Hit-to-lead optimization and discovery of a potent, and orally bioavailable G protein coupled receptor kinase 2 (GRK2) inhibitor.

G-protein coupled receptor kinase 2 (GRK2), which is upregulated in the failing heart, appears to play a critical role in heart failure (HF) progression in part because enhanced GRK2 activity promotes dysfunction of ß-adrenergic signaling and myocyte death. An orally bioavailable GRK2 inhibitor could offer unique therapeutic outcomes that cannot be attained by current heart failure treatments that directly target GPCRs or angiotensin-converting enzyme. Herein, we describe the discovery of a potent, selective, and orally bioavailable GRK2 inhibitor, 8h, through high-throughput screening, hit-to-lead optimization, structure-based design, molecular modelling, synthesis, and biological evaluation. In the cellular target engagement assays, 8h enhances isoproterenol-mediated cyclic adenosine 3',5'-monophosphate (cAMP) production in HEK293 cells overexpressing GRK2. Compound 8h was further evaluated in a human stem cell-derived cardiomyocyte (HSC-CM) contractility assay and potentiated isoproterenol-induced beating rate in HSC-CMs.

Optimization and biological evaluation of thiazole-bis-amide inverse agonists of RORγt.

The nuclear receptor retinoic acid receptor-related orphan receptor gamma t (RORγt) is a transcription factor that drives Th17 cell differentiation and IL-17 production in both innate and adaptive immune cells. The IL-23/IL-17 pathway is implicated in major autoimmune and inflammatory diseases. RORγt lies at the core of this pathway and represents an attractive opportunity for intervention with small molecule therapeutics. Despite diverse chemical series having been reported, combining high potency and nuclear receptor selectivity with good physicochemical properties remains a challenging endeavor in the field of RORγt drug discovery. We recently described the discovery and evaluation of a new class of potent and selective RORγt inverse agonists based on a thiazole scaffold. Herein we describe the successful optimization of this class by incorporation of an additional amide moiety at the 4-position of the thiazole core. In several optimization cycles, we have reduced human PXR activation, improved solubility, and increased potency while maintaining nuclear receptor selectivity. X-ray crystallographic analysis of compound 1g bound in the sterol binding site of the ligand binding domain of RORγt was largely consistent with an earlier structure, guiding further insight into the molecular mechanism for RORγt inhibition with this series. Compound 1g is orally bioavailable, potent in a human whole blood assay and proved to be efficacious in an ex-vivo IL-17A assay, and was selected for preclinical evaluation.

3-Substituted Quinolines as RORγt Inverse Agonists.

We have previously reported the syntheses of a series of 3,6-disubstituted quinolines as modulators of the retinoic acid receptor-related orphan receptor gamma t (RORγt). These molecules are potent binders but are high molecular weight and they exhibited poor solubility at pH 2 and pH 7. This manuscript details our efforts at improving physical chemical properties for this series of compounds by increasing the diversity at the 3-position (i.e. introducing heteroatoms and lowering the molecular weight). These efforts have led to molecules which are potent binders with improved solubility.

Discovery of a highly selective chemical inhibitor of matrix metalloproteinase-9 (MMP-9) that allosterically inhibits zymogen activation.

Aberrant activation of matrix metalloproteinases (MMPs) is a common feature of pathological cascades observed in diverse disorders, such as cancer, fibrosis, immune dysregulation, and neurodegenerative diseases. MMP-9, in particular, is highly dynamically regulated in several pathological processes. Development of MMP inhibitors has therefore been an attractive strategy for therapeutic intervention. However, a long history of failed clinical trials has demonstrated that broad-spectrum MMP inhibitors have limited clinical utility, which has spurred the development of inhibitors selective for individual MMPs. Attaining selectivity has been technically challenging because of sequence and structural conservation across the various MMPs. Here, through a biochemical and structural screening paradigm, we have identified JNJ0966, a highly selective compound that inhibited activation of MMP-9 zymogen and subsequent generation of catalytically active enzyme. JNJ0966 had no effect on MMP-1, MMP-2, MMP-3, MMP-9, or MMP-14 catalytic activity and did not inhibit activation of the highly related MMP-2 zymogen. The molecular basis for this activity was characterized as an interaction of JNJ0966 with a structural pocket in proximity to the MMP-9 zymogen cleavage site near Arg-106, which is distinct from the catalytic domain. JNJ0966 was efficacious in reducing disease severity in a mouse experimental autoimmune encephalomyelitis model, demonstrating the viability of this therapeutic approach. This discovery reveals an unprecedented pharmacological approach to MMP inhibition, providing an opportunity to improve selectivity of future clinical drug candidates. Targeting zymogen activation in this manner may also allow for pharmaceutical exploration of other enzymes previously viewed as intractable drug targets.

Identification and biological evaluation of thiazole-based inverse agonists of RORγt.

The nuclear receptor retinoic acid receptor-related orphan receptor gamma t (RORγt) is a transcription factor that drives Th17 cell differentiation and IL-17 production in both innate and adaptive immune cells. The IL-23/IL-17 pathway is implicated in major autoimmune and inflammatory diseases. RORγt lies at the core of this pathway and represents an attractive opportunity for intervention with a small molecule. Despite diverse chemical series having been reported, combining high potency and nuclear receptor selectivity with good physicochemical properties remains a challenging endeavor in the field of RORγt drug discovery. We describe the discovery and evaluation of a new class of potent and selective RORγt inverse agonists based on a thiazole core. Acid analog 1j demonstrated oral bioavailability in rats and was potent in a human whole blood assay, suggesting potential utility in treating autoimmune and inflammatory diseases such as psoriasis. X-ray crystallographic data helped to elucidate the molecular mechanism for RORγt inhibition with this series.

Identification and structure activity relationships of quinoline tertiary alcohol modulators of RORγt.

A high-throughput screen of the ligand binding domain of the nuclear receptor retinoic acid-related orphan receptor gamma t (RORγt) employing a thermal shift assay yielded a quinoline tertiary alcohol hit. Optimization of the 2-, 3- and 4-positions of the quinoline core using structure-activity relationships and structure-based drug design methods led to the discovery of a series of modulators with improved RORγt inhibitory potency and inverse agonism properties.

6-Substituted quinolines as RORγt inverse agonists.

We identified 6-substituted quinolines as modulators of the retinoic acid receptor-related orphan receptor gamma t (RORγt). The synthesis of this class of RORγt modulators is reported, and optimization of the substituents at the quinoline 6-position that produced compounds with high affinity for the receptor is detailed. This effort identified molecules that act as potent, full inverse agonists in a RORγt-driven cell-based reporter assay. The X-ray crystal structures of two full inverse agonists from this chemical series bound to the RORγt ligand binding domain are disclosed, and we highlight the interaction of a hydrogen-bond acceptor on the 6-position substituent of the inverse agonist with Glu379:NH as a conserved binding contact.

Discovery of Potent and Orally Bioavailable Pyridine N-Oxide-Based Factor XIa Inhibitors through Exploiting Nonclassical Interactions.

Activated factor XI (FXIa) inhibitors are promising novel anticoagulants with low bleeding risk compared with current anticoagulants. The discovery of potent FXIa inhibitors with good oral bioavailability has been challenging. Herein, we describe our discovery effort, utilizing nonclassical interactions to improve potency, cellular permeability, and oral bioavailability by enhancing the binding while reducing polar atoms. Beginning with literature-inspired pyridine N-oxide-based FXIa inhibitor 1, the imidazole linker was first replaced with a pyrazole moiety to establish a polar C-H···water hydrogen-bonding interaction. Then, structure-based drug design was employed to modify lead molecule 2d in the P1' and P2' regions, with substituents interacting with key residues through various nonclassical interactions. As a result, a potent FXIa inhibitor 3f (Ki = 0.17 nM) was discovered. This compound demonstrated oral bioavailability in preclinical species (rat 36.4%, dog 80.5%, and monkey 43.0%) and displayed a dose-dependent antithrombotic effect in a rabbit arteriovenous shunt model of thrombosis.

Rational design and synthesis of aminopiperazinones as ß-secretase (BACE) inhibitors.

Aminopiperazinone inhibitors of BACE were identified by rational design. Structure based design guided idea prioritization and initial racemic hit 18a showed good activity. Modification in decoration and chiral separation resulted in the 40 nM inhibitor, (-)-37, which showed in vivo reduction of amyloid beta peptides. The crystal structure of 18a showed a binding mode driven by interaction with the catalytic aspartate dyad and distribution of the biaryl amide decoration towards S1 and S3 pockets.

Structural determination of estrogen-related receptor gamma in the presence of phenol derivative compounds.

We screened the ligand-binding domain of estrogen-related receptor (ERR) gamma in ThermoFluor, in an effort to develop chemical tools and decipher the biology of this orphan nuclear receptor. Several ligands were found to stabilize thermodynamically the protein. Amongst the ligands were bisphenol A (BPA) and 4-chloro-3-methyl phenol (ClCH3Ph). These ligands were further characterized and found to be competitive for 4-hydroxytamoxifen (4OHT) binding, a known reported antagonist ligand for ERRgamma, but functionally they did not enhance or disrupt affinity of the receptor for co-activator peptides. The preservation of the constitutive active conformation of the receptor in the presence of these two ligands was confirmed upon the determination of the co-crystal structures. The structures of BPA and ClCH3Ph were determined to a resolution of 2.1 and 2.3A, respectively, and the antagonist 4OHT was refined to 2.5A resolution. In the presence of BPA and ClCH3Ph the receptor maintained the transcriptional active conformation as reported previously for the apo-protein in the presence of a co-activator peptide fragment. In addition the ERRgamma-BPA structure identifies an interaction between the phenolic-OH and the side chain of N346. The preservation of the constitutive active conformation of the receptor in the presence of the small phenol compounds suggest that the biological activity of the receptor might be regulated by a natural occurring ligand.

Potent, nonpeptide inhibitors of human mast cell tryptase. Synthesis and biological evaluation of novel spirocyclic piperidine amide derivatives.

We have explored a series of spirocyclic piperidine amide derivatives (5) as tryptase inhibitors. Thus, 4 (JNJ-27390467) was identified as a potent, selective tryptase inhibitor with oral efficacy in two animal models of airway inflammation (sheep and guinea pig asthma models). An X-ray co-crystal structure of 4 x tryptase revealed a hydrophobic pocket in the enzyme's active site, which is induced by the phenylethynyl group and is comprised of amino acid residues from two different monomers of the tetrameric protein.

Orally efficacious thrombin inhibitors with cyanofluorophenylacetamide as the P2 motif.

2-Cyano-6-fluorophenylacetamide was explored as a novel P2 scaffold in the design of thrombin inhibitors. Optimization around this structural motif culminated in 14, which is a potent thrombin inhibitor (K(i)=1.2nM) that exhibits robust efficacy in canine anticoagulation and thrombosis models upon oral administration.

Outcome of the First wwPDB/CCDC/D3R Ligand Validation Workshop.

Crystallographic studies of ligands bound to biological macromolecules (proteins and nucleic acids) represent an important source of information concerning drug-target interactions, providing atomic level insights into the physical chemistry of complex formation between macromolecules and ligands. Of the more than 115,000 entries extant in the Protein Data Bank (PDB) archive, ∼75% include at least one non-polymeric ligand. Ligand geometrical and stereochemical quality, the suitability of ligand models for in silico drug discovery and design, and the goodness-of-fit of ligand models to electron-density maps vary widely across the archive. We describe the proceedings and conclusions from the first Worldwide PDB/Cambridge Crystallographic Data Center/Drug Design Data Resource (wwPDB/CCDC/D3R) Ligand Validation Workshop held at the Research Collaboratory for Structural Bioinformatics at Rutgers University on July 30-31, 2015. Experts in protein crystallography from academe and industry came together with non-profit and for-profit software providers for crystallography and with experts in computational chemistry and data archiving to discuss and make recommendations on best practices, as framed by a series of questions central to structural studies of macromolecule-ligand complexes. What data concerning bound ligands should be archived in the PDB? How should the ligands be best represented? How should structural models of macromolecule-ligand complexes be validated? What supplementary information should accompany publications of structural studies of biological macromolecules? Consensus recommendations on best practices developed in response to each of these questions are provided, together with some details regarding implementation. Important issues addressed but not resolved at the workshop are also enumerated.

Discovery and cocrystal structure of benzodiazepinedione HDM2 antagonists that activate p53 in cells.

HDM2 binds to an alpha-helical transactivation domain of p53, inhibiting its tumor suppressive functions. A miniaturized thermal denaturation assay was used to screen chemical libraries, resulting in the discovery of a novel series of benzodiazepinedione antagonists of the HDM2-p53 interaction. The X-ray crystal structure of improved antagonists bound to HDM2 reveals their alpha-helix mimetic properties. These optimized molecules increase the transcription of p53 target genes and decrease proliferation of tumor cells expressing wild-type p53.

Fragment screening purely with protein crystallography.

We screen for fragments using X-ray crystallography as the primary screen. There are several unique features in our screening methodology. As a result of using X-ray diffraction as our primary screen, we do not use affinity data to bias our data collection or design in progressing hits toward a lead. Another difference in our methodology is that we choose to group our compounds as shape-similar groups. We also screen in a first pass mode without recollecting failed diffraction experiments. This method of screening results in an average loss of 5-10% of the data sets for the primary screen. The remaining data sets offer enough information to successfully advance three to five scaffolds into the secondary library design. We do not deconvolute the wells which show evidence of fragment binding by repeating the soaks with single compounds. Instead, evaluation of the possible fragments is done by refinement and examination of the resulting electron density difference maps. These methods allow us to complete the initial screen of a primary library of fragments in less than 3 months. A secondary library of fragments is designed using the base structures with electron density envelopes from the successful fragment hits of the primary library. Chemistry is chosen to probe interactions with the target and push the observed binding pocket limits in order to more clearly define the plasticity and range of possible extensions to the scaffolds chosen. The secondary library compounds are also screened in shape-similar groupings of five that are chosen without the knowledge of binding affinity. Our approach is a completely orthogonal one from traditional high-throughput screening in finding novel compounds.

Potency variation of small-molecule chymase inhibitors across species.

Chymases (EC 3.4.21.39) are mast cell serine proteinases that are variably expressed in different species and, in most cases, display either chymotryptic or elastolytic substrate specificity. Given that chymase inhibitors have emerged as potential therapeutic agents for treating various inflammatory, allergic, and cardiovascular disorders, it is important to understand interspecies differences of the enzymes as well as the behavior of inhibitors with them. We have expressed chymases from humans, macaques, dogs, sheep (MCP2 and MCP3), guinea pigs, and hamsters (HAM1 and HAM2) in baculovirus-infected insect cells. The enzymes were purified and characterized with kinetic constants by using chromogenic substrates. We evaluated in vitro the potency of five nonpeptide inhibitors, originally targeted against human chymase. The inhibitors exhibited remarkable cross-species variation of sensitivity, with the greatest potency observed against human and macaque chymases, with K(i) values ranging from approximately 0.4 to 72nM. Compounds were 10-300-fold less potent, and in some instances ineffective, against chymases from the other species. The X-ray structure of one of the potent phosphinate inhibitors, JNJ-18054478, complexed with human chymase was solved at 1.8A resolution to further understand the binding mode. Subtle variations in the residues in the active site that are already known to influence chymase substrate specificity can also strongly affect the compound potency. The results are discussed in the context of selecting a suitable animal model to study compounds ultimately targeted for human chymase.

Discovery and clinical evaluation of 1-{N-[2-(amidinoaminooxy)ethyl]amino}carbonylmethyl-6-methyl-3-[2,2-difluoro-2-phenylethylamino]pyrazinone (RWJ-671818), a thrombin inhibitor with an oxyguanidine P1 motif.

We have identified RWJ-671818 (8) as a novel, low molecular weight, orally active inhibitor of human alpha-thrombin (K(i) = 1.3 nM) that is potentially useful for the acute and chronic treatment of venous and arterial thrombosis. In a rat deep venous thrombosis model used to assess antithrombotic efficacy, oral administration of 8 at 30 and 50 mg/kg reduced thrombus weight by 87 and 94%, respectively. In an anesthetized rat antithrombotic model, where electrical stimulation of the carotid artery created a thrombus, 8 prolonged occlusion time 2- and 3-fold at 0.1 and 1.0 mg/kg, i.v., respectively, and more than doubled activated clotting time and activated partial thromboplastin time at the higher dose. This compound had excellent oral bioavailability of 100% in dogs with an estimated half-life of approximately 3 h. On the basis of its noteworthy preclinical data, 8 was advanced into human clinical trials and successfully progressed through phase 1 studies.

Structural basis for elastolytic substrate specificity in rodent alpha-chymases.

Divergence of substrate specificity within the context of a common structural framework represents an important mechanism by which new enzyme activity naturally evolves. We present enzymological and x-ray structural data for hamster chymase-2 (HAM2) that provides a detailed explanation for the unusual hydrolytic specificity of this rodent alpha-chymase. In enzymatic characterization, hamster chymase-1 (HAM1) showed typical chymase proteolytic activity. In contrast, HAM2 exhibited atypical substrate specificity, cleaving on the carboxyl side of the P1 substrate residues Ala and Val, characteristic of elastolytic rather than chymotryptic specificity. The 2.5-A resolution crystal structure of HAM2 complexed to the peptidyl inhibitor MeOSuc-Ala-Ala-Pro-Ala-chloromethylketone revealed a narrow and shallow S1 substrate binding pocket that accommodated only a small hydrophobic residue (e.g. Ala or Val). The different substrate specificities of HAM2 and HAM1 are explained by changes in four S1 substrate site residues (positions 189, 190, 216, and 226). Of these, Asn(189), Val(190), and Val(216) form an easily identifiable triplet in all known rodent alpha-chymases that can be used to predict elastolytic specificity for novel chymase-like sequences. Phylogenetic comparison defines guinea pig and rabbit chymases as the closest orthologs to rodent alpha-chymases.

2-(2-Chloro-6-fluorophenyl)acetamides as potent thrombin inhibitors.

2-(2-Chloro-6-fluorophenyl)acetamides having 2,2-difluoro-2-aryl/heteroaryl-ethylamine P3 and oxyguanidine P1 substituents are potent thrombin inhibitors (K(i)=0.9-33.9 nM). 2-(5-Chloro-pyridin-2-yl)-2,2-difluoroethylamine was the best P3 substituent, yielding the most potent inhibitor (K(i)=0.7 nM). Replacing the P3 heteroaryl group with a phenyl ring or replacing the difluoro substitution with dimethyl or cyclopropyl groups in the linker reduced the affinity for thrombin significantly. The aminopyridine P1s also provided an increase in potency.

Crystal structure of the tyrosine kinase domain of colony-stimulating factor-1 receptor (cFMS) in complex with two inhibitors.

The cFMS proto-oncogene encodes for the colony-stimulating factor-1 receptor, a receptor-tyrosine kinase responsible for the differentiation and maturation of certain macrophages. Upon binding its ligand colony-stimulating factor-1 cFMS autophosphorylates, dimerizes, and induces phosphorylation of downstream targets. We report the novel crystal structure of unphosphorylated cFMS in complex with two members of different classes of drug-like protein kinase inhibitors. cFMS exhibits a typical bi-lobal kinase fold, and its activation loop and DFG motif are found to be in the canonical inactive conformation. Both ATP competitive inhibitors are bound in the active site and demonstrate a binding mode similar to that of STI-571 bound to cABL. The DFG motif is prevented from switching into the catalytically competent conformation through interactions with the inhibitors. Activation of cFMS is also inhibited by the juxtamembrane domain, which interacts with residues of the active site and prevents formation of the activated kinase. Together the structures of cFMS provide further insight into the autoinhibition of receptor-tyrosine kinases via their respective juxtamembrane domains; additionally the binding mode of two novel classes of kinase inhibitors will guide the design of novel molecules targeting macrophage-related diseases.