Targeting the mechanisms of tumoral immune tolerance with small-molecule inhibitors.

Cancer immunotherapy has been predominantly focused on biologically based intervention strategies. However, recent advances in the understanding of tumour-host interactions at the molecular level have revealed targets that might be amenable to intervention with small-molecule inhibitors. In particular, key effectors of tumoral immune escape have been identified that contribute to a dominant toleragenic state that is suspected of limiting the successful implementation of treatment strategies that rely on boosting immune function. Within the context of the pathophysiology of cancer-associated immune tolerance, this Review delineates potential molecular targets for therapeutic intervention and the progress that has been made in developing small-molecule inhibitors.

Phase 2 study of the JAK kinase inhibitor ruxolitinib in patients with refractory leukemias, including postmyeloproliferative neoplasm acute myeloid leukemia.

We conducted a phase 2 study of ruxolitinib in patients with relapsed/refractory leukemias. Patients with acceptable performance status (0-2), adequate organ function, and no active infection, received ruxolitinib 25 mg orally twice a day for 4 weeks (1 cycle). Response was assessed after every 2 cycles of treatment, and patients who completed 2 cycles were allowed to continue treatment until disease progression. Dose escalation to 50 mg twice daily was permitted in patients demonstrating a benefit. Thirty-eight patients, with a median age of 69 years (range, 45-88), were treated. The median number of prior therapies was 2 (range, 1-6). Twelve patients had JAK2V617F mutation. Patients received a median of 2 cycles of therapy (range, 1-22). Three of 18 patients with postmyeloproliferative neoplasm (MPN) acute myeloid leukemia (AML) showed a significant response; 2 achieved complete remission (CR) and one achieved a CR with insufficient recovery of blood counts (CRi). The responding patients with palpable spleens also had significant reductions in spleen size. Overall, ruxolitinib was very well tolerated with only 4 patients having grade 3 or higher toxicity. Ruxolitinib has modest antileukemic activity as a single agent, particularly in patients with post-MPN AML. The study was registered at www.clinicaltrials.gov as NCT00674479.

Targeting ADAM-mediated ligand cleavage to inhibit HER3 and EGFR pathways in non-small cell lung cancer.

We describe here the existence of a heregulin-HER3 autocrine loop, and the contribution of heregulin-dependent, HER2-mediated HER3 activation to gefitinib insensitivity in non-small cell lung cancer (NSCLC). ADAM17 protein, a major ErbB ligand sheddase, is upregulated in NSCLC and is required not only for heregulin-dependent HER3 signaling, but also for EGFR ligand-dependent signaling in NSCLC cell lines. A selective ADAM inhibitor, INCB3619, prevents the processing and activation of multiple ErbB ligands, including heregulin. In addition, INCB3619 inhibits gefitinib-resistant HER3 signaling and enhances gefitinib inhibition of EGFR signaling in NSCLC. These results show that ADAM inhibition affects multiple ErbB pathways in NSCLC and thus offers an excellent opportunity for pharmacological intervention, either alone or in combination with other drugs.

Preclinical characterization of the selective JAK1/2 inhibitor INCB018424: therapeutic implications for the treatment of myeloproliferative neoplasms.

Constitutive JAK2 activation in hematopoietic cells by the JAK2V617F mutation recapitulates myeloproliferative neoplasm (MPN) phenotypes in mice, establishing JAK2 inhibition as a potential therapeutic strategy. Although most polycythemia vera patients carry the JAK2V617F mutation, half of those with essential thrombocythemia or primary myelofibrosis do not, suggesting alternative mechanisms for constitutive JAK-STAT signaling in MPNs. Most patients with primary myelofibrosis have elevated levels of JAK-dependent proinflammatory cytokines (eg, interleukin-6) consistent with our observation of JAK1 hyperactivation. Accordingly, we evaluated the effectiveness of selective JAK1/2 inhibition in experimental models relevant to MPNs and report on the effects of INCB018424, the first potent, selective, oral JAK1/JAK2 inhibitor to enter the clinic. INCB018424 inhibited interleukin-6 signaling (50% inhibitory concentration [IC(50)] = 281nM), and proliferation of JAK2V617F(+) Ba/F3 cells (IC(50) = 127nM). In primary cultures, INCB018424 preferentially suppressed erythroid progenitor colony formation from JAK2V617F(+) polycythemia vera patients (IC(50) = 67nM) versus healthy donors (IC(50) > 400nM). In a mouse model of JAK2V617F(+) MPN, oral INCB018424 markedly reduced splenomegaly and circulating levels of inflammatory cytokines, and preferentially eliminated neoplastic cells, resulting in significantly prolonged survival without myelosuppressive or immunosuppressive effects. Preliminary clinical results support these preclinical data and establish INCB018424 as a promising oral agent for the treatment of MPNs.

Selective inhibition of IDO1 effectively regulates mediators of antitumor immunity.

Indoleamine 2,3-dioxygenase-1 (IDO1; IDO) mediates oxidative cleavage of tryptophan, an amino acid essential for cell proliferation and survival. IDO1 inhibition is proposed to have therapeutic potential in immunodeficiency-associated abnormalities, including cancer. Here, we describe INCB024360, a novel IDO1 inhibitor, and investigate its roles in regulating various immune cells and therapeutic potential as an anticancer agent. In cellular assays, INCB024360 selectively inhibits human IDO1 with IC(50) values of approximately 10nM, demonstrating little activity against other related enzymes such as IDO2 or tryptophan 2,3-dioxygenase (TDO). In coculture systems of human allogeneic lymphocytes with dendritic cells (DCs) or tumor cells, INCB024360 inhibition of IDO1 promotes T and natural killer (NK)-cell growth, increases IFN-gamma production, and reduces conversion to regulatory T (T(reg))-like cells. IDO1 induction triggers DC apoptosis, whereas INCB024360 reverses this and increases the number of CD86(high) DCs, potentially representing a novel mechanism by which IDO1 inhibition activates T cells. Furthermore, IDO1 regulation differs in DCs versus tumor cells. Consistent with its effects in vitro, administration of INCB024360 to tumor-bearing mice significantly inhibits tumor growth in a lymphocyte-dependent manner. Analysis of plasma kynurenine/tryptophan levels in patients with cancer affirms that the IDO pathway is activated in multiple tumor types. Collectively, the data suggest that selective inhibition of IDO1 may represent an attractive cancer therapeutic strategy via up-regulation of cellular immunity.

Discovery of an orally-bioavailable CC Chemokine Receptor 2 antagonist derived from an acyclic diaminoalcohol backbone.

We describe an isostere-driven approach to improve upon a previously-described series of capped dipeptide antagonists of CC Chemokine Receptor 2 (CCR2). Modification of the substitution around the isostere was combined with additional changes in a distal aromatic substituent to provide single-digit nanomolar antagonists of CCR2. These studies led to the identification of 18, a compound that was suitable for studies in murine models of CCR2 activity.

Benzimidazoles as benzamide replacements within cyclohexane-based CC chemokine receptor 2 (CCR2) antagonists.

We describe the design, synthesis, and evaluation of benzimidazoles as benzamide replacements within a series of trisubstituted cyclohexane CCR2 antagonists. 7-Trifluoromethylbenzimidazoles displayed potent binding and functional antagonism of CCR2 while being selective over CCR3. These benzimidazoles were also incorporated into lactam-containing antagonists, thus completely eliminating the customary bis-amide.

Selective inhibition of JAK1 and JAK2 is efficacious in rodent models of arthritis: preclinical characterization of INCB028050.

Inhibiting signal transduction induced by inflammatory cytokines offers a new approach for the treatment of autoimmune diseases such as rheumatoid arthritis. Kinase inhibitors have shown promising oral disease-modifying antirheumatic drug potential with efficacy similar to anti-TNF biologics. Direct and indirect inhibition of the JAKs, with small molecule inhibitors like CP-690,550 and INCB018424 or neutralizing Abs, such as the anti-IL6 receptor Ab tocilizumab, have demonstrated rapid and sustained improvement in clinical measures of disease, consistent with their respective preclinical experiments. Therefore, it is of interest to identify optimized JAK inhibitors with unique profiles to maximize therapeutic opportunities. INCB028050 is a selective orally bioavailable JAK1/JAK2 inhibitor with nanomolar potency against JAK1 (5.9 nM) and JAK2 (5.7 nM). INCB028050 inhibits intracellular signaling of multiple proinflammatory cytokines including IL-6 and IL-23 at concentrations <50 nM. Significant efficacy, as assessed by improvements in clinical, histologic and radiographic signs of disease, was achieved in the rat adjuvant arthritis model with doses of INCB028050 providing partial and/or periodic inhibition of JAK1/JAK2 and no inhibition of JAK3. Diminution of inflammatory Th1 and Th17 associated cytokine mRNA levels was observed in the draining lymph nodes of treated rats. INCB028050 was also effective in multiple murine models of arthritis, with no evidence of suppression of humoral immunity or adverse hematologic effects. These data suggest that fractional inhibition of JAK1 and JAK2 is sufficient for significant activity in autoimmune disease models. Clinical evaluation of INCB028050 in RA is ongoing.

gamma-Lactams as glycinamide replacements in cyclohexane-based CC chemokine receptor 2 (CCR2) antagonists.

We describe the design, synthesis, and evaluation, of gamma-lactams as glycinamide replacements within a series of di- and trisubstituted cyclohexane CCR2 antagonists. The lactam-containing trisubstituted cyclohexanes proved to be more potent than the disubstituted analogs, as trisubstituted analog, lactam 13, displayed excellent activity (CCR2 binding IC(50)=1.0 nM and chemotaxis IC(50) = 0.5 nM) and improved metabolic stability over its parent glycinamide.

Pharmacological characterization of INCB3344, a small molecule antagonist of human CCR2.

The chemokine receptor 2 (CCR2) directs migration of monocytes and has been proposed to be a drug target for chronic inflammatory diseases. INCB3344 was first published as a small molecule nanomolar inhibitor of rodent CCR2. Here, we show that INCB3344 can also bind human CCR2 (hCCR2) with high affinity, having a dissociation constant (K(d)) of approximately 5nM. The binding of the compound to the receptor is rapid and reversible. INCB3344 potently inhibits hCCR2 binding of monocyte chemoattractant protein-1 (MCP-1) and MCP-1-induced signaling and function in hCCR2-expressing cells, including ERK phosphorylation and chemotaxis, and is competitive against MCP-1 in vitro. INCB3344 also blocks MCP-1 binding to monocytes in human whole blood, with potency consistent with in vitro studies. The whole blood binding assay described here can be used for monitoring pharmacodynamic activity of CCR2 antagonists in both preclinical models and in the clinic.

Discovery of trisubstituted cyclohexanes as potent CC chemokine receptor 2 (CCR2) antagonists.

A series of trisubstituted cyclohexanes was designed, synthesized and evaluated as CC chemokine receptor 2 (CCR2) antagonists. This led to the identification of two distinct substitution patterns about the cyclohexane ring as potent and selective CCR2 antagonists. Compound 36 exhibited excellent binding (CCR2 IC(50)=2.4 nM) and functional antagonism (calcium flux IC(50)=2.0 nM and chemotaxis IC(50)=5.1 nM).

Novel sulfone-containing di- and trisubstituted cyclohexanes as potent CC chemokine receptor 2 (CCR2) antagonists.

Potent sulfone-containing di- and trisubstituted cyclohexanes were synthesized and evaluated as CC chemokine receptor 2 (CCR2) antagonists. This led to the trisubstituted derivative 54, which exhibited excellent binding (CCR2 IC(50)=1.3nM) and functional antagonism (calcium flux IC(50)=0.5nM and chemotaxis IC(50)=0.2nM). The superiority of the trisubstituted scaffold was rationalized to be the result of a conformational rigidification, which provided insight into the bioactive conformation of this chemotype.

Treatment-Induced Tumor Cell Apoptosis and Secondary Necrosis Drive Tumor Progression in the Residual Tumor Microenvironment through MerTK and IDO1.

Efferocytosis is the process by which apoptotic cells are cleared from tissue by phagocytic cells. The removal of apoptotic cells prevents them from undergoing secondary necrosis and releasing their inflammation-inducing intracellular contents. Efferocytosis also limits tissue damage by increasing immunosuppressive cytokines and leukocytes and maintains tissue homeostasis by promoting tolerance to antigens derived from apoptotic cells. Thus, tumor cell efferocytosis following cytotoxic cancer treatment could impart tolerance to tumor cells evading treatment-induced apoptosis with deleterious consequences in tumor residual disease. We report here that efferocytosis cleared apoptotic tumor cells in residual disease of lapatinib-treated HER2+ mammary tumors in MMTV-Neu mice, increased immunosuppressive cytokines, myeloid-derived suppressor cells (MDSC), and regulatory T cells (Treg). Blockade of efferocytosis induced secondary necrosis of apoptotic cells, but failed to prevent increased tumor MDSCs, Treg, and immunosuppressive cytokines. We found that efferocytosis stimulated expression of IFN-γ, which stimulated the expression of indoleamine-2,3-dioxegenase (IDO) 1, an immune regulator known for driving maternal-fetal antigen tolerance. Combined inhibition of efferocytosis and IDO1 in tumor residual disease decreased apoptotic cell- and necrotic cell-induced immunosuppressive phenotypes, blocked tumor metastasis, and caused tumor regression in 60% of MMTV-Neu mice. This suggests that apoptotic and necrotic tumor cells, via efferocytosis and IDO1, respectively, promote tumor 'homeostasis' and progression. SIGNIFICANCE: These findings show in a model of HER2+ breast cancer that necrosis secondary to impaired efferocytosis activates IDO1 to drive immunosuppression and tumor progression.

Discovery of disubstituted cyclohexanes as a new class of CC chemokine receptor 2 antagonists.

We describe the design, synthesis, and evaluation of novel disubstituted cyclohexanes as potent CCR2 antagonists. Exploratory SAR studies led to the cis-disubstituted derivative 22, which displayed excellent binding affinity for CCR2 (binding IC50 = 5.1 nM) and potent functional antagonism (calcium flux IC50 = 18 nM and chemotaxis IC 50 = 1 nM). Site-directed mutagenesis studies with 22 suggest the compound is binding near the key receptor residue Glu291, however, 22 is not reliant on Glu291 for its binding affinity.

Synthesis and evaluation of cis-3,4-disubstituted piperidines as potent CC chemokine receptor 2 (CCR2) antagonists.

A series of cis-3,4-disubstituted piperidines was synthesized and evaluated as CC chemokine receptor 2 (CCR2) antagonists. Compound 24 emerged with an attractive profile, possessing excellent binding (CCR2 IC(50)=3.4 nM) and functional antagonism (calcium flux IC(50)=2.0 nM and chemotaxis IC(50)=5.4 nM). Studies to explore the binding of these piperidine analogs utilized a key CCR2 receptor mutant (E291A) with compound 14 and revealed a significant reliance on Glu291 for binding.

Selective inhibition of ADAM metalloproteases as a novel approach for modulating ErbB pathways in cancer.

PURPOSE: ErbB receptor signaling pathways are important regulators of cell fate, and their dysregulation, through (epi)genetic alterations, plays an etiologic role in multiple cancers. ErbB ligands are synthesized as membrane-bound precursors that are cleaved by members of the ADAM family of zinc-dependent metalloproteases. This processing, termed ectodomain shedding, is essential for the functional activation of ErbB ligands. Recent studies suggest that elevated levels of ErbB ligands may circumvent the effectiveness of ErbB-targeted therapeutics. Here, we describe the discovery and preclinical development of potent, selective inhibitors of ErbB ligand shedding. EXPERIMENTAL DESIGN: A series of biochemical and cell-based assays were established to identify selective inhibitors of ErbB ligand shedding. The therapeutic potential of these compounds was assessed in multiple in vivo models of cancer and matrix metalloprotease-related toxicity. RESULTS: INCB3619 was identified as a representative selective, potent, orally bioavailable small-molecule inhibitor of a subset of ADAM proteases that block shedding of ErbB ligands. Administration of INCB3619 to tumor-bearing mice reduced ErbB ligand shedding in vivo and inhibited ErbB pathway signaling (e.g., phosphorylation of Akt), tumor cell proliferation, and survival. Further, INCB3619 synergized with clinically relevant cancer therapeutics and showed no overt or compounding toxicities, including fibroplasia, the dose-limiting toxicity associated with broad-spectrum matrix metalloprotease inhibitors. CONCLUSIONS: Inhibition of ErbB ligand shedding offers a potentially novel and well-tolerated therapeutic strategy for the treatment of human cancers and is currently being evaluated in the clinic.

First-in-Human Phase I Study of the Oral Inhibitor of Indoleamine 2,3-Dioxygenase-1 Epacadostat (INCB024360) in Patients with Advanced Solid Malignancies.

Purpose: Indoleamine 2,3-dioxygenase-1 (IDO1) catalyzes the degradation of tryptophan to N-formyl-kynurenine. Overexpressed in many solid malignancies, IDO1 can promote tumor escape from host immunosurveillance. This first-in-human phase I study investigated the maximum tolerated dose, safety, pharmacokinetics, pharmacodynamics, and antitumor activity of epacadostat (INCB024360), a potent and selective inhibitor of IDO1.Experimental Design: Fifty-two patients with advanced solid malignancies were treated with epacadostat [50 mg once daily or 50, 100, 300, 400, 500, 600, or 700 mg twice daily (BID)] in a dose-escalation 3 + 3 design and evaluated in 28-day cycles. Treatment was continued until disease progression or unacceptable toxicity.Results: One dose-limiting toxicity (DLT) occurred at the dose of 300 mg BID (grade 3, radiation pneumonitis); another DLT occurred at 400 mg BID (grade 3, fatigue). The most common adverse events in >20% of patients overall were fatigue, nausea, decreased appetite, vomiting, constipation, abdominal pain, diarrhea, dyspnea, back pain, and cough. Treatment produced significant dose-dependent reductions in plasma kynurenine levels and in the plasma kynurenine/tryptophan ratio at all doses and in all patients. Near maximal changes were observed at doses of ≥100 mg BID with >80% to 90% inhibition of IDO1 achieved throughout the dosing period. Although no objective responses were detected, stable disease lasting ≥16 weeks was observed in 7 of 52 patients.Conclusions: Epacadostat was generally well tolerated, effectively normalized kynurenine levels, and produced maximal inhibition of IDO1 activity at doses of ≥100 mg BID. Studies investigating epacadostat in combination with other immunomodulatory drugs are ongoing. Clin Cancer Res; 23(13); 3269-76. ©2017 AACR.

INCB24360 (Epacadostat), a Highly Potent and Selective Indoleamine-2,3-dioxygenase 1 (IDO1) Inhibitor for Immuno-oncology.

A data-centric medicinal chemistry approach led to the invention of a potent and selective IDO1 inhibitor 4f, INCB24360 (epacadostat). The molecular structure of INCB24360 contains several previously unknown or underutilized functional groups in drug substances, including a hydroxyamidine, furazan, bromide, and sulfamide. These moieties taken together in a single structure afford a compound that falls outside of "drug-like" space. Nevertheless, the in vitro ADME data is consistent with the good cell permeability and oral bioavailability observed in all species (rat, dog, monkey) tested. The extensive intramolecular hydrogen bonding observed in the small molecule crystal structure of 4f is believed to significantly contribute to the observed permeability and PK. Epacadostat in combination with anti-PD1 mAb pembrolizumab is currently being studied in a phase 3 clinical trial in patients with unresectable or metastatic melanoma.

Selective inhibition of ADAM metalloproteases blocks HER-2 extracellular domain (ECD) cleavage and potentiates the anti-tumor effects of trastuzumab.

The HER-2 receptor tyrosine kinase is an important regulator of cell proliferation and survival, and it is a clinically validated target of therapeutic intervention for HER-2 positive breast cancer patients. Its extracellular domain (ECD) is frequently cleaved by protease(s) in HER-2 overexpressing breast cancer patients, rendering the remaining membrane-bound portion (p95) a constitutively activated kinase. The presence of both serum ECD and cellular p95 protein has been linked to poor clinical outcome as well as reduced effectiveness of some therapeutic treatments. We have identified a series of potent, selective small molecule inhibitors of ADAM proteases, exemplified here by INCB003619, and demonstrate that these inhibitors effectively block HER-2 cleavage in HER-2 overexpressing human breast cancer cell lines. Intriguingly, when used in combination, INCB003619 dramatically enhances the antiproliferative activity of suboptimal doses of the anti-HER-2 antibody, trastuzumab, in HER-2 overexpressing/shedding breast cancer cell lines, accompanied by reduced ERK and AKT phosphorylation. Furthermore, INCB003619, in combination with trastuzumab, augments the pro-apoptotic and antiproliferative effects of the chemotherapeutic agent paclitaxel. Consistent with these in vitro data, INCB003619 reduces serum ECD levels and enhances the antitumor effect of trastuzumab in a xenograft tumor model derived from the HER-2 overexpressing BT-474 breast cancer cell line. Collectively, these findings suggest that blocking HER-2 cleavage with selective ADAM inhibitors may represent a novel therapeutic approach for treating HER-2 overexpressing breast cancer patients.

Mechanism of tumor rejection with doublets of CTLA-4, PD-1/PD-L1, or IDO blockade involves restored IL-2 production and proliferation of CD8(+) T cells directly within the tumor microenvironment.

BACKGROUND: Blockade of immune inhibitory pathways is emerging as an important therapeutic modality for the treatment of cancer. Single agent treatments have partial anti-tumor activity in preclinical models and in human cancer patients. Inasmuch as the tumor microenvironment shows evidence of multiple immune inhibitory mechanisms present concurrently, it has been reasoned that combination therapies may be required for optimal therapeutic effect. METHODS: To test this notion, we utilized permutations of anti-CTLA-4 mAb, anti-PD-L1 mAb, and/or the IDO inhibitor INCB23843 in the murine B16.SIY melanoma model. RESULTS: All three combinations showed markedly improved tumor control over single treatments, with many mice achieving complete tumor rejection. This effect was seen in the absence of vaccination or adoptive T cell therapy. The mechanism of synergy was investigated to examine the priming versus effector phase of the anti-tumor immune response. Only a minimal increase in priming of anti-tumor T cells was observed at early time points in the tumor-draining lymph nodes (TdLN). In contrast, as early as three days after therapy initiation, a marked increase in the capacity of tumor-infiltrating CD8(+) T cells to produce IL-2 and to proliferate was found in all groups treated with the effective combinations. Treatment of mice with FTY720 to block new T cell trafficking from secondary lymphoid structures still enabled restoration of IL-2 production and proliferation by intratumoral T cells, and also retained most of the tumor growth control. CONCLUSIONS: Our data suggest that the therapeutic effect of these immunotherapies was mainly mediated through direct reactivation of T cells in situ. These three combinations are attractive to pursue clinically, and the ability of intratumoral CD8(+) T cells to produce IL-2 and to proliferate could be an important biomarker to integrate into clinical studies.