The kynurenine pathway presents multi-faceted metabolic vulnerabilities in cancer

The kynurenine pathway (KP) and associated catabolites play key roles in promoting tumor progression and modulating the host anti-tumor immune response. To date, considerable focus has been on the role of indoleamine 2,3-dioxygenase 1 (IDO1) and its catabolite, kynurenine (Kyn). However, increasing evidence has demonstrated that downstream KP enzymes and their associated metabolite products can also elicit tumor-microenvironment immune suppression. These advancements in our understanding of the tumor promotive role of the KP have led to the conception of novel therapeutic strategies to target the KP pathway for anti-cancer effects and reversal of immune escape. This review aims to 1) highlight the known biological functions of key enzymes in the KP, and 2) provide a comprehensive overview of existing and emerging therapies aimed at targeting discrete enzymes in the KP for anti-cancer treatment.

Targeting the tumor microenvironment by liposomal Epacadostat in combination with liposomal gp100 vaccine

Indoleamine-2,3-dioxygenase (IDO1) pathway has vital role in cancer immune escape and its upregulation leads to immunosuppressive environment which is associated with poor prognosis and progression in various cancers like melanoma. Previously, we showed the antitumoral efficacy of nanoliposomal form of Epacadostat (Lip-EPA), as an IDO1 inhibitor. Herein, we used Lip-EPA as a combination approach with liposomal gp100 (Lip-gp100) anti-cancer vaccine in melanoma model. Here, we showed that B16F10 tumor express IDO1 so using Lip-EPA will enhance the efficacy of vaccine therapy. The biodistribution of ICG-labelled liposomal form of EPA showed the remarkable accumulation of drug at tumor site. In an in vivo study, Lip-EPA enhanced the antitumor efficacy of Lip-gp100 in which the IDO mRNA expression was decreased (~ fourfold) in tumor samples. Also, we identified a significant increase in the number of infiltrated T lymphocytes (p < 0.0001) with enhanced in interferon gamma (IFN-γ) production (p < 0.0001). Additionally, Lip-EPA + Lip-gp100 significantly modulated intratumoral regulatory T cells which altogether resulted in the highest delay in tumor growth (TGD = 56.54%) and increased life span (ILS > 47.36%) in treated mice. Our study demonstrated that novel combination of Lip-EPA and Lip-gp100 was effective treatment with capability of being used in further clinical studies.

Indoleamine 2,3-dioxygenase 1 in circumventing checkpoint inhibitor responses: Updated

Metabolic alterations occur commonly in tumor cells as a way to adapt available energetic sources for their proliferation, survival and resistance. Indoleamine 2,3-dioxygenase 1 (IDO1) is an intracellular enzyme catalyzing tryptophan degradation into kynurenine. IDO1 expression shows a rise in the stroma of many types of human cancers, and it provides a negative feedback mechanism for cancer evasion from immunosurveillance. Upregulation of IDO1 correlates with cancer aggression, poor prognosis and shortened patient survival. The increased activity of this endogenous checkpoint impairs effector T cell function, increases regulatory T cell (Treg) population and induces immune tolerance, so its inhibition potentiates anti-tumor immune responses and reshapes immunogenic state of tumor microenvironment (TME) presumably through normalizing effector T cell activity. A point is that the expression of this immunoregulatory marker is upregulated after immune checkpoint inhibitor (ICI) therapy, and that it has inducible effect on expression of other checkpoints. These are indicative of the importance of IDO1 as an attractive immunotherapeutic target and rationalizing combination of IDO1 inhibitors with ICI drugs in patients with advanced solid cancers. In this review, we aimed to discuss about the impact of IDO1 on tumor immune ecosystem, and the IDO1-mediated bypass of ICI therapy. The efficacy of IDO1 inhibitor therapy in combination with ICIs in advanced/metastatic solid tumors is also a focus of this paper.

Metabolic modulation of immune checkpoints and novel therapeutic strategies in cancer

Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) or programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1)-based immune checkpoint inhibitors (ICIs) have led to significant improvements in the overall survival of patients with certain cancers and are expected to benefit patients by achieving complete, long-lasting remissions and cure. However, some patients who receive ICIs either fail treatment or eventually develop immunotherapy resistance. The existence of such patients necessitates a deeper understanding of cancer progression, specifically nutrient regulation in the tumor microenvironment (TME), which includes both metabolic cross-talk between metabolites and tumor cells, and intracellular metabolism in immune and cancer cells. Here we review the features and behaviors of the TME and discuss the recently identified major immune checkpoints. We comprehensively and systematically summarize the metabolic modulation of tumor immunity and immune checkpoints in the TME, including glycolysis, amino acid metabolism, lipid metabolism, and other metabolic pathways, and further discuss the potential metabolism-based therapeutic strategies tested in preclinical and clinical settings. These findings will help to determine the existence of a link or crosstalk between tumor metabolism and immunotherapy, which will provide an important insight into cancer treatment and cancer research.

Immunotherapy for Melanoma

Melanoma is the leading cause of death from skin cancer and is responsible for over 7000 deaths in the USA each year alone. For many decades, limited treatment options were available for patients with metastatic melanoma; however, over the last decade, a new era in treatment dawned for oncologists and their patients. Targeted therapy with BRAF and MEK inhibitors represents an important cornerstone in the treatment of metastatic melanoma; however, this chapter carefully reviews the past and current therapy options available, with a significant focus on immunotherapy-based approaches. In addition, we provide an overview of the results of recent advances in the adjuvant setting for patients with resected stage III and stage IV melanoma, as well as in patients with melanoma brain metastases. Finally, we provide a brief overview of the current research efforts in the field of immuno-oncology for melanoma.

Bempegaldesleukin Plus Nivolumab in First-Line Metastatic Melanoma

Therapies that produce deep and durable responses in patients with metastatic melanoma are needed. This phase II cohort from the international, single-arm PIVOT-02 study evaluated the CD122-preferential interleukin-2 pathway agonist bempegaldesleukin (BEMPEG) plus nivolumab (NIVO) in first-line metastatic melanoma.

Therapeutic Advancements Across Clinical Stages in Melanoma, With a Focus on Targeted Immunotherapy

Melanoma is the most fatal skin cancer. In the early stages, it can be safely treated with surgery alone. However, since 2011, there has been an important revolution in the treatment of melanoma with new effective treatments. Targeted therapy and immunotherapy with checkpoint inhibitors have changed the history of this disease. To date, more than half of advanced melanoma patients are alive at 5 years; despite this breakthrough, approximately half of the patients still do not respond to treatment. For these reasons, new therapeutic strategies are required to expand the number of patients who can benefit from immunotherapy or combination with targeted therapy. Current research aims at preventing primary and acquired resistance, which are both responsible for treatment failure in about 50% of patients. This could increase the effectiveness of available drugs and allow for the evaluation of new combinations and new targets. The main pathways and molecules under study are the IDO inhibitor, TLR9 agonist, STING, LAG-3, TIM-3, HDAC inhibitors, pegylated IL-2 (NKTR-214), GITR, and adenosine pathway inhibitors, among others (there are currently about 3000 trials that are evaluating immunotherapeutic combinations in different tumors). Other promising strategies are cancer vaccines and oncolytic viruses. Another approach is to isolate and remove immune cells (DCs, T cells, and NK cells) from the patient's blood or tumor infiltrates, add specific gene fragments, expand them in culture with growth factors, and re-inoculate into the same patient. TILs, TCR gene transfer, and CAR-T therapy follow this approach. In this article, we give an overview over the current status of melanoma therapies, the clinical rationale for choosing treatments, and the new immunotherapy approaches.

The "Great Debate" at Immunotherapy Bridge 2020, December 3rd, 2020

As part of the 2020 Immunotherapy Bridge virtual congress (December 2nd–3rd, Italy), the Great Debate session featured counterpoint views from leading experts on three clinical questions in immunotherapy today. The first of these was whether antitumoral vaccination is still a treatment option. The second topic debated whether anti-programmed death (PD)-1/PD-ligand (L)1 blockade should be the backbone for immunotherapy combination. Finally, the use of innovative study designs and surrogate endpoints was considered from both an academic and industry perspective. For each topic, two experts presented the argument and counter-argument in support of two different points of view. As with previous Bridge congresses, the debates were assigned by meeting Chairs and positions taken by experts during the debates may not have necessarily reflected their respective personal view. The views summarised in this article are based on available evidence but may reflect personal interpretation of these data, clinical experience and subjective opinion of the speaker.

Discovery of Imidazopyridines as Potent Inhibitors of Indoleamine 2,3-Dioxygenase 1 for Cancer Immunotherapy

Indoleamine 2,3-dioxygenase 1 (IDO1) has been identified as a target for small-molecule immunotherapy for the treatment of a variety of cancers including renal cell carcinoma and metastatic melanoma. This work focuses on the identification of IDO1 inhibitors containing replacements or isosteres for the amide found in BMS-986205, an amide-containing, IDO1-selective inhibitor currently in phase III clinical trials. Detailed subsequently are efforts to identify a structurally differentiated IDO1 inhibitor via the pursuit of a variety of heterocyclic isosteres, leading to the discovery of highly potent, imidazopyridine-containing IDO1 inhibitors.

Role of tryptophan metabolism in cancers and therapeutic implications

Tryptophan (Trp) metabolism is associated with diverse biological processes, including nerve conduction, inflammation, and the immune response. The majority of free Trp is broken down through the kynurenine (Kyn) pathway (KP), in which indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) catalyze the rate-limiting step. Clinical studies have demonstrated that Trp metabolism promotes tumor progression due to modulation of the immunosuppressive microenvironment through multiple mechanisms. In this process, IDO-expressing dendritic cells (DCs) exhibit tolerogenic potential and orchestrate T cell immune responses. Various signaling molecules control IDO expression, initiating the immunoregulatory pathway of Trp catabolism. Based on these characteristics, KP enzymes and catabolites are emerging as significant prognostic indicators and potential therapeutic targets of cancer. The physiological and oncologic roles of Trp metabolism are briefly summarized here, along with great challenges for treatment strategies.

Macrophages/Microglia Represent the Major Source of Indolamine 2,3-Dioxygenase Expression in Melanoma Metastases of the Brain

The manifestation of brain metastases in patients with advanced melanoma is a common event that limits patient's survival and quality of life. The immunosuppressive properties of the brain parenchyma are very different compared to the rest of the body, making it plausible that the current success of cancer immunotherapies is specifically limited here. In melanoma brain metastases, the reciprocal interplay between immunosuppressive mediators such as indoleamine 2, 3-dioxygenase (IDO) or programmed cell death-ligand 1 (PD-L1) in the context of neoplastic transformation are far from being understood. Therefore, we analyzed the immunoreactive infiltrate (CD45, CD3, CD8, Forkhead box P3 [FoxP3], CD11c, CD23, CD123, CD68, Allograft Inflammatory factor 1[AIF-1]) and PD-L1 with respect to IDO expression and localization in melanoma brain metastases but also in matched metastases at extracranial sites to correlate intra- and interpatient data with therapy response and survival. Comparative tissue analysis identified macrophages/microglia as the major source of IDO expression in melanoma brain metastases. In contrast to the tumor infiltrating lymphocytes, melanoma cells per se exhibited low IDO expression levels paralleled by cell surface presentation of PD-L1 in intracranial metastases. Absolute numbers and pattern of IDO-expressing cells in metastases of the brain correlated with recruitment and localization of CD8⁺ T cells, implicating dynamic impact on the regulation of T cell function in the brain parenchyma. However, paired analysis of matched intra- and extracranial metastases identified significantly lower fractions of cytotoxic CD8⁺ T cells in intracranial metastases while all other immune cell populations remain unchanged. In line with the already established clinical benefit for PD-L1 expression in extracranial melanoma metastases, Kaplan-Meier analyses correlated PD-L1 expression in brain metastases with favorable outcome in advanced melanoma patients undergoing immune checkpoint therapy. In summary, our data provide new insights into the landscape of immunosuppressive factors in melanoma brain metastases that may be useful in the implication of novel therapeutic strategies for patients undergoing cancer immunotherapy.

The therapeutic potential of targeting tryptophan catabolism in cancer

Based on its effects on both tumour cell intrinsic malignant properties as well as anti-tumour immune responses, tryptophan catabolism has emerged as an important metabolic regulator of cancer progression. Three enzymes, indoleamine-2,3-dioxygenase 1 and 2 (IDO1/2) and tryptophan-2,3-dioxygenase (TDO2), catalyse the first step of the degradation of the essential amino acid tryptophan (Trp) to kynurenine (Kyn). The notion of inhibiting IDO1 using small-molecule inhibitors elicited high hopes of a positive impact in the field of immuno-oncology, by restoring anti-tumour immune responses and synergising with other immunotherapies such as immune checkpoint inhibition. However, clinical trials with IDO1 inhibitors have yielded disappointing results, hence raising many questions. This review will discuss strategies to target Trp-degrading enzymes and possible down-stream consequences of their inhibition. We aim to provide comprehensive background information on Trp catabolic enzymes as targets in immuno-oncology and their current state of development. Details of the clinical trials with IDO1 inhibitors, including patient stratification, possible effects of the inhibitors themselves, effects of pre-treatments and the therapies the inhibitors were combined with, are discussed and mechanisms proposed that might have compensated for IDO1 inhibition. Finally, alternative approaches are suggested to circumvent these problems.

Immunotherapy for Melanoma

While melanoma is less common than some other skin cancers, it is responsible for nearly 10,000 deaths in the USA each year alone. For many decades, very limited treatment options were available for patients with metastatic melanoma. However, recent breakthroughs have brought new hopes for patients and providers. While targeted therapy with BRAF and MEK inhibitors represents an important cornerstone in the treatment of metastatic melanoma, this chapter carefully reviews the past and current therapy options available, with a significant focus on immunotherapy-based approaches. In addition, we provide an overview of the results of recent advances in the adjuvant setting for patients with resected stage III and stage IV melanoma, as well as in patients with melanoma brain metastases. Finally, we provide a quick overview over the current research efforts in the field of immuno-oncology and melanoma.

Immune Checkpoint Blockade: The New Frontier in Cancer Treatment

Immune checkpoint blockers have revolutionized cancer treatment in recent years. These agents are now approved for the treatment of several malignancies, including melanoma, squamous and non-squamous non-small cell lung cancer, renal cell carcinoma, urothelial carcinoma, and head and neck squamous cell carcinoma. Studies have demonstrated the significant impact of immunotherapy versus standard of care on patient outcomes, including durable response and extended survival. The use of immunotherapy-based combination therapy has been shown to further extend duration of response and survival. Immunotherapies function through modulation of the immune system, which can lead to immune-mediated adverse events (imAEs). These include a range of dermatologic, gastrointestinal, endocrine, and hepatic toxicities, as well as other less common inflammatory events. ImAEs are typically low grade and manageable when identified early and treated with appropriate measures. Identifying the right patient for the right therapy will become more important as new immunotherapies and immunotherapy-based combinations are approved and costs of cancer care continue to rise.

Immunotherapy of Melanoma: Facts and Hopes

Melanoma is among the most sensitive of malignancies to immune modulation. Although multiple trials conducted over decades with vaccines, cytokines, and cell therapies demonstrated meaningful responses in a small subset of patients with metastatic disease, a true increase in overall survival (OS) within a randomized phase III trial was not observed until the development of anti-CTLA-4 (ipilimumab). Further improvements in OS for metastatic disease were observed with the anti-PD-1-based therapies (nivolumab, pembrolizumab) as single agents or combined with ipilimumab. A lower bound for expected 5-year survival for metastatic melanoma is currently approximately 35% and could be as high as 50% for the nivolumab/ipilimumab combination among patients who would meet criteria for clinical trials. Moreover, a substantial fraction of long-term survivors will likely remain progression-free without continued treatment. The hope and major challenge for the future is to understand the immunobiology of tumors with primary or acquired resistance to anti-PD-1 or anti-PD-1/anti-CTLA-4 and to develop effective immune therapies tailored to individual patient subsets not achieving long-term clinical benefit. Additional goals include optimal integration of immune therapy with nonimmune therapies, the development and validation of predictive biomarkers in the metastatic setting, improved prognostic and predictive biomarkers for the adjuvant setting, understanding mechanisms of and decreasing toxicity, and optimizing the duration of therapy.

Indoleamine-2,3-Dioxygenase in Non-Small Cell Lung Cancer: A Targetable Mechanism of Immune Resistance Frequently Coexpressed With PD-L1

The immune regulatory enzyme indoleamine-2,3-dioxygenase (IDO-1) suppresses T cell responses and may reduce efficacy of therapies targeting immune checkpoints such as programmed death receptor-1/programmed death ligand-1 (PD-1/PD-L1). Early phase clinical trials combining IDO-1 and PD-1/PD-L1 inhibitors have shown some promise in non-small cell lung cancers (NSCLCs). However, the coexpression of IDO-1 and PD-L1 has not been thoroughly investigated, and the potential for IDO-1 immunohistochemical expression as a therapeutic biomarker is unknown. One hundred two cases of NSCLC (51 adenocarcinomas, 9 adenosquamous carcinomas, and 42 squamous cell carcinomas) were evaluated for IDO-1 and PD-L1 expression by immunohistochemistry. IDO-1 expression was identified in 43% of NSCLC (42% of adenocarcinomas, 44% of adenosquamous carcinomas, and 43% of squamous cell carcinomas). Coexpression with PD-L1 (≥1%) was common (27% overall; 27% of adenocarcinomas, 33% of adenosquamous carcinomas, and 26% of squamous cell carcinomas). A smaller population of tumors showed isolated PD-L1 (25% overall; 16% of adenocarcinomas, 44% of adenosquamous carcinomas, and 33% of squamous cell carcinomas) or IDO-1 expression (15% overall; 14% of adenocarcinomas, 11% of adenosquamous carcinomas, and 17% of squamous cell carcinomas). In summary, IDO-1 is commonly expressed by NSCLC, and its frequent coexpression with PD-L1 may account for the increased efficacy seen with dual blockade of PD-1/PD-L1 and IDO in clinical studies. IDO-1 immunohistochemistry may be a useful biomarker for selection of patients who could benefit from dual-agent therapy and should be evaluated in prospective clinical trials using PD-1/PD-L1 and IDO inhibitors.

Epacadostat plus pembrolizumab versus placebo plus pembrolizumab in patients with unresectable or metastatic melanoma (ECHO-301/KEYNOTE-252): a phase 3, randomised, double-blind study

BACKGROUND

Immunotherapy combination treatments can improve patient outcomes. Epacadostat, an IDO1 selective inhibitor, and pembrolizumab, a PD-1 inhibitor, showed promising antitumour activity in the phase 1-2 ECHO-202/KEYNOTE-037 study in advanced melanoma. In this trial, we aimed to compare progression-free survival and overall survival in patients with unresectable stage III or IV melanoma receiving epacadostat plus pembrolizumab versus placebo plus pembrolizumab.

METHODS

In this international, randomised, placebo-controlled, double-blind, parallel-group, phase 3 trial, eligible participants were aged 18 years or older, with unresectable stage III or IV melanoma previously untreated with PD-1 or PD-L1 checkpoint inhibitors, an ECOG performance status of 0 or 1, and had a known BRAF^V600 mutant status or consented to BRAF^V600 mutation testing during screening. Patients were stratified by PD-L1 expression and BRAF^V600 mutation status and randomly assigned (1:1) through a central interactive voice and integrated web response system to receive epacadostat 100 mg orally twice daily plus pembrolizumab 200 mg intravenously every 3 weeks or placebo plus pembrolizumab for up to 2 years. We used block randomisation with a block size of four in each stratum. Primary endpoints were progression-free survival and overall survival in the intention-to-treat population. The safety analysis population included randomly assigned patients who received at least one dose of study treatment. The study was stopped after the second interim analysis; follow-up for safety is ongoing. This study is registered with ClinicalTrials.gov, number NCT02752074.

FINDINGS

Between June 21, 2016, and Aug 7, 2017, 928 patients were screened and 706 patients were randomly assigned to receive epacadostat plus pembrolizumab (n=354) or placebo plus pembrolizumab (n=352). Median follow-up was 12·4 months (IQR 10·3-14·5). No significant differences were found between the treatment groups for progression-free survival (median 4·7 months, 95% CI 2·9-6·8, for epacadostat plus pembrolizumab vs 4·9 months, 2·9-6·8, for placebo plus pembrolizumab; hazard ratio [HR] 1·00, 95% CI 0·83-1·21; one-sided p=0·52) or overall survival (median not reached in either group; epacadostat plus pembrolizumab vs placebo plus pembrolizumab: HR 1·13, 0·86-1·49; one-sided p=0·81). The most common grade 3 or worse treatment-related adverse event was lipase increase, which occurred in 14 (4%) of 353 patients receiving epacadostat plus pembrolizumab and 11 (3%) of 352 patients receiving placebo plus pembrolizumab. Treatment-related serious adverse events were reported in 37 (10%) of 353 patients receiving epacadostat plus pembrolizumab and 32 (9%) of 352 patients receiving placebo plus pembrolizumab. There were no treatment-related deaths in either treatment group.

INTERPRETATION

Epacadostat 100 mg twice daily plus pembrolizumab did not improve progression-free survival or overall survival compared with placebo plus pembrolizumab in patients with unresectable or metastatic melanoma. The usefulness of IDO1 inhibition as a strategy to enhance anti-PD-1 therapy activity in cancer remains uncertain.

FUNDING

Incyte Corporation, in collaboration with Merck Sharp & Dohme.

Inter- and intrapatient heterogeneity of indoleamine 2,3-dioxygenase expression in primary and metastatic melanoma cells and the tumour microenvironment

AIMS

Indoleamine 2,3-dioxygenase (IDO), an immunomodulatory enzyme, facilitates immune escape by tumours and promotes tumour progression. IDO inhibitors with and without additional anti-PD-1 therapy have been evaluated in recent and ongoing melanoma clinical trials, but IDO expression in melanoma tumours, and therefore its potential role as a predictive biomarker remains unknown. This study sought to evaluate IDO expression in immunotherapy-naive metastatic melanoma patients in order to determine patterns of expression in corresponding primary melanomas, locoregional metastases and distant metastases.

METHODS AND RESULTS

Here, we evaluated IDO expression using immunohistochemistry in 99 melanoma tumour samples from 43 immunotherapy-naive patients with metastatic melanoma to determine patterns of expression in primary melanomas (n = 29), locoregional metastases (n = 36) and distant metastases (n = 34). Thirty-seven per cent of patients demonstrated tumour IDO expression in at least one specimen. Twelve of 35 patients (34%) with longitudinal specimens (i.e. two or more separate specimens from different disease stages in the same patient) displayed heterogeneous IDO staining between samples. Tumour IDO expression positively correlated with tumour-infiltrating lymphocyte (TIL) score as well as the number of IDO-expressing mononuclear cells in the primary melanoma (P < 0.0001 and P = 0.0011, respectively) and nodal metastases (P = 0.049 and P = 0.037, respectively), but not in distant metastases. Furthermore, tumour IDO expression correlated positively with PD-L1 expression by melanoma cells among all specimens (P = 0.0073).

CONCLUSIONS

Therefore, while assessment of tumour IDO expression warrants evaluation in melanoma patient cohorts treated with IDO inhibitors dosed at levels proven to inhibit the target by pharmacodynamic assessment, its utility as a biomarker may be limited by intertumoral heterogeneity.

From immune checkpoints to vaccines: The past, present and future of cancer immunotherapy

Cancer is a worldwide medical problem with significant repercussions on individual patients and societies as a whole. In order to alter the outcomes of this deadly disease the treatment of cancer over the centuries has undergone a unique evolution. However, utilizing the best treatment modalities and achieving cures or long-term durable responses have been inconsistent and limited, that is until recently. Contemporary research has highlighted a fundamental gap in our understanding of how we approach treating cancer, by revealing the intricate relationship between the immune system and tumors. In this atmosphere, the growth of immunotherapy has not only forever changed our understanding of cancer biology, but the manner by which we treat patients. It's paradigm shifting success has led to the approval of over 10 different immunotherapeutic agents, including checkpoint inhibitors, vaccine-based therapies, oncolytic viruses and T cell directed therapies for nearly 20 different indications across countless tumor types. Despite the breakthroughs that have occurred in the field of immunotherapy, it has not been the panacea for all cancers. With a deeper understanding of the immune system we have been able to peer into tumor immune escape and therapy resistance. Simultaneously this understanding has paved the way for the investigation and development of novel immune system altering agents and combinatorial therapies. In this chapter we review the immune system and its intricate relationship with cancer, the evolution of immunotherapy, its current landscape, and future directions in the context of resistance mechanisms and the challenges faced by immunotherapy against cancer.

Reimagining IDO Pathway Inhibition in Cancer Immunotherapy via Downstream Focus on the Tryptophan-Kynurenine-Aryl Hydrocarbon Axis

Significant progress has been made in cancer immunotherapy with checkpoint inhibitors targeting programmed cell death protein 1 (PD-1)-programmed death-ligand 1 signaling pathways. Tumors from patients showing sustained treatment response predominately demonstrate a T cell-inflamed tumor microenvironment prior to, or early on, treatment. Not all tumors with this phenotype respond, however, and one mediator of immunosuppression in T cell-inflamed tumors is the tryptophan-kynurenine-aryl hydrocarbon receptor (Trp-Kyn-AhR) pathway. Multiple mechanisms of immunosuppression may be mediated by this pathway including depletion of tryptophan, direct immunosuppression of Kyn, and activity of Kyn-bound AhR. Indoleamine 2,3-dioxygenase 1 (IDO1), a principle enzyme in Trp catabolism, is the target of small-molecule inhibitors in clinical development in combination with PD-1 checkpoint inhibitors. Despite promising results in early-phase clinical trials in a range of tumor types, a phase III study of the IDO1-selective inhibitor epacadostat in combination with pembrolizumab showed no difference between the epacadostat-treated group versus placebo in patients with metastatic melanoma. This has led to a diminution of interest in IDO1 inhibitors; however, other approaches to inhibit this pathway continue to be considered. Novel Trp-Kyn-AhR pathway inhibitors, such as Kyn-degrading enzymes, direct AhR antagonists, and tryptophan mimetics are advancing in early-stage or preclinical development. Despite uncertainty surrounding IDO1 inhibition, ample preclinical evidence supports continued development of Trp-Kyn-AhR pathway inhibitors to augment immune-checkpoint and other cancer therapies.

Recent success and limitations of immune checkpoint inhibitors for cancer: a lesson from melanoma

Several researches have been carried over the last few decades to understand of how cancer evades the immune system and thus to identify therapies that could directly act on patient's immune system in the way of restore or induce a response to cancer. As a consequence, "cancer immunotherapy" is conquering predominantly the modern scenario of the fight against cancer. The recent clinical success of immune checkpoint inhibitors (ICIs) has created an entire new class of anti-cancer drugs and restored interest in the field of immuno-oncology, leading to regulatory approvals of several agents for the treatment of a variety of malignancies. The first to be approved in 2011 was the anti-CTLA-4 antibody ipilimumab for the treatment of unresectable or metastatic melanoma. Subsequently, the anti-PD-1s, nivolumab and pembrolizumab, received regulatory approvals for the treatment of melanoma and several other cancers. More recently, three anti-PD-L1 antibodies have received approval: atezolizumab and durvalumab for locally advanced or metastatic urothelial carcinoma and metastatic non-small cell lung cancer (NSCLC) and avelumab for the treatment of locally advanced or metastatic urothelial carcinoma and metastatic Merkel cell carcinoma. This review, starting from the results of melanoma trials, highlights in turn different ICIs and data for different indications in several malignancies are included under each drug class.

Targeting indoleamine-2,3-dioxygenase in cancer: Scientific rationale and clinical evidence

Immunotherapy through immune checkpoint blockers (ICBs) is quickly transforming cancer treatment by improving patients' outcomes. However, innate and acquired resistance to ICBs remain a major challenge in clinical settings. Indoleamine 2,3-dioxygenases (IDOs) are enzymes involved in tryptophan catabolism with a central immunosuppressive function within the tumor microenvironment. IDOs are over-expressed in cancer patients and have increasingly been associated with worse outcomes and a poor prognosis. Preclinical data have shown that combining IDO and checkpoint inhibition might be a valuable strategy to improve the efficacy of immunotherapy. Currently, several IDO inhibitors have been evaluated in clinical trials, showing favorable pharmacokinetic profiles and promising efficacy. This review describes the mechanisms involved in IDO-mediated immune suppression and its role in cancer immune escape, focusing on the potential clinical application of IDO inhibitors as an immunotherapy strategy for cancer treatment.

Emerging Strategies in Systemic Therapy for the Treatment of Melanoma

Recent years have seen major improvements in survival of patients with advanced melanoma with the advent of various novel systemic immunotherapies and targeted therapies. As our understanding of these agents and their various mechanisms of action improves, even more impressive outcomes are being achieved through use of various combination strategies, including the combining of different immunotherapies with one another as well as with other modalities. However, despite the improved outcomes that have been achieved in advanced melanoma, responses to treatment are heterogeneous and may not always be durable. Additional advances in therapy are required, and several emerging strategies are a focus of interest. These include the investigation of several new immunotherapy and/or targeted therapy combinations, such as checkpoint inhibitors (anti-PD-1/anti-CTLA-4) with other immunotherapies (e.g., indoleamine 2,3 dioxygenase [IDO] inhibitors, antilymphocyte activation 3 [anti-LAG-3], histone deacetylase [HDAC] inhibitors, Toll-like receptor 9 [TLR-9] agonists, antiglucocorticoid-induced tumor necrosis factor receptor [anti-GITR], pegylated interleukin-2 [IL-2]), combined targeted therapies (e.g., MEK and CDK4/6 coinhibition), and combined immunotherapy and targeted therapy (e.g., the triplet combination of BRAF/MEK inhibition with anti-PD-1s). The identification of novel therapeutic targets in the MAP kinase pathway also offers opportunities to improve outcomes by overcoming de novo and acquired resistance to BRAF/MEK inhibition (e.g., the development of ERK inhibitors). In addition, adoptive cell transfer, the infusion of large numbers of activated autologous lymphocytes, may have a potential role in patients whose disease has progressed after immunotherapy. Taken together, these new approaches offer further potential to increase systemic treatment options and improve long-term outcomes for patients with advanced melanoma.

TIGIT: a novel immunotherapy target moving from bench to bedside

Treatment strategies for patients with advanced solid tumors have traditionally been based on three different paradigms: surgery, cytotoxics (chemotherapy or radiation therapy) and targeted therapies. Immunotherapy has emerged as a novel treatment paradigm in our armamentarium. Unfortunately, most patients still do not benefit from immunotherapy. These patients often have "cold tumors" characterized by a paucity of effector T cells in the tumor microenvironment, low mutational load, low neoantigen burden and often an immunosuppressive tumor microenvironment. TIGIT is an immunoreceptor inhibitory checkpoint that has been implicated in tumor immunosurveillance. Expression of TIGIT has been demonstrated in both NK cells and T cells and plays a role in their activation and maturation. TIGIT competes with immunoactivator receptor CD226 (DNAM-1) for the same set of ligands: CD155 (PVR or poliovirus receptor) and CD112 (Nectin-2 or PVRL2). TIGIT's role in tumor immunosurveillance is analogous to the PD-1/PD-L1 axis in tumor immunosuppression. Both TIGIT and PD-1 are upregulated in a variety of different cancers. Anti-TIGIT antibodies have demonstrated synergy with anti-PD-1/PD-L1 antibodies in pre-clinical models. Currently, there are multiple first-in-man phase I trials hoping to exploit this new pathway and improve response rates with existing immunotherapies.

PD-L1 and IDO expression in cervical and vulvar invasive and intraepithelial squamous neoplasias: implications for combination immunotherapy

AIMS

The immunoregulatory enzyme indoleamine dioxygenase 2,3 (IDO) has been implicated in cervical and vulvar squamous carcinomas (SCC) and may represent a mechanism of resistance to anti-PD-1/anti-PD-L1 therapy. However, the relationship between IDO and PD-L1 has not been well-investigated.

METHODS AND RESULTS

Sixty-five cases of cervical and vulvar intraepithelial neoplasia and SCC were assessed for IDO and PD-L1 expression. Overall, tumoral PD-L1 expression was seen in 72% of SCC, while 50% expressed IDO; co-expression was seen in 42%. Using the combined positive score (CPS) threshold of 1 to account for both tumoral and immune staining, 83% of SCC expressed PD-L1, 61% expressed IDO and 53% showed co-expression. Cervical SCCs were significantly more likely than human papillomavirus (HPV)-related vulvar SCCs to express tumoral IDO (75% versus 13%, P < 0.001) and demonstrate an IDO CPS ≥ 1 (88% versus 25%, P < 0.001); no significant differences were seen for PD-L1. Additionally, there were no significant differences in IDO and PD-L1 expression in dVIN-associated versus HPV-associated vulvar SCC. In contrast to SCC, the majority of intraepithelial lesions were entirely negative for tumoral PD-L1 and IDO and had a CPS score of <1.

CONCLUSIONS

In summary, IDO and PD-L1 co-expression is common in cervical SCCs and, to a lesser extent, vulvar SCCs. These data suggest a role for combination immunotherapy in a subset of cervical SCCs as well as select vulvar SCCs. Expression for both markers is less common in intraepithelial lesions, providing no strong support for this form of immunotherapy in the absence of invasion.

Phase Ia study of the indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor navoximod (GDC-0919) in patients with recurrent advanced solid tumors

BACKGROUND

Indoleamine-2,3-dioxygenase 1 (IDO1) catalyzes the oxidation of tryptophan into kynurenine and is partially responsible for acquired immune tolerance associated with cancer. The IDO1 small molecule inhibitor navoximod (GDC-0919, NLG-919) is active as a combination therapy in multiple tumor models.

METHODS

This open-label Phase Ia study assessed safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary anti-tumor activity of navoximod in patients with recurrent/advanced solid tumors, administered as 50-800 mg BID on a 21/28 day and at 600 mg on a 28/28 day schedule. Plasma kynurenine and tryptophan were longitudinally evaluated and tumor assessments were performed.

RESULTS

Patients (n = 22) received a median of 3 cycles of navoximod. No maximum tolerated dose was reached. One dose-limiting toxicity of Grade 4 lower gastrointestinal hemorrhage was reported. Adverse events (AEs) regardless of causality in ≥20% of patients included fatigue (59%), cough, decreased appetite, and pruritus (41% each), nausea (36%), and vomiting (27%). Grade ≥ 3 AEs occurred in 14/22 patients (64%), and were related to navoximod in two patients (9%). Navoximod was rapidly absorbed (Tmax ~ 1 h) and exhibited dose-proportional increases in exposure, with a half-life (t1/2 ~ 11 h) supportive of BID dosing. Navoximod transiently decreased plasma kynurenine from baseline levels with kinetics consistent with its half-life. Of efficacy-evaluable patients, 8 (36%) had stable disease and 10 (46%) had progressive disease.

CONCLUSIONS

Navoximod was well-tolerated at doses up to 800 mg BID decreasing plasma kynurenine levels consistent with its half-life. Stable disease responses were observed.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02048709 .

Combination Immunotherapy in Non-small Cell Lung Cancer

PURPOSE OF REVIEW

Checkpoint blockade has changed the treatment landscape in non-small cell lung cancer (NSCLC), but single-agent approaches are effective for only a select subset of patients. Here, we will review the evidence for combination immunotherapies in NSCLC and the clinical data evaluating the efficacy of this approach.

RECENT FINDINGS

Clinical trials evaluating combination PD-1 and CTLA-4 blockade as well as PD-1 in combination with agents targeting IDO1, B7-H3, VEGF, and EGFR show promising results. Additional studies targeting other immune pathways like TIGIT, LAG-3, and cellular therapies are ongoing. Combination immunotherapy has the potential to improve outcomes in NSCLC. Data from early clinical trials is promising and reveals that these agents can be administered together safely without a significant increase in toxicity. Further studies are needed to evaluate their long-term safety and efficacy and to determine appropriate patient selection.

Targeting the microenvironment in solid tumors

Tumorigenesis is a complex and dynamic process involving different cellular and non-cellular elements composed of tumor microenvironment (TME). The interaction of TME with cancer cells is responsible for tumor development, progression and drug resistance. TME consists of non malignant cells of the tumor such as cancer associated fibroblasts (CAFs), endothelial cells and pericytes composing tumor vasculature, immune and inflammatory cells, bone marrow derived cells, and the extracellular matrix (ECM) establishing a complex cross-talk with tumor. These interactions contribute towards proliferation and invasion of the tumor by producing growth factors, chemokines and matrix-degrading enzymes. ECM is a complex system containing macromolecules with distinctive physical, biochemical and biomechanical properties. During tumorigenesis this system is deregulated favoring the generation of tumorigenic microenvironment enhancing tumor-associated angiogenesis and inflammation. An important step of anticancer treatment is the identification of the biological alterations present in TME in order to target these key molecular players. Multitargeted approaches, providing a simultaneous inhibition of TME components, may offer a more efficient way to treat cancer. In this manuscript we overview the function of each components of TME and the treatments targeting the key players.

A Longitudinal Analysis of IDO and PDL1 Expression during Immune- or Targeted Therapy in Advanced Melanoma

A deepened understanding of the cellular and molecular processes in the tumor microenvironment is necessary for the development of precision immunotherapy (IT). We simultaneously investigated CD3, PDL1, and IDO by immunohistochemistry in paired biopsies from various organs of 43 metastatic melanoma patients treated with IT and targeted therapy (TT). Intraindividual biopsies taken after a period of weeks to months demonstrate discordant results in 30% of the cases. Overlap of IDO and PDL1 increased after therapy. IT only marginally impacted PDL1 expression over time in contrast to TT. Standardized repeated assessments of multiple immune markers in repeated biopsies will generate detailed insights in melanoma's immune evolution and adaption during therapies and might be used to support treatment decisions.