RIP3 induces apoptosis independent of pronecrotic kinase activity.

Receptor-interacting protein kinase 3 (RIP3 or RIPK3) has emerged as a central player in necroptosis and a potential target to control inflammatory disease. Here, three selective small-molecule compounds are shown to inhibit RIP3 kinase-dependent necroptosis, although their therapeutic value is undermined by a surprising, concentration-dependent induction of apoptosis. These compounds interact with RIP3 to activate caspase 8 (Casp8) via RHIM-driven recruitment of RIP1 (RIPK1) to assemble a Casp8-FADD-cFLIP complex completely independent of pronecrotic kinase activities and MLKL. RIP3 kinase-dead D161N mutant induces spontaneous apoptosis independent of compound, whereas D161G, D143N, and K51A mutants, like wild-type, only trigger apoptosis when compound is present. Accordingly, RIP3-K51A mutant mice (Rip3(K51A/K51A)) are viable and fertile, in stark contrast to the perinatal lethality of Rip3(D161N/D161N) mice. RIP3 therefore holds both necroptosis and apoptosis in balance through a Ripoptosome-like platform. This work highlights a common mechanism unveiling RHIM-driven apoptosis by therapeutic or genetic perturbation of RIP3.

Crystal structures of human RIP2 kinase catalytic domain complexed with ATP-competitive inhibitors: Foundations for understanding inhibitor selectivity.

Receptor interacting protein 2 (RIP2) is an intracellular kinase and key signaling partner for the pattern recognition receptors NOD1 and NOD2 (nucleotide-binding oligomerization domain-containing proteins 1 and 2). As such, RIP2 represents an attractive target to probe the role of these pathways in disease. In an effort to design potent and selective inhibitors of RIP2 we established a crystallographic system and determined the structure of the RIP2 kinase domain in an apo form and also in complex with multiple inhibitors including AMP-PCP (ß,γ-Methyleneadenosine 5'-triphosphate, a non-hydrolysable adenosine triphosphate mimic) and structurally diverse ATP competitive chemotypes identified via a high-throughput screening campaign. These structures represent the first set of diverse RIP2-inhibitor co-crystal structures and demonstrate that the protein possesses the ability to adopt multiple DFG-in as well as DFG-out and C-helix out conformations. These structures reveal key protein-inhibitor structural insights and serve as the foundation for establishing a robust structure-based drug design effort to identify both potent and highly selective inhibitors of RIP2 kinase.

The amino-acid substituents of dipeptide substrates of cathepsin C can determine the rate-limiting steps of catalysis.

We examined the cathepsin C-catalyzed hydrolysis of dipeptide substrates of the form Yaa-Xaa-AMC, using steady-state and pre-steady-state kinetic methods. The substrates group into three kinetic profiles based upon the broad range observed for k(cat)/K(a) and k(cat) values, pre-steady-state time courses, and solvent kinetic isotope effects (sKIEs). The dipeptide substrate Gly-Arg-AMC displayed large values for k(cat)/K(a) (1.6 ± 0.09 µM(-1) s(-1)) and k(cat) (255 ± 6 s(-1)), an inverse sKIE on k(cat)/K(a) ((D)(k(cat)/K(a)) = 0.6 ± 0.15), a modest, normal sKIE on k(cat) ((D)k(cat) = 1.6 ± 0.2), and immeasurable pre-steady-state kinetics, indicating an extremely fast pre-steady-state rate (>400 s(-1)). (Errors on fitted values are omitted in the text for clarity but may be found in Table 2.) These results conformed to a kinetic model where the acylation (k(ac)) and deacylation (k(dac)) half-reactions are very fast and similar in value. The second substrate type, Gly-Tyr-AMC and Ser-Tyr-AMC, the latter the subject of a comprehensive kinetic study (Schneck et al. (2008) Biochemistry 47, 8697-8710), were found to be less active substrates compared to Gly-Arg-AMC, with respective k(cat)/K(a) values of 0.49 ± 0.07 µM(-1 )s(-1) and 5.3 ± 0.5 µM(-1 )s(-1), and k(cat) values of 28 ± 1 s(-1) and 25 ± 0.5 s(-1). Solvent kinetic isotope effects for Ser-Tyr-AMC were found to be inverse for k(cat)/K(a) ((D)(k(cat)/K(a)) = 0.74 ± 0.05) and normal for k(cat) ((D)k(cat) = 2.3 ± 0.1) but unlike Gly-Arg-AMC, pre-steady-state kinetics of Gly-Tyr-AMC and Ser-Tyr-AMC were measurable and characterized by a single-exponential burst, with fast transient rates (490 s(-1) and 390 s(-1), respectively), from which it was determined that k(ac) ≫ k(dac) ∼ k(cat). The third substrate type, Gly-Ile-AMC, gave very low values of k(cat)/K(a) (0.0015 ± 0.0001 µM(-1) s(-1)) and k(cat) (0.33 ± 0.02 s(-1)), no sKIEs, ((D)(k(cat)/K(a)) = 1.05 ± 0.5 and (D)k(cat) = 1.06 ± 0.4), and pre-steady-state kinetics exhibited a discernible, but negligible, transient phase. For this third class of substrate, kinetic modeling was consistent with a mechanism in which k(dac) > k(ac) ∼ k(cat), and for which an isotope-insensitive step in the acylation half-reaction is the slowest. The combined results of these studies suggested that the identity of the amino acid at the P(1) position of the substrate is the main determinant of catalysis. On the basis of these kinetic data, together with crystallographic studies of substrate analogues and molecular dynamics analysis with models of acyl-enzyme intermediates, we present a catalytic model derived from the relative rates of the acylation vs deacylation half-reactions of cathepsin C. The chemical steps of catalysis are proposed to be dependent upon the conformational freedom of the amino acid substituents for optimal alignment for thiolation (acylation) or hydrolysis (deacylation). These studies suggest ideas for inhibitor design for papain-family cysteine proteases and strategies to progress drug discovery for other classes of disease-relevant cysteine proteases.

The synthesis and preclinical evaluation in rhesus monkey of [¹8F]MK-6577 and [¹¹C]CMPyPB glycine transporter 1 positron emission tomography radiotracers.

Two positron emission tomography radiotracers for the glycine transporter 1 (GlyT1) are reported here. Each radiotracer is a propylsulfonamide-containing benzamide and was labeled with either carbon-11 or fluorine-18. [¹¹C]CMPyPB was synthesized by the alkylation of a 3-hydroxypyridine precursor using [¹¹C]MeI, and [¹8F]MK-6577 was synthesized by a nucleophilic aromatic substitution reaction using a 2-chloropyridine precursor. Each tracer shows good uptake into rhesus monkey brain with the expected distribution of highest uptake in the pons, thalamus, and cerebellum and lower uptake in the striatum and gray matter of the frontal cortex. In vivo blockade and chase studies of [¹8F]MK-6577 showed a large specific signal and reversible binding. In vitro autoradiographic studies with [¹8F]MK-6577 showed a large specific signal in both rhesus monkey and human brain slices and a distribution consistent with the in vivo results and those reported in the literature. In vivo metabolism studies in rhesus monkeys demonstrated that only more-polar metabolites are formed for each tracer. Of these two tracers, [¹8F]MK-6577 was more extensively characterized and is a promising clinical positron emission tomography tracer for imaging GlyT1 and for measuring GlyT1 occupancy of therapeutic compounds.

Phenoxyacetic acids as PPARδ partial agonists: synthesis, optimization, and in vivo efficacy.

A series of phenoxyacetic acids as subtype selective and potent hPPARδ partial agonists is described. Many analogues were readily accessible via a single solution-phase synthetic route which resulted in the rapid identification of key structure-activity relationships (SAR), and the discovery of two potent exemplars which were further evaluated in vivo. Details of the SAR, optimization, and in vivo efficacy of this series are presented herein.

Synthesis and structure-activity relationships of a series of 3-aryl-4-isoxazolecarboxamides as a new class of TGR5 agonists.

A series of 3-aryl-4-isoxazolecarboxamides identified from a high-throughput screening campaign as novel, potent agonists of the human TGR5 G-protein-coupled receptor is described. Many analogues were readily accessible via solution-phase synthesis which resulted in the rapid identification of key structure-activity relationships (SAR), and the discovery of potent exemplars (up to pEC50=9). Details of the SAR and optimization of this series are presented herein.

Parallel synthesis of N-biaryl quinolone carboxylic acids as selective M(1) positive allosteric modulators.

An iterative analog library synthesis approach was employed in the exploration of a quinolone carboxylic acid series of selective M(1) positive allosteric modulators, and strategies for improving potency and plasma free fraction were identified.

Discovery of GlyT1 inhibitors with improved pharmacokinetic properties.

Glycine transporter 1 (GlyT1) represents a novel target for the treatment of schizophrenia via the potentiation of glutamatergic NMDA receptors. The discovery of 4,4-disubstituted piperidine inhibitors of GlyT1 which exhibit improved pharmacokinetic properties, including oral bioavailability, is discussed.

Discovery and Lead-Optimization of 4,5-Dihydropyrazoles as Mono-Kinase Selective, Orally Bioavailable and Efficacious Inhibitors of Receptor Interacting Protein 1 (RIP1) Kinase.

RIP1 kinase regulates necroptosis and inflammation and may play an important role in contributing to a variety of human pathologies, including inflammatory and neurological diseases. Currently, RIP1 kinase inhibitors have advanced into early clinical trials for evaluation in inflammatory diseases such as psoriasis, rheumatoid arthritis, and ulcerative colitis and neurological diseases such as amyotrophic lateral sclerosis and Alzheimer's disease. In this paper, we report on the design of potent and highly selective dihydropyrazole (DHP) RIP1 kinase inhibitors starting from a high-throughput screen and the lead-optimization of this series from a lead with minimal rat oral exposure to the identification of dihydropyrazole 77 with good pharmacokinetic profiles in multiple species. Additionally, we identified a potent murine RIP1 kinase inhibitor 76 as a valuable in vivo tool molecule suitable for evaluating the role of RIP1 kinase in chronic models of disease. DHP 76 showed efficacy in mouse models of both multiple sclerosis and human retinitis pigmentosa.

Discovery of a First-in-Class Receptor Interacting Protein 1 (RIP1) Kinase Specific Clinical Candidate (GSK2982772) for the Treatment of Inflammatory Diseases.

RIP1 regulates necroptosis and inflammation and may play an important role in contributing to a variety of human pathologies, including immune-mediated inflammatory diseases. Small-molecule inhibitors of RIP1 kinase that are suitable for advancement into the clinic have yet to be described. Herein, we report our lead optimization of a benzoxazepinone hit from a DNA-encoded library and the discovery and profile of clinical candidate GSK2982772 (compound 5), currently in phase 2a clinical studies for psoriasis, rheumatoid arthritis, and ulcerative colitis. Compound 5 potently binds to RIP1 with exquisite kinase specificity and has excellent activity in blocking many TNF-dependent cellular responses. Highlighting its potential as a novel anti-inflammatory agent, the inhibitor was also able to reduce spontaneous production of cytokines from human ulcerative colitis explants. The highly favorable physicochemical and ADMET properties of 5, combined with high potency, led to a predicted low oral dose in humans.

Cell-Based Selection Expands the Utility of DNA-Encoded Small-Molecule Library Technology to Cell Surface Drug Targets: Identification of Novel Antagonists of the NK3 Tachykinin Receptor.

DNA-encoded small-molecule library technology has recently emerged as a new paradigm for identifying ligands against drug targets. To date, this technology has been used with soluble protein targets that are produced and used in a purified state. Here, we describe a cell-based method for identifying small-molecule ligands from DNA-encoded libraries against integral membrane protein targets. We use this method to identify novel, potent, and specific inhibitors of NK3, a member of the tachykinin family of G-protein coupled receptors (GPCRs). The method is simple and broadly applicable to other GPCRs and integral membrane proteins. We have extended the application of DNA-encoded library technology to membrane-associated targets and demonstrate the feasibility of selecting DNA-tagged, small-molecule ligands from complex combinatorial libraries against targets in a heterogeneous milieu, such as the surface of a cell.

Discovery of positive allosteric modulators for the metabotropic glutamate receptor subtype 5 from a series of N-(1,3-diphenyl-1H- pyrazol-5-yl)benzamides that potentiate receptor function in vivo.

This report describes the discovery of the first centrally active allosteric modulators of the metabotropic glutamate receptor subtype 5 (mGluR5). Appropriately substituted N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamides (e.g., 8) have been identified as a novel class of potent positive allosteric modulators of mGluR5 that potentiate the response to glutamate. An iterative analogue library synthesis approach provided potentiators with excellent potency and selectivity for mGluR5 (vs mGluRs 1-4, 7, 8). Compound 8q demonstrated in vivo proof of concept in an animal behavior model where known antipsychotics are active, supporting the development of new antipsychotics based on the NMDA hypofunction model for schizophrenia.

Efficient synthesis of imidazoles from aldehydes and 1,2-diketones using microwave irradiation.

[reaction: see text] A simple, high-yielding synthesis of 2,4,5-trisubstituted imidazoles from 1,2-diketones and aldehydes in the presence of NH(4)OAc is described. Under microwave irradiation, alkyl-, aryl-, and heteroaryl-substituted imidazoles are formed in yields ranging from 80 to 99%. Short syntheses of lepidiline B and trifenagrel illustrate the utility of this approach.

Nω-NITRO-Nω'-SUBSTITUTED GUANIDINES: A SIMPLE CLASS OF NITRIC OXIDE SYNTHASE INHIBITORS.

A series of Nω-nitro-Nω'-substituted guanidines has been prepared as potential inhibitors of the human Nitric Oxide Synthase (NOS) isoforms. The reported utility of aminoguanidine and nitroarginine in iNOS inhibition points to a potential similar utility for analogs of nitro-guanidine. The compound library was tested against the three isoforms of Nitric Oxide Synthase (eNOS, iNOS and nNOS). Several candidates showed excellent activity and good selectivity for nNOS. One particular compound even demonstrated good selectivity for iNOS. The potential usefulness of such selective inhibitors is discussed.

Discovery of 3-aryl-4-isoxazolecarboxamides as TGR5 receptor agonists.

A series of 3-aryl-4-isoxazolecarboxamides identified from a high-throughput screening campaign as novel, potent small molecule agonists of the human TGR5 G-protein coupled receptor is described. Subsequent optimization resulted in the rapid identification of potent exemplars 6 and 7 which demonstrated improved GLP-1 secretion in vivo via an intracolonic dose coadministered with glucose challenge in a canine model. These novel TGR5 receptor agonists are potentially useful therapeutics for metabolic disorders such as type II diabetes and its associated complications.

Challenges in the development of mGluR5 positive allosteric modulators: the discovery of CPPHA.

This Letter describes, for the first time, the synthesis and SAR, developed through an iterative analog library approach, that led to the discovery of the positive allosteric modulator (PAM) of the metabotropic glutamate receptor mGluR5 CPPHA. Binding to a unique allosteric binding site distinct from other mGluR5 PAMs, CPPHA has been the focus of numerous pharmacology studies by several laboratories.

p38 MAP kinase inhibitors. Part 3: SAR on 3,4-dihydropyrimido[4,5-d]pyrimidin-2-ones and 3,4-dihydropyrido[4,3-d]pyrimidin-2-ones.

p38 inhibitors based on 3,4-dihydropyrimido[4,5-d]pyrimidin-2-one and 3,4-dihydropyrido[4,3-d]pyrimidin-2-one platforms were synthesized and preliminary SAR explored. Among the pyrimido-pyrimidones the emergence of two sub-types of analogs-C7-amino-pyrimidines such as 24 and C7-amino-piperidines such as 42-characterized with good p38 inhibition and better off-target profiles in terms of ion channel activities was significant. Representative compound 54 in the pyrido-pyrimidone class was found to be equipotent with corresponding analog in the quinazolinone series.

Acetonitrile/water gas-phase reaction products observed by use of atmospheric pressure chemical ionization: adducts formed with sulfonamides.

Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the two most common mass spectrometric ionization methods used in the pharmaceutical industry. However, APCI analysis can sometimes lead to ambiguity in compound characterization and quantitation due to gas-phase reactions occurring between acetonitrile and water in the plasma, and between these plasma-generated compounds and the analyte. During the analysis of various sultams and sulfonamides we observed signals corresponding to m/z [M+44](+) and [M+60](+). Various solvent conditions and collisionally activated dissociation MS(n) experiments revealed that under the high-energy plasma conditions of APCI, the acetonitrile/water solvent mixture reacts undergoing acid-catalyzed hydrolysis producing acetamide, 59 Da. Further, the highly reactive 43 Da species ethanimine is also produced. These two compounds, normally not observed in APCI analysis, are stabilized by the sulfonamide and appear as adduct species in the mass spectra. The sulfone oxygens and the lone pair of electrons on the amide nitrogen play a role in stabilizing this adduct.

A novel selective positive allosteric modulator of metabotropic glutamate receptor subtype 5 has in vivo activity and antipsychotic-like effects in rat behavioral models.

We found that 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) is a potent and selective positive allosteric modulator of the metabotropic glutamate receptor subtype 5 (mGluR5). In Chinese hamster ovary cells expressing human mGluR5, CDPPB potentiated threshold responses to glutamate in fluorometric Ca2+ assays more than 7-fold with an EC50 value of approximately 27 nM. At 1 microM, CDPPB shifted mGluR5 agonist concentration response curves to glutamate, quisqualate, and (R,S)-3,5-dihydroxyphenylglycine 3- to 9-fold to the left. At higher concentrations, CDPPB exhibited agonist-like activity on cells expressing mGluR5. No other activity was observed on any other mGluR or cell type at concentrations up to 10 microM. CDPPB had no effect on [3H]quisqualate binding to mGluR5 but did compete for binding of [3H]methoxyPEPy, an analog of the selective mGluR5 negative allosteric modulator MPEP. CDPPB was found to be brain penetrant and reversed amphetamine-induced locomotor activity and amphetamine-induced deficits in prepulse inhibition in rats, two models sensitive to antipsychotic drug treatment. These results demonstrate that positive allosteric modulation of mGluR5 produces behavioral effects, suggesting that such modulation serves as a viable approach to increasing mGluR5 activity in vivo. These effects are consistent with the hypothesis that allosteric potentiation of mGluR5 may provide a novel approach for development of antipsychotic agents.