Development of Brain-Tumor-Targeted Benzothiazole-Based Boron Complex for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a precision treatment technology that ideally damages only boron-accumulating cells. The effectiveness of BNCT depends on the amount of boron in the tumor cells and the concentration ratio between normal and tumor tissues. Therefore, for successful brain-tumor treatment using BNCT, it is essential to develop a drug with high blood–brain barrier (BBB) permeability and high tumor accumulation. The benzothiazole-based boron complex 4-(benzo[ d ]thiazol-2-yl)phenylboronic acid (BTPB) is a hydrophobic, low-molecular-weight compound that has shown high BBB permeability and brain accumulation. The highest boron concentration of BTPB is 36.11 ± 2.73 μg/g (at 1 h post-injection) in the brain, and the highest brain/blood ratio is 3.94 ± 0.46 (at 2 h post-injection), which is sufficient for the BNCT drug condition. In addition, BTPB showed good tumor-targeting ability in vivo in a U87MG glioma tumor model. In this study, we conducted a biological evaluation of BTPB compared to boronophenylalanine as a novel drug for BNCT.