Discovery of 5-(pyridin-3-yl)-1H-indole-4,7-diones as indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors

Early studies demonstrated that over expression of indoleamine 2,3-dioxygenase (IDO1) in tumor microenvironment results in tumor immune escape. Herein, in order to simplify the structure of two kinds of IDO1 inhibitors from marine alkaloid, Exiguamine A and Tsitsikammamines, we designed, synthesized a series of 1H-indole-4,7-dione derivatives and evaluated their inhibitory activity in IDO1 enzyme and in IFN-γ stimulated Hela cells in vitro. The structure-activity relationship demonstrated that 5-(pyridin-3-yl)-1H-indole-4,7-dione is a promising scaffold for IDO1 inhibitors and most compounds with this core showed moderate inhibition potency at micromole level. Our further enzyme kinetics experiments reveal that these new developed compounds might act as reversible competitive inhibitors of IDO1.     

Development of a series of novel o-phenylenediamine-based indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors

A novel series of o-phenylenediamine-based inhibitors of indoleamine 2,3-dioxygenase (IDO) has been identified. IDO is a heme-containing enzyme, overexpressed in the tumor microenvironment of many cancers, which can contribute to the suppression of the host immune system. Synthetic modifications to a previously described diarylether series resulted in an additional degree of molecular diversity which was exploited to afford compounds that demonstrated significant potency in the HeLa human cervical cancer IDO1 assay..     

Design,synthesis and structure-activity relationship study of novel naphthoindolizine and indolizinoquinoline-5,12-dione derivatives as IDO1 inhibitors

Indoleamine 2,3-dioxygenase 1 (IDO1) is regarded as a promising target for cancer immunotherapy. Many naphthoquinone derivatives have been reported as IDO1 inhibitors so far. Herein, two series of naphthoquinone derivatives, naphthoindolizine and indolizinoquinoline-5,12-dione derivatives, were synthesized and evaluated for their IDO1 inhibitory activity. Most of the target compounds showed significant inhibition potency and high selectivity for IDO1 over tryptophan 2,3-dioxygenase (TDO). The structure-activity relationship was also summarized. The most potent compounds 5c (IC₅₀ 23?nM, IDO1 enzyme), and 5b′ (IC₅₀ 372?nM, HeLa cell) were identified as promising lead compounds.     

Synthesis of novel tryptanthrin derivatives as dual inhibitors of indoleamine 2,3-dioxygenase 1 and tryptophan 2,3-dioxygenase

Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) are promising drug development targets due to their implications in pathologies such as cancer and neurodegenerative diseases. The search for IDO1 inhibitor has been intensely pursued but there is a paucity of potent TDO and IDO1/TDO dual inhibitors. Natural product tryptanthrin has been confirmed to bear IDO1 and/or TDO inhibitory activities. Herein, twelve novel tryptanthrin derivatives were synthesized and evaluated for the IDO1 and TDO inhibitory potency. All of the compounds were found to be IDO1/TDO dual inhibitors, in particular, compound 9a and 9b bore IDO1 inhibitory activity similar to that of INCB024360, and compound 5a and 9b had remarkable TDO inhibitory activity superior to that of the well-known TDO inhibitor LM10. This work enriches the collection of IDO1/TDO dual inhibitors and provides chemical molecules for potential development into drugs.     

Discovery and preliminary structure–activity relationship of 1H-indazoles with promising indoleamine-2,3-dioxygenase 1 (IDO1) inhibition properties

Indoleamine 2,3-dioxygenase 1 (IDO1)-mediated kynurenine pathway of tryptophan degradation is identified as an important immune effector pathway in the tumor cells to escape a potentially effective immune response. IDO1 is an attractive target for anticancer therapy and the discovery of IDO1 inhibitors has been intensely ongoing in both academic research laboratories and pharmaceutical organizations. Our study discovered that 1H-indazole was a novel key pharmacophore with potent IDO1 inhibitory activity. A series of new 1H-indazole derivatives were synthesized and determined the enzyme inhibitory activities, and the compound 2g exhibited the highest activity with an IC₅₀ value of 5.3 μM. The structure–activity relationships (SARs) analysis of the 1H-indazole derivatives as novel IDO1 inhibitors indicated that the 1H-indazole scaffold is necessary for IDO1 inhibition, and the substituent groups at the both 4-position and 6-position largely affect inhibitory activity. The docking model exhibited that the effective interactions of 1H-indazoles with ferrous ion of heme and key residues of hydrophobic Pocket A and B ensured the IDO1 inhibitory activities. The study suggested that the 1H-indazole was a novel interesting scaffold for IDO inhibition for further development.     

A multicomponent approach in the discovery of indoleamine 2,3-dioxygenase 1 inhibitors: Synthesis,biological investigation and docking studies

Indoleamine 2,3-dioxygenase plays a crucial role in immune tolerance and has emerged as an attractive target for cancer immunotherapy. In this study, the Passerini and Ugi multicomponent reactions have been employed to assemble a small library of imidazothiazoles that target IDO1. While the p-bromophenyl and the imidazothiazole moieties have been kept fixed, a full SAR study has been performed on the side-chain, leading to the discovery of nine compounds with sub-micromolar IC₅₀ values in the enzyme-based assay. Compound 7d, displaying a α-acyloxyamide substructure, is the most potent compound, with an IC₅₀ value of 0.20?µM, but a low activity in a cell-based assay. Compound 6o, containing a α-acylaminoamide moiety, shows an IC₅₀ value of 0.81?µM in the IDO1-based assay, a full biocompatibility at 10?µM, together with a modest inhibitory activity in A375 cells. Molecular docking studies show that both 7d and 6o display a unique binding mode in the IDO1 active site, with the side-chain protruding in an additional pocket C, where a crucial hydrogen bond is formed with Lys238. Overall, this work describes an isocyanide based-multicomponent approach as a straightforward and versatile tool to rapidly access IDO1 inhibitors, providing a new direction for their future design and development.     

Synthesis of 4- and 5-arylthiazolinethiones as inhibitors of indoleamine 2,3-dioxygenase

Docking studies of 4-phenylthiazolinethione on human IDO1 suggest complexation of the heme iron by the exocyclic sulfur atom further reinforced by hydrophobic interactions of the phenyl ring within pocket A of the enzyme. On this basis, chemical modifications were proposed to increase inhibition activity. Synthetic routes had to be adapted and optimized to yield the desired substituted 4- and 5-arylthiazolinethiones. Their biological evaluation shows that 5-aryl regioisomers are systematically less potent than the corresponding 4-aryl analogs. Substitution on the phenyl ring does not significantly increase inhibition potency, except for 4-Br and 4-Cl derivatives.     

Rational design,synthesis and biological evaluation of ubiquinone derivatives as IDO1 inhibitors

Indoleamine 2,3-dioxygenase 1 (IDO1) is an attractive therapeutic target for the treatment of cancer, chronic viral infections and neurological disorders characterized by pathological immune stimulation. Herein, a series of known metal-chelating ubiquinone derivatives were designed, synthesized and evaluated for the IDO1 inhibiting activities. The docking studies showed that the compounds 11, 16, 18 and coenzyme-Q1 exhibited different binding modes to IDO1 protein. Among these compounds, the most active compound is 16d with an IC₅₀ of 0.13 μM in enzymatic assay. The results reveal that a possible halogen bonding interaction between the bromine atom (3-Br) and Cys129 significantly enhances the inhibition activity against IDO1. This study provides structural insights of the interactions between ubiquinone analogues and IDO1 protein for the further modification and optimization.     

Discovery and characterisation of hydrazines as inhibitors of the immune suppressive enzyme,indoleamine 2,3-dioxygenase 1 (IDO1)

Screening of a fragment library identified 2-hydrazinobenzothiazole as a potent inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme expressed by tumours that suppresses the immune system. Spectroscopic studies indicated that 2-hydrazinobenzothiazole interacted with the IDO1 haem and in silico docking predicted that the interaction was through hydrazine. Subsequent studies of hydrazine derivatives identified phenylhydrazine (IC₅₀ = 0.25 ± 0.07 μM) to be 32-fold more potent than 2-hydrazinobenzothiazole (IC₅₀ = 8.0 ± 2.3 μM) in inhibiting rhIDO1 and that it inhibited cellular IDO1 at concentrations that were noncytotoxic to cells. Here, phenylhydrazine is shown to inhibit IDO1 through binding to haem.     

A highly potent and selective inhibitor Roxyl-WL targeting IDO1 promotes immune response against melanoma

Indoleamine 2,3-dioxygenase 1 (IDO1) activity links to immune escape of cancers. Inhibition of IDO1 provides a new approach for cancer treatment. Most clinical IDO1 drugs show marginal efficacy as single agents. On basis of molecular docking and pharmacophore modelling, a novel inhibitor Roxyl-WL was discovered with a half maximal inhibitory concentration (IC50) value of 1?nM against IDO1 and 10–100-fold increased potent activity compared with IDO1 drugs in clinical trials. Roxyl-WL displayed excellent kinase spectrum selectivity with no activity out of the 337 protein kinases. In vitro, Roxyl-WL effectively augmented the proliferation of T cells and reduced the number of regulatory T cell (Tregs).When administered to melanoma (B16F10) tumor-bearing mice orally, Roxyl-WL significantly suppressed tumor growth and induced immune response.     

Antitumour agents as inhibitors of tryptophan 2,3-dioxygenase

The involvement of tryptophan 2,3-dioxygenase (TDO) in cancer biology has recently been described, with the enzyme playing an immunomodulatory role, suppressing antitumour immune responses and promoting tumour cell survival and proliferation. This finding reinforces the need for specific inhibitors of TDO that may potentially be developed for therapeutic use. In this work we have screened ∼2800 compounds from the library of the National Cancer Institute USA and identified seven potent inhibitors of TDO with inhibition constants in the nanomolar or low micromolar range. All seven have antitumour properties, killing various cancer cell lines. For comparison, the inhibition potencies of these compounds were tested against IDO and their inhibition constants are reported. Interestingly, this work reveals that NSC 36398 (dihydroquercetin, taxifolin), with an in vitro inhibition constant of ∼16 μM, is the first TDO-selective inhibitor reported.     

Correlation of indoleamine-2,3-dioxigenase 1 inhibitory activity of 4,6-disubstituted indazole derivatives and their heme binding affinity

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-containing enzyme that acts on the first and rate-limiting step of the tryptophan/kynurenine pathway. Since the pathway is one of the means of cancer immune evasion, IDO1 inhibitors have drawn interest as potential therapeutics for cancers. We found a 4,6-disubstituted indazole 1 as a hit compound that showed both IDO1 inhibitory activity and binding affinity for IDO1 heme. Structural modification of 1 yielded compound 6, whose relatively large substituent at the 4-position and proper size substituent at the 6-position were found to be important for the enhancement of IDO1 inhibitory activity and heme affinity. A series of compounds synthesized in this work were evaluated by in silico docking simulations and by in vitro experiments using a C129Y mutant of the pocket-A of IDO1. Our results revealed that proper substituents at the 6- and 4-positions of the compounds interact with pockets A and B, respectively, and that, in particular, a good fit in pocket-A is important for the compounds’ biological activities. Absorption spectral analysis of these compounds showed that they strongly bound to the ferrous heme rather than its ferric heme. Furthermore, we observed that the heme affinities of these compounds strongly correlate with their IDO1 inhibitory activities.     

Latest developments in tryptophan metabolism: Understanding its role in B cell immunity

One of the most essential and important building blocks of life is the tryptophan amino acid. As such, the pathways surrounding its metabolism are often crucial for the maintenance of proper cell activity and homeostasis. The ratios of tryptophan to kynurenine, mainly mediated by indoleamine 2,3-dioxygenase activity, is a key parameter in the inflammation as well as immunomodulation of both aseptic and septic diseases. As a result, several studies have been published to better understand the mechanisms by which the tryptophan pathways lead to such outcomes. Many have focused on gut health and cells associated with the given environment, the majority of which constitute regulatory T cells and T helper 17 cells. However, recent studies have highlighted the role of this molecular pathway on its capacity to modulate B cells functions and humoral immunity. Accordingly, the focus of this short review is to examine the key tryptophan pathways and their impact on B cells demonstrated by those studies. A better understanding of the role of tryptophan and its metabolites is crucial for its use in disease prevention and treatments.     

Design,synthesis and biological evaluation of 2,5-dimethylfuran-3-carboxylic acid derivatives as potential IDO1 inhibitors

Indoleamine 2,3-dioxygenase 1 (IDO1) plays a vital role in tumor immune escape and has emerged as a promising target for cancer immunotherapy. In this study, a novel series of 2,5-dimethylfuran-3-carboxylic acid derivatives were designed, synthesized and evaluated for inhibitory activities against IDO1, and their structure-activity relationship was investigated. Among these, compound 19a exhibited excellent IDO1 inhibitory activity (HeLa cellular IC₅₀?=?4.0?nM, THP-1 cellular IC₅₀?=?4.6?nM). Further molecular docking studies revealed that the compound 19a formed a coordinate bond with the heme iron through the carboxylic acid moiety. These results indicate that compound 19a is a potential IDO1 inhibitor for further investigation.     

Discovery of potent and efficacious pyrrolopyridazines as dual JAK1/3 inhibitors

A series of potent dual JAK1/3 inhibitors have been developed from a moderately selective JAK3 inhibitor. Substitution at the C6 position of the pyrrolopyridazine core with aryl groups provided exceptional biochemical potency against JAK1 and JAK3 while maintaining good selectivity against JAK2 and Tyk2. Translation to in vivo efficacy was observed in a murine model of chronic inflammation. X-ray co-crystal structure determination confirmed the presumed inhibitor binding orientation in JAK3. Efforts to reduce hERG channel inhibition will be described.     

Discovery of novel phenoxybenzamide analogues as Raf/HDAC dual inhibitors

Histone deacetylase (HDAC) inhibitors as an important epigenetic therapeutic strategy affect signaling networks and act synergistically with kinase inhibitors for the treatment of cancer. Herein we presented a series of novel phenoxybenzamide analogues with inhibition of Raf and HDAC. Among them, compound 10e showed potent antiproliferative activities against Hepg2 and MDA-MB-468 in cellular assays. This work may lay the foundation for developing novel dual Raf/HDAC inhibitors as potential anticancer therapeutics.     

Long noncoding RNA lnc-sox5 modulates CRC tumorigenesis by unbalancing tumor microenvironment

Long non-coding RNAs (LncRNAs) have been recently regarded as systemic regulators in multiple biologic processes including tumorigenesis. In this study, we observed the expression of lncRNA lnc-sox5 was significantly increased in colorectal cancer (CRC). Despite the CRC cell growth, cell cycle and cell apoptosis was not affected by lnc-sox5 knock-down, lnc-sox5 knock-down suppressed CRC cell migration and invasion. In addition, xenograft animal model suggested that lnc-sox5 knock-down significantly suppressed the CRC tumorigenesis. Our results also showed that the expression of indoleamine 2,3-dioxygenase 1 (IDO1) was significantly reduced by lnc-sox5 knock-down and therefore modulated the infiltration and cytotoxicity of CD3⁺CD8⁺T cells. Taken together, these results suggested that lnc-sox5 unbalances tumor microenvironment to regulate colorectal cancer progression.     

Investigation of multi-target-directed ligands (MTDLs) with butyrylcholinesterase (BuChE) and indoleamine 2,3-dioxygenase 1 (IDO1) inhibition: The design,synthesis of miconazole analogues targeting Alzheimer’s disease

In our endeavor towards the development of potent multi-target ligands for the treatment of Alzheimer’s disease, miconazole was identified to show BuChE-IDO1 dual-target inhibitory effects. Morris water maze test indicated that miconazole obviously ameliorated the cognitive function impaired by scopolamine. Furthermore, it showed good safety in primary hepatotoxicity evaluation. Based on these results, we designed, synthesized, and evaluated a series of miconazole derivatives as BuChE-IDO1 dual-target inhibitors. Out of the 12 compounds, 5i and 5j exhibited the best potency in enzymatic evaluation, thus were selected for subsequent behavioral study, in which the two compounds exerted much improved effect than tacrine. Meanwhile, 5i and 5j displayed no apparent hepatotoxicity. The results suggest that miconazole analogue offers an attractive starting point for further development of new BuChE-IDO1 dual-target inhibitors against Alzheimer’s disease.     

Identification of novel 7-amino-5-methyl-1,6-naphthyridin-2(1H)-one derivatives as potent PI3K/mTOR dual inhibitors

Inhibition of the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway is one of the most intensively studied approaches to cancer therapy. Rational design led to the identification of novel 7-amino-5-methyl-1,6-naphthyridin-2(1H)-one derivatives as potent PI3K/mTOR dual inhibitors. Design, synthesis and structure activity relationship are reported.     

Discovery of benzenesulfonamide derivatives as potent PI3K/mTOR dual inhibitors with in vivo efficacies against hepatocellular carcinoma

The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is related to cellular activities. Abnormalities of this signaling pathway were discovered in various cancers, including hepatocellular carcinoma (HCC). The PI3K/mTOR dual inhibitors were proposed to have enhanced antitumor efficacies by targeting multiple points of the signaling pathway. We synthesized a series of propynyl-substituted benzenesulfonamide derivatives as PI3K/mTOR dual inhibitors. Compound 7k (NSC781406) was identified as a highly potent dual inhibitor, which exhibited potent tumor growth inhibition in the hepatocellular carcinoma BEL-7404 xenograft model. Compound 7k may be a potential therapeutic drug candidate for HCC.