Department of Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, RI 02881, USA.
Chem Biol Interact. 2010 Dec 5;188(3):512-25. doi: 10.1016/j.cbi.2010.09.018. Epub 2010 Oct 20.
Constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are closely related orphan nuclear receptor proteins that share several ligands and target overlapping sets of genes involved in homeostasis and all phases of drug metabolism. CAR and PXR are involved in the development of certain diseases, including diabetes, metabolic syndrome and obesity. Ligand screens for these receptors so far have typically focused on steroid hormone analogs with pharmacophore-based approaches, only to find relatively few new hits. Multiple CAR isoforms have been detected in human liver, with the most abundant being the constitutively active reference, CAR1, and the ligand-dependent isoform CAR3. It has been assumed that any compound that binds CAR1 should also activate CAR3, and so CAR3 can be used as a ligand-activated surrogate for CAR1 studies. The possibility of CAR3-specific ligands has not, so far, been addressed. To investigate the differences between CAR1, CAR3 and PXR, and to look for more CAR ligands that may be of use in quantitative structure-activity relationship (QSAR) studies, we performed a luciferase transactivation assay screen of 60 mostly non-steroid compounds. Known active compounds with different core chemistries were chosen as starting points and structural variants were rationally selected for screening. Distinct differences in agonist versus inverse agonist/antagonist effects were seen in 49 compounds that had some ligand effect on at least one receptor and 18 that had effects on all three receptors; eight were CAR1 ligands only, three were CAR3 only ligands and four affected PXR only. This work provides evidence for new CAR ligands, some of which have CAR3-specific effects, and provides observational data on CAR and PXR ligands with which to inform in silico strategies. Compounds that demonstrated unique activity on any one receptor are potentially valuable diagnostic tools for the investigation of in vivo molecular targets.
组成型雄烷受体 (CAR) 和孕烷 X 受体 (PXR) 是密切相关的孤儿核受体蛋白，它们共享几种配体，并且靶向重叠的基因集，这些基因涉及内稳态和药物代谢的所有阶段。CAR 和 PXR 参与某些疾病的发展，包括糖尿病、代谢综合征和肥胖症。这些受体的配体筛选迄今为止通常侧重于基于药效团的甾体激素类似物方法，结果只发现了相对较少的新靶点。在人类肝脏中已经检测到多种 CAR 同工型，其中最丰富的是组成型激活的对照物 CAR1 和配体依赖性同工型 CAR3。人们假设任何与 CAR1 结合的化合物也应该激活 CAR3，因此 CAR3 可以作为 CAR1 研究的配体激活替代物。到目前为止，尚未解决 CAR3 特异性配体的可能性。为了研究 CAR1、CAR3 和 PXR 之间的差异，并寻找可能用于定量构效关系 (QSAR) 研究的更多 CAR 配体，我们对 60 种主要非甾体化合物进行了荧光素酶转激活测定筛选。选择具有不同核心化学结构的已知活性化合物作为起始点，并进行合理选择结构变体进行筛选。在至少一种受体上具有某些配体作用的 49 种化合物中观察到激动剂与反向激动剂/拮抗剂作用的明显差异，而在 18 种化合物中则在三种受体上均具有作用；八种是 CAR1 配体，三种是 CAR3 配体，四种是 PXR 配体。这项工作为新的 CAR 配体提供了证据，其中一些具有 CAR3 特异性作用，并提供了关于 CAR 和 PXR 配体的观察数据，这些数据可用于信息学策略。在任何一种受体上表现出独特活性的化合物是研究体内分子靶标的潜在有价值的诊断工具。
