone marrow-specific drug-delivery system for clinical applications.