Optimal Therapeutic Strategies for Radioimmunotherapy

Abstract

Radioimmunotherapy (RIT) is one aspect of a more general therapeutic approach which involves the biological targeting of ionising radiation to tumours. The distinguishing feature of RIT is the use of immunologically based targeting molecules such as antibodies and their fragments. Some useful and encouraging clinical results have been achieved with antibody-targeted therapy (Press et al. 1993; Hird et al. 1993; Riva et al. 1994). There are, however, other possible molecules which may be used for tumour targeting. One of the most promising of these is meta-iodobenzylguanidine (mIBG) which has certain structural similarities to noradrenaline. This agent is in clinical use for the biologically targeted radiotherapy of neuroblastoma and phaeochromocytoma (Voute et al. 1991; Lashford et al. 1992). In the future it is very likely that other classes of targeting molecule will also find application for tumour targeting. Which class of radionuclide to use depends on the manner in which the targeting molecule becomes associated with the targeted tumour cell. At present radionuclides which emit β-particles are used to the virtual exclusion of all others, although the potential of α-emitting radionuclides is also being explored (Junghans et al. 1993; Vaidyanathan and Zalutsky 1992). These are reasonable choices if the targeting molecule is bound to the cell surface or internalised to non-nuclear regions.