Science and technology of the emerging nanomedicines in cancer therapy: A primer for physicians and pharmacists.

Nanomedicine, the medical applications of devices based on nanotechnology, promises an endless range of applications from biomedical imaging to drug and gene delivery. The size range of the nanomaterials is strictly defined as 1-100 nm, although many marketed nanomedicines are in the submicron range of 100-1000 nm. The major advantages of using nanomaterials as a carrier for anticancer agents are the possibility of targeted delivery to the tumor; their physical properties such as optical and magnetic properties, which can be exploited for developing contrast agents for tumor imaging; their ability to hold thousands of molecules of a drug and deliver at the required site and also the ability to overcome solubility and stability issues. Currently, there are several nanotechnology-enabled diagnostic and therapeutic agents undergoing clinical trials and a few already approved by Food and Drug Administration. Targeted delivery of anticancer agents is achieved by exploiting a unique characteristic of the rapidly dividing tumor cells called "the enhanced permeability and retention effect." Nanoparticles with mean diameter between 100 and 200 nm or even above 200 nm have also been reported to be taken up by tumor cells via the enhanced permeability and retention effect. In addition to this passive targeting based on size, the nanoparticle surface may be modified with a variety of carefully chosen ligands that would interact with specific receptors on the surface of the tumor cells, thus imparting additional specificity for active targeting. Regional release of a drug contained in a nanoparticulate system by the application of external stimuli such as hyperthermia to a thermosensitive device is another innovative strategy for targeted delivery. Nanoparticles protect the enclosed drug from rapid elimination from the body, keep them in circulation for prolonged periods and often evade expulsion by the efflux pump mechanisms, which also leads to avoidance of development of resistance. This review focuses on the science and technology of Food and Drug Administration-approved cancer nanomedicines such as Abraxane, Doxil, DaunoXome and those drug-delivery systems that have reached an advanced stage of clinical development utilizing liposomes, albumin nanospheres, thermosensitive devices and gold nanoshells.