Tumor-Selective Delivery of Macromolecular Drugs via the EPR Effect: Background and Future Prospects

This paper briefly documents the history of the discovery of the EPR (enhanced permeability and retention) effect and elucidates an analogy between bacterial infection involving proteases that trigger kinin generation and cancer. The EPR effect of macromolecules in cancer tissues is defined, and the distinction between the EPR effect (with reference to clearance of macromolecules from the interstitial space of tumor tissues) and the simple passive targeting of drugs to tumors is described. Additional points of discussion include the uniqueness of tumor vessels, the influence of kinin and other vascular mediators such as nitric oxide (NO) and prostaglandins, and the heterogeneity of the EPR effect. Two…