ONX-0914 (PR-957)

ONX-0914, previously known as PR-975, is a potent inhibitor of immunoproteasome, a form of proteasome generating peptides presented on major histocompatibility complex (MHC) class I molecule to cytotixic T cells, which selectively induces conformational changes in the S1 binding pocket of the immunoproteasome subunit β5i (low molecular mass polypeptide 7/LMP7) rather than the constitutive proteasome subunit β5 in human and mouse cells. ONX-0914 is able to block the production of proinflammatory cytokines from human peripheral blood mononuclear cells (PBMCs), activate mouse splenocytes, inhibit IL-17-producing T cells under TH17-polarizing cytokines in vitro, and attenuate disease progression of diabetes, arthritis, and colitis in mouse models.

Reference

Denise Niewerth, Niels E. Franke, Gerrit Jansen, Yehuda G. Assaraf, Johan van Meerloo, Christopher. Kirk, Jeremiah Degenhardt, Janet Anderl, Aaron D. Schimmer, Sonja Zweegman, Valerie de Haas, Terzah M. Horton, Gertjan J.L. Kaspers, and Jacqueline Cloos. Higer ratio immune vs. constitutive proteasome level as novel indicator of sensitivity of pediatric acute leukemia cells to proteasome inhibitors. Haematologica 2013.

Khalid W. Kalim, Michael Basler, Christopher J. Kirk and Marcus Groettrup. Immunoproteasome subunit LMP7 deficiency and inhibition suppresses Th1 and Th17 but enhances regulatory T cell differentiation. J Immunol 2012; 189:4182-4193

Therapeutic Potential of Immunoproteasome Inhibition in Duchenne Muscular Dystrophy.[Pubmed:27506451]

Mol Ther. 2016 Nov;24(11):1898-1912.

Duchenne muscular dystrophy is an inherited fatal genetic disease characterized by mutations in dystrophin gene, causing membrane fragility leading to myofiber necrosis and inflammatory cell recruitment in dystrophic muscles. The resulting environment enriched in proinflammatory cytokines, like IFN-gamma and TNF-alpha, determines the transformation of myofiber constitutive proteasome into the immunoproteasome, a multisubunit complex involved in the activation of cell-mediate immunity. This event has a fundamental role in producing peptides for antigen presentation by MHC class I, for the immune response and also for cytokine production and T-cell differentiation. Here, we characterized for the first time the presence of T-lymphocytes activated against revertant dystrophin epitopes, in the animal model of Duchenne muscular dystrophy, the mdx mice. Moreover, we specifically blocked i-proteasome subunit LMP7, which was up-regulated in dystrophic skeletal muscles, and we demonstrated the rescue of the dystrophin expression and the amelioration of the dystrophic phenotype. The i-proteasome blocking lowered myofiber MHC class I expression and self-antigen presentation to T cells, thus reducing the specific antidystrophin T cell response, the muscular cell infiltrate, and proinflammatory cytokine production, together with muscle force recovery. We suggest that i-proteasome inhibition should be considered as new promising therapeutic approach for Duchenne muscular dystrophy pathology.

No prolongation of skin allograft survival by immunoproteasome inhibition in mice.[Pubmed:28582644]

Mol Immunol. 2017 Aug;88:32-37.

The immunoproteasome, a distinct class of proteasomes, which is inducible under inflammatory conditions and constitutively expressed in monocytes and lymphocytes, is known to shape the antigenic repertoire presented on major histocompatibility complex (MHC) class I molecules. Moreover, inhibition of the immunoproteasome subunit LMP7 ameliorates clinical symptoms of autoimmune diseases in vivo and was shown to suppress the development of T helper cell (Th) 1 and Th17 cells and to promote regulatory T-cell (Treg) generation independently of its function in antigen processing. Since Th1 and Th17 cells are detrimental and Treg cells are critical for transplant acceptance, we investigated the influence of the LMP7-selective inhibitor ONX 0914 in a mixed lymphocyte reaction (MLR) in vitro as well as on allograft rejection in a MHC-disparate (C57BL/6 to BALB/c) and a multiple minor histocompatibility antigen (miHA)-disparate (B10.Br to C3H) model of skin transplantation in vivo. Although we observed reduced allo-specific IL-17 production of T cells in vitro, we found that selective inhibition of LMP7 had neither an influence on allograft survival in an MHC-mismatch model nor in a multiple minor mismatch skin transplantation model. We conclude that inhibition of the immunoproteasome is not effective in prolonging skin allograft survival in skin allotransplantation.

Structural Elucidation of a Nonpeptidic Inhibitor Specific for the Human Immunoproteasome.[Pubmed:28098422]

Chembiochem. 2017 Mar 16;18(6):523-526.

Selective inhibition of the immunoproteasome is a promising approach towards the development of immunomodulatory drugs. Recently, a class of substituted thiazole compounds that combine a nonpeptidic scaffold with the absence of an electrophile was reported in a patent. Here, we investigated the mode of action of the lead compound by using a sophisticated chimeric yeast model of the human immunoproteasome for structural studies. The inhibitor adopts a unique orientation perpendicular to the beta5i substrate-binding channel. Distinct interactions between the inhibitor and the subpockets of the human immunoproteasome account for its isotype selectivity.

ONX-0914, a selective inhibitor of immunoproteasome, ameliorates experimental autoimmune myasthenia gravis by modulating humoral response.[Pubmed:28844501]

J Neuroimmunol. 2017 Oct 15;311:71-78.

Accumulating evidence shows that the immunoproteasome participates in the immune response, beyond its initial role in the protein degradation. Here, we tested the effects of the selective immunoproteasome inhibitor, ONX-0914, on experimental autoimmune myasthenia gravis (EAMG). We found that ONX-0914 ameliorated the severity of ongoing EAMG by reducing the autoantibody affinity, accompanied with decreased Tfh cells and antigen presenting cells. Also it reduced the percentage of Th17 cells and inhibited the secretion of IL-17. Our data indicated ONX-0914 may bring benefit for MG therapy.

PR-957, a selective inhibitor of immunoproteasome subunit low-MW polypeptide 7, attenuates experimental autoimmune neuritis by suppressing Th17-cell differentiation and regulating cytokine production.[Pubmed:28096232]

FASEB J. 2017 Apr;31(4):1756-1766.

Experimental autoimmune neuritis (EAN) is a CD4(+) T-cell-mediated autoimmune inflammatory demyelinating disease of the peripheral nervous system. It has been replicated in an animal model of human inflammatory demyelinating polyradiculoneuropathy, Guillain-Barre syndrome. In this study, we evaluated the therapeutic efficacy of a selective inhibitor of the immunoproteasome subunit, low-MW polypeptide 7 (PR-957) in rats with EAN. Our results showed that PR-957 significantly delayed onset day, reduced severity and shortened duration of EAN, and alleviated demyelination and inflammatory infiltration in sciatic nerves. In addition to significantly regulating expression of the cytokine profile, PR-957 treatment down-regulated the proportion of proinflammatory T-helper (Th)17 cells in sciatic nerves and spleens of rats with EAN. Data presented show the role of PR-957 in the signal transducer and activator of transcription 3 (STAT3) pathway. PR-957 not only decreased expression of IL-6 and IL-23 but also led to down-regulation of STAT3 phosphorylation in CD4(+) T cells. Regulation of the STAT3 pathway led to a reduction in retinoid-related orphan nuclear receptor gamma t and IL-17 production. Furthermore, reduction of STAT3 phosphorylation may have directly suppressed Th17-cell differentiation. Therefore, our study demonstrates that PR-957 could potently alleviate inflammation in rats with EAN and that it may be a likely candidate for treating Guillain-Barre syndrome.-Liu, H., Wan, C., Ding, Y., Han, R., He, Y., Xiao, J., Hao, J. PR-957, a selective inhibitor of immunoproteasome subunit low-MW polypeptide 7, attenuates experimental autoimmune neuritis by suppressing Th17-cell differentiation and regulating cytokine production.