Wednesday, January 13, 2010

What is the optimal liposome size for liposomes that target tumors?

Many people blindly use 100 nm liposomes when they target cancer tumors. Not many people know the reason behind using 100 nm liposomes.

In tumor tissue, the vasculature is discontinuous, and pore sizes vary from 100 to 780 nm. By comparison, normal vascular endothelium is around 2 nm in most tissues, 6 nm in postcapillary venules, 40–60 nm for the kidney glomerulus, and up to 150 nm for sinusoidal epithelium
of the liver and spleen. In order for the liposomes to extravasate (to pass through the walls of a vessel into the surrounding tumor tissues) they should be around 100 nm or less in order to pass through the pores.

In general, for a given liposome composition, the larger the liposome, the faster the clearance by the RES.