Structure-Based Design of Pan-Selective Peptide Epoxyketones for the Three Human Immunoproteasome Active Sites

The proteasome inhibitors bortezomib, carfilzomib, and ixazomib all act by inhibiting multiple active sites of both constitutive proteasomes and immunoproteasomes. These clinical anticancer drugs are effective, but also display side effects, and evidence is amassing that their toxicity arises from constitutive proteasome inhibition. In this work, we describe the structure-guided discovery of a new class of pan-immunoproteasome-selective inhibitors. We identified the peptide epoxyketone BocPip-Ser (8), which targets all three human immunoproteasome active sites potently and with excellent selectivity over constitutive proteasome active sites (IC50 values for i-subunits ≤ 0.92 μM; IC50 ratio β1c/β1i: 13, β2c/β2i: 14, β5c/β5i: 18; Table 1 and Figure 3). We propose compound 8 (BocPip-Ser), which is of a similar size and general properties as carfilzomib, as a lead compound for the development of improved drugs targeting hematological cancers, and possibly also autoimmune diseases, driven by immunoproteasome but not constitutive proteasome activities.蛋白酶体抑制剂硼替佐米（bortezomib）、卡非佐米（carfilzomib）与伊沙佐米（ixazomib）均通过抑制组成型蛋白酶体（constitutive proteasome）与免疫蛋白酶体（immunoproteasome）的多个活性位点发挥作用。这类临床抗肿瘤药物疗效确切，但同时存在不良反应；越来越多证据表明，其毒性源于对组成型蛋白酶体的抑制作用。本研究报道了一类基于结构导向发现的新型泛免疫蛋白酶体选择性抑制剂。我们筛选得到肽环氧酮类化合物BocPip-Ser（8），该化合物可强效靶向人源免疫蛋白酶体全部三个活性位点，且相较于组成型蛋白酶体活性位点展现出优异的选择性：免疫蛋白酶体亚基的半数抑制浓度（IC50）≤0.92 μM；各亚基的IC50比值分别为β1c/β1i=13、β2c/β2i=14、β5c/β5i=18（详见表1与图3）。本研究提出，化合物8（BocPip-Ser）的分子尺寸与基本理化性质与卡非佐米相近，可作为先导化合物，用于开发靶向血液系统恶性肿瘤的改良药物，也有望用于治疗依赖免疫蛋白酶体而非组成型蛋白酶体活性的自身免疫性疾病。