Reconstituted Sendai virus envelopes as biological carriers: dual role of F protein in binding and fusion with liver cells

We have assessed the potential of reconstituted Sendai viral envelopes containing only the fusion protein (F-virosomes) as biological carriers for the delivery of drugs and macromolecules. [<SUP>125</SUP>I]lysozyme entrapped in F-virosome is used to study its distribution in various organs of Balb/c mouse in vivo as a function of dose and time. F-virosomes injected intravenously are rapidly cleared from circulation. A major percentage (55-60%) of vesicle contents is delivered to liver at 15 min after injection, showing thereby the liver to be the major site for the accumulation of vesicles. Uptake of virosomes by liver is found to reach a near saturation level at a dose of 0.5 mg F-protein associated with virosomes. In competition studies, the inhibitory effect of asialofetuin on the uptake of F-virosomes suggests the involvement of asialoglycoprotein receptor in its recognition by hepatic parenchymal cells. Incorporation of asialoganglioside-GM<SUB>1</SUB> in the F-virosomes enhanced the uptake by about 1.6-fold. The observed specific interaction of hepatic receptor with F-protein containing a terminal galactose moiety is further supported by degalactosylation of F-virosomes with hard-shelled clam exoglycosidase. The uptake of degalactosylated F-virosomes by liver is found to be significantly reduced. The subcellular radioactivity profile in liver cells exhibits a considerable decrease in cytosolic localisation of the degalactosylated F-virosomal contents with a concomitant increase in their accumulation in lysosomal/mitochondrial fraction as compared to the untreated virosomes. Trypsinized and heat-treated F-virosomes also reflect similar subcellular distribution profile as that of degalactosylated virosomes. Moreover, F-virosomes are able to interact and deliver [<SUP>125</SUP>I]lysozyme to the HepG2 cells in culture in the presence of a potent inhibitor of endocytotic process. These results indicate the involvement of specific binding of F-proteins with hepatic receptors followed by their fusion with the membrane of liver cells in the delivery of [<SUP>125</SUP>I]lysozyme. The findings reported here open up the possibility of using F-virosomes with defined specificity as fusogenic vehicles for efficient delivery of drugs and biologically active macromolecules both in vivo and in vitro