Selective phosphodiesterase (PDE) 4 and dual PDE3/4 inhibitors have attracted considerable interest as potential therapeutic agents for the treatment of respiratory diseases, largely by virtue of their anti-inflammatory (PDE4) and bifunctional bronchodilator/anti-inflammatory (PDE3/4) effects. Many of these agents have, however, failed in early development for various reasons, including dose-limiting side effects when administered orally and lack of sufficient activity when inhaled. Indeed, only one selective PDE4 inhibitor, the orally active roflumilast-n-oxide, has to date received marketing authorization. The majority of the compounds that have failed were, however, orally administered and non-selective for either PDE3 (A,B) or PDE4 (A,B,C,D) subtypes. Developing an inhaled dual PDE3/4 inhibitor that is rapidly cleared from the systemic circulation, potentially with subtype specificity, may represent one strategy to improve the therapeutic index and also exhibit enhanced efficacy versus inhibition of either PDE3 or PDE4 alone, given the potential positive interactions with regard to anti-inflammatory and bronchodilator effects that have been observed pre-clinically with dual inhibition of PDE3 and PDE4 compared with inhibition of either isozyme alone. This MiniReview will summarize recent clinical data obtained with PDE inhibitors and the potential for these drugs to treat COPD and other inflammatory airways diseases such as asthma and cystic fibrosis.

SummaryChronic obstructive pulmonary disease (COPD) is characterized by an abnormal innate immune response. We have investigated the changes in the innate immune response of COPD alveolar macrophages exposed to both cigarette smoke and Toll-like receptor (TLR) stimulation. COPD and control alveolar macrophages were exposed to cigarette smoke extract (CSE) followed by TLR-2, -4 and -5 ligands [Pam3CSK4, lipopolysaccharide (LPS) and phase I flagellin (FliC), respectively] or non-typeable Haemophilus influenzae (NTHi). CSE exposure suppressed TLR-induced tumour necrosis factor (TNF)-α, interleukin (IL)-6, IL-10 and regulated on activation, normal T cell expressed and secreted (RANTES) production in both COPD and control alveolar macrophages, but had no effect on interleukin 8 (CXCL8) production. Similarly, CSE suppressed NTHi-induced TNF-α but not NTHiinduced CXCL8 production in COPD alveolar macrophages. Gene expression analysis showed that CSE suppressed LPS-induced TNF-α transcription but not CXCL8 transcription in COPD alveolar macrophages. The dampening effect of CSE on LPS-induced cytokine production was associated with a reduction in p38, extracellular signal regulated kinase (ERK) and p65 activation. In conclusion, CSE caused a reduced innate immune response in COPD alveolar macrophages, with the exception of persistent CXCL8 production. This could be a mechanism by which alveolar macrophages promote neutrophil chemotaxis under conditions of oxidative stress and bacterial exposure.

We investigated the short-term bronchodilator effects of RPL554 (an inhaled dual phosphodiesterase 3 and 4 inhibitor) combined with other bronchodilators in chronic obstructive pulmonary disease patients with reversibility (>150 mL to short-acting bronchodilators).Study 1 was a six-way, placebo-controlled crossover study (n=36) with single doses of RPL554 (6 mg), salbutamol (200 µg), ipratropium (40 µg), RPL554 (6 mg)+salbutamol (200 µg), RPL554 (6 mg)+ipratropium (40 µg) or placebo. Study 2 was a three-way crossover study (n=30) of tiotropium (18 µg) combined with RPL554 (1.5 or 6 mg) or placebo for 3 days. Forced expiratory volume in 1 s (FEV1), lung volumes and specific airway conductance (sGaw) were measured.In study 1, peak FEV1 change compared with placebo was similar with RPL554, ipratropium and salbutamol (mean 223, 199 and 187 mL, respectively). The peak FEV1 was higher for RPL554+ipratropium versus ipratropium (mean difference 94 mL; p<0.0001) and RPL554+salbutamol versus salbutamol (mean difference 108 mL; p<0.0001). In study 2 (day 3), both RPL554 doses caused greater peak FEV1 effects than placebo. The average FEV1(0–12 h) increase was greater with RPL554 6 mg only versus placebo (mean difference 65 mL; p=0.0009). In both studies, lung volumes and sGaw showed greater RPL554 combination treatment effects versus monotherapy.RPL554 combined with standard bronchodilators caused additional bronchodilation and hyperinflation reduction.

The 2nd Cross Company Respiratory Symposium (CCRS), held in Horsham, U.K. in 2012, brought together representatives from across the pharmaceutical industry with expert academics, in the common interest of improving the design and translational predictiveness of in vivo models of respiratory disease. Organized by the respiratory representatives of the European Federation of Pharmaceutical Industries and Federations (EFPIA) group of companies involved in the EU-funded project (U-BIOPRED), the aim of the symposium was to identify state-of-the-art improvements in the utility and design of models of respiratory disease, with a view to improving their translational potential and reducing wasteful animal usage. The respiratory research and development community is responding to the challenge of improving translation in several ways: greater collaboration and open sharing of data, careful selection of the species, complexity and chronicity of the models, improved practices in preclinical research, continued refinement in models of respiratory diseases and their sub-types, greater understanding of the biology underlying human respiratory diseases and their sub-types, and finally greater use of human (and especially disease-relevant) cells, tissues and explants. The present review highlights these initiatives, combining lessons from the symposium and papers published in Clinical Science arising from the symposium, with critiques of the models currently used in the settings of asthma, idiopathic pulmonary fibrosis and COPD. The ultimate hope is that this will contribute to a more rational, efficient and sustainable development of a range of new treatments for respiratory diseases that continue to cause substantial morbidity and mortality across the world.