Discovery and characterization of [(cyclopentyl)ethyl]benzoic acid inhibitors of microsomal prostaglandin E synthase-1.

We describe a novel class of acidic mPGES-1 inhibitors with nanomolar enzymatic and human whole blood (HWB) potency. Rational design in conjunction with structure-based design led initially to the identification of anthranilic acid 5, an mPGES-1 inhibitor with micromolar HWB potency. Structural modifications of 5 improved HWB potency by over 1000×, reduced CYP2C9 single point inhibition, and improved rat clearance, which led to the selection of [(cyclopentyl)ethyl]benzoic acid compound 16 for clinical studies. Compound 16 showed an IC80 of 24nM for inhibition of PGE2 formation in vitro in LPS-stimulated HWB. A single oral dose resulted in plasma concentrations of 16 that exceeded its HWB IC80 in both rat (5mg/kg) and dog (3mg/kg) for over twelve hours.

Identification and Characterization of Novel Microsomal Prostaglandin E Synthase-1 Inhibitors for Analgesia.

Prostaglandin (PG) E2 plays a critical role in eliciting inflammation. Nonsteroidal anti-inflammatory drugs and selective inhibitors of cyclooxygenase, which block PGE2 production, have been used as key agents in treating inflammation and pain associated with arthritis and other conditions. However, these agents have significant side effects such as gastrointestinal bleeding and myocardial infarction, since they also block the production of prostanoids that are critical for other normal physiologic functions. Microsomal prostaglandin E2 synthase-1 is a membrane-bound terminal enzyme in the prostanoid pathway, which acts downstream of cyclooxygenase 2 and is responsible for PGE2 production during inflammation. Thus, inhibition of this enzyme would be expected to block PGE2 production without inhibiting other prostanoids and would provide analgesic efficacy without the side effects. In this report, we describe novel microsomal prostaglandin E2 synthase-1 inhibitors that are potent in blocking PGE2 production and are efficacious in a guinea pig monoiodoacetate model of arthralgia. These molecules may be useful in treating the signs and symptoms associated with arthritis.

Discovery of substituted-2,4-dimethyl-(naphthalene-4-carbonyl)amino-benzoic acid as potent and selective EP4 antagonists.

A novel series of EP4 antagonists, based on a quinoline scaffold, has been discovered. Medicinal chemistry efforts to optimize the potency of the initial hit are described. A highly potent compound in a clinically relevant human whole blood assay was identified. Selectivity and pharmacokinetic profiles of this compound are discussed.

Discovery of potent aryl-substituted 3-[(3-methylpyridine-2-carbonyl) amino]-2,4-dimethyl-benzoic acid EP4 antagonists with improved pharmacokinetic profile.

Two new series of EP4 antagonists containing a 3-methylaryl-2-carbonyl core have been identified. One series has a 3-substituted-phenyl core, while the other one incorporates a 3-substituted pyridine. Both series led to compounds with potent activity in functional and human whole blood (hWB) assays. In the pyridine series, compound 7a was found to be a highly potent and selective EP4 antagonist, with suitable rat and dog pharmacokinetic profiles.

Identification and biological activity of 6-alkyl-substituted 3-methyl-pyridine-2-carbonyl amino dimethyl-benzoic acid EP4 antagonists.

Continued SAR optimization of a series of 3-methylpyridine-2-carbonyl amino-2,4-dimethyl-benzoic acid led to the selection of compound 4f for clinical studies. Compound 4f showed an IC50 of 123nM for inhibition of PGE2-induced TNFα reduction in an ex vivo LPS-stimulated human whole blood assay (showing >10-fold increase over clinical compound CJ-023,423). Pharmacokinetic profile, selectivity and in vivo efficacy comparing 4f to NSAID diclofenac in the monoiodoacetic acid (MIA) pain model and adjuvant induced arthritis (AIA) inflammatory model are included.

Characterization of 3,3-dimethyl substituted N-aryl piperidines as potent microsomal prostaglandin E synthase-1 inhibitors.

Here we report on novel, potent 3,3-dimethyl substituted N-aryl piperidine inhibitors of microsomal prostaglandin E synthases-1(mPGES-1). Example 14 potently inhibited PGE2 synthesis in an ex vivo human whole blood (HWB) assay with an IC50 of 7nM. In addition, 14 had no activity in human COX-1 or COX-2 assays at 30µM, and failed to inhibit human mPGES-2 at 62.5µM in a microsomal prep assay. These data are consistent with selective mPGES-1-mediated reduction of PGE2. In dog, 14 had oral bioavailability (74%), clearance (3.62mL/(min*kg)) and volume of distribution (Vd,ss=1.6L/kg) values within our target ranges. For these reasons, 14 was selected for further study.

Discovery and characterization of a potent and selective EP4 receptor antagonist.

EP4 is a prostaglandin E2 receptor that is a target for potential anti-nociceptive therapy. Described herein is a class of amphoteric EP4 antagonists which reverses PGE2-induced suppression of TNFα production in human whole blood. From this class, a potent and highly bioavailable compound (6) has been selected for potential clinical studies. EP4 binding and functional data, selectivity, and pharmacokinetic properties of this compound are included.

Structure-based, multi-targeted drug discovery approach to eicosanoid inhibition: Dual inhibitors of mPGES-1 and 5-lipoxygenase activating protein (FLAP).

BACKGROUND: Due to the importance of both prostaglandins (PGs) and leukotrienes (LTs) as pro-inflammatory mediators, and the potential for eicosanoid shunting in the presence of pathway target inhibitors, we have investigated an approach to inhibiting the formation of both PGs and LTs as part of a multi-targeted drug discovery effort. METHODS: We generated ligand-protein X-ray crystal structures of known inhibitors of microsomal prostaglandin E2 synthase-1 (mPGES-1) and the 5-Lipoxygenase Activating Protein (FLAP), with their respective proteins, to understand the overlapping pharmacophores. We subsequently used molecular modeling and structure-based drug design (SBDD) to identify hybrid structures intended to inhibit both targets. RESULTS: This work enabled the preparation of compounds 4 and 5, which showed potent in vitro inhibition of both targets. SIGNIFICANCE: Our findings enhance the structural understanding of mPGES-1 and FLAP's unique ligand binding pockets and should accelerate the discovery of additional dual inhibitors for these two important integral membrane protein drug targets.

Identification and characterization of noncalcemic, tissue-selective, nonsecosteroidal vitamin D receptor modulators.

Vitamin D receptor (VDR) ligands are therapeutic agents for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. VDR ligands also show immense potential as therapeutic agents for autoimmune diseases and cancers of skin, prostate, colon, and breast as well as leukemia. However, the major side effect of VDR ligands that limits their expanded use and clinical development is hypercalcemia that develops as a result of the action of these compounds mainly on intestine. In order to discover VDR ligands with less hypercalcemia liability, we sought to identify tissue-selective VDR modulators (VDRMs) that act as agonists in some cell types and lack activity in others. Here, we describe LY2108491 and LY2109866 as nonsecosteroidal VDRMs that function as potent agonists in keratinocytes, osteoblasts, and peripheral blood mononuclear cells but show poor activity in intestinal cells. Finally, these nonsecosteroidal VDRMs were less calcemic in vivo, and LY2108491 exhibited more than 270-fold improved therapeutic index over the naturally occurring VDR ligand 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in an in vivo preclinical surrogate model of psoriasis.

Analgesic and anti-inflammatory properties of novel, selective, and potent EP4 receptor antagonists.

Prostaglandin (PG) E2 is the key driver of inflammation associated with arthritic conditions. Inhibitors of PGE 2 production (NSAIDs and Coxibs) are used to treat these conditions, but carry significant side effect risks due to the inhibition of all prostanoids that play important physiological function. The activities of PGE 2 are transduced through various receptor sub-types. Prostaglandin E2 type 4 receptor (EP4) is associated with the development of inflammation and autoimmunity. We therefore are interested in identifying novel EP4 antagonists to treat the signs and symptoms of arthritis without the potential side effects of PGE 2 modulators such as NSAIDs and Coxibs. Novel EP4 antagonists representing distinct chemical scaffolds were identified using a variety of in vitro functional assays and were shown to be selective and potent. The compounds were shown to be efficacious in animal models of analgesia, inflammation, and arthritis.

Discovery and Characterization of 2-Acylaminoimidazole Microsomal Prostaglandin E Synthase-1 Inhibitors.

As part of a program aimed at the discovery of antinociceptive therapy for inflammatory conditions, a screening hit was found to inhibit microsomal prostaglandin E synthase-1 (mPGES-1) with an IC50 of 17.4 µM. Structural information was used to improve enzyme potency by over 1000-fold. Addition of an appropriate substituent alleviated time-dependent cytochrome P450 3A4 (CYP3A4) inhibition. Further structure-activity relationship (SAR) studies led to 8, which had desirable potency (IC50 = 12 nM in an ex vivo human whole blood (HWB) assay) and absorption, distribution, metabolism, and excretion (ADME) properties. Studies on the formulation of 8 identified 8·H3PO4 as suitable for clinical development. Omission of a lipophilic portion of the compound led to 26, a readily orally bioavailable inhibitor with potency in HWB comparable to celecoxib. Furthermore, 26 was selective for mPGES-1 inhibition versus other mechanisms in the prostanoid pathway. These factors led to the selection of 26 as a second clinical candidate.

Novel Autotaxin Inhibitors for the Treatment of Osteoarthritis Pain: Lead Optimization via Structure-Based Drug Design.

In an effort to develop a novel therapeutic agent aimed at addressing the unmet need of patients with osteoarthritis pain, we set out to develop an inhibitor for autotaxin with excellent potency and physical properties to allow for the clinical investigation of autotaxin-induced nociceptive and neuropathic pain. An initial hit identification campaign led to an aminopyrimidine series with an autotaxin IC50 of 500 nM. X-ray crystallography enabled the optimization to a lead compound that demonstrated favorable potency (IC50 = 2 nM), PK properties, and a robust PK/PD relationship.

Crystal Structures of mPGES-1 Inhibitor Complexes Form a Basis for the Rational Design of Potent Analgesic and Anti-Inflammatory Therapeutics.

Microsomal prostaglandin E synthase 1 (mPGES-1) is an α-helical homotrimeric integral membrane inducible enzyme that catalyzes the formation of prostaglandin E2 (PGE2) from prostaglandin H2 (PGH2). Inhibition of mPGES-1 has been proposed as a therapeutic strategy for the treatment of pain, inflammation, and some cancers. Interest in mPGES-1 inhibition can, in part, be attributed to the potential circumvention of cardiovascular risks associated with anti-inflammatory cyclooxygenase 2 inhibitors (coxibs) by targeting the prostaglandin pathway downstream of PGH2 synthesis and avoiding suppression of antithrombotic prostacyclin production. We determined the crystal structure of mPGES-1 bound to four potent inhibitors in order to understand their structure-activity relationships and provide a framework for the rational design of improved molecules. In addition, we developed a light-scattering-based thermal stability assay to identify molecules for crystallographic studies.

A Nonsecosteroidal Vitamin D Receptor Modulator Ameliorates Experimental Autoimmune Encephalomyelitis without Causing Hypercalcemia.

Vitamin D receptor (VDR) agonists are currently the agents of choice for the treatment of psoriasis, a skin inflammatory indication that is believed to involve an autoimmune component. 1,25-dihydroxyvitamin D3 [1,25-(OH)(2)D(3)], the biologically active metabolite of vitamin D, has shown efficacy in animal autoimmune disease models of multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, and type I diabetes. However, the side effect of 1,25-(OH)(2)D(3) and its synthetic secosteroidal analogs is hypercalcemia, which is a major impediment in their clinical development for autoimmune diseases. Hypercalcemia develops as a result of the action of VDR agonists on the intestine. Here, we describe the identification of a VDR modulator (VDRM) compound A that was transcriptionally less active in intestinal cells and as a result exhibited less calcemic activity in vivo than 1,25-(OH)(2)D(3). Cytokine analysis indicated that the VDRM not only modulated the T-helper cell balance from Th1 to Th2 effector function but also inhibited Th17 differentiation. Finally, we demonstrate that the oral administration of compound A inhibited the induction and progress of experimental autoimmune encephalomyelitis in mice without causing hypercalcemia.

Regulation of NFATc2 gene expression by the transcription factor Runx2.

NFATc2 is a transcription factor that has been shown to function as a repressor of cartilage cell growth and differentiation in mice. In order to understand the transcriptional regulation of NFATc2 gene expression, we have cloned and characterized approximately 2.5 kb 5'-flanking regions of the mouse and human NFATc2 genes. Sequence analysis of the promoters revealed putative binding sites for the Runx family of transcription factors, of which one member, Runx2, plays a key role in chondrocyte maturation and osteoblast differentiation. Using promoter-reporter assays we have shown that Runx2 overexpression results in a significant increase in NFATc2 transactivation in fibroblastic, mesenchymal and chondrocytic cells. Runx2 overexpression also resulted in a substantial increase in endogenous NFATc2 mRNA levels in C3H10T1/2 mesenchymal cells implicating the NFATc2 gene as a potential downstream target of Runx2. Our results suggest that the role of Runx2 in promoting chondrocyte maturation and hypertrophy may be mediated, at least in part, via the stimulation of NFATc2 expression.

Differential regulation of cytokine-induced MMP-1 and MMP-13 expression by p38 kinase inhibitors in human chondrosarcoma cells: potential role of Runx2 in mediating p38 effects.

OBJECTIVE: To investigate mitogen activated protein (MAP) kinase pathways for their ability to differentially regulate the expression of matrix metalloprotease (MMP)-1 and -13 in human chondrosarcoma cells using pathway-selective inhibitors. DESIGN: Human chondrosarcoma cell lines (SW1353 and JJ012) and human articular chondrocytes (HACs) were treated with cytokines (IL-1beta and TNFalpha) and the expression of MMP-1 and -13 was analyzed. The effects of MAP kinase inhibitors on cytokine-induced expression of MMP-1 and -13 were evaluated using ELISA and Western blot analyses. The possible involvement of the Runx2 pathway in mediating p38 effects on MMP-13 expression was analyzed using promoter-reporter assays, ELISA and immunoprecipitation analyses. RESULTS: IL-1beta and TNFalpha strongly induced the expression of MMP-1 and -13 in SW1353 cells and HACs, whereas only TNFalpha was found to induce the expression of these two MMPs in JJ012 cells. Cytokine treatment did not result in a significant increase in the activity of MMPs because of the excess production of endogenous tissue inhibitors of metalloproteases (TIMPs). Treatment with p38 kinase inhibitors (SB203580 and SB242235) strongly inhibited cytokine-induced MMP-13 expression in a dose-dependent fashion while having a somewhat weaker inhibitory effect on MMP-1 expression. In contrast, inhibitors of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) pathways did not inhibit the expression of either MMP. Overexpression of Runx2 robustly stimulated the transcriptional activation of MMP-13 but had no effect on MMP-1 expression. Furthermore, IL-1beta induced the phosphorylation of Runx2, and this effect was blocked by a p38 kinase inhibitor. Our data suggest that Runx2 is likely to be a key downstream mediator of p38 effects in the differential regulation of IL-1beta induced MMP-13 expression. CONCLUSIONS: These studies demonstrate the differential inhibition of cytokine-induced MMP-1 and -13 expression by p38 kinase inhibitors in human chondrosarcoma cells. Our studies also suggest the involvement of Runx2, at least in part, in mediating the effects of p38 on MMP-13 expression.

Regulation of the human ADAMTS-4 promoter by transcription factors and cytokines.

ADAMTS-4 (aggrecanase-1) is a metalloprotease that plays a role in aggrecan degradation in the cartilage extracellular matrix. In order to understand the regulation of ADAMTS-4 gene expression we have cloned and characterized a functional 4.5kb human ADAMTS-4 promoter. Sequence analysis of the promoter revealed the presence of putative binding sites for nuclear factor of activated T cells (NFAT) and Runx family of transcription factors that are known to regulate chondrocyte maturation and differentiation. Using promoter-reporter assays and mRNA analysis we have analyzed the role of chondrocyte-expressed transcription factors NFATp and Runx2 and have shown that ADAMTS-4 is a potential downstream target of these two factors. Our results suggest that inhibition of the expression/function of NFATp and/or Runx2 may enable us to modulate aggrecan degradation in normal physiology and/or in degenerative joint diseases. The ADAMTS-4 promoter would serve as a valuable mechanistic tool to better understand the regulation of ADAMTS-4 expression by signaling pathways that modulate cartilage matrix breakdown.

Distinct pathways of extracellular signal-regulated kinase activation by growth factors, fibronectin and parathyroid hormone 1-34.

Growth factors, hormones, and matrix proteins regulate osteoblast proliferation and differentiation, acting through cognate receptors. Since each of the receptors are coupled to a variety of distinct signal transduction pathways, in this report we evaluated whether there is a common convergent intermediate step that allows cross-talk among the various pathways. Since extracellular signal-regulated kinases 1 and 2 (Erk1/2) play a role in mitogenesis and differentiation processes, we evaluated the effects of various osteotrophic factors on Erk1/2 phosphorylation in osteoblasts. Osteoblasts isolated from the metaphyseal marrow (MM) and diaphyseal marrow (DM) of 4-6 week old male rat longitudinal bones were grown to confluency and Erk1/2-phosphorylation was evaluated using antibodies that recognized either the total or the phosphorylated form of the kinase. There was very little Erk1/2 phosphorylation in cells kept in suspension. Both MM and DM cells attached to fibronectin (FN), demonstrated Erk1/2 phosphorylation that persisted for at least up to 8h. Platelet-derived growth factor AB (PDGF-AB) induced a transient and robust Erk1/2 phosphorylation that was attenuated by 2h. Studies with specific inhibitors indicated that the effects of these factors were mediated by protein kinase C, by receptor tyrosine kinase, as well as by protein phosphatases. Parathyroid hormone (PTH 1-34), a bone anabolic agent however, caused a down-regulation of FN stimulated Erk1/2 phosphorylation in MM derived cells. The inhibitory effect of PTH was mediated through cAMP-dependent protein kinase A (PKA) activation. The data collectively suggest that a combination of diverse extracellular stimuli regulates Erk1/2 phosphorylation that may ultimately influence osteoblast proliferation and/or differentiation.

Protein Kinase C is a mediator of the synthesis and secretion of osteoprotegerin in osteoblast-like cells.

Osteoprotegerin (OPG) is a member of the TNF receptor superfamily and plays a critical role in the development of osteoclasts from precursor cells. OPG is produced by a variety of cells of mesenchymal origin and has been demonstrated to be present in osteoblasts and osteocytes. However, the mechanisms of regulation of OPG production and secretion are not known. Using a highly specific polyclonal antibody, we demonstrate that OPG is synthesized and secreted by osteoblast-like cells in culture. We further show that phorbol myristate acetate, an activator of protein kinase C, activated the secretion of OPG. Further, the increased secretion of OPG correlated well with a corresponding increase in OPG mRNA abundance. In addition, OPG promoter stably integrated into an osteoblast cell line was activated by phorbol myristate acetate. The increase in OPG expression was blocked by an inhibitor of protein kinase C, although the basal OPG expression was not altered. These results suggest that activation of the protein kinase C pathway may play a critical role in OPG expression.