Synthesis and biological evaluation of novel 4-hydroxytamoxifen analogs as estrogen-related receptor gamma inverse agonists

Research progress on tamoxifen and its analogs associated with nuclear receptors

Tamoxifen, a triphenylethylene-based selective estrogen-receptor modulator, is a landmark drug for the treatment of breast cancer and is also used for treating liver cancer and osteoporosis. Structural studies of tamoxifen have led to the synthesis of more than 20 novel tamoxifen analogs as receptor modulators, including 16 ERα modulators 2-17, an ERRβ inverse agonist 19 and six ERRγ inverse agonists 20-25. This paper summarizes the research progress and structure-activity relationships of tamoxifen analogs modulating these three nuclear receptors reported in the literature, and introduces the relationship between these three nuclear receptor-mediated diseases and tamoxifen analogs to guide the research of novel tamoxifen analogs.

The Tumor Microenvironment and the Estrogen Loop in Thyroid Cancer

Thyroid cancer (TC) cells employ multiple signaling pathways, such as PI3K/AKT/mTOR and RAS/Raf/MAPK, fostering cell proliferation, survival and metastasis. Through a complex interplay with immune cells, inflammatory mediators and stroma, TC cells support an immunosuppressive, inflamed, pro-carcinogenic TME. Moreover, the participation of estrogens in TC pathogenesis has previously been hypothesized, in view of the higher TC incidence observed among females. In this respect, the interactions between estrogens and the TME in TC could represent a relevant, unexplored area of research. We thereby collectively reviewed the available evidence concerning the potential carcinogenic role of estrogens in TC, specifically focusing on their crosstalk with the TME.

An Inverse Agonist GSK5182 Increases Protein Stability of the Orphan Nuclear Receptor ERRγ via Inhibition of Ubiquitination

The orphan nuclear receptor, estrogen-related receptor γ (ERRγ) is a constitutively active transcription factor involved in mitochondrial metabolism and energy homeostasis. GSK5182, a specific inverse agonist of ERRγ that inhibits transcriptional activity, induces a conformational change in ERRγ, resulting in a loss of coactivator binding. However, the molecular mechanism underlying the stabilization of the ERRγ protein by its inverse agonist remains largely unknown. In this study, we found that GSK5182 inhibited ubiquitination of ERRγ, thereby stabilizing the ERRγ protein, using cell-based assays and confocal image analysis. Y326 of ERRγ was essential for stabilization by GSK5182, as ligand-induced stabilization of ERRγ was not observed with the ERRγ-Y326A mutant. GSK5182 suppressed ubiquitination of ERRγ by the E3 ligase Parkin and subsequent degradation. The inhibitory activity of GSK5182 was strong even when the ERRγ protein level was elevated, as ERRγ bound to GSK5182 recruited a corepressor, small heterodimer partner-interacting leucine zipper (SMILE), through the activation function 2 (AF-2) domain, without alteration of the nuclear localization or DNA-binding ability of ERRγ. In addition, the AF-2 domain of ERRγ was critical for the regulation of protein stability. Mutants in the AF-2 domain were present at higher levels than the wild type in the absence of GSK5182. Furthermore, the ERRγ-L449A/L451A mutant was no longer susceptible to GSK5182. Thus, the AF-2 domain of ERRγ is responsible for the regulation of transcriptional activity and protein stability by GSK5182. These findings suggest that GSK5182 regulates ERRγ by a unique molecular mechanism, increasing the inactive form of ERRγ via inhibition of ubiquitination.

Using in vitro ADME data for lead compound selection: An emphasis on PAMPA pH 5 permeability and oral bioavailability

Membrane permeability plays an important role in oral drug absorption. Caco-2 and Madin-Darby Canine Kidney (MDCK) cell culture systems have been widely used for assessing intestinal permeability. Since most drugs are absorbed passively, Parallel Artificial Membrane Permeability Assay (PAMPA) has gained popularity as a low-cost and high-throughput method in early drug discovery when compared to high-cost, labor intensive cell-based assays. At the National Center for Advancing Translational Sciences (NCATS), PAMPA pH 5 is employed as one of the Tier I absorption, distribution, metabolism, and elimination (ADME) assays. In this study, we have developed a quantitative structure activity relationship (QSAR) model using our ∼6500 compound PAMPA pH 5 permeability dataset. Along with ensemble decision tree-based methods such as Random Forest and eXtreme Gradient Boosting, we employed deep neural network and a graph convolutional neural network to model PAMPA pH 5 permeability. The classification models trained on a balanced training set provided accuracies ranging from 71% to 78% on the external set. Of the four classifiers, the graph convolutional neural network that directly operates on molecular graphs offered the best classification performance. Additionally, an ∼85% correlation was obtained between PAMPA pH 5 permeability and in vivo oral bioavailability in mice and rats. These results suggest that data from this assay (experimental or predicted) can be used to rank-order compounds for preclinical in vivo testing with a high degree of confidence, reducing cost and attrition as well as accelerating the drug discovery process. Additionally, experimental data for 486 compounds (PubChem AID: 1645871) and the best models have been made publicly available (https://opendata.ncats.nih.gov/adme/).

Frontline Science: Estrogen-related receptor γ increases poly(I:C)-mediated type I IFN expression in mouse macrophages

Although type I IFNs (IFN-I) are important for the innate and adaptive immune responses to suppress viral replication, prolonged IFN-I signaling in macrophages suppresses the immune response. Nuclear receptor estrogen-related receptor γ (ERRγ) regulates the transcription of genes involved in endocrine and metabolic functions. However, the role of ERRγ in macrophage immune responses to viruses remains largely unknown. ERRγ expression was significantly induced in mouse bone marrow-derived macrophages (BMDMs) treated with polyinosinic-polycytidylic acid (poly(I:C)). Our results indicated that the induction of ERRγ expression by poly(I:C) is mediated through activation of the cytoplasmic dsRNA receptors, retinoic acid-inducible gene I and melanoma differentiation-associated protein 5. In BMDMs, overexpression of ERRγ significantly increased gene expression and secretion of the IFN-I genes, IFN-α and IFN-β, whereas abolition of ERRγ significantly attenuated poly(I:C)-mediated IFN-I secretion. Chromatin immunoprecipitation assays and mutation analyses of the IFN-I promoters revealed that ERRγ regulates the transcription of IFN-α and IFN-β by binding to a conserved ERR response element in each promoter region. Finally, GSK5182 significantly suppressed poly(I:C)-mediated induction of IFN-I gene expression and secretion in BMDMs. Taken together, these findings reveal a previously unrecognized role for ERRγ in the transcriptional control of innate and adaptive immune response to dsRNA virus replication.

An orally available inverse agonist of estrogen-related receptor gamma showed expanded efficacy for the radioiodine therapy of poorly differentiated thyroid cancer

Estrogen-related receptor gamma (ERRγ) is the NR3B subgroup of associated transcription factors. In this report, a new generation of a potent and selective ERRγ inverse agonist (25) with good biocompatibility was proposed. We also explored the potential of the newly developed compound 25 in the PDTC model to expand the original indications from ATC. In addition, an X-ray crystallographic study of the ligand and ERRγ co-complex showed that 25 completely binds to the target protein (PDB 6KNR). Its medicinal chemistry, including a distinctive structural study to in vivo results, denotes that 25 may be directed towards the development of a pivotal treatment for ERRγ-related cancers.

Protein modification by thiolactone homocysteine chemistry: a multifunctionalized human serum albumin theranostic

As the most abundant protein with a variety of physiological functions, albumin has been used extensively for the delivery of therapeutic molecules. Thiolactone chemistry provides a powerful tool to prepare spin-labeled albumin-based multimodal imaging probes and therapeutic agents. We report the synthesis of a tamoxifen homocysteine thiolactone derivative and its use in thiol-'click' chemistry to prepare multi-functionalized serum albumin. The released sulfhydryl group of the homocysteine functional handle was labeled with a nitroxide reagent to prepare a spin-labeled albumin-tamoxifen conjugate confirmed by MALDI-TOF-MS, EPR spectroscopy, UV-vis and fluorescent emission spectra. This is the basis for a novel multimodal tamoxifen-albumin theranostic with a significant (dose-dependent) inhibitory effect on the proliferation of malignant cells. The response of human glioblastoma multiforme T98G cells and breast cancer MCF-7 cells to tamoxifen and its albumin conjugates was different in tumor cells with different expression level of ERα in our experiments. These results provide further impetus to develop a serum protein for delivery of tamoxifen to cancer cells.

Synthesis and evaluation of an orally available "Y"-shaped biaryl peroxisome proliferator-activated receptor δ agonist

In this study, we designed and synthesized several novel "Y"-shaped biaryl PPARδ agonists. Structure-activity relationship (SAR) studies demonstrated that compound 3a was the most active agonist with an EC₅₀ of 2.6 nM. We also synthesized and evaluated enantiospecific R and S isomers of compound 3a to confirm that R isomer (EC₅₀ = 0.7 nM) shows much more potent activity than S isomer (EC₅₀ = 6.1 nM). Molecular docking studies between the PPAR ligand binding domain and enantiospecific R and S isomers of compound 3a were performed. In vitro absorption, distribution, metabolism, excretion, and toxicity (ADMET) and in vivo PK profiles show that compound 3a possesses superior drug-like properties including good bioavailability. Our overall results clearly demonstrate that this orally administrable PPARδ agonist 3a is a viable drug candidate for the treatment of various PPARδ-related disorders.

pH-permeability profiles for drug substances: Experimental detection, comparison with human intestinal absorption and modelling

The influence of pH on human intestinal absorption is frequently not considered in early drug discovery studies in the modelling and subsequent prediction of intestinal absorption for drug candidates. To bridge this gap, in this study, experimental membrane permeability data were measured for current and former drug substances with a parallel artificial membrane permeability assay (PAMPA) at different pH values (3, 5, 7.4 and 9). The presented data are in good agreement with human intestinal absorption, showing a clear influence of pH on the efficiency of intestinal absorption. For the measured data, simple and general quantitative structure-activity relationships (QSARs) were developed for each pH that makes it possible to predict the pH profiles for passive membrane permeability (i.e., a pH-permeability profile), and these predictions coincide well with the experimental data. QSARs are also proposed for the data series of highest and intrinsic membrane permeability. The molecular descriptors in the models were analysed and mechanistically related to the interaction pattern of permeability in membranes. In addition to the regression models, classification models are also proposed. All models were successfully validated and blind tested with external data. The models are available in the QsarDB repository (http://dx.doi.org/10.15152/QDB.203).

Design, synthesis, and evaluation of simple phenol amides as ERRγ agonists

Herein we report the design and synthesis of a series of simple phenol amide ERRγ agonists based on a hydrazone lead molecule. Our structure activity relationship studies in this series revealed the phenol portion of the molecule to be required for activity. Attempts to replace the hydrazone with more suitable chemotypes led to a simple amide as a viable alternative. Differential hydrogen-deuterium exchange experiments were used to help understand the structural basis for binding to ERRγ and aid in the development of more potent ligands.

Identification of novel inverse agonists of estrogen-related receptors ERRγ and ERRβ

Estrogen-related receptors (ERRs, α, β, and γ) are orphan nuclear receptors most closely related in sequence to estrogen receptors (ERα and ERβ). Much attention has been paid recently to the functions of ERRs for their potential roles as new therapeutic targets implicated in the etiology of metabolic disorders. While no endogenous ligand has been identified for any of the ERR isoforms to date, the potential for using synthetic small molecules to modulate their activity has been demonstrated. In the present study, a series of novel inverse agonists of ERRγ and ERRβ were synthesized using regio- and stereo-specific direct substitution of triarylethylenes. These compounds were evaluated for their ability to modulate the activities of ERRs. The rational directed substitution approach and extensive SAR studies resulted in the discovery of compound 4a (DY40) as the most potent ERRγ inverse agonist described to date with mixed ERRγ/ERRβ functional activities, which potently suppressed the transcriptional functions of ERRγ with IC₅₀=0.01μM in a cell-based reporter gene assay and antagonized ERRγ with a potency approximately 60 times greater than its analog Z-4-OHT (Z-4-hydroxytamoxifen). In addition, compound 3h (DY181) was identified as the most potent synthetic inverse agonist for the ERRβ that exhibited excellent selectivity over ERRα/γ in functional assays. This selectivity was also supported by computational docking models that suggest DY181 forms more extensive hydrogen bound network with ERRβ which should result in higher binding affinity on ERRβ over ERRγ.