Tumor targeting properties liposomes

Ishida O et al (2001) Liposomes bearing polyethyleneglycol-coupled transferrin with intracellular targeting property to the solid tumors in vivo. Pharm Res 18 1042-1048... 

Liposomes form spontaneously when lipids are dispersed in aqueous media. They consist of a bilayer membrane which captures a pool of water in its center. The practical value of liposomes derives from two unioue properties 1) their ability to entrap either water-soluble materials in tne internal water reservoir or liposoluble compounds in the lipid bilayer and 2) their compatibility witn natural membranes, making them safe for medical application. They have attracted considerable interest as delivery systems, such as carriers of drugs to specific targets in the treatment of cancer tumors and in enzyme therapy (1) and in various diagnostic tests using fluorescent makers (2) and radiolabels (3). Liposomes are fragile structures created in water as a result of a delicate balance of interacting forces which arise when amphiphilic compounds are added to water. In most practical applications liposomes have to be... 

The use of nanocontainers, such as low-density lipoproteins (LDL) or liposomes is the important approach directed to selective delivery of therapeutics into tumors. One of the observed differences between tumor cells and their normal counterparts is the rate of metabolism of low-density lipoproteins (LDLs). The LDL vesicle comprises a phospholipids/cholesterol shell with a diameter of approximately 15-20 nm, filled with cholesteryl and glyceryl esters of long-chain alkyl carboxylic acids. This difference is based on the increased need that tumor cells possess for cholesterol to facilitate new membrane formation. The overexpression of the LDL receptors on the tumor cell membrane is responsible for its LDL accretion. This provides a basis for cellular differentiation and the targeting of tumor cells with boron if cholesteryl esters of the LDL core are replaced with a boron species that would simulate cholesterol in its physiochanical properties. This concept was proposed by Kahl in the early 1990s. The initial compounds synthesized were esters of carborane carboxylic acid with various fatty acid alcohols [80]. Later, some other derivatives of cholesterol were synthesized [81,82] and LDLs were proposed as tumor delivery agents for carborane-containing porphyrins [83]. 

---