Radioactive iodine (I-131) has long been used clinically for patients with metastatic differentiated thyroid cancer. However, some patients are refractory to repetitive I-131 treatment, despite the targeted regions showing sufficient iodine uptake. In such patients, beta-particle therapy using I-131 is inadequate and another strategy is needed using more effective radionuclide targeting the sodium/iodide symporter (NIS). Astatine (At-211) is receiving increasing attention as an alpha-emitter for targeted radionuclide therapy. At-211 is a halogen element with similar chemical properties to iodine. Alpha particles emitted from At-211 has higher linear energy transfer as compared to beta particles from I-131 and exert a better therapeutic effect by inducing DNA double strand breaks and free radical formation. Thus, targeted alpha therapy using At-211 is highly promising for the treatment of advanced differentiated thyroid cancer.
Single intravenous administration of TAH-1005 is performed in patients with differentiated thyroid cancer (papillary cancer, follicular cancer) who cannot obtain therapeutic effect with standard treatment or who have difficulty in implementing and continuing standard treatment. The safety, pharmacokinetics, absorbed dose, and efficacy will be evaluated to determine the recommended dose for Phase II clinical trial.