Liposomes

Liposomes are small spheres consisting of a lipid shell and a hollow center. Much like cells, the lipid bilayer separates the content of the sphere from the outside. This solves both of the problems. First, the drug is protected form the water environment of the plasma, and also the proteins present in the blood. This method has been commercialized and one example is the Stealth from Alza. In their version of liposomal encapsulation, an polyethylene glycol (PEG) coating is applied to the liposome inhibit immune responses to the liposomes and increase the lifetime of the liposome and drug. Currently the Stealth system is being used to delivery Doxil, an anti-cancer treatment to patients.

As demonstrated by the Stealth delivery system, liposomes have the advantage of being easily derivatizable. In addition to PEG coatings to decrease its immunogenicity, targeting molecules can be incorporated. For instance, antibodies-coated liposomes have been studied as a drug delivery vessel for over 10 years.