Application of drug delivery system to neutron capture therapy for cancer

Tumour cell destruction in boron neutron-capture therapy (BNCT) is due to the nuclear reaction between 10B and thermal neutrons (10B + 1n → 7Li + 4He (α) + 2.31 MeV (93.7%) / 2.79 MeV (6.3%)). The resulting lithium ions and α particles are high linear energy transfer (LET) particles which give high biological effect. Their short range in tissue (5 - 9 μm) restricts radiation damage to those cells in which boron atoms are located at the time of neutron irradiation. BNCT has been applied clinically for the treatment of malignant brain tumors, malignant melanoma, head and neck cancer and hepatoma etc, recently. Sodium borocaptate (Na210B12H11SH; BSH) and boronophenylalanine (10BPA) are currently being used in clinical treatments. These low molecule compounds are easily clearanced from the cancer cells and blood, so high accumulation and selective delivery of boron compounds into tumor tissues and cancer cells are most important to achieve effective BNCT and to avoid damage of adjacent healthy cells. To achieve the selective delivery of boron atoms to cancer cells, drug delivery system (DDS) becomes an attractive intelligent technology as targeting and controlled release of drugs. (author)