The development of new radiopharmaceuticals.

The development of new radiopharmaceuticals is the basis of the continuing growth of nuclear medicine. Chemical interactions of electron clouds in their three-dimensional conformations bring together, in the process of molecular recognition, the reaction of antibody and antigen, receptor and ligand, enzyme and substrate, hormone and response site. This convergence enables the computer design of molecules such as ligands to fit computer-displayed conformational models showing active centres, positive and negative charges and other interactions. Indeed, given a particular molecule, a complementary binding structure can be devised. The hybridoma approach to monoclonal antibody production is being superceded by the bacterial bioengineer. The gene for the hypervariable region from the spleen cells of immunized mouse can be coupled with the myeloma gene. The polymerase chain reaction can duplicate the DNA a million times over in 20 min and the result transfected into a bacterial plasmid to produce the antibody. These scientific problems are soluble in principle and are being solved. However, so much damage to this developing biological field is being done by regulatory authorities that one must ask who should or can regulate the regulators. These problems have to be overcome in order to provide the new radiopharmaceuticals that are the food and wine of nuclear medicine.