Earl F. Kimble

Preclinical pharmacology of lumiracoxib: a novel selective inhibitor of cyclooxygenase-2

1 This manuscript presents the preclinical profile of lumiracoxib, a novel cyclooxygenase‐2 (COX‐2) selective inhibitor. 2 Lumiracoxib inhibited purified COX‐1 and COX‐2 with Ki values of 3 and 0.06 μM, respectively. In cellular assays, lumiracoxib had an IC50 of 0.14 μM in COX‐2‐expressing dermal fibroblasts, but caused no inhibition of COX‐1 at concentrations up to 30 μM (HEK 293 cells transfected with human COX‐1). 3 In a human whole blood assay, IC50 values for lumiracoxib were 0.13 μM for COX‐2 and 67 μM for COX‐1 (COX‐1/COX‐2 selectivity ratio 515). 4 Lumiracoxib was rapidly absorbed following oral administration in rats with peak plasma levels being reached between 0.5 and 1 h. 5 Ex vivo, lumiracoxib inhibited COX‐1‐derived thromboxane B2 (TxB2) generation with an ID50 of 33 mg kg−1, whereas COX‐2‐derived production of prostaglandin E2 (PGE2) in the lipopolysaccharide‐stimulated rat air pouch was inhibited with an ID50 value of 0.24 mg kg−1. 6 Efficacy of lumiracoxib in rat models of hyperalgesia, oedema, pyresis and arthritis was dose‐dependent and similar to diclofenac. However, consistent with its low COX‐1 inhibitory activity, lumiracoxib at a dose of 100 mg kg−1 orally caused no ulcers and was significantly less ulcerogenic than diclofenac (P<0.05). 7 Lumiracoxib is a highly selective COX‐2 inhibitor with anti‐inflammatory, analgesic and antipyretic activities comparable with diclofenac, the reference NSAID, but with much improved gastrointestinal safety.

Selective functional inhibition of JAK‐3 is sufficient for efficacy in collagen‐induced arthritis in mice

OBJECTIVE All gamma-chain cytokines signal through JAK-3 and JAK-1 acting in tandem. We undertook this study to determine whether the JAK-3 selective inhibitor WYE-151650 would be sufficient to disrupt cytokine signaling and to ameliorate autoimmune disease pathology without inhibiting other pathways mediated by JAK-1, JAK-2, and Tyk-2. METHODS JAK-3 kinase selective compounds were characterized by kinase assay and JAK-3-dependent (interleukin-2 [IL-2]) and -independent (IL-6, granulocyte-macrophage colony-stimulating factor [GM-CSF]) cell-based assays measuring proliferation or STAT phosphorylation. In vivo, off-target signaling was measured by IL-22- and erythropoietin (EPO)-mediated models, while on-target signaling was measured by IL-2-mediated signaling. Efficacy of JAK-3 inhibitors was determined using delayed-type hypersensitivity (DTH) and collagen-induced arthritis (CIA) models in mice. RESULTS In vitro, WYE-151650 potently suppressed IL-2-induced STAT-5 phosphorylation and cell proliferation, while exhibiting 10-29-fold less activity against JAK-3-independent IL-6- or GM-CSF-induced STAT phosphorylation. Ex vivo, WYE-151650 suppressed IL-2-induced STAT phosphorylation, but not IL-6-induced STAT phosphorylation, as measured in whole blood. In vivo, WYE-151650 inhibited JAK-3-mediated IL-2-induced interferon-gamma production and decreased the natural killer cell population in mice, while not affecting IL-22-induced serum amyloid A production or EPO-induced reticulocytosis. WYE-151650 was efficacious in mouse DTH and CIA models. CONCLUSION In vitro, ex vivo, and in vivo assays demonstrate that WYE-151650 is efficacious in mouse CIA despite JAK-3 selectivity. These data question the need to broadly inhibit JAK-1-, JAK-2-, or Tyk-2-dependent cytokine pathways for efficacy.

Preclinical pharmacology of robenacoxib: a novel selective inhibitor of cyclooxygenase‐2

This manuscript reports the results of preclinical studies in the rat with robenacoxib, a novel selective cyclooxygenase (COX)-2 inhibitor. Robenacoxib selectively inhibited COX-2 in vitro as evidenced from COX-1:COX-2 IC50 ratios of 27:1 in purified enzyme preparations and >967:1 in isolated cell assays. Binding to COX-1 was rapid and readily reversible (dissociation t(1/2) << 1 min), whilst COX-2 binding was slowly reversible (t(1/2) = 25 min). In vivo, robenacoxib inhibited PGE2 production (an index of COX-2 inhibition) in lipopolysaccharide (LPS)-stimulated air pouches (ID50 0.3 mg/kg) and for at least 24 h in zymosan-induced inflammatory exudate (at 2 mg/kg). Robenacoxib was COX-1 sparing, as it inhibited serum TxB2 synthesis ex vivo (an index of COX-1 inhibition) only at very high doses (100 mg/kg but not at 2-30 mg/kg). Robenacoxib inhibited carrageenan-induced paw oedema (ID50 0.40-0.48 mg/kg), LPS-induced fever (ID50 1.1 mg/kg) and Randall-Selitto pain (10 mg/kg). Robenacoxib was highly bound to plasma protein (99.9% at 50 ng/mL in vitro). After intravenous dosing, clearance was 2.4 mL/min/kg and volume of distribution at steady-state was 306 mL/kg. Robenacoxib was preferentially distributed into inflammatory exudate; the AUC for exudate was 2.9 times higher than for blood and the MRT in exudate (15.9 h) was three times longer than in blood (5.3 h). Robenacoxib produced significantly less gastric ulceration and intestinal permeability as compared with the reference nonsteroidal anti-inflammatory drug (NSAID), diclofenac, and did not inhibit PGE2 or 6-keto PGF(1alpha) concentrations in the stomach and ileum at 30 mg/kg. Robenacoxib also had no relevant effects on kidney function at 30 mg/kg. In summary, results of preclinical studies in rats studies suggest that robenacoxib has an attractive pharmacological profile for potential use in the intended target species, cats and dogs.

The Effects of Diclofenac Sodium on Arachidonic Acid Metabolism

Evidence has been presented that inhibition by diclofenac sodium of the production of leukotrienes by cells participating in the inflammatory process is due to a decreased availability of intracellular arachidonic acid which results from enhanced uptake of the substrate into triglyceride pools. The diminished leukotriene production does not result from direct inhibition of 5-lipoxygenase or phospholipase A2. Reduced availability of arachidonic acid would also limit production of prostaglandins, although in this case manifestation is obscured by the potent inhibitory effect of diclofenac sodium on cyclooxygenase. This recently discovered action of diclofenac sodium, which has been characterized by studies on isolated leukocytes, appears to be operative in vivo. Consistent with this mechanism, and not explainable by classical cyclooxygenase inhibition, diclofenac sodium inhibited leukotriene production in whole blood from drug-treated animals and also suppressed leukocyte infiltration of subcutaneously implanted sponges. The latter effect contrasts with increased infiltration frequently obtained with other NSAIDs and thought to reflect enhanced production of leukotrienes. In conclusion, the findings suggest that patient acceptance or preference for diclofenac sodium is not merely subjective but has a logical scientific basis.

Characterization of CGS 8515 as a selective 5-lipoxygenase inhibitor using in vitro and in vivo models

CGS 8515 inhibited 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B4 synthesis in guinea pig leukocytes (IC50 = 0.1 microM). The compound did not appreciably affect cyclooxygenase (sheep seminal vesicles), 12-lipoxygenase (human platelets), 15-lipoxygenase (human leukocytes) and thromboxane synthetase (human platelets) at concentrations up to 100 microM. CGS 8515 inhibited A23187-induced formation of leukotriene products in whole blood (IC50 values of 0.8 and 4 microM, respectively, for human and rat) and in isolated rat lung (IC50 less than 1 microM) in vitro. The selectivity of the compound as a 5-lipoxygenase inhibitor was confirmed in rat whole blood by the 20-70-fold separation of inhibitory effects on the formation of leukotriene from prostaglandin products. Ex vivo and in vivo studies with rats showed that CGS 8515, at an oral dose of 2-50 mg/kg, significantly inhibited A23187-induced production of leukotrienes in whole blood and in the lung. The effect persisted for at least 6 h in the ex vivo whole blood model. CGS 8515, at oral doses as low as 5 mg/kg, significantly suppressed exudate volume and leukocyte migration in the carrageenan-induced pleurisy and sponge models in the rat. Inhibitory effects of the compound on inflammatory responses and leukotriene production in leukocytes and target organs are important parameters suggestive of its therapeutic potential in asthma, psoriasis and inflammatory conditions.

Novel pyrrolidine ureas as C-C chemokine receptor 1 (CCR1) antagonists.

Monocyte infiltration is implicated in a variety of diseases including multiple myeloma, rheumatoid arthritis, and multiple sclerosis. C-C chemokine receptor 1 (CCR1) is a chemokine receptor that upon stimulation, particularly by macrophage inflammatory protein 1alpha (MIP-1alpha) and regulated on normal T-cell expressed and secreted (RANTES), mediates monocyte trafficking to sites of inflammation. High throughput screening of our combinatorial collection identified a novel, moderately potent CCR1 antagonist 3. The library hit 3 was optimized to the advanced lead compound 4. Compound 4 inhibited CCR1 mediated chemotaxis of monocytes with an IC(50) of 20 nM. In addition, the compound was highly selective over other chemokine receptors. It had good microsomal stability when incubated with rat and human liver microsomes and showed no significant cytochrome P450 (CYP) inhibition. Pharmacokinetic evaluation of the compound in the rat showed good oral bioavailability.

Discovery and characterization of triaminotriazine aniline amides as highly selective p38 kinase inhibitors.

The p38 mitogen-activated protein (MAP) kinases are a family of serine/threonine protein kinases that play important roles in cellular responses to inflammation and external stress. Inhibitors of the p38 MAP kinase have shown promise for potential treatment of inflammatory disorders such as rheumatoid arthritis, acute coronary syndrome, psoriasis, and Crohns disease. We identified a novel class of p38 inhibitors via high-throughput screening. PS200981 [3-(4-(1,4-diazepan-1-yl)-6-(((1S,2R,5S)-6,6-dimethylbicyclo[3.1.1]heptan-2-yl)methylamino)-1,3,5-triazin-2-ylamino)-4-methylbenzamide], a representative compound identified from screening a collection of combinatorial libraries, amounting to 2.1 million compounds, inhibits p38α kinase and the lipopolysaccharide (LPS)-induced increase in tumor necrosis factor (TNF) α levels in cell media of human monocytes with IC50 values of 1 μM. The screening data revealed a preferred synthon, 3-amino-4-methyl benzamide, which is critical for the activity against p38. This synthon appeared almost exclusively in screening hits including PS200981, and slight variations of this synthon including 3-amino benzamide and 2-amino-4-methyl benzamide also contained in the library were inactive. PS200981 is equally potent against the α and β forms of p38 but did not inhibit p38γ and is >25-fold selective versus a panel of other kinases. PS200981 inhibited the LPS-induced increase in TNFα levels when administered at 30 mg/kg to mice. Selectivity and in vivo activity of this class of p38 inhibitors was further demonstrated by PS166276 [(R)-3-(4-(isobutyl(methyl)-amino)-6-(pyrrolidin-3-ylamino)-1,3,5-triazin-2-ylamino)-4-methylbenzamide], a highly structurally related but more potent and less cytotoxic inhibitor, in several intracellular signaling assays, and in LPS-challenged mice. Overall, this novel class of p38 inhibitors is potent, active in vitro and in vivo, and is highly selective.

2-Benzimidazolyl-9-(chroman-4-yl)-purinone derivatives as JAK3 inhibitors.

A novel class of Janus tyrosine kinase 3 (JAK3) inhibitors based on a 2-benzimidazoylpurinone core structure is described. Through substitution of the benzimidazoyl moiety and optimization of the N-9 substituent of the purinone, compound 24 was identified incorporating a chroman-based functional group. Compound 24 shows excellent kinase activity, good oral bioavailability and demonstrates efficacy in an acute mechanistic mouse model through inhibition of interleukin-2 (IL-2) induced interferon-gamma (INF-gamma) production.

Novel pyrrolidine heterocycles as CCR1 antagonists

A novel series of pyrrolidine heterocycles was prepared and found to show potent inhibitory activity of CCR1 binding and CCL3 mediated chemotaxis of a CCR1-expressing cell line. A potent, optimized triazole lead from this series was found to have acceptable pharmacokinetics and microsomal stability in rat and is suitable for further optimization and development.

Discovery of 2-aminoimidazopyridine adenosine A(2A) receptor antagonists.

A novel series of adenosine A(2A) receptor antagonists was identified by high-throughput screening of an encoded combinatorial compound collection. The initial hits were optimized for A(2A) binding affinity, A(1) selectivity, and in vitro microsomal stability generating orally available 2-aminoimidazo[4,5-b]pyridine-based A(2A) antagonist leads.