Nuclear medicine: proof of principle for targeted drugs in diagnosis and therapy.

Delivering a drug to a specific target in the body is comparable to the "magic bullet principle" applied in Nuclear Medicine. If clinical medicine today found treatment options by targeting specific receptors, proteins or enzymes by "small-molecule drugs" it utilizes concepts that have been initially described by Nobel Laureate George von Hevesy as "tracer principle". This article is going to show that molecular imaging probes in Nuclear Medicine can be regarded as proof of principle of many of recent trends in diagnosis and therapy and offers exciting opportunities for further developments. Radioiodine therapy of benign and malignant thyroid disease has been established in Nuclear Medicine over six decades ago and is a fine example for using the same highly specific probe for diagnosis and treatment of a given disease. The use of radio labeled monoclonal antibodies against surface receptors of tumor cells (e.g. CEA) dominated diagnostic Nuclear Medicine in the eighties and sees a recent revival in lymphoma treatment radioimmunotherapy. Finally Nuclear Medicine has shown that it may advance drug development by visualizing its biodistribution and site of action. On the other hand some drugs like somatostatin analogues have been reinvented as diagnostic and therapeutic probes over a decade after their initial introduction as therapeutics. Molecular Imaging and targeted therapy are merging and potentiate their individual strength. Nuclear Medicine has ample experience in applying Molecular Imaging in clinical research and practice and has a bright future in this exciting field.