Novel class of benzoic acid ester derivatives as potent PDE4 inhibitors for inhaled administration in the treatment of respiratory diseases

Optimization of M3 Antagonist-PDE4 Inhibitor (MAPI) Dual Pharmacology Molecules for the Treatment of COPD

Aiming at the inhaled treatment of pulmonary diseases, the optimization process of the previously reported MAPI compound 92a is herein described. The project was focused on overcoming the chemical stability issue and achieving a balanced bronchodilator/anti-inflammatory profile in rats in order to be confident in a clinical effect without having to overdose at one of the biological targets. The chemical strategy was based on fine-tuning of the substitution pattern in the muscarinic and PDE4 structural portions of the dual pharmacology compounds, also making use of the analysis of a proprietary crystal structure in the PDE4 catalytic site. Compound 10f was identified as a chemically stable, potent, and in vivo balanced MAPI lead compound, as assessed in bronchoconstriction and inflammation assays in rats after intratracheal administration. After the in-depth investigation of the pharmacological and solid-state profile, 10f proved to be safe and suitable for development.

PDE4 Inhibitors: Profiling Hits through the Multitude of Structural Classes

Cyclic nucleotide phosphodiesterases 4 (PDE4) are a family of enzymes which specifically promote the hydrolysis and degradation of cAMP. The inhibition of PDE4 enzymes has been widely investigated as a possible alternative strategy for the treatment of a variety of respiratory diseases, including chronic obstructive pulmonary disease and asthma, as well as psoriasis and other autoimmune disorders. In this context, the identification of new molecules as PDE4 inhibitors continues to be an active field of investigation within drug discovery. This review summarizes the medicinal chemistry journey in the design and development of effective PDE4 inhibitors, analyzed through chemical classes and taking into consideration structural aspects and binding properties, as well as inhibitory efficacy, PDE4 selectivity and the potential as therapeutic agents.

Phosphodiesterase inhibitors and lung diseases

Phosphodiesterase enzymes (PDE) have long been known as regulators of cAMP and cGMP, second messengers involved in various signaling pathways and expressed in a variety of cell types implicated in respiratory diseases such as airway smooth muscle and inflammatory cells making them a key target for the treatment of lung diseases as chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis, and pulmonary hypertension (PH). The first reported PDE inhibitor was the xanthine, theophylline, described as a non-specific PDE inhibitor and whilst this drug is effective, it also has a range of unwanted side effects. In an attempt to improve the therapeutic window of xanthines, a number of selective PDE inhibitors have been developed for the treatment of respiratory diseases with only the selective PDE 4 inhibitor, roflumilast, being approved for the treatment of severe COPD. However, roflumilast also has a very narrow therapeutic window due to a number of important doses limiting side effects, particularly in the gastrointestinal tract. However, there continues to be research carried out in this field to identify improved selective PDE inhibitors, both by targeting other PDE subtypes (e.g., PDE 7 found in a number of inflammatory and immune cells) and through development of selective PDE inhibitors for pulmonary administration to reduce systemic exposure and improve the side effect profile. This approach has been exemplified by the development of ensifentrine, a dual PDE 3-PDE 4 inhibitor, an inhaled drug that has recently completed two successful Phase III clinical trials in patients with COPD.

Anomalous 1 H NMR chemical shift behavior of substituted benzoic acid esters

Benzoic acid esters represent key building blocks for many drug discovery and development programs and have been advanced as potent PDE4 inhibitors for inhaled administration for treatment of respiratory diseases. This class of compounds has also been employed in myriad industrial processes and as common food preservatives. Recent work directed toward the synthesis of intermediates for a proprietary medicinal chemistry program led us to observe that the ¹ H NMR chemical shifts of substituents ortho to the benzoic acid ester moiety defied conventional iterative chemical shift prediction protocols. To explore these unexpected results, we initiated a detailed computational study employing density functional theory (DFT) calculations to better understand the unexpectedly large variance in expected versus experimental NMR chemical shifts.

Virtual and In Vitro Screening of Natural Products Identifies Indole and Benzene Derivatives as Inhibitors of SARS-CoV-2 Main Protease (Mpro)

The rapid spread of the coronavirus disease 2019 (COVID-19) resulted in serious health, social, and economic consequences. While the development of effective vaccines substantially reduced the severity of symptoms and the associated deaths, we still urgently need effective drugs to further reduce the number of casualties associated with SARS-CoV-2 infections. Machine learning methods both improved and sped up all the different stages of the drug discovery processes by performing complex analyses with enormous datasets. Natural products (NPs) have been used for treating diseases and infections for thousands of years and represent a valuable resource for drug discovery when combined with the current computation advancements. Here, a dataset of 406,747 unique NPs was screened against the SARS-CoV-2 main protease (M^pro) crystal structure (6lu7) using a combination of ligand- and structural-based virtual screening. Based on 1) the predicted binding affinities of the NPs to the M^pro, 2) the types and number of interactions with the M^pro amino acids that are critical for its function, and 3) the desirable pharmacokinetic properties of the NPs, we identified the top 20 candidates that could potentially inhibit the M^pro protease function. A total of 7 of the 20 top candidates were subjected to in vitro protease inhibition assay and 4 of them (4/7; 57%), including two beta carbolines, one N-alkyl indole, and one Benzoic acid ester, had significant inhibitory activity against M^pro protease. These four NPs could be developed further for the treatment of COVID-19 symptoms.

An Overview of PDE4 Inhibitors in Clinical Trials: 2010 to Early 2022

Since the early 1980s, phosphodiesterase 4 (PDE4) has been an attractive target for the treatment of inflammation-based diseases. Several scientific advancements, by both academia and pharmaceutical companies, have enabled the identification of many synthetic ligands for this target, along with the acquisition of precise information on biological requirements and linked therapeutic opportunities. The transition from pre-clinical to clinical phase was not easy for the majority of these compounds, mainly due to their significant side effects, and it took almost thirty years for a PDE4 inhibitor to become a drug i.e., Roflumilast, used in the clinics for the treatment of chronic obstructive pulmonary disease. Since then, three additional compounds have reached the market a few years later: Crisaborole for atopic dermatitis, Apremilast for psoriatic arthritis and Ibudilast for Krabbe disease. The aim of this review is to provide an overview of the compounds that have reached clinical trials in the last ten years, with a focus on those most recently developed for respiratory, skin and neurological disorders.

Synthesis of N-Heteroarenemethyl Esters via C–C Bond Cleavage of Acyl Cyanides Under Transition Metal-Free Conditions

A practical method to synthesize N-heteroaryl esters from N-heteroaryl methanols with acyl cyanides via C–C bond cleavage without using any transition metal is demonstrated here. The use of Na₂CO₃/15-crown-5 couple enables access to a series of N-heteroaryl esters in high efficiency. This protocol is operationally simple and highly environmentally benign producing only cyanides as byproducts.

The PDE4 Inhibitor Tanimilast Blunts Proinflammatory Dendritic Cell Activation by SARS-CoV-2 ssRNAs

Phosphodiesterase 4 (PDE4) inhibitors are immunomodulatory drugs approved to treat diseases associated with chronic inflammatory conditions, such as COPD, psoriasis and atopic dermatitis. Tanimilast (international non-proprietary name of CHF6001) is a novel, potent and selective inhaled PDE4 inhibitor in advanced clinical development for the treatment of COPD. To begin testing its potential in limiting hyperinflammation and immune dysregulation associated to SARS-CoV-2 infection, we took advantage of an in vitro model of dendritic cell (DC) activation by SARS-CoV-2 genomic ssRNA (SCV2-RNA). In this context, Tanimilast decreased the release of pro-inflammatory cytokines (TNF-α and IL-6), chemokines (CCL3, CXCL9, and CXCL10) and of Th1-polarizing cytokines (IL-12, type I IFNs). In contrast to β-methasone, a reference steroid anti-inflammatory drug, Tanimilast did not impair the acquisition of the maturation markers CD83, CD86 and MHC-II, nor that of the lymph node homing receptor CCR7. Consistent with this, Tanimilast did not reduce the capability of SCV2-RNA-stimulated DCs to activate CD4⁺ T cells but skewed their polarization towards a Th2 phenotype. Both Tanimilast and β-methasone blocked the increase of MHC-I molecules in SCV2-RNA-activated DCs and restrained the proliferation and activation of cytotoxic CD8⁺ T cells. Our results indicate that Tanimilast can modulate the SCV2-RNA-induced pro-inflammatory and Th1-polarizing potential of DCs, crucial regulators of both the inflammatory and immune response. Given also the remarkable safety demonstrated by Tanimilast, up to now, in clinical studies, we propose this inhaled PDE4 inhibitor as a promising immunomodulatory drug in the scenario of COVID-19.

Phosphodiesterase‑4 inhibitors: a review of current developments (2013-2021)

INTRODUCTION

Cyclic nucleotide phosphodiesterase 4 (PDE4) is responsible for the hydrolysis of cAMP, which has become an attractive therapeutic target for lung, skin, and severe neurological diseases. Here, we review the current status of development of PDE4 inhibitors since 2013 and discuss the applicability of novel medicinal-chemistry strategies for identifying more efficient and safer inhibitors.

AREAS COVERED

This review summarizes the clinical development of PDE4 inhibitors from 2013 to 2021, focused on their pharmacophores, the strategies to reduce the side effects of PDE4 inhibitors and the development of subfamily selective PDE4 inhibitors.

EXPERT OPINION

To date, great efforts have been made in the development of PDE4 inhibitors, and researchers have established a comprehensive preclinical database and collected some promising data from clinical trials. Although four small-molecule PDE4 inhibitors have been approved by FDA for the treatment of human diseases up to now, further development of other reported PDE4 inhibitors with strong potency has been hampered due to the occurrence of severe side effects. There are currently three main strategies for overcoming the dose limitation and systemic side effects, which provide new opportunities for the clinical development of new PDE4 inhibitors.

Tanimilast, A Novel Inhaled Pde4 Inhibitor for the Treatment of Asthma and Chronic Obstructive Pulmonary Disease

Chronic respiratory diseases are the third leading cause of death, behind cardiovascular diseases and cancer, affecting approximately 550 million of people all over the world. Most of the chronic respiratory diseases are attributable to asthma and chronic obstructive pulmonary disease (COPD) with this latter being the major cause of deaths. Despite differences in etiology and symptoms, a common feature of asthma and COPD is an underlying degree of airways inflammation. The nature and severity of this inflammation might differ between and within different respiratory conditions and pharmacological anti-inflammatory treatments are unlikely to be effective in all patients. A precision medicine approach is needed to selectively target patients to increase the chance of therapeutic success. Inhibitors of the phosphodiesterase 4 (PDE4) enzyme like the oral PDE4 inhibitor roflumilast have shown a potential to reduce inflammatory-mediated processes and the frequency of exacerbations in certain groups of COPD patients with a chronic bronchitis phenotype. However, roflumilast use is dampened by class related side effects as nausea, diarrhea, weight loss and abdominal pain, resulting in both substantial treatment discontinuation in clinical practice and withdrawal from clinical trials. This has prompted the search for PDE4 inhibitors to be given by inhalation to reduce the systemic exposure (and thus optimize the systemic safety) and maximize the therapeutic effect in the lung. Tanimilast (international non-proprietary name of CHF6001) is a novel highly potent and selective inhaled PDE4 inhibitor with proven anti-inflammatory properties in various inflammatory cells, including leukocytes derived from asthma and COPD patients, as well as in experimental rodent models of pulmonary inflammation. Inhaled tanimilast has reached phase III clinical development by showing promising pharmacodynamic results associated with a good tolerability and safety profile, with no evidence of PDE4 inhibitors class-related side effects. In this review we will discuss the main outcomes of preclinical and clinical studies conducted during tanimilast development, with particular emphasis on the characterization of the pharmacodynamic profile that led to the identification of target populations with increased therapeutic potential in inflammatory respiratory diseases.

Developing inhaled drugs for respiratory diseases: A medicinal chemistry perspective

Despite the devastating impact of many lung diseases on human health, there is still a significant unmet medical need in respiratory diseases, for which inhaled delivery represents a crucial strategy. More guidance on how to design and carry out multidisciplinary inhaled projects is needed. When designing inhaled drugs, the medicinal chemist must carefully balance the physicochemical properties of the molecule to achieve optimal target engagement in the lung. Although the medicinal chemistry strategy is unique for each project, and will change depending on multiple factors, such as the disease, target, systemic risk, delivery device, and formulation, general guidelines aiding inhaled drug design can be applied and are summarised in this review.

Discovery of M3 Antagonist-PDE4 Inhibitor Dual Pharmacology Molecules for the Treatment of Chronic Obstructive Pulmonary Disease

In this paper, we report the discovery of dual M₃ antagonist-PDE4 inhibitor (MAPI) compounds for the inhaled treatment of pulmonary diseases. The identification of dual compounds was enabled by the intuition that the fusion of a PDE4 scaffold derived from our CHF-6001 series with a muscarinic scaffold through a common linking ring could generate compounds active versus both the transmembrane M₃ receptor and the intracellular PDE4 enzyme. Two chemical series characterized by two different muscarinic scaffolds were investigated. SAR optimization was aimed at obtaining M₃ nanomolar affinity coupled with nanomolar PDE4 inhibition, which translated into anti-bronchospastic efficacy ex vivo (inhibition of rat trachea contraction) and into anti-inflammatory efficacy in vitro (inhibition of TNFα release). Among the best compounds, compound 92a achieved the goal of demonstrating in vivo efficacy and duration of action in both the bronchoconstriction and inflammation assays in rat after intratracheal administration.

Phosphodiesterase 4 inhibitors attenuate virus-induced activation of eosinophils from asthmatics without affecting virus binding

Acute respiratory virus infections, such as influenza and RSV, are predominant causes of asthma exacerbations. Eosinophils act as a double-edged sword in exacerbations in that they are activated by viral infections but also can capture and inactivate respiratory viruses. Phosphodiesterase type 4 (PDE4) is abundantly expressed by eosinophils and has been implicated in their activation. This exploratory study aims to determine whether these opposing roles of eosinophils activation of eosinophils upon interaction with virus can be modulated by selective PDE4 inhibitors and whether eosinophils from healthy, moderate and severe asthmatic subjects respond differently. Eosinophils were purified by negative selection from blood and subsequently exposed to RSV or influenza. Prior to exposure to virus, eosinophils were treated with vehicle or selective PDE4 inhibitors CHF6001 and GSK256066. After 18 hours of exposure, influenza, but not RSV, increased CD69 and CD63 expression by eosinophils from each group, which were inhibited by PDE4 inhibitors. ECP release, although not stimulated by virus, was also attenuated by PDE4 inhibitors. Eosinophils showed an increased Nox2 activity upon virus exposure, which was less pronounced in eosinophils derived from mild and severe asthmatics and was counteracted by PDE4 inhibitors. PDE4 inhibitors had no effect on binding of virus by eosinophils from each group. Our data indicate that PDE4 inhibitors can attenuate eosinophil activation, without affecting virus binding. By attenuating virus-induced responses, PDE4 inhibitors may mitigate virus-induced asthma exacerbations.

Phosphodiesterase isoforms and cAMP compartments in the development of new therapies for obstructive pulmonary diseases

The second messenger molecule 3'5'-cyclic adenosine monophosphate (cAMP) imparts several beneficial effects in lung diseases such as asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). While cAMP is bronchodilatory in asthma and COPD, it also displays anti-fibrotic properties that limit fibrosis. Phosphodiesterases (PDEs) metabolize cAMP and thus regulate cAMP signaling. While some existing therapies inhibit PDEs, there are only broad family specific inhibitors. The understanding of cAMP signaling compartments, some centered around lipid rafts/caveolae, has led to interest in defining how specific PDE isoforms maintain these signaling microdomains. The possible altered expression of PDEs, and thus abnormal cAMP signaling, in obstructive lung diseases has been poorly explored. We propose that inhibition of specific PDE isoforms can improve therapy of obstructive lung diseases by amplifying specific cAMP signals in discreet microdomains.

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.

CHF6001 Inhibits NF-κB Activation and Neutrophilic Recruitment in LPS-Induced Lung Inflammation in Mice

Inhibitors of phosphodiesterase 4 (PDE4) are potent anti-inflammatory agents, inhibiting the production of inflammatory mediators through the elevation of intracellular cAMP concentrations. We studied the activity of a novel PDE4 inhibitor, CHF6001, both in vitro in human cells and in vivo, using bioluminescence imaging (BLI) in mice lung inflammation. Mice transiently transfected with the luciferase gene under the control of an NF-κB responsive element (NF-κB-luc) have been used to assess the in vivo anti-inflammatory activity of CHF6001 in lipopolysaccharide (LPS)-induced lung inflammation. BLI as well as inflammatory cells and the concentrations of pro-inflammatory cytokines were monitored in bronchoalveolar lavage fluids (BALF) while testing in vitro its ability to affect the production of leukotriene B₄ (LTB₄), measured by LC/MS/MS, by LPS/LPS/N-formyl--methionyl--leucyl-phenylalanine (fMLP)-activated human blood. CHF6001 inhibited the production of LTB₄ in LPS/fMLP-activated human blood at sub-nanomolar concentrations. LPS-induced an increase of BLI signal in NF-κB-luc mice, and CHF6001 administered by dry powder inhalation decreased in parallel luciferase signal, cell airway infiltration, and pro-inflammatory cytokine concentrations in BALF. The results obtained provide in vitro and in vivo evidence of the anti-inflammatory activity of the potent PDE4 inhibitor CHF6001, showing that with a topical administration that closely mimics inhalation in humans, it efficiently disrupts the NF-κB activation associated with LPS challenge, an effect that may be relevant for the prevention of exacerbation episodes in chronic obstructive pulmonary disease subjects.

The PDE4 inhibitor CHF6001 modulates pro-inflammatory cytokines, chemokines and Th1- and Th17-polarizing cytokines in human dendritic cells

Phosphodiesterase 4 (PDE4) inhibitors are used to treat autoimmune and inflammatory diseases, such as psoriasis and chronic obstructive pulmonary disease (COPD). CHF6001 is a novel, potent and selective inhaled PDE4 inhibitor in development for the treatment of COPD. When tested in vitro on human dendritic cells (DCs), CHF6001 decreased the release of pro-inflammatory cytokines (TNF-α and IL-6), chemokines (CXCL8, CCL3, CXCL10 and CCL19) and of Th1- and Th17-polarizing cytokines (IL-12, IL-23 and IL-1β). In contrast to β-methasone, a reference steroid anti-inflammatory drug, CHF6001 increased the secretion of CCL22, a Th2 recruiting chemokine, and the expression of the lymph node homing receptor CCR7. Accordingly, the migration of DCs to CCR7 ligands was increased, while migration to pro-inflammatory chemokines was decreased. Of note, the action of CHF6001 was apparently mediated by a promoter-specific decrease in NF-κB p65 recruitment, independent of perturbation of LPS signalling or NF-κB nuclear translocation. Our results indicate that CHF6001 can modulate DC pro-inflammatory Th1/Th17 polarizing potential by fine tuning the transcriptional activity of the master inflammatory transcription factor NF-κB. Therefore, CHF6001 may prove useful to control Th1/Th17-polarized inflammatory diseases such as COPD.

Targeted Treatments for Chronic Obstructive Pulmonary Disease (COPD) Using Low-Molecular-Weight Drugs (LMWDs)

Chronic obstructive pulmonary disease (COPD) is a very common and frequently fatal airway disease. Current therapies for COPD depend mainly on long-acting bronchodilators, which cannot target the pathogenic mechanisms of chronic inflammation in COPD. New pharmaceutical therapies for the inflammatory processes of COPD are urgently needed. Several anti-inflammatory targets have been identified based on increased understanding of the pathogenesis of COPD, which raises new hopes for targeted treatment of this fatal respiratory disease. In this review, we discuss the recent advances in bioactive low-molecular-weight drugs (LMWDs) for the treatment of COPD and, in addition to the first-line drug bronchodilators, focus particularly on low-molecular-weight anti-inflammatory agents, including modulators of inflammatory mediators, inflammasome inhibitors, protease inhibitors, antioxidants, PDE4 inhibitors, kinase inhibitors, and other agents. We also provide new insights into targeted COPD treatments using LMWDs, particularly small-molecule agents.

Phosphodiesterases as therapeutic targets for respiratory diseases

Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) and asthma, affect millions of people all over the world. Cyclic adenosine monophosphate (cAMP) which is one of the most important second messengers, plays a vital role in relaxing airway smooth muscles and suppressing inflammation. Given its vast role in regulating intracellular responses, cAMP provides an attractive pharmaceutical target in the treatment of chronic respiratory diseases. Phosphodiesterases (PDEs) are enzymes that hydrolyze cyclic nucleotides and help control cyclic nucleotide signals in a compartmentalized manner. Currently, the selective PDE4 inhibitor, roflumilast, is used as an add-on treatment for patients with severe COPD associated with bronchitis and a history of frequent exacerbations. In addition, other novel PDE inhibitors are in different phases of clinical trials. The current review provides an overview of the regulation of various PDEs and the potential application of selective PDE inhibitors in the treatment of COPD and asthma. The possibility to combine various PDE inhibitors as a way to increase their therapeutic effectiveness is also emphasized.

Safety, tolerability, and pharmacokinetics of single and repeat ascending doses of CHF6001, a novel inhaled phosphodiesterase-4 inhibitor: two randomized trials in healthy volunteers

PURPOSE

The purpose of this study was to evaluate safety, tolerability, and pharmacokinetics (PK) of CHF6001, an inhaled phosphodiesterase-4 inhibitor.

MATERIALS AND METHODS

Two healthy volunteer, randomized, double-blind, placebo-controlled studies were conducted. In each, Part 1 evaluated single ascending doses, with PK sampling up to 48 hours post-dose; Part 2 evaluated multiple ascending doses (Study 1, 7 days; Study 2, 14 days), with PK sampling up to 24 hours post-dose on first and last day of each period. In Study 1, treatments were administered via single-dose dry-powder inhaler (SDDPI; Aerolizer): Part 1, 20, 100, 200, 400, 800, 1,600, and 2,000 µg or placebo; Part 2, 100, 300, 600, 1,200, and 1,600 µg or placebo once daily (OD). In Study 2, treatments were administered via multi-dose dry-powder inhaler (MDDPI; NEXThaler): Part 1, 2,400, 4,000, and 4,800 µg or placebo; Part 2, 1,200, 2,000, or 2,400 µg twice daily (BID) or placebo. Modeling and simulation then compared OD and BID dosing via MDDPI.

RESULTS

There was a clear correlation between CHF6001 dose and plasma concentration, following single and multiple doses and using SDDPI and MDDPI. CHF6001 plasma concentration area under the curve (AUC) was dose proportional, with steady state slopes of the fitted line of 0.95 (90% CI: 0.86, 1.04) for AUC0-24 h in Study 1, and 0.85 (90% CI: 0.38, 1.32) for AUC0-12 h in Study 2. Bioavailability waŝ30% higher with MDDPI than SDDPI. The PK simulation confirmed dose proportionality; the same total daily dose OD or BID via MDDPI resulted in similar 24 hours exposure, with BID dosing providing smaller fluctuation and lower maximum concentration. CHF6001 was well tolerated with no relationship between dose and adverse events.

CONCLUSION

CHF6001 demonstrated a good safety profile. There was a clear dose proportionality for systemic exposure, with higher bioavailability via MDDPI, suggesting that the MDDPI provides better pulmonary drug deposition. BID dosing was associated with a better exposure profile.

Role of efflux transporters in the absorption, distribution and elimination in rodents of a novel PDE4 inhibitor, CHF6001

CHF6001 is a new and potent PDE4 inhibitor for the treatment of human lung diseases, designed for topical administration by inhalation. In preclinical assessment CHF6001 appeared safe and devoid of emetic effect, which is typical side effect of PDE4 inhibitors in humans. CHF6001 absorption, distribution and excretion were evaluated in rats by PO and IV administration of [14C]CHF6001; additionally the role of transporters was investigated by using transfected cells expressing either human transporters or MDR1 and BCRP KO mice. [14C]CHF6001 intravenously administered as bolus distributed in all the tissues (with very low levels in brain and fetus) and it was mainly eliminated in bile. Following oral administration [14C]CHF6001 about half of the dose was absorbed through the gut. In vitro, CHF6001 was a substrate of human membrane transporters MDR1 and BCRP. In wild and BCRP KO mice CHF6001 was not detectable in brain, whereas it was measurable in Mdr1a/b KO mice. Therefore, in animal species Mdr1a/b plays a significant role in CHF6001 disposition, limiting its distribution into brain and contributing to the safety profile observed in preclinical evaluation. This behavior was confirmed by the results of the first human studies, where CHF6001 was safe and with no emetic effect at all the evaluated doses.

Discovery and Optimization of Thiazolidinyl and Pyrrolidinyl Derivatives as Inhaled PDE4 Inhibitors for Respiratory Diseases

Phosphodiesterase 4 (PDE4) is a key cAMP-metabolizing enzyme involved in the pathogenesis of inflammatory disease, and its pharmacological inhibition has been shown to exert therapeutic efficacy in chronic obstructive pulmonary disease (COPD). Herein, we describe a drug discovery program aiming at the identification of novel classes of potent PDE4 inhibitors suitable for pulmonary administration. Starting from a previous series of benzoic acid esters, we explored the chemical space in the solvent-exposed region of the enzyme catalytic binding pocket. Extensive structural modifications led to the discovery of a number of heterocycloalkyl esters as potent in vitro PDE4 inhibitors. (S*,S**)-18e and (S*,S**)-22e, in particular, exhibited optimal in vitro ADME and pharmacokinetics properties and dose-dependently counteracted acute lung eosinophilia in an experimental animal model. The optimal biological profile as well as the excellent solid-state properties suggest that both compounds have the potential to be effective topical agents for treating respiratory inflammatory diseases.

Synthesis of 14 C- and 2 H-labelled CHF6001: A new potent PDE4 inhibitor

An 8-step preparation of ¹⁴ C-labelled CHF6001, a potent phosphodiesterase 4 inhibitor in the treatment of respiratory diseases, is described. An overall yield of approximately 9% was obtained starting from copper[¹⁴ C]cyanide. The synthesis of a stable labelled version of CHF6001 is also reported using the commercially available trideuterated bromomethylcyclopropane as starting material.

C-H Functionalization of Azines

Azines, which are six-membered aromatic compounds containing one or more nitrogen atoms, serve as ubiquitous structural cores of aromatic species with important applications in biological and materials sciences. Among a variety of synthetic approaches toward azines, C-H functionalization represents the most rapid and atom-economical transformation, and it is advantageous for the late-stage functionalization of azine-containing functional molecules. Since azines have several C-H bonds with different reactivities, the development of new reactions that allow for the functionalization of azines in a regioselective fashion has comprised a central issue. This review describes recent advances in the C-H functionalization of azines categorized as follows: (1) S_NAr reactions, (2) radical reactions, (3) deprotonation/functionalization, and (4) metal-catalyzed reactions.

Airway inflammation in asthma: key players beyond the Th2 pathway

PURPOSE OF REVIEW

The Th2 pathway starts with the binding of IL-4 to the IL-4 receptor followed by the phosphorylation of signal transducer and activator of transcription 6 and the activation of GATA3. The most important question relates to the sources of IL-4 and IL-4 related inflammation. Which cells other than Th2 cells are responsible for airway inflammation in asthma?

RECENT FINDINGS

Accumulating data indicate that basophils contribute to endothelium-related IL-4-dependent inflammation. There is also a dendritic cell-related alternative for the induction of Th2 cells via Notch signalling. GATA3 deoxyribozyme improves asthma that is not clearly related to T-cells. The innate immune response in allergy is linked to mast cells, basophils, and the innate lymphoid cell type 2 (ILC2). ILC2s respond to IL-25, IL-33, thymic stromal lymphopoietin, and leukotrienes by producing IL-4, IL-5, and IL-13. In addition to all this inflammatory-cell-driven asthma, increasing evidence has emerged relating to smooth muscle cell activation, the endothelial and epithelial barrier functions, and improvements in the barrier function. The elevation of intracellular cyclic adenosine monophosphate because of the use of phosphodiesterase inhibitors adds to the prevention of epithelial-endothelial leakage, supports airway smooth muscle relaxation, and is immunosuppressive.

CONCLUSION AND SUMMARY

IL-4 is the predominant Th2 cell cytokine. Many more cells, including eosinophils, basophils, mast cells, and ILC2, contribute to the production of IL-4 in the airways. Epithelial cells and endothelial cells lose barrier function in the context of allergic airway inflammation, and this could be at least partially remedied by increasing the intracellular cyclic adenosine monophosphate levels through phosphodiesterase inhibition.

Anti-inflammatory effects of the novel inhaled phosphodiesterase type 4 inhibitor CHF6001 on virus-inducible cytokines

Respiratory virus infections precipitate asthma and chronic obstructive pulmonary disease (COPD) exacerbations, with most exacerbations due to rhinovirus infection. Both asthma and COPD exacerbations are not well controlled by steroid therapies, and there is a much research interest in finding improved therapies or combinations of therapies for controlling exacerbations. CHF6001 is a new, inhaled highly potent and selective phosphodiesterase type 4 (PDE4) inhibitor. Using in vitro human bronchial epithelial cells (BEAS‐2B), we investigated the potential anti‐inflammatory effects of CHF6001 on rhinovirus (RV1B)‐induced cytokines. Cytokine mRNA was measured by real‐time PCR, while protein release was measured by ELISA. CHF6001 was used in a 7‐point dose–response curve (1000–0.001 nmol/L) as a 1.5‐h pretreatment prior to infection in comparison with roflumilast. Both roflumilast and CHF6001 reduced RV1B‐induced IL‐8, IL‐29, IP‐10, and RANTES mRNA and protein in a concentration‐dependent manner. Generally, CHF6001 was 13‐ to 16‐fold more potent (subnanomolar EC₅₀ values) than roflumilast at reducing IL‐8, IL‐29, IP‐10, and RANTES mRNA and protein release, but had similar efficacies. In combination with the steroid fluticasone propionate (1 nmol/L), CHF6001 had additive effects, significantly reducing RV‐induced cytokines when compared with steroid or CHF6001 alone. Combined low‐dose steroid and low‐dose CHF6001 had a similar efficacy as high‐dose steroid or CHF6001 alone, indicating the combination had steroid and PDE4 inhibitor sparing effects. Overall results indicate that PDE4 inhibitors have anti‐inflammatory activity against virus‐induced inflammatory mediators and that CHF6001 is more potent than roflumilast.

Design, synthesis, and pharmacological evaluation of highly potent and selective dipeptidyl peptidase-4 inhibitors

The optimization of a series of fused β-homophenylalanine inhibitors of dipeptidyl peptidase-4 (DPP-4) is described. Modification on the P2-binding moiety of 6 (IC50 = 10 nM) led to the discovery of β-homophenylalanine derivatives containing pyrrolidin-2-ylmethyl amides. The introduction of a sulfamine in the meta position of the phenyl ring improved the potency against DPP-4 (6-12-fold increase). Compound 14k showed DPP-4 inhibitory activity with an IC50 value of 0.87 nM. Meanwhile, in vivo experiments exhibited that 14h had an efficiency comparable to sitagliptin at the dose of 10 mg/kg.

In vitro and in vivo metabolism of CHF 6001, a selective phosphodiesterase (PDE4) inhibitor

1. The metabolism of CHF 6001, a novel PDE4 inhibitor, was determined in vitro in mouse, rat, dog, monkey and human microsomes and hepatocytes and in vivo in plasma, urine, feces and bile of rats after intravenous and intratracheal administration. 2. The behavior of CHF 6001 in microsomes and hepatocytes changed across species. CYP3A4/5 isoenzymes were identified to be the primary enzymes responsible for the metabolism of CHF 6001 in human liver microsomes. 3. In the rat, CHF 6001 was found extensively metabolized in urine, feces and bile, but not in plasma, where CHF 6001 was the main compound present. The metabolite profiles were different in the four biological matrices from both qualitative and quantitative point of view. 4. CHF 6001 was metabolized through hydrolysis with the formation of the alcohol CHF 5956, loss of a chlorine atom, loss of the N-oxide, hydroxylation, loss of the cyclopropylmethyl group in the alcohol moiety, conjugation with glucuronic acid, glutathione and cysteine-glycine. 5. The major metabolite present in the bile was isolated and characterized by nuclear magnetic resonance analysis. It derived from CHF 6001 through contraction of the pyridine-N-oxide ring to N-hydroxy pyrrole and conjugation with glucuronic acid.

CHF6001 I: a novel highly potent and selective phosphodiesterase 4 inhibitor with robust anti-inflammatory activity and suitable for topical pulmonary administration

This study examined the pharmacologic characterization of CHF6001 [(S)-3,5-dichloro-4-(2-(3-(cyclopropylmethoxy)-4-(difluoromethoxy)phenyl)-2-(3-(cyclopropylmethoxy)-4-(methylsulfonamido)benzoyloxy)ethyl)pyridine 1-oxide], a novel phosphodiesterase (PDE)4 inhibitor designed for treating pulmonary inflammatory diseases via inhaled administration. CHF6001 was 7- and 923-fold more potent than roflumilast and cilomilast, respectively, in inhibiting PDE4 enzymatic activity (IC50 = 0.026 ± 0.006 nM). CHF6001 inhibited PDE4 isoforms A-D with equal potency, showed an elevated ratio of high-affinity rolipram binding site versus low-affinity rolipram binding site (i.e., >40) and displayed >20,000-fold selectivity versus PDE4 compared with a panel of PDEs. CHF6001 effectively inhibited (subnanomolar IC50 values) the release of tumor necrosis factor-α from human peripheral blood mononuclear cells, human acute monocytic leukemia cell line macrophages (THP-1), and rodent macrophages (RAW264.7 and NR8383). Moreover, CHF6001 potently inhibited the activation of oxidative burst in neutrophils and eosinophils, neutrophil chemotaxis, and the release of interferon-γ from CD4(+) T cells. In all these functional assays, CHF6001 was more potent than previously described PDE4 inhibitors, including roflumilast, UK-500,001 [2-(3,4-difluorophenoxy)-5-fluoro-N-((1S,4S)-4-(2-hydroxy-5-methylbenzamido)cyclohexyl)nicotinamide], and cilomilast, and it was comparable to GSK256066 [6-((3-(dimethylcarbamoyl)phenyl)sulfonyl)-4-((3-methoxyphenyl)amino)-8-methylquinoline-3-carboxamide]. When administered intratracheally to rats as a micronized dry powder, CHF6001 inhibited liposaccharide-induced pulmonary neutrophilia (ED50 = 0.205 μmol/kg) and leukocyte infiltration (ED50 = 0.188 μmol/kg) with an efficacy comparable to a high dose of budesonide (1 μmol/kg i.p.). In sum, CHF6001 has the potential to be an effective topical treatment of conditions associated with pulmonary inflammation, including asthma and chronic obstructive pulmonary disease.

CHF6001 II: a novel phosphodiesterase 4 inhibitor, suitable for topical pulmonary administration--in vivo preclinical pharmacology profile defines a potent anti-inflammatory compound with a wide therapeutic window

CHF6001 [(S)-3,5-dichloro-4-(2-(3-(cyclopropylmethoxy)-4-(difluoromethoxy)phenyl)-2-(3-(cyclopropylmethoxy)-4-(methylsulfonamido)benzoyloxy)ethyl)pyridine 1-oxide] is a novel phosphodiesterase 4 (PDE4) inhibitor designed for use in pulmonary diseases by inhaled administration. Intratracheal administration of CHF6001 to ovalbumin-sensitized Brown-Norway rats suppressed the antigen-induced decline of lung functions (ED50 = 0.1 µmol/kg) and antigen-induced eosinophilia (ED50 = 0.03 µmol/kg) when administered (0.09 μmol/kg) up to 24 hours before antigen challenge, in agreement with CHF6001-sustained lung concentrations up to 72 hours after intratracheal treatment (mean residence time 26 hours). Intranasal, once daily administration of CHF6001 inhibited neutrophil infiltration observed after 11 days of tobacco smoke exposure in mice, both upon prophylactic (0.15-0.45 µmol/kg per day) or interventional (0.045-0.45 µmol/kg per day) treatment. CHF6001 was ineffective in reversing ketamine/xylazine-induced anesthesia (a surrogate of emesis in rat) up to 5 µmol/kg administered intratracheally, a dose 50- to 150-fold higher than anti-inflammatory ED50 observed in rats. When given topically to ferrets, no emesis and nausea were evident up to 10 to 20 µmol/kg, respectively, whereas the PDE4 inhibitor GSK-256066 (6-[3-(dimethylcarbamoyl)phenyl]sulfonyl-4-(3-methoxyanilino)-8-methylquinoline-3-carboxamide) induced nausea at 1 µmol/kg intratracheally. A 14-day inhalation toxicology study in rats showed a no-observed-adverse-effect level dose of 4.4 µmol/kg per day for CHF6001, lower than the 0.015 μmol/kg per day for GSK-256066. CHF6001 was found effective and extremely well tolerated upon topical administration in relevant animal models, and may represent a step forward in PDE4 inhibition for the treatment of asthma and chronic obstructive respiratory disease.

cAMP-specific phosphodiesterase inhibitors: promising drugs for inflammatory and neurological diseases

INTRODUCTION

PDEs are key enzymes in the adenosine and guanosine cyclic nucleotides (cAMP and cGMP) signaling cascade. Their inhibition increases cyclic nucleotide levels inside the cell. Thus, pharmacological modulation of PDE activity can have profound effects on the function of cells and organ systems throughout the body.

AREAS COVERED

Among the large PDE families, only PDE4, PDE7 and PDE8 are cAMP-specific hydrolyzing enzymes. cAMP is an important second messenger not only by its involvement in a vast number of physiological processes but also by activation of protein kinase A, exchange protein activated by cAMP (Epac) and cAMP response element-binding (CREB) or cyclic nucleotide-gated channels. Clearly, such enzymes represent ideal drug targets for the pharmacological treatment of many pathologies. The discovery and development of small molecules targeting cAMP-specific PDEs reported in the last 5 years is the focus of the present review.

EXPERT OPINION

The first PDE4 inhibitors recently reached the market, having avoided, by different strategies, their dose-limiting side effects (after more than two decades of drug development). Meanwhile, new cAMP-specific PDE7 and PDE8 inhibitors emerged as effective and safe drugs for severe unmet diseases. The therapeutic potential of these inhibitors will be tested in the near future, as many of these drug candidates are ready to start clinical trials.

Novel Roflumilast analogs as soft PDE4 inhibitors

PDE4 inhibitors are of high interest for treatment of a wide range of inflammatory or autoimmune diseases. Their potential however has not yet been realized due to target-associated side effects, resulting in a low therapeutic window. We herein report the design, synthesis and evaluation of novel PDE4 inhibitors containing a γ-lactone structure. Such molecules are designed to undergo metabolic inactivation when entering circulation, thereby limiting systemic exposure and reducing the risk for side effects. The resulting inhibitors were highly active on both PDE4B1 and PDE4D2 and underwent rapid degradation in human plasma by paraoxonase 1. In contrast, their metabolites displayed markedly reduced permeability and/or on-target activity.

Efficacious inhaled PDE4 inhibitors with low emetic potential and long duration of action for the treatment of COPD

Oral phosphodiesterase 4 (PDE4) inhibitors, such as cilomilast and roflumilast, have been shown to be efficacious against chronic obstructive pulmonary disease (COPD). However, these drugs have been hampered by mechanism-related side effects such as nausea and emesis at high doses. Compounds administered by inhalation are delivered directly to the site of action and may improve the therapeutic index required to overcome side effects. This paper describes systematic and rational lead optimization to deliver highly potent, long-acting, and efficacious preclinical inhaled PDE4 inhibitors with low emetic potential.

Dual PDE3/4 and PDE4 inhibitors: novel treatments for COPD and other inflammatory airway diseases

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.

Base-catalyzed retro-Claisen condensation: a convenient esterification of alcohols via C–C bond cleavage of ketones to afford acylating sources

The base-catalyzed esterification of alcohols via retro-Claisen condensation has been demonstrated for the first time.