Discovery of Novel Azetidine Amides as Potent Small-Molecule STAT3 Inhibitors

M13, an anthraquinone compound isolated from Morinda officinalis alleviates the progression of the osteoarthritis via the regulation of STAT3

BACKGROUND

Osteoarthritis (OA) is characterized by the progressive deterioration of articular cartilage, leading to joint pain and functional impairment. OA severely impacts quality of life and presents a substantial societal burden. Currently, effective treatment options remain limited. Morinda officinalis (MO), a traditional Chinese herb, is commonly used to treat rheumatoid arthritis and alleviate joint pain. M13, an anthraquinone extracted from MO, has shown significant anti-inflammatory properties, making it a promising candidate for the treatment of OA. However, its role in inhibiting OA progression and the mechanisms involved remain poorly understood.

PURPOSE

The objective of this study is to examine the impact of M13 on osteoarthritis and uncover the mechanisms.

METHODS

The effects of M13 on OA were assessed using TNF-α induced chondrocyte models and mice with destabilization of the medial meniscus (DMM). Celecoxib was used as a positive control. We evaluated the expression of factors related to chondrocyte degeneration and inflammation through qRT-PCR, immunoblotting, and immunofluorescence. Chondrocyte viability was measured using CCK-8 assays, EdU staining, and flow cytometry. Molecular docking, molecular dynamics simulations and isothermal titration calorimetry (ITC) were performed to evaluate the binding efficacy of target proteins. Additionally, the therapeutic effects of M13 in OA mice were confirmed through in vivo experiments.

RESULTS

In primary murine chondrocytes, M13 rescued TNF-α-induced matrix degradation and loss of vitality while suppressing ROS generation. Mechanistically, STAT3 was identified as a target protein of M13, through which M13 mitigated OA by inhibiting the STAT3 signaling pathway. Further in vivo experiments demonstrated that M13 reduced the scores of the Osteoarthritis Research Society International (OARSI), alleviating cartilage impairment. M13 enhanced levels of collagen II and aggrecan in cartilage tissue while decreasing the amounts of cartilage-degrading proteins ADAMTS-5 and MMP13.

CONCLUSION

This is the first study to validate that M13 mitigates the inflammation and damage in cartilage tissue by blocking the STAT3 signaling pathway. These findings hold promise for enhancing innovative clinical interventions targeting OA.

Small Molecule Induces Time-Dependent Inhibition of Stat3 Dimerization and DNA-Binding Activity and Regresses Human Breast Tumor Xenografts

Aberrantly-active signal transducer and activator of transcription (Stat)3 has a causal role in many human cancers and represents a validated anticancer drug target, though it has posed significant challenge to drug development. A new small molecule, JKB887, was identified through library screening and is predicted to interact with Lys591, Arg609 and Pro63 in the phospho-tyrosine (pTyr)-binding pocket of the Stat3 SH2 domain. JKB887 inhibited Stat3 DNA-binding activity in vitro in a time-dependent manner, with IC50 of 2.2-4.5 μM at 30-60-min incubation. It directly disrupted both the Stat3 binding to the cognate, high-affinity pTyr (pY) peptide, GpYLPQTV-NH2 in fluorescent polarization assay with IC50 of 3.5-5.5 μM at 60-90-min incubation, and to the IL-6 receptor/gp130 or Src in treated malignant cells. Treatment with JKB887 selectively blocked constitutive Stat3 phosphorylation, nuclear translocation and transcriptional activity, and Stat3-regulated gene expression, and decreased viable cell numbers, cell growth, colony formation, migration, and survival in human or mouse tumor cells. By contrast, JKB887 had minimal effects on Stat1, pErk1/2MAPK, pShc, pJAK2, or pSrc induction, or on cells that do not harbor aberrantly-active Stat3. Additionally, JKB887 inhibited growth of human breast cancer xenografts in mice. JKB887 is a Stat3-selective inhibitor with demonstrable antitumor effects against Stat3-dependent human cancers.

Targeting Disulfidptosis with Potentially Bioactive Natural Products in Metabolic Cancer Therapy

BACKGROUND

Metabolic cancers are defined by metabolic reprogramming. Although this reprograming drives rapid tumour growth and invasion, it also reveals specific metabolic vulnerabilities that can be therapeutically exploited in cancer therapy. A novel form of programmed cell death, known as disulfidptosis, was identified last year; tumour cells with high SLC7A11 expression undergo disulfidptosis when deprived of glucose. Natural products have attracted increasing attention and have shown potential to treat metabolic cancers through diverse mechanisms.

METHODS

We systematically searched electronic databases involving PubMed, Web of Science, Gooale Scholar. To ensue comprehensive exploration, keywords including metabolic reprogramming, metabolic cancer, disulfidptosis, natural products and some other words were employed.

RESULTS

In this review, we focus on the shared characteristics and metabolic vulnerabilities of metabolic cancers. Additionally, we discuss the molecular mechanisms underlying disulfidptosis and highlight key regulatory genes. Furthermore, we predict bioactive natural products that target disulfidptosis-related genes, offering new perspectives for anticancer strategies through the modulation of disulfidptosis.

CONCLUSIONS

By summarizing current research progress, this review mainly analyzed the potential mechanisms of natural products in the treatment of metabolic cancer.

The latest perspectives of small molecules FMS kinase inhibitors

FMS kinase is a type III tyrosine kinase receptor that plays a central role in the pathophysiology and management of several diseases, including a range of cancer types, inflammatory disorders, neurodegenerative disorders, and bone disorders among others. In this review, the pathophysiological pathways of FMS kinase in different diseases and the recent developments of its monoclonal antibodies and inhibitors during the last five years are discussed. The biological and biochemical features of these inhibitors, including binding interactions, structure-activity relationships (SAR), selectivity, and potencies are discussed. The focus of this article is on the compounds that are promising leads and undergoing advanced clinical investigations, as well as on those that received FDA approval. In this article, we attempt to classify the reviewed FMS inhibitors according to their core chemical structure including pyridine, pyrrolopyridine, pyrazolopyridine, quinoline, and pyrimidine derivatives.

Direct transformation of benzyl esters into esters, amides, and anhydrides using catalytic ferric(III) chloride under mild conditions

A facile one-pot transformation of benzyl esters into esters, amides, and anhydrides is described. α,α-Dichlorodiphenylmethane and FeCl3 were employed as the chlorinating agent and catalyst respectively to convert benzyl esters into acid chloride intermediates, which directly reacted with alcohols, amines, and carboxylic acids. Various esters, amides, and anhydrides were readily obtained with high yields under mild conditions. This method is promising for the practical synthesis of esters, amides, and anhydrides from benzyl esters.

Potential Energy Surfaces Sampled in Cremer-Pople Coordinates and Represented by Common Force Field Functionals for Small Cyclic Molecules

The complex conformations of the cyclic moieties impact the physical and chemical properties of molecules. In this work, we chose 22 molecules of four-, five-, and six-membered rings and performed a thorough conformational sampling using Cremer-Pople coordinates. With consideration of symmetries, we obtained a total of 1504 conformational structures for four-membered, 5576 for five-membered, and 13509 for six-membered rings. All well-known and many less well-known conformers for each molecule were identified. We represented the potential energy surfaces (PESs) by fitting the data to common analytical force field (FF) functional forms. We found that the general features of PESs can be described by the essential FF functional forms; however, the accuracy of representation can be improved remarkably by including the torsion-bond and torsion-angle coupling terms. The best fit yields R-squared (R²) values close to 1.0 and mean absolute errors in energy less than 0.3 kcal/mol.

Discovery of new STAT3 inhibitors as anticancer agents using ligand-receptor contact fingerprints and docking-augmented machine learning

STAT3 belongs to a family of seven vital transcription factors. High levels of STAT3 are detected in several types of cancer. Hence, STAT3 inhibition is considered a promising therapeutic anti-cancer strategy. In this work, we used multiple docked poses of STAT3 inhibitors to augment training data for machine learning QSAR modeling. Ligand-Receptor Contact Fingerprints and scoring values were implemented as descriptor variables. Escalating docking-scoring consensus levels were scanned against orthogonal machine learners, and the best learners (Random Forests and XGBoost) were coupled with genetic algorithm and Shapley additive explanations (SHAP) to identify critical descriptors that determine anti-STAT3 bioactivity to be translated into pharmacophore model(s). Two successful pharmacophores were deduced and subsequently used for in silico screening against the National Cancer Institute (NCI) database. A total of 26 hits were evaluated in vitro for their anti-STAT3 bioactivities. Out of which, three hits of novel chemotypes, showed cytotoxic IC50 values in the nanomolar range (35 nM to 6.7 μM). However, two are potent dihydrofolate reductase (DHFR) inhibitors and therefore should have significant indirect STAT3 inhibitory effects. The third hit (cytotoxic IC50 = 0.44 μM) is purely direct STAT3 inhibitor (devoid of DHFR activity) and caused, at its cytotoxic IC50, more than two-fold reduction in the expression of STAT3 downstream genes (c-Myc and Bcl-xL). The presented work indicates that the concept of data augmentation using multiple docked poses is a promising strategy for generating valid machine learning models capable of discriminating active from inactive compounds.

Boronic Acid: A Novel Pharmacophore Targeting Src Homology 2 (SH2) Domain of STAT3

SH2 domains have been recognized as promising targets for various human diseases. However, targeting SH2 domains with phosphopeptides or small-molecule inhibitors derived from bioisosteres of the phosphate group is still challenging. Identifying novel bioisosteres of the phosphate group to achieve favorable in vivo potency is urgently needed. Here, we report the feasibility of targeting the STAT3-SH2 domain with a boronic acid group and the identification of a highly potent inhibitor compound 7 by replacing the carboxylic acid of compound 4 with a boronic acid. Compound 7 shows higher binding affinity, better cellular potency, more favorable PK profiles, and higher in vivo antitumor activity than 4. The stronger anticancer effect of 7 partially stems from its covalent binding mode with the SH2 domain, verified by the washout experiments. The relatively high level of sequence conservation among SH2 domains makes the results presented here of general significance.

Inhibiting STAT3 signaling pathway by natural products for cancer prevention and therapy: In vitro and in vivo activity and mechanisms of action

Signal transducer and activator of transcription 3 (STAT3) plays a critical role in signal transmission from the plasma membrane to the nucleus, regulating the expression of genes involved in essential cell functions and controlling the processes of cell cycle progression and apoptosis. Thus, STAT3 has been elucidated as a promising target for developing anticancer drugs. Many natural products have been reported to inhibit the STAT3 signaling pathway during the past two decades and have exhibited significant anticancer activities in vitro and in vivo. However, there is no FDA-approved STAT3 inhibitor yet. The major mechanisms of these natural product inhibitors of the STAT3 signaling pathway include targeting the upstream regulators of STAT3, directly binding to the STAT3 SH2 domain and inhibiting its activation, inhibiting STAT3 phosphorylation and/or dimerization, and others. In the present review, we have systematically discussed the development of these natural product inhibitors of STAT3 signaling pathway as well as their in vitro and in vivo anticancer activity and mechanisms of action. Outlooks and perspectives on the associated challenges are provided as well.

Novel potent azetidine-based compounds irreversibly inhibit Stat3 activation and induce antitumor response against human breast tumor growth in vivo

Signal transducer and activator of transcription (Stat)3 is a valid anticancer therapeutic target. We have discovered a highly potent chemotype that amplifies the Stat3-inhibitory activity of lead compounds to levels previously unseen. The azetidine-based compounds, including H172 (9f) and H182, irreversibly bind to Stat3 and selectively inhibit Stat3 activity (IC₅₀ 0.38-0.98 μM) over Stat1 or Stat5 (IC₅₀ > 15.8 μM) in vitro. Mass spectrometry detected the Stat3 cysteine peptides covalently bound to the azetidine compounds, and the key residues, Cys426 and Cys468, essential for the high potency inhibition, were confirmed by site-directed mutagenesis. In triple-negative breast cancer (TNBC) models, treatment with the azetidine compounds inhibited constitutive and ligand-induced Stat3 signaling, and induced loss of viable cells and tumor cell death, compared to no effect on the induction of Janus kinase (JAK)2, Src, epidermal growth factor receptor (EGFR), and other proteins, or weak effects on cells that do not harbor aberrantly-active Stat3. H120 (8e) and H182 as a single agent inhibited growth of TNBC xenografts, and H278 (hydrochloric acid salt of H182) in combination with radiation completely blocked mouse TNBC growth and improved survival in syngeneic models. We identify potent azetidine-based, selective, irreversible Stat3 inhibitors that inhibit TNBC growth in vivo.

Cascade synthetic strategies opening access to medicinal-relevant aliphatic 3- and 4-membered N-heterocyclic scaffolds

Cascade reactions are often 'employed' by nature to construct structurally diverse nitrogen-containing heterocycles in a highly stereoselective fashion, i.e., secondary metabolites important for pharmacy. Nitrogen-containing heterocycles of three- and four-membered rings, as standalone and bicyclic compounds, inhibit different enzymes and are pharmacophores of approved drugs or drug candidates considered in many therapies, e.g. anticancer, antibacterial or antiviral. Domino transformations are in most cases in line with modern green chemistry concepts due to atom economy, one-pot procedures often without use the protective groups, time-saving and at markedly lower costs than multistep transformations. The tandem approaches can help to obtain novel N-heterocyclic scaffolds, functionalized according to structural requirements of the target in cells, taking into account the nature of functional group and stereochemistry. On the other hand cascade strategies allow to modify small N-heterocyclic rings in a systematic way, which is beneficial for structure-activity relationship (SAR) analyses. This review is focused on the biological relevance of the N-heterocyclic scaffolds with smaller 3- and 4-membered rings among approved drugs and leading structures of drug candidates. The cascade synthetic strategies offering N-heterocyclic scaffolds, at relatively good yields and high stereoselectivity, are discussed here. The review covers mainly years from 2015 to 2021.

Novel inhibitors of the STAT3 signaling pathway: an updated patent review (2014-present)

INTRODUCTION

STAT3 is a critical transcription factor that transmits signals from the cell surface to the nucleus, thus influencing the transcriptional regulation of some oncogenes. The inhibition of the activation of STAT3 is considered a promising strategy for cancer therapy. Numerous STAT3 inhibitors bearing different scaffolds have been reported to date, with a few of them having been considered in clinical trials.

AREAS COVERED

This review summarizes the advances on STAT3 inhibitors with different structural skeletons, focusing on the structure-activity relationships in the related patent literature published from 2014 to date.

EXPERT OPINION

Since the X-ray crystal structure of STAT3β homo dimer bound to DNA was solved in 1998, the development of STAT3 inhibitors has gone through a boom in recent years. However, none of them have been approved for marketing, probably due to the complex biological functions of the STAT3 signaling pathway, including its character and the poor drug-like physicochemical properties of its inhibitors. Nonetheless, targeting STAT3 continues to be an exciting field for the development of anti-tumor agents along with the emergence of new STAT3 inhibitors with unique mechanisms of action.

Structure-activity relationship studies on O-alkylamino-tethered salicylamide derivatives with various amino acid linkers as potent anticancer agents

In our continued SAR study efforts, a series of O-alkylamino-tethered salicylamide derivatives with various amino acid linkers has been designed, synthesized, and biologically evaluated as potent anticancer agents. Five selected compounds with different representative chemical structures were found to show broad anti-proliferative activities, effective against all tested ER-positive breast cancer (BC) and triple-negative breast cancer (TNBC) cell lines with low micromolar IC₅₀ values. Among these compounds, compound 9a (JMX0293) maintained good potency against MDA-MB-231 cell line (IC₅₀ = 3.38 ± 0.37 μM) while exhibiting very low toxicity against human non-tumorigenic breast epithelial cell line MCF-10A (IC₅₀ > 60 μM). Further mechanistic studies showed that compound 9a could inhibit STAT3 phosphorylation and contribute to apoptosis in TNBC MDA-MB-231 cells. More importantly, compound 9a significantly suppressed MDA-MB-231 xenograft tumor growth in vivo without significant toxicity, indicating its great potential as a promising anticancer drug candidate for further clinical development.

Strain-release arylations for the bis-functionalization of azetidines

The addition of nucleophilic organometallic species onto in situ generated azabicyclobutanes enables the selective formation of 3-arylated azetidine intermediates through strain-release. Single pot strategies were further developed for the N-arylation of resulting azetidines, employing either S_NAr reactions or Buchwald-Hartwig couplings.

Nifuroxazide Mitigates Angiogenesis in Ehlrich's Solid Carcinoma: Molecular Docking, Bioinformatic and Experimental Studies on Inhibition of Il-6/Jak2/Stat3 Signaling

Nifuroxazide is an antidiarrheal medication that has promising anticancer activity against diverse types of tumors. The present study tested the anticancer activity of nifuroxazide against Ehrlich’s mammary carcinoma grown in vivo. Furthermore, we investigated the effect of nifuroxazide on IL-6/jak2/STAT3 signaling and the possible impact on tumor angiogenesis. The biological study was supported by molecular docking and bioinformatic predictions for the possible effect of nifuroxazide on this signaling pathway. Female albino mice were injected with Ehrlich carcinoma cells to produce Ehrlich’s solid tumors (ESTs). The experimental groups were as follows: EST control, EST + nifuroxazide (5 mg/kg), and EST + nifuroxazide (10 mg/kg). Nifuroxazide was found to reduce tumor masses (730.83 ± 73.19 and 381.42 ± 109.69 mg vs. 1099.5 ± 310.83) and lessen tumor pathologies. Furthermore, nifuroxazide downregulated IL-6, TNF-α, NFk-β, angiostatin, and Jak2 proteins, and it also reduced tumoral VEGF, as indicated by ELISA and immunohistochemical analysis. Furthermore, nifuroxazide dose-dependently downregulated STAT3 phosphorylation (60% and 30% reductions, respectively). Collectively, the current experiment shed light on the antitumor activity of nifuroxazide against mammary solid carcinoma grown in vivo. The antitumor activity was at least partly mediated by inhibition of IL-6/Jak2/STAT3 signaling that affected angiogenesis (low VEGF and high angiostatin) in the EST. Therefore, nifuroxazide might be a promising antitumor medication if appropriate human studies will be conducted.

TRIOMPHE: Transcriptome-Based Inference and Generation of Molecules with Desired Phenotypes by Machine Learning

One of the most challenging tasks in the drug-discovery process is the efficient identification of small molecules with desired phenotypes. In this study, we propose a novel computational method for omics-based de novo drug design, which we call TRIOMPHE (transcriptome-based inference and generation of molecules with desired phenotypes). We investigated the correlation between chemically induced transcriptome profiles (reflecting cellular responses to compound treatment) and genetically perturbed transcriptome profiles (reflecting cellular responses to gene knock-down or gene overexpression of target proteins) in terms of ligand-target interactions. Subsequently, we developed novel machine learning methods to generate the chemical structures of new molecules with desired transcriptome profiles in the framework of a variational autoencoder. The use of desired transcriptome profiles enables the automatic design of molecules that are likely to have bioactivities for target proteins of interest. We showed that our methods can generate chemically valid molecules that are likely to have biological activities on 10 target proteins; moreover, they can outperform previous methods that had the same objective. Our omics-based structure generator is expected to be useful for the de novo design of drugs for a variety of target proteins.

Degradation products of azetidine core G334089 - Isolation, structure elucidation and pathway

An extensive forced degradation study using hydrolytic degradation conditions was performed on G334089, the S-enantiomer of the free fatty acid receptor 2 (FFA2) antagonist GLPG0974, to identify the degradation product structures and discern degradation pathways. Not all degradation products generated ions in the MS spectra, while several others were isomers, so more rigorous degradation conditions were applied to increase the degradant yield. Esterification of the degradants facilitated isolation via preparative HPLC and subsequent NMR and MS characterisation. The determined structures, retention times and fragmentation patterns were used to identify the original degradation products and postulate a degradation pathway. In addition to the expected amide bond hydrolysis, a second degradation mechanism involving azetidine activation through formation of an azetidinium ion was demonstrated.

Recent Update on Development of Small-Molecule STAT3 Inhibitors for Cancer Therapy: From Phosphorylation Inhibition to Protein Degradation

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various biological processes, including proliferation, metastasis, angiogenesis, immune response, and chemoresistance. In normal cells, STAT3 is tightly regulated to maintain a transiently active state, while persistent STAT3 activation occurs frequently in cancers, associating with a poor prognosis and tumor progression. Targeting the STAT3 protein is a potentially promising therapeutic strategy for tumors. Although none of the STAT3 inhibitors has been marketed yet, a few of them have succeeded in entering clinical trials. This Review aims to systematically summarize the progress of the last 5 years in the discovery of directive STAT3 small-molecule inhibitors and degraders, focusing primarily on their structural features, design strategies, and bioactivities. We hope this Review will shed light on future drug design and inhibitor optimization to accelerate the discovery process of STAT3 inhibitors or degraders.