Bortezomib (originally codenamed PS-341) is the first therapeutic proteasome inhibitor to the tested in humans. It is approved in the U.S. for treating relapsed multiple myeloma and mantle cell lymphoma. [1] The drug is an N-protected dipeptide and can be written as Pyz-Phe-boroLeu, which stands for pyrazinoic acid, phenylalanine and Leucine with a boronic acid instead of a carboxylic acid. Peptides are written N-terminus to C-terminus, and this convention is used here even though the "C-terminus" is a boronic acid instead of a carboxylic acid. While multiple mechanisms are likely to be involved, proteasome inhibition may prevent degradation of pro-apoptotic factors, permitting activation of programmed cell death in neoplastic cells dependent upon suppression of pro-apoptotic pathways. Recently, it was found that bortezomib caused a rapid and dramatic change in the levels of intracellular peptides that are produced by the proteasome. [2] Some intracellular peptides have been shown to be biologically active, and so the effect of bortezomib on the levels of intracellular peptides may contribute to the biological and/or side effects of the drug.

A potent (Ki = 0.6 nM), specific and reversible proteasome inhibitor. It inhibits cell proliferation of H460 cells (Human non-small cell lung cancer cell lines) with an IC₅₀ of 0.1 µM.

References:
1. Takimoto CH, Calvo E. "Principles of Oncologic Pharmacotherapy" in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) Cancer Management: A Multidisciplinary Approach. 11 ed. 2008.
2. Gelman JS, Sironi J, Berezniuk I, Dasgupta S, Castro LM, Gozzo FC, Ferro ES, Fricker LD (2013). "Alterations of the intracellular peptidome in response to the proteasome inhibitor bortezomib". In Gartel, Andrei L. PLoS One 8 (8): e53263.