Targeting Tryptophan Dioxygenase Degradation for Suppression of Tumor Immune Evasion

摘要 色氨酸降解途径被用来防止健康细胞中不受限制的免疫激活。 然而，肿瘤劫持了这一机制以逃避免疫监视。这一途径的关键酶， 色氨酸2，3-双加氧酶(TDO)和吲哚胺2，3-双加氧酶(IDO)是已建立的免疫检查点 蛋白质。肿瘤增强其表达以阻止T细胞增殖并诱导T细胞死亡，从而避免 免疫系统监测和提高肿瘤细胞的迁移能力。因此，抑制这些检查点 通过小分子疗法治疗癌细胞中的酶已成为一种潜在的免疫疗法 策略。迫切需要通过一种创新的方法开发出新的代理，该方法具有坚实的 了解其潜在的化学和生物学知识，以促进整体科学知识和 最终帮助公众健康长寿。从一项基础科学-临床联合研究中，我们发现了一种 人TDO中催化的L-色氨酸(L-Trp)结合部位，它与L-Trp的结合比TdO更紧密得多 催化亚铁血红素中心。新发现的L-色氨酸结合位点参与调节TDO的活性和稳定性 通过抑制泛素依赖的降解，负载L-色氨酸。这一发现启发了我们提出 一个中心假设是，这个新发现的信号位点是TDO药物开发的致命弱点。 这一应用将填补寻找蛋白质降解配体的关键需求，以探索其生物医学 潜力。为此，我们将设计一种具有新的作用模式的化合物来破坏信号的稳定 没有增强蛋白质稳定性的Tdo或结合位点。这些试剂不会以催化活性为目标 TDO，但反而会干扰其耐降解性信号。我们将评估有希望的化合物的效果 在人体TDO细胞模型上验证创新方法和目标。最终，这部作品将开启 为设计针对免疫检查点蛋白人类TDO的革命性新抑制剂打开了大门。

ABSTRACT The tryptophan degradation pathway is used to prevent unrestrained immune activation in healthy cells. However, tumors hijack this mechanism to escape immune surveillance. The key enzymes of this pathway, tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO), are established immune checkpoint proteins. Tumors enhance their expression to block T cell proliferation and induce T cell death, thereby avoiding immune system surveillance and increasing tumor cell migration capacity. Thus, inhibiting these checkpoint enzymes in cancer cells by small molecule-based therapies has emerged as a potential immunotherapeutic strategy. There is a critical need for new agents developed from an innovative approach with a solid understanding of their underlying chemistry and biology, to advance the overall scientific knowledge and to ultimately help the public live long healthy lives. From a joint basic science-clinical study we identified a non- catalytic L-tryptophan (L-Trp) binding site in human TDO, which binds L-Trp surprisingly much tighter than the catalytic heme site. The newly discovered L-Trp binding site is involved in regulating TDO activity and stability by suppressing ubiquitin-dependent degradation when loaded with L-Trp. This finding has inspired us to propose a central hypothesis that this newly discovered signaling site is an Achilles' heel of TDO for drug development. This application will fill the critical need to identify protein-degrading ligands for exploring their biomedical potential. Towards this end, we will design compounds with a novel mode of action that destabilize the signaling site of TDO or bind without enhancing the protein stability. These agents will not target the catalytic activity of TDO but instead will disrupt its degradation resistance signal. We will assess the effects of promising compounds on human TDO in cellular models to validate the innovative approach and target. In the end, this work will open the door for designing revolutionarily new inhibitors targeting the immune checkpoint protein human TDO.