Proteasome irreversible

Bortezomib is the hrst therapeutic proteasome inhibitor. It inhibits the activity of the 26S-proteasoom protein complex which regulates protein expression and function and thus plays a role for cell homeostasis. It is used for the treatment of relapsed mulh-ple myeloma. Following intravenous administrahon bortezomib is mainly metabolised with an elimina-hon halflife of 5-15 h. It is frequently associated with somehmes irreversable neuropathy. Myelosuppression may be dose limiting. 

Groll M, Huber R, Potts BCM (2006) Crystal Structures of Salinosporamide A (NPI-0052) and B (NPI-0047) in Complex with the 20S Proteasome Reveal Important Consequences of (3-Lactone Ring Opening and a Mechanism for Irreversible Binding. J Am Chem Soc 128 5136... 

These mechanistic studies reveal NPI-0052 as a minimalist among protea-some inhibitors, in that each atom is used to maximum efficiency for inhibitor binding to the active site followed by the two-step reaction that renders it irreversibly bound. In fact, NPI-0052 clearly exceeds atom-for-atom efficiency of any currently known proteasome inhibitor. 

Peptide boronates are much more potent proteasome inhibitors than aldehydes [43[. Boronate-proteasome adducts have much more slower dissociation rates than proteasome-aldehyde adducts, and although boronates are considered reversible inhibitors, the inhibition is practically irreversible over a period of hours. In addition, PS-341 inhibits serine proteases 1000-fold weaker than it does the proteasome [43[. This combination of potency, selectivity and metabolic stability makes the peptide boronates better drug candidates than other classes of proteasome inhibitors. In vitro and mouse xenograft studies of PS-341 have shown anti-tumor activity in a variety of tumor types. DFLB and PS-273 are usefiil fluorescent active site probes binding of these inhibitors enhances the fluorescence of their environment-sensitive dansyl and naphthyl moieties [44]. 

Lactacystin is a Streptomyces metabolite that selectively modifies the fiS subunit of the mammalian proteasome and irreversibly blocks its activity. Other proteolytic sites of the proteasome are also modified and reversibly inhibited, but at much slower rates [45, 46). 

Peptide vinyl sulfones are synthetic irreversible proteasome inhibitors that covalently modify its catalytic / subunits [47]. They are easier to synthesize than other irreversible proteasome inhibitors, and they do not inhibit serine proteases. 

Groll M, Huber R, Potts BC. Crystal structures of Salinospo-ramide A NPI-0052 and B NPI-0047 in complex with the 20S proteasome reveal important consequences of beta-lactone ring opening and a mechanism for irreversible binding. J. Am. Chem. Soc. 2006 128 5136-5141. 

The catalytic role of the N-terminal threonine of ft subunits was soon extended to eukaryotic proteasomes by the observation that binding of lactacystin, a Streptomyces metabolite, to the mammalian /1-type subunit /15/X irreversibly inhibits its proteolytic activity... 

In recent years, a number of structurally distinct compounds targeting the proteasome have reached the clinic, amongst others the covalent and irreversible inhibitor carfilzomib [5]. The structure of carfilzomib is based on that of the natural product, epoxomicin, that also features the epoxyketone electrophilic trap. Indeed, numerous natural product proteasome inhibitors with a distinguishing electrophile grafted onto a peptidic core have been described over the years, including lactacystin, syringolin A (SylA), and fellutamide B. An important class of synthetic covalent proteasome inhibitors is represented by the peptide vinyl sulfones, whereas numerous noncovalent proteasome inhibitors have been discovered as well (e.g., TMC 95A). 

Activity-based probes (ABPs) are tagged covalent and irreversible enzyme inhibitors. Formation of a stable covalent bond ensures that the inhibitor will remain attached to the polypeptide after protein denaturation, after which the tag (radio-isotope, biotin, fluorophore) allows visualization and/or identification of the thus modified enzyme or enzyme family. The first proteasome ABP described comprised a tritium-labeled lactacystin analog [6,7]. Proteasome bands are visualized on one-dimensional SDS-PAGE (sodium docecylsulfate-polyacrylamide gel electrophoresis) gel in an autoradiogram after treatment with a radiolabeled... 

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