NANOPARTICLES FOR DELIVERY OF DRUGS, DNA, OR RNA
Because nanoparticles can be targeted to specific tissues, they can be used to deliver a variety of biologically active molecules, including both pharmaceuticals and genetic engineering constructs.
Large polymeric molecules such as DNA may themselves be compacted to form nanoparticles of around 50 to 200 nm in size. This involves addition of positively charged molecules (e.g., cationic lipids, polylysine) to neutralize the negative charge of the phosphate groups of the nucleic acid backbone. Other molecules may be added to promote selectivity for certain cells or tissues.
Alternatively, hollow nanoparticles (nanoshells) may obviously be used to carry other, smaller molecules. Such nanoshells must be made from biocompatible materials such as polyethyleneimine (PEI) or chitosan. The latter alternative seems popular at present, because it is both naturally derived and biodegradable. Chitin is a beta-1,4-linked polymer of N-acetyl-D-glucosamine. It is found in the cell walls of insects and fungi and among biopolymers is second only in natural abundance to cellulose. Chitosan is derived from chitin by removing most of the acetyl groups by alkali treatment.
An interesting approach that combines two trendy technologies is using nanoshells to carry siRNA (short interfering RNA). Delivery of siRNA triggers RNA interference, which results in the destruction of target mRNA. The siRNA may be targeted against mRNA from genes expressed preferentially in cancer cells or genes characteristic of certain viruses.