Proteasome composition in immune cells implies special immune­cell­specific immunoproteasome function.

Immunoproteasomes are a special class of proteasomes, which can be induced with IFN-γ in an inflammatory environment. In recent years, it became evident that certain immune cell types constitutively express high levels of immunoproteasomes. However, information regarding the basal expression of proteolytically active immunoproteasome subunits in different types of immune cells is still rare. Hence, we quantified standard proteasome subunits (ß1c, ß2c, ß5c) and immunoproteasome subunits (LMP2, MECL-1, LMP7) in the major murine (CD4+ T cells, CD8+ T cells, CD19+ B cells, CD11c+ dendritic cells, CD49d+ natural killer cells, Ly-6G+ neutrophils) and human immune cell (CD4+ T cells, CD8+ T cells, CD19+ B cells, CD1c+CD141+ myeloid dendritic cells, CD56+ natural killer cells, granulocytes) subsets. The different human immune cell types were isolated from peripheral blood and the murine immune cell subsets from spleen. We found that proteasomes of most immune cell subsets mainly consist of immunoproteasome subunits. Our data will serve as a reference and guideline for immunoproteasome expression and imply a special role of immunoproteasomes in immune cells.

Proteasome Inhibitors and Their Pharmacokinetics, Pharmacodynamics, and Metabolism.

The proteasome is responsible for mediating intracellular protein degradation and regulating cellular function with impact on tumor and immune effector cell biology. The proteasome is found predominantly in two forms, the constitutive proteasome and the immunoproteasome. It has been validated as a therapeutic drug target through regulatory approval with 2 distinct chemical classes of small molecular inhibitors (boronic acid derivatives and peptide epoxyketones), including 3 compounds, bortezomib (VELCADE), carfilzomib (KYPROLIS), and ixazomib (NINLARO), for use in the treatment of the plasma cell neoplasm, multiple myeloma. Additionally, a selective inhibitor of immunoproteasome (KZR-616) is being developed for the treatment of autoimmune diseases. Here, we compare and contrast the pharmacokinetics (PK), pharmacodynamics (PD), and metabolism of these 2 classes of compounds in preclinical models and clinical studies. The distinct metabolism of peptide epoxyketones, which is primarily mediated by microsomal epoxide hydrolase, is highlighted and postulated as a favorable property for the development of this class of compound in chronic conditions.

Zetomipzomib (KZR-616) attenuates lupus in mice via modulation of innate and adaptive immune responses.

Zetomipzomib (KZR-616) is a selective inhibitor of the immunoproteasome currently undergoing clinical investigation in autoimmune disorders. Here, we characterized KZR-616 in vitro and in vivo using multiplexed cytokine analysis, lymphocyte activation and differentiation, and differential gene expression analysis. KZR-616 blocked production of >30 pro-inflammatory cytokines in human peripheral blood mononuclear cells (PBMCs), polarization of T helper (Th) cells, and formation of plasmablasts. In the NZB/W F1 mouse model of lupus nephritis (LN), KZR-616 treatment resulted in complete resolution of proteinuria that was maintained at least 8 weeks after the cessation of dosing and was mediated in part by alterations in T and B cell activation, including reduced numbers of short and long-lived plasma cells. Gene expression analysis of human PBMCs and tissues from diseased mice revealed a consistent and broad response focused on inhibition of T, B, and plasma cell function and the Type I interferon pathway and promotion of hematopoietic cell lineages and tissue remodeling. In healthy volunteers, KZR-616 administration resulted in selective inhibition of the immunoproteasome and blockade of cytokine production following ex vivo stimulation. These data support the ongoing development of KZR-616 in autoimmune disorders such as systemic lupus erythematosus (SLE)/LN.

Discovery and Early Clinical Development of Selective Immunoproteasome Inhibitors.

Inhibitors of the proteolytic activity of the 20S proteasome have transformed the treatment of multiple B-cell malignancies. These agents have also been employed with success in the treatment of patients with autoimmune diseases and immune-mediated disorders. However, new agents are needed to fully unlock the potential of proteasome inhibitors as immunomodulatory drugs. The discovery that selective inhibitors of the immunoproteasome possess broad anti-inflammatory activity in preclinical models has led to the progression of multiple compounds to clinical trials. This review focuses on the anti-inflammatory potential of immunoproteasome inhibition and the early development of KZR-616, the first selective inhibitor of the immunoproteasome to reach clinical testing.