Report of the consultants' meeting on comparative laboratory evaluation of therapeutic radionuclides and radiopharmaceuticals

Therapeutic radiopharmaceuticals consist of two components - the radionuclide and the biological carrier. With regard to the radionuclide, an advantage of targeted radiotherapy is that there are a wide variety of radionuclides with different physical half-lives and radiation qualities that can be applied for this purpose. An important task is to select a radionuclide that is compatible with the needs of a particular clinical application. The identification of the ideal targeted radiotherapeutic for each potential clinical application is a difficult task because of the multitude of variables that must be considered, some relating to the radioisotope, and others to the biological carrier. Hence it is recommended that a Co-ordinated Research Programme be established by the Agency to enable participants to acquire and intercompare the methodological expertise to evaluate the relative merit of therapeutic radiopharmaceuticals. These studies will be performed using a model system selected either from those described in this report or a promising agent that has emerged in the time since this meeting. The molecular carrier will be labelled with 131I, 125I as well as other therapeutic radionuclides available to the participant (for example, 90Y, 186Re, 188Re, 153Sm, 166Ho, 165Dy). The potential radiopharmaceuticals will then be compared in a progression of studies evaluating biological integrity after labelling, internalisation and residualization of radioactivity in the tumour cell, in vitro cytotoxicity, tissue distribution, normal organ toxicity (determination of the maximum tolerated dose) and finally, therapeutic efficacy