Drugs DOI 10.1007/s40265-014-0303-8

CURRENT OPINION

Phosphodiesterase Inhibitors for Chronic Obstructive Pulmonary Disease: What Does the Future Hold? Maria Gabriella Matera • Paola Rogliani Luigino Calzetta • Mario Cazzola

•

Ó Springer International Publishing Switzerland 2014

Abstract Phosphodiesterase-4 (PDE4) inhibitors have broad anti-inflammatory activity, inhibiting the airway inflammation associated with chronic obstructive pulmonary disease (COPD), especially by reducing airway neutrophils that are key cells in COPD. A careful evaluation of the results of several meta-analyses allows us to consider the use of PDE4 inhibitors as very important in those patients with COPD who are particularly susceptible to exacerbations, the so-called ‘frequent exacerbators’. Consequently, PDE4 inhibitors should be used earlier and more frequently than is the case today, but they are prescribed sporadically because of side effects. Several strategies are conceivable to avoid side effects, but, unfortunately, many of these approaches are yet to be successfully translated into clinical effectiveness after several decades of research. A novel alternative approach is to administer multiple drugs simultaneously or drugs capable of two distinct primary pharmacological actions

M. G. Matera Department of Experimental Medicine, Section of Pharmacology ‘‘L. Donatelli’’, Second University of Naples, Naples, Italy P. Rogliani  M. Cazzola Department of Systems Medicine, University of Rome Tor Vergata, Rome, Italy L. Calzetta Department of Pulmonary Rehabilitation, San Raffaele Pisana Hospital, IRCCS, Rome, Italy M. Cazzola (&) Dipartimento di Medicina dei Sistemi, Universita` di Roma Tor Vergata, Via Montpellier 1, 00133 Rome, Italy e-mail: [email protected]

based on distinct pharmacophores (bifunctional drugs) in order to produce additive or synergistic effects and, consequently, to dispense these drugs at lower doses, inducing fewer side effects. The fact that we have realized that there is a need to target simultaneously more PDEs unquestionably represents an advance in the possible use of PDE inhibitors. Actually, the possibility that multivalent (multifunctional) ligands, which feature two or more pharmacophores, may deliver superior efficacy is an approach that is being explored. Recognizing the role of specific targeted therapy aimed at subcellular domains has changed our understanding of the use of PDE inhibitors, and offers an opportunity to improve both the therapeutic tolerability and efficacy of these drugs. Key Points The present scenario is characterized by the awareness that PDE4 inhibitors are potentially useful drugs; however, they should be used earlier and more frequently than is the case today, but they are prescribed sporadically because of side effects. Because of the participation of multiple PDE variants in a complex signalling network involving major regulatory mechanisms, the super PDE family should be considered a major target to treat COPD. A novel alternative approach is to administer multiple drugs simultaneously or drugs capable of two distinct primary pharmacological actions based on distinct pharmacophores (bifunctional drugs) in order to produce additive or synergistic effects and, consequently, to dispense these drugs at lower doses, inducing fewer side effects.

M. G. Matera et al.

1 Introduction Cyclic adenosine 30 ,50 -monophosphate (cAMP) plays an important role in the activation and recruitment of inflammatory cells into airways and in the regulation of airway smooth muscle (ASM) tone [1]. Elevation of cAMP levels leads to ASM relaxation and bronchodilation; it also inhibits a number of immune and inflammatory responses, including T-cell activation and proliferation, tumour necrosis factor (TNF)-a production in monocytes and macrophages, superoxide anion production in eosinophils, and eosinophil chemotaxis by inflammatory mediators [2]. The amount of cAMP can increase within cells by inhibiting several cyclic nucleotide phosphodiesterases (PDEs) [1]. PDE4 is the predominant PDE expressed in neutrophils, T cells and macrophages, and therefore its inhibition may also have inhibitory effects upon both inflammatory and immune cells [1]. Chronic inflammation plays a central role in chronic obstructive pulmonary disease (COPD), and is characterized by an increase in neutrophils, macrophages and CD8? T lymphocytes in small and large airways as well as in lung parenchyma and pulmonary vasculature [2, 3]. Therefore, it is not surprising that over the past 2 decades or so, many researchers have become interested in the cAMP-specific PDE4 family because they considered it a potential intracellular target that could be exploited to therapeutic advantage for COPD and a multitude of diseases associated with COPD [4]. Many PDE4 inhibitors have been tested in recent years, and numerous studies with PDE4 inhibitors in COPD have been performed, with diverging end points and outcomes, such as lung function, exacerbations, health-related quality of life and symptoms. However, only roflumilast has been approved for use in patients with COPD. In fact, the European Medicines Agency, in April 2010, recommended approval of roflumilast for the ‘‘maintenance treatment of patients with severe COPD associated with chronic bronchitis who have a history of frequent exacerbations’’ [5], whereas the US Food and Drug Administration, in February 2011, approved roflumilast to decrease the frequency of exacerbations or worsening of symptoms from severe COPD, but not to treat another form of COPD, which involves primary emphysema [6]. Nevertheless, the 2014 Global Initiative for Chronic Obstructive Pulmonary Disease (GOLD) recommendations suggest prescribing it only to those patients with a high risk of exacerbations and more symptoms who are not adequately controlled by longacting bronchodilators [7]. These different indications and limitations, all focused only on the use of roflumilast in the prevention of exacerbations,

generate uncertainties in those who want to prescribe roflumilast. This is probably why many physicians are still trying to understand the real role of PDE4 inhibitors in COPD treatment. Meta-analyses of published data or pooled analyses of primary data generated using PDE4 inhibitors in COPD could help us by providing good insights into the role of these drugs. 2 What Meta-analyses Tell Us A recent Cochrane analysis of 29 separate randomized controlled trials (RCTs) studying roflumilast (15 trials, 12,654 patients) or cilomilast (14 trials, 6,457 patients) with a duration between 6 weeks and 1 year documented that, in people with COPD, PDE4 inhibitors offered benefit over placebo, providing a small improvement in lung function and reducing the likelihood of exacerbations [8]. Commenting on these findings, the Authors stated that they would expect that out of 100 people who took PDE4 inhibitors every day for a year, 24 would experience at least one exacerbation, which is six fewer than in others who did not receive these medicines [8]. However, PDE4 inhibitors only provided a small effect on levels of breathlessness and quality of life [7]. Moreover, 5–10 % of people enrolled in RCTs reported gastrointestinal side effects such as diarrhoea, nausea and vomiting. Besides, weight loss was common, and there was also a two- to three-fold increase in the risk of sleep or mood disturbance [8]. These findings are surely interesting because, as correctly stressed by Yan et al. [9], who carried out a metaanalysis focused on roflumilast and reached the same final remarks, we should be very careful in prescribing a PDE4 inhibitor, considering some significant adverse events and the lack of clinical evidence on several important clinical endpoints. In effect, we should identify the patient who may benefit from such treatment and follow him/her over time in order to monitor the occurrence of any adverse event. Tailoring therapy with PDE4 inhibitors in the right patient seems to be a real possibility. In fact, a post hoc analysis of two phase III studies (M2-124; M2-125) found that roflumilast (500 mg daily for 1 year) transformed COPD patients classified as frequent exacerbators at the beginning of the trial into a more stable, infrequent exacerbator phenotype [10]. Another post hoc, pooled analysis of these two largescale trials in patients with severe and very severe COPD showed a significant reduction in exacerbations with roflumilast treatment and identified a subgroup of patients who are most likely to benefit from this treatment namely those patients with chronic bronchitis [11]. Roflumilast reduced

PDE Inhibitors in COPD

exacerbation rates and improved lung function in patients who received concomitant long-acting b2-adrenoceptor agonist (LABA), regardless of prior inhaled corticosteroid (ICS) use, age and smoking status [12]. This information supports the possibility of using roflumilast in a large number of patients with COPD. However, we must always keep in mind that treatment with roflumilast is associated with progressive improvement in airway function but not in resting lung hyperinflation, defined as an abnormal increase in the volume of air remaining in the lungs at the end of spontaneous expiration, or in exercise endurance [13]. Lung hyperinflation commonly accompanies expiratory flow limitation in patients with COPD and likely contributes to both the intensity and the distinct qualitative sensations of dyspnoea [14]. Consequently, it is not surprising that a meta-analysis of four RCTs involving 4,767 patients with forced expiratory volume in 1 s (FEV1) \80 % showed that roflumilast statistically improved the transition dyspnoea index (TDI) focal score, but failed to decrease the Shortness of Breath Questionnaire (SOBQ) [15]. The overall effect sizes were lower than the minimum clinically important difference of the TDI and the SOBQ, respectively. This is an important limitation because dyspnoea is the primary symptom limiting exercise in patients with more advanced disease, and often leads to avoidance of activity, with consequent skeletal muscle deconditioning [14].

3 Which Scenario Can Be Opened? A careful evaluation of the results of all these meta-analyses allows us to consider the use of PDE4 inhibitors as very important in those patients with COPD who are particularly susceptible to exacerbations, the so-called ‘frequent exacerbators’, a subgroup of patients who enter a destructive cycle of frequent exacerbations with associated poorer outcome, a characteristic that appears to be maintained over time [16]. This is important information because the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) exacerbation study showed that overall, 22 % of patients with GOLD stage 2 disease, 33 % with GOLD stage 3, and 47 % with GOLD stage 4 had frequent exacerbations (two or more episodes in the first year of follow-up) [16], a phenomenon that is, therefore, of great dimension. Even more important, the same study documented that the single best predictor of exacerbations, across all GOLD stages, was a history of exacerbations [17]. Since persisting and/or an increased propensity for inflammation is a feature of the frequent exacerbators [16], with higher levels of sputum interleukin (IL)-6 and IL-8

even in the stable state [18] and sputum IL-6 and plasma fibrinogen continuing to increase more rapidly over time [19], therapeutics with anti-inflammatory properties seem to be crucial in the prevention of COPD exacerbations [20]. PDE4 inhibitors have broad anti-inflammatory activity, inhibiting the airway inflammation associated with COPD, especially by reducing airway neutrophils that are key cells in COPD [21]. These characteristics explain why PDE inhibitors may influence the occurrence of exacerbations in COPD, although they were not designed for this indication. Nowadays, the question arises whether it would be appropriate to use PDE4 inhibitors in all frequent exacerbators, while the GOLD recommendations insert this class as an alternative therapy in frequent exacerbators, regardless of whether symptomatic or not, and always in combination with a long-acting bronchodilator and possibly an ICS [7]. New research indicates that most effective anti-inflammatory activity is obtained with the combination of a PDE4 inhibitor plus an oral corticosteroid, although the combination of a PDE4 inhibitor plus formoterol also shows additive anti-inflammatory properties in COPD neutrophils [22]. This is not surprising because it is well known that steroid insensitivity in COPD is at least partially due to glucocorticoid receptor (GR)-a downregulation [23], and there is documentation that roflumilast upregulates GR-a in cigarette smoke extract-exposed bronchial epithelial cells, thereby restoring glucocorticoid sensitivity [24]. Moreover, roflumilast N-oxide, the active metabolite of roflumilast, reverses corticosteroid resistance and shows strong anti-inflammatory effects in combination with corticosteroids on neutrophils from patients with COPD [25]. These effects suggest synergy between the two compounds in vivo and potentially in COPD patients. These findings thus carry significant implications for COPD treatment. In a recent very interesting review, Giembycz and Newton [4] presented evidence that a corticosteroid, LABA, and PDE4 inhibitor in combination can interact in a complex manner to induce a panel of genes that could act collectively to suppress inflammation and improve lung function. Central to this concept is that this drug combination produces a unique gene induction fingerprint that is not reproduced by any components of the triple therapy alone. The clinical efficacy of a PDE4 inhibitor when combined with an ICS and a LABA is therefore attributable, in part, to the individual, additive, and often cooperative actions of these drugs on gene transcription [26]. Lately, it has been shown that the combination of dexamethasone with PDE4 inhibitors results in an additive antiinflammatory effect. This addition appears to be due to effects on different transcription factors, in particular on mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) [27]. It is not surprising, therefore, that roflumilast, when added to triple therapy, reduces exacerbations in

M. G. Matera et al.

severe COPD patients [28] and, surprisingly, seems to reduce inflammation in the smaller airways, resulting in reduced hyperinflation and changing internal airflow distribution [29]. If this is confirmed by large clinical trials, it is obvious that the inclusion of a PDE4 inhibitor in the therapeutic scheme will occur earlier than is currently suggested by the GOLD recommendations [7]. Unfortunately, the wider use of roflumilast is dose limited by its side effect profile, mainly by its gastrointestinal side effects caused by the inhibition of PDE4 isoforms, possibly PDE4D, in the emetic centre in the brain [30, 31], and weight loss [30]. Such side effects have also stopped the development of several orally active PDE inhibitors [32]. The present scenario is thus characterized by the awareness that PDE4 inhibitors are potentially useful drugs. We have realized that they should be used earlier and more frequently than is the case today, but we know that they are prescribed sporadically because of their side effects.

4 How Can We Change this Scenario? The interesting effect of roflumilast in preventing COPD exacerbations has encouraged constant interest in PDE inhibitors, and, since side effects limit the PDE4 inhibitors use, also in approaches to overcome the limitations of current PDE inhibitors. However, all orally administered PDE4 inhibitors that have been tested so far have a low therapeutic ratio, and there are particular concerns for the gastrointestinal side effects, which have stopped the development of these drugs or limited their wider use. Several strategies are feasible to avoid such problems. The following approaches have been suggested: deliver the drug through the inhaled route, develop subtype selective PDE4 inhibitors, use dual PDE inhibitors, interfere with PDE4 activation, target proteins that are involved in locating PDE4 to specific microcellular domains, and, finally, explore the potential of antisense oligonucleotides [1, 31, 32]. Regrettably, many of these approaches are yet to be successfully translated into clinical effectiveness. The lack of a solid alternative is the likely reason why tetomilast (OPC-6535), an oral PDE4 inhibitor that may inhibit the development of emphysema by attenuating pulmonary inflammation, is under clinical development in COPD, although nausea and vomiting, but also abdominal pain, indigestion and gas, are frequent side effects [33]. A phase IIa multicentre, randomized, double-blind, placebocontrolled study that must assess the pharmacodynamics, efficacy, and safety of tetomilast in patients with emphysema is currently recruiting participants [34]. Another study that investigated the efficacy and safety of tetomilast

in COPD patients, using the measurement of trough FEV1 over time as the primary endpoint, was successfully completed [35], but the results have not been published yet. It is intriguing that PDE4 inhibitors can also be inhaled, which reduces systemic exposure and, likely, associated side effects. Some inhaled PDE4 inhibitors (AWD 12-281, tofimilast, UK500001) have progressed to the clinic, but they have shown little or no efficacy in patients with COPD [36–38]. Others are still in preclinical development (ASP3258 [39], SCH900182 [40], PDE-423 [41], and NCS 613 [42] (Table 1). GSK256066, a slow- and tight-binding inhibitor of PDE4 that is highly selective for PDE4 over other PDEs such as 1, 2, 3, 5, 6 and 7, and shows efficacy in animal models of pulmonary inflammation [43], was in clinical development for allergic rhinitis, asthma, and COPD, but is not currently listed in the company’s pipeline [44]. The reasons for these failures given the extraordinary potency of some of these compounds as PDE4 inhibitors remain a mystery, but it is hoped that newer compounds [45] may show improved effectiveness. Despite the negative results obtained so far with the inhaled PDE4 inhibitors, the ClinicalTrials.gov website lists a new inhaled PDE4, CHF6001, which is in a phase IIa study in COPD patients that aims to evaluate its safety, tolerability, pharmacodynamics (effect on biological markers of inflammation in induced sputum and in blood, and on pulmonary function) and pharmacokinetics after 28days of daily inhaled dosing [46]. CHF6001 proved to be a highly potent and selective PDE4 inhibitor with an antiinflammatory potency superior to roflumilast and comparable to GSK256066 [47]. Although the use of inhaled PDE inhibitors is an interesting way to reduce the side effects, it is doubtful that they are able to influence systemic inflammation, whereas oral compounds seem to be able to reduce it. Recently, it has been documented that roflumilast for 12 weeks decreased systemic inflammatory activity in patients with COPD [48]. The current relative lack of interest in the development of new PDE4 inhibitors is due, in our opinion, not only to the inability to synthesize compounds that are both active and safe, but also, and mainly, to having realized that, although individual PDEs regulate selective cAMP signalling pathways, the dysregulation of multiple signalling pathways contributes to the pathogenesis and clinical presentations of a complex disease such as COPD [49]. For this reason, it has been suggested that several PDEs must be targeted at the same time to obtain an effective treatment. This seems to be a smart approach because cyclic nucleotide PDEs comprise 11 gene-related families of isozymes (PDE1 to PDE11) and at least 21 isoforms with numerous splice variants that are classified on the basis of amino acid sequence homology, substrate specificity inhibitor selectivity, tissue and cell distribution,

PDE Inhibitors in COPD Table 1 Phosphodiesterase (PDE) inhibitors under development for treating chronic obstructive pulmonary disease Class/drug

Manufacturer

Administration route

Status

Tetomilast

Otsuka

Oral

Phase II

GSK256066

GlaxoSmithKline

Inhaled

CHF6001

Chiesi Farmaceutici

Inhaled

Phase II, likely discontinued Phase II

ASP3258

Astellas Pharma

Inhaled

Preclinical development

SCH900182

Schering-Plough

Inhaled

Preclinical development

PDE-423

Medicinal Science Division at the Korea Research Institute of Chemical Technology Faculte´ de Pharmacie, Illkirch, France

Inhaled

Preclinical development

Inhaled

Preclinical development

Verona Pharma

Inhaled

Phase II

No information available

No information available

No information available

LASSBio, Faculdade de Farma´cia, Universidade Federal do Rio de Janeiro

Oral

Preclinical development

Kyowa Hakko Kogyo

Inhalation

Preclinical development, likely discontinued

GS-5759

Gilead Sciences

Inhaled

Preclinical development

Hybrids that combine both salmeterol and the PDE4 inhibitors roflumilast or phthalazinone

Jiangsu Hansoh Pharmaceutical Research Institute

Inhaled

Preclinical development

Inhaled (?)

Preclinical development, likely discontinued

PDE4 inhibitors

NCS 613 Dual PDE3–PDE4 inhibitors RPL 554 Dual PDE4–PDE7 inhibitors IR-284 Dual PDE4–PDE5 inhibitors LASSBio596 Dual PDE1–PDE4 inhibitors KF19514

Dual b2-adrenoceptor agonists–PDE4 inhibitors

Dual muscarinic receptor antagonist–PDE4 inhibitors UCB-101333-3

Union Chimique Belge Pharma

regulation by kinases, protein–protein interaction and subcellular distribution [1]. We could theoretically produce additive or synergistic effects if we were able to target different PDEs in different cells using multiple drugs simultaneously or drugs capable of two distinct primary pharmacological actions based on distinct pharmacophores (bifunctional drugs) [50]. Consequently, we could administer these drugs at lower doses and, thus, induce fewer side effects [50]. It is our opinion that bifunctional drugs could be an exciting new approach to the treatment of COPD, where there remains significant unmet need, and become highly significant future treatments for patients suffering from this disorder [50].

5 Evolution in PDE Inhibitors A solid body of evidence has shown that PDE3 and 4 are present in ASM, and PDE3, 4 and 7 are found in the majority of inflammatory cells that can be involved in the pathogenesis of COPD [1, 50]. Also PDE3 and PDE7 are specific inactivators of cAMP. Definitely, the PDE3 isoenzyme seems to predominate functionally in ASM, and its inhibition, rather than PDE4 inhibition, elicits ASM relaxation, whereas the PDE4 isoenzyme is the predominant isoenzyme in the majority of inflammatory cells, including neutrophils, which are implicated in the pathogenesis of COPD, and PDE7 is involved in T cell activation [1, 50].

M. G. Matera et al.

This recognition has led to the development of drugs having dual inhibitory activity for both PDE3 and PDE4 in order to obtain both bronchodilator and anti-inflammatory activity in the same molecule [49], whereas the development of dual PDE4–PDE7 inhibitors would yield a novel class of drugs that would be expected to block the T-cell component of a disease, partly through PDE7 inhibition, and possess anti-inflammatory properties [51] (Table 1). The possibility that multivalent (multifunctional) ligands, which contain two or more pharmacophores, may produce larger efficacy is also an approach that is under investigation [4, 52]. 5.1 Dual PDE3–PDE4 Inhibitors Two early dual PDE3–PDE4 inhibitors (zardaverine and benafentrine) had modest and short-lived bronchodilatory effects in humans [53]. Some newer compounds having both PDE3 and 4 inhibitory activities have been described, but these have been stopped at the preclinical stage because of unwanted gastrointestinal side effects [54]. However, another novel inhaled PDE3/4 inhibitor, RPL 554, exhibits a broad range of both bronchoprotective and anti-inflammatory activities [55]. It relaxes human bronchi and can interact with a muscarinic receptor antagonist to produce a synergistic inhibition of ASM tone [56]. Early clinical studies have shown that it has both bronchodilator and anti-inflammatory actions at the same dose [57], representing a potentially new class of drug for the treatment of patients with COPD [58], either alone or in combination with antimuscarinic drugs. Its pharmacokinetic profile is very interesting. Being rapidly eliminated from plasma, RPL 554 does not accumulate and has a low systemic bioavailability. Consequently, adverse events are usually mild and of equal frequency to those observed in placebotreated groups [59]. 5.2 Dual PDE4–PDE7 Inhibitors Inhibitors of PDE7 elevate cAMP, which leads to a variety of cellular effects and inhibition of cellular inflammation and the immune responses. Thus, selective inhibition of PDE7 may prove to be another mechanism by which to inhibit the activity of inflammatory cells [60]. Therefore, a number of PDE7-selective inhibitors have been developed [61], but their anti-inflammatory action is relatively weak [62]. On the contrary, a combination of PDE7 and PDE4 inhibitors (e.g., BRL 50481 and rolipram) potentiates the effects observed by single administration of PDE4 or PDE7 inhibitor used alone [63]. The co-expression of PDE4 and PDE7 in most immunoinflammatory cells and the synergistic effects of PDE7- and PDE4-selective drugs in the

suppression of inflammation in cell-based studies have fuelled speculation that dual inhibition of PDE7 and PDE4 could be an effective strategy to treat COPD [32]. However, this approach does not seem to be really effective because greater anti-inflammatory activity over a PDE4 inhibitor alone has not been persuasively demonstrated [64]. IR-284 is a dual PDE4–PDE7 inhibitor, but there is no published study that has documented its effects in COPD. Nonetheless, TPI 1100, which comprises two antisense oligonucleotides targeting the messenger RNA (mRNA) for the PDE4B/4D and PDE7A isoforms, has been shown to reduce neutrophil influx and key cytokines in an established smoking mouse model [65]. 5.3 Dual PDE4–PDE5 Inhibitors The idea of combining an anti-inflammatory PDE4 inhibitor and a pulmonary vaso-relaxing PDE5 inhibitor in COPD patients with co-existing pulmonary hypertension is an attractive concept. In fact, in addition to the relaxation of pulmonary vascular smooth muscle, selective PDE5 inhibitors are also able to induce bronchodilation [66] and suppress the pulmonary inflammation and the hyperreactivity of the airway that follow allergen and lipopolysaccharide (LPS) challenge [67]. Thus, it has been suggested that a new molecule that inhibits PDE4 and PDE5 could act at multiple levels in COPD, reducing lung inflammation and, possibly, remodelling as well as decreasing arterial pulmonary hypertension, and improving lung function [68]. LASSBio596, designed as a hybrid of thalidomide and aryl sulfonamide, is an agent that exhibits potent inhibitory effects on PDE4 and PDE5 [69]. In a murine model of elastase-induced emphysema, LASSBio596 reduced lung inflammation and remodelling and improved lung mechanics [70]. Interestingly, it has also been documented that LASSBio596 has the potential to block fibroproliferation [71]. However, it is likely that the clinical development of dual PDE4–PDE5 inhibitors will not occur, because of clinical trials with selective PDE5 inhibitors that have not shown efficacy but have apparently worsened gas exchange [72]. 5.4 Dual PDE1–PDE4 Inhibitors Since pathological airway remodelling is mediated by PDE1 and PDE1 inhibitors block smooth muscle mitogenesis [73], combined PDE1 and PDE4 inhibitors could have utility in COPD [64]. The dual PDE1/4 inhibitor KF19514 is reported to suppress inflammation and arrest airway remodelling, at least in a murine model of chronic asthma [74].

PDE Inhibitors in COPD

5.5 Dual b2-adrenoceptor Agonists–PDE4 Inhibitors Another means to develop a medicine with both antiinflammatory and bronchodilator activity is to link covalently a PDE4 inhibitor to a LABA [64]. Typically, the head group of an existing LABA has been fused to a variety of structurally dissimilar PDE4 inhibitors. A potential advantage of these compounds is that both b2agonists and PDE4 inhibitors rely on modulation of the second messenger cAMP to elicit their effects, and it is possible that the combination could provide additive or synergistic anti-inflammatory activity in the lung. GS-5759 is a novel bifunctional PDE4 inhibitor/LABA that displays PDE4 inhibition and b2-agonism comparable to roflumilast and indacaterol, respectively [75]. In a preclinical evaluation, it inhibited TNFa, IL-6 and chemokine (C–C motif) ligand (CCL) 3 generation from LPS-stimulated human monocytes and formyl-methionyl-leucyl-phenylalanine-induced superoxide production from human neutrophils and also suppressed release of CCL5, chemokine (C–X–C motif) ligand 10, granulocyte-macrophage colony-stimulating factor and endothelin-1 from human lung fibroblasts and was a potent inhibitor of carbacholinduced trachea smooth muscle tone in the guinea-pig [75]. More recently, a series of molecules that combine the anti-inflammatory PDE4 inhibitors roflumilast or phthalazinone with the LABAs salmeterol [76] or formoterol [77] have been described, and are another potential example of a new drug class that combine anti-inflammatory and bronchodilator actions in a single molecule, although to date, there are very limited biological data on these molecules. 5.6 Dual Muscarinic Receptor Antagonists–PDE4 Inhibitors Also, bifunctional compounds in which a PDE4 inhibitor is connected to a muscarinic receptor antagonist have been described [4, 49]. Four simultaneous patents describe the dual mechanism approach combining PDE4 inhibitor/M3 antagonist, using a variety of linking groups. In each case, the PDE4 motif is the known pyrazolopyridine from earlier work, and the patents describe different combination of linkers and biaryl-containing muscarinic antagonistic fragments [78]. Another molecule with such dual activity is UCB-101333-3, a 4,6-diaminopyrimidine [79, 80]. In mice, UCB-101333-3, given intranasally, inhibited cigarette smoke-induced pulmonary neutrophilia and reduced the leukocyte burden and keratinocytes (KC) levels (the murine equivalent of IL-8) in bronchoalveolar lavage fluid. It also protected against the development of cadmium-induced emphysema in mice [80].

6 What We Still Need to Know in Order to Optimize the Use of PDE Inhibitors It is generally accepted that because of the participation of multiple PDE variants in a complex signalling network involving major regulatory mechanisms, the super PDE family should be considered a major target to treat COPD [81]. The fact that we have realized that there is a need to target simultaneously more PDEs unquestionably represents an advance in the possible use of PDE inhibitors. Nonetheless, since compartmentalization allows distinct pools of cyclic nucleotide to interact with particular effectors, inhibitors that are applied without respect to functional localization elicit numerous unwanted effects, as is the case even with the current generation of more specific PDE inhibitors [81]. Therefore, it is now mandatory to understand whether selective manipulation of pools of cyclic nucleotides, at specific locations, may avoid global off-target effects in other compartments and improve efficacy [82]. Specifically, the documentation that individual PDEs control select cyclic nucleotide-regulated events by their integration into specific multi-molecular regulatory signalling complexes, termed ‘signalosomes’, and through their regulation of cAMP or cyclic guanosine monophosphate (cGMP) levels within distinct and largely non-overlapping intracellular cyclic nucleotide compartments [83] supports the theorem that the disruption of cyclic nucleotide-mediated events within specific individual signalosome-based compartments will have more specific effects than agents that do not discriminate between these compartments and instead inhibit other members of the same PDE family [49]. Consequently, the tethering or targeting of individual PDEs to selected signalosomes at different subcellular locations should allow individual PDEs to assume specific functional roles in the compartmentalized regulation of specific cyclic nucleotide signalling pathways, as well as physiological and pathophysiological responses [49]. The acquisition of these notions is completely changing our understanding on the use of PDE inhibitors. In fact, specific targeted therapy aimed at subcellular domains represents not only a challenge, but also an opportunity to improve both the therapeutic tolerability and efficacy of these drugs [82]. Acknowledgments M. Cazzola has been a consultant at Verona Pharma and Chiesi Farmaceutici. L. Calzetta has been a consultant at Verona Pharma. No sources of funding were used to support the writing of this manuscript. Conflict of interest M. G. Matera and P. Rogliani have no relevant conflict of interest with regard to this manuscript.

M. G. Matera et al.

References 1. Page CP, Spina D. Phosphodiesterase inhibitors in the treatment of inflammatory diseases. Handb Exp Pharmacol. 2011;204: 391–414. 2. Spina D. Phosphodiesterase-4 inhibitors in the treatment of inflammatory lung disease. Drugs. 2003;63:2575–94. 3. Gan WQ, Man SF, Senthilselvan A, Sin DD. Association between chronic obstructive pulmonary disease and systemic inflammation: a systematic review and a metaanalysis. Thorax. 2004;59: 574–8. 4. Giembycz MA, Newton R. How phosphodiesterase 4 inhibitors work in patients with chronic obstructive pulmonary disease of the severe, bronchitic, frequent exacerbator phenotype. Clin Chest Med. 2014;35:203–17. 5. European Medicines Agency. Daxas – Roflumilast. http://www.ema. europa.eu/docs/en_GB/document_library/Summary_of_opinion_-_ Initial_authorisation/human/001179/WC500089626.pdf. Last accessed 28 May 2014. 6. FDA. US Food and Drug Administration FDA approves new drug to treat chronic obstructive pulmonary disease. http://www.fda. gov/NewsEvents/Newsroom/PressAnnouncements/ucm244989. htm. Last accessed 28 May 2014. 7. Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management, and prevention of COPD. 2014. Global Initiative for Chronic Obstructive Lung Disease. http://www.goldcopd.org/Guidelines/guidelines-resources.html. Last accessed 9 June 2014. 8. Chong J, Leung B, Poole P. Phosphodiesterase 4 inhibitors for chronic obstructive pulmonary disease. Cochrane Database Syst Rev 2013;11:CD002309. 9. Yan JH, Gu WJ, Pan L. Efficacy and safety of roflumilast in patients with stable chronic obstructive pulmonary disease: a meta-analysis. Pulm Pharmacol Ther. 2014;27:83–9. 10. Wedzicha JA, Rabe KF, Martinez FJ, et al. Efficacy of roflumilast in the chronic obstructive pulmonary disease frequent exacerbator phenotype. Chest. 2013;143:1302–11. 11. Rennard SI, Calverley PM, Goehring UM, Bredenbro¨ker D, Martinez FJ. Reduction of exacerbations by the PDE4 inhibitor roflumilast—the importance of defining different subsets of patients with COPD. Respir Res. 2011;12:18. 12. Hanania NA, Calverley PM, Dransfield MT, et al. Pooled subpopulation analyses of the effects of roflumilast on exacerbations and lung function in COPD. Respir Med. 2014;108:366–75. 13. O’Donnell DE, Bredenbro¨ker D, Brose M, et al. Physiological effects of roflumilast at rest and during exercise in COPD. Eur Respir J. 2012;39:1104–12. 14. O’Donnell DE. Hyperinflation, dyspnea, and exercise intolerance in chronic obstructive pulmonary disease. Proc Am Thorac Soc. 2006;3:180–4. 15. Pan L, Guo YZ, Zhang B, Yan JH. Does roflumilast improve dyspnea in patients with chronic obstructive pulmonary disease? A meta-analysis. J Thorac Dis. 2013;5:422–9. 16. Wedzicha JA, Brill SE, Allinson JP, Donaldson GC. Mechanisms and impact of the frequent exacerbator phenotype in chronic obstructive pulmonary disease. BMC Med. 2013;11:181. 17. Hurst JR, Vestbo J, Anzueto A, et al. Susceptibility to exacerbation in chronic obstructive pulmonary disease. N Eng J Med. 2010;363:1128–38. 18. Bhowmik A, Seemungal TA, Sapsford RJ, Wedzicha JA. Relation of sputum inflammatory markers to symptoms and lung function changes in COPD exacerbations. Thorax. 2000;55:114–20. 19. Donaldson GC, Seemungal TA, Patel IS, et al. Airway and systemic inflammation and decline in lung function in patients with COPD. Chest. 2005;128:1995–2004.

20. Han MK, Martinez FJ. Pharmacotherapeutic approaches to preventing acute exacerbations of chronic obstructive pulmonary disease. Proc Am Thorac Soc. 2011;8:356–62. 21. Grootendorst DC, Gauw SA, Verhoosel RM, et al. Reduction in sputum neutrophil and eosinophil numbers by the PDE4 inhibitor roflumilast in patients with COPD. Thorax. 2007;62:1081–7. 22. Milara J, Lluch J, Cano P, et al. Anti-inflammatory effects of dexamethasone, roflumilast N-oxide, formoterol and their combinations in human neutrophils from healthy and chronic obstructive pulmonary disease patients [abstract]. Am J Respir Crit Care Med. 2014;189:A2746. 23. Barnes PJ. Corticosteroids: the drugs to beat. Eur J Pharmacol. 2006;533:2–14. 24. Reddy AT, Lakshmi SP, Reddy RC. Roflumilast-glucocorticoid synergy in COPD [abstract]. Am J Respir Crit Care Med. 2014;189:A6666. 25. Milara J, Lluch J, Almudever P, et al. Roflumilast N-oxide reverses corticosteroid resistance in neutrophils from patients with chronic obstructive pulmonary disease. J Allergy Clin Immunol. 2014;134:314–22. 26. Giembycz MA, Newton R. Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies. Handb Exp Pharmacol. 2011;204:415–46. 27. Grundy S, Plumb J, Kaur M, et al. Additive anti-inflammatory effect of glucocorticoids and PDE4 inhibitors on COPD CD8 cells [abstract]. Eur Respir J. 2014;44(suppl):P1515. 28. Mun˜oz-Esquerre M, Diez-Ferrer M, Monto´n C, et al. Roflumilast added to triple therapy in severe COPD patients with frequent exacerbations: efficacy and tolerability [abstract]. Eur Respir J. 2014;44(suppl):P560. 29. De Backer J, Vos W, Van Holsbeke C, et al. A double blind placebo controlled study to assess the effect of roflumilast in addition to LABA/LAMA/ICS treatment in COPD patients using novel biomarkers [abstract]. Eur Respir J. 2014;44(suppl):4670. 30. Tashkin DP. Roflumilast: the new orally active, selective phophodiesterase-4 inhibitor, for the treatment of COPD. Expert Opin Pharmacother. 2014;15:85–96. 31. Spina D. PDE4 inhibitors: current status. Br J Pharmacol. 2008;155:308–15. 32. Page CP, Spina D. Selective PDE inhibitors as novel treatments for respiratory diseases. Curr Opin Pharmacol. 2012;12:275–86. 33. Bickston SJ, Snider KR, Kappus MR. Tetomilast: new promise for phosphodiesterase-4 inhibitors? Expert Opin Investig Drugs. 2012;21:1845–9. 34. ClinicalTrials.gov. Pilot Study of Tetomilast in Chronic Obstructive Pulmonary Disease (COPD) Associated With Emphysema (EMPHASIS). http://clinicaltrials.gov/ct2/show/ study/NCT00874497?term=tetomilast&rank=3. Last accessed 27 June 2014. 35. ClinicalTrials.gov. To Investigate the Efficacy and Safety of OPC-6535 in Chronic Obstructive Pulmonary Disease (COPD) Patients. http://clinicaltrials.gov/ct2/show/NCT00917150?term= tetomilast&rank=2. Last accessed 27 June 2014. 36. Gutke HJ, Guse JH, Khobzaoui M, et al. AWD-12-281 (inhaled) (elbion/GlaxoSmithKline). Curr Opin Investig Drugs. 2005; 6:1149–58. 37. Danto S, Wei GC, Gill J. A randomized, double-blind, placebocontrolled, parallel group, six-week study of the efficacy and safety of tofimilast dry powder for inhalation (DPI) in adults with COPD [abstract]. Am J Respir Crit Care Med. 2007;175:A131. 38. Vestbo J, Tan L, Atkinson G, Ward J. A controlled trial of 6-weeks’ treatment with a novel inhaled phosphodiesterase type4 inhibitor in COPD. Eur Respir J. 2009;33:1039–44.

PDE Inhibitors in COPD 39. Kobayashi M, Kubo S, Iwata M, et al. Anti-asthmatic effect of ASP3258, a novel phosphodiesterase 4 inhibitor. Int Immunopharmacol. 2011;11:732–9. 40. Chapman RW, House A, Richard J, et al. Pharmacology of SCH900182, a potent, selective inhibitor of PDE4 for inhaled administration [abstract]. Am J Respir Crit Care Med. 2010;181:A5671. 41. Kwak HJ, Nam JY, Song JS, et al. Discovery of a novel orally active PDE-4 inhibitor effective in an ovalbumin induced asthma murine model. Eur J Pharmacol. 2012;685:141–8. 42. Yougbare I, Morin C, Senouvo FY, et al. NCS 613, a potent and specific PDE4 inhibitor, displays antiinflammatory effects on human lung tissues. Am J Physiol Lung Cell Mol Physiol. 2011;301:L441–50. 43. Nials AT, Tralau-Stewart CJ, Gascoigne MH, et al. In vivo characterization of GSK256066, a high-affinity inhaled phosphodiesterase 4 inhibitor. J Pharmacol Exp Ther. 2011;337:137–44. 44. GlaxoSmithKline. Product development pipeline 2013. February 2013. http://www.gsk.com/content/dam/gsk/globals/documents/ pdf/GSK%202013%20Pipeline.pdf. Last accessed 14 March 2014. 45. Armani E, Amari G, Rizzi A, et al. A novel class of benzoic acid ester derivatives as potent PDE4 inhibitors for inhaled administration in the treatment of respiratory diseases. J Med Chem. 2014;57:793–816. 46. ClinicalTrials.gov. Safety, Tolerability and Efficacy of 28-day Inhaled CHF 6001 DPI in COPD Patients. http://clinicaltrials.gov/ ct2/show/NCT01730404?term=PDE?COPD&recr=Open&rank= 4. Last accessed 27 June 2014. 47. Moretto N, Caruso P, Marchini G, et al. CHF6001 is a novel highly potent and selective phosphodiesterase 4 (PDE4) inhibitor with a robust in vitro anti-inflammatory profile [abstract]. Am J Respir Crit Care Med. 2014;189:A6725. 48. Marquez-Martin E, Ortega Ruiz F, Campano E, et al. Reduction in systemic inflammation by the PDE4 inhibitor roflumilast in patients with COPD [abstract]. Eur Respir J 2014;44 (suppl):P926. 49. Maurice DH, Ke H, Ahmad F, et al. Advances in targeting cyclic nucleotide phosphodiesterases. Nat Rev Drug Discov. 2014;13:290–314. 50. Page C, Cazzola M. Bifunctional drugs for the treatment of asthma and chronic obstructive pulmonary disease. Eur Respir J. 2014;44:475–82. 51. Boswell-Smith V, Cazzola M, Page CP. Are phosphodiesterase inhibitors just more theophylline? J Allergy Clin Immunol. 2006;117:1237–43. 52. Chung FK. Phosphodiesterase inhibitors in airways disease. Eur J Pharmacol. 2006;533:110–7. 53. Foster RW, Rakshi K, Carpenter JR, Small RC. Trials of the bronchodilator activity of the isoenzyme-selective phosphodiesterase inhibitor AH 21-132 in healthy volunteers during a methacholine challenge test. Br J Clin Pharmacol. 1992;34:527–34. 54. Ochiai K, Takita S, Kojima A, et al. Phosphodiesterase inhibitors. Part 5: hybrid PDE3/4 inhibitors as dual bronchorelaxant/antiinflammatory agents for inhaled administration. Bioorg Med Chem Lett. 2013;23:375–81. 55. Boswell-Smith V, Spina D, Oxford AW, et al. The pharmacology of two novel long-acting phosphodiesterase 3/4 inhibitors, RPL554 [9,10-dimethoxy-2(2,4,6-trimethylphenylimino)-3-(Ncarbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1a]isoquinolin-4-one] and RPL565 [6,7-dihydro-2-(2,6-diisopropylphenoxy)-9,10-dimethoxy-4Hpyrimido[6,1-a]isoquinolin-4one]. J Pharmacol Exp Ther. 2006;318:840–8. 56. Calzetta L, Page CP, Spina D, et al. Effect of the mixed phosphodiesterase 3/4 inhibitor RPL554 on human isolated bronchial smooth muscle tone. J Pharmacol Exp Ther. 2013;346:414–23.

57. Franciosi LG, Diamant Z, Banner KH, et al. Efficacy and safety of RPL 554, a dual PDE3 and PDE4 inhibitor, in healthy volunteers and in patients with asthma or chronic obstructive pulmonary disease: findings from four clinical trials. Lancet Respir Med. 2013;1:714–27. 58. Wedzicha JA. Dual PDE3/4 inhibition: a novel approach to airway disease? Lancet Respir Med. 2013;1:669–70. 59. Abbott-Banner KH, Page CP. Dual PDE3/4 and PDE4 inhibitors: novel treatments for COPD and other inflammatory airway diseases. Basic Clin Pharmacol Toxicol. 2014;114:365–76. 60. Jones NA, Leport M, Holand T, et al. Phosphodiesterase (PDE) 7 in inflammatory cells from patients with asthma and COPD. Pulm Pharmacol Ther. 2007;20:60–8. 61. Safavi M, Baeeri M, Abdollahi M. New methods for the discovery and synthesis of PDE7 inhibitors as new drugs for neurological and inflammatory disorders. Expert Opin Drug Discov. 2013;8:733–51. 62. Smith SJ, Cieslinski LB, Newton R, et al. Discovery of BRL 50481 [3-(N, N-dimethylsulfonamido)-4-methyl-nitrobenzene], a selective inhibitor of phosphodiesterase 7: in vitro studies in human monocytes, lung macrophages, and CD8?T-lymphocytes. Mol Pharmacol. 2004;66:1679–89. 63. Fortin M, D’Anjou H, Higgins ME, et al. A multi-target antisense approach against PDE4 and PDE7 reduces smoke-induced lung inflammation in mice. Respir Res. 2009;10:39. 64. Giembycz MA, Maurice DH. Cyclic nucleotide-based therapeutics for chronic obstructive pulmonary disease. Curr Opin Pharmacol. 2014;16:89–107. 65. Seguin RM, Ferrari N. Emerging oligonucleotide therapies for asthma and chronic obstructive pulmonary disease. Expert Opin Investig Drugs. 2009;18:1505–17. 66. Charan NB. Does sildenafil also improve breathing? Chest. 2001;120:305–6. 67. Toward TJ, Smith N, Broadley KJ. Effect of phosphodiesterase-5 inhibitor, sildenafil (Viagra), in animal models of airways disease. Am J Respir Crit Care Med. 2004;169:227–34. 68. Giembycz MA. Life after PDE4: overcoming adverse events with dual-specificity phosphodiesterase inhibitors. Curr Opin Pharmacol. 2005;5:238–44. 69. Rocco PR, Momesso DP, Figueira RC, et al. Therapeutic potential of a new phosphodiesterase inhibitor in acute lung injury. Eur Respir J. 2003;22:20–7. 70. Guimaraes IH, Padilha GDA, Lopes-Pacheco M, et al. Therapy with a new phosphodiesterase 4 and 5 inhibitor in experimental elastase-induced emphysema [abstract]. Am J Respir Crit Care Med. 2014;189:A6557. 71. Campos HS, Xisto DG, Oliveira MB, et al. Protective effects of phosphodiesterase inhibitors on lung function and remodeling in a murine model of chronic asthma. Braz J Med Biol Res. 2006;39:283–7. 72. Blanco I, Santos S, Gea J, et al. Sildenafil to improve respiratory rehabilitation outcomes in COPD: a controlled trial. Eur Respir J. 2013;42:982–92. 73. Chan S, Yan C. PDE1 isozymes, key regulators of pathological vascular remodeling. Curr Opin Pharmacol. 2011;11:720–4. 74. Kita T, Fujimura M, Myou S, et al. Effects of KF19514, a phosphodiesterase 4 and 1 inhibitor, on bronchial inflammation and remodeling in a murine model of chronic asthma. Allergol Int. 2009;58:267–75. 75. Tannheimer SL, Sorensen EA, Cui Z-H, et al. The in vitro pharmacology of GS-5759, a novel bifunctional phosphodiesterase 4 inhibitor and long acting b2-adrenoceptor agonist. J Pharmacol Exp Ther. 2014;349:85–93. 76. Liu A, Huang L, Wang Z, et al. Hybrids consisting of the pharmacophores of salmeterol and roflumilast or phthalazinone: dual

M. G. Matera et al.

77.

78. 79.

80.

b2-adrenoceptor agonists-PDE4 inhibitors for the treatment of COPD. Bioorg Med Chem Lett. 2013;23:1548–52. Huang L, Shan W, Zhou Q, et al. Design, synthesis and evaluation of dual pharmacology b2-adrenoceptor agonists and PDE4 inhibitors. Bioorg Med Chem Lett. 2014;24:249–53. Phillips G, Salmon M. Bifunctional compounds for the treatment of COPD. Ann Rep Med Chem. 2012;47:209–22. Provins L, Christophe B, Danhaive P, et al. First dual M3 antagonists-PDE4 inhibitors: synthesis and SAR of 4,6-diaminopyrimidine derivatives. Bioorg Med Chem Lett. 2006;16:1834–9. Provins L, Christophe B, Danhaive P, et al. Dual M3 antagonistsPDE4 inhibitors. Part 2: synthesis and SAR of 3-substituted azetidinyl derivatives. Bioorg Med Chem Lett. 2007;17:3077–80.

81. Keravis T, Lugnier C. Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments. Br J Pharmacol. 2012;165:1288–305. 82. Lomas O, Zaccolo M. Phosphodiesterases maintain signaling fidelity via compartmentalization of cyclic nucleotides. Physiology (Bethesda). 2014;29:141–9. 83. Kritzer MD, Li J, Dodge-Kafka K, Kapiloff MS. AKAPs: the architectural underpinnings of local cAMP signaling. J Mol Cell Cardiol. 2012;52:351–8.