Delivery to cancer cells of antisense L-myc oligonucleotides incorporated in fusogenic, cationic-lipid-reconstituted influenza-virus envelopes (cationic virosomes).

Antisense oligodeoxy-nucleoside phosphorothioates (OPTs) of L-myc were encapsulated into reconstituted influenza-virus-A envelopes (virosomes). The envelopes of the virosomes consisted of a single positively charged (cationic) lipid bilayer. Binding of cationic virosomes to cellular receptors that are membrane glycoproteins or glycolipids containing terminal sialic acid is mediated by the hemagglutinin glycoprotein (HA) of the influenza virus. After internalization through receptor-mediated endocytosis, cationic virosomes fuse efficiently with the membranes of the endosomal-cell compartment, and as a consequence the encapsulated OPT are delivered to the cell cytoplasma. Examination by fluorescence microscopy of the cellular uptake of cationic virosomes containing fluorescein-labeled OPT showed rapid and efficient incorporation of virosomes. Addition of cationic virosomes (75-150 microl) containing antisense L-myc OPT in the picomolar range to small-cell-lung-cancer (SCLC) cell cultures that expressed highly the L-myc oncogene led to strong inhibition of thymidine incorporation in a concentration-dependent manner. Virosome-entrapped sense L-myc OPT and random-order OPT had only minimal effects on the thymidine uptake. Cells of SCLC cell line NCI-H82 expressing a very low level of L-myc were not affected by antisense-L-myc virosomes. In Western-blot analysis, expression of L-myc protein was suppressed in the antisense-virosome-treated NCI-H209 cells but not in untreated control NCI-H209 cells. These results suggest that cationic virosomes may have great potential as an efficient delivery system for antisense oligonucleotides in cancer therapy.