Recent topics and perspectives in radiopharmaceuticals

Recently, radiopharmaceuticals have rapidly advanced in nuclear medicine diagnosis. In the development of new radiopharmaceuticals, as nuclear medicine required 'functional imaging', the most characteristic ability, it is necessary to design that their biodistributions should reflect regional functions and biochemical processes. Functional diagnosis of the neurotransmission for neuropsychiatric disorders, including Parkinson's disease, Alzheimer's dementia et al., is one of the most effective category of nuclear medicine. In the past 15 years, many PET-radiotracers have been studied and produced excellent results. PET-radiotracers, however, have the limitation of general use, so developments of SPECT-radiotracers have been expected. Some of them were successful and used for clinical studies, for example 123I-Iomazenil (benzodiazepine receptor imaging agent) and 123I-IBF (dopamine D2 receptor imaging agent). At present in this field, the development of presynaptic dopamine transporter imaging agents with tropane derivatives for Parkinson's disease diagnosis are exceedingly active, expressed as 'tropane war'. 123I-β-CIT and some other tropanes have already been used for clinical studies. At this time, the success of tropanes labeled with 99mTc, more widespread than 123I, is epoch-making in the advance of radiopharmaceuticals. These studies will promote the developments of high-quality 99mTc radiopharmaceuticals and they will provide us more information in nuclear medicine. (J.P.N.)