Recent discovery of indoleamine-2,3-dioxygenase 1 inhibitors targeting cancer immunotherapy

Accepted Manuscript Recent discovery of indoleamine-2,3-dioxygenase 1 inhibitors targeting cancer immunotherapy Tianwei Weng, Xiaqiu Qiu, Jubo Wang, Zhiyu Li, Jinlei Bian PII:

S0223-5234(17)30991-1

DOI:

10.1016/j.ejmech.2017.11.088

Reference:

EJMECH 9963

To appear in:

European Journal of Medicinal Chemistry

Received Date: 19 April 2017 Revised Date:

4 June 2017

Accepted Date: 28 November 2017

Please cite this article as: T. Weng, X. Qiu, J. Wang, Z. Li, J. Bian, Recent discovery of indoleamine-2,3dioxygenase 1 inhibitors targeting cancer immunotherapy, European Journal of Medicinal Chemistry (2017), doi: 10.1016/j.ejmech.2017.11.088. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Recent discovery of indoleamine-2,3-dioxygenase 1 inhibitors targeting cancer immunotherapy Tianwei Weng a, Xiaqiu Qiu a, Jubo Wang a, Zhiyu Li a,*, Jinlei Bian a,* a

Department of Medicinal Chemistry, China Pharmaceutical University, #24 Tongjiaxiang, Nanjing 210009, P.R. China *Corresponding authors. E-mail: [email protected], E-mail:[email protected]

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Abstract There has been great attention on indoleamine-2,3-dioxygenase 1 (IDO1) around cancer immunotherapy because of its role in enabling cancers to evade the immune system. The most recent spurt of high potent IDO1 inhibitors has been driven by the solution of the increased

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crystal structures of inhibitors with IDO1. Though the structural information of the active site of IDO1 obtained from the crystals are quite similar, the structures of reported potent

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inhibitors are quite different. Besides, while thousands of bioactive small molecule inhibitors of IDO1 exist, to date, only five compounds have entered clinical trials. In an effort to obtain more clinical drugs targeting IDO1, more comprehensive understanding of the active site of IDO1 and the structures of existing potent IDO1 inhibitors are necessary. Thus, this review mainly focus on the key features reported from specific crystal structures of IDO1 and an overview of the most recently developed IDO1 inhibitors under investigation and their other

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derived applications which may contribute to a better usage in cancer immunotherapy.

Keywords

Abbreviations

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Immune escape, crystal structures, IDO1 inhibitors, cancer immunotherapy

KP, kynurenine pathway; Trp, tryptophan; KYN, kynurenine; IDO1, indoleamine

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2,3-dioxygenase 1; IDO2, indoleamine 2,3-dioxygenase 2; TDO, tryptophan 2,3-dioxygenase; IFN, interferon; PGE2, prostaglandin E2; Tregs, regulatory T Cells; 4PI, 4-phenylimidazole; SAR,

structure-activity

1-Methyl-tryptophan;

relationships; L1MT,

1-(2-fluoroethyl)-ᴅʟ-tryptophan;

HTS,

D1MT,

1-Methyl-D-tryptophan;

1-Methyl-L-tryptophan; high-throughput

screening;

1MT,

1-FE-ᴅʟ-Trp, Tryptanthrin,

indolo[2,1-b]quinazolin-6,12-dione; DPPH, diphenylpicrylhydrazyl; SPR, surface plasmon resonance.

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ACCEPTED MANUSCRIPT 1. Introduction Cancer immunotherapy, which was nominated for ‘Year Breakthrough of Cancer Research 2013’ by Science magazine [1], is currently entering an exciting new era and impressive clinical results are anticipated [2-4]. To date, over 50 phase III trials in cancer immunotherapy are in progress [5]. Among attractive immunotherapy approaches, immune checkpoint therapy

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which targets regulatory pathways to enhance the antitumor immune responses of T cells has led to important clinical advances in cancer, following the approval of ipilumumab, pembrolizumab, and nivolumab by FDA [6-7]. Despite these successes, currently available drugs on the market are mostly biologics including antibodies, proteins, engineered T cells

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and oncolytic viruses [8-11]. The biological drugs are well known for the existence of several defects in clinical, such as (i) low targeting efficiency via vein administration; (ii) invalid

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when used in oral therapy; (iii) difficult to quickly reach the level of exposure dose in the tumor microenvironment and (iv) expensive. Thus, the development of small molecule drugs for immune checkpoint therapy could offer several advantages that might be complementary and potentially synergistic to large biological molecules. Targeting key dioxygenases in tryptophan-kynurenine metabolism is an efficient way to discover small molecules modulating the immune system [12]. Immune escape, which is

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characterized by lacking ability of the immune system to eradicate malignant transformed cells, is a hallmark of cancer progression [13]. A central role in immune escape has been ascribed to the kynurenine pathway (KP) of tryptophan (Trp) metabolism [14]. The pathway induces the depletion of Trp and the production of kynurenine (KYN) metabolites (KP, Fig. 1)

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[15-17], both responsible for local immunosuppression. Thus, the KP for Trp catabolism has become an attractive target for drug discovery related to cancer. The first and rate limiting

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step of KP pathway is carried out by one of three heme-containing enzymes, indoleamine 2,3-dioxygenase 1 (IDO1) [EC 1.13.11.17], indoleamine 2,3-dioxygenase 2 (IDO2) [EC 1.13.11] and tryptophan 2,3-dioxygenase (TDO) [EC 1.13.11.11]. Specifically, IDO1, as well as IDO2 and TDO, can catalyze the cleavage of the 2,3-double bond of indole ring in ʟ-Trp and the cleavage product, N-formyl-ʟ-kynurenine, is hydrolysed spontaneously or by enzymatic reaction to form ʟ-KYN (Fig. 1).

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Fig. 1. Partial steps of Trp metabolism performed by IDO1.

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Although IDO1, IDO2 and TDO all catalyze the same biochemical reaction, they share only limited biological function, tissue expression and substrate specificity. Among them,

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IDO1 and IDO2 are two isoforms of IDO, sharing 43% sequence identity and being endowed with distinct biochemical features that support the hypothesis of their diverse biological roles [18-21]. IDO1 is an extrahepatic cytosolic enzyme distributed in many human tissues, including placenta, lung, small and large intestines, colon, spleen, liver, kidney, stomach, and brain [22], which is responsible for non-dietary catabolism of Trp and implicated in tumoral immune resistance [23-25]. However, IDO2 has a different expression pattern due to its

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predominant expression in in kidney tubules, liver and spermatozoa [19, 26]. Furthermore, IDO2 showed very low Trp degradation activity and existed functional genic polymorphisms as well as multiple splice variants [27-29], which lead to its unclear physiological role. As for TDO, a distantly related tetrameric enzyme mainly expressed in the liver, catalyzes the same

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reaction as IDO. Under certain stimuli, TDO is also expressed in other tissues, including epididymis, placenta, testis, brain and pregnant uterus [30-33]. Nevertheless, contrasted with

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the immune regulatory role of IDO, TDO functions to maintain Trp homeostasis and is highly stereospecific for the ʟ-Trp. Among the initial enzymes in the KP, IDO1 is the most key target for cancer immunotherapy under extensive investigation [15-16, 34-35], whose protein structure and catalytic mechanism have been well described. Many types of cancer cells and tumor environmental cells could express IDO1 in a constitutive manner [36] and high IDO1 expression usually results in poor prognosis in a variety of cancer types [37]. Indeed, results from in vitro and in vivo studies have suggested that IDO1 inhibitors enhance the efficacy of therapeutic vaccination and conventional chemotherapy [24, 37], and are synergistic with radiation therapy [38]. Thus, the development of IDO1 inhibitors are garnering increasingly 3

ACCEPTED MANUSCRIPT attention in academia and pharmaceutical companies, including Pfizer Inc., Roche Pharma Ltd., Bristol-Myers Squibb Co.. In addition, several small molecule inhibitors have entered clinical trials [5] and different features reported from specific crystal structures of the enzyme [39], further pursuing the development of small molecule inhibitors of IDO1. Hence, to further boosting the research in this field, we summarized the most recent and potent IDO1

order to indicate a direction for the research in this aspect. 2. Functional roles of IDO1 in immune escape

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small molecule inhibitors and give a brief description of their other derived applications, in

One immune escape strategy that has been extensively investigated and well described is

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the role of the immunomodulatory enzyme IDO1. IDO1 is not constitutively expressed but requires stimulation by type I/II interferons (IFN), prostaglandin E2 (PGE2), IL-2, CTLA-4 ligation, viruses, and bacterial LPS [40]. And IDO1 is highly expressed in placenta

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(preventing the rejection of allogeneic fetuses), inflammatory tissues, and human tumors [41]. By co-opting IDO1 activity, tumor cells can effectively mask their rapid cellular growth and evade the host immune response. In detail, IDO1 activity has a dual effect on the immune tolerogenic environment, including a depletion of local Trp storages and an accumulation of KYN products [42-44]. As the important component of immune system to remove antigen

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presenting tumor cells, T cell lymphocytes must divide to be activated and are preferentially sensitive to both of these conditions. Both metabolic modifications are responsible for local immunosuppression following several potential mechanisms, such as T cell proliferation blocked in the G1 phase of the cell cycle by Trp shortage and T cell apoptosis due to toxicity

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of accumulated Trp catabolites [45-46]. Besides, IDO1-mediated Trp catabolism facilitates differentiation of regulatory T Cells (Tregs) [47], which are known as a key component of

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acquired tolerance to tumors. Recent investigations have shown that IDO1 upregulation is associated with increased Treg numbers in malignant melanoma [48]. It also has been identified that Tregs can participate in the silencing of T cells response by acting to enforce a dominant negative regulation on T cells activation, proliferation, and cytokine production (Fig. 2) [40].

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Fig. 2. Mechanism of action of IDO1 in immune escape.

3. Structures of IDO1

IDO1 is a monomeric 45 kDa heme-containing oxidase that is active with the heme iron in the ferrous (Fe2+) form rather than the ferric (Fe3+) form. However, IDO1 is prone to autoxidation despite of no changes in the heme oxidation state through the catalytic cycle of

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IDO1. Therefore, a reductant is necessary to reactivate the enzyme. Until 2006, the structural features of the enzyme were disclosed for the first time by two published crystal structures of IDO1, 4-phenylimidazole (4PI)-bound structure (PDB code: 2D0T) (Fig. 3A) and cyanide-bound structure (PDB code: 2D0U) [49]. Structurally, the active site of IDO1

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comprises two lipophilic regions: a large pocket (pocket A, Fig. 3) containing the heme group, which is the site of Trp catalysis, and a lipophilic area at the binding site entrance (pocket B,

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Fig. 3). The crystal structures of IDO1 in complex with two ligands mentioned, are different mainly in the hindered access to pocket A [50], which suggests some flexibility in the active site. Over the past decade, almost all studies of IDO1 inhibitors optimize their lead compounds to rationalize some features or structure-activity relationships (SAR) on the basis of crystal structure information on 4PI-bound structure or related plausible docking models [15]. Considering that 4PI is a fragment-like inhibitor and interacts directly with heme iron and pocket A without pocket B, conflicting binding modes have been reported, for example, for Amg-1 [51-52], which points out the problem of the validity of predicted binding modes. In 2014, two new crystal structures of IDO1 bound to the larger ligands, directly interacting with IDO1 protein at both pockets A and B, Amg-1 (PDB code: 4PK5) (Fig. 3B) and 5

ACCEPTED MANUSCRIPT imidazothiazole compound (PDB code: 4PK6) became available [52], characterized by a larger A pocket and different shapes and sizes of the B pocket, thus further expanded catalytic site. In 2016, crystal structures of IDO1 complexed with GDC-0919 analogues (PDB code: 5ETW, 5EK2, 5EK3, 5EK4) (Fig. 3C), which featured an extensive hydrogen bond network with IDO1 for the first time, were reported for gaining a better understanding of the binding

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mechanism of IDO1 and further providing molecular insights to design novel and potent inhibitors [53]. Recently, the complex structure of IDO1/INCB14943 (INCB024360 analogue) (PDB code: 5XE1) (Fig. 3D) was resolved with some unique features, such as the oxime nitrogen bind with heme iron and halogen bond interaction with Cys129 [54], which

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confirmed the benefit of the network of hydrogen bonds for ligands to adopt an appropriate conformation to bind with IDO1 protein again. Specially, analysis the recently reported crystal structures, we find that the two accessory binding pockets of the enzyme are formed

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according to the shape of the inhibitor. Different inhibitors may induce conformational rearrangements which further expand the volume of the catalytic site (Fig. 3). Pocket A is localized above the sixth coordination site of the iron-heme protruding into the small domain provided by multiple key residues such as Ser167 and Cys129, whereas the pocket B is located at the entrance of the channel to the catalytic site including residues that are

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recognized fundamental for IDO1 activity by mutagenesis experiments such as Arg231, Phe226 and Phe227. This observation suggests that multiple conformations of the enzyme may affect to recognize different inhibitors by shaping the volume of catalytic site of IDO1. Structure-based ligand design is an efficient approach in modern drug development for targets.

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Thus, deeper insight of ligand-IDO1 interactions within the active site of the target is necessary. We believe that more and more different features reported from specific crystal

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structures of the enzyme, may contribute to the design of novel potent and selective inhibitors of IDO1.

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Fig. 3. Crystal structures of IDO1. (A) 4PI- (PDB ID: 2D0T), (B) Amg-1- (PDB ID: 4PK5), (C) GDC-0919 analogue- (PDB ID: 5EK4) and (D) INCB14943- (PDB ID: 5XE1) bound.

4. Current status of IDO1 inhibitors in clinical trials

Since the participation of IDO1 in oncogenesis was first uncovered in 2003 [20], not

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surprisingly then, the recent years have witnessed many attempts to discover and develop potential IDO1 inhibitors. As a result of this, thousands of compounds have been reported according to the scientific and patent literature. Despite this, to the best of our knowledge, only five small-molecule compounds are currently undergoing an extensive development

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programme (either alone or in combination) [5], whereas other IDO1 inhibitors reported seem to be suboptimal for clinical development. Here we select some completed and/or ongoing

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clinical trials using IDO1 inhibitors (Table 1). Among these, 1-Methyl-D-tryptophan (D1MT, indoximod, 1, Fig. 4) (IDO1 IC50 > 100 µM, HeLa IC50 = 1.5 mM, HT29 IC50 = 1.5 mM) [55-56] is in phase I/II clinical studies at NewLink Genetics Corp. for the treatment of metastatic prostate cancer, acute myeloid leukemia, primary malignant brain tumors, metastatic pancreatic cancer, metastatic breast cancer, metastatic melanoma, as well as non-small cell lung cancer. However, a growing body of preclinical/clinical studies suggest that at variance with the ʟ enantiomer, 1 seemingly acts as an IDO1 inhibitor via two reported mechanisms of action, that is, by modifying the Trp carriage across cell membranes [57] and/or mimicking Trp to alter cellular signals downstream of IDO1 pathway [58]. Subsequently, the safety and efficacy of two 2nd 7

ACCEPTED MANUSCRIPT generation IDO1 inhibitors are being evaluated in clinical trials across a wide range of indications and combinations. The N-hydroxyamidine INCB024360 (epacadostat, 2, Fig. 4) (IDO1 IC50 = 72 nM, HeLa IC50 = 7.1 nM, Human DCs IC50 = 13 nM, HEK 293/MSR-human IDO1 IC50 = 15 nM, OCI-M2 human AML cells IC50 = 3.4 nM, THP-1 human AML cells IC50 = 23 nM) [56], is in phase II/III clinical trials at Incyte Corp., used as a monotherapy as well

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as in combination use with various antibody, for the treatment of advanced or metastatic cancers. In 2016, orphan drug designation was assigned to 2 in America for the treatment of stage IIB-IV melanoma. Moreover, 2 was proved to impede tumor growth in a dose- and lymphocyte-dependent fashion and be well-tolerated in efficacy and preclinical toxicology

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studies [59]. Another IDO1 inhibitor, the imidazole GDC-0919 (navoximod, 3, Fig. 4) (IDO1 IC50 = 13 nM, TDO IC50 = 140 nM, T-REX-293 IDO1 IC50 = 75 nM, T-REX-293 TDO IC50 = 1.5 µM) [60], is in phase I clinical trials at NewLink Genetics Corp. in collaboration with

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Genentech Inc. in subjects with recurrent advanced solid tumors. The in vivo study revealed that treatment with 3 led to a significant reduction of tumor size and the ability of 3 to suppress tumor growth was highly relevant to its functional immune response [61]. Recently, two latest 2nd/3rd generation IDO1 inhibitors have also entered into clinical trials within the last few months. PF-0684003 (EOS-200271, 4, Fig. 4) (IDO1 IC50 = 410 nM, TDO IC50 > 50

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µM, HeLa IC50 = 1.8 µM, Human Leukocytes IC50 = 3.4 µM, SKOV3 human IDO1 IC50 = 70 nM, P815 mouse IDO1 IC50 = 94 nM, THP-1 human AML cells IC50 = 1.7 µM) [62-63] from Pfizer Inc./iTeos Therapeutics SA, is in phase I clinical trials for the treatment of patients with grade IV glioblastoma or grade III anaplastic glioma and its low potential for off-target

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activity was determined in a panel of receptors, ion channels, transporters and enzymes [62]. BMS-986205 (ONO-7701, 5, Fig. 4) (IDO1 IC50 = 1.7 nM, SKOV3 IC50 = 3.4 nM) [64], is

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being evaluated at Bristol-Myers Squibb Co. in phase I/II clinical trials in combination with nivolumab in patients with advanced cancers. Early clinical development of BMS-986205 is also ongoing at Ono Pharmaceutical Co., Ltd. in Japan for hematologic cancer and solid tumors. In summary, the above-mentioned five compounds appear to provide a promising starting point for the development of IDO1 inhibitors targeting cancer immunotherapy and give us a better understanding of the applications of IDO1 inhibitors in combination with other therapies.

Table 1 Selected completed and/or ongoing clinical trials using IDO1 inhibitors.

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ACCEPTED MANUSCRIPT Study Title

Study Drug

I/ NCT00567931

1-Methyl-D-tryptophan

INCB024360

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I/ NCT01195311 II/ NCT01685255

II/ NCT01822691

NCT02042430

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GDC-0919

PF-06840003

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Phase II Study of Sipuleucel-T and Indoximod for Patients With Refractory Metastatic Prostate Cancer Immunotherapy Combination Study in Advanced Previously Treated Non-Small Cell Lung Cancer Epacadostat and Vaccine Therapy in Treating Patients With Stage III-IV Melanoma DEC-205/NY-ESO-1 Fusion Protein CDX-1401, Poly ICLC, and IDO1 Inhibitor INCB024360 in Treating Patients With Ovarian, Fallopian Tube, or Primary Peritoneal Cancer in Remission Safety and Efficacy of CRS-207 With Epacadostat in Platinum Resistant Ovarian, Fallopian, or Peritoneal Cancer Study of DPX-Survivac Vaccine Therapy and Epacadostat in Patients With Recurrent Ovarian Cancer Combination with checkpoint inhibitors Study of IDO Inhibitor in Combination With Checkpoint Inhibitors for Adult Patients With Metastatic Melanoma

I/ NCT02048709 I/ NCT02764151

I/ NCT01191216 II/ NCT01792050 I/II/ NCT02052648 I/II/ NCT02077881

1-Methyl-D-tryptophan + Temozolomide

I/ NCT02502708

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1-Methyl-D-tryptophan + Docetaxel 1-Methyl-D-tryptophan + Docetaxel/Paclitaxel 1-Methyl-D-tryptophan + Temozolomide/Bevacizumab 1-Methyl-D-tryptophan + Nab-Paclitaxel/Gemcitabine

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Single Agent 1-Methyl-D-Tryptophan in Treating Patients With Metastatic or Refractory Solid Tumors That Cannot Be Removed By Surgery A Dose-escalation Study in Subjects With Advanced Malignancies A Phase 2 Study of the IDO Inhibitor INCB024360 Versus Tamoxifen for Subjects With Biochemical-recurrent-only EOC, PPC or FTC Following Complete Remission With First-line Chemotherapy Phase II INCB024360 Study for Patients With Myelodysplastic Syndromes Epacadostat Before Surgery in Treating Patients With Newly Diagnosed Stage III-IV Epithelial Ovarian, Fallopian Tube, or Primary Peritoneal Cancer Indoleamine 2,3-Dioxygenase Inhibitor in Advanced Solid Tumors First in Patient Study for PF-06840003 in Malignant Gliomas Combination with Cytotoxic Chemotherapy 1-Methyl-D-Tryptophan and Docetaxel in Treating Patients With Metastatic Solid Tumors Study of Chemotherapy in Combination With IDO Inhibitor in Metastatic Breast Cancer Study of IDO Inhibitor and Temozolomide for Adult Patients With Primary Malignant Brain Tumors Study of IDO Inhibitor in Combination With Gemcitabine and Nab-Paclitaxel in Patients With Metastatic Pancreatic Cancer Study of the IDO Pathway Inhibitor, Indoximod, and Temozolomide for Pediatric Patients With Progressive Primary Malignant Brain Tumors A Study of Indoximod in Combination With (7+3) Chemotherapy in Patients With Newly Diagnosed Acute Myeloid Leukemia Azacitidine Combined With Pembrolizumab and Epacadostat in Subjects With Advanced Solid Tumors Combination with Vaccine Vaccine Therapy and 1-MT in Treating Patients With Metastatic Breast Cancer

Phase/ ClinicalTrials.gov Identifier

1-Methyl-D-tryptophan + Idarubicin/Cytarabine

I/II/ NCT02835729

Azacitidine + INCB024360/Pembrolizumab

I/II/ NCT02959437

1-Methyl-D-tryptophan + adenovirus-p53 transduced dendritic cell (DC) vaccine 1-Methyl-D-tryptophan + Sipuleucel-T 1-Methyl-D-tryptophan + Tergenpumatucel-L/Docetaxel INCB024360 + MELITAC 12.1 Peptide Vaccine INCB024360 + DEC-205/NY-ESO-1 Fusion Protein CDX-1401/Poly ICLC

I/II/ NCT01042535

INCB024360 + CRS-207/Pembrolizumab

I/II/ NCT02575807

INCB024360 + DPX-Survivac/Cyclophosphamide

I/ NCT02785250

1-Methyl-D-tryptophan + Ipilimumab/Nivolumab/Pembroliz umab

I/II/ NCT02073123

II/ NCT01560923 I/II/ NCT02460367 II/ NCT01961115 I/II/ NCT02166905

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INCB024360 + Atezolizumab

I/ NCT02298153

INCB024360 + Durvalumab

I/II/ NCT02318277

INCB024360 + Nivolumab

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INCB024360 + Pembrolizumab

I/II/ NCT02327078

I/ NCT02559492

INCB024360 + Pembrolizumab

III/ NCT02752074

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INCB039110+ INCB024360 /INCB050465

INCB024360 + Pembrolizumab GDC-0919 + Atezolizumab

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A Phase 1/2 Study Exploring the Safety, Tolerability, and Efficacy of Pembrolizumab in Combination With Epacadostat in Subjects With Selected Cancers A Study of Atezolizumab in Combination With Epacadostat in Subjects With Previously Treated Stage IIIB or Stage IV Non-Small Cell Lung Cancer and Previously Treated Stage IV Urothelial Carcinoma A Study of Epacadostat in Combination With Durvalumab in Subjects With Selected Advanced Solid Tumors A Study of the Safety, Tolerability, and Efficacy of Epacadostat Administered in Combination With Nivolumab in Select Advanced Cancers INCB039110 Combined With INCB024360 and/or INCB039110 Combined With INCB050465 in Advanced Solid Tumors A Phase 3 Study of Pembrolizumab + Epacadostat or Placebo in Subjects With Unresectable or Metastatic Melanoma Study of INCB024360 Alone and In Combination With Pembrolizumab in Solid Tumors A Study of GDC-0919 and Atezolizumab Combination Treatment in Participants With Locally Advanced or Metastatic Solid Tumors An Investigational Immuno-therapy Study of BMS-986205 Given in Combination With Nivolumab in Cancers That Are Advanced or Have Spread

BMS-986205 + Nivolumab

I/ NCT02862457 I/ NCT02298153 I/II/ NCT02658890

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Indoximod: same as 1-Methyl-D-tryptophan; Epacadostat: same as INCB024360

Fig. 4. IDO1 inhibitors in clinical trials.

5. The most recently developed promising IDO1 inhibitors under investigation In addition to the above IDO1 inhibitors in clinical trials, the search for novel inhibitor scaffolds has made great progress both in academia and in pharmaceutical companies. In the following we classify the most potent small-molecule inhibitors of IDO1 in recent years and give a brief description of their other derived applications, also concluded their SAR when available. 5.1. Trp Analogs 10

ACCEPTED MANUSCRIPT Most of Trp analogs have provided important proof-of-principle demonstrations as IDO1 inhibitors in the past several decades, such as keto-indole derivatives 6 (IDO1 IC50 = 13 µM) [65-66], tryptoline derivatives 7 (IDO1 IC50 = 46 µM) [67] and arylthioindole derivatives 8 (IDO1 IC50 = 7 µM) (Fig. 5) [68]. However, these small molecule compounds, which showed modest potencies and poor physical properties, appear to be marginal drug candidates [69-70].

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The most frequently used inhibitor of IDO1, 1-Methyl-tryptophan (1MT, 9, Fig. 5) (IDO1 IC50 = 380 µM, COS-1 monkey kidney cells IC50 = 267 µM) [71-72] of this class exists as two stereoisomers: 1-Methyl-L-tryptophan (L1MT, 10, Fig. 5) (IDO1 IC50 = 498.7 µM, HEK293 IC50 = 18.4 µM) [73], usually as justification for publishing equally weak inhibitors, and 1 as aforesaid, currently in Phase I/II clinical trials. 11

C-ʟ-1MTrp and 11C-ᴅ-1MTrp (11 and 12, Fig. 5), were

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In 2015, two novel radioprobes,

developed as PET probes by Xie L et al. for pharmacokinetic imaging of the checkpoint

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inhibitor 1MT, and even detection of IDO1-positive tumors [74]. PET/CT imaging in rats revealed the isomers of 1MT have markedly different in vivo distributions and actions, following the highest distribution of radioactivity observed in the pancreas and kidney, for 11 and 12, respectively. Contemporaneous with Xie’s group, 1-(2-fluoroethyl)-ᴅʟ-tryptophan (1-FE-ᴅʟ-Trp)

and

its

three

radiotracers,

1-[18F]FE-ᴅʟ-Trp,

1-[18F]FE-ʟ-Trp

and

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1-[18F]FE-ᴅ-Trp, (13, 14, 15 and 16, Fig. 5) were synthesized by Henrottin J et al. to facilitate i) the clinical detection and discrimination of IDO1-expressing cells in cancer imaging, and ii) the preclinical and clinical development and validation of new IDO1 inhibitors [75-76]. According to in vitro enzymatic assays, 13 (Km = 70 µM) was validated as a good and specific

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substrate for IDO1 but not for TDO, which made three radiotracers, with relatively long half-life time ([18F]t1/2 = 109.7 min), to be highly desirable and valuable tools for

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IDO1-positive cancer imaging. Among these radiotracers, 15 exhibited the highest specificity and affinity for IDO1-expressing cells, as compared to the two other substrates 14 and 16. In

addition

to

new

applications

of

Trp

analogs

in

cancer

imaging,

two

Pt(IV)-(D)-1-methyltryptophan conjugates 17 and 18 (Fig. 5) were investigated recently for cancer immuno-chemotherapy, as a combination of immunomodulation and DNA cross-link-triggered apoptosis [77]. Immunoblotting and qRT-PCR presented that 18 preferentially targeted IDO1 than 17 to enhance T-cell proliferation. And 18 (A2780 IC50 = 0.20 µM, A2780/CP70 IC50 = 0.26 µM, NIH:OVCAR3 IC50 = 1.37 µM, SKOV3 IC50 = 1.02 µM) was also evaluated to display 3.5-40-fold potency in IDO1-expressing cells, such as A2780 and SKOV3 of human ovarian cancer cells, over cisplatin and [cisplatin+D1MT] by MTT assay. 11

ACCEPTED MANUSCRIPT In summary, given that metabolic enzymes often evolve an affinity for their natural substrate, closely in line with the physiological concentration of the substrate (~ 60 µM for circulating Trp) [78-81], more and more attention should be paid to the development of potent IDO1 inhibitors with non-Trp related frameworks. However, the search for new applications of Trp analogs, such as cancer imaging and cancer immuno-chemotherapy, are worthy of

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further studying.

5.2. Imidazoles

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Fig. 5. Examples of Trp analogs.

In 1989, 4PI (19, Fig. 6) (IDO1 IC50 = 48 µM) [82], a known heme binder, was identified

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as a weak non-competitive inhibitor of IDO1 [83], and its cocrystallization with IDO1 was published in 2006 [49], paving the way for structure-based in silico design and the synthesis of novel inhibitors. The search for imidazole IDO1 inhibitors has been intensely pursued firstly by NewLink Genetics Corp. Then, in 2008, derivatives with substituents on the phenyl ring [82], was the first example to improve the IDO1 inhibitory potency relative to the parent 4PI, with the most success for 2-hydroxy analogue 20 (IDO1 IC50 = 4.8 µM), 3-thiol analogue 21 (IDO1 IC50 = 7.6 µM) and 4-thiol analogue 22 (IDO1 IC50 = 7.7 µM) (Fig. 6). More details were published in their subsequent 2009 application [84], which showed no significant improvement in the inhibitory activity. On the basis of these results, in 2011, an extensive series of O-substituted 2′-hydroxyl-4-phenylimidazoles, featuring a long extension into the 12

ACCEPTED MANUSCRIPT pocket B, were reported with nanomolar potency (23, Fig. 6) [85]. And in 2012, a large number of the tricyclic compounds possessing a fused phenyl-imidazole scaffold, were reported with an IDO1 inhibition in the nanomolar range (24, Fig. 6) [86], which led to the identification of GDC-0919 in phase I clinical trials as mentioned earlier. Moreover, bioisosteric replacements of the imidazole motif in the tricyclic compounds by other

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nitrogen-containing five-membered rings led to activity variations of several orders of

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magnitude [87], making the orientation of the fused imidazole ring less important (25, Fig. 6).

Fig. 6. Examples of imidazole compounds.

Other pharma companies with tricyclic IDO1 inhibitors in their pipeline at present are

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Hangzhou Innogate Pharma Co., Ltd. [88], Shanghai De Novo Pharmatech Co., Ltd. [89-90] and Redx Pharma plc [91-92]. In summary, the modification mainly focus on the

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replacements of the benzene motif by 5- or 6- membered heteroaryl groups to fill pocket A and introduction of bulky hydrophobic groups to interact with pocket B. The bioisosteric replacements of the imidazole motif, usually focus on the orientation of the fused imidazole ring, to combine the heme iron. In general, introduction of an o-fluoro substituent on the phenyl ring makes an extra halogen bonding interaction with surrounding amino acid residues in pocket A (Fig. 7). In addition to tricyclic imidazole derivatives, the imidazothiazole scaffold provides an interesting alternative for novel IDO1 inhibitors. In 2011, Amg-1 (29, Fig. 6) (IDO1 IC50 = 3.0 µM, IDO2 IC50 > 250.0 µM, TDO IC50 > 62.5 µM) was reported to selectively inhibit IDO1 following a high-throughput screening (HTS) of Amgen Inc. [51]. Later in 2014, on the 13

ACCEPTED MANUSCRIPT basis of the crystal structure of IDO1/29 complex, rational compound optimization of 29 contributed to imidazothiazole inhibitors [52], which occupied both pocket A and pocket B.

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Among them, the most active compound described herein is 30 (Fig. 6) (IDO1 IC50 = 77 nM).

5.3. N-Hydroxyamidines

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Fig.7. Representative structure of tricyclic imidazole derivatives and preliminary SAR conclusions.

N-hydroxyamidines can be used as pro-drugs of amidines, which is an important tool in

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drug discovery [93]. In 2009, an N-hydroxyamidine hit with micromolar potency was discovered from a HTS of Incyte Corp. [94]. Subsequent optimization of the hit 31 (Fig. 8)

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(IDO1 IC50 = 1.5 µM, TDO IC50 = 10 µM, HeLa IC50 = 1 µM) brought about a proof-of-concept lead 32 (INCB14943, Fig. 8) (IDO1 IC50 = 67 nM, TDO IC50 > 10 µM, HeLa IC50 = 19 nM, Murine B16 IC50 = 46 nM) with poor oral bioavailability, which suppressed kynurenine generation in vivo, and inhibited tumor growth in the murine B16-GM-CSF model. Besides, further structure modifications showed that N-hydroxyamidine motif was critical for inhibiting IDO1 in this series as N-methoxyamidine, amidine, aminoamidine, amide and thioamide caused a large decrease in inhibitory potency. Not so long ago, the complex structure of IDO1/32 supported the notion that 32 bound to heme iron in IDO1 protein through the oxime nitrogen [54].

14

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Fig. 8. Examples of N-hydroxyamidines.

A flurry of patents of Incyte Corp. for subsequent modifications of N-hydroxyamidines

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[95-102] focused attention on i) introduction of an additional side chain to replace the 4-amino group; ii) replacements of 1,2,5-oxadiazole core structure by 5- or 6- membered aryl or heteroaryl groups and iii) small electrophilic substituents in its phenylic or other counterpart (Fig. 9). Among these modifications, only derivatives with a urea motif as the lateral side chain, were distinguished by excellent IDO1 inhibition properties in the nanomolar range [102], such as 2 above [103-104]. Lately, further optimization on the lateral

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side chain of 2, led to effective IDO1 inhibitors 35 (Fig. 9) (IDO1 IC50 = 11 nM, HeLa IC50 = 1.8 nM) and 40 (Fig. 9) (IDO1 IC50 = 18 nM, HeLa IC50 = 3 nM), with good pharmacokinetic and pharmacodynamic profiles [105-106].

Encouraged by the important clinical advances of 2 in cancer immunotherapy, a series of F-carboximidamide compounds with low nanomolar IC50, e.g. 18F-IDO5L (41, Fig. 8) (HeLa

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IC50 = 17.9 nM, t1/2 < 0.5 h, via oral administration) [107-108], were reported as novel probes

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for the PET imaging to predict IDO1-related cancer diagnostic and monitor therapeutic efficacy of IDO1 inhibitors. In 2015, N-hydroxyamidine derivatives with substituted alkyl or cycloalkyl instead of 1,2,5-oxadiazole ring, e.g. 42 (Fig. 8) (IDO1 IC50 < 1 µM), were also reported as IDO1 inhibitors by Bristol-Myers Squibb Co. [109]. Later in 2016, a new series of nitrobenzofurazan derivatives of N-hydroxyamidines were proved to be potent inhibitors of IDO1 in the nanomolar rang and exhibit no/negligible amount of cytotoxicity in MDA-MB-231 cell, with strong selectivity for IDO1 over TDO [110], e.g. the most potent compound 43 (Fig. 8) (IDO1 IC50 = 59 nM, TDO IC50 = 94 µM, MDA-MB-231 IC50 = 50 nM). In conclusion, the presence of N-hydroxyamidine moiety in the above compounds’ core 15

ACCEPTED MANUSCRIPT structure could be the driving force for their strong inhibitory activities, while 1,2,5-oxadiazole core is not necessary. Moreover, radioisotope-labeled analogues of this class could also be considered as good molecular probes for IDO1-targeted imaging on the basis of

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their excellent in vivo and in vitro properties.

Fig.9. Representative structure of N-hydroxyamidines.

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5.4. Tryptanthrin Derivatives

Tryptanthrin (indolo[2,1-b]quinazolin-6,12-dione) (44, Fig. 10), with various biological activities such as antitumor activity, is a natural product of the Chinese medicinal plants

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Polygonum tinctorium and Isatis tinctoria. Despite of several reported possible mechanisms underlying antitumor effects of 44 [111-115], its specific mechanisms like quinones remain an open question. In 2013, 44 (IDO1 IC50 = 7.15 µM, HEK293 IC50 = 53.7 nM) was discovered as a novel inhibitor scaffold for IDO1 through screening indole-based structures [73]. Synthesis of three series of 13 tryptanthrin derivatives afforded the optimized analog 45 (Fig. 10) (IDO1 IC50 = 534 nM, HEK293 IC50 = 23.0 nM), exhibiting 5- 6-fold enhancement of T cell proliferation than 10. Different from many quinones [116-120] and iminoquinones [121-122], which may act as redox-cycling compounds to paradoxically inhibit IDO1, the scaffold’s activity on IDO1 was proved to have no bearing on its reduction potentials by the diphenylpicrylhydrazyl (DPPH) assay. At the same time, surface plasmon resonance (SPR) 16

ACCEPTED MANUSCRIPT assay demonstrated that 45 (KD = 46.8 µM) directly bound to purified IDO1 protein. Further in vivo studies on LLC Tumor-Bearing Mice suggested that 45 as a single agent, dramatically inhibited IDO1 activity and suppressed tumor growth, as well as reduced the numbers of Foxp3+ Tregs. In conclusion, the tryptanthrin scaffold provides a promising starting point for IDO1

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inhibitors with nanomolar potency and continuing motivation for drug candidates from natural product. By summarizing the SAR of 13 analogs of this class, we concluded that a good synthetic analog should contain some or all of the following features: the tryptanthrin scaffold should be retained; substituent groups on A ring, especially at the 2-position, result in

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the decrease of activity; electron-withdrawing groups on B ring, especially at the 8-position, are necessary for IDO1 inhibition (Fig. 10), which were also demonstrated by Guda R et al.

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[123].

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Fig. 10. Examples of tryptanthrin derivatives.

5.5. Phenyl Benzenesulfonylhydrazides

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HTS strategy is extensively carried out on library screening by measuring kynurenine formation in enzymatic assay with purified recombinant human IDO1 protein. In 2014, 2-phenyl benzeneethanesulfonylhydrazide (46, Fig. 11) was identified as a promising hit, as a result of its poor cell permeability, with potent IDO1 enzymatic activity but poor cellular activity (IDO1 IC50 = 167 nM, HeLa EC50 > 10 µM) by screening of an in-house library [124-125]. Subsequent modification of 46 led to the identification of phenyl benzenesulfonylhydrazide as a novel structural scaffold of IDO1 inhibitors, with the compound 47 (Fig. 11) potent in vitro but not in vivo (IDO1 IC50 = 130 nM, HeLa EC50 = 85 nM), showing no inhibition on tumor growth in the murine melanoma B16F10 syngeneic model. Nevertheless, the proposed binding modes of 47 showed that the oxygen of the sulfone 17

ACCEPTED MANUSCRIPT group could interact with the heme iron. Further lead optimization of 47 resulted in analog 48 (Fig. 11), a potent, selective, and orally bioavailable IDO1 inhibitor, which demonstrated 59 % oral bioavailability and 73 % of tumor growth delay in the murine CT26 syngeneic model, after oral administration of 400 mg/kg. Whereas benzenesulfonamides, structure similar to the derivatives above, have been as

KYN

production

inhibitors

[126],

IDO1

inhibitors

with

phenyl

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reported

benzenesulfonylhydrazide moiety exhibit activity at submicromolar level and include one or more of the following structural elements contributing to the inhibitory potency: an aromatic fragment, bicyclic best, to fill limited space of pocket A; an electron-rich atom, here O, that

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can coordinate to the heme iron; two free NH-group that can hydrogen bond to surrounding amino acid residues or to the heme 7-propionate; small electrophilic substituents, especially in

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para-position, on the phenyl ring in pocket B (Fig. 11).

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Fig. 11. Examples of phenyl benzenesulfonylhydrazides.

5.6. Other Scaffolds with moderate IDO1 inhibition

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Thirty-five hits (IDO1 IC50 < 20 µM) were identified via screening of NCI Diversity Set III compound library of 1597 compounds against IDO1. Subsequent removal of thirty-five hits guided by five structural filters and PubChem Bioassay database lead to five IDO1 inhibitors thioaminal, phenanthroimidazole, benzoxadiazole, pyrimidinone and indolonoxide (49, 50, 51, 52 and 53, Fig. 12) (IDO1 IC50 = 3.3-12 µM) [127], accompanied by phenylhydrazine (IDO1 IC50 = 0.25 µM) and 2-hydrazinobenzothiazole (IDO1 IC50 = 8 µM) (54 and 55, Fig. 12) reported also by Ching LM et al.[128], Despite of limited SAR studies of this group, the parent 52 (IDO1 IC50 = 7.5 µM, LLTC IC50 = 4.4 µM) exhibited excellent cell permeability, negligible cytotoxicity at concentrations that inhibit the enzyme and low promiscuity, making the pyrimidinone scaffold a promise for an IDO1 inhibitor drug development program. 18

ACCEPTED MANUSCRIPT Coincidentally, 1-Indanone was discovered to a novel key pharmacophore with potent IDO1 inhibitory activity since a potential hit compound 56 (Fig. 12) (IDO1 IC50 = 2.8 µM, HeLa EC50 = 9.2 µM) identified via structure-based virtual screening [129]. The direct interaction between compound 56 (KD = 9.8 µM) and IDO1 protein was also validated by SPR analysis. Subsequent structural optimizations of 56 merely brought out compound 57

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(Fig. 12) with restored inhibitory activity (IDO1 IC50 = 5.3 µM, HeLa EC50 = 9.7 µM), moderate metabolic stability and moderate permeation. SAR analysis revealed that the hydroxyl group at C-3 position in ring C and ketone group in ring B of the 1-Indanone scaffold were critical for inhibitory activities, so that 1-Indanone was a novel interesting

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scaffold for IDO1 inhibition for further development.

These two novel scaffolds with moderate IDO1 inhibition, pyrimidinone scaffold and 1-Indanone scaffold, could provide a promising starting point for the development of IDO1

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inhibitors.

Fig. 12. Examples of other scaffolds with moderate IDO1 inhibition.

6. Conclusion and future perspective Although IDO1 is traditionally thought to be responsible for non-dietary catabolism of Trp, recent investigations have shown that IDO1 activity has distinct effects on various immune cell subsets, which shapes the immunological milieu and becomes embroiled in immune escape in human cancers [41-42,130]. As reported in recent studies, high IDO1 expression is characteristic of poor prognosis in a variety of human tumors [37]. Indeed, several studies 19

ACCEPTED MANUSCRIPT have offered evidence that that IDO1 inhibitors can exert antitumor effects, enhancing the efficacy of therapeutic vaccination and conventional chemotherapy [24,37], and synergistic with radiation therapy [39]. Considering that an IDO1 gene knockout mouse has been reported to be viable and healthy [131], IDO1 inhibition by small molecule inhibitors will be unlikely to produce severe mechanism-based side effects. Besides, clinical applications of

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these small molecules have several advantages, that is, (i) easy to produce and deliver, (ii) inexpensive, (iii) compatible with other therapies including conventional chemotherapies and newly developed immunotherapies. Thus, the novel potent IDO1 inhibitors is urgent to be developed.

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In just the past few decades, intense efforts to develop IDO1 inhibitors have yielded thousands of compounds with different potent scaffolds. While known as bioactive small molecule inhibitors of IDO1, most of them either show low potency or is failed in vivo assay,

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making them better suited to proof-of-concept experiments than clinical translation. By far, five small-molecule compounds, D1MT, INCB024360, GDC-0919, PF-0684003 and BMS-986205, have entered clinical trials (either alone or in combination) [5]. Besides, until 2006, the structural features of the enzyme IDO1 and clues on its binding mode of 4PI were disclosed for the first time [49]. In the past few years, crystal structures of IDO1 bound to the

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larger inhibitors than 4PI became available. Through the comparative analysis of four representative crystal structures (Fig. 3), we found that the shape and size of the catalytic site of IDO1 are formed according to the conformational rearrangements of the enzyme induced by different inhibitors, which suggests some flexibility in the active site. Considering that

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pocket B is provided by multiple key residues, such as Arg231, Phe226 and Phe227, which are recognized fundamental for IDO1 activity, we should pay more attention to crystal

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structure information on the interaction between IDO1 and its inhibitor complex at pocket B. In addition, the elucidation of SAR at pocket B may benefit the medicinal chemistry arena aiding the design of novel potent and selective inhibitors of IDO1. Indeed, the search for novel inhibitor scaffolds has made a great progress both in academia and in pharmaceutical companies. Among these structures, Trp analogs, which act as mimics of Trp, may exhibit high specificity and affinity for IDO1, and have the potential for the PET imaging to predict IDO1-related cancer diagnostic and monitor therapeutic efficacy of IDO1 inhibitors. This series of compounds may aim at new applications, such as cancer immuno-chemotherapy and may also be used in conjugation with other targeted inhibitors. Moreover, attention should be paid to the development in non-Trp related frameworks, thus improving the potency of IDO1 inhibitors for potential clinical trial assessment. As a result of 20

ACCEPTED MANUSCRIPT their best IDO1 inhibitory potency in nanomolar range, attractive small molecules with different

inhibitor

scaffolds,

benzenesulfonylhydrazides

and

including

imidazoles,

tryptanthrin

N-hydroxyamidines,

derivatives,

are

phenyl

needed

to

make further modifications for even more potent drug candidates in clinical trials and further provide success stories for extent and structure of preclinical IDO1 inhibitors, as well as

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search for new applications like Trp analogs. While these scaffolds with moderate IDO1 inhibition, such as pyrimidinone scaffold and 1-Indanone scaffold, could contribute a lot to the structural diversity for the future development of highly potent IDO1 inhibitors.

As tumor cells upregulate multiple immune checkpoint pathways when evading the

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immune response, selective inhibition of enzyme IDO1 is not sufficient to promote tumor regression in a majority of patients, making combinations of IDO1 inhibitors and several other immune checkpoint molecules appear to be an appropriate way to increase clinical

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benefit. However, additional clinical work is required for a better understanding of the clinical potential for this strategy (e.g. safety, efficacy) in patients with cancer. Moreover, a personalized approach with IDO1 inhibitors may result in maximal efficacy in a diverse population of patients. Therefore, the results of the ongoing combination studies with IDO1

Acknowledgements

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inhibitors and other immune-oncology drugs are eagerly awaited.

We are thankful for the financial support of the National Natural Science Foundation of

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China (no. 21372260).

21

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Fig. 1. Partial steps of Trp metabolism performed by IDO1.

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Fig. 2. Mechanism of action of IDO1 in immune escape.

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ACCEPTED MANUSCRIPT Fig. 3. Crystal structures of IDO1. (A) 4PI- (PDB ID: 2D0T), (B) Amg-1- (PDB ID: 4PK5), (C) GDC-0919 analogue- (PDB ID: 5EK4) and (D) INCB14943- (PDB ID: 5XE1)

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bound.

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Fig. 4. IDO1 inhibitors in clinical trials.

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Fig. 5. Examples of Trp analogs.

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Fig. 6. Examples of imidazoles.

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ACCEPTED MANUSCRIPT Fig. 7. Representative structure of tricyclic imidazole derivatives and preliminary SAR

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conclusions.

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Fig. 8. Examples of N-hydroxyamidines.

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Fig. 9. Representative structure of N-hydroxyamidines.

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Fig. 10. Examples of tryptanthrin derivatives.

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Fig. 11. Examples of phenyl benzenesulfonylhydrazides.

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Fig. 12. Examples of other scaffolds with moderate IDO1 inhibition.

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ACCEPTED MANUSCRIPT Table 1 Selected completed and/or ongoing clinical trials using IDO1 inhibitors. Study Title

Study Drug

I/ NCT00567931

1-Methyl-D-tryptophan

INCB024360

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I/ NCT01195311 II/ NCT01685255

II/ NCT01822691

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NCT02042430

GDC-0919

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PF-06840003

1-Methyl-D-tryptophan + Docetaxel 1-Methyl-D-tryptophan + Docetaxel/Paclitaxel 1-Methyl-D-tryptophan + Temozolomide/Bevacizumab 1-Methyl-D-tryptophan + Nab-Paclitaxel/Gemcitabine

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Single Agent 1-Methyl-D-Tryptophan in Treating Patients With Metastatic or Refractory Solid Tumors That Cannot Be Removed By Surgery A Dose-escalation Study in Subjects With Advanced Malignancies A Phase 2 Study of the IDO Inhibitor INCB024360 Versus Tamoxifen for Subjects With Biochemical-recurrent-only EOC, PPC or FTC Following Complete Remission With First-line Chemotherapy Phase II INCB024360 Study for Patients With Myelodysplastic Syndromes Epacadostat Before Surgery in Treating Patients With Newly Diagnosed Stage III-IV Epithelial Ovarian, Fallopian Tube, or Primary Peritoneal Cancer Indoleamine 2,3-Dioxygenase Inhibitor in Advanced Solid Tumors First in Patient Study for PF-06840003 in Malignant Gliomas Combination with Cytotoxic Chemotherapy 1-Methyl-D-Tryptophan and Docetaxel in Treating Patients With Metastatic Solid Tumors Study of Chemotherapy in Combination With IDO Inhibitor in Metastatic Breast Cancer Study of IDO Inhibitor and Temozolomide for Adult Patients With Primary Malignant Brain Tumors Study of IDO Inhibitor in Combination With Gemcitabine and Nab-Paclitaxel in Patients With Metastatic Pancreatic Cancer Study of the IDO Pathway Inhibitor, Indoximod, and Temozolomide for Pediatric Patients With Progressive Primary Malignant Brain Tumors A Study of Indoximod in Combination With (7+3) Chemotherapy in Patients With Newly Diagnosed Acute Myeloid Leukemia Azacitidine Combined With Pembrolizumab and Epacadostat in Subjects With Advanced Solid Tumors Combination with Vaccine Vaccine Therapy and 1-MT in Treating Patients With Metastatic Breast Cancer

Phase/ ClinicalTrials.gov Identifier

Phase II Study of Sipuleucel-T and Indoximod for Patients With Refractory Metastatic Prostate Cancer Immunotherapy Combination Study in Advanced Previously Treated Non-Small Cell Lung Cancer Epacadostat and Vaccine Therapy in Treating Patients With Stage III-IV Melanoma DEC-205/NY-ESO-1 Fusion Protein CDX-1401, Poly ICLC, and IDO1 Inhibitor INCB024360 in Treating Patients With Ovarian, Fallopian Tube, or Primary Peritoneal Cancer in Remission Safety and Efficacy of CRS-207 With Epacadostat in Platinum Resistant Ovarian, Fallopian, or Peritoneal Cancer Study of DPX-Survivac Vaccine Therapy and Epacadostat in Patients With Recurrent Ovarian Cancer Combination with checkpoint inhibitors

I/ NCT02048709 I/ NCT02764151 I/ NCT01191216 II/ NCT01792050 I/II/ NCT02052648 I/II/ NCT02077881

1-Methyl-D-tryptophan + Temozolomide

I/ NCT02502708

1-Methyl-D-tryptophan + Idarubicin/Cytarabine

I/II/ NCT02835729

Azacitidine + INCB024360/Pembrolizumab

I/II/ NCT02959437

1-Methyl-D-tryptophan + adenovirus-p53 transduced dendritic cell (DC) vaccine 1-Methyl-D-tryptophan + Sipuleucel-T 1-Methyl-D-tryptophan + Tergenpumatucel-L/Docetaxel INCB024360 + MELITAC 12.1 Peptide Vaccine INCB024360 + DEC-205/NY-ESO-1 Fusion Protein CDX-1401/Poly ICLC

I/II/ NCT01042535

INCB024360 + CRS-207/Pembrolizumab

I/II/ NCT02575807

INCB024360 + DPX-Survivac/Cyclophosphamide

I/ NCT02785250

II/ NCT01560923 I/II/ NCT02460367 II/ NCT01961115 I/II/ NCT02166905

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ACCEPTED MANUSCRIPT 1-Methyl-D-tryptophan + Ipilimumab/Nivolumab/Pembroliz umab INCB024360 + Pembrolizumab

I/II/ NCT02073123

INCB024360 + Atezolizumab

I/ NCT02298153

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INCB024360 + Durvalumab

I/II/ NCT02318277

INCB024360 + Nivolumab

I/II/ NCT02327078

I/ NCT02559492

INCB024360 + Pembrolizumab

III/ NCT02752074

INCB024360 + Pembrolizumab

I/ NCT02862457 I/ NCT02298153

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Study of IDO Inhibitor in Combination With Checkpoint Inhibitors for Adult Patients With Metastatic Melanoma A Phase 1/2 Study Exploring the Safety, Tolerability, and Efficacy of Pembrolizumab in Combination With Epacadostat in Subjects With Selected Cancers A Study of Atezolizumab in Combination With Epacadostat in Subjects With Previously Treated Stage IIIB or Stage IV Non-Small Cell Lung Cancer and Previously Treated Stage IV Urothelial Carcinoma A Study of Epacadostat in Combination With Durvalumab in Subjects With Selected Advanced Solid Tumors A Study of the Safety, Tolerability, and Efficacy of Epacadostat Administered in Combination With Nivolumab in Select Advanced Cancers INCB039110 Combined With INCB024360 and/or INCB039110 Combined With INCB050465 in Advanced Solid Tumors A Phase 3 Study of Pembrolizumab + Epacadostat or Placebo in Subjects With Unresectable or Metastatic Melanoma Study of INCB024360 Alone and In Combination With Pembrolizumab in Solid Tumors A Study of GDC-0919 and Atezolizumab Combination Treatment in Participants With Locally Advanced or Metastatic Solid Tumors An Investigational Immuno-therapy Study of BMS-986205 Given in Combination With Nivolumab in Cancers That Are Advanced or Have Spread

GDC-0919 + Atezolizumab

BMS-986205 + Nivolumab

I/II/ NCT02658890

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Indoximod: same as 1-Methyl-D-tryptophan; Epacadostat: same as INCB024360

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ACCEPTED MANUSCRIPT Highlights

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Functional roles of IDO1 in immune escape are illuminated. Representative crystal structures of IDO1are listed in turn and compared with each other. Current status of IDO1 inhibitors in clinical trials are covered. Most recently developed IDO1 inhibitors with an emphasis on their chemical structures and their other derived applications are highlighted.