The element boron neighbors carbon in the periodic table, exists in plentiful supply throughout the universe and reaches a long arm across the periodic table in order to form stable compounds with a wide variety of other elements. The most important chemical property shared by carbon and boron is the ability of both these elements to form large families of discrete structures by bonding to themselves. Thus, boron atoms form stable bonds to other boron atoms when forming polyhedral borane clusters. Carbon, of course, adopts the same behavior while creating organic chemistry. Rapid advances made during the past fifty years have now established such boron clusters as the basis of a nearly infinite number of new species containing elements from throughout the periodic table. This new science supports an ever increasing scope of molecular structures having extraordinary chemical, biological, thermal and photochemical stabilities. Such properties provide unique applications not possible with other elements including carbon. While borane and hydrocarbon derivatives share many related structural features and functions, borane species are apparently stable in the presence of enzyme systems which have supported the evolution of life (at least on this planet) and they appear, at this time, to be inert to enzymatic degradation reactions. Another unique feature of boron is its isotopic distribution of 10B (20%) and 11B (80%) accompanied by the very great propensity of 10B to capture a slow neutron and fission to cytotoxic 4He and 7Li nuclei. This process is accompanied by the liberation of about 2.4 MeV of kinetic energy and a 0.5 MeV gamma-photon (the boron neutron capture reaction). This nuclear reaction provides the basis of boron neutron capture therapy of cancer (BNCT) and the nonmalignant disease, arthritis.
Boron-Rich Nanoscale Delivery Agents for the Boron Neutron Capture Therapy of Cancer (BNCT)
Boron Neutron Capture Therapy of Cancer (BNCT) is a targeted, tumor cell-selective binary radiation therapy based upon the very facile capture of a thermal neutron by the 10B nucleus. This nuclear fission reaction produces both 4He and 7Li+ nuclei along with about 2.4 MeV of kinetic energy and weak &gamma-radiation. Since the energetic and cytotoxic product ions travel only about one cell diameter in tissue one may specify the cell type to be destroyed by placing innocent 10B nuclei on or within only the doomed cells. For a detailed discussion on BNCT, please see Professor Hawthorne's Faculty Research Lecture.
The multidisciplinary nature of this research effort involves chemistry, biology, nuclear physics, medicine, and related specialties. Methods devised for bringing 10B nuclei to tumor cells in therapeutic amounts are correlated with the structure of a generalized cell and the various cellular compartments available for boron localization. The outlook for BNCT is especially bright at this time because of rapid developments in the fields of bioorganometallic chemistry, microbiology, immunology, and nuclear science, to name but a few. Very effective boron delivery vehicles have been demonstrated, and through the interaction of chemistry, biology and nuclear science, these species are undergoing further improvement and evaluation at MU.