Endogenous vitamin E metabolites mediate allosteric PPARγ activation with unprecedented co-regulatory interactions.

Vitamin E exhibits pharmacological effects beyond established antioxidant activity suggesting involvement of unidentified mechanisms. Here, we characterize endogenously formed tocopherol carboxylates and the vitamin E mimetic garcinoic acid (GA) as activators of the peroxisome proliferator-activated receptor gamma (PPARγ). Co-stimulation of PPARγ with GA and the orthosteric agonist pioglitazone resulted in additive transcriptional activity. In line with this, the PPARγ-GA complex adopted a fully active conformation and interestingly contained two bound GA molecules with one at an allosteric site. A co-regulator interaction scan demonstrated an unanticipated co-factor recruitment profile for GA-bound PPARγ compared with canonical PPARγ agonists and gene expression analysis revealed different effects of GA and pioglitazone on PPAR signaling in hepatocytes. These observations reveal allosteric mechanisms of PPARγ modulation as an alternative avenue to PPARγ targeting and suggest contributions of PPARγ activation by α-13-tocopherolcarboxylate to the pharmacological effects of vitamin E.

l-Thyroxin and the Nonclassical Thyroid Hormone TETRAC Are Potent Activators of PPARγ.

Thyroid hormones (THs) operate numerous physiological processes through modulation of the nuclear thyroid hormone receptors and several other proteins. We report direct activation of the nuclear peroxisome proliferator-activated receptor gamma (PPARγ) and retinoid X receptor (RXR) by classical and nonclassical THs as another molecular activity of THs. The T4 metabolite TETRAC was the most active TH on PPARγ with nanomolar potency and binding affinity. We demonstrate that TETRAC promotes PPARγ/RXR signaling in cell-free, cellular, and in vivo settings. Simultaneous activation of the heterodimer partners PPARγ and RXR resulted in high dimer activation efficacy. Compared to fatty acids as known natural ligands of PPARγ and RXR, TETRAC differs markedly in its molecular structure and the PPARγ-TETRAC complex revealed a distinctive binding mode of the TH. Our observations suggest a potential connection of TH and PPAR signaling through overlapping ligand recognition and may hold implications for TH and PPAR pharmacology.

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.

Computer-Assisted Discovery and Structural Optimization of a Novel Retinoid X Receptor Agonist Chemotype.

As universal heterodimer partners of many nuclear receptors, the retinoid X receptors (RXRs) constitute key transcription factors. They regulate cell proliferation, differentiation, inflammation, and metabolic homeostasis and have recently been proposed as potential drug targets for neurodegenerative and inflammatory diseases. Owing to the hydrophobic nature of RXR ligand binding sites, available synthetic RXR ligands are lipophilic, and their structural diversity is limited. Here, we disclose the computer-assisted discovery of a novel RXR agonist chemotype and its systematic optimization toward potent RXR modulators. We have developed a nanomolar RXR agonist with high selectivity among nuclear receptors and superior physicochemical properties compared to classical rexinoids that appears suitable for in vivo applications and as lead for future RXR-targeting medicinal chemistry.

Urate transporter inhibitor lesinurad is a selective peroxisome proliferator-activated receptor gamma modulator (sPPARγM) in vitro.

Gout is the most common arthritic disease in human but was long neglected and therapeutic options are not satisfying. However, with the recent approval of the urate transporter inhibitor lesinurad, gout treatment has experienced a major innovation. Here we show that lesinurad possesses considerable modulatory potency on peroxisome proliferator-activated receptor γ (PPARγ). Since gout has a strong association with metabolic diseases such as type 2 diabetes, this side-activity appears as very valuable contributing factor to the clinical efficacy profile of lesinurad. Importantly, despite robustly activating PPARγ in vitro, lesinurad lacked adipogenic activity, which seems due to differential coactivator recruitment and is characterized as selective PPARγ modulator (sPPARγM).

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.