Enhanced Permeability and Retention (EPR) Efect: Basis for Drug Targeting to Tumor

Abstract

Tumor vascular permeability is becoming increasingly important in tumor biology because of its critical role in tumor growth and perhaps in metastasis, as well as in the selective delivery of anticancer agents, particularly macromolecular compounds, to tumors (see Refs. 1–5 for reviews). This issue of vascular permeability is significant primarily in tumorous tissues (and in inflammatory tissues). Macromolecular (or polymeric) drugs are of interest because they are in the class of substances manifesting enhanced extravasation in tumor tissue. The tumor-selective phenomenon has been characterized and termed the enhanced permeability and retention (EPR) effect of macromolecules and lipidic particles (2–4). One can best take advantage of this unique EPR effect for tumor-targeted delivery of drugs. Thus, polymeric drugs and microparticles, including micellar compounds or liposomes, can be delivered with greater selectivity to tumors because of the EPR effect.