Discovery of potent and selective PPARα/δ dual antagonists and initial biological studies

Development of Heterocyclic PPAR Ligands for Potential Therapeutic Applications

The family of nuclear peroxisome proliferator-activated receptors (PPARα, PPARβ/δ, and PPARγ) is a set of ligand-activated transcription factors that regulate different functions in the body. Whereas activation of PPARα is known to reduce the levels of circulating triglycerides and regulate energy homeostasis, the activation of PPARγ brings about insulin sensitization and increases the metabolism of glucose. On the other hand, PPARβ when activated increases the metabolism of fatty acids. Further, these PPARs have been claimed to be utilized in various metabolic, neurological, and inflammatory diseases, neurodegenerative disorders, fertility or reproduction, pain, and obesity. A series of different heterocyclic scaffolds have been synthesized and evaluated for their ability to act as PPAR agonists. This review is a compilation of efforts on the part of medicinal chemists around the world to find novel compounds that may act as PPAR ligands along with patents in regards to PPAR ligands. The structure-activity relationship, as well as docking studies, have been documented to better understand the mechanistic investigations of various compounds, which will eventually aid in the design and development of new PPAR ligands. From the results of the structural activity relationship through the pharmacological and in silico evaluation the potency of heterocycles as PPAR ligands can be described in terms of their hydrogen bonding, hydrophobic interactions, and other interactions with PPAR.

Design, Synthesis, and Biological Evaluation of Triazolone Derivatives as Potent PPARα/δ Dual Agonists for the Treatment of Nonalcoholic Steatohepatitis

Peroxisome proliferator-activator receptors α/δ (PPARα/δ) are regarded as potential therapeutic targets for nonalcoholic steatohepatitis (NASH). However, PPARα/δ dual agonist GFT-505 exhibited poor anti-NASH effects in a phase III clinical trial, probably due to its weak PPARα/δ agonistic activity and poor metabolic stability. Other reported PPARα/δ dual agonists either exhibited limited potency or had unbalanced PPARα/δ agonistic activity. Herein, we report a series of novel triazolone derivatives as PPARα/δ dual agonists. Among them, compound H11 exhibited potent and well-balanced PPARα/δ agonistic activity (PPARα EC50 = 7.0 nM; PPARδ EC50 = 8.4 nM) and a high selectivity over PPARγ (PPARγ EC50 = 1316.1 nM) in PPAR transactivation assays. The crystal structure of PPARδ in complex with H11 revealed a unique PPARδ-agonist interaction. H11, which had excellent PK properties and a good safety profile, showed potent in vivo anti-NASH effects in preclinical models. Together, H11 holds a great promise for treating NASH or other inflammatory and fibrotic diseases.

Rational Multitargeted Drug Design Strategy from the Perspective of a Medicinal Chemist

The development of multitarget-directed ligands (MTDLs) has become a widely focused research topic, but rational design remains as an enormous challenge. This paper reviews and discusses the design strategy of incorporating the second activity into an existing single-active ligand. If the binding sites of both targets share similar endogenous substrates, MTDLs can be designed by merging two lead compounds with similar functional groups. If the binding sites are large or adjacent to the solution, two key pharmacophores can be fused directly. If the binding regions are small and deep inside the proteins, the linked-pharmacophore strategy might be the only way. The added pharmacophores of second targets should not affect the binding mode of the original ones. Moreover, the inhibitory activities of the two targets need to be adjusted to achieve an optimal ratio.

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.

Catalytic Preparation of 1-Aryl-Substituted 1,2,4-Triazolium Salts

1,4-Diaryl- and 1-aryl-4-alkyl-substituted 1,2,4-triazolium salts are convenient air-stable precursors to carbenes used both as organocatalysts or as ligands for transition metal complexes. Traditionally, they are prepared via a multistep synthetic pathway with the low-yielding formation of the triazolium ring occurring in the last step. We have developed an alternative two-step synthesis involving the conversion of a primary amine or aniline derivative to the corresponding 4-substituted triazole followed by a copper-catalyzed arylation with diaryliodonium salts. This transition metal-catalyzed arylation can be carried out under mild conditions in acetonitrile and is tolerant toward both water and oxygen. Additionally, the high functional group tolerance of the protocol described here gives easy access to triazolium salts containing heterocyclic substituents or sulfides.

Virtual identification of novel peroxisome proliferator-activated receptor (PPAR) α/δ dual antagonist by 3D-QSAR, molecule docking, and molecule dynamics simulation

The therapeutic potential of PPARs antagonists extends beyond diabetes. PPARs antagonists represent a new drug class that holds promise as a broadly applicable therapeutic approach for cancer treatment. Thus, there is a strong need to develop a rational design strategy for creating PPARs antagonists. In this study, three-dimensional quantitative structure-activity relationship (3D-QSAR) models of PPARα receptor (CoMFA-1, q ² = 0.636, r ² = 0.953; CoMSIA-1, q ² = 0.779, r ² = 0.999) and PPARδ receptor (CoMFA-2, q ² = 0.624, r ² = 0.906; CoMSIA-2, q ² = 0.627, r ² = 0.959) were successfully constructed using 35 triazolone ring derivatives. Contour map analysis revealed that the electrostatic and hydrophobic fields played vital roles in the bioactivity of dual antagonists. Molecular docking studies suggested that the hydrogen bonding, electrostatic and hydrophobic interactions all influenced the binding of receptor-ligand complex. Based on the information obtained above, we designed a series of compounds. The docking results were mutually validated with 3D-QSAR results. Three-dimensional-QSAR and absorption, distribution, metabolism, excretion and toxicity (ADMET) predictions indicated that 19 newly designed compounds possessed excellent biological activity and physicochemical properties. In summary, this research could provide theoretical guidance for the structural optimization of novel PPARα and δ dual antagonists. Communicated by Ramaswamy H. Sarma.

New Approaches to Cancer Therapy: Combining Fatty Acid Amide Hydrolase (FAAH) Inhibition with Peroxisome Proliferator-Activated Receptors (PPARs) Activation

Over the course of the past decade, peroxisome proliferator-activated receptors (PPARs) have been identified as part of the cannabinoid signaling system: both phytocannabinoids and endocannabinoids are capable of binding and activating these nuclear receptors. Fatty acid amide hydrolase (FAAH) hydrolyzes the endocannabinoid anandamide and other N-acylethanolamines. These substances have been shown to have numerous anticancer effects, and indeed the inhibition of FAAH has multiple beneficial effects that are mediated by PPARα subtype and by PPARγ subtype, especially antiproliferation and activation of apoptosis. The substrates of FAAH are also PPAR agonists, which explains the PPAR-mediated effects of FAAH inhibitors. Much like cannabinoid ligands and FAAH inhibitors, PPARγ agonists show antiproliferative effects on cancer cells, suggesting that additive or synergistic effects may be achieved through the positive modulation of both signaling systems. In this Miniperspective, we discuss the development of novel FAAH inhibitors able to directly act as PPAR agonists and their promising utilization as leads for the discovery of highly effective anticancer compounds.