Recent innovations in asthma therapy

Chronotherapeutics--a chronopharmaceutical approach to drug delivery in the treatment of asthma

Bronchial asthma is a chronic inflammatory disorder of the airways associated with airflow obstruction that is reversible spontaneously or with treatment. Bronchial asthma is a disease based on established circadian rhythm. The symptoms of asthma worsen during midnight to early morning and therefore it is required to deliver the drug in such fashion that effective treatment can be obtained during the time of asthma attacks. Chronotherapy is an approach that fulfills the criteria of drug delivery at a specific time as per the pathophysiological need of the disease, to improve patient compliance. The current article focuses on the chronotherapy of bronchial asthma, methodologies involved for the existing systems, recent updates and different chronopharmaceutical technologies currently available in the market. Chronotherapy with different categories of bronchial asthma medications also has been reviewed.

Characterization of enzymes responsible for biotransformation of the new antileukotrienic drug quinlukast in rat liver microsomes and in primary cultures of rat hepatocytes

The promising new drug quinlukast, 4-(4-(quinoline-2′-yl-methoxy)phenylsulphanyl)benzoic acid (VÚFB 19363), is under investigation for its anti-inflammatory and anti-asthmatic effects. The main metabolite of quinlukast identified in incubations of rat microsomal fraction, and in primary culture of rat hepatocytes, is quinlukast sulfoxide (M2). Also, several other metabolites of quinlukast were found: two dihydrodiol derivatives (M3, M5) and quinlukast sulfone (M4). This study was conducted to characterize the enzymes involved in quinlukast biotransformation in rat in-vitro. Primary cultures of rat hepatocytes were treated with inducers of different cytochrome P450s (CYPs) for 48 h. Quinlukast (100 μm) was incubated for 24 h in a primary culture of induced or control hepatocytes. The effects of CYP inhibitors, ketoconazole, methylpyrazole, metyrapone and α-naphthoflavone (2, 10, 50 μm), on quinlukast metabolism were tested in induced and control hepatocytes. Significant induction of M2 (6 times), M5 (twice) and M3 (by 50%) formation by dexamethasone and strong concentration-dependent inhibition by ketoconazole indicated that CYP3A participates in formation of these metabolites. CYP1A catalyses formation of metabolite M3 mainly, as β-naphthoflavone induced (10 times) production of M3 and a strong inhibitory effect of α-naphthoflavone on its formation was observed. A significant inhibitory effect of quinlukast (2, 10, 50 μm) on ethoxyresorufin, methoxyresorufin and benzyloxyresorufin O-dealkylase activity was observed as well.

Chronobiology and chronotherapy of allergic rhinitis and bronchial asthma

Study of the chronobiology of allergic rhinitis (AR) and bronchial asthma (BA) and the chronopharmacology and chronotherapy of the medications used in their treatment began five decades ago. AR is an inflammatory disease of the upper airway tissue with hypersensitivity to specific environmental antigens, resulting in further local inflammation, vasomotor changes, and mucus hypersecretion. Symptoms include sneezing, nasal congestion, and runny and itchy nose. Approximately 25% of children and 40% of adults in USA are affected by AR during one or more seasons of the year. The manifestation and severity of AR symptoms exhibit prominent 24-h variation; in most persons they are worse overnight or early in the morning and often comprise nighttime sleep, resulting in poor daytime quality of life, compromised school and work performance, and irritability and moodiness. BA is also an inflammatory medical condition of the lower airways characterized by hypersensitivity to specific environmental antigens, resulting in greater local inflammation as well as bronchoconstriction, vasomotor change, and mucus hypersecretion. In USA an estimated 6.5 million children and 15.7 million adults have BA. The onset and worsening of BA are signaled by chest wheeze and/or croupy cough and difficult and labored breathing. Like AR, BA is primarily a nighttime medical condition. AR is treated with H1-antagonist, decongestant, and anti-inflammatory (glucocorticoid and leukotriene receptor antagonist and modifier) medications. Only H1-antagonist AR medications have been studied for their chronopharmacology and potential chronotherapy. BA is treated with some of the same medications and also theophylline and beta2-agonists. The chronopharmacology and chronotherapy of many classes of BA medications have been explored. This article reviews the rather extensive knowledge of the chronobiology of AR and BA and the chronopharmacology and chronotherapy of the various medications used in their treatment.

Optimization of imidazole 5-lipoxygenase inhibitors and selection and synthesis of a development candidate

Structural modification of imidazole 5-lipoxygenase (5-LO) inhibitors for optimizing inhibitory potency, pharmacokinetic behavior and toxicity (ocular) profile led to 4-{3-[4-(2-methyl-1H-imidazol-1-yl)phenylthio]}phenyl-3,4,5,6-tetrahydro-2H-pyran-4-carboxamide (6) with no observable ocular toxicity. The orally active and safe imidazole 5-LO inhibitor 6 was selected as a clinical candidate and advanced to clinical studies. An improved synthesis of 6 is also discussed.

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.

Role of cysteinyl leukotrienes in nociceptive and inflammatory conditions in experimental animals

The leukotrienes are potent inflammatory mediators, which may have a role in inflammatory diseases such as allergic rhinitis, inflammatory bowl disease and asthma. Zafirlukast, a cysteinyl leukotriene receptor antagonist, is claimed to be effective in asthma. However, it is not known whether these leukotrienes are involved in nociceptive and peripheral inflammation. The present study aimed to assess the role of cysteinyl leukotrienes in nociceptive and inflammatory conditions in experimental animals. Central nociception was assessed with tail-flick and hot-plate methods and peripheral nociception was assessed by acetic acid-induced chemonociception in mice. Local administration (intraplantar) of carrageenan-induced hyperalgesia and inflammation, measured by paw withdrawal latency and paw volumes, respectively. Zafirlukast (2.5--20 mg/kg, p.o.) produced a significant and dose-dependent antinociceptive and antiinflammatory effect against acetic acid-induced chemonociception in mice and carrageenan-induced paw oedema in rats, respectively. Zafirlukast (2.5 and 5.0 mg/kg, p.o.) also attenuated the carrageenan-provoked hyperalgesia but did not alter the pain threshold in central nociception up to 20 mg/kg. Zafirlukast (5 and 10 mg/kg ) significantly inhibited exudate formation and migration of polymorphonuclear leukocytes in carrageenan-induced pleurisy. Further, zafirlukast (5 mg/kg) also reduced myeloperoxidase activity in carrageenan-treated paw. When nimesulide (2 mg/kg, p.o.) was co-administered with zafirlukast, the antinociceptive, antihyperalgesic and antiinflammatory effects of nimesulide were significantly increased as compared to the per se effect. The results indicate that cysteinyl leukotrienes are involved in nociceptive/inflammatory conditions. It is expected that combination of cysteinyl leukotriene receptor antagonist with cyclooxygenase inhibitor would prove to be a novel approach to treat complex inflammatory conditions.