Chan W Y, McKinzie D L, Bose S, Mitchell S N, Witkin J M, Thompson R C, Christopoulos A, Lazareno S, Birdsall N J M, Bymaster F P, Felder C C
Neuroscience Discovery Research, Lilly Research Centre, Surrey GU20 6PH, United Kingdom.
Proc Natl Acad Sci U S A. 2008 Aug 5;105(31):10978-83. doi: 10.1073/pnas.0800567105. Epub 2008 Aug 4.
Current antipsychotics provide symptomatic relief for patients suffering from schizophrenia and related psychoses; however, their effectiveness is variable and many patients discontinue treatment due to side effects. Although the etiology of schizophrenia is still unclear, a leading hypothesis implicates an imbalanced dopaminergic system. Muscarinic acetylcholine (ACh) receptors regulate dopamine levels in key areas of the brain involved in psychosis, with the M(4) subtype emerging as a key regulator of dopaminergic hyperactivity. Unfortunately, no selective small molecule tools exist to provide pharmacological validation of this hypothesis. Here, we describe the discovery of a small molecule modulator, LY2033298, that is highly selective for human M(4) receptors by virtue of targeting an allosteric site on this receptor. Pharmacological assays confirmed the selectivity of LY2033298 for the M(4) receptor and revealed the highest degree of positive allosteric enhancement of ACh potency thus far identified. Radioligand binding assays also show this compound to directly potentiate agonist binding while having minimal effects on antagonist binding. Mutational analysis identified a key amino acid (D(432)) in the third extracellular loop of the human M(4) receptor to be critical for selectivity and agonist potentiation by LY2033298. Importantly, LY2033298 was active in animal models predictive of clinical antipsychotic drug efficacy indicating its potential use as a first-in-class, selective, allosteric muscarinic antipsychotic agent.
目前的抗精神病药物能为患有精神分裂症及相关精神病的患者缓解症状；然而，其疗效存在差异，许多患者因副作用而停止治疗。尽管精神分裂症的病因仍不明确，但一个主要假说是多巴胺能系统失衡。毒蕈碱型乙酰胆碱（ACh）受体调节参与精神病的大脑关键区域的多巴胺水平，其中M(4)亚型成为多巴胺能亢进的关键调节因子。不幸的是，目前没有选择性小分子工具来对这一假说进行药理学验证。在此，我们描述了一种小分子调节剂LY2033298的发现，它通过靶向人M(4)受体上的一个变构位点，对该受体具有高度选择性。药理学分析证实了LY2033298对M(4)受体的选择性，并揭示了迄今为止所确定的ACh效力的最高程度的正变构增强。放射性配体结合分析也表明该化合物能直接增强激动剂结合，而对拮抗剂结合的影响最小。突变分析确定人M(4)受体第三个细胞外环中的一个关键氨基酸（D(432)）对LY2033298的选择性和激动剂增强作用至关重要。重要的是，LY2033298在预测临床抗精神病药物疗效的动物模型中具有活性，表明其有潜力作为一流的选择性变构毒蕈碱抗精神病药物使用。
