753A LIPOSOME ENTRAPMENT OF DNA AND TRANSFER TO MAMMALIAN CELLS

Abstract

We investigated techniques for entrapment of DNA in phospholipid vesicles (liposomes) and transfer to mammalian cells. Large unilamellar vesicles prepared by reverse-phase evaporation were superior to other methods of liposome preparation and entrapped 25-35% of radioactively labelled lambda DNA into neutral phosphatidylcholine:cholesterol liposomes (7:2 molar ratio). The proportion of DNA entrapped was dependent on the lipid concentration and independent of the DNA concentration between 0.2 - 20 ug/ml. Entrapped lambda DNA remained intact and resistant to deoxyribonuclease digestion as judged by agarose gel electrophoresis. The reverse-phase method was also used to incorporate DNA into negatively-charged phosphatidylserine:phosphatidylcholine: cholesterol liposomes (2:7:2). To test for transfer of functional DNA into mammalian cells, we incubated liposome-entrapped SV40 DNA with monkey kidney cells in vitro. Infectious plaque formation was not observed using the neutral liposomes but did occur under similar conditions when the DNA was encapsulated into phosphatidylserine-containing vesicles. Preliminary experiments with the negatively-charged liposomes suggested that post-treatment of the cells with 10% dimethylsulfoxide increased frequency of plaques ~ 2-fold while 30% glycerol stimulated plaque formation at least 10-fold, confirming the recent report of Fraley et al. (J. Biol. Chem. 255:10431, 1980). This method of packaging exogenous DNA for delivery to mammalian cells may prove useful in gene transfer experiments.