A dipeptide boronic acid analogue with antineoplastic activity. Bortezomib reversibly inhibits the 26S proteasome, a large protease complex that degrades ubiquinated proteins. By blocking the targeted proteolysis normally performed by the proteasome, bortezomib disrupts various cell signaling pathways, leading to cell cycle arrest, apoptosis, and inhibition of angiogenesis. Specifically, the agent inhibits nuclear factor (NF)-kappaB, a protein that is constitutively activated in some cancers, thereby interfering with NF-kappaB-mediated cell survival, tumor growth, and angiogenesis. In vivo, bortezomib delays tumor growth and enhances the cytotoxic effects of radiation and chemotherapy. OR A substance used in a type of radiation therapy called boron neutron capture therapy. Boron phenylalanine is injected into a blood vessel and collects in tumor cells. The patient then receives radiation therapy with atomic particles called neutrons. The neutrons react with boron phenylalanine to kill the tumor cells without harming normal cells. Also called BPA.