Epacadostat stabilizes the apo-form of IDO1 and signals a pro-tumorigenic pathway in human ovarian cancer cells

The tryptophan-degrading enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is a plastic immune checkpoint molecule that potently orchestrates immune responses within the tumor microenvironment (TME). As a heme-containing protein, IDO1 catalyzes the conversion of the essential amino acid tryptophan into immunoactive metabolites, called kynurenines. By depleting tryptophan and enriching the TME with kynurenines, IDO1 catalytic activity shapes an immunosuppressive TME. Accordingly, the inducible or constitutive IDO1 expression in cancer correlates with a negative prognosis for patients, representing one of the critical tumor-escape mechanisms. However, clinically trialed IDO1 catalytic inhibitors disappointed the expected anti-tumor efficacy. Interestingly, the non-enzymatic apo-form of IDO1 is still active as a transducing protein, capable of promoting an immunoregulatory phenotype in dendritic cells (DCs) as well as a pro-tumorigenic behavior in murine melanoma. Moreover, the IDO1 catalytic inhibitor epacadostat can induce a tolerogenic phenotype in plasmacytoid DCs, overcoming the catalytic inhibition of IDO1. Based on this recent evidence, IDO1 plasticity was investigated in the human ovarian cancer cell line, SKOV-3, that constitutively expresses IDO1 in a dynamic balance between the holo- and apo-protein, and thus potentially endowed with a dual function (i.e., enzymatic and non-enzymatic). Besides inhibiting the catalytic activity, epacadostat persistently stabilizes the apo-form of IDO1 protein, favoring its tyrosine-phosphorylation and promoting its association with the phosphatase SHP-2. In SKOV-3 cells, both these early molecular events activate a signaling pathway transduced by IDO1 apo-protein, which is independent of its catalytic activity and contributes to the tumorigenic phenotype of SKOV-3 cells. Overall, our findings unveiled a new mechanism of action of epacadostat on IDO1 target, repositioning the catalytic inhibitor as a stabilizer of the apo-form of IDO1, still capable of transducing a pro-tumorigenic pathway in SKOV-3 tumor. This mechanism could contribute to clarify the lack of effectiveness of epacadostat in clinical trials and shed light on innovative immunotherapeutic strategies to tackle IDO1 target.

The immunomodulatory role of IDO1-Kynurenine-NAD+ pathway in switching cold tumor microenvironment in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is the most common exocrine tumor of the pancreas characterized by late diagnosis, adverse overall 5-year survival, a higher propensity for metastatic disease, and lack of efficacy of systemic therapy options. These adverse outcomes can be partly attributed to complex tumor microenvironment (TME). Over the past decade, immunotherapy has revolutionized the management of certain cancers; thus far, the immunologically 'non-inflamed' tumor microenvironment in PDACs has proven to be challenging. Indolamine 2,3-dioxygenase 1 (IDO1) is the rate-limiting enzyme in the catabolic pathway of L-Tryptophan, an essential amino acid, that gives rise to the immunosuppressive metabolite Kynurenine. IDO1, Indolamine 2,3-dioxygenase 2 (IDO2), and Tryptophan 2,3-dioxygenase (TDO) are the key enzymes in the tryptophan catabolic pathway but we focus on the role of the predominant enzyme form IDO1 in this review. Nicotinamide phosphoribosyl transferase (iNAMPT) regulates the intracellular concentration of NAD and is upregulated in the tumor. In light of the potential role of IDO1 as a driver of hostile TME in PDAC and NAD⁺ as a key coenzyme in anti-tumor immune response, this review urges focus on extensive research and initiation of clinical trials using IDO1 and NAMPT inhibitors in pancreatic cancer in the future.

A Phase II Study of Epacadostat and Pembrolizumab in Patients with Advanced Sarcoma

PURPOSE

Epacadostat, an indole 2,3 dioxygenase 1 (IDO1) inhibitor, proposed to shift the tumor microenvironment toward an immune-stimulated state, showed early promise in melanoma but has not been studied in sarcoma. This study combined epacadostat with pembrolizumab, which has modest activity in select sarcoma subtypes.

PATIENTS AND METHODS

This phase II study enrolled patients with advanced sarcoma into five cohorts including (i) undifferentiated pleomorphic sarcoma (UPS)/myxofibrosarcoma, (ii) liposarcoma (LPS), (iii) leiomyosarcoma (LMS), (iv) vascular sarcoma, including angiosarcoma and epithelioid hemangioendothelioma (EHE), and (v) other subtypes. Patients received epacadostat 100 mg twice daily plus pembrolizumab at 200 mg/dose every 3 weeks. The primary endpoint was best objective response rate (ORR), defined as complete response (CR) and partial response (PR), at 24 weeks by RECIST v.1.1.

RESULTS

Thirty patients were enrolled [60% male; median age 54 years (range, 24-78)]. The best ORR at 24 weeks was 3.3% [PR, n = 1 (leiomyosarcoma); two-sided 95% CI, 0.1%-17.2%]. The median PFS was 7.6 weeks (two-sided 95% CI, 6.9-26.7). Treatment was well tolerated. Grade 3 treatment-related adverse events occurred in 23% (n = 7) of patients. In paired pre- and post-treatment tumor samples, no association was found between treatment and PD-L1 or IDO1 tumor expression or IDO-pathway-related gene expression by RNA sequencing. No significant changes in serum tryptophan or kynurenine levels were observed after baseline.

CONCLUSIONS

Combination epacadostat and pembrolizumab was well tolerated and showed limited antitumor activity in sarcoma. Correlative analyses suggested that inadequate IDO1 inhibition was achieved.

The catalytic inhibitor epacadostat can affect the non-enzymatic function of IDO1

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme chronically activated in many cancer patients and its expression and activity correlate with a poor prognosis. In fact, it acts as an immune regulator and contributes to tumor-induced immunosuppression by determining tryptophan deprivation and producing immunosuppressive metabolites named kynurenines. These findings made IDO1 an attractive target for cancer immunotherapy and small-molecule inhibitors, such as epacadostat, have been developed to block its enzymatic activity. Although epacadostat was effective in preclinical models and in early phase trials, it gave negative results in a metastatic melanoma randomized phase III study to test the benefit of adding epacadostat to the reference pembrolizumab therapy. However, the reason for the epacadostat failure in this clinical trial has never been understood. Our data suggest that a possible explanation of epacadostat ineffectiveness may rely on the ability of this drug to enhance the other IDO1 immunoregulatory mechanism, involving intracellular signaling function. These findings open up a new perspective for IDO1 inhibitors developed as new anticancer drugs, which should be carefully evaluated for their ability to block not only the catalytic but also the signaling activity of IDO1.

Phase 1/2 study of epacadostat in combination with durvalumab in patients with metastatic solid tumors

BACKGROUND

Targeting programmed cell death protein 1 (PD-1) and indoleamine 2,3-dioxygenase (IDO1) pathways is an appealing option for cancer treatment.

METHODS

The open-label, phase 1/2 ECHO-203 study evaluated the safety, tolerability, and efficacy of the IDO1 inhibitor epacadostat in combination with durvalumab, a human anti-PD-L1 monoclonal antibody in adult patients with advanced solid tumors.

RESULTS

The most common treatment-related adverse events were fatigue (30.7%), nausea (21.0%), decreased appetite (13.1%), pruritus (12.5%), maculopapular rash (10.8%), and diarrhea (10.2%). Objective response rate (ORR) in the overall phase 2 population was 12.0%. Higher ORR was observed in immune checkpoint inhibitor (CPI)-naïve patients (16.1%) compared with patients who had received previous CPI (4.1%). Epacadostat pharmacodynamics were evaluated by comparing baseline kynurenine levels with those on therapy at various time points. Only the 300-mg epacadostat dose showed evidence of kynurenine modulation, albeit unsustained.

CONCLUSIONS

Epacadostat plus durvalumab was generally well tolerated in patients with advanced solid tumors. ORR was low, and evaluation of kynurenine concentration from baseline to cycle 2, day 1, and cycle 5, day 1, suggested >300 mg epacadostat twice daily is needed to ensure sufficient drug effect.

CLINICAL TRIAL INFORMATION

A study of epacadostat (INCB024360) in combination with durvalumab (MEDI4736) in subjects with selected advanced solid tumors (ECHO-203) (NCT02318277).

Epacadostat Plus Pembrolizumab and Chemotherapy for Advanced Solid Tumors: Results from the Phase I/II ECHO-207/KEYNOTE-723 Study

BACKGROUND

Epacadostat, an oral, selective inhibitor of IDO1, has shown activity when administered with pembrolizumab. We evaluated the addition of chemotherapy to epacadostat and pembrolizumab in patients with advanced or metastatic solid tumors. One proposed mechanism of resistance to PD-1 checkpoint inhibition is through immunosuppression mediated by L-kynurenine. IDO1, indoleamine-2,3-dioxygenase 1 is the rate-limiting enzyme catalyzing the conversion of L-tryptophan to L-kynurenine. If IDO1 is a mechanism of tumor escape from checkpoint inhibition, then addition of an IDO1 inhibitor with a PD-1 checkpoint inhibitor could enable tumor response to immunotherapy.

METHODS

Patients received one of 7 tumor-appropriate chemotherapy regimens. Pembrolizumab 200 mg was infused intravenously every 3 weeks. Epacadostat 100 mg was administered orally twice daily. The primary objectives of phase I were determining safety/tolerability and defining the maximum tolerated or pharmacologically active dose of epacadostat. Phase II of the study was designed to enroll efficacy-expansion cohorts and to assess changes in the tumor and tumor microenvironment via mandatory-biopsy cohorts.

RESULTS

A total of 70 patients were enrolled. Twelve patients were enrolled in the phase II mandatory-biopsy cohorts. Due to early study closure, efficacy expansion did not enroll. Grades 3 and 4 treatment-emergent adverse events (TEAEs) occurred in 78.6% of patients. Neutropenia and disease progression were the only grades 3 and 4 TEAEs reported in ≥10.0% of patients. One treatment-related death was reported. The ORR was 31.4% across all treatment groups.

CONCLUSION

The combination of epacadostat 100 mg bid with pembrolizumab and chemotherapy had an acceptable safety profile. This regimen showed antitumor activity across multiple types of advanced or metastatic solid tumors (ClinicalTrials.gov Identifier: NCT03085914).

Immune-regulated IDO1-dependent tryptophan metabolism is source of one-carbon units for pancreatic cancer and stellate cells

Cancer cells adapt their metabolism to support elevated energetic and anabolic demands of proliferation. Folate-dependent one-carbon metabolism is a critical metabolic process underpinning cellular proliferation supplying carbons for the synthesis of nucleotides incorporated into DNA and RNA. Recent research has focused on the nutrients that supply one-carbons to the folate cycle, particularly serine. Tryptophan is a theoretical source of one-carbon units through metabolism by IDO1, an enzyme intensively investigated in the context of tumor immune evasion. Using in vitro and in vivo pancreatic cancer models, we show that IDO1 expression is highly context dependent, influenced by attachment-independent growth and the canonical activator IFNγ. In IDO1-expressing cancer cells, tryptophan is a bona fide one-carbon donor for purine nucleotide synthesis in vitro and in vivo. Furthermore, we show that cancer cells release tryptophan-derived formate, which can be used by pancreatic stellate cells to support purine nucleotide synthesis.

Protective Effects of Necrostatin-1 in Acute Pancreatitis: Partial Involvement of Receptor Interacting Protein Kinase 1

Acute pancreatitis (AP) is a severe and potentially fatal disease caused predominantly by alcohol excess and gallstones, which lacks a specific therapy. The role of Receptor-Interacting Protein Kinase 1 (RIPK1), a key component of programmed necrosis (Necroptosis), is unclear in AP. We assessed the effects of RIPK1 inhibitor Necrostatin-1 (Nec-1) and RIPK1 modification (RIPK1K45A: kinase dead) in bile acid (TLCS-AP), alcoholic (FAEE-AP) and caerulein hyperstimulation (CER-AP) mouse models. Involvement of collateral Nec-1 target indoleamine 2,3-dioxygenase (IDO) was probed with the inhibitor Epacadostat (EPA). Effects of Nec-1 and RIPK1K45A were also compared on pancreatic acinar cell (PAC) fate in vitro and underlying mechanisms explored. Nec-1 markedly ameliorated histological and biochemical changes in all models. However, these were only partially reduced or unchanged in RIPK1K45A mice. Inhibition of IDO with EPA was protective in TLCS-AP. Both Nec-1 and RIPK1K45A modification inhibited TLCS- and FAEE-induced PAC necrosis in vitro. Nec-1 did not affect TLCS-induced Ca2+ entry in PACs, however, it inhibited an associated ROS elevation. The results demonstrate protective actions of Nec-1 in multiple models. However, RIPK1-dependent necroptosis only partially contributed to beneficial effects, and actions on targets such as IDO are likely to be important.

IDO1-Targeted Therapy Does Not Control Disease Development in the Eµ-TCL1 Mouse Model of Chronic Lymphocytic Leukemia

Simple Summary

The tryptophan-catabolizing enzyme IDO1 and its metabolite kynurenine were shown to be enhanced in patients with chronic lymphocytic leukemia (CLL), and their involvement in T cell suppression and immune escape was suggested. As we have observed increased IDO1 expression and kynurenine serum levels in the Eµ-TCL1 mouse model of CLL, we evaluated the therapeutic potential of targeting IDO1 in preclinical treatment studies with two IDO1 inhibitors in mice developing CLL. As both studies revealed only minor effects of IDO1 inhibition on leukemia development and the immune compartment at early time points of treatment which disappeared over time, our data suggest that even though IDO1 might be involved in immunosuppressive mechanisms in CLL, its targeting is not sufficient for preventing immune escape. Thus, compensatory mechanisms beyond IDO1 seem to be of relevance to prevent clinically relevant benefits with IDO1-targeting drugs.

Abstract

Indoleamine-2,3-dioxygenase 1 (IDO1), a tryptophan (Trp)-catabolizing enzyme producing metabolites such as kynurenine (Kyn), is expressed by myeloid-derived suppressor cells (MDSCs) and associated with cancer immune escape. IDO1-expressing monocytic MDSCs were shown to accumulate in patients with chronic lymphocytic leukemia (CLL) and to suppress T cell activity and induce suppressive regulatory T cells (Tregs) in vitro. In the Eµ-TCL1 mouse model of CLL, we observed a strong upregulation of IDO1 in monocytic and granulocytic MDSCs, and a significantly increased Kyn to Trp serum ratio. To explore the potential of IDO1 as a therapeutic target for CLL, we treated mice after adoptive transfer of Eµ-TCL1 leukemia cells with the IDO1 modulator 1-methyl-D-tryptophan (1-MT) which resulted in a minor reduction in leukemia development which disappeared over time. 1-MT treatment further led to a partial rescue of the immune cell changes that are induced with CLL development. Similarly, treatment of leukemic mice with the clinically investigated IDO1 inhibitor epacadostat reduced the frequency of Tregs and initially delayed CLL development slightly, an effect that was, however, lost at later time points. In sum, despite the observed upregulation of IDO1 in CLL, its inhibition is not sufficient to control leukemia development in the Eµ-TCL1 adoptive transfer model.

Human type 1 and type 2 conventional dendritic cells express indoleamine 2,3-dioxygenase 1 with functional effects on T cell priming

Dendritic cells (DCs) are key regulators of the immune system that shape T cell responses. Regulation of T cell induction by DCs may occur via the intracellular enzyme indoleamine 2,3‐dioxygenase 1 (IDO), which catalyzes conversion of the essential amino acid tryptophan into kynurenine. Here, we examined the role of IDO in human peripheral blood plasmacytoid DCs (pDCs), and type 1 and type 2 conventional DCs (cDC1s and cDC2s). Our data demonstrate that under homeostatic conditions, IDO is selectively expressed by cDC1s. IFN‐γ or TLR ligation further increases IDO expression in cDC1s and induces modest expression of the enzyme in cDC2s, but not pDCs. IDO expressed by conventional DCs is functionally active as measured by kynurenine production. Furthermore, IDO activity in TLR‐stimulated cDC1s and cDC2s inhibits T cell proliferation in settings were DC‐T cell cell‐cell contact does not play a role. Selective inhibition of IDO1 with epacadostat, an inhibitor currently tested in clinical trials, rescued T cell proliferation without affecting DC maturation status or their ability to cross‐present soluble antigen. Our findings provide new insights into the functional specialization of human blood DC subsets and suggest a possible synergistic enhancement of therapeutic efficacy by combining DC‐based cancer vaccines with IDO inhibition.

Indoleamine 2,3-Dioxygenase 1 Inhibitor-Loaded Nanosheets Enhance CAR-T Cell Function in Esophageal Squamous Cell Carcinoma

In chimeric antigen receptor (CAR)-T cell therapy, the role and mechanism of indoleamine 2, 3 dioxygenase 1 (IDO1) in enhancing antitumor immunity require further study. IDO1 is one of the most important immunosuppressive proteins in esophageal squamous cell carcinoma (ESCC). However, the IDO1 inhibitor, epacadostat, has failed in phase III clinical trials; its limited capacity to inhibit IDO1 expression at tumor sites was regarded as a key reason for clinical failure. In this study, we innovatively loaded the IDO1 inhibitor into hyaluronic acid-modified nanomaterial graphene oxide (HA-GO) and explored its potential efficacy in combination with CAR-T cell therapy. We found that inhibition of the antitumor effect of CAR-T cells in ESCC was dependent on the IDO1 metabolite kynurenine. Kynurenine could suppress CAR-T cell cytokine secretion and cytotoxic activity. Inhibiting IDO1 activity significantly enhanced the antitumor effect of CAR-T cells in vitro and in vivo. Our findings suggested that IDO1 inhibitor-loaded nanosheets could enhance the antitumor effect of CAR-T cells compared with free IDO1 inhibitor. Nanosheet-loading therefore provides a promising approach for improving CAR-T cell therapeutic efficacy in solid tumors.

Dexamethasone Induces the Expression and Function of Tryptophan-2-3-Dioxygenase in SK-MEL-28 Melanoma Cells

Tryptophan-2,3-dioxygenase (TDO) is one of the key tryptophan-catabolizing enzymes with immunoregulatory properties in cancer. Contrary to expectation, clinical trials showed that inhibitors of the ubiquitously expressed enzyme, indoleamine-2,3-dioxygenase-1 (IDO1), do not provide benefits in melanoma patients. This prompted the hypothesis that TDO may be a more attractive target. Because the promoter of TDO harbors glucocorticoid response elements (GREs), we aimed to assess whether dexamethasone (dex), a commonly used glucocorticoid, modulates TDO expression by means of RT-PCR and immunofluorescence and function by assessing cell proliferation and migration as well as metalloproteinase activity. Our results show that, in SK-Mel-28 melanoma cells, dex up-regulated TDO and its downstream effector aryl hydrocarbon receptor (AHR) but not IDO1. Furthermore, dex stimulated cellular proliferation and migration and potentiated MMP2 activity. These effects were inhibited by the selective TDO inhibitor 680C91 and enhanced by IDO1 inhibitors. Taken together, our results demonstrate that the metastatic melanoma cell line SK-Mel-28 possesses a functional TDO which can also modulate cancer cell phenotype directly rather than through immune suppression. Thus, TDO appears to be a promising, tractable target in the management or the treatment of melanoma progression.

A concise review of bioanalytical methods of small molecule immuno-oncology drugs in cancer therapy

Immuno-oncology (IO) is an emerging option to treat cancer malignancies. In the last two years, IO has accounted for more than 90% of the new active drugs in various therapeutic indications of oncology drug development. Bioanalytical methods used for the quantitation of various IO small molecule drugs have been summarized in this review. The most commonly used are HPLC and LC-MS/MS methods. Determination of IO drugs from biological matrices involves drug extraction from the biological matrix, which is mostly achieved by simple protein precipitation, liquid-liquid extraction and solid-phase extraction. Subsequently, quantitation is usually achieved by LC-MS/MS, but HPLC-UV has also been employed. The bioanalytical methods reported for each drug are briefly discussed and tabulated for easy access. Our review indicates that LC-MS/MS is a versatile and reliable tool for the sensitive, rapid and robust quantitation of IO drugs.

Trial watch: IDO inhibitors in cancer therapy

Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the first, rate-limiting step of the so-called “kynurenine pathway”, which converts the essential amino acid L-tryptophan (Trp) into the immunosuppressive metabolite L-kynurenine (Kyn). While expressed constitutively by some tissues, IDO1 can also be induced in specific subsets of antigen-presenting cells that ultimately favor the establishment of immune tolerance to tumor antigens. At least in part, the immunomodulatory functions of IDO1 can be explained by depletion of Trp and accumulation of Kyn and its derivatives. In animal tumor models, genetic or pharmacological IDO1 inhibition can cause the (re)activation of anticancer immune responses. Similarly, neoplasms expressing high levels of IDO1 may elude anticancer immunosurveillance. Therefore, IDO1 inhibitors represent promising therapeutic candidates for cancer therapy, and some of them have already entered clinical evaluation. Here, we summarize preclinical and clinical studies testing IDO1-targeting interventions for oncologic indications.

Phase 1 study of epacadostat in combination with atezolizumab for patients with previously treated advanced nonsmall cell lung cancer

Epacadostat is a potent and highly selective inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1). Here we report results from the open-label, dose-escalation, Phase 1b ECHO-110 study evaluating epacadostat plus atezolizumab in patients with previously treated Stage IIIB/IV nonsmall cell lung cancer (NSCLC). Eligible patients had received ≥1 prior line of platinum-based chemotherapy (≥2 cycles) and no prior checkpoint/IDO inhibitors treatment. Oral epacadostat (25, 50, 75, 100, 200 or 300 mg) was administered twice daily (BID) with intravenous atezolizumab 1,200 mg every 3 weeks (Q3W). Primary endpoints were safety, tolerability and dose-limiting toxicities (DLTs). Twenty-nine patients received ≥1 dose of treatment. The maximum tolerated dose of epacadostat was not reached. Two patients had DLTs: one patient with Grade 3 dehydration and hypotension (epacadostat 200 mg BID); one patient with Grade 3 hyponatremia and Grade 4 autoimmune encephalitis (epacadostat 300 mg BID). Twenty-three patients (79%) had treatment-related adverse events (AEs); seven patients (24%) experienced Grade 3/4 events; five patients (17%) discontinued treatment due to treatment-related AEs. No fatal treatment-related AEs occurred. One patient achieved a partial response (objective response rate, 3%), which was maintained for 8.3 months; eight patients had stable disease. Baseline tumoral programmed cell death ligand 1 (PD-L1) and IDO expression were low among patients with evaluable samples (1 of 23 expressed PD-L1; 5 of 17 expressed IDO). Epacadostat pharmacokinetics was comparable to historical controls. Epacadostat, at doses up to 300 mg BID, combined with atezolizumab 1,200 mg Q3W was well tolerated in patients with previously treated NSCLC, although clinical activity was limited.

Inhibition Mechanism of Indoleamine 2, 3-Dioxygenase 1 (IDO1) by Amidoxime Derivatives and Its Revelation in Drug Design: Comparative Molecular Dynamics Simulations

For cancer treatment, in addition to the three standard therapies of surgery, chemotherapy, and radiotherapy, immunotherapy has become the fourth internationally-recognized alternative treatment. Indoleamine 2, 3-dioxygenase 1 (IDO1) catalyzes the conversion of tryptophan to kynurenine causing lysine depletion, which is an important target in the research and development of anticancer drugs. Epacadostat (INCB024360) is currently one of the most potent IDO1 inhibitors, nevertheless its inhibition mechanism still remains elusive. In this work, comparative molecular dynamics simulations were performed to reveal that the high inhibitory activity of INCB024360 mainly comes from two aspects: disturbing the ligand delivery tunnel and then preventing small molecules such as oxygen and water molecules from accessing the active site, as well as hindering the shuttle of substrate tryptophan with product kynurenine through the heme binding pocket. The scanning of key residues showed that L234 and R231 residues both were crucial to the catalytic activity of IDO1. With the association with INCB024360, L234 forms a stable hydrogen bond with G262, which significantly affects the spatial position of G262-A264 loop and then greatly disturbs the orderliness of ligand delivery tunnel. In addition, the cleavage of hydrogen bond between G380 and R231 increases the mobility of the GTGG conserved region, leading to the closure of the substrate tryptophan channel. This work provides new ideas for understanding action mechanism of amidoxime derivatives, improving its inhibitor activity and developing novel inhibitors of IDO1.

Cell based functional assays for IDO1 inhibitor screening and characterization

Indoleamine 2,3-dioxygenase 1 (IDO1) is a new immune-oncology target and its inhibitors have shown promise in the clinic especially in combination with other immune-stimulating agents. Here we describe two robust cell-based assays for screening IDO1 inhibitors. Both assays can be easily adopted by most laboratories and utilized for screening of IDO1 inhibitors. Endogenous IDO1 expression is induced in a cancer cell line with interferon gamma and its activity is assessed by measuring kynurenine secreted into the media. The effect of cancer cell IDO1 induction and inhibition on T cell activation is evaluated in a co-culture assay using Jurkat T cell line. Additional readouts assessing cell viability are employed for early detection of false positive IDO1 inhibitors and toxic compounds. Clinical candidates epacadostat and BMS-986205 were evaluated in the assays as control compounds, the former can completely inhibit IDO1 activity while the maximum effect of the later is limited (to about 80% in our system) consistent with the differences in their interaction with IDO1. Nanomolar concentrations of both compounds rescued IDO1 mediated inhibition of T cell activation. However, treatment with micromolar concentrations of BMS-986205 blocked Jurkat T cell activation and after prolonged incubation induced cell death.

Potential Underprediction of Warfarin Drug Interaction From Conventional Interaction Studies and Risk Mitigation: A Case Study With Epacadostat, an IDO1 Inhibitor

Drug-drug interaction (DDI) studies involving warfarin are typically conducted with subtherapeutic doses of warfarin to ensure the safety of volunteers. However, this approach may potentially have a systemic bias of underestimating pharmacodynamic (PD) DDI effect on warfarin at therapeutic levels of anticoagulation. We demonstrate here the utility of model-based DDI prediction for a clinically relevant warfarin regimen, using the example of epacadostat (INCB024360), the first-in-class indoleamine 2,3-dioxygenase 1 inhibitor in clinical development as a novel orally active immuno-oncological therapy. Observed data from a dedicated clinical DDI study using subtherapeutic warfarin suggested warfarin pharmacokinetics (PK), but not PD (anticoagulation), was significantly affected by concomitant epacadostat. However, subsequent PK/PD modeling and simulations indicated a clinically important DDI effect on warfarin PD at a higher baseline of the international normalization ratio (INR) and enabled recommendation of warfarin dose adjustment that is dependent on epacadostat dosing regimen and target INR.

Population Pharmacokinetic and Pharmacodynamic Modeling of Epacadostat in Patients With Advanced Solid Malignancies

Epacadostat (EPA, INCB024360) is a selective inhibitor of the enzyme indoleamine 2,3-dioxygenase 1 (IDO1) and is being developed as an orally active immunotherapy to treat advanced malignancies. In the first clinical study investigating the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of EPA in oncology patients, increasing doses of EPA ranging from 50 mg once daily to 700 mg twice daily were administered as a monotherapy to 52 subjects with advanced solid tumors. The EPA plasma concentration-time profiles were adequately described by a population PK model comprised of the first-order kinetics of oral absorption with 2-compartment distribution and constant clearance from the central compartment. Body weight was the only significant covariant to influence EPA PK. Determination of EPA's on-target potency, ie, its half-maximal inhibitory concentration (IC₅₀ ) against IDO1, is important for dose selection but complicated by the bioconversion of tryptophan (TRP) to kynurenine (KYN) catalyzed by both IDO1 and TRP 2,3-dioxygenase (TDO). In vitro and ex vivo, the IC₅₀ was estimated following the selective induction of IDO1, rendering the TDO activity relatively insignificant; however, it was desirable to determine the in vivo IC₅₀ without inducing an IDO1 abundance. A mechanistic population PD model was developed based on time-matched EPA, TRP, and KYN plasma concentrations in 44 oncology patients, and EPA in vivo IC₅₀ was estimated to be ∼70 nM, consistent with the ex vivo value independently determined. The model suggests that ∼60% and 40% of TRP→KYN bioconversion was mediated by IDO1 and TDO, respectively, in the cancer patients at baseline. For this study population of limited numbers of subjects, neither age nor sex was a significant covariate for EPA PK or PD.

Determination of epacadostat, a novel IDO1 inhibitor in mouse plasma by LC-MS/MS and its application to a pharmacokinetic study in mice

A sensitive, specific and rapid LC-ESI-MS/MS method has been developed and validated for the quantification of epacadostat in mouse plasma using tolbutamide as an internal standard (IS) as per regulatory guidelines. Sample preparation was accomplished through a protein precipitation. Chromatographic separation was performed on an Atlantis dC₁₈ column using a binary gradient using mobile phase A (acetonitrile) and B (0.2% formic acid in water) at a flow rate of 0.90 mL/min. Elution of epacadostat and IS occurred at ~2.41 and 2.51 min, respectively. The total chromatographic run time was 3.2 min. A linear response function was established in the concentration range of 1.07-533 ng/mL. The intra- and inter-day accuracy and precision were in the ranges of 1.81-12.9 and 3.80-11.1%, respectively. This novel method has been applied to a pharmacokinetic study in mice.