Co‐inhibition of immunoproteasome subunits LMP2 and LMP7 is required to block autoimmunity

Abstract

Cells of hematopoietic origin express high levels of the immunoproteasome, a cytokine‐inducible proteasome variant comprising the proteolytic subunits LMP2 (β1i), MECL‐1 (β2i), and LMP7 (β5i). Targeting the immunoproteasome in pre‐clinical models of autoimmune diseases with the epoxyketone inhibitor ONX 0914 has proven to be effective. ONX 0914 was previously described as a selective LMP7 inhibitor. Here, we show that PRN1126, developed as an exclusively LMP7‐specific inhibitor, has limited effects on IL‐6 secretion, experimental colitis, and experimental autoimmune encephalomyelitis (EAE). We demonstrate that prolonged exposure of cells with ONX 0914 leads to inhibition of both LMP7 and LMP2. Co‐inhibition of LMP7 and LMP2 with PRN1126 and LMP2 inhibitors LU‐001i or ML604440 impairs MHC class I cell surface expression, IL‐6 secretion, and differentiation of naïve T helper cells to T helper 17 cells, and strongly ameliorates disease in experimental colitis and EAE. Hence, co‐inhibition of LMP2 and LMP7 appears to be synergistic and advantageous for the treatment of autoimmune diseases.

Immunoproteasome Inhibition Impairs T and B Cell Activation by Restraining ERK Signaling and Proteostasis

“…Two new findings have changed our knowledge in this respect. First, recent evidence unraveled that pre-clinically efficacious doses of ONX 0914 inhibit both, LMP7 and LMP2 ( 64 ), which explains the LMP2-co-dependency of ONX 0914-treatment effects in T cell activation (Figure 1 ). Second, while IP expression in lymphoid cells is known for decades, the high extent to which IPs account for the total proteasome content of naïve lymphocytes was underestimated.…”

Proteasomal Protein Degradation: Adaptation of Cellular Proteolysis With Impact on Virus—and Cytokine-Mediated Damage of Heart Tissue During Myocarditis

“…Beyond the tumor-suppressive potential of ONX 0914 ( 60 , 61 ), pre-clinical research utilizing this compound and other i-proteasome-selective inhibitors revealed additional putative clinical scenarios, where such drugs might improve current medical treatment. Pioneering work by the Groettrup group and others highlighted the therapeutic potential of i-proteasome inhibitors for mitigation of autoimmune-driven inflammatory tissue damage ( 50 , 59 , 62 – 64 ). KZR-616—an ortholog of ONX 0914 with high selectivity for the human i-proteasome—passed successfully phase I trials and is now in phase II trials for patients with systemic lupus erythematosus.…”

ONX 0914 Lacks Selectivity for the Cardiac Immunoproteasome in CoxsackievirusB3 Myocarditis of NMRI Mice and Promotes Virus-Mediated Tissue Damage

“…Undisputedly, the i-proteasome strongly enhances CD8 + T cell responses for some pathogens [15][16][17], yet there are also examples where the standard proteasome can efficiently compensate for the lack of intact i-proteasome activity [18,19]. Of the different compounds which can experimentally accomplish inhibition of the i-proteasome, ONX 0914 is the best characterized [20,21]. Whereas physiologically desired effects achieved by treatment with the epoxyketone ONX 0914 requires a combined inhibition of both LMP7 and LMP2 [20,21], there is also a LMP7-selective dipeptide inhibitor available which shows potent immunosuppressive activity [22].…”

“…Of the different compounds which can experimentally accomplish inhibition of the i-proteasome, ONX 0914 is the best characterized [20,21]. Whereas physiologically desired effects achieved by treatment with the epoxyketone ONX 0914 requires a combined inhibition of both LMP7 and LMP2 [20,21], there is also a LMP7-selective dipeptide inhibitor available which shows potent immunosuppressive activity [22]. Another compound referred to as PRN1126, developed as an exclusively LMP7-specific inhibitor shows, however, limited in vivo effects on adverse immune responses [21].…”

“…Whereas physiologically desired effects achieved by treatment with the epoxyketone ONX 0914 requires a combined inhibition of both LMP7 and LMP2 [20,21], there is also a LMP7-selective dipeptide inhibitor available which shows potent immunosuppressive activity [22]. Another compound referred to as PRN1126, developed as an exclusively LMP7-specific inhibitor shows, however, limited in vivo effects on adverse immune responses [21]. Nevertheless, the availability of selective i-proteasome inhibitors paved the way towards the definition of new functions of the i-proteasome.…”