Liposomal nanomedicines: an emerging field.

Liposomal nanoparticles (LNs) encapsulating therapeutic agents, or liposomal nanomedicines (LNMs), represent one of the most advanced classes of drug delivery systems, with several currently on the market and many more in clinical trials. During the past 20 years, a variety of techniques have been developed for encapsulating both conventional drugs and the new genetic drugs (plasmid DNA-containing therapeutic genes, antisense oligonucleotides, and small, interfering RNA [siRNA]) within LNs encompassing a very specific set of properties: a diameter centered on 100 nm, a high drug-to-lipid ratio, excellent retention of the encapsulated drug, and a long (>6 hours) circulation lifetime. Particles with these properties tend to accumulate at sites of disease, such as tumors, where the endothelial layer is "leaky" and allows extravasation of particles with small diameters. Thus, LNs protect the drug during circulation, prevent it from reaching healthy tissues, and permit its accumulation at sites of disease. We will discuss recent advances in this field involving conventional anticancer drugs as well as gene-delivery, immunostimulatory, and gene-silencing applications involving the new genetic drugs. LNMs have the potential to offer new treatments in such areas as cancer therapy, vaccine development, and cholesterol management.