Hazel Joan Dyke

Update on the therapeutic potential of PDE4 inhibitors

Phosphodiesterase (PDE) enzymes are responsible for the inactiviation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterase 4 (PDE4) is a cAMP specific phosphodiesterase expressed in inflammatory cells such as eosinophils. Inhibition of PDE4 results in an elevation of cAMP in these cells, which in turn downregulates the inflammatory response. The anti-inflammatory effects of PDE4 inhibitors have been well documented both in vitro and in vivo in a range of animal models. The potential use of PDE4 inhibitors as anti-inflammatory agents for the treatment of diseases such as asthma, chronic obstructive pulmonary disease (COPD) and multiple sclerosis (MS), has received considerable attention from the pharmaceutical industry but to date, there are no selective PDE4 inhibitors on the market. Early PDE4 inhibitors, such as rolipram suffered from dose limiting side effects, including nausea and emesis, which severely restricted their therapeutic utility. Second generation compounds such as cilomilast have been identified with reduced side effect liability. Indeed, cilomilast is showing good therapeutic effects in clinical trials for asthma and COPD and represents the most advanced selective PDE4 inhibitor for any indication. The utility of this class of inhibitor in other inflammatory diseases is less well advanced. However, data in animal models of rheumatoid arthritis (RA) and MS suggests that there is also significant potential for PDE4 inhibitors as treatments for these diseases and the results of clinical trials in these disease areas are eagerly awaited.

Identification of Imidazo-Pyrrolopyridines as Novel and Potent JAK1 Inhibitors.

A therapeutic rationale is proposed for the treatment of inflammatory diseases, such as rheumatoid arthritis (RA), by specific targeting of the JAK1 pathway. Examination of the preferred binding conformation of clinically effective, pan-JAK inhibitor 1 led to identification of a novel, tricyclic hinge binding scaffold 3. Exploration of SAR through a series of cycloamino and cycloalkylamino analogues demonstrated this template to be highly tolerant of substitution, with a predisposition to moderate selectivity for the JAK1 isoform over JAK2. This study culminated in the identification of subnanomolar JAK1 inhibitors such as 22 and 49, having excellent cell potency, good rat pharmacokinetic characteristics, and excellent kinase selectivity. Determination of the binding modes of the series in JAK1 and JAK2 by X-ray crystallography supported the design of analogues to enhance affinity and selectivity.

The therapeutic potential of PDE4 inhibitors.

Phosphodiesterase enzymes are responsible for the inactivation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterase 4 (PDE4) is a cAMP specific phosphodiesterase expressed in inflammatory cells such as eosinophils. Inhibition of PDE4 results in an elevation of cAMP in these cells, which in turn downregulates the inflammatory response. The anti-inflammatory effects of PDE4 inhibitors have been well documented both in vitro and in vivo in a variety of animal models. The potential use of PDE4 inhibitors as anti-inflammatory agents for the treatment of asthma and other inflammatory disorders has received considerable attention from the pharmaceutical industry, but to date, there are no selective PDE4 inhibitors on the market. Early PDE4 inhibitors, typified by rolipram, suffered from dose-limiting side effects, including nausea and emesis, which severely restricted their therapeutic utility. Second generation compounds, including CDP840 and SB207499 (Ariflo), have been identified with reduced side effect liability. Recent evidence suggests a correlation between side effects and the ability of compounds to bind at the so-called high affinity rolipram binding site (HPDE), whilst beneficial effects appear to correlate with binding at the catalytic site. A number of companies are actively pursuing compounds which exhibit improved affinity for the catalytic site and reduced affinity for the HPDE, in the expectation that this will provide compounds with an improved therapeutic index.

Recent developments in the discovery of MCH-1R antagonists for the treatment of obesity – an update

Since the discovery and characterisation of melanin-concentrating hormone (MCH) and its role in the regulation of food intake and energy expenditure, there has been increasing interest in this cyclic peptide. The identification of the MCH-1 receptor (MCH-1R) in 1999 initiated the search for small molecules that could block the effects of MCH and provide novel agents for the treatment of obesity. A large number of companies is now actively pursuing MCH-1R antagonists and a wide range of structural types have been reported. Several compounds have been reported to be efficacious in rodent models of obesity and two compounds have recently entered into human clinical trials.

1H-Pyrazolo[3,4-g]hexahydro-isoquinolines as selective glucocorticoid receptor antagonists with high functional activity.

Addition of the 4-fluorophenylpyrazole group to the previously described 2-azadecalin glucocorticoid receptor (GR) antagonist 1 resulted in significantly enhanced functional activity. SAR of the bridgehead substituent indicated that whereas groups as small as methyl afforded high GR binding, GR functional activity was enhanced by larger groups such as benzyl, substituted ethers, and aminoalkyl derivatives. GR antagonists with binding and functional activity comparable to mifepristone were discovered (e.g., 52: GR binding K(i) 0.7 nM; GR reporter gene functional K(i) 0.6 nM) and found to be highly selective over other steroid receptors. Analogues 43 and 45 had >50% oral bioavailability in the dog.

Synthesis and structure–activity relationships of guanine analogues as phosphodiesterase 7 (PDE7) inhibitors

The synthesis of a novel series of guanine analogues is reported. The compounds have been assessed in vitro and some analogues have been found to be inhibitors of phosphodiesterase type 7 (PDE7).

Identification and optimisation of a series of substituted 5-pyridin-2-yl-thiophene-2-hydroxamic acids as potent histone deacetylase (HDAC) inhibitors

Further investigation of a series of thienyl-based hydroxamic acids that included ADS100380 and ADS102550 led to the identification of the 5-pyridin-2-yl-thiophene-2-hydroxamic acid 3c, which possessed modest HDAC inhibitory activity. Substitution at the 5- and 6-positions of the pyridyl ring of compound 3c provided compounds 5a-g, 7a, b, 9, and 13a. Compound 5b demonstrated improved potency, in vitro DMPK profile, and rat oral bioavailability, compared to ADS102550. Functionalisation of the pendent phenyl group of compounds 5b, 5e and 13a provided analogues that possessed excellent enzyme inhibition and anti-proliferative activity.

Synthesis and profile of SCH351591, a novel PDE4 inhibitor

The syntheses and pharmacological profiles of some 2-trifluoromethyl-8-methoxyquinoline-5-carboxamides are described. SCH351591 is a potent selective inhibitor of phosphodiesterase type 4 (PDE4).

8-Methoxyquinolines as PDE4 inhibitors

The synthesis and pharmacological profile of a novel series of 2-substituted 8-methoxyquinolines is described. The 2-trifluoromethyl compound was found to be a potent inhibitor of phosphodiesterase type 4 (PDE4).

Modulation of 11β-hydroxysteroid dehydrogenase type 1 activity by 1,5-substituted 1H-tetrazoles

Inhibitors of 11beta-hydroxysteroid dehydrogenase (11beta-HSD1) show promise as drugs to treat metabolic disease and CNS disorders such as cognitive impairment. A series of 1,5-substituted 1H-tetrazole 11beta-HSD1 inhibitors has been discovered and chemically modified. Compounds are selective for 11beta-HSD1 over 11beta-HSD2 and possess good cellular potency in human and murine 11beta-HSD1 assays. A range of in vitro stabilities are observed in human liver microsome assays.