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，仅在美国就有670万患者受到影响。迄今为止，还没有确定治疗剂，并且通常处方的治疗剂（多奈哌齐、美金刚）补救症状，但在治疗潜在病症方面完全无效。当代文献表明，神经毒性犬尿氨酸途径（KP）代谢产物的积累可能会促进AD的发病机制。一种这样的神经毒性KP代谢物喹啉酸（QUIN）激动N-甲基-D-天冬氨酸（NMDA）受体并发挥广谱神经毒性，特别是在海马和纹状体中。值得注意的是，海马的神经变性是AD痴呆的标志。因此，QUIN生物合成的调节提供了治疗AD的有吸引力的方法。在拟议的研究中，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是一种四聚体血红素依赖性酶，负责KP的速率决定第一步。我们的目标不是靶向血红素依赖性TDO活性位点，而是靶向在活性四聚体的稳定性中起关键作用的非催化结合位点。拟议研究的中心假设是，小分子介导的这种非催化位点的不稳定化构成了一种调节神经毒性KP代谢物的新方法，因此是治疗AD的新方法。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的非催化位点选择性小分子降解剂。目标2将通过一系列生物化学测定来评估目标1中产生的化合物的治疗可行性。具体而言，将通过ELISA测定、定量KP代谢物分析和等温量热法测量每种化合物的TDO降解作用。将通过MDCK和微粒体稳定性试验评估选定化合物的药代动力学特征。总之，这些目标将提供CNS渗透剂TDO降解剂，并表征其对神经毒性KP代谢物增殖的药理作用。所确定的配体可以作为有价值的工具化合物的后续研究在翻译神经科学询问的作用KP代谢产物在AD发病机制。

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.