Cancer Therapy Using Nanoscience and Nuclear Processes

M. Frederick Hawthorne, Professor of Radiology and
Director, International Institute of Nano and Molecular Medicine
University of Missouri

The boron-10, or ¹⁰B, isotope is unique due to its great ability to capture neutrons from its surroundings and undergo a violent nuclear reaction. This property is not shared by the only other isotope of boron, ¹¹B, and the various isotopic forms of the so-called light elements which comprise living tissue (hydrogen, carbon, nitrogen, and oxygen). Boron is non-toxic to animals. The neutron capture and fission reaction of ¹⁰B yields cytotoxic

lithium and helium ions which together share 2·MeV of kinetic energy. A gamma photon is also produced which is of minor importance. The beauty of this reaction in its application to cancer therapy is based upon the short distances that the Li and He ions travel from their point of creation before they lose effectiveness. This distance is about the diameter of a cancer cell. Neutrons are relatively benign as used here and they are obtained from a nuclear reactor such as the MU Research Reactor in Columbia. The cancer therapy derived from these circumstances is called boron neutron capture therapy (BNCT) and it has several very favorable features such as the ability to be turned on or off at will, very high selectivity for cancer cells and the need for only a single therapeutic session to treat patients. In practice, boron-10 containing nanoparticles are selectively delivered to cancer cells using a variety of techniques, the boron-labeled cancer cells are then briefly irradiated with neutrons and the neutron capture process occurs within the cancer cells. Normal cells are not targeted and not affected. The tumor cells are selectively killed by the high-energy and short-range Li and He particles produced within the cancer cells, one lethal process is DNA double-strand breaking in the cancer cell nucleus. While the major nuclear and biological components of the BNCT process are in place, the necessary boron chemistry requires further work. Promising indications obtained with previously unknown ¹⁰B-rich nanoparticles targeted for cancer cells suggest that proof-of-principle results for the BNCT process will soon be secured. The types of tumors which may be treated using BNCT remains to be medically defined, but head and neck lesions are most likely to be the initial targets. All aspects of this unique and very selective binary radiation method for cancer therapy will be presented.