Synthesis and pharmacological characterization of 1-benzyl-4-aminoindole-based thyroid hormone receptor β agonists

Thyroid Hormone Receptor-β Agonists in NAFLD Therapy: Possibilities and Challenges

Nonalcoholic fatty liver disease (NAFLD) is a progressive metabolic liver disease with an unknown pathogenesis and no FDA-approved drug treatment to date. Hypothyroidism has been identified as a risk factor for NAFLD as thyroxine is required for regulating metabolism in adults. Thyroxine has been shown to reduce fat in the livers of murine models with experimentally induced NAFLD. The use of synthetic thyroxine has been shown to increase lipid metabolism leading to weight loss; however, thyroxine has also been shown to cause many side effects, especially in the heart. Overcoming these cardiac side effects involves designing agonists specific to one of the 2 gene subtypes for the thyroid hormone (TH) receptor (TR), TRβ. While the other TH receptor subtype, TRα, is mainly expressed in the heart and is responsible for thyroxine's cardiac function, TRβ is mainly expressed in the liver and is involved in liver function. Using TRβ-specific agonists to treat NAFLD can prevent cardiac and other adverse side effects. Several TRβ-specific agonists have shown positive therapeutic effects in NAFLD animal models and have entered clinical trials. We seek to provide a comprehensive updated reference of TRβ-specific agonists in this review and explore the future therapeutic potential of TRβ-specific activation in the treatment of NAFLD.

Thyroid hormone analogs for the treatment of dyslipidemia: past, present, and future

OBJECTIVE

Treatment of dyslipidemia is a major burden for public health. Thyroid hormone regulates lipid metabolism by binding the thyroid hormone receptor (TR), but the use of thyroid hormone to treat dyslipidemia is not indicated due to its deleterious effects on heart, bone, and muscle. Thyroid hormone analogs have been conceived to selectively activate TR in the liver, thus reducing potential side-effects.

METHODS

The authors searched the PubMed database to review TR and the action of thyromimetics in vitro and in animal models. Then, all double-blind, placebo controlled trials that analyzed the use of thyroid hormone analog for the treatment of dyslipidemia in humans were included. Finally, the ongoing research on the use of TR agonists was searched, searching the US National Institutes of Health Registry and the WHO International Clinical Trial Registry Platform (ICTRP).

RESULTS

Thyromimetics were tested in humans for the treatment of dyslipidemia, as a single therapeutic agent or as an add-on therapy to the traditional lipid-lowering drugs. In most trials, thyromimetics lowered total cholesterol, low-density lipoprotein cholesterol, and triglycerides, but their use has been associated with adverse side-effects, both in pre-clinical studies and in humans.

CONCLUSIONS

The use of thyromimetics for the treatment of dyslipidemia is not presently recommended. Future possible clinical applications might include their use to promote weight reduction. Thyromimetics might also represent an interesting alternative, both for the treatment of non-alcoholic steatohepatitis, and type 2 diabetes due to their positive effects on insulin sensitivity. Finally, additional experimental and clinical studies are needed for a better comprehension of the effect(s) of a long-term therapy.

Systemic optimization and structural evaluation of quinoline derivatives as transthyretin amyloidogenesis inhibitors

Wild type transthyretin (TTR) and mutant TTR misfold and misassemble into a variety of extracellular insoluble amyloid fibril and/or amorphous aggregate, which are associated with a variety of human amyloid diseases. To develop potent TTR amyloidogenesis inhibitors, we have designed and synthesized a focused library of quinoline derivatives by Pd-catalyzed coupling reaction and by the Horner-Wadsworth-Emmons reaction. The resulting 2-alkynylquinoline derivatives, (E)-2-alkenylquinoline derivatives, and (E)-3-alkenylquinoline derivatives were evaluated to inhibit TTR amyloidogenesis by utilizing the acid-mediated TTR fibril formation. Among these quinoline derivatives, compound 14c exhibited the most potent anti-TTR fibril formation activity in the screening studies, with IC50 values of 1.49 μM against WT-TTR and 1.63 μM against more amyloidogenic V30 M TTR mutant. That is comparable to that of approved therapeutic drug, tafamidis, to ameliorate transthyretin-related amyloidosis. Furthermore, rationalization of the increased efficacy of compound 14c bearing a hydrophobic substituent, such as chloride, was carried out by utilizing in silico docking study that could focus on the region of the thyroid hormone thyroxine (T4) binding sites. Additionally, the most potent compound 14c exhibited good pharmacokinetics properties. Taken together, the novel quinoline derivatives could potentially be explored as potential drug candidates to treat the human TTR amyloidosis.

Thyroid Hormone Mimetics: the Past, Current Status and Future Challenges

The association between thyroid hormone status and plasma levels of low-density lipoprotein cholesterol has raised the awareness for the development of thyroid hormone mimetics as lipid-lowering agents. The discovery of the two main types of thyroid hormone receptors (α and β) as well as the development of novel combinatorial chemistry providing organ specificity has drastically improved the selectivity of these compounds. In the past decades, several thyroid hormone mimetics have been investigated with the purpose of lowering low-density lipoprotein cholesterol levels. However, until now, none of the thyromimetics reached the stage of completing a phase III clinical trial without deleterious side effects. Here, we review the currently available literature on thyromimetics investigated for the treatment of dyslipidemia, their rise, their downfall and the challenges for the development of novel agents.

Characterisation of liver-specific distribution of a novel 1-benzyl-4-aminoindole-based thyroid hormone receptor β agonist, SKL-13784: comparison with GC-1

1. SKL-13784, a novel series of 1-benzyl-4-aminoindole-based thyroid hormone receptor β (TRβ)-selective agonists, showed higher liver selectivity than GC-1 and was poorly distributed in the heart and brain. We aimed to clarify the mechanism of liver selectivity of SKL-13784 through a comparative study with GC-1. 2. Media-loss assays using fresh rat hepatocytes showed that the Oatp family may have been involved in liver uptake for both compounds and that SKL-13784 was more efficiently taken up than GC-1. 3. In addition, the media-loss assay results showed that hepatic uptake was important in eliminating both compounds in rats. 4. The low passive permeability of SKL-13784 on the parallel artificial membrane permeability assay (PAMPA) contributed to the limited distribution of SKL-13784 into extrahepatocytes. 5. Biliary extraction was a major route of SKL-13784 and GC-1 disposition. SKL-13784 was excreted into bile unchanged and in its glucuronide form, whereas almost all GC-1 in bile was in its glucuronide form. In bile duct-cannulated rats, a 4.3-fold decrease in t1/2 of SKL-13784 was observed, implicating enterohepatic biliary recirculation. 6. The selective distribution of SKL-13784 in the liver was largely due to efficient uptake via hepatic transporters.