Introduction: The ubiquitin-proteasome system is responsible for maintaining protein homeostasis and regulating a variety of cellular processes. The constitutive proteasome is expressed in all cells while the immunoproteasome (IP) is predominantly found in cells of hematopoietic origin. In other cells, the expression of IP can be induced under the influence of cytokines released by T cells during acute immune and stress responses. Inhibitors of IP are of significant interest, because it is expected that selective inhibition of the IP would cause fewer adverse effects. Areas covered: There is a considerable interest on patenting IP-specific inhibitors. Relevant patents and patent applications disclosing IP inhibitors are summarized and divided into two parts according to the chemical characteristics of compounds. We also briefly report on the biochemical methods used in the patents to profile the characteristics of IP inhibitors. Expert opinion: Several selective inhibitors of IP with a promising ability to address autoimmune and inflammatory diseases are being developed. Peptidic compounds are prevalent and the most advanced IP-selective compounds to date, ONX-0914 and KZR-616, are tripeptideepoxyketone-based molecules. However, some patents disclose that IP-selective inhibition is possible with compounds possessing non-peptidic scaffolds indicating countless possibilities to address inhibition of IP in the future.
COBISS.SI-ID: 4522609
Proteasomes contribute to maintaining protein homeostasis and their inhibition is beneficial in certain types of cancer and in autoimmune diseases. However, the inhibition of the proteasomes in healthy cells leads to unwanted side-effects and significant effort has been made to identify inhibitors specific for the immunoproteasome, especially to treat diseases which manifest increased levels and activity of this proteasome isoform. Here, we report our efforts to discover fragment-sized inhibitors of the human immunoproteasome. The screening of an in-house library of structurally diverse fragments resulted in the identification of benzo[d]oxazole-2(3H)-thiones, benzo[d]thiazole-2(3H)-thiones, benzo[d]imidazole-2(3H)-thiones, and 1-methylbenzo[d]imidazole-2(3H)-thiones (with a general term benzoXazole-2(3H)-thiones) as inhibitors of the chymotrypsin-like ([beta]5i) subunit of the immunoproteasome. A subsequent structure-activity relationship study provided us with an insight regarding growing vectors. Binding to the [beta]5i subunit was shown and selectivity against the [beta]5 subunit of the constitutive proteasome was determined. Thorough characterization of these compounds suggested that they inhibit the immunoproteasome by forming a disulfide bond with the Cys48 available specifically in the [beta]5i active site. To obtain fragments with biologically more tractable covalent interaction, we performed a warhead scan, which yielded benzoXazole-2-carbonitriles as promising starting points for the development of selective immunoproteasome inhibitors with non-peptidic scaffolds.
COBISS.SI-ID: 60628739
Targeted covalent inhibition and the use of irreversible chemical probes are important strategies in chemical biology and drug discovery. To date, the availability and reactivity of cysteine residues amenable for covalent targeting have been evaluated by proteomic and computational tools. Here, we present a toolbox of fragments containing a 3,5-bis(trifluoromethyl)phenyl core that was equipped with chemically diverse electrophilic warheads showing a range of reactivities. We characterized the library members for their reactivity, aqueous stability and specificity for nucleophilic amino acids. By screening this library against a set of enzymes amenable for covalent inhibition, we showed that this approach experimentally characterized the accessibility and reactivity of targeted cysteines. Interesting covalent fragment hits were obtained for all investigated cysteine-containing enzymes, including immunoproteasome.
COBISS.SI-ID: 31846915
The benzimidazole-2-thione scaffold is present in many drugs encompassing various therapeutic areas. Due to the broad spectrum of bioactivities it also represents an important starting point in drug discovery campaigns, especially those based on fragment-based design. Despite simple structures the tautomerism and regioisomerism of substituted benzimidazole-2-thiones makes unambiguous structural analysis difficult. Tautomeric duplicates are present in commercial libraries resulting in two tautomers being sold as different products. To showcase an example of appropriate structural determination, we synthesized and characterized a set of benzimidazole-2-thiones with different positions of a chlorine atom on the ring. Using NOESY and 13C NMR spectroscopy, we determined that the thione tautomer predominates in the thione-thiol equilibrium. Furthermore, NOESY and HMBC experiments confirmed the position of the substituents on the benzimidazole-2-thione ring.
COBISS.SI-ID: 4768113
Large-scale virtual screening of boronic acid derivatives was performed to identify nonpeptidic covalent inhibitors of the %5i subunit of the immunoproteasome. A hierarchical virtual screening cascade including noncovalent and covalent docking steps was applied to a virtual library of over 104,000 compounds. Then, 32 virtual hits were selected, out of which five were experimentally confirmed. Biophysical and biochemical tests showed micromolar binding affinity and time-dependent inhibitory potency for two compounds. These results validate the computational protocol that allows the screening of large compound collections. One of the lead-like boronic acid derivatives identified as a covalent immunoproteasome inhibitor is a suitable starting point for chemical optimization.
COBISS.SI-ID: 4765297