D1 dopamine receptor positive allosteric modulators as a practical treatment for cognitive decline

D1多巴胺受体阳性变构调节剂作为认知功能减退的实用疗法 摘要：激活D1多巴胺(DA)受体(D1R)是治疗阿尔茨海默病或其他疾病(如精神分裂症和帕金森病)中观察到的认知功能下降的一种有前途的治疗策略。Goldman-Rakic和他的同事的工作表明，前额叶皮质(PFC)中D1R活动的最佳水平是学习和记忆最佳表现所必需的。这导致了PFC中D1R活动与认知功能关系的倒U假设。在低水平的D1R信号中，例如在疾病状态下，认知功能是次优的。在压力下观察到的极高水平的D1R活动时，认知功能也处于次优水平。在阿尔茨海默病模型中，D1R激动剂在改善认知能力下降方面显示出良好的疗效，然而，正畸D1R激动剂固有的临床易感性限制了它们的治疗翻译。D1R阳性变构调节剂(PAM)具有高选择性、更大的治疗窗口和降低耐受性的潜力。我们已经从高通量筛选(HTS)中鉴定出四种结构不同的HIT支架。初步的药理学特征已经证实这些HITS是D1R PAM化合物，本身没有可测量的D1R激动剂。这项提案的重点是选择性地将这些受攻击的化合物推进到治疗线索中。 所有四个HTS化合物在结构上都与已知的DA配体不同，它们的D1R PAM活性已得到重新确认。在广泛的药理研究中，两种化合物(噻吩基和嘧啶酮基化合物)得到了进一步的表征。这两个化合物都增强了DA刺激的G蛋白和arrestin介导的信号转导，并增加了DA对D1R的亲和力。噻吩类化合物已被证明是一种有用的化学工具，并使我们能够确定第二个D1R变构结合位点，据我们所知，这是这种支架所独有的。当联合测试时，最大有效浓度的噻吩基和嘧啶酮基PAM比单独使用PAM在更大程度上增强DA刺激的信号。如果不引用独立调节这两个不同PAM作用的两个D1R变构位点的存在，这些数据很难解释。用化合物B和DETQ重复这样的联合实验，DETQ是分别由百时美施贵宝和礼来公司开发的已知的与细胞内环2(ICL2)结合的D1R PAM。化合物B和DETQ均与噻吩化学型相加，但不与嘧啶化合型相加，进一步表明D1R至少有两个独立的PAM结合部位。我们努力的一个主要焦点将是优化噻吩HIT支架，该支架以D1R内一个新的和未探索的变构位置为目标，以促进治疗线索的开发。D1R PAM的治疗潜力和迄今为止的累积证据支持进一步研究新的支架和有希望的先导化合物的药理学特征。这种系统的方法将提供最先进的工具分子来研究D1R变构部位，并促进D1R PAM的治疗作用。

Title: D1 dopamine receptor positive allosteric modulators as a practical treatment for cognitive decline Summary: Activation of the D1 dopamine (DA) receptor (D1R) is a promising treatment strategy for the cognitive decline observed in Alzheimer’s disease or other disorders such as schizophrenia and Parkinson’s disease. Work by Goldman-Rakic and colleagues has shown that an optimum level of D1R activity in the prefrontal cortex (PFC) is required for optimum performance in learning and memory. This has led to the inverted-U hypothesis for the relationship of D1R activity in the PFC and cognitive function. At low levels of D1R signaling, such as in diseased states, cognitive function is suboptimum. At extremely high levels of D1R activity, as observed during stress, cognitive function is also at suboptimum levels. D1R agonists have shown promising efficacy in Alzheimer’s disease models for ameliorating cognitive decline, however the clinical liability inherent with orthosteric D1R agonists has limited their therapeutic translation. D1R positive allosteric modulators (PAMs) have the potential for high selectivity, larger therapeutic windows and reduced tolerance. We have identified four structurally distinct hit scaffolds from high-throughput screening (HTS). Preliminary pharmacological characterization has validated these hits as D1R PAM compounds with no measurable D1R agonism on their own. The focus of this proposal is to selectively advance these hit compounds into therapeutic leads. All four HTS hits are structurally distinct from known DA ligands and their D1R PAM activities have been reconfirmed. Two hits (thiophene- and pyrimidone-based compounds) have been further characterized in a wide range of pharmacological studies. Both compounds potentiate DA-stimulated G protein- and -arrestin-mediated signaling and increase the affinity of DA for the D1R. The thiophene hit has proven useful as a chemical tool and allowed us to identify a second D1R allosteric binding site that, to our knowledge, is unique to this scaffold. When tested in combination, maximally effective concentrations of both thiophene- and pyrimidone-based PAMs potentiate DA-stimulated signaling to a greater extent than either PAM alone. These data are difficult to explain without invoking the existence of two D1R allosteric sites that independently mediate the actions of these two different PAMs. Such combination experiments were repeated with Compound B and DETQ, known intracellular loop 2 (ICL2)-binding D1R PAMs that were developed by Bristol-Myers Squibb and Eli Lilly, respectively. Both Compound B and DETQ were additive with the thiophene chemotype, but not with the pyrimidone chemotype, further suggesting that the D1R has at least two separate PAM binding sites. A major focus of our efforts will be to optimize the thiophene hit scaffold that targets a novel and unexplored allosteric site within the D1R to facilitate the development of therapeutic leads. The therapeutic potential for D1R PAMs and the cumulative evidence to date supports further investigation of new scaffolds and the pharmacological characterization of promising lead compounds. Such a systematic approach will provide state-of-the-art tool molecules to investigate D1R allosteric sites as well as advance the therapeutic utility of D1R PAMs.