ABSTRACT
Specific targeting of radioactive agents to tumor cells has been a major goal of the in vivo use of monoclonal antibodies (MoAb) for diagnostic and therapeutic purposes. However, only a relatively small amount of the injected dose of MoAbs is bound by the tumor, while MoAb conjugated to radioisotope keep circulating in the blood stream and in normal tissue. Indeed, a relatively low tumor to non-tumor ratio is one of the major drawbacks of the use of antibodies for tumor radioimaging. The avidin-biotin system is widely used for in vitro applications, in immunohistochemistry, for the stepwise construction of macromolecular complexes onto specific target molecules in order to make them detectable by chemical or physical methods. The affinity of avidin for biotin is extremely high. The combined use of biotin and avidin and MoAb not only enhances the effect of MoAb at the binding site but also allows one to separate the delivery of the MoAb and the radioactive label.
