title: Development of next-generation macromolecular drugs based on the EPR effect: challenges and pitfalls.
abstract: BACKGROUND
  A major problem with conventional antitumor therapeutics is nonselective delivery of cytotoxic drugs to normal vital organs and tissues but little delivery to tumor tissues.
  
  
  METHODS
  Here, the authors describe the tumor selective delivery of antitumor drugs by taking advantage of nano-sized drugs and the means to augment it further. Based on the enhanced permeability and retention (EPR) effect, the mechanism for more efficient universal tumor delivery using macromolecular drugs to cover wider tumor types than single molecular target is discussed. Unique properties of solid tumor vasculature in the tumor tissue are discussed, especially leakiness of the blood vessels and factors involved and impaired clearance of macromolecular drugs from the tumor interstitium via the lymphatic system. The criteria for such macromolecular drugs or nanomedicines for effective accumulation at tumor sites is commented on as well as the importance of long plasma retention time of such drugs and a need to release active principles from nanoparticles at target sites. Methods to augment the EPR effect and tumor delivery (2 - 3 times) and its application to photodynamic therapy are also discussed.
  
  
  CONCLUSIONS
  Tumor selective delivery of antitumor drugs based on the EPR effect can be accomplished and augmented by modulating the tumor environment. This methodology is favorable not only for tumor therapy but also for tumor imaging.
authors.affiliation: Sojo University, Institute for Drug Delivery Science , Ikeda 4-22-1, Nishi-ku, Kumamoto, 860-0082 , Japan hirmaeda@ph.sojo-u.ac.jp.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nakamura
authors.forename: Jun
authors.initials: J
authors.lastname: Fang
authors.forename: Fang
authors.initials: F
authors.lastname: Jun
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Maeda
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage*; D001672:Biocompatible Materials / Q000008:administration & dosage / Q000494:pharmacology; D002199:Capillary Permeability / Q000187:drug effects* / Q000502:physiology; D016503:Drug Delivery Systems / Q000379:methods*; D046911:Macromolecular Substances / Q000008:administration & dosage / Q000494:pharmacology; D053758:Nanoparticles / Q000008:administration & dosage; D009369:Neoplasms / Q000098:blood supply / Q000188:drug therapy* / Q000473:pathology; D004364:Pharmaceutical Preparations
chemical_list: D000970:Antineoplastic Agents; D001672:Biocompatible Materials; D046911:Macromolecular Substances; D004364:Pharmaceutical Preparations
keywords: application of EPR effect to PDT; augmentation of EPR effect; barriers to tumor delivery; enhanced permeability and retention effect of solid tumor; macromolecular drug; nanomedicine; tumor selective drug delivery