Figure 1.

(A) Scheme showing plasmid (DNA) encapsulated in pegylated immunoliposomes constructed from neutral lipids. There are approximately 3000 strands of polyethylene glycol of 2000 Da molecular mass, designated PEG 2000, attached to the liposome surface, and about 1% of the PEG strands is conjugated with an mAb to a BBB receptor. (B) The mean diameter of the pegylated liposomes encapsulating the pGL2 plasmid DNA is 73 nm. (C) Liposomes before (lane 2) and after (lane 1) DNase 1/exonuclease III treatment were resolved with 0.8% agarose gel electrophoresis followed by ethidium bromide (Et Br) staining. DNA molecular weight size standards are shown in the left hand side. Approximately 50% of the DNA associated with the pegylated liposome was bound to the exterior of the liposome (lane 2), and the exteriorized DNA was quantitatively removed by the nuclease treatment (lane 1). A trace amount of the pGL2 plasmid was radiolabeled with ³²P, and film autoradiography of the gel showed a single 5.8-kb band with no low molecular weight radiolabeled DNA. (D) The conjugation of the OX26 mAb to the pegylated liposomes carrying the encapsulated pGL2 plasmid DNA after nuclease digestion is demonstrated by Sepharose CL-4B gel filtration chromatography. A trace amount of the encapsulated pGL2 plasmid DNA was labeled with ³²P, and a trace amount of the OX26 mAb was radiolabeled with ³H. The study shows the comigration of the conjugated OX26 mAb and the encapsulated pGL2 plasmid DNA.