Radiopharmaceuticals: state of the art

In the past four years most of the effort in radiopharmaceutical chemistry has been devoted to compounds for positron emission tomography, but widespread use of this technique is still compromised by its high cost. On the other hand, steady progress has also been made in the development of technetium-99m-labelled radiopharmaceuticals. A variety of 99mTc-labelled agents is now available or in clinical evaluation for the study of brain perfusion (99mTc-labelled HMPAO, ECD, MRP20), myocardial perfusion (99mTc-labelled MIBI, teboroxime and phosphines) and renal function (99mTc-MAG3, 99mTc-L,L-EC). Different direct reduction methods and indirect conjugation methods have been developed to label antibodies or their fragments efficiently with 99mTc with preservation of immunoreactivity. However, the strict requirements of the regulatory authorities with respect to purification and quality of these preparations limit their use drastically in clinical practice. Radiopharmaceuticals labelled with beta-emitting radionuclides for radioimmunotherapy and palliative treatment of skeletal metastases are receiving increasing interest. Numerous agents are now available for imaging inflammation, but more clinical experience is required to determine which of them is the most appropriate. The growing importance of radiolabelled receptor-imaging agents is apparent from the commercial availability of the first such compound in Europe.