Anti-inflammatory potential of the selective phosphodiesterase 4 inhibitor N-(3,5-dichloro-pyrid-4-yl)-[1-(4-fluorobenzyl)-5-hydroxy-indole-3-yl]-glyoxylic acid amide (AWD 12-281), in human cell preparations

Exploring the Therapeutic Landscape: A Narrative Review on Topical and Oral Phosphodiesterase-4 Inhibitors in Dermatology

Phosphodiesterase-4 (PDE4) is involved in the synthesis of inflammatory cytokines that mediate several chronic inflammatory disorders, including psoriasis and atopic dermatitis. In recent years, the therapeutic armamentarium in dermatology has expanded with the introduction of PDE4 inhibitors, both in oral and topical formulations. PDE4 inhibitors have gained increasing interest due to their remarkable safety record and ease of prescription, as evidenced by the recent influx of literature detailing its off-label uses. Apremilast was the first PDE4 inhibitor approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for psoriasis, psoriatic arthritis, and oral ulcers of Behcet's disease. Off-label use has been reported in diverse dermatological conditions, including aphthous stomatitis, chronic actinic dermatitis, atopic dermatitis, cutaneous sarcoidosis, hidradenitis suppurativa, lichen planus, and discoid lupus erythematosus. Roflumilast is a PDE4 inhibitor that was approved by the FDA and the EMA as an oral treatment of chronic obstructive pulmonary disease. Since patent expiration, several generic formulations of oral roflumilast have become available, and various studies have documented its off-label use in psoriasis and other dermatological conditions such as hidradenitis suppurativa, recurrent oral aphthosis, nummular eczema, lichen planus, and Behçet's disease. Topical roflumilast has received FDA approval for treatment of plaque psoriasis and seborrheic dermatitis. The favorable safety profile encourages its long-term use as an alternative to corticosteroids, addressing the chronic nature of many dermatological conditions. New oral PDE4 inhibitors are being developed, such as orismilast (LEO-32731), mufemilast (Hemay005), difamilast (OPA-15406) or lotamilast (E6005/RVT-501), among others. This narrative review provides a comprehensive synthesis of the pharmacology, clinical efficacy, safety profile, and practical considerations regarding the oral and topical use of PDE4 inhibitors in dermatology.

PDE4 Inhibitors and their Potential Combinations for the Treatment of Chronic Obstructive Pulmonary Disease: A Narrative Review

Chronic Obstructive Pulmonary Disease (COPD) is associated with cough, sputum production, and a reduction in lung function, quality of life, and life expectancy. Currently, bronchodilator combinations (β2-agonists and muscarinic receptor antagonists, dual therapy) and bronchodilators combined with inhaled corticosteroids (ICS), triple therapy, are the mainstays for the management of COPD. However, the use of ICS in triple therapy has been shown to increase the risk of pneumonia in some patients. These findings have laid the foundation for developing new therapies that possess both anti-inflammatory and/or bronchodilation properties. Phosphodiesterase-4 (PDE4) inhibitors have been reported as an effective therapeutic strategy for inflammatory conditions, such as asthma and COPD, but their use is limited because of class-related side effects. Efforts have been made to mitigate these side effects by targeting the PDE4B subtype of PDE4, which plays a pivotal role in the anti-inflammatory effects. Unfortunately, no selective oral PDE4B inhibitors have progressed to clinical trials. This has led to the development of inhaled PDE4 inhibitors to minimize systemic exposure and maximize the therapeutic effect. Another approach, the bronchodilation property of PDE3 inhibitors, is combined with anti-inflammatory PDE4 inhibitors to develop dual inhaled PDE4/PDE3 inhibitors. A few of these dual inhibitors have shown positive effects and are in phase 3 studies. The current review provides an overview of various PDE4 inhibitors in the treatment of COPD. The possibility of studying different selective PDE4 inhibitors and dual PDE3/4 inhibitors in combination with currently available treatments as a way forward to increase their therapeutic effectiveness is also emphasized.

BI 1015550: an investigational phosphodiesterase 4B (PDE4B) inhibitor for lung function decline in idiopathic pulmonary fibrosis (IPF)

INTRODUCTION

The two available therapies for idiopathic pulmonary fibrosis (IPF), pirfenidone and nintedanib, slow down but do not halt IPF progression. Therefore, several agents with specific molecular targets have been recently investigated to find a cure for IPF. Phosphodiesterase 4 (PDE4) inhibition is known for its anti-inflammatory and antifibrotic properties. BI 1015550, an oral preferential inhibitor of the isoform PDE4B, could express complementary activity to current therapies in IPF and other forms of progressive pulmonary fibrosis.

AREAS COVERED

In this review, we first provide an overview toof the current IPF treatment market, followed by the description of pharmacokinetics and pharmacodynamics of BI 1015550. The main preclinical and early clinical evidence on BI 1015550 is then described, as well as its potential as an IPF treatment.

EXPERT OPINION

Oral treatment with BI 1015550 was shown to stabilize lung function as compared to placebo over 12 weeks, both among patients with and without background antifibrotic use, with an acceptable safety profile in a phase 2 trial, and a phase 3 trial has been initiated. To date, this represents to date the largest effect size for an IPF investigational drug tested in a phase 2 trial with the shortest duration.

Advances in the Development of Phosphodiesterase-4 Inhibitors

Cyclic nucleotide phosphodiesterase 4 (PDE4) specifically hydrolyzes cyclic adenosine monophosphate (cAMP) and plays vital roles in biological processes such as cancer development. To date, PDE4 inhibitors have been widely studied as therapeutics for the treatment of various diseases such as chronic obstructive pulmonary disease, and many of them have progressed to clinical trials or have been approved as drugs. Herein, we review the advances in the development of PDE4 inhibitors in the past decade and will focus on their pharmacophores, PDE4 subfamily selectivity, and therapeutic potential. Hopefully, this analysis will lead to a strategy for development of novel therapeutics targeting PDE4.

Inhaled Phosphodiesterase 4 (PDE4) Inhibitors for Inflammatory Respiratory Diseases

PDE4 inhibitors can suppress a variety of inflammatory cell functions that contribute to their anti-inflammatory actions in respiratory diseases like chronic obstructive pulmonary disease (COPD) and asthma. The systemically delivered PDE4 inhibitor roflumilast has been approved for use in a subset of patients with severe COPD with chronic bronchitis and a history of exacerbations. Use of systemically delivered PDE4 inhibitors has been limited by systemic side effects. Inhaled PDE4 inhibitors have been considered as a viable alternative to increase tolerability and determine the maximum therapeutic potential of PDE4 inhibition in respiratory diseases.

Anti-inflammatory effects of the phosphodiesterase type 4 inhibitor CHF6001 on bronchoalveolar lavage lymphocytes from asthma patients

BACKGROUND

Lymphocytes play a key role in asthma pathophysiology, secreting various cytokines involved in chronic inflammation. CHF6001 is a highly potent and selective phosphodiesterase type 4 (PDE4) inhibitor designed for inhaled administration and has been shown to reduce the late asthmatic response. However, the effect of PDE4 inhibition on the different cytokines produced by lung lymphocytes from asthma patients has not been examined.

METHODS

This study investigated the anti-inflammatory effects of CHF6001 and the corticosteroid, 17-BMP, on T-cell receptor (TCR) stimulated Th1, Th2 and Th17 cytokine release from bronchoalveolar lavage (BAL) cells from mild (n = 12) and moderate asthma (n = 12) patients.

RESULTS

CHF6001 inhibited IFNγ, IL-2 and IL-17, but not IL-13, secretion from both mild and moderate asthma patient BAL cells; there was a greater effect on IFNγ and IL-2 than IL-17. The corticosteroid inhibited all four cytokines from both patient groups, but was less effective in cells from more severe patients. CHF6001 had a greater inhibitory effect on IFNγ and IL-2 than 17-BMP.

CONCLUSION

The PDE4 inhibitor CHF6001 had a greater effect on Th1 cytokines from TCR-stimulated BAL cells than corticosteroid. This pharmacological effect suggests the therapeutic potential for PDE4 inhibitors to be used in the subset of more severe asthma patients with increased airway levels of IFNγ.

Therapeutic potential of ASP3258, a selective phosphodiesterase 4 inhibitor, on chronic eosinophilic airway inflammation

We investigated and compared the pharmacological effects of a PDE4 inhibitor ASP3258 (3-[4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl] propanoic acid), with those of roflumilast, the most clinically advanced PDE4 inhibitor known. ASP3258 inhibited human PDE4A, 4B, 4C, and 4D with respective IC(50) values of 0.036, 0.050, 0.45, and 0.035 nmol/l, all approximately 3-6 times more potent than roflumilast. ASP3258 inhibited LPS-induced TNF-α production and PHA-induced IL-5 production in human whole blood cells with respective IC(50) values of 110 and 100 nmol/l, both approximately 10 times less potent than roflumilast. Repeatedly administered ASP3258 and roflumilast both suppressed chronic airway eosinophilia induced by repeated exposure to ovalbumin in Brown Norway rats with respective ED(50) values of 0.092 and 0.17 mg/kg. We also evaluated the toxicological profiles of ASP3258. Although PDE4 inhibitors induce emesis by mimicking the pharmacological action of an α(2)-adrenoceptor antagonist, repeated administration of ASP3258 (3 mg/kg) had no such inhibitory effect on rats anesthetized with α(2) - adrenoceptor agonist. PDE4 inhibitors are also known to induce vascular injury in rats. Although repeatedly administered ASP3258 (3 and 10 mg/kg) significantly increased plasma fibrinogen, a biomarker for toxicity, 1 mg/kg of ASP3258 did not. These results suggest that ASP3258 is an attractive PDE4 inhibitor for treating chronic eosinophilic airway inflammation due to asthma.

The effect of HS-111, a novel thiazolamine derivative, on apoptosis and angiogenesis of hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is one of the most common malignancies, yet there have been no significant advances in effective therapeutics. In this study, HS-111 was synthesized as a novel thiazolamine derivative, N-(5-(2-chlorobenzyl) thiazole-2-yl) benzofuran-2-carboxamide, and its anticancer effect and mechanism were examined in human HCC cells. HS-111 strongly suppressed the growth of HCC cells in a dose-dependent manner. Also, apoptosis by HS-111 was identified by DAPI and TUNEL staining, and the increases of the cleaved caspase-3 were observed. In addition, HS-111 decreased protein expression of hypoxia-inducible factor (HIF-1α) and secretion of vascular endothelial growth factor (VEGF), and inhibited tube formation and the migration of human umbilical vein endothelial cells (HUVECs). These results showed that HS-111 not only inhibited cell growth and angiogenesis, but also induced apoptosis of human HCC cells. We suggest that HS-111 may be a potential candidate for chemotherapy against HCC.

Discovery of a novel orally active PDE-4 inhibitor effective in an ovalbumin-induced asthma murine model

Phosphodiesterase-4 (PDE-4) is responsible for metabolizing adenosine 3',5'-cyclic monophosphate that reduces the activation of a wide range of inflammatory cells including eosinophils. PDE-4 inhibitors are under development for the treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease. Herein, we report a novel PDE-4 inhibitor, PDE-423 (3-[1-(3-cyclopropylmethoxy-4-difluoromethoxybenzyl)-1H-pyrazol-3-yl]-benzoic acid), which shows good in vitro and in vivo oral activities. PDE-423 exhibited in vitro IC(50)s of 140 nM and 550 nM in enzyme assay and cell-based assay, respectively. In vivo study using ovalbumin-induced asthmatic mice revealed that PDE-423 reduced methacholine-stimulated airway hyperreactivity in a dose-dependent manner by once daily oral administration (ED(50)=18.3 mg/kg), in parallel with decreased eosinophil peroxidase activity and improved lung histology. In addition, PDE-423 was effective in diminishing lipopolysaccharide-induced neutrophilia in vivo as well as in vitro. Oral administration of PDE-423 (100 mg/kg) had no effect on the duration of xylazine/ketamine-induced anesthesia and did not induce vomiting incidence in ferrets up to the dose of 1000 mg/kg. The present study indicates that a novel PDE-4 inhibitor, PDE-423, has good pharmacological profiles implicating this as a potential candidate for the development of a new anti-asthmatic drug.

Hesperetin, a Selective Phosphodiesterase 4 Inhibitor, Effectively Suppresses Ovalbumin-Induced Airway Hyperresponsiveness without Influencing Xylazine/Ketamine-Induced Anesthesia

Hesperetin, a selective phosphodiesterase (PDE)4 inhibitor, is present in the traditional Chinese medicine, “Chen Pi.” Therefore, we were interested in investigating its effects on ovalbumin- (OVA-) induced airway hyperresponsiveness, and clarifying its rationale for ameliorating asthma and chronic obstructive pulmonary disease (COPD). Hesperetin was revealed to have a therapeutic (PDE4_H/PDE4_L) ratio of >11. Hesperetin (10 ~ 30 μmol/kg, intraperitoneally (i.p.)) dose-dependently and significantly attenuated the airway hyperresponsiveness induced by methacholine. It also significantly suppressed the increases in total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, and levels of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon-γ, and tumor necrosis factor-α in bronchoalveolar lavage fluid (BALF). It dose-dependently and significantly suppressed total and OVA-specific immunoglobulin E levels in the BALF and serum. However, hesperetin did not influence xylazine/ketamine-induced anesthesia, suggesting that hesperetin has few or no emetic effects. In conclusion, the rationales for ameliorating allergic asthma and COPD by hesperetin are anti-inflammation, immunoregulation, and bronchodilation.

Hesperetin-7,3'-O-dimethylether selectively inhibits phosphodiesterase 4 and effectively suppresses ovalbumin-induced airway hyperresponsiveness with a high therapeutic ratio

Background

Hesperetin was reported to selectively inhibit phosphodiesterase 4 (PDE4). While hesperetin-7,3'-O-dimethylether (HDME) is a synthetic liposoluble hesperetin. Therefore, we were interested in investigating its selectivity on PDE4 and binding ability on high-affinity rolipram-binding sites (HARBs) in vitro, and its effects on ovalbumin-induced airway hyperresponsiveness in vivo, and clarifying its potential for treating asthma and chronic obstructive pulmonary disease (COPD).

Methods

PDE1~5 activities were measured using a two-step procedure. The binding of HDME on high-affinity rolipram-binding sites was determined by replacing 2 nM [³H]-rolipram. AHR was assessed using the FlexiVent system and barometric plethysmography. Inflammatory cells were counted using a hemocytometer. Cytokines were determined using mouse T helper (Th)1/Th2 cytokine CBA kits, and total immunoglobulin (Ig)E or IgG_2a levels were done using ELISA method. Xylazine (10 mg/kg)/ketamine (70 mg/kg)-induced anesthesia was performed.

Results

HDME revealed selective phosphodiesterase 4 (PDE4) inhibition with a therapeutic (PDE4_H/PDE4_L) ratio of 35.5 in vitro. In vivo, HDME (3~30 μmol/kg, orally (p.o.)) dose-dependently and significantly attenuated the airway resistance (R_L) and increased lung dynamic compliance (C_dyn), and decreased enhanced pause (P_enh) values induced by methacholine in sensitized and challenged mice. It also significantly suppressed the increases in the numbers of total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, and levels of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon-γ, and tumor necrosis factor-α in bronchoalveolar lavage fluid (BALF) of these mice. In addition, HDME (3~30 μmol/kg, p.o.) dose-dependently and significantly suppressed total and ovalbumin-specific immunoglobulin (Ig)E levels in the BALF and serum, and enhanced IgG_2a level in the serum of these mice.

Conclusions

HDME exerted anti-inflammatory effects, including suppression of AHR, and reduced expressions of inflammatory cells and cytokines in this murine model, which appears to be suitable for studying the effects of drugs on atypical asthma and COPD, and for screening those on typical asthma. However, HDME did not influnce xylazine/ketamine-induced anesthesia. Thus HDME may have the potential for use in treating typical and atypical asthma, and COPD.

Biochanin a, a phytoestrogenic isoflavone with selective inhibition of phosphodiesterase 4, suppresses ovalbumin-induced airway hyperresponsiveness

The present study investigated the potential of biochanin A, a phytoestrogenic isoflavone of red clover (Triflolium pratense), for use in treating asthma or chronic obstructive pulmonary disease (COPD). Biochanin A (100 μmol/kg, orally (p.o.)) significantly attenuated airway resistance (R_L), enhanced pause (P_enh), and increased lung dynamic compliance (C_dyn) values induced by methacholine (MCh) in sensitized and challenged mice. It also significantly suppressed an increase in the number of total inflammatory cells, neutrophils, and eosinophils, and levels of cytokines, including interleukin (IL)-2, IL-4, IL-5, and tumor necrosis factor (TNF)-α in bronchoalveolar lavage fluid (BALF) of the mice. However, it did not influence interferon (IFN)-γ levels. Biochanin A (100 μmol/kg, p.o.) also significantly suppressed the total and ovalbumin (OVA)-specific immunoglobulin E (IgE) levels in the serum and BALF, and enhanced the total IgG_2a level in the serum of these mice. The PDE4_H/PDE4_L value of biochanin A was calculated as >35. Biochanin A did not influence xylazine/ketamine-induced anesthesia. Biochanin A (10~30 μM) significantly reduced cumulative OVA (10~100 μg/mL)-induced contractions in the isolated guinea pig trachealis, suggesting that it inhibits degranulation of mast cells. In conclusion, red clover containing biochanin A has the potential for treating allergic asthma and COPD.

S-Petasin, the Main Sesquiterpene of Petasites formosanus, Inhibits Phosphodiesterase Activity and Suppresses Ovalbumin-Induced Airway Hyperresponsiveness

S-Petasin is the main sesquiterpene of Petasites formosanus, a traditional folk medicine used to treat hypertension, tumors and asthma in Taiwan. The aim of the present study was to investigate its inhibitory effects on phosphodiesterase (PDE) 1–5, and on ovalbumin (OVA)-induced airway hyperresponsiveness (AHR) in a murine model of allergic asthma. S-Petasin concentration-dependently inhibited PDE3 and PDE4 activities with 50% inhibitory concentrations (IC₅₀) of 25.5, and 17.5 μM, respectively. According to the Lineweaver-Burk analysis, S-petasin competitively inhibited PDE3 and PDE4 activities with respective dissociation constants for inhibitor binding (K_i) of 25.3 and 18.1 μM, respectively. Both IC₅₀ and K_i values for PDE3 were significantly greater than those for PDE4. S-Petasin (10–30 μmol/kg, administered subcutaneously (s.c.)) dose-dependently and significantly attenuated the enhanced pause (P_enh) value induced by methacholine (MCh) in sensitized and challenged mice. It also significantly suppressed the increases in total inflammatory cells, lymphocytes, neutrophils, eosinophils and levels of cytokines, including interleukin (IL)-2, IL-4 and IL-5, tumor necrosis factor (TNF)-α and interferon (IFN)-γ in bronchoalveolar lavage fluid (BALF) of these mice. In addition, S-petasin (10–30 μmol/kg, s.c.) dose-dependently and significantly attenuated total and OVA-specific immunoglobulin E (IgE) levels in the serum and BALF, and enhanced the IgG_2a level in serum of these mice. The PDE4_H value of S-petasin was >300 μM; therefore, its PDE4_H/PDE4_L value was calculated to be >17. In conclusion, the present results for S-petasin at least partially explain why Petasites formosanus is used as a folk medicine to treat asthma in Taiwan.

Pharmacology, clinical efficacy, and tolerability of phosphodiesterase-4 inhibitors: impact of human pharmacokinetics

Since more than two decades anti-inflammatory effects of inhibitors of phosphodiesterase-4 have been described in numerous cellular and animal studies and were finally confirmed in clinical trials. The path from an early, pioneering study with Ro20-1724 showing reduction of psoriatric plaque size in 1979 to modern PDE4 inhibitors such as oral apremilast in development for psoriasis, the inhaled PDE4 inhibitor GSK256066 in development for asthma and COPD and finally roflumilast, the first PDE4 inhibitor approved and currently marketed as an oral, once-daily remedy for severe COPD was marked by large progress in chemical optimization based on improved understanding of PDE4 biology and drug-like properties determining the appropriate pharmacokinetic profile. In this chapter aspects of the pharmacology and clinical efficacy of PDE4 inhibitors, which have been in clinical development over the years are summarized with specific emphasis on their clinical pharmacokinetic properties.

Genistein, a competitive PDE1-4 inhibitor, may bind on high-affinity rolipram binding sites of brain cell membranes and then induce gastrointestinal adverse effects

The affinities of genistein on phosphodiesterase (PDE)1-4 and cause of gastrointestinal adverse effects of genistein remain unclear. Female BALB/c mice were actively sensitized by intraperitoneal injections of ovalbumin and challenged by aerosolized ovalbumin (1%). After secondary challenge, aerosolized methacholine (6.25-50mg/ml) induced increases of enhanced pause (P(enh)) values in conscious mice in a concentration-dependent manner. Genistein (30-100 micromol/kg, i.p.) markedly inhibited methacholine (12.5-50mg/ml)-induced increase of P(enh) value in the sensitized and challenged mice. In addition, genistein significantly reduced total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils in bronchoalveolar lavage fluid, with the exception that lymphocytes and neutrophils were not significantly inhibited by genistein at the lowest dose (10 micromol/kg). Genistein also markedly attenuated the release of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. Genistein competitively inhibited PDE1-4, with a K(i) value ranging from 4.3 to 13.7 microM. Genistein (3-300 microM) concentration-dependently displaced 2nM [(3)H]-rolipram bound on high-affinity rolipram binding sites of brain cell membranes. The therapeutic ratio of genistein was calculated to be 7.9. Genistein (100 micromol/kg, s.c.) significantly shortened xylazine/ketamine-induced anesthesia, suggesting that genistein administered at a higher dose may have gastrointestinal adverse effects. In conclusion, owing to the low therapeutic ratio of genistein, the gastrointestinal adverse effects may be induced via the binding of genistein on high-affinity rolipram binding sites of brain cell membranes, when it is used for a long term or at higher doses for treating allergies, asthma or chronic obstructive pulmonary disease.

Ayanin, a non-selective phosphodiesterase 1-4 inhibitor, effectively suppresses ovalbumin-induced airway hyperresponsiveness without affecting xylazine/ketamine-induced anesthesia

In recent in vitro reports, the IC(50) value of ayanin (quercetin-3,7,4'-O-trimethylether) was 2.2microM for inhibiting interleukin (IL)-4 production from purified basophils, and its therapeutic ratio was >19. Therefore, we were interested in investigating the effects on ovalbumin induced airway hyperresponsiveness in vivo, and to clarify its potential for treating asthma. Ayanin (30-100micromol/kg, orally (p.o.)) dose-dependently and significantly attenuated the enhanced pause (P(enh)) value induced by methacholine in sensitized and challenged mice. It also significantly suppressed the increases in total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, and levels of cytokines, including IL-2, IL-4, IL-5, and tumor necrosis factor (TNF)-alpha in bronchoalveolar lavage fluid of these mice. However, at 100micromol/kg, it significantly enhanced the level of interferon (IFN)-gamma. In addition, ayanin (30-100micromol/kg, p.o.) dose-dependently and significantly suppressed total and OVA-specific immunoglobulin (Ig)E levels in the serum and bronchoalveolar lavage fluid, and enhanced the IgG(2a) level in serum of these mice. In the present results, ayanin did not affect xylazine/ketamine-induced anesthesia, suggesting that ayanin has few or no adverse effects, such as nausea, vomiting, and gastric hypersecretion. In conclusion, the above results suggest that ayanin may have the potential for use in treating allergic asthma.

Therapeutic targets for persistent airway inflammation in refractory asthma

The management of refractory asthma remains a compelling clinical problem that contributes significantly to the morbidity of patients as well as posing a financial burden to the health system. Treatment failure in this group of patients is associated with continued airway inflammation and dampening of the inflammatory cascade is the focus of much research in this area. Continued airway inflammation has been associated with higher patient morbidity and is being increasingly measured using markers of systemic and local inflammation in order to target therapy more effectively. This review focuses on the published evidence for both established and novel treatments in refractory asthma that act to control this pathological inflammatory process. No clear treatment yet exists to control this process and further research into inhibiting newly elucidated inflammatory pathways or new drugs more effectively or accurate targeting existing pathways are discussed along with the clinical evidence and the relative merits of each treatment.

Doxofylline: a promising methylxanthine derivative for the treatment of asthma and chronic obstructive pulmonary disease

BACKGROUND

Doxofylline, a methylxanthine derivative, has recently drawn attention because of its better safety profile and similar efficacy over the most widely prescribed analogue, theophylline, indicated for asthma and chronic obstructive pulmonary disease.

OBJECTIVE

This article attempts to discuss the pharmacodynamics/pharmacokinetics and clinical efficacy of doxofylline.

METHOD

An extensive search in three electronic databases (Unbound Medline, Pubmed and Sciencedirect) and internet search engines (Scirus and Google Scholar) were used to identify the clinical studies on doxofylline. The literature search was carried out without time constraints to ensure maximum coverage of existing literature on doxofylline.

RESULTS/CONCLUSION

In a relatively large number of comparative studies, doxofylline is indicated to have less affinity for alpha(1) and alpha(2) receptors than theophylline. Unlike theophylline, doxofylline does not antagonize calcium channels, nor does it interfere with the influx of calcium into the cells, which probably reduces the cardiac side effects. Moreover, it does not affect sleep rhythm, gastric secretions, heart rate and rhythm and CNS functioning. Numerous reports available regarding the better tolerability of doxofylline than theophylline prove it as a potential bronchodilator with promising pharmacological behavior. However, despite its superior safety and clinical efficacy, the potential of doxofylline has not been fully exploited.

Luteolin, a non-selective competitive inhibitor of phosphodiesterases 1-5, displaced [3H]-rolipram from high-affinity rolipram binding sites and reversed xylazine/ketamine-induced anesthesia

The aim of the present study was to investigate the mode of action of luteolin on phisphodiesterase (PDE) 1-5, and the possible adverse effects, such as nausea, vomiting, and gastric hypersecretion, determined by replacing [(3)H]-rolipram binding and reversing xylazine/ketamine-induced anesthesia. The reversing effect was reported to occur through a presynaptic alpha(2)-adrenoceptor inhibition and trigger vomiting in ferrets. In contrast, clonidine, an alpha(2)-adrenoceptor agonist, prevented emesis induced by PDE4 inhibitors in ferrets. According to the Lineweaver-Burk analysis, luteolin (3-30 microM) competitively inhibited PDE1-5 activities, with K(i) values of 15.0, 6.4, 13.9, 11.1, and 9.5 microM, respectively, which did not significantly differ from each other. The equilibrium dissociation constant (K(d)) and maximal density (B(max)) for [(3)H]-rolipram binding at high-affinity rolipram binding sites of guinea pig brain cell membranes were 10.1 nM and 3.7 p mol/g of tissue, respectively. The EC(50) (PDE4(H)) values of luteolin and Ro 20-1724, a selective PDE4 inhibitor, for displacing 2 nM [(3)H]-rolipram binding were 11.2 microM and 45.6 nM, respectively. The therapeutic (PDE4(H)/PDE4(L)) ratios of luteolin and Ro 20-1724 were calculated to be 0.6, and 0.004, respectively. Both luteolin (10-30 micromol/kg, s.c.) and Ro 20-1724 (0.1-1 micromol/kg, s.c.) significantly reversed the xylazine/ketamine-induced anesthesia in mice. Although luteolin non-selectively and competitively inhibited PDE1-5, only PDE4 inhibition contributed to a reversing effect. In conclusion, because of the low therapeutic (PDE4(H)/PDE4(L)) ratio of luteolin, the gastrointestinal adverse effects such as nausea, vomiting and gastric hypersecretion should be carefully monitored, whenever luteolin is used for treating allergies, asthma or chronic obstructive pulmonary disease.

The identification of a novel phosphodiesterase 4 inhibitor, 1-ethyl-5-{5-[(4-methyl-1-piperazinyl)methyl]-1,3,4-oxadiazol-2-yl}-N-(tetrahydro-2H-pyran-4-yl)-1H-pyrazolo[3,4-b]pyridin-4-amine (EPPA-1), with improved therapeutic index using pica feeding in rats as a measure of emetogenicity

Clinical utility of phosphodiesterase 4 (PDE4) inhibitors as anti-inflammatory agents has, to date, been limited by adverse effects including nausea and emesis, making accurate assessment of emetic versus anti-inflammatory potencies critical to the development of inhibitors with improved therapeutic indices. In the present study we determined the in vitro and in vivo anti-inflammatory potencies of the first-generation PDE4 inhibitor, rolipram, the second-generation inhibitors, roflumilast and cilomilast, and a novel third generation inhibitor, 1-ethyl-5-{5-[(4-methyl-1-piperazinyl)methyl]-1,3,4-oxadiazol-2-yl}-N-(tetrahydro-2H-pyran-4-yl)-1H-pyrazolo[3,4-b]pyridin-4-amine (EPPA-1). The rank-order potency against lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha production by human peripheral blood mononuclear cells was roflumilast (IC(50) = 5 nM) > EPPA-1 (38) > rolipram (269) > cilomilast (389), and against LPS-induced pulmonary neutrophilia in the rat was EPPA-1 (D(50) = 0.042 mg/kg) > roflumilast (0.24) > rolipram (3.34) > cilomilast (4.54). Pica, the consumption of non-nutritive substances in response to gastrointestinal stress, was used as a surrogate measure for emesis, giving a rank-order potency of rolipram (D(50) = 0.495 mg/kg) > roflumilast (1.6) > cilomilast (6.4) > EPPA-1 (24.3). The low and high emetogenic activities of EPPA-1 and rolipram, respectively, detected in the pica model were confirmed in a second surrogate model of emesis, reversal of alpha(2)-adrenoceptor-mediated anesthesia in the mouse. The rank order of therapeutic indices derived in the rat [(pica D(50))/(neutrophilia D(50))] was EPPA-1 (578) > roflumilast (6.4) > cilomilast (1.4) > rolipram (0.15), consistent with the rank order derived in the ferret [(emesis D(50))/(neutrophilia D(50))]. These data validate rat pica feeding as a surrogate for PDE4 inhibitor-induced emesis in higher species, and identify EPPA-1 as a novel PDE4 inhibitor with an improved therapeutic index.

Prostaglandin E(2) suppresses staphylococcal enterotoxin-induced eosinophilia-associated cellular responses dominantly through an E-prostanoid 2-mediated pathway in nasal polyps

BACKGROUND

Recent investigations have revealed that staphylococcal enterotoxins (SEs), COX metabolism, or both might participate in the pathogenesis of eosinophilic airway diseases, such as chronic rhinosinusitis with nasal polyposis.

OBJECTIVE

We sought to determine whether COX metabolism, especially prostaglandin (PG) E(2), plays a significant role in SE-induced cellular responses in nasal polyps.

METHODS

Dispersed nasal polyp cells (DNPCs) were prepared from nasal polyps by means of enzymatic digestion. DNPCs were cultured with SEB in the presence or absence of COX inhibitors (diclofenac and indomethacin) for 72 hours; then the levels of IL-5, IL-13, RANTES, and eotaxin in the supernatants were measured. The effect of PGE(2) on SEB-induced responses by diclofenac-treated DNPCs was examined, especially in terms of receptor specificity.

RESULTS

DNPCs produced significant amounts of IL-5, IL-13, and RANTES in response to SEB. COX inhibitors significantly increased the production of these cytokines. The degree of local eosinophilia was significantly and positively correlated with the changes in IL-5 production induced by diclofenac treatment. PGE(2) significantly and dose-dependently inhibited SEB-induced IL-5, IL-13, and RANTES production by diclofenac-treated DNPCs. E-prostanoid (EP) 2 receptor-selective agonist strongly inhibited the production of all 3 cytokines. EP3 and EP4 receptor-selective agonists partially suppressed these responses, whereas EP1 receptor-selective agonist did not. Interestingly, all of the combined treatments with 2 of the 4 EP receptor-selective agonists significantly inhibited the SEB-induced responses by diclofenac-treated DNPCs.

CONCLUSIONS

These results suggest that PGE(2) inhibits the pathogenesis of SEB-induced eosinophilic inflammation primarily through the EP2-mediated pathway in patients with chronic rhinosinusitis with nasal polyposis.

Enhanced PDE4B expression augments LPS-inducible TNF expression in ethanol-primed monocytes: relevance to alcoholic liver disease

Increased plasma and hepatic TNF-alpha expression is well documented in patients with alcoholic hepatitis and is implicated in the pathogenesis of alcoholic liver disease. We have previously shown that monocytes from patients with alcoholic hepatitis show increased constitutive and LPS-induced NF-kappaB activation and TNF-alpha production. Our recent studies showed that chronic ethanol exposure significantly decreased cellular cAMP levels in both LPS-stimulated and unstimulated monocytes and Kupffer cells, leading to an increase in LPS-inducible TNF-alpha production by affecting NF-kappaB activation and induction of TNF mRNA expression. Accordingly, the mechanisms underlying this ethanol-induced decrease in cellular cAMP leading to an increase in TNF expression were examined in monocytes/macrophages. In this study, chronic ethanol exposure was observed to significantly increase LPS-inducible expression of cAMP-specific phosphodiesterase (PDE)4B that degrades cellular cAMP. Increased PDE4B expression was associated with enhanced NF-kappaB activation and transcriptional activity and subsequent priming of monocytes/macrophages leading to enhanced LPS-inducible TNF-alpha production. Selective inhibition of PDE4 by rolipram abrogated LPS-mediated TNF-alpha expression at both protein and mRNA levels in control and ethanol-treated cells. Notably, PDE4 inhibition did not affect LPS-inducible NF-kappaB activation but significantly decreased NF-kappaB transcriptional activity. These findings strongly support the pathogenic role of PDE4B in the ethanol-mediated priming of monocytes/macrophages and increased LPS-inducible TNF production and the subsequent development of alcoholic liver disease (ALD). Since enhanced TNF expression plays a significant role in the evolution of clinical and experimental ALD, its downregulation via selective PDE4B inhibitors could constitute a novel therapeutic approach in the treatment of ALD.

Inhibitory effects of quercetin derivatives on phosphodiesterase isozymes and high-affinity [(3) H]-rolipram binding in guinea pig tissues

Rolipram has high (PDE4(H)) and low (PDE4(L)) affinities for phosphodiesterase (PDE)-4, respectively. In general, it is believed that inhibitions by PDE4(H) and PDE4(L) are respectively associated with an adverse response and with anti-inflammatory and bronchodilating effects. This has provided a rational basis for designing new compounds with high PDE4(H)/PDE4(L) ratios. In the present study, we attempted to determine the PDE4(H)/PDE4(L) ratios of quercetin (1), qercetin-3-O-methylether (3-MQ, 2), quercetin-3,7,4'-O-trimethylether (ayanin, 3), quercetin-3,7,3',4'-O- tetramethylether (QTME, 4), quercetin-3,5,7,3',4'-O-petamethylether (QPME, 5), quercetin-3,5,7,3',4'-O-pentaacetate (QPA, 6), and quercetin-3-O-methyl-5,7,3',4'-O-tetraacetate (QMTA, 7). The activities of PDE1 approximately 5, which were partially separated from homogenates of guinea pig lungs and hearts, were measured by a two-step procedure using adenosine 3',5'-cyclic monophosphate (cAMP) with [(3) H]-cAMP or guanosine 3',5'-cyclic monophosphate (cGMP) with [(3) H]-cGMP as substrates. The IC(50) values of all of these compounds except quercetin (1), 3-MQ (2), and QMTA (7) on PDE1 approximately 5 inhibition were determined. The anti-inflammatory effects of PDE4 inhibitors were reported to be associated with inhibition of PDE4 catalytic activity. Therefore, these IC(50) values for PDE4 inhibition were taken as the PDE4(L) values. The effective concentration (EC(50)), at which one half of the [(3) H]-rolipram bound to high-affinity rolipram binding sites (HARBSs) of brain cell membranes was replaced, was defined as the PDE4(H) value. In the present results, the PDE4(H)/PDE4(L) ratios of quercetin (1), ayanin (3), and QPME (5) were >30, >19, and 11, respectively (Table 1), which are higher than or equal to that of AWD12-281, the selective PDE4 inhibitor with the greatest potential currently undergoing clinical trials for treating asthma and chronic obstructive pulmonary disease.

Small-molecule inhibitors of PDE-IV and -VII in the treatment of respiratory diseases and chronic inflammation

Targeting phosphodiesterase IV (PDE-IV) with small-molecule inhibitors as a therapeutic for chronic inflammatory disorders has been an active area of research interest for many years. The major drawback, however, has been to develop pharmacophores that would differentiate between targeting isoforms of PDE-IV associated with inflammation, as opposed to those that cause emesis, a major side effect associated with PDE-IV inhibition. Several different approaches have been employed, including designing subtype selective PDE-IV inhibitors. A recent approach has been to develop chemotypes that target PDE-VII, a cAMP-specific PDE, expressed widely in immune and pro-inflammatory cells. It is hypothesized that dual inhibitors, which function to inhibit both PDE-IV and VII, may achieve a higher therapeutic index and thereby exhibit a lower propensity to cause adverse side effects that are characteristic when targeting PDE-IV alone. This review focuses on the major classes of compounds that are presently being studied for their potential to inhibit PDE-VII and discusses the available data in the development of dual PDE-IV and -VII inhibitors, their biologic activity and their scope as a therapeutic choice in chronic inflammatory diseases.

The potential role of roflumilast: the new phosphodiesterase-4 inhibitor

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of roflumilast in the treatment of asthma and chronic obstructive pulmonary disease (COPD).

DATA SOURCES

Studies, review articles, and meeting abstracts evaluating roflumilast were obtained from MEDLINE (1966-May 16, 2006), EMBASE (1980-May 16, 2006), and International Pharmaceutical Abstracts (1970-May 16, 2006) databases. Key terms used in all of the database searches were roflumilast, phosphodiesterase-4 inhibitor, asthma, chronic obstructive pulmonary disease, and COPD. Company Web sites were reviewed, and bibliographies of selected articles were evaluated for pertinent articles.

STUDY SELECTION AND DATA EXTRACTION

In vitro, in vivo, and animal studies were selected, as were published human studies on the efficacy and safety of roflumilast. Due to limited published data on its safety, efficacy, pharmacokinetics, and drug interactions, meeting abstracts were also selected. Data retrieved from abstracts only is indicated in the references.

DATA SYNTHESIS

Roflumilast is a phosphodiesterase-4 (PDE-4) inhibitor which, due to its selective inhibition of the PDE 4 isoenzyme, has potential antiinflammatory and antimodulatory effects in the pulmonary system. It has been studied as an oral tablet in doses of 250 or 500 microg/day. Animal data and clinical trials have demonstrated roflumilast's efficacy and safety as an antiinflammatory and antimodulatory agent for use in asthma and COPD, with no documented drug interactions and a favorable adverse effect profile.

CONCLUSIONS

Roflumilast may be an additional option in the treatment of asthma and COPD due to its ease of administration and a seemingly favorable adverse event profile. However, more research is needed to solidify roflumilast's place in therapy.

Keynote review: phosphodiesterase-4 as a therapeutic target

Cyclic AMP (cAMP) is a key second messenger in all cells. It is compartmentalized within cells and its levels are controlled, as a result of spatially discrete signaling cassettes controlling its generation, detection and degradation. Underpinning compartmentalized cAMP signaling are approximately 20 members of the phosphodiesterase-4 (PDE4) family. The selective inhibition of this family generates profound, functional effects and PDE4 inhibitors are currently under development to provide potential, novel therapeutics for the treatment of inflammatory diseases, such as asthma, chronic obstructive pulmonary disease and psoriasis, as well as treating depression and serving as cognitive enhancers. Here, we delineate the range of PDE4 isoforms, their role in signaling, their structural biology and related preclinical and clinical pharmacology.

Theophylline as ‘Add-on’ Therapy to Cetirizine in Patients with Chronic Idiopathic Urticaria

BACKGROUND

Chronic urticaria is a prevalent condition associated with substantial disability. Its pathogenesis is not clearly understood and is divided into autoimmune and chronic idiopathic urticaria (CIU). We investigated if the non-specific phosphodiesterase inhibitor theophylline could provide additional benefit to the histamine-1 receptor (H-1R) antagonist cetirizine in CIU.

METHODS

This was a double-blind, placebo-controlled, parallel study. Patients were randomized to receive either cetirizine and theophylline (200 mg twice daily; group A, 67 subjects) or cetirizine and placebo for 6 months (group B, 67 subjects). Group A patients took theophylline for 6 more months. Response was assessed by visual analog scale (VAS) and treatment effectiveness score (TES). Blood theophylline levels were also determined at visit t=1 and t=7.

RESULTS

The study was completed by 54 of the 67 patients (80.6%) in group A and 51 of the 67 patients (76.1%) in group B. The physician VAS values for group A were lower after t=3, while the patient VAS values were decreased after t=2. The physician and patient TES values in group A were statistically higher (p<0.05) at all time points except for t=1. At least 1 month of theophylline addition was necessary to obtain statistically significant benefit over cetirizine, and reducing theophylline by 50% during phase 2 did not alter this benefit. Pruritus values were reduced, but not statistically significant.

CONCLUSIONS

Addition of theophylline to conventional H-1R antagonists was well tolerated without any adverse effects and provided considerable additional benefit in the management of CIU.

Agents against cytokine synthesis or receptors

Various cytokines play a critical role in pathophysiology of chronic inflammatory lung diseases including asthma and chronic obstructive pulmonary disease (COPD). The increasing evidence of the involvement of these cytokines in the development of airway inflammation raises the possibility that these cytokines may become the novel promising therapeutic targets. Studies concerning the inhibition of interleukin (IL)-4 have been discontinued despite promising early results in asthma. Although blocking antibody against IL-5 markedly reduces the infiltration of eosinophils in peripheral blood and airway, it does not seem to be effective in symptomatic asthma, while blocking IL-13 might be more effective. On the contrary, anti-inflammatory cytokines themselves such as IL-10, IL-12, IL-18, IL-23 and interferon-gamma may have a therapeutic potential. Inhibition of TNF-alpha may also be useful in severe asthma or COPD. Many chemokines are also involved in the inflammatory response of asthma and COPD through the recruitment of inflammatory cells. Several small molecule inhibitors of chemokine receptors are now in development for the treatment of asthma and COPD. Antibodies that block IL-8 reduce neutrophilic inflammation. Chemokine CC3 receptor antagonists, which block eosinophil chemotaxis, are now in clinical development for asthma therapy. As many cytokines are involved in the pathophysiology of inflammatory lung diseases, inhibitory agents of the synthesis of multiple cytokines may be more useful tools. Several such agents are now in clinical development.

Theophylline as "add-on" therapy in patients with delayed pressure urticaria: a prospective self-controlled study

Delayed pressure urticaria (DPU) is a skin condition that involves the gradual development of wheals and edema at sites of physical pressure. Its pathogenesis is not clear and histamine-1 receptor (H-1R) antagonists provide only partial relief. In this prospective, clinical study, we investigated the effect of theophylline, which has a long history of benefit in allergic asthma, added to cetirizine in patients with DPU. Twenty three patients received during period 1 cetirizine (10 mg po QD) and theophylline (200 mg po BID) for 6 months, followed by period 2 of 1 month washout with only rescue medication as needed, and then by period 3 with cetirizine (10 mg QD plus placebo (BID) for 5 more months. The addition of theophylline resulted in statistically significant improvement over cetirizine alone by 2 months and continued for the duration of treatment. Treatment of cultured human mast cells with theophylline (10 microM) did not inhibit allergic histamine release, but the in vivo beneficial effect of theophylline may require significant pretreatment period to manifest itself, or may involve inhibition of other mast cell dependent mediators. A double-blind study, accompanied by serum histamine and tryptase levels, should be in order.

Phosphodiesterase-4 as a potential drug target

Phosphodiesterase-4 (PDE4) is the predominant enzyme in some specific cell types that is responsible for the degradation of the second messenger, cAMP. Consequently, PDE4 plays a crucial role in cell signalling and, as such, it has been the target of clinical drug development of various indications, ranging from anti-inflammation to memory enhancement. In this review, the fundamental biological role of PDE4 in intracellular signalling, its tissue distribution and regulation are described. The historical development of various chemical classes of PDE4 inhibitors and the challenges that face these inhibitors as therapeutics are also discussed. Finally, recent advances in the structural biology of PDE4 and their complexes with various inhibitors, as well as its potential impact on the rational design of potent and selective PDE4 inhibitors, are presented.

Cyclic nucleotide phosphodiesterase (PDE) superfamily: a new target for the development of specific therapeutic agents

Cyclic nucleotide phosphodiesterases (PDEs), which are ubiquitously distributed in mammalian tissues, play a major role in cell signaling by hydrolyzing cAMP and cGMP. Due to their diversity, which allows specific distribution at cellular and subcellular levels, PDEs can selectively regulate various cellular functions. Their critical role in intracellular signaling has recently designated them as new therapeutic targets for inflammation. The PDE superfamily represents 11 gene families (PDE1 to PDE11). Each family encompasses 1 to 4 distinct genes, to give more than 20 genes in mammals encoding the more than 50 different PDE proteins probably produced in mammalian cells. Although PDE1 to PDE6 were the first well-characterized isoforms because of their predominance in various tissues and cells, their specific contribution to tissue function and their regulation in pathophysiology remain open research fields. This concerns particularly the newly discovered families, PDE7 to PDE11, for which roles are not yet established. In many pathologies, such as inflammation, neurodegeneration, and cancer, alterations in intracellular signaling related to PDE deregulation may explain the difficulties observed in the prevention and treatment of these pathologies. By inhibiting specifically the up-regulated PDE isozyme(s) with newly synthesized potent and isozyme-selective PDE inhibitors, it may be potentially possible to restore normal intracellular signaling selectively, providing therapy with reduced adverse effects.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

Selective phosphodiesterase-4 inhibitors in chronic obstructive lung disease

PURPOSE OF REVIEW

Chronic obstructive pulmonary disease (COPD) is a disease state characterized by airflow limitation that is usually progressive. In addition, an abnormal inflammatory response of the lungs to noxious particles or gases can be seen throughout the airways, parenchyma, and pulmonary vasculature. So far, anti-inflammatory medications (eg, inhaled corticosteroids) have failed to show a major effect on the decline of lung function in COPD patients. Novel anti-inflammatory therapies such as selective phosphodiesterase 4 (PDE4) inhibitors are in clinical development. Their potential role in the management of COPD is described in this review.

RECENT FINDINGS

Some of the selective PDE4 inhibitors have demonstrated in vitro and in vivo anti-inflammatory activity on cells commonly linked to airway inflammation in COPD, such as neutrophils. While these agents seem to offer only a modest improvement in lung function compared with other bronchodilators, their anti-inflammatory effects appear to provide some substantial benefits in reducing exacerbations and improving health-related quality of life.

SUMMARY

Based on the available data, the second generation of selective PDE4 inhibitors will likely provide additional therapeutic options for the management of COPD. These agents may become an important tool in the treatment of this disease, since they target three important components of COPD: airway obstruction, inflammation, and structural changes.

PDE4 inhibitors as new anti-inflammatory drugs: effects on cell trafficking and cell adhesion molecules expression

Phosphodiesterase 4 (PDE4) is a major cyclic AMP-hydrolyzing enzyme in inflammatory and immunomodulatory cells. The wide range of inflammatory mechanisms under control by PDE4 points to this isoenzyme as an attractive target for new anti-inflammatory drugs. Selective inhibitors of PDE4 have demonstrated a broad spectrum of anti-inflammatory activities including the inhibition of cellular trafficking and microvascular leakage, cytokine and chemokine release from inflammatory cells, reactive oxygen species production, and cell adhesion molecule expression in a variety of in vitro and in vivo experimental models. The initially detected side effects, mainly nausea and emesis, appear at least partially overcome by the 'second generation' PDE4 inhibitors, some of which like roflumilast and cilomilast are in the later stages of clinical development for treatment of chronic obstructive pulmonary disease. These new drugs may also offer opportunities for treatment of other inflammatory diseases.

New therapies for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is the most common lung disease, carrying a significant mortality and morbidity. None of the therapeutic interventions currently available alter the progression of the disease. As our understanding of the basic mechanisms of alveolar destruction and airflow limitation improves, new targets are identified that may eventually result in treatment options which will affect the progression of this disease. In this review, we discuss some of the novel therapeutic options recently developed that may have an impact on the management of COPD. Future directions in research and development of pharmacological agents based on improved understanding of COPD are also discussed.