3 Radioisotopes and Nanomedicine

Nanomedicine, the medical application of nanotechnology, is poised to make a major impact on the diagnosis and treatment of many diseases. It is a relatively new branch of science that involves harnessing the unique properties of particles that are nanometers in scale (nanoparticles) for both diagnostic and therapeutic applications. Nanoparticles (NPs) can be engineered with precise sizes, shapes, compositions and surface chemistries for specific applications. In particular, nanoparticles are uniquely suited for the treatment of cancers and cardiovascular diseases. NPs can be engineered with surface targeting ligands against cancer markers or atherosclerosis markers, which in turn allow the specific detection of as well as specific drug delivery to these diseases. In the case of cancer, nanoparticles also preferentially accumulate in tumors due to the enhanced permeability and retention (EPR) effect (Noguchi et al. 1998). Although nanomedicine is a relatively new field, it has been quickly translated into clinical medicine and has led to a number of clinically-approved agents. Today, there are more than twenty nanoparticle therapeutics in clinical use. Furthermore, a 2006 global survey conducted by the European Science and Technology Observatory (Duconge et al.) revealed that more than 150 companies are developing nanoscale therapeutics, highlighting the high enthusiasm for nanoparticle-based therapeutics (Wagner et al. 2006). While nanomedicine has many facets, radioisotopes have been an integral component. Radioisotopes have been extensively utilized in the development of nanoparticle-based therapeutics. Radiolabeling has been the predominant method for the accurate assessment of biodistribution, circulation half-life, and pharmacokinetics of nanoparticles. In addition, there has been great interest in developing nanoparticles with dual diagnostic and therapeutic functionalities (theranostics) and radioisotopes have been a natural fit for the diagnostic component. Lastly, therapeutic radioisotopes can also be delivered by nanoparticles, especially for the treatment of cancer. In this chapter, we will review the various applications of radioisotopes in nanomedicine in detail. We also plan to discuss the methods of incorporating radioisotopes into nanoparticles as well as preclinical and clinical data on radioisotope containing nanoparticle diagnostics and therapeutics.