Holmium for Use in Cancer Therapy

Over the last few decades, holmium (Ho) has been investigated for its application in laser surgery, magnetic resonance imaging, and internal and topical radionuclide therapy. Ho has a 100% natural abundance of holmium-165, which is a stable nuclide that can undergo a process called neutron-activation to generate radioactive holmium-166 (¹⁶⁶Ho). ¹⁶⁶Ho emits β^–particles and γ photons, with a half-life of 26.8 h; β^–particles can damage a cancer cell’s DNA, while γ photons allow for ¹⁶⁶Ho to be imaged in vivo and easily quantitated prior to, or during, dosing. This article gives a thorough account of the work being done around the world on ¹⁶⁶Ho for use as an internal or topical radionuclide therapy against cancer. Our research group and others have generated compelling data that support the use of ¹⁶⁶Ho as a radiotherapeutic in the clinic, especially since pharmaceutical formulations can be made while non-radioactive (Ho) and then made radioactive (¹⁶⁶Ho) just prior to use.