Chapter 30. Progress in the Development of Radioimaging Agents

Abstract

Publisher Summary One recent classification system views radioimaging agents as either substrate nonspecific in which the compound does not participate in a specific chemical reaction or substrate specific in which the substrate must participate in a definite chemical reaction or take part in a specific ligand-substrate interaction. Radioactive gases for lung ventilation, labeled cells as blood pool or spleen imaging agents, tagged particles for delineating capillary beds, and radiocolloids for uptake in the reticuloendothelial system are examples of substrate non-specific radiodiagnostics, Enzyme substrates or inhibitors, receptor binding ligands, metabolically trapped biomolecules and their models, and antibodies to site-associated antigens are prime examples of substrate specific radiopharmaceuticals. At present, there are 48 radiopharmaceuticals available. Technetium labeled (Tc-99m) ligands, colloids, and particles are predominate on the NDA list, but many of these substances would be classified as substrate nonspecific agents. A few organic radiopharmaceuticals, both substrate nonspecific and substrate specific, have achieved commercialization; these include radioiodinated rose bengal, fibrinogen, oleic acid, human serum albumin, hippuric acid, as well as radiomercury chlormerodrin and Se-75 selenomethionine. Contemporary research concerns of radiopharmaceutical chemists are the development of convenient and rapid labeling methods for introducing radiohalogens into biologically important carrier molecules, preparation and evaluation of radio halogenated imaging agents, synthesis and structural studies on metal ion radionuclide-containing pharmaceuticals, rapid incorporation of positron-emitting isotopes into imaging agents, antibody transport of imaging nuclides to target tissues, and quantitative structure-distribution studies of radioactive diagnostics.