Targeted Delivery of Radiolabeled Imaging and Therapeutic Agents: Bifunctional Radiopharmaceuticals

Abstract

Clinical application of radioactive diagnostic and therapeutic agents constitutes one of the great advances in noninvasive medicine, nuclear medicine. The radioactive agents used in the nuclear medical field are called "radiopharmaceuticals," and are required to exhibit high and specific localization of radioactivity into target tissue. Among radionuclides used in radiopharmaceuticals, radiometals such as 99mTc and (111)In have received much attention because of their nuclear physical characteristics and widespread availability. However, since these metallic elements are not constituents of bioactive molecules, they cannot simply replace common constituent atoms in biologically interesting compounds. Thus, demand for biospecific radiopharmaceuticals constitutes a great challenge in rational design of biologically active molecules labeled with metallic radionuclides, and evolves into a generation of bifunctional radiopharmaceuticals. Molecules contain both a biologically active site and a chelating group for binding the metallic radionuclide in which attachment of a chelating group does not affect the inherent biospecificity of the mother compound. This paper describes recent progress in research of macro- and small-molecular bifunctional radiopharmaceuticals for targeted diagnosis and therapy.