title: Oxidative deboronation of the peptide boronic acid proteasome inhibitor bortezomib: contributions from reactive oxygen species in this novel cytochrome P450 reaction.
abstract: Bortezomib (1) is a potent first-in-class dipeptidyl boronic acid proteasome inhibitor employed in the treatment of patients with relapsed multiple myeloma where the disease is refractory to conventional lines of therapy. The potency of 1 is owed primarily to the presence of the boronic acid moiety, one which is suited to establish a tetrahedral intermediate with the active site N-terminal threonine residue of the proteasome. Hence, deboronation of 1 represents a deactivation pathway for this chemotherapeutic agent. Deboronation of 1 affords a near equal mixture of diastereomeric carbinolamide metabolites (M1/M2) and represents the principal metabolic pathway observed in humans. In vitro results from human liver microsomes and human cDNA-expressed cytochrome P450 enzymes (P450) indicate a role for P450 in the deboronation of 1. Use of 18O-labeled oxygen under controlled atmospheres confirmed an oxidative mechanism in the P450-mediated deboronation of 1, as 18O was found incorporated in both M1 and M2. Chemically generated reactive oxygen species (ROS), such as those generated as byproducts during P450 catalysis, were also found to deboronate 1 resulting in the formation of M1 and M2. Known to undergo efficient redox cycling, P450 2E1 was found to catalyze the deboronation of 1 predominantly to the carbinolamide metabolites M1 and M2, as well as to a pair of peroxycarbinolamides, 2 and 3. The presence of superoxide dismutase (SOD) and catalase prevented the deboronation of 1, thus, supporting the involvement of ROS in the P450 2E1-catalyzed deboronation reaction. The presence of SOD and catalase also protected 1 against P450 3A4-catalyzed deboronation, albeit to a lesser extent. The remaining deboronation activity observed in the P450 3A4 reaction may suggest the involvement of the more conventional activated enzyme-oxidants previously described for P450. Our present findings indicate that the oxidase activity of P450 (i.e., formation of ROS) represents a mechanism of deboronation.
authors.affiliation: Department of Drug Metabolism and Pharmacokinetics, Drug Safety and Disposition, Millennium Pharmaceuticals, Inc., Cambridge, Massachusetts 02139, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Labutti
authors.forename: Ian
authors.initials: I
authors.lastname: Parsons
authors.forename: Ron
authors.initials: R
authors.lastname: Huang
authors.forename: Gerald
authors.initials: G
authors.lastname: Miwa
authors.forename: Liang-Shang
authors.initials: LS
authors.lastname: Gan
authors.forename: J Scott
authors.initials: JS
authors.lastname: Daniels
mesh_terms: D001880:Boranes / Q000737:chemistry*; D001897:Boronic Acids / Q000737:chemistry* / Q000494:pharmacology; D000069286:Bortezomib; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000201:enzymology; D010084:Oxidation-Reduction; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000737:chemistry* / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000737:chemistry*
chemical_list: D001880:Boranes; D001897:Boronic Acids; D061988:Proteasome Inhibitors; D011719:Pyrazines; D017382:Reactive Oxygen Species; D000069286:Bortezomib; D003577:Cytochrome P-450 Enzyme System