Activity Screening of Fatty Acid Mimetic Drugs Identified Nuclear Receptor Agonists.

Fatty acid mimetics (FAM) are bioactive molecules acting through the binding sites of endogenous fatty acid metabolites on enzymes, transporters, and receptors. Due to the special characteristics of these binding sites, FAMs share common chemical features. Pharmacological modulation of fatty acid signaling has therapeutic potential in multiple pathologies, and several FAMs have been developed as drugs. We aimed to elucidate the promiscuity of FAM drugs on lipid-activated transcription factors and tested 64 approved compounds for activation of RAR, PPARs, VDR, LXR, FXR, and RXR. The activity screening revealed nuclear receptor agonism of several FAM drugs and considerable promiscuity of NSAIDs, while other compound classes evolved as selective. These screening results were not anticipated by three well-established target prediction tools, suggesting that FAMs are underrepresented in bioactivity data for model development. The screening dataset may therefore valuably contribute to such tools. Oxaprozin (RXR), tianeptine (PPARδ), mycophenolic acid (RAR), and bortezomib (RAR) exhibited selective agonism on one nuclear receptor and emerged as attractive leads for the selective optimization of side activities. Additionally, their nuclear receptor agonism may contribute relevant and valuable polypharmacology.

Structural optimization and in vitro profiling of N-phenylbenzamide-based farnesoid X receptor antagonists.

Activation of the nuclear farnesoid X receptor (FXR) which acts as cellular bile acid sensor has been validated as therapeutic strategy to counter liver disorders such as non-alcoholic steatohepatitis by the clinical efficacy of obeticholic acid. FXR antagonism, in contrast, is less well studied and potent small molecule FXR antagonists are rare. Here we report the systematic optimization of a novel class of FXR antagonists towards low nanomolar potency. The most optimized compound antagonizes baseline and agonist induced FXR activity in a full length FXR reporter gene assay and represses intrinsic expression of FXR regulated genes in hepatoma cells. With this activity and a favorable toxicity-, stability- and selectivity-profile it appears suitable to further study FXR antagonism in vitro and in vivo.

Development and Profiling of Inverse Agonist Tools for the Neuroprotective Transcription Factor Nurr1.

The ligand-sensing transcription factor nuclear receptor related 1 (Nurr1) evolves as an appealing target to treat neurodegenerative diseases. Despite its therapeutic potential observed in various rodent models, potent modulators for Nurr1 are lacking as pharmacological tools. Here, we report the structure-activity relationship and systematic optimization of indole-based inverse Nurr1 agonists. Optimized analogues decreased the receptor's intrinsic transcriptional activity by up to more than 90% and revealed preference for inhibiting Nurr1 monomer activity. In orthogonal cell-free settings, we detected displacement of NCoRs and disruption of the Nurr1 homodimer as molecular modes of action. The inverse Nurr1 agonists reduced the expression of Nurr1-regulated genes in T98G cells, and treatment with an inverse Nurr1 agonist mimicked the effect of Nurr1 silencing on interleukin-6 release from LPS-stimulated human astrocytes. The indole-based inverse Nurr1 agonists valuably extend the toolbox of Nurr1 modulators to further probe the role of Nurr1 in neuroinflammation, cancer, and beyond.

Development and in†vitro Profiling of Dual FXR/LTA4H Modulators.

Designed polypharmacology presents as an attractive strategy to increase therapeutic efficacy in multi-factorial diseases by a directed modulation of multiple involved targets with a single molecule. Such an approach appears particularly suitable in non-alcoholic steatohepatitis (NASH) which involves hepatic steatosis, inflammation and fibrosis as pathological hallmarks. Among various potential pharmacodynamic mechanisms, activation of the farnesoid X receptor (FXRa) and inhibition of leukotriene A4 hydrolase (LTA4Hi) hold promise to counteract NASH according to preclinical and clinical observations. We have developed dual FXR/LTA4H modulators as pharmacological tools, enabling evaluation of this polypharmacology concept to treat NASH and related pathologies. The optimized FXRa/LTA4Hi exhibits well-balanced dual activity on the intended targets with sub-micromolar potency and is highly selective over related nuclear receptors and enzymes rendering it suitable as tool to probe synergies of dual FXR/LTA4H targeting.

A New FXR Ligand Chemotype with Agonist/Antagonist Switch.

Therapeutic modulation of the bile acid-sensing transcription factor farnesoid X receptor (FXR) is an appealing strategy to counteract hepatic and metabolic diseases. Despite the availability of several highly potent FXR agonists structural diversity of FXR modulators is limited, and new ligand scaffolds are needed. Here we report structure-activity relationship elucidation of a new FXR modulator chemotype whose activity can be tuned between agonism and antagonism by two minor structural modifications. Starting from a weak FXR/PPAR agonist, we have developed selective FXR activators and antagonists with nanomolar to low-micromolar potencies and binding affinities. The new FXR ligand chemotype modulates the FXR activity in the native cellular setting, is endowed with favorable metabolic stability, and lacks cytotoxicity. It valuably expands the collection of FXR modulators as a new scaffold for FXR-targeted drug discovery.

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.

Structure-Based Design of Dual Partial Peroxisome Proliferator-Activated Receptor γ Agonists/Soluble Epoxide Hydrolase Inhibitors.

Polypharmaceutical regimens often impair treatment of patients with metabolic syndrome (MetS), a complex disease cluster, including obesity, hypertension, heart disease, and type II diabetes. Simultaneous targeting of soluble epoxide hydrolase (sEH) and peroxisome proliferator-activated receptor γ (PPARγ) synergistically counteracted MetS in various in vivo models, and dual sEH inhibitors/PPARγ agonists hold great potential to reduce the problems associated with polypharmacy in the context of MetS. However, full activation of PPARγ leads to fluid retention associated with edema and weight gain, while partial PPARγ agonists do not have these drawbacks. In this study, we designed a dual partial PPARγ agonist/sEH inhibitor using a structure-guided approach. Exhaustive structure-activity relationship studies lead to the successful optimization of the designed lead. Crystal structures of one representative compound with both targets revealed potential points for optimization. The optimized compounds exhibited favorable metabolic stability, toxicity, selectivity, and desirable activity in adipocytes and macrophages.

Design and Structural Optimization of Dual FXR/PPARδ Activators.

Nonalcoholic steatohepatitis (NASH) is considered as severe hepatic manifestation of the metabolic syndrome and has alarming global prevalence. The ligand-activated transcription factors farnesoid X receptor (FXR) and peroxisome proliferator-activated receptor (PPAR) δ have been validated as molecular targets to counter NASH. To achieve robust therapeutic efficacy in this multifactorial pathology, combined peripheral PPARδ-mediated activity and hepatic effects of FXR activation appear as a promising multitarget approach. We have designed a minimal dual FXR/PPARδ activator scaffold by rational fusion of pharmacophores derived from selective agonists. Our dual agonist lead compound exhibited weak agonism on FXR and PPARδ and was structurally refined to a potent and balanced FXR/PPARδ activator in a computer-aided fashion. The resulting dual FXR/PPARδ modulator comprises high selectivity over related nuclear receptors and activates the two target transcription factors in native cellular settings.

A triple farnesoid X receptor and peroxisome proliferator-activated receptor α/δ activator reverses hepatic fibrosis in diet-induced NASH in mice.

Non-alcoholic steatohepatitis (NASH) - a hepatic manifestation of the metabolic syndrome - is a multifactorial disease with alarming global prevalence. It involves steatosis, inflammation and fibrosis in the liver, thus demanding multiple modes of action for robust therapeutic efficacy. Aiming to fuse complementary validated anti-NASH strategies in a single molecule, we have designed and systematically optimized a scaffold for triple activation of farnesoid X receptor (FXR), peroxisome proliferator-activated receptor (PPAR) α and PPARδ. Pilot profiling of the resulting triple modulator demonstrated target engagement in native cellular settings and in mice, rendering it a suitable tool to probe the triple modulator concept in vivo. In DIO NASH in mice, the triple agonist counteracted hepatic inflammation and reversed hepatic fibrosis highlighting the potential of designed polypharmacology in NASH.

Dual Farnesoid X Receptor/Soluble Epoxide Hydrolase Modulators Derived from Zafirlukast.

The nuclear farnesoid X receptor (FXR) and the enzyme soluble epoxide hydrolase (sEH) are validated molecular targets to treat metabolic disorders such as non-alcoholic steatohepatitis (NASH). Their simultaneous modulation in vivo has demonstrated a triad of anti-NASH effects and thus may generate synergistic efficacy. Here we report dual FXR activators/sEH inhibitors derived from the anti-asthma drug Zafirlukast. Systematic structural optimization of the scaffold has produced favorable dual potency on FXR and sEH while depleting the original cysteinyl leukotriene receptor antagonism of the lead drug. The resulting polypharmacological activity profile holds promise in the treatment of liver-related metabolic diseases.

A Selective Modulator of Peroxisome Proliferator-Activated Receptor γ with an Unprecedented Binding Mode.

The nuclear peroxisome proliferator-activated receptor γ has well-validated therapeutic potential in metabolic, inflammatory, and neurodegenerative pathologies, but its activation is also associated with marked adverse effects and novel modes of PPARγ modulation are required. Here, we report the discovery and profiling of a new PPARγ modulator chemotype endowed with remarkable potency and a distinct binding mode in the orthosteric PPARγ ligand-binding site. Its R-enantiomer evolved as a eutomer regarding PPARγ activation with a high eudysmic ratio. The new PPARγ modulator revealed outstanding selectivity over the PPARα and PPARδ subtypes and did not promote adipogenesis in primary human fibroblasts, discriminating it from established agonists.

Therapeutic modulation of retinoid X receptors - SAR and therapeutic potential of RXR ligands and recent patents.

Introduction: Retinoid X receptor (RXR) agonists have a limited role in cancer therapy with bexarotene and alitretinoin as approved drugs but their use is limited by adverse effects. Several evidence from in vitro, in vivo, and small clinical studies points to various further potential applications of RXR ligands in neurodegenerative and inflammatory diseases. Areas covered: The authors review known RXR ligand classes with their key structure-activity relationships and recent reports on pharmacological effects of RXR modulation. Based on these aspects, the authors evaluate recent patents claiming novel RXR ligands or their use. Expert opinion: While the use of RXR modulators has been claimed in several novel and promising indications, little progress has been made in the development of innovative rexinoids with improved (subtype-)selectivity. Next-generation RXR modulators that selectively target the RXR subtypes for individual indications may be required to exhaustively exploit the therapeutic potential of RXRs.

Computer-Assisted Selective Optimization of Side-Activities-from Cinalukast to a PPARα Modulator.

Automated computational analogue design and scoring can speed up hit-to-lead optimization and appears particularly promising in selective optimization of side-activities (SOSA) where possible analogue diversity is confined. Probing this concept, we employed the cysteinyl leukotriene receptor 1 (CysLT1 R) antagonist cinalukast as lead for which we discovered peroxisome proliferator-activated receptor α (PPARα) modulatory activity. We automatically generated a virtual library of close analogues and classified these roughly 8000 compounds for PPARα agonism and CysLT1 R antagonism using automated affinity scoring and machine learning. A computationally preferred analogue for SOSA was synthesized, and in vitro characterization indeed revealed a marked activity shift toward enhanced PPARα activation and diminished CysLT1 R antagonism. Thereby, this prospective application study highlights the potential of automating SOSA.

A Novel Biphenyl-based Chemotype of Retinoid X Receptor Ligands Enables Subtype and Heterodimer Preferences.

The nuclear retinoid X receptors (RXRs) are key ligand sensing transcription factors that serve as universal nuclear receptor heterodimer partners and are thus involved in numerous physiological processes. Therapeutic targeting of RXRs holds high potential but available RXR activators suffer from limited safety. Selectivity for RXR subtypes or for certain RXR heterodimers are promising strategies for safer RXR modulation. Here, we report systematic structure-activity relationship studies on biphenyl carboxylates as new RXR ligand chemotype. We discovered specific structural modifications that enhance potency on RXRs, govern subtype preference, and vary modulation of different RXR heterodimers. Fusion of these structural motifs enabled specific tuning of subtype preferential profiles with markedly improved potency. Our results provide further evidence that RXR subtype selective ligands can be designed and present a novel chemotype of RXR modulators that can be tuned for subtype and heterodimer preferences.

Tuning Nuclear Receptor Selectivity of Wy14,643 towards Selective Retinoid X Receptor Modulation.

The fatty acid sensing nuclear receptor families retinoid X receptors (RXRs) and peroxisome proliferator-activated receptors (PPARs) hold therapeutic potential in neurodegeneration. Valuable pleiotropic activities of Wy14,643 in models of such conditions exceed its known PPAR agonistic profile. Here, we characterize the compound as an RXR agonist explaining the pleiotropic effects and report its systematic structure-activity relationship analysis with the discovery of specific molecular determinants driving activity on PPARs and RXRs. We have designed close analogues of the drug comprising selective and dual agonism on RXRs and PPARs that may serve as superior pharmacological tools to study the role and interplay of the nuclear receptors in various pathologies. A systematically optimized high potency RXR agonist revealed activity in vivo and active concentrations in brain. With its lack of RXR/liver X receptor-mediated side effects and superior profile compared to classical rexinoids, it establishes a new class of innovative RXR modulators to overcome key challenges in RXR targeting drug discovery.

Development of Nuclear Receptor Modulators.

With 49 members identified thus far, the superfamily of nuclear receptors offers a large number of targets to be pharmacologically exploited. Some nuclear receptors already look back to a successful history as drug targets, while others still lack any identified ligand. The development of small molecules targeting nuclear receptor is a challenging task and has to consider not only high affinity binding but also aspects as the nuclear localization of the target protein or transactivation efficacy. In this chapter, we summarize characteristics of nuclear receptors as target family, strategies of hit and lead identification, and the variety of methods for in vitro characterization of nuclear receptor modulators. A detailed method chapter describes an example optimization of a nuclear receptor modulator as well as hybrid reporter gene assays as a very flexible method of choice for in vitro characterization. Thereby, the chapter provides an introduction to nuclear receptor ligand development.

Selective Optimization of Pranlukast to Farnesoid†X Receptor Modulators.

Selective optimization of side activities (SOSA) offers an alternative entry to early drug discovery and may provide rapid access to bioactive new chemical entities with desirable properties. SOSA aims to reverse a drug's side activities through structural modification and to design out the drug's original main action. We identified a moderate side activity for the cysteinyl leukotriene receptor 1 (CysLT1 R) antagonist pranlukast on the farnesoid X receptor (FXR). Systematic structural modification of the drug allowed remarkable optimization of its partial FXR agonism to sub-nanonmolar potency. The resulting FXR modulators lack any activity on CysLT1 R and are characterized by high selectivity, high metabolic stability, and low toxicity. With their favorable in vitro profile, these SOSA-derived FXR modulators constitute a new FXR ligand chemotype that appears suitable for further preclinical evaluation.

Boosting Anti-Inflammatory Potency of Zafirlukast by Designed Polypharmacology.

Multitarget design offers access to bioactive small molecules with potentially superior efficacy and safety. Particularly multifactorial chronic inflammatory diseases demand multiple pharmacological interventions for stable treatment. By minor structural changes, we have developed a close analogue of the cysteinyl-leukotriene receptor antagonist zafirlukast that simultaneously inhibits soluble epoxide hydrolase and activates peroxisome proliferator-activated receptor γ. The triple modulator exhibits robust anti-inflammatory activity in vivo and highlights the therapeutic potential of designed multitarget agents.