Discovery of MK-0952, a selective PDE4 inhibitor for the treatment of long-term memory loss and mild cognitive impairment.

The structure-activity relationship of a novel series of 8-biarylnaphthyridinones acting as type 4 phosphodiesterase (PDE4) inhibitors for the treatment of long-term memory loss and mild cognitive impairment is described herein. The manuscript describes a new paradigm for the development of PDE4 inhibitor targeting CNS indications. This effort led to the discovery of the clinical candidate MK-0952, an intrinsically potent inhibitor (IC(50)=0.6 nM) displaying limited whole blood activity (IC(50)=555 nM). Supporting in vivo results in two preclinical efficacy tests and one test assessing adverse effects are also reported. The comparative profiles of MK-0952 and two other Merck compounds are described to validate the proposed hypothesis.

The discovery and synthesis of highly potent subtype selective phosphodiesterase 4D inhibitors.

The SAR study of a series of 6-aryloxymethyl-8-aryl substituted quinolines is described. Optimization of the series led to the discovery of compound 26b, a highly potent (IC50=0.6 nM) and selective PDE4D inhibitor with a 75-fold selectivity over the A, B, and C subtypes and over 18,000-fold selectivity against other PDE family members. Rat pharmacokinetics and tissue distribution are also summarized.

Alkyl-bridged substituted 8-arylquinolines as highly potent PDE IV inhibitors.

Substituted 8-arylquinoline analogs bearing alkyl-linked side chain were identified as potent inhibitors of type 4 phophodiesterase. These compounds address the potential liabilities of the clinical candidate L-454560. The pharmacokinetic profile of the best analogs and the in vivo efficacy in an ovalbumin-induced bronchoconstriction assay in conscious guinea pigs are reported.

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).

Design, synthesis, and biological evaluation of 8-biarylquinolines: a novel class of PDE4 inhibitors.

The structure-activity relationship of a novel series of 8-biarylquinolines acting as type 4 phosphodiesterase (PDE4) inhibitors is described herein. Prototypical compounds from this series are potent and non-selective inhibitors of the four distinct PDE4 (IC(50)<10 nM) isozymes (A-D). In a human whole blood in vitro assay, they inhibit (IC(50)<0.5 microM) the LPS-induced release of the cytokine TNF-alpha. Optimized inhibitors were evaluated in vivo for efficacy in an ovalbumin-induced bronchoconstriction model in conscious guinea pigs. Their propensity to produce an emetic response was evaluated by performing pharmacokinetic studies in squirrel monkeys. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of efficacy over emesis.

Interspecies in vitro metabolism of the phosphodiesterase-4 (PDE4) inhibitor L-454,560.

L-454,560 is a potent phosphodiesterase 4 (PDE4) inhibitor which was identified as a development candidate for the treatment of asthma and chronic obstructive pulmonary disease (COPD). As part of the discovery of this compound, interspecies in vitro metabolism data was generated using liver microsomes and hepatocytes in order to understand the metabolic fate of the compound. In microsomes, metabolism of the 3-methyl-1,2,4-oxadiazole ring was the predominant pathway observed, including ring cleavage. In rat hepatocytes, hydroxylation of the methyl group on the oxadiazole ring and double-bond isomerization were the most abundant metabolites observed. No major species differences were found in terms of microsomal metabolite profiles. The use of LC with UV and MS detection is highlighted, as well as information from tandem mass spectrometry and NMR.

Nitrogen-bridged substituted 8-arylquinolines as potent PDE IV inhibitors.

Potent inhibitors of the human PDE IV enzyme are described. Substituted 8-arylquinoline analogs bearing nitrogen-linked side chain were identified as potent inhibitors based on the SAR described herein. The pharmacokinetic profile of the best analog and the in vivo efficacy in an ovalbumin-induced bronchoconstriction assay in conscious guinea pigs are reported.

Lack of clinical efficacy of a phosphodiesterase-4 inhibitor for treatment of heaves in horses.

Phosphodiesterase-4 (PDE 4) enzyme inhibitors have been shown to have anti-inflammatory properties in various animal disease processes and therefore could be effective drugs for the treatment of equine airway diseases. The purpose of this study was to evaluate the efficacy and adverse effects of the PDE 4 inhibitor L-826,141 in horses with heaves. In a blinded parallel design, horses with heaves exposed daily to moldy hay were given a placebo for 14 days and then administered either L-826,141 (n = 6; loading dose of 1 mg/kg IV followed by 0.5 mg/kg IV q48h) or dexamethasone (n = 6; 0.04 mg/kg IV q24h) from days 15 to 29 (study 1). Pulmonary function and bronchoalveolar (BAL) cytology were evaluated weekly from baseline (day 0) to 29 days. In study 2, horses were treated with L-826,141 (1.0 mg/kg IV q24h) for 8 days. Although ex vivo lipopolysaccharide-induced tumor necrosis factor (TNF)-alpha and LTB4 production by fresh blood were inhibited up to 90% after repeated administrations of L-826,141, this treatment failed to improve lung function. In contrast, dexamethasone (positive control) treatment resulted in significant improvement in lung mechanics and airway function in all horses. Neither drug had a significant effect on BAL total cell counts and differential cytology. Administration of the PDE 4 inhibitor L-826,141 for up to 14 days to horses with heaves was not associated with an improvement in airway function or inflammation. These findings suggest that the PDE 4 enzyme is not a key mediator of lung inflammation in heaves.

Substituted coumarins as potent 5-lipoxygenase inhibitors.

Leukotriene biosynthesis inhibitors have potential as therapeutic agents for asthma and inflammatory diseases. A novel series of substituted coumarin derivatives has been synthesized and the structure-activity relationship was evaluated with respect to their ability to inhibit the formation of leukotrienes via the human 5-lipoxygenase enzyme.

Discovery of a substituted 8-arylquinoline series of PDE4 inhibitors: structure-activity relationship, optimization, and identification of a highly potent, well tolerated, PDE4 inhibitor.

The discovery and SAR of a new series of substituted 8-arylquinoline PDE4 inhibitors are herein described. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of emesis to efficacy in several animal models. Typical optimized compounds from this series are potent inhibitors of PDE4 (IC(50)<1nM) and also of LPS-induced TNF-alpha release in human whole blood (IC(50)<0.5microM). The same compounds are potent inhibitors of ovalbumin-induced bronchoconstriction in conscious guinea pigs (EC(50)<0.1mg/kg ip) but require a dose of about 10mg/kg po in the squirrel monkey to produce an emetic response. From this series of compounds, 23a (L-454,560) was identified as an optimized compound.

Optimization of a tertiary alcohol series of phosphodiesterase-4 (PDE4) inhibitors: structure-activity relationship related to PDE4 inhibition and human ether-a-go-go related gene potassium channel binding affinity.

A SAR study on the tertiary alcohol series of phosphodiesterase-4 (PDE4) inhibitors related to 1 is described. In addition to inhibitory potency against PDE4 and the lipopolysaccharide-induced production of TNFalpha in human whole blood, the binding affinity of these compounds for the human ether-a-go-go related gene (hERG) potassium channel (an in vitro measure for the potential to cause QTc prolongation) was assessed. Four key structural moieties in the molecule were studied, and the impact of the resulting modifications in modulating these activities was evaluated. From these studies, (+)-3d (L-869,298) was identified as an optimized structure with respect to PDE4 inhibitory potency, lack of binding affinity to the hERG potassium channel, and pharmacokinetic behavior. (+)-3d exhibited good in vivo efficacy in several models of pulmonary function with a wide therapeutic index with respect to emesis and prolongation of the QTc interval.

Substituted 2-pyridinemethanol derivatives as potent and selective phosphodiesterase-4 inhibitors.

The synthesis and the phosphodiesterase-4 (PDE4) inhibitory activity of 2-pyridinemethanol derivatives is described. The evaluation of the structure-activity relationship (SAR) in this series of novel PDE4 inhibitors led to the identification of compound 9 which exhibits excellent in vitro activity, desirable pharmacokinetic parameters and good efficacy in animal models of bronchoconstriction.

Substituted aminopyridines as potent and selective phosphodiesterase-4 inhibitors.

The synthesis and the biological evaluation of new potent phosphodiesterase type 4 (PDE4) inhibitors are presented. This new series was elaborated by replacement of the metabolically resistant phenyl hexafluorocarbinol of L-791,943 (1) by a substituted aminopyridine residue. The structure-activity relationship of N-substitution on 3 led to the identification of (-)-3n which exhibited a good PDE4 inhibitor activity (HWB-TNFalpha=0.12 microM) and an improved pharmacokinetic profile over L-791,943 (rat t(1/2)=2 h). (-)-3n was well tolerated in ferret with an emetic threshold of 30 mg/kg (po) and was found to be active in the ovalbumin-induced bronchoconstriction model in guinea pig (54%, 0.1 mg/kg, ip) as well as the ascaris-induced bronchoconstriction model in sheep (64%/97%, early/late, 0.5 mg/kg, iv).

Substituted 4-(2,2-diphenylethyl)pyridine-N-oxides as phosphodiesterase-4 inhibitors: SAR study directed toward the improvement of pharmacokinetic parameters.

A detailed SAR study directed toward the optimization of pharmacokinetic parameters for analogues of L-791,943 is reported. The introduction of a soft metabolic site on this structure permitted the identification of L-826,141 as a potent phosphodiesterase type 4 (PDE4) inhibitor that is well absorbed and that presents a shorter half-life than L-791,943 in a variety of animal species. The efficacy of L-826,141 is also demonstrated in different in vivo models.

Discovery of L-791,943: a potent, selective, non emetic and orally active phosphodiesterase-4 inhibitor.

Structure-activity relationship studies directed toward improving the potency and metabolic stability of CDP-840 (3) resulted in the discovery of L-791,943 (11n) as a potent (HWB TNF-alpha = 0.67 microM) and orally active phosphodiesterase type 4 (PDE4) inhibitor. This compound, which bears a stable bis-difluoromethoxy catechol and a pendant hexafluorocarbinol, exhibited a long half-life in rat and in squirrel monkey. It is well tolerated in ferret with an emetic threshold greater than 30 mg/kg (po) and was found to be active in the ovalbumin-induced bronchoconstriction model in guinea pig and in the ascaris-induced bronchoconstriction models in sheep and squirrel monkey.

Comparison of inhibition of ovalbumin-induced bronchoconstriction in guinea pigs and in vitro inhibition of tumor necrosis factor-alpha formation with phosphodiesterase 4 (PDE4) selective inhibitors.

Phosphodiesterase 4 (PDE4) inhibitors elevate cyclic adenosine 5'-monophosphate (cAMP), and this elevation has been shown to inhibit inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha). Using TNF-alpha as a biomarker, we have developed transcription-based assays to examine inhibition of PDE4 activity in human and guinea pig whole blood. In vitro inhibition by PDE4 inhibitors was measured using quantitative PCR (qPCR) analysis of TNF-alpha mRNA levels in whole blood stimulated with lipopolysaccharide (LPS). The kinetics of human TNF-alpha mRNA production were analyzed and shown to be highest 4 hr following LPS stimulation. The guinea pig displayed kinetics of TNF-alpha transcription similar to those of the human. Analysis of inhibition of human TNF-alpha protein production was performed by immunoassay and shown to correlate with inhibition of transcription for three of the four compounds tested. Roflumilast was found to be 9-fold more potent for TNF-alpha inhibition in the qPCR assay than in the protein assay. The potencies of L-826,141 and roflumilast were determined in human and guinea pig whole blood by qPCR, with IC(50) values of 270 and 20 nM, respectively, in humans and 100 and 10 nM, respectively, in guinea pigs. These results show that the potency of PDE4 inhibitors can be monitored in whole blood using a transcription-based assay, and that this type of assay can be adapted to various species provided the TNF-alpha nucleotide sequence is known. The in vitro whole blood IC(50) for TNF-alpha inhibition was compared to inhibition in the ovalbumin-challenged guinea pig model of bronchoconstriction. Obtaining plasma levels at the IC(50) determined in vitro for L-826,141 and roflumilast provides significant inhibition of bronchoconstriction. This suggests that TNF-alpha can be used as a whole blood biomarker in the guinea pig for PDE4 inhibition in this inflammatory model.