Boron nanoparticles in chemotherapy and radiotherapy: the synthesis, state-of-the-art, and prospects

Boron neutron capture therapy (BNCT) is a radiotherapy method for cancer treatment based on the nuclear reaction of the stable 10B isotope with epithermal neutrons that produces high-energy particles affecting the localization site of the isotope. Currently, only two low molecular weight boron-containing compounds (boronophenylalanine and sodium mercaptododecaborate) have been approved for clinical use as targeting agents for BNCT. In spite of positive effects of these substances, certain drawbacks including the low 10B atom content per molecule and low tumor tropism make them of limited use. This review focuses on new-generation targeting agents for BNCT, such as elemental boron, boron carbide, and boron nitride nanoparticles (NPs). Their main advantage is the high content of 10B atoms, e.g., a 3-nm elemental boron NP contains 12000 atoms (cf. 20000 atoms for a 50-nm NP). This allows one to reach the concentration range necessary for successful implementation of BNCT. Information is analyzed and summarized on methods for the synthesis and biological applications of the title targeting agents for BNCT and combined chemotherapy, where NPs can also simultaneously act as drug carriers.