Screening of Chelidonium majus isoquinoline alkaloids reveals berberine and chelidonine as selective ligands for the nuclear receptors RORß and HNF4α, respectively.

The nuclear receptors hepatocyte nuclear factor 4α (HNF4α) and retinoic acid receptor-related orphan receptor-ß (RORß) are ligand-regulated transcription factors and potential drug targets for metabolic disorders. However, there is a lack of small molecular, selective ligands to explore the therapeutic potential in further detail. Here, we report the discovery of greater celandine (Chelidonium majus) isoquinoline alkaloids as nuclear receptor modulators: Berberine is a selective RORß inverse agonist and modulated target genes involved in the circadian clock, photoreceptor cell development, and neuronal function. The structurally related chelidonine was identified as a ligand for the constitutively active HNF4α receptor, with nanomolar potency in a cellular reporter gene assay. In human liver cancer cells naturally expressing high levels of HNF4α, chelidonine acted as an inverse agonist and downregulated genes associated with gluconeogenesis and drug metabolism. Both berberine and chelidonine are promising tool compounds to further investigate their target nuclear receptors and for drug discovery.

A Fluorescence-Based Reporter Gene Assay to Characterize Nuclear Receptor Modulators.

Reporter gene assays are critical tools of nuclear receptor research for characterizing the effects of ligands on nuclear receptor activity. Common luciferase-based techniques require expensive substrates and are typically performed in endpoint format. Here, we describe a versatile reporter gene assay to observe nuclear receptor activity with fluorescent proteins as reporters. This setting is highly cost-efficient and enables observation of nuclear receptor activity over time with multiple measurements from one plate.

Development of a Potent Nurr1 Agonist Tool for In Vivo Applications.

Nuclear receptor related 1 (Nurr1) is a neuroprotective transcription factor and an emerging target in neurodegenerative diseases. Despite strong evidence for a role in Parkinson's and Alzheimer's disease, pharmacological control and validation of Nurr1 are hindered by a lack of suitable ligands. We have discovered considerable Nurr1 activation by the clinically studied dihydroorotate dehydrogenase (DHODH) inhibitor vidofludimus calcium and systematically optimized this scaffold to a Nurr1 agonist with nanomolar potency, strong activation efficacy, and pronounced preference over the highly related receptors Nur77 and NOR1. The optimized compound induced Nurr1-regulated gene expression in astrocytes and exhibited favorable pharmacokinetics in rats, thus emerging as a superior chemical tool to study Nurr1 activation in vitro and in vivo.

Mechanistic Impact of Different Ligand Scaffolds on FXR Modulation Suggests Avenues to Selective Modulators.

The bile-acid sensing nuclear farnesoid X receptor (FXR) is an attractive target for the treatment of hepatic and metabolic diseases, but application of this chemotherapeutic concept remains limited due to adverse effects of FXR activation observed in clinical trials. To elucidate the mechanistic basis of FXR activation at the molecular level, we have systematically studied FXR co-regulator interactions and dimerization in response to seven chemically diverse FXR ligands. Different molecular effects on FXR activation mediated by different scaffolds were evident and aligned with characteristic structural changes within the ligand binding domain of FXR. A partial FXR agonist acted mainly through co-repressor displacement from FXR and caused an FXR-regulated gene expression pattern markedly differing from FXR agonist effects. These results suggest selective modulation of FXR dimerization and co-regulator interactions for different ligands, offering a potential avenue for the design of gene- or tissue-selective FXR modulators.

Oxaprozin Analogues as Selective RXR Agonists with Superior Properties and Pharmacokinetics.

The retinoid X receptors (RXR) are ligand-activated transcription factors involved in multiple regulatory networks as universal heterodimer partners for nuclear receptors. Despite their high therapeutic potential in many pathologies, targeting of RXR has only been exploited in cancer treatment as the currently available RXR agonists suffer from exceptional lipophilicity, poor pharmacokinetics (PK), and adverse effects. Aiming to overcome the limitations and to provide improved RXR ligands, we developed a new potent RXR ligand chemotype based on the nonsteroidal anti-inflammatory drug oxaprozin. Systematic structure-activity relationship analysis enabled structural optimization toward low nanomolar potency similar to the well-established rexinoids. Cocrystal structures of the most active derivatives demonstrated orthosteric binding, and in vivo profiling revealed superior PK properties compared to current RXR agonists. The optimized compounds were highly selective for RXR activation and induced RXR-regulated gene expression in native cellular and in vivo settings suggesting them as excellent chemical tools to further explore the therapeutic potential of RXR.