Pretargeting of carcinomas with the avidin-biotin system

Diagnosis and experimental therapy of cancer have been performed with encouraging results using radiolabelled monoclonal antibodies. However, the high background due to non-specific uptake by normal tissue and blood is a major drawback in antibody-guided tumor detection. Various strategies have been proposed to overcome this problem, such as computed background subtraction, use of a second antibody, and local delivery. An antibody is a slow 'bullet' for tumor targeting, since in many lesions it requires two or three days to accumulate. The use of fragments such as F(ab')2 or Fab, which display a faster blood clearance than whole antibody, improves tumor localization to a sufficient extent (hours) to allow the use of the most suitable radionuclides, e.g. 99m-Tc. In therapeutic applications we are still far away from the optimal condition in terms of the absolute amount of radioactivity delivered to the tumor. The high specificity of antibodies could be exploited at its best by delaying ...