Discovery of Highly Selective Inhibitors of the Immunoproteasome Low Molecular Mass Polypeptide 2 (LMP2) Subunit

Abstract

Building upon the success of bortezomib (VELCADE) and carfilzomib (KYPROLIS), the design of a next generation of inhibitors targeting specific subunits within the immunoproteasome is of interest for the treatment of autoimmune disease. There are three catalytic subunits within the immunoproteasome (low molecular mass polypeptide-7, -2, and multicatalytic endopeptidase complex subunit-1; LMP7, LMP2, and MECL-1), and a campaign was undertaken to design a potent and selective LMP2 inhibitor with sufficient properties to allow for sustained inhibition . Screening a focused library of epoxyketones revealed a series of potent dipeptides that were optimized to provide the highly selective inhibitor ().

Immunoproteasome functions explained by divergence in cleavage specificity and regulation

“…The second-generation proteasome inhibitor, carfilzomib (CFZ; Kyprolis or PR-171), which also targets the CT-L subunits, uses an irreversible epoxyketone warhead and shows reduced off-target inhibition, while circumventing resistance against bortezomib ( Arastu-Kapur et al, 2011 ; Siegel et al, 2012 ). Recently, considerable effort has been dedicated toward the development of iP-selective inhibitors ( Johnson et al, 2017 ; Dubiella et al, 2015 ; Sosič et al, 2016 ; Muchamuel et al, 2009 ) in the interest of selectively targeting iP-dominant cells for the treatment of autoimmune disorders and certain cancers. In particular, the epoxyketone inhibitor, ONX 0914 (PR-957), which preferentially inhibits the LMP7 subunit, was able to block cytokine production and attenuate disease progression in a rheumatoid arthritis mouse model at a significantly lower dose than bortezomib or CFZ ( Muchamuel et al, 2009 ).…”

Development of Novel Amides as Noncovalent Inhibitors of Immunoproteasomes

“…Column chromatography was carried out on Merck silica gel (200-400 mesh). 1 Ha nd 13 CNMR spectra were recorded on aV arian 300 MHz NMR spectrometer operating at frequencies of 300.13 and 75.47 MHz, respectively,o ro naVarian 500 MHz spectrometer operating at 499.74 and 125.73 MHz, respectively.T he residual signal of the deuterated solvent was used as an internal standard. Chemical shifts d are given in ppm and coupling constants J are expressed in Hz.…”

“…[9][10][11] In this context, several b5i and/or b1i immunoproteasome-selective inhibitors have been identified. [12][13][14] Furthermore,i nr ecent years, noncovalent proteasome/immunoproteasomei nhibitors have been generated, thus providing important insighti nto the basic concepts of noncovalent proteasome inhibitor design. [15][16][17][18] In this context, our research group has been actively involvedi nt he developmento fn ovel 20S proteasome inhibitors.…”

Chlorocarbonylsulfenyl Chloride Cyclizations Towards Piperidin-3-yl-oxathiazol-2-ones as Potential Covalent Inhibitors of Threonine Proteases

“…6 In addition, many of the investigational compounds are peptide-like compounds and this represents a serious limitation to their metabolic stability and bioavailability. 5 To overcome these problems, multiple approaches can be found in literature: design of reversible proteasome inhibitors, 12 use of structural differences in the binding sites of both proteasomes in structure-based drug design, 13,14 design of highly selective and hydrolytically more stable peptidic compounds, 15 design of highly selective non-peptidic compounds, 16 use of non-catalytic residues or allosteric sites in inhibitor design, 17 and the design of selective electrophilic warheads. 18 The majority of these compounds are covalent irreversible inhibitors bearing an electrophilic warhead that is capable of reacting with the N-terminal threonine residue in the catalytic active site of the examined protease.…”