Synthesis and biological evaluation of biaryl alkyl ethers as inhibitors of IDO1.

Starting from the dialkylaniline indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor lead 3 (IDO1 HeLa IC50 = 7.0 nM), an iterative process of synthesis and screening led to cyclized analog 21 (IDO1 HeLa IC50 = 3.6 nM) which maintained the high potency of 3 while addressing issues of lipophilicity, cytochrome P450 (CYP) inhibition, hERG (human potassium ion channel Kv11.1) inhibition, Pregnane X Receptor (PXR) transactivation, and oxidative metabolic stability. An x-ray crystal structure of a biaryl alkyl ether 11 bound to IDO1 was obtained. Consistent with our earlier results, compound 11 was shown to bind to the apo form of the enzyme.

Discovery and Preclinical Pharmacology of an Oral Bromodomain and Extra-Terminal (BET) Inhibitor Using Scaffold-Hopping and Structure-Guided Drug Design.

Inhibition of the bromodomain and extra-terminal (BET) family of adaptor proteins is an attractive strategy for targeting transcriptional regulation of key oncogenes, such as c-MYC. Starting with the screening hit 1, a combination of structure-activity relationship and protein structure-guided drug design led to the discovery of a differently oriented carbazole 9 with favorable binding to the tryptophan, proline, and phenylalanine (WPF) shelf conserved in the BET family. Identification of an additional lipophilic pocket and functional group optimization to optimize pharmacokinetic (PK) properties culminated in the discovery of 18 (BMS-986158) with excellent potency in binding and functional assays. On the basis of its favorable PK profile and robust in vivo activity in a panel of hematologic and solid tumor models, BMS-986158 was selected as a candidate for clinical evaluation.

Conformational-Analysis-Guided Discovery of 2,3-Disubstituted Pyridine IDO1 Inhibitors.

IDO1 inhibitors have shown promise as immunotherapies for the treatment of a variety of cancers, including metastatic melanoma and renal cell carcinoma. We recently reported the identification of several novel heme-displacing IDO1 inhibitors, including the clinical molecules linrodostat (BMS-986205) and BMS-986242. Both molecules contain quinolines that, while being present in successful medicines, are known to be potentially susceptible to oxidative metabolism. Efforts to swap this quinoline with an alternative aromatic system led to the discovery of 2,3-disubstituted pyridines as suitable replacements. Further optimization, which included lowering ClogP in combination with strategic fluorine incorporation, led to the discovery of compound 29, a potent, selective IDO1 inhibitor with robust pharmacodynamic activity in a mouse xenograft model.

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.

Discovery and Preclinical Evaluation of BMS-986242, a Potent, Selective Inhibitor of Indoleamine-2,3-dioxygenase 1.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme-containing dioxygenase enzyme implicated in cancer immune response. This account details the discovery of BMS-986242, a novel IDO1 inhibitor designed for the treatment of a variety of cancers including metastatic melanoma and renal cell carcinoma. Given the substantial interest around this target for cancer immunotherapy, we sought to identify a structurally differentiated clinical candidate that performs comparably to linrodostat (BMS-986205) in terms of both in vitro potency and in vivo pharmacodynamic effect in a mouse xenograft model. On the basis of its preclinical profile, BMS-986242 was selected as a candidate for clinical development.

Enhanced antitumor immunity by a novel small molecule HPK1 inhibitor.

BACKGROUND: Hematopoietic progenitor kinase 1 (HPK1 or MAP4K1) has been demonstrated as a negative intracellular immune checkpoint in mediating antitumor immunity in studies with HPK1 knockout and kinase dead mice. Pharmacological inhibition of HPK1 is desirable to investigate the role of HPK1 in human immune cells with therapeutic implications. However, a significant challenge remains to identify a small molecule inhibitor of HPK1 with sufficient potency, selectivity, and other drug-like properties suitable for proof-of-concept studies. In this report, we identified a novel, potent, and selective HPK1 small molecule kinase inhibitor, compound K (CompK). A series of studies were conducted to investigate the mechanism of action of CompK, aiming to understand its potential application in cancer immunotherapy. METHODS: Human primary T cells and dendritic cells (DCs) were investigated with CompK treatment under conditions relevant to tumor microenvironment (TME). Syngeneic tumor models were used to assess the in vivo pharmacology of CompK followed by human tumor interrogation ex vivo. RESULTS: CompK treatment demonstrated markedly enhanced human T-cell immune responses under immunosuppressive conditions relevant to the TME and an increased avidity of the T-cell receptor (TCR) to recognize viral and tumor-associated antigens (TAAs) in significant synergy with anti-PD1. Animal model studies, including 1956 sarcoma and MC38 syngeneic models, revealed improved immune responses and superb antitumor efficacy in combination of CompK with anti-PD-1. An elevated immune response induced by CompK was observed with fresh tumor samples from multiple patients with colorectal carcinoma, suggesting a mechanistic translation from mouse model to human disease. CONCLUSION: CompK treatment significantly improved human T-cell functions, with enhanced TCR avidity to recognize TAAs and tumor cytolytic activity by CD8+ T cells. Additional benefits include DC maturation and priming facilitation in tumor draining lymph node. CompK represents a novel pharmacological agent to address cancer treatment resistance.

Preclinical Characterization of Linrodostat Mesylate, a Novel, Potent, and Selective Oral Indoleamine 2,3-Dioxygenase 1 Inhibitor.

Tumors can exploit the indoleamine 2,3-dioxygenase 1 (IDO1) pathway to create an immunosuppressive microenvironment. Activated IDO1 metabolizes tryptophan into immunosuppressive kynurenine, leading to suppressed effector T-cell (Teff) proliferation, allowing for tumor escape from host immune surveillance. IDO1 inhibition counteracts this immunosuppressive tumor microenvironment and may improve cancer outcomes, particularly when combined with other immunotherapies. Linrodostat mesylate (linrodostat) is a potent, selective oral IDO1 inhibitor that occupies the heme cofactor-binding site to prevent further IDO1 activation and is currently in multiple clinical trials for treatment of patients with advanced cancers. Here, we assess the in vitro potency, in vivo pharmacodynamic (PD) activity, and preclinical pharmacokinetics (PKs) of linrodostat. Linrodostat exhibited potent cellular activity, suppressing kynurenine production in HEK293 cells overexpressing human IDO1 and HeLa cells stimulated with IFNγ, with no activity against tryptophan 2,3-dioxygenase or murine indoleamine 2,3-dioxygenase 2 detected. Linrodostat restored T-cell proliferation in a mixed-lymphocyte reaction of T cells and allogeneic IDO1-expressing dendritic cells. In vivo, linrodostat reduced kynurenine levels in human tumor xenograft models, exhibiting significant PD activity. Linrodostat demonstrated a PK/PD relationship in the xenograft model, preclinical species, and samples from patients with advanced cancers, with high oral bioavailability in preclinical species and low to moderate systemic clearance. Our data demonstrate that linrodostat potently and specifically inhibits IDO1 to block an immunosuppressive mechanism that could be responsible for tumor escape from host immune surveillance with favorable PK/PD characteristics that support clinical development.

Critical role of kinase activity of hematopoietic progenitor kinase 1 in anti-tumor immune surveillance.

Immunotherapy has fundamentally changed the landscape of cancer treatment. Despite the encouraging results with the checkpoint modulators, response rates vary widely across tumor types, with a majority of patients exhibiting either primary resistance without a significant initial response to treatment or acquired resistance with subsequent disease progression. Hematopoietic progenitor kinase 1 (HPK1) is predominantly expressed in hematopoietic cell linages and serves as a negative regulator in T cells and dendritic cells (DC). While HPK1 gene knockout (KO) studies suggest its role in anti-tumor immune responses, the involvement of kinase activity and thereof its therapeutic potential remain unknown. To investigate the potential of pharmacological intervention using inhibitors of HPK1, we generated HPK1 kinase dead (KD) mice which carry a single loss-of-function point mutation in the kinase domain and interrogated the role of kinase activity in immune cells in the context of suppressive factors or the tumor microenvironment (TME). Our data provide novel findings that HKP1 kinase activity is critical in conferring suppressive functions of HPK1 in a wide range of immune cells including CD4+, CD8+, DC, NK to Tregs, and inactivation of kinase domain was sufficient to elicit robust anti-tumor immune responses. These data support the concept that an HPK1 small molecule kinase inhibitor could serve as a novel agent to provide additional benefit in combination with existing immunotherapies, particularly to overcome resistance to current treatment regimens.

Immune-modulating enzyme indoleamine 2,3-dioxygenase is effectively inhibited by targeting its apo-form.

For cancer cells to survive and proliferate, they must escape normal immune destruction. One mechanism by which this is accomplished is through immune suppression effected by up-regulation of indoleamine 2,3-dioxygenase (IDO1), a heme enzyme that catalyzes the oxidation of tryptophan to N-formylkynurenine. On deformylation, kynurenine and downstream metabolites suppress T cell function. The importance of this immunosuppressive mechanism has spurred intense interest in the development of clinical IDO1 inhibitors. Herein, we describe the mechanism by which a class of compounds effectively and specifically inhibits IDO1 by targeting its apo-form. We show that the in vitro kinetics of inhibition coincide with an unusually high rate of intrinsic enzyme-heme dissociation, especially in the ferric form. X-ray crystal structures of the inhibitor-enzyme complexes show that heme is displaced from the enzyme and blocked from rebinding by these compounds. The results reveal that apo-IDO1 serves as a unique target for inhibition and that heme lability plays an important role in posttranslational regulation.

Development of a series of novel o-phenylenediamine-based indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors.

A novel series of o-phenylenediamine-based inhibitors of indoleamine 2,3-dioxygenase (IDO) has been identified. IDO is a heme-containing enzyme, overexpressed in the tumor microenvironment of many cancers, which can contribute to the suppression of the host immune system. Synthetic modifications to a previously described diarylether series resulted in an additional degree of molecular diversity which was exploited to afford compounds that demonstrated significant potency in the HeLa human cervical cancer IDO1 assay. .

Identification and optimization of a novel series of indoleamine 2,3-dioxygenase inhibitors.

The discovery of a series of structurally-novel biaryl urea IDO inhibitors is described. Optimization of a micromolar hit through iterative cycles of synthesis and screening in an assay measuring IDO-mediated intracellular conversion of tryptophan to kynurenine led to potent inhibitors with favorable selectivity and metabolic stability profiles.

Pharmacology of smac mimetics; chemotype differentiation based on physical association with caspase regulators and cellular transport.

Cellular levels of inhibitor of apoptosis (IAP) proteins are elevated in multiple human cancers and their activities often play a part in promoting cancer cell survival by blocking apoptotic pathways, controlling signal transduction pathways and contributing to resistance. These proteins function through interactions of their BIR (baculoviral IAP repeat) protein domains with pathway components and these interactions are endogenously antagonized by Smac/Diablo (second mitochondrial activator of caspases/direct IAP binding protein with low isoelectric point). This report describes development of synthetic smac mimetics (SM) and compares their binding, antiproliferative and anti-tumor activities. All dimeric antagonists inhibit in vitro smac tetrapeptide binding to recombinant IAP proteins, rescue IAP-bound caspase-3 activity and show anti-proliferative activity against human A875 melanoma cells. One heterodimeric SM, SM3, binds tightly to IAP proteins in vitro and slowly dissociates (greater than two hours) from these protein complexes compared to the other antagonists. In addition, in vitro SM anti-proliferation potency is influenced by ABCB1 transporter (ATP-binding cassette, sub-family B; MDR1, P-gp) activities and one antagonist, SM5, does not appear to be an ABCB1 efflux pump substrate. All dimeric smac mimetics inhibit the growth of human melanoma A875 tumors implanted in athymic mice at well-tolerated doses. One antagonist, SM4, shows broad spectrum in vivo anti-tumor activity and modulates known pharmacodynamic markers of IAP antagonism. These data taken together demonstrate the range of diverse dimeric IAP antagonist activities and supports their potential as anticancer agents.

Discovery of Clinical Candidate BMS-906024: A Potent Pan-Notch Inhibitor for the Treatment of Leukemia and Solid Tumors.

Structure-activity relationships in a series of (2-oxo-1,4-benzodiazepin-3-yl)-succinamides identified highly potent inhibitors of γ-secretase mediated signaling of Notch1/2/3/4 receptors. On the basis of its robust in vivo efficacy at tolerated doses in Notch driven leukemia and solid tumor xenograft models, 12 (BMS-906024) was selected as a candidate for clinical evaluation.

BMS-871: a novel orally active pan-Notch inhibitor as an anticancer agent.

This Letter describes synthesis, SAR, and biological activity of (2-oxo-1,4-benzodiazepin-3-yl)-succinamides as inhibitors of γ-secretase mediated signaling of Notch receptors. Optimization of this series led to the identification of BMS-871 (compound 30) which displayed robust in vivo efficacy in Notch-dependent leukemia and solid tumor xenograft models.

Synergy between chemotherapeutic agents and CTLA-4 blockade in preclinical tumor models.

Ipilimumab, a cytotoxic T-lymphocyte antigen-4 (CTLA-4) binding agent, has proven to be an effective monotherapy for metastatic melanoma and has shown antitumor activity in trials when administered with other therapeutic agents. We hypothesized that the combination of ipilimumab with chemotherapeutic agents, such as ixabepilone, paclitaxel, etoposide, and gemcitabine, may produce therapeutic synergy based on distinct but complementary mechanisms of action for each drug and unique cellular targets. This concept was investigated using a mouse homolog of ipilimumab in preclinical murine tumor models, including SA1N fibrosarcoma, EMT-6 mammary carcinoma, M109 lung carcinoma, and CT-26 colon carcinoma. Results of CTLA-4 blockade in combination with one of various chemotherapeutic agents demonstrate that synergy occurs in settings where either agent alone was not effective in inducing tumor regression. Furthermore, when combined with CTLA-4 blockade, ixabepilone, etoposide, and gemcitabine elicited prolonged antitumor effects in some murine models with induction of a memory immune response. Future investigations are warranted to determine which specific chemo-immunotherapy combinations, if any, will produce synergistic antitumor effects in the clinical setting.

Design, synthesis, functional and structural characterization of an inhibitor of N-acetylneuraminate-9-phosphate phosphatase: observation of extensive dynamics in an enzyme/inhibitor complex.

The design, synthesis and characterization of a phosphonate inhibitor of N-acetylneuraminate-9-phosphate phosphatase (HDHD4) is described. Compound 3, where the substrate C-9 oxygen was replaced with a nonlabile CH2 group, inhibits HDHD4 with a binding affinity (IC50 11µM) in the range of the native substrate Neu5Ac-9-P (compound 1, Km 47µM). Combined SAR, modeling and NMR studies are consistent with the phosphonate group in inhibitor 3 forming a stable complex with native Mg(2+). In addition to this key interaction, the C-1 carboxylate of the sugar interacts with a cluster of basic residues, K141, R104 and R72. Comparative NMR studies of compounds 3 and 1 with Ca(2+) and Mg(2+) are indicative of a highly dynamic process in the active site for the HDHD4/Mg(2+)/3 complex. Possible explanations for this observation are discussed.

Antitumor and antiangiogenic activities of BMS-690514, an inhibitor of human EGF and VEGF receptor kinase families.

PURPOSE: The extensive involvement of the HER kinases in epithelial cancer suggests that kinase inhibitors targeting this receptor family have the potential for broad spectrum antitumor activity. BMS-690514 potently inhibits all three HER kinases, and the VEGF receptor kinases. This report summarizes data from biochemical and cellular pharmacology studies, as well as antitumor activity of BMS-690514. EXPERIMENTAL DESIGN: The potency and selectivity of BMS-690514 was evaluated by using an extensive array of enzymatic and binding assays, as well as cellular assays that measure proliferation and receptor signaling. Antitumor activity was evaluated by using multiple xenograft models that depend on HER kinase signaling. The antiangiogenic properties of BMS-690514 were assessed in a matrigel plug assay, and effect on tumor blood flow was measured by dynamic contrast-enhanced MRI. RESULTS: BMS-690514 is a potent and selective inhibitor of epidermal growth factor receptor (EGFR), HER2, and HER4, as well as the VEGF receptor kinases. It inhibits proliferation of tumor cells with potency that correlates with inhibition of receptor signaling, and induces apoptosis in lung tumor cells that have an activating mutation in EGFR. Antitumor activity was observed with BMS-690514 at multiple doses that are well tolerated in mice. There was evidence of suppression of tumor angiogenesis and endothelial function by BMS-690514, which may contribute to its efficacy. CONCLUSIONS: By combining inhibition of two receptor kinase families, BMS-690524 is a novel targeted agent that disrupts signaling in the tumor and its vasculature.

The antiangiogenic activity in xenograft models of brivanib, a dual inhibitor of vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1 kinases.

Tumor angiogenesis is a complex and tightly regulated network mediated by various proangiogenic factors. The fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) family of growth factors, and associated tyrosine kinase receptors have a major influence in tumor growth and dissemination and may work synergistically to promote angiogenesis. Brivanib alaninate is the orally active prodrug of brivanib, a selective dual inhibitor of FGF and VEGF signaling. Here, we show that brivanib demonstrates antitumor activity in a broad range of xenograft models over multiple dose levels and that brivanib alaninate shows dose-dependent efficacy equivalent to brivanib in L2987 human tumor xenografts. Brivanib alaninate (107 mg/kg) reduced tumor cell proliferation as determined by a 76% reduction in Ki-67 staining and reduced tumor vascular density as determined by a 76% reduction in anti-CD34 endothelial cell staining. Furthermore, Matrigel plug assays in athymic mice showed that brivanib alaninate inhibited angiogenesis driven by VEGF or basic FGF alone, or combined. Dynamic contrast-enhanced magnetic resonance imaging, used to assess the effects of brivanib alaninate on tumor microcirculation, showed a marked decrease in gadopentetate dimeglumine contrast agent uptake at 107 mg/kg dose, with a reduction in area under the plasma concentration-time curve from time 0 to 60 minutes at 24 and 48 hours of 54% and 64%, respectively. These results show that brivanib alaninate is an effective antitumor agent in preclinical models across a range of doses, and that efficacy is accompanied by changes in cellular and vascular activities.

Discovery of N-(4-(2-amino-3-chloropyridin-4-yloxy)-3-fluorophenyl)-4-ethoxy-1-(4-fluorophenyl)-2-oxo-1,2-dihydropyridine-3-carboxamide (BMS-777607), a selective and orally efficacious inhibitor of the Met kinase superfamily.

Substituted N-(4-(2-aminopyridin-4-yloxy)-3-fluoro-phenyl)-1-(4-fluorophenyl)-2-oxo-1,2-dihydropyridine-3-carboxamides were identified as potent and selective Met kinase inhibitors. Substitution of the pyridine 3-position gave improved enzyme potency, while substitution of the pyridone 4-position led to improved aqueous solubility and kinase selectivity. Analogue 10 demonstrated complete tumor stasis in a Met-dependent GTL-16 human gastric carcinoma xenograft model following oral administration. Because of its excellent in vivo efficacy and favorable pharmacokinetic and preclinical safety profiles, 10 has been advanced into phase I clinical trials.