Selective uptake of surface-modified phospholipid vesicles by bone marrow macrophages in vivo

An advantage of using vesicles (liposomes) as drug delivery carriers is that their pharmacokinetics can be controlled by surface characteristics, which can permit specific delivery of the encapsulated agents to organs or cells in vivo. Here we report a vesicle formulation which targets the bone marrow after intravenous injection in rabbits. Surface modification of the vesicle with an anionic amphiphile; L-glutamic acid, N-(3-carboxy-1-oxopropyl)-, 1,5-dihexadecyl ester (SA) results in significant targeting of vesicles to bone marrow. Further incorporation of as little as 0.6 mol% of poly(ethylene glycol)-lipid (PEG-DSPE) passively enhanced the distribution of SA-vesicles into bone marrow and inhibited hepatic uptake. In this model, more than 60% of the intravenously injected vesicles were distributed to bone marrow within 6 h after administration of a small dose of lipid (15 mg/kg b.w.). Histological evidence indicates that the targeting was achieved due to uptake by bone marrow macrophages (BMMphi). The efficient delivery of encapsulated scintigraphic and fluorescent imaging agents to BMMphi suggests that vesicles are promising carriers for the specific targeting of BMMphi and may be useful for delivering a wide range of therapeutic agents to bone marrow.