dioleoyl-phosphatidylethanolamine and 1-2-dimyristoylphosphatidylethanolamine

This study investigates the impact of the chemical nature of lipids and additive on the formulation and properties of pH sensitive liposomes. The objective is to understand the respective role of the formulation parameters on the liposome properties in order to optimize the conditions for efficient encapsulation of doxorubicin (DOX). These liposomes should be stable at physiological pH, and disrupt in slightly acidic media such as the tumor microenvironment to release their DOX load. The major challenge for encapsulating DOX in pH sensitive liposomes lies in the fact that this drug is soluble at low pH (when the pH-sensitive liposomes are not stable), but the DOX aqueous solubility decreases in the pH conditions corresponding to the stability of the pH-sensitive liposomes. The study of pH-sensitivity of liposomes was conducted using carboxyfluorescein (CF) encapsulated in high concentration, i.e. quenched, and following the dye dequenching as sensor of the liposome integrity. We studied the impact of (i) the chemical nature of lipids (dioleoyl phosphatidyl ethanolamine (DOPE), palmitoyl-oleoyl phosphatidyl ethanolamine (POPE) and dimyristoyl phosphatidyl ethanolamine (DMPE)) and (ii) the lipid/stabilizing agent ratio (alpha-tocopheryl succinate), on the pH sensitivity of the liposomes. Optimized liposome formulations were then selected for the encapsulation of DOX by an active loading procedure, i.e. driven by a difference in pH inside and outside the liposomes. Numerous experimental conditions were explored, in function of the pH gradient and liposome composition, which allowed identifying critical parameters for the efficient DOX encapsulation in pH-sensitive liposomes.

Topics: alpha-Tocopherol; Chemistry, Pharmaceutical; Doxorubicin; Fluoresceins; Hydrogen-Ion Concentration; Lipids; Liposomes; Phosphatidylethanolamines; Solubility; Tumor Microenvironment

A gene transfer vector has been developed utilising anionic liposomes as a carrier of plasmid DNA (pEGlacZ, 7.6 kb) to transfect CD3+ T lymphocytes (Jurkat cells). The plasmid DNA that contained the Escherichia coli beta-galactosidase reporter gene was condensed using poly-l-lysine of molecular mass 20,700 (PLK99) to form a polyplex which was interacted with several anionic liposome formulations to form lipopolyplexes. The liposome formulations where based on dioleoylphosphatidylethanolamine (DOPE) in combination with cholesterol and dioleoylphosphatidylcholine (DOPC) and oleic acid, or dimyristoylphosphatidylethanolamine (DMPE). For targeting to the Jurkat cells distearoylphosphatidylethanolamine (DSPE) linked to poly (ethylene glycol) molecular mass 2,000 and coupled to anti-CD3 antibody was incorporated. The polyplexes and lipopolyplexes were characterised in terms of size, zeta potential, agarose gel electrophoresis and electron microscopy and the permeability of the lipopolyplexes to liposome-encapsulated glucose was determined. The polyplexes consisted of a mixed population of rod-like structures (53-160 nm long and 23-31 nm diameter) and spheres (18-30 nm diameter). The lipopolyplexes retained a permeability barrier although were more permeable to glucose than their component liposomes. The poly-l-lysine condensing agent was still susceptible to pronase digestion suggesting that the polyplex was associated with the outer surface of the liposome. The lipopolyplexes with lipid composition DOPE/cholesterol/OA/DSPE-PEG2000 anti-CD3+ PLK99-plasmid DNA had significant gene transfer activity, as monitored by beta-galactosidase expression, that depended on the charge ratio of the component polyplex and the lipid/DNA weight ratio. The anti-CD3 antibody, the liposomal lipid and pH sensitivity were essential for transfection activity.

Topics: Antibodies; DNA; Genetic Vectors; Humans; Hydrogen-Ion Concentration; Jurkat Cells; Liposomes; Macromolecular Substances; Microscopy, Electron; Phosphatidylethanolamines; Polylysine; Pronase; Transfection