Regulation of cardiac nitric oxide signaling by nuclear ß-adrenergic and endothelin receptors.

At the cell surface, ßARs and endothelin receptors can regulate nitric oxide (NO) production. ß-adrenergic receptors (ßARs) and type B endothelin receptors (ETB) are present in cardiac nuclear membranes and regulate transcription. The present study investigated the role of the NO pathway in the regulation of gene transcription by these nuclear G protein-coupled receptors. Nitric oxide production and transcription initiation were measured in nuclei isolated from the adult rat heart. The cell-permeable fluorescent dye 4,5-diaminofluorescein diacetate (DAF2 DA) was used to provide a direct assessment of nitric oxide release. Both isoproterenol and endothelin increased NO production in isolated nuclei. Furthermore, a ß3AR-selective agonist, BRL 37344, increased NO synthesis whereas the ß1AR-selective agonist xamoterol did not. Isoproterenol increased, whereas ET-1 reduced, de novo transcription. The NO synthase inhibitor l-NAME prevented isoproterenol from increasing either NO production or de novo transcription. l-NAME also blocked ET-1-induced NO-production but did not alter the suppression of transcription initiation by ET-1. Inhibition of the cGMP-dependent protein kinase (PKG) using KT5823 also blocked the ability of isoproterenol to increase transcription initiation. Furthermore, immunoblotting revealed eNOS, but not nNOS, in isolated nuclei. Finally, caged, cell-permeable isoproterenol and endothelin-1 analogs were used to selectively activate intracellular ß-adrenergic and endothelin receptors in intact adult cardiomyocytes. Intracellular release of caged ET-1 or isoproterenol analogs increased NO production in intact adult cardiomyocytes. Hence, activation of the NO synthase/guanylyl cyclase/PKG pathway is necessary for nuclear ß3ARs to increase de novo transcription. Furthermore, we have demonstrated the potential utility of caged receptor ligands in selectively modulating signaling via endogenous intracellular G protein-coupled receptors.

The identification of 4,7-disubstituted naphthoic acid derivatives as UDP-competitive antagonists of P2Y14.

A weak, UDP-competitive antagonist of the pyrimidinergic receptor P2RY(14) with a naphthoic acid core was identified through high-throughput screening. Optimization provided compounds with improved potency but poor pharmacokinetics. Acylglucuronidation was determined to be the major route of metabolism. Increasing the electron-withdrawing nature of the substituents markedly reduced glucuronidation and improved the pharmacokinetic profile. Additional optimization led to the identification of compound 38 which is an 8 nM UDP-competitive antagonist of P2Y(14) with a good pharmacokinetic profile.

Synthesis and SAR of pyrimidine-based, non-nucleotide P2Y14 receptor antagonists.

A weak antagonist of the pyrimidinergic receptor P2Y(14) containing a dihydropyridopyrimidine core was identified through high-throughput screening. Subsequent optimization led to potent, non-UTP competitive antagonists and represent the first reported non-nucleotide antagonists of this receptor. Compound 18q was identified as a 10 nM P2Y(14) antagonist with good oral bioavailability and provided sufficient exposure in mice to be used as a tool for future in vivo studies.

Difluoroethylamines as an amide isostere in inhibitors of cathepsin K.

The trifluoroethylamine group found in cathepsin K inhibitors like odanacatib can be replaced by a difluoroethylamine group. This change increased the basicity of the nitrogen which positively impacted the log D. This translated into an improved oral bioavailability in pre-clinical species. Difluoroethylamine compounds exhibit a similar potency against cathepsin K and selectivity profile against other cathepsins when compared to trifluoroethylamine analogs.

The discovery of MK-0674, an orally bioavailable cathepsin K inhibitor.

MK-0674 is a potent and selective cathepsin K inhibitor from the same structural class as odanacatib with a comparable inhibitory potency profile against Cat K. It is orally bioavailable and exhibits long half-life in pre-clinical species. In vivo studies using deuterated MK-0674 show stereoselective epimerization of the alcohol stereocenter via an oxidation/reduction cycle. From in vitro incubations, two metabolites could be identified: the hydroxyleucine and the glucuronide conjugate which were confirmed using authentic synthetic standards.

Identification of a nonbasic, nitrile-containing cathepsin K inhibitor (MK-1256) that is efficacious in a monkey model of osteoporosis.

Herein, we report on the identification of nonbasic, potent, and highly selective, nitrile-containing cathepsin K (Cat K) inhibitors that are built on our previously identified cyclohexanecarboxamide core structure. Subsequent to our initial investigations, we have found that incorporation of five-membered heterocycles as P2-P3 linkers allowed for the introduction of a methyl sulfone P3-substitutent that was not tolerated in inhibitors containing a six-membered aromatic P2-P3 linker. The combination of a five-membered N-methylpyrazole linker and a methyl sulfone in P3 yielded subnanomolar Cat K inhibitors that were minimally shifted (<10-fold) in our functional bone resorption assay. Issues that arose because of metabolic demethylation of the N-methylpyrazole were addressed through introduction of a 2,2,2-trifluoroethyl substituent. This culminated in the identification of 31 (MK-1256), a potent (Cat K IC 50 = 0.62 nM) and selective (>1100-fold selectivity vs Cat B, L, S, C, H, Z, and V, 110-fold vs Cat F) inhibitor of cathepsin K that is efficacious in a monkey model of osteoporosis.

Discovery of [(3-bromo-7-cyano-2-naphthyl)(difluoro)methyl]phosphonic acid, a potent and orally active small molecule PTP1B inhibitor.

A series of quinoline/naphthalene-difluoromethylphosphonates were prepared and were found to be potent PTP1B inhibitors. Most of these compounds bearing polar functionalities or large lipophilic residues did not show appreciable oral bioavailability in rodents while small and less polar analogs displayed moderate to good oral bioavailability. The title compound was found to have the best overall potency and pharmacokinetic profile and was found to be efficacious in animal models of diabetes and cancer.

Substituted 2,2-bisaryl-bicycloheptanes as novel and potent inhibitors of 5-lipoxygenase activating protein.

The discovery and SAR of a novel series of substituted 2,2-bisaryl-bicycloheptane inhibitors of 5-lipoxygenase activating protein (FLAP) are herein described. SAR studies have shown that 2,5-substitution on the exo-aryl group is optimal for potency. The most potent compounds in this series have an ortho-nitrogen aryl linked with a methyleneoxy as the 5-substituent and a polar group such as a urethane as the 2-substituent. One of the most potent compounds identified is the 5-benzothiazolymethoxy-2-pyridinylcarbamate derivative 2 (FLAP IC(50)=2.8 nM) which blocks 89% of ragweed induced urinary LTE(4) production in dogs (at an I.V. dose of 2.5 microg/kg/min). This compound inhibits calcium ionophore stimulated LTB(4) production in both human polymorphonuclear (PMN) leukocytes and human whole blood (IC(50)=2.0 and 33 nM, respectively).

The discovery of odanacatib (MK-0822), a selective inhibitor of cathepsin K.

Odanacatib is a potent, selective, and neutral cathepsin K inhibitor which was developed to address the metabolic liabilities of the Cat K inhibitor L-873724. Substituting P1 and modifying the P2 side chain led to a metabolically robust inhibitor with a long half-life in preclinical species. Odanacatib was more selective in whole cell assays than the published Cat K inhibitors balicatib and relacatib. Evaluation in dermal fibroblast culture showed minimal intracellular collagen accumulation relative to less selective Cat K inhibitors.

Conformation-assisted inhibition of protein-tyrosine phosphatase-1B elicits inhibitor selectivity over T-cell protein-tyrosine phosphatase.

PTP-1B represents an attractive target for the treatment of type 2 diabetes and obesity. Given the role that protein phosphatases play in the regulation of many biologically relevant processes, inhibitors against PTP-1B must be not only potent, but also selective. It has been extremely difficult to synthesize inhibitors that are selective over the highly homologous TCPTP. We have successfully exploited the conservative Leu119 to Val substitution between the two enzymes to synthesize a PTP-1B inhibitor that is an order of magnitude more selective over TCPTP. Structural analyses of PTP-1B/inhibitor complexes show a conformation-assisted inhibition mechanism as the basis for selectivity. Such an inhibitory mechanism may be applicable to other homologous enzymes.

Identification of a potent and selective non-basic cathepsin K inhibitor.

Based on our previous study with trifluoroethylamine as a P2-P3 amide isostere of cathepsin K inhibitor, further optimization led to identification of compound 22 (L-873724) as a potent and selective non-basic cathepsin K inhibitor. This compound showed excellent pharmacokinetics and efficacy in an ovariectomized (OVX) rhesus monkey model. The volumes of distribution close to unity were consistent with this compound not being lysosomotropic, which is a characteristic of basic cathepsin K inhibitors.

Enzyme occupancy measurement of intracellular protein tyrosine phosphatase 1B using photoaffinity probes.

Protein tyrosine phosphatase 1B (PTP1B) is believed to be one of the enzymes involved in down-regulating the insulin receptor and is a drug target for the treatment of type II diabetes. To better understand the in vitro and in vivo behavior of PTP1B inhibitors, a cell-based assay to directly measure enzyme occupancy of PTP1B by inhibitors using photoaffinity labeling was developed. Two photoaffinity probes were synthesized containing the photolabile diazirine moiety. These photoprobes were specific for PTP1B and T-cell protein tyrosine phosphatase over CD45, with the most potent photoprobe having an IC(50) value of 0.2nM for PTP1B. Activation of the photoprobes with a 40-W UV lamp in the presence of purified AspTyrLysAspAspAspAspLys (Flag)-PTP1B formed a 1:1 irreversible adduct with the enzyme. The photolabeling was competed by known PTP1B inhibitors, vanadate, and the peptide inhibitor N-benzoyl-l-glutamyl-[4-phosphono(difluoromethyl)]-l-phenylalanyl-[4-phosphono(difluoromethyl)]l-phenylalanineamide (BzN-EJJ-amide). In HepG2 (human hepatoma cell line) cells, endogenous PTP1B was labeled by the UV-activated photoprobes in both lysed and intact cells. Enzyme occupancy measurements were conducted with a series of PTP1B inhibitors using the photoprobe affinity assay. Several compounds were shown to bind to endogenous PTP1B in the HepG2 intact cells.

Synthesis of a novel peptidic photoaffinity probe for the PTP-1B enzyme.

The synthesis of a novel radioactive peptidic photoaffinity probe for the PTP-1B enzyme as well as some SAR leading to the choice of this compound as a photoaffinity probe are presented.

Structure based design of a series of potent and selective non peptidic PTP-1B inhibitors.

A series of benzotriazole phenyldifluoromethylphosphonic acids were found to be potent PTP-1B inhibitors. Molecular modeling on the X-ray crystal structure of the lead structure led to the design of potent PTP-1B inhibitors that show moderate selectivity against TC-PTP, a very closely related protein tyrosine phosphatase.

The structural basis for the selectivity of benzotriazole inhibitors of PTP1B.

Protein tyrosine phosphatase 1B (PTP1B) has been implicated in the regulation of the insulin signaling pathway and represents an attractive target for the design of inhibitors in the treatment of type 2 diabetes and obesity. Inspection of the structure of PTP1B indicates that potent PTP1B inhibitors may be obtained by targeting a secondary aryl phosphate-binding site as well as the catalytic site. We report here the crystal structures of PTP1B in complex with first and second generation aryldifluoromethyl-phosphonic acid inhibitors. While all compounds bind in a previously unexploited binding pocket near the primary binding site, the second generation compounds also reach into the secondary binding site, and exhibit moderate selectivity for PTP1B over the closely related T-cell phosphatase. The molecular basis for the selectivity has been confirmed by single point mutation at position 52, where the two phosphatases differ by a phenylalanine-to-tyrosine switch. These compounds present a novel platform for the development of potent and selective PTP1B inhibitors.

Pyridazinones as selective cyclooxygenase-2 inhibitors.

Pyridazinone was found to be an excellent core template for selective COX-2 inhibitors. Two potent, selective and orally active COX-2 inhibitors, which were highly efficacious in rat paw edema and rat pyresis models, have been obtained.

3,4-Diaryl-5-hydroxyfuranones: highly selective inhibitors of cyclooxygenase-2 with aqueous solubility.

The introduction of a hydroxyl group into the 5-position of the diaryl furanone system provides highly selective inhibitors of cyclooxygenase-2. These molecules can be converted into their sodium salts which are water soluble, facilitating intravenous formulation. These salts show excellent potency in rat models of pain, fever and inflammation.