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 carrie rs for the delivery of drugs and macromolecules. [I-125]lysozyme entra pped 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 i njected intravenously are rapidly cleared from circulation. A major pe rcentage (55-60%) of vesicle contents is delivered to liver at 15 min after injection, showing thereby the liver to be the major site for th e accumulation of vesicles. Uptake of virosomes by liver is found to r each a near saturation level at a dose of 0.5 mg F-protein associated with virosomes. In competition studies, the inhibitory effect of asial ofetuin on the uptake of F-virosomes suggests the involvement of asial oglycoprotein receptor in its recognition by hepatic parenchymal cells . Incorporation of asialoganglioside-GM1 in the F-virosomes enhanced t he uptake by about 1.6-fold. The observed specific interaction of hepa tic receptor with F-protein containing a terminal galactose moiety is further supported by degalactosylation of F-virosomes with hard-shelle d clam exoglycosidase. The uptake of degalactosylated F-virosomes by l iver is found to be significantly reduced. The subcellular radioactivi ty profile in liver cells exhibits a considerable decrease in cytosoli c localisation of the degalactosylated F-virosomal contents with a con comitant increase in their accumulation in lysosomal/mitochondrial fra ction as compared to the untreated virosomes. Trypsinized and heat-tre ated F-virosomes also reflect similar subcellular distribtuion profile as that of degalactosylated virosomes. Moreover, F-virosomes are able to interact and deliver [I-125]lysozyme to the HepG2 cells in culture in the presence of a potent inhibitor of endocytotic process. These r esults 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 [I-125]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.