Radiotargeted gene therapy.

The radiotargeted gene therapy approach to localizing radionuclides at tumor sites involves inducing tumor cells to synthesize a membrane-expressed receptor with a high affinity for injected radiolabeled ligands. A second strategy involves transduction of the sodium iodide symporter (NIS) and free radionuclide therapy. Using the first strategy, induction of high levels of human somatostatin receptor subtype 2 expression and selective tumor uptake, imaging, or growth inhibition with radiolabeled somatostatin analogs has been achieved in human tumor xenograft models. Therapy studies have been performed on several tumor xenograft models with various radionuclides using the NIS radiotargeted gene therapy approach. The use of gene transfer technology to induce expression of high-affinity membrane receptors or transporters can enhance the specificity and extent of radioligand or radionuclide localization in tumors, and the use of radionuclides with appropriate emissions can deliver radiation-absorbed cytotoxic doses across several cell diameters to compensate for limited transduction efficiency. Clinical studies are needed to determine the most promising of these new therapeutic approaches.