Indoleamine 2,3-dioxygenase 1 Inhibitory Activity Research Articles

Discovery of Indoleamine 2,3-Dioxygenase 1 (IDO-1) Inhibitors Based on Ortho-Naphthaquinone-Containing Natural Product.

There is great interest in developing small molecules agents capable of reversing tumor immune escape to restore the body’s immune system. As an immunosuppressive enzyme, indoleamine 2,3-dioxygenase 1 (IDO-1) is considered a promising target for oncology immunotherapy. Currently, none of IDO-1 inhibitors have been launched for clinical practice yet. Thus, the discovery of new IDO-1 inhibitors is still in great demand. Herein, a series of diverse ortho-naphthaquinone containing natural product derivatives were synthesized as novel IDO-1 inhibitors. Among them, 1-ene-3-ketone-17-hydroxyl derivative 12 exhibited significantly improved enzymatic and cellular inhibitory activity against IDO-1 when compared to initial lead compounds. Besides, the molecular docking study disclosed that the two most potent compounds 11 and 12 have more interactions within the binding pocket of IDO-1 via hydrogen-bonding, which may account for their higher IDO-1 inhibitory activity.

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.

Inhibitory effects of flavonoids isolated from Sophora flavescens on indoleamine 2,3-dioxygenase 1 activity

Indoleamine 2,3-dioxygenase 1 (IDO1), a tryptophan catabolising enzyme, is known as a tumour cell survival factor that causes immune escape in several types of cancer. Flavonoids of Sophora flavescens have a variety of biological benefits for humans; however, cancer immunotherapy effect has not been fully investigated. The flavonoids (1–6) isolated from S. flavescens showed IDO1 inhibitory activities (IC50 4.3–31.4 µM). The representative flavonoids (4–6) of S. flavescens were determined to be non-competitive inhibitors of IDO1 by kinetic analyses. Their binding affinity to IDO1 was confirmed using thermal stability and surface plasmon resonance (SPR) assays. The molecular docking analysis and mutagenesis assay revealed the structural details of the interactions between the flavonoids (1–6) and IDO1. These results suggest that the flavonoids (1–6) of S. flavescens, especially kushenol E (6), as IDO1 inhibitors might be useful in the development of immunotherapeutic agents against cancers.

Discovery of cyanopyridine scaffold as novel indoleamine-2,3-dioxygenase 1 (IDO1) inhibitors through virtual screening and preliminary hit optimisation

With the aim of discovering novel IDO1 inhibitors, a combined similarity search and molecular docking approach was employed to the discovery of 32 hit compounds. Testing the screened hit compounds has led to several novel submicromolar inhibitors. Especially for compounds LVS-019 with cyanopyridine scaffold, showed good IDO1 inhibitory activity. To discover more compounds with similar structures to LVS-019, a shape-based model was then generated on the basis of it and the second-round virtual screening was carried out leading to 23 derivatives. Molecular docking studies suggested a possible binding mode of LVS-019, which provides a good starting point for the development of cyanopyridine scaffold compounds as potent IDO1 inhibitor. To improve potency of these hits, we further designed and synthesised another 14 derivatives of LVS-019. Among these compounds, LBJ-10 showed improved potency compared to the hits and displayed comparable potency to the control GDC-0919 analogue. LBJ-10 can serve as ideal leads for further modifications as IDO1 inhibitors for cancer treatment.

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.

Design, synthesis and biological evaluation of novel naphthoquinone derivatives as IDO1 inhibitors

Indoleamine 2,3-dioxygenase 1 (IDO1) mediated kynurenine pathway of tryptophan degradation is identified as an appealing and novel target in immunotherapy for the treatment of cancer. In this study, a novel series of naphthoquinone derivatives were synthesized, characterized and evaluated for their inhibitory activities against IDO1, and their structure−activity relationship was investigated. Among them, compounds T16, T44, T47, T49, T53 and T54 displayed potent IDO1 inhibitory activities with IC50 values ranging between 18 and 61 nM, which are more potent than INCB024360 undergoing clinical trial III evaluation. In addition, compounds T28, T44 and T53 decreased the kynurenine levels in rat plasma by 30%–50%. Compounds exhibiting excellent IDO1 inhibitory activities were also evaluated for their inhibitory activities against tryptophan 2,3-dioxygenase (TDO). Of which, compound T28 (IDO1 IC50 = 120 nM) showed promising TDO inhibition (IC50 72 nM) and was identified as an IDO1/TDO dual inhibitor.

Chiral resolution, absolute configuration determination, and stereo-activity relationship study of IDO1 inhibitor NLG919

NLG919 (1) with two chiral carbon atoms on its chemical structure is a potent indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor. We developed an effective way to prepare all stereoisomers of 1, the key step being the chiral resolution of racemic intermediate 2. The optimal resolution solvent system was identified as dichloromethane and n-pentane or petroleum ether. Using (−)-di-p-toluoyl-d-tartaric acid as resolution reagent, optical pure (R)-2 (e.e. > 99%, yield = 70%) was obtained. The mechanism of chiral resolution was clarified through single-crystal X-ray diffraction of the diastereomeric salt. The absolute configurations of four stereoisomers of 1 were established through electronic circular dichroism spectra, quantum chemical calculation and transition metal method. Their IDO1 inhibitory activity was assessed by pharmacological experiments in vitro and in mouse, demonstrating that S configuration of C5 played an important role on the inhibition of IDO1, while the stereochemistry on C2′ exerted little effect on the IDO1 inhibitory activity in mouse.

Discovery of Novel Inhibitors of Indoleamine 2,3-Dioxygenase 1 Through Structure-Based Virtual Screening.

Indoleamine 2,3-dioxygenase 1 (IDO1) is an intracellular monomeric heme-containing enzyme that catalyzes the first and the rate limiting step in catabolism of tryptophan via the kynurenine (KYN) pathway, which plays a significant role in the proliferation and differentiation of T cells. IDO1 has been proven to be an attractive target for anticancer therapy and chronic viral infections. In the present study, a class of IDO1 inhibitors with novel scaffolds were identified by virtual screening and biochemical validation, in which the compound DC-I028 shows moderate IDO1 inhibitory activity with an IC50 of 21.61 μM on enzymatic level and 89.11 μM on HeLa cell. In the following hit expansion stage, DC-I02806, an analog of DC-I028, showed better inhibitory activity with IC50 about 18 μM on both enzymatic level and cellular level. The structure–activity relationship (SAR) of DC-I028 and its analogs was then discussed based on the molecular docking result. The novel IDO1 inhibitors of DC-I028 and its analogs may provide useful clues for IDO1 inhibitor development.

Abstract 4138: In vitro and in vivo models for evaluation of inhibitors of tryptophan dioxygenases

Abstract Cancers co-opt indoleamine 2,3-dioxygenase 1 (IDO1) as a mechanism for evading the immune system, and IDO1 inhibitors have emerged as a promising new approach for the treatment cancer through their potential to restore antitumor immunity and to synergise with existing therapies. As part of our investigations into novel small molecule inhibitors of IDO1, we screened a number of human and murine tumor lines for expression of tryptophan dioxygenases. All the human and murine tumor lines that we tested were found not to express tryptophan dioxygenases unless induced with IFN-gamma. Our screen included testing 50 primary human melanoma lines developed from tumor samples obtained New Zealand Melanoma patients (NZMel lines) for expression of IDO1 and IDO2. After co-culture with IFN-gamma, 84% of the NZMel lines were IDO1+ and IDO2+; 4% were IDO1+ only; 2 % were IDO2+ only; whilst 10% did not express either IDO1 or IDO2. Tryprophan dioxygenase (TDO) was not detected in any of the NZMel lines before or after IFN-gamma exposure. To overcome the need for IFN-gamma induction for our cell based assays of IDO1 inhibitory activity of our novel compounds, we transfected the wild-type murine Lewis Lung carcinoma line (LLTC) to constitutively express murine IDO1 (LLTC-mIDO1) or human IDO1 (LLTC-hIDO1), and used these engineered lines to assay for potential species selectivity of our inhibitors. IDO1 expression in the lines was consistent and stable, but when LLTC-hIDO1 cells were implanted subcutaneously into syngeneic mice for in vivo testing of inhibitors, we found considerable heterogeneity in IDO1 expression between tumors. Approximately half of the tumors from the same batch of implants were completely negative for IDO1 expression by Western blot analysis. More intriguingly, when fragments of an IDO1+ or an IDO1- donor tumor were implanted into new recipients, the same degree of intertumoral heterogeneity in IDO1 expression was seen in the subsequent generation of tumors. In contrast, subcutaneous tumors developing from murine GL261 glioma cells similarly engineered to over-express hIDO1 (GL261-hIDO1) were homogeneous in their expression of hIDO1, and were used for subsequent in vivo studies of intratumoral IDO1expression on its effects on immune cell infiltrates and tumor growth. GL261-hIDO1 tumors had a significantly faster growth rate than the wild-type tumors, and 24 days after implantation, had reached a mean tumor volume of 3600 mm3 compared to a mean tumor volume of 500 mm3 of wild-type tumors. Analysis of the immune cell infiltrates, showed that 14-day GL261 wild-type tumors had a 3-fold higher percentage of CD3+ T cells than that in GL261-hIDO1 tumors. CD8+ cells made up 55% and 25% of the CD3+ cells in wild-type and GL261-hIDO1 tumors, respectively. Percentage of Foxp3+ (Treg) cells was higher in GL261-hIDO1 tumors compared to that in wild-type tumors. Citation Format: Lai-Ming Ching, Petr Tomek, Brian D. Palmer, Sofian Tijono, Kimiora Henare, Lukas M. Braun. In vitro and in vivo models for evaluation of inhibitors of tryptophan dioxygenases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4138. doi:10.1158/1538-7445.AM2017-4138

A Novel High Throughput Virtual Screening Protocol to Discover New Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitors.

Indoleamine 2,3-dioxygenase 1 (IDO1) plays an important role in the immune escape of tumors and has emerged as a promising target for cancer immunotherapy. Despite its potential in immuno-oncology, very few chemotypes have been reported to date. Here, we disigned a novel high throughput virtual screening (HTVS) cascade protocol, combining both pharmacophore modeling and molecular docking and it was employed to query commercially available compounds to identify novel inhibitors. Among the 23 compounds selected for the in vitro IDO1 inhibitory activity assay, five compounds exhibit greater than 20% inhibition at a test concentration of 10 µM, with two compounds having an IC50 value of 23.8 and 8.8 µM, respectively. The novel scaffold together with a ligand efficiency of 0.28 kcal/mol per heavy atom makes both compounds as suitable starting points for future chemistry elaboration. Our HTVS protocol was validated and could be employed in discovery of IDO1 inhibitors.

Discovery of a Novel Scaffold as an Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitor Based on the Pyrrolopiperazinone Alkaloid, Longamide B.

Indoleamine 2,3-dioxygenase 1 (IDO1) has emerged as a key target for cancer therapy, as IDO1 plays a critical role in the capacity of tumor cells to evade the immune system. The pyrrolopiperazinone alkaloid longamide B and its derivatives were identified as novel IDO1 inhibitors based on docking studies and small library synthesis. The thioamide derivative showed higher IDO1 inhibitory activity than longamide B, and displayed an activity similar to that of a representative IDO1 inhibitor, 1-methyl-tryptophan. These results suggest that the pyrrolopiperazinone scaffold of longamide B could be used in the development of IDO1 inhibitors.

Fused Heterocyclic Compounds as Potent Indoleamine-2,3-dioxygenase 1 Inhibitors.

Uncontrolled metabolism of l-tryptophan (l-Trp) in the immune system has been recognized as a critical cellular process in immune tolerance. Indoleamine 2,3-dioxygenase 1 (IDO1) enzyme plays an important role in the metabolism of a local l-Trp through the kynurenine pathway in the immune systems. In this regard, IDO1 has emerged as a therapeutic target for the treatment of diseases that are associated with immune suppression like chronic infections, cancer, and others. In this study, we synthesized a series of pyridopyrimidine, pyrazolopyranopyrimidine, and dipyrazolopyran derivatives. Further lead optimizations directed to the identification of potent compounds, 4j and 4l (IC50 = 260 and 151 nM, respectively). These compounds also exhibited IDO1 inhibitory activities in the low nanomolar range in MDA-MB-231 cells with very low cytotoxicity. Stronger selectivity for the IDO1 enzyme (>300-fold) over tryptophan 2,3-dioxygenase (TDO) enzyme was also observed for these compounds. Hence, these fused heterocyclic compounds are attractive candidates for the advanced study of IDO1-dependent cellular function and immunotherapeutic applications.

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 5.3μM. 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.

Crystal Structures and Structure-Activity Relationships of Imidazothiazole Derivatives as IDO1 Inhibitors.

Indoleamine 2,3-dioxygenase 1 (IDO1) is considered as a promising target for the treatment of several diseases, including neurological disorders and cancer. We report here the crystal structures of two IDO1/IDO1 inhibitor complexes, one of which shows that Amg-1 is directly bound to the heme iron of IDO1 with a clear induced fit. We also describe the identification and preliminary optimization of imidazothiazole derivatives as novel IDO1 inhibitors. Using our crystal structure information and structure-activity relationships (SAR) at the pocket-B of IDO1, we found a series of urea derivatives as potent IDO1 inhibitors and revealed that generation of an induced fit and the resulting interaction with Phe226 and Arg231 are essential for potent IDO1 inhibitory activity. The results of this study are very valuable for understanding the mechanism of IDO1 activation, which is very important for structure-based drug design (SBDD) to discover potent IDO1 inhibitors.

The Tumor-Selective Cytotoxic Agent β-Lapachone is a Potent Inhibitor of IDO1.

β-lapachone is a naturally occurring 1,2-naphthoquinone-based compound that has been advanced into clinical trials based on its tumor-selective cytotoxic properties. Previously, we focused on the related 1,4-naphthoquinone pharmacophore as a basic core structure for developing a series of potent indoleamine 2,3-dioxygenase 1 (IDO1) enzyme inhibitors. In this study, we identified IDO1 inhibitory activity as a previously unrecognized attribute of the clinical candidate β-lapachone. Enzyme kinetics-based analysis of β-lapachone indicated an uncompetitive mode of inhibition, while computational modeling predicted binding within the IDO1 active site consistent with other naphthoquinone derivatives. Inhibition of IDO1 has previously been shown to breach the pathogenic tolerization that constrains the immune system from being able to mount an effective anti-tumor response. Thus, the finding that β-lapachone has IDO1 inhibitory activity adds a new dimension to its potential utility as an anti-cancer agent distinct from its cytotoxic properties, and suggests that a synergistic benefit can be achieved from its combined cytotoxic and immunologic effects.