Small Molecule Degraders of Tryptophan 2,3-Dioxygenase Enzyme (TDO) as Novel Treatments for Neurodegenerative Disease

神经退行性疾病是一种新兴的公共卫生危机，阿尔茨海默病（AD）是第六大死亡原因，仅在美国就影响了670万患者。迄今为止，尚未发现任何治疗药物，常用的处方治疗药物（多奈哌齐、美金刚）可以缓解症状，但对治疗潜在疾病完全无效。当代文献表明，神经毒性犬尿氨酸途径（KP）代谢物的积累可能促进AD的发病。其中一种神经毒性KP代谢物，喹啉酸（QUIN），使n -甲基- d-天冬氨酸（NMDA）受体痛苦，并产生广谱神经毒性，特别是在海马和纹状体中。值得注意的是，海马体的神经变性是阿尔茨海默氏症的一个标志。因此，调节QUIN生物合成为治疗AD提供了一种有吸引力的方法。在我们提出的研究中，我们的目标是通过靶向色氨酸2,3-双加氧酶（TDO）来调节CNS内的QUIN生物合成。TDO是一种四聚血红素依赖酶，负责KP的第一步速率决定。我们的目标不是血红素依赖的TDO活性位点，而是在活性四聚体的稳定性中起关键作用的非催化结合位点。该研究的中心假设是，小分子介导的非催化位点的不稳定构成了调节神经毒性KP代谢物的新途径，从而成为治疗AD的新途径。我们将通过两个互补的目标来检验这一假设。目标1将利用计算建模和化学合成来提供TDO的非催化选择性小分子降解剂。Aim 2将通过一系列生化分析来评估Aim 1中产生的化合物的治疗可行性。具体来说，每种化合物的TDO降解效果将通过ELISA测定、定量KP代谢物分析和等温量热法来测量。选定化合物的药代动力学特征将通过MDCK和微粒体稳定性试验进行评估。总之，这些目标将提供cns渗透TDO降解物，并表征其对神经毒性KP代谢物传播的药理作用。所鉴定的配体可以作为有价值的工具化合物，用于转化神经科学的后续研究，以询问KP代谢物在AD发病机制中的作用。

Neurodegenerative disease is an emerging public health crisis with Alzheimer’s disease (AD) being the 6th leading cause of death that affects 6.7M patients in the US alone. To date, no curative agents have been identified, and commonly prescribed therapeutics (donepezil, memantine) remediate symptoms, but are wholly ineffective at treating the underlying condition. Contemporary literature suggests that the build-up of neurotoxic kynurenine pathway (KP) metabolites might promote AD pathogenesis. One such neurotoxic KP metabolite, quinolinic acid (QUIN), agonizes the N-methyl-D-aspartate (NMDA) receptor and exerts broad-spectrum neurotoxicity, particularly in the hippocampus and striatum. Notably, neurodegeneration of the hippocampus is a hallmark of AD dementia. As such, regulation of QUIN biosynthesis offers an attractive approach to the treatment of AD. In the proposed research, we aim to regulate QUIN biosynthesis within the CNS by targeting the tryptophan 2,3-dioxygenase enzyme (TDO). TDO is a tetrameric heme-dependent enzyme responsible for the rate-determining first step of the KP. Rather than target the heme-dependent TDO active site, we aim to target a non-catalytic binding site that plays a critical role in the stability of the active tetramer. The central hypothesis of the proposed research is that small molecule-mediated destabilization of this non-catalytic site constitutes a novel approach to the regulation of neurotoxic KP metabolites, and thus a novel approach to the treatment of AD. We will test this hypothesis through two complementary aims. Aim 1 will utilize computational modeling and chemical synthesis to deliver non-catalytic site-selective small molecule degraders of TDO. Aim 2 will assess the therapeutic viability of compounds generated in aim 1 through a series of biochemical assays. Specifically, the TDO degrading effects of each compound will be measured via an ELISA assay, quantitative KP metabolite profiling, and isothermal calorimetry. The pharmacokinetic profiles of select compounds will be assessed via MDCK and microsomal stability assays. Together, these aims will deliver CNS-penetrant TDO degraders and characterize their pharmacological effects on the propagation of neurotoxic KP metabolites. The ligands identified could serve as valuable tool compounds for follow-up studies in translational neuroscience to interrogate the role of KP metabolites in AD pathogenesis.