Bortezomib. Molecular model of the proteasome inhibitor drug bortezomib (chemical formula C19.H25.B.N4.O4), used to treat cancers. This was the first therapeutic proteasome inhibitor to be tested in humans. It has been used in the treatment of multiple myeloma and mantle cell lymphoma. Atoms are represented as spheres and are colour-coded: carbon (turquoise), hydrogen (white), nitrogen (blue), oxygen (red) and boron (orange).