The effect of poloxamer-407 on liposome stability and targeting to bone marrow: comparison with polystyrene microspheres

In accordance with our previous studies in the rabbit (Ilium L. and Davis S.S., Life Sci., 40 (1987) 1553–1560), coating of model polystyrene microspheres (70 nm in size) with poloxamer-407 was found to prevent their hepatic sequestration and to redirect a significant proportion of intravenously injected particles to the bone marrow in rats. In contrast, preincubation of a stable and ‘solid’ small unilamellar liposome preparation (DSPC/Chol/DCP in a molar ratio of 7: 7:1) with poloxamer-407 provided no evidence of poloxamer penetration or adsorption onto the vesicles, as determined by photon correlation spectroscopy and laser doppler anemometry. Further, no significant difference on biodistribution of poloxamer-preincubated liposomes was observed in comparison to control vesicles following intravenous administration into rats.