Evidence that cyclic AMP phosphodiesterase inhibitors suppress interleukin-2 release from murine splenocytes by interacting with a 'low-affinity' phosphodiesterase 4 conformer

In vivo effective dibenzo[b,d]furan-1-yl-thiazoles as novel PDE-4 inhibitors

Herein we report the synthesis, PDE-4B and TNF-α inhibitory activities of a few dibenzo[b,d]furan-1-yl-thiazole derivatives. The hydroxycyclohexanol amide derivatives 14, 18, 24, 29, 31 and 33 exhibited promising in vitro PDE-4B and TNF-α inhibitory activities. Compound 24 showed good systemic availability in preclinical animal models and was also found to be non-toxic (exploratory mutagenicity test). Further it exhibited promising results in in vivo asthma/COPD and Uveitis models.

Phosphodiesterase inhibitors: history of pharmacology

The first pharmacological investigations of phosphodiesterase (PDE) inhibitors were developed with the clinical efficacies of drugs isolated from coffee, cacao and tea but only later their relevant ingredients were identified as xanthines that act as PDE. With its diuretic, inotropic and bronchodilating clinical efficacy, use of theophylline anticipated the clinical goals, which were later approached with the first-generation of weakly selective PDE inhibitors in the period from 1980 to 1990. Pharmacological and clinical research with these early compounds provided a vast pool of information regarding desired and adverse actions - although most of these new drugs had to be discontinued due to severe adverse effects. The pharmacological models for cardiac, vascular and respiratory indications were analysed for their PDE isoenzyme profiles, and when biochemical and molecular biological approaches expanded our knowledge of the PDE superfamily, the purified isoenzymes that were now available opened the door for more systematic studies of inhibitors and for generation of highly selective isoenzyme-specific drugs. The development of simple screening models and clinically relevant indication models reflecting the growing knowledge about pathomechanisms of disease are summarised here for today's successful application of highly selective PDE3, PDE4 and PDE5 inhibitors. The interplay of serendipitous discoveries, the establishment of intelligent pharmacological models and the knowledge gain by research results with new substances is reviewed. The broad efficacies of new substances in vitro, the enormous biodiversity of the PDE isoenzyme family and the sophisticated biochemical pharmacology enabled Viagra to be the first success story in the field of PDE inhibitor drug development, but probably more success stories will follow.

A cell-based PDE4 assay in 1536-well plate format for high-throughput screening

The cyclic nucleotide phosphodiesterases (PDEs) are intracellular enzymes that catalyze the hydrolysis of 3,'5'-cyclic nucleotides, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), to their corresponding 5'nucleotide monophosphates. These enzymes play an important role in controlling cellular concentrations of cyclic nucleotides and thus regulate a variety of cellular signaling events. PDEs are emerging as drug targets for several diseases, including asthma, cardiovascular disease, attention-deficit hyperactivity disorder, Parkinson's disease, and Alzheimer's disease. Although biochemical assays with purified recombinant PDE enzymes and cAMP or cGMP substrate are commonly used for compound screening, cell-based assays would provide a better assessment of compound activity in a more physiological context. The authors report the development and validation of a new cell-based PDE4 assay using a constitutively active G-protein-coupled receptor as a driving force for cAMP production and a cyclic nucleotide-gated cation channel as a biosensor in 1536-well plates.

Differential effects of PDE4 inhibitors on cortical neurons and T-lymphocytes

Inhibitors of PDE4 (cAMP-specific phosphodiesterase) induce side effects, including nausea and emesis, that limit their therapeutic potential. We investigated the function of two catalytically active conformations of PDE4 (a low-affinity conformer detected by conventional cAMP hydrolytic activity and a high-affinity conformer detected by [(3)H]rolipram binding) in neuronal cells. We assessed enhancement of beta-adrenoceptor-mediated cAMP accumulation in cortical neurons in vitro by eleven PDE4 inhibitors with diverse biochemical profiles. The compounds tested have a wide inhibition range of PDE4 catalytic activity and [(3)H]rolipram binding. Inhibition potency for PDE4 catalytic activity and [(3)H]rolipram binding for each compound was different. Potency in augmentation of cAMP correlated significantly with the inhibitory effect on [(3)H]rolipram binding, but not with that against PDE4 catalytic activity. On the other hand, the inhibitory effect on proliferation of T-lymphocytes of the same PDE4 inhibitors correlated both with inhibition of PDE4 catalytic activity and with inhibition of [(3)H]rolipram binding. These findings indicate that the high affinity PDE4 conformer exists at a high level in cortical neurons and is important in the regulation of cAMP. Furthermore, the relative contributions of the two PDE4 conformers in cell function may cause different PDE4 inhibitor effects on cortical neurons and T-lymphocytes.

Treating COPD with PDE 4 inhibitors

While the pathogenesis of chronic obstructive pulmonary disease (COPD) is incompletely understood, chronic inflammation is a major factor. In fact, the inflammatory response is abnormal, with CD8+ T-cells, CD68+ macrophages, and neutrophils predominating in the conducting airways, lung parenchyma, and pulmonary vasculature. Elevated levels of the second messenger cAMP can inhibit some inflammatory processes. Theophylline has long been used in treating asthma; it causes bronchodilation by inhibiting cyclic nucleotide phosphodiesterase (PDE), which inactivates cAMP. By inhibiting PDE, theophylline increases cAMP, inhibiting inflammation and relaxing airway smooth muscle. Rather than one PDE, there are now known to be more than 50, with differing activities, substrate preferences, and tissue distributions. Thus, the possibility exists of selectively inhibiting only the enzyme(s) in the tissue(s) of interest. PDE 4 is the primary cAMP-hydrolyzing enzyme in inflammatory and immune cells (macrophages, eosinophils, neutrophils). Inhibiting PDE 4 in these cells leads to increased cAMP levels, down-regulating the inflammatory response. Because PDE 4 is also expressed in airway smooth muscle and, in vitro, PDE 4 inhibitors relax lung smooth muscle, selective PDE 4 inhibitors are being developed for treating COPD. Clinical studies have been conducted with PDE 4 inhibitors; this review concerns those reported to date.

The effects of a novel phosphodiesterase 7A and -4 dual inhibitor, YM-393059, on T-cell-related cytokine production in vitro and in vivo

YM-393059, (+/-)-N-(4,6-dimethylpyrimidin-2-yl)-4-[2-(4-methoxy-3-methylphenyl)-5-(4-methylpiperazin-1-yl)-4,5,6,7-tetrahydro-1H-indol-1-yl]benzenesulfonamide difumarate, is a novel phosphodiesterase (PDE) inhibitor that inhibited the PDE7A isoenzyme with a high potency (IC50=14 nM) and PDE4 with a moderate potency (IC50=630 nM). In a cell-based assay, YM-393059 was found to inhibit anti-CD3 antibody, Staphylococcal enterotoxin B, and phytohaemagglutinin-induced interleukin (IL)-2 production in mouse splenocytes with IC50 values ranging from 0.48 to 1.1 microM. It also inhibited anti-CD3 antibody-induced interferon (IFN)-gamma and IL-4 production in splenocytes with IC50 values of 1.8 and 2.8 microM, respectively. YM-393059's inhibition of anti-CD3 antibody-stimulated cytokine (IL-2, IFN-gamma, and IL-4) production was 20- to 31-fold weaker than that of YM976, a selective PDE4 inhibitor. However, orally administered YM-393059 and YM976 inhibited anti-CD3 antibody-induced IL-2 production equipotently in mice. In addition, YM-393059 inhibited lipopolysaccharide-induced tumor necrosis factor-alpha production in vivo more potently than IL-2 (ED50 values of 2.1 mg/kg and 74 mg/kg). In contrast to YM976, YM-393059 did not shorten the duration of alpha2-adrenoceptor agonist-induced sleep in mice, which is a model for the assessment of the typical side effects caused by PDE4 inhibitors, nausea and emesis. YM-393059 is a novel and attractive compound for the treatment of a wide variety of T-cell-mediated diseases.

Antidepressant-like effects of PDE4 inhibitors mediated by the high-affinity rolipram binding state (HARBS) of the phosphodiesterase-4 enzyme (PDE4) in rats

RATIONALE

Phosphodiesterase-4 (PDE4) has two conformation states based on rolipram binding, the high-affinity rolipram binding state (HARBS) and the low-affinity rolipram binding state (LARBS); their functions remain to be fully explained.

OBJECTIVE

Experiments were carried out to determine the roles of the HARBS and LARBS in the mediation of antidepressant-like effects on behavior.

MATERIALS AND METHODS

Two animal models sensitive to antidepressant drugs, the forced-swim test (FST), and the differential-reinforcement-of-low-rate (DRL) 72-s operant schedule, were used to examine the antidepressant-like effects of rolipram, CDP840, and piclamilast, PDE4 inhibitors that interact differentially with the HARBS and LARBS, and MEM1018 and MEM1091, two novel PDE4 inhibitors. Drug discrimination vs rolipram and rolipram competition binding assays also were carried out.

RESULTS

In the FST, rolipram and piclamilast, both at 0.1 mg/kg, produced an antidepressant-like effect, i.e., reduced immobility and increased swimming, whereas, 1 mg/kg of CDP840 or 0.5 mg/kg of MEM1018 or MEM1091 was required to produce a similar effect. Consistent with this, only rolipram and piclamilast produced antidepressant-like effects in rats under the DRL schedule of reinforcement, as evidenced by decreased response rates and increased reinforcement rates. In addition, in rats trained to discriminate rolipram from its vehicle, only rolipram and piclamilast substituted. Finally, [(3)H]rolipram and [(3)H]piclamilast binding analysis revealed that CDP840 and the two novel PDE4 inhibitors MEM1018 and MEM1091 exhibited a lower affinity for the HARBS than did rolipram.

CONCLUSION

These results suggest that the HARBS of PDE4 is the primary conformation important for antidepressant-like effects on behavior.

The therapeutic potential of PDE4 inhibitors

Phosphodiesterase enzymes are responsible for the inactivation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterase 4 (PDE4) is a cAMP specific phosphodiesterase expressed in inflammatory cells such as eosinophils. Inhibition of PDE4 results in an elevation of cAMP in these cells, which in turn downregulates the inflammatory response. The anti-inflammatory effects of PDE4 inhibitors have been well documented both in vitro and in vivo in a variety of animal models. The potential use of PDE4 inhibitors as anti-inflammatory agents for the treatment of asthma and other inflammatory disorders has received considerable attention from the pharmaceutical industry, but to date, there are no selective PDE4 inhibitors on the market. Early PDE4 inhibitors, typified by rolipram, suffered from dose-limiting side effects, including nausea and emesis, which severely restricted their therapeutic utility. Second generation compounds, including CDP840 and SB207499 (Ariflo), have been identified with reduced side effect liability. Recent evidence suggests a correlation between side effects and the ability of compounds to bind at the so-called high affinity rolipram binding site (HPDE), whilst beneficial effects appear to correlate with binding at the catalytic site. A number of companies are actively pursuing compounds which exhibit improved affinity for the catalytic site and reduced affinity for the HPDE, in the expectation that this will provide compounds with an improved therapeutic index.

Phosphodiesterase-4 inhibitors in the treatment of inflammatory lung disease

Phosphodiesterases (PDE) belong to an important family of proteins that regulate the intracellular levels of cyclic nucleotide second messengers. Targeting PDE with selective inhibitors may offer novel therapeutic strategies in the treatment of various conditions, and in the context of respiratory disease these include asthma and chronic obstructive pulmonary disease (COPD). The rationale for such an approach stems, in part, from the clinical efficacy of theophylline, an orally active drug that is purportedly a nonselective PDE inhibitor. In addition, intracellular cyclic adenosine monophosphate (cAMP) levels regulate the function of many of the cells thought to contribute to the pathogenesis of respiratory diseases such as asthma and COPD, and these cells also selectively express PDE4. This has offered pharmaceutical companies the opportunity to selectively targeting these enzymes for the treatment of these diseases. Finally, the success of targeting PDE5 in the treatment of erectile dysfunction provides clinical proof of concept for the targeting of PDE in disease. Whether a 'Viagra' of the airways can be found for the treatment of asthma and COPD remains to be seen, but positive results from recent clinical studies examining the efficacy of selective PDE4 inhibitors such as cilomilast and roflumilast offer some optimism. However, one of the major issues to be resolved is the tolerability profile associated with this drug class that is a consequence of PDE4 inhibition. While cilomilast and roflumilast have low emetic potential they are not free from emesis and various strategies are being investigated in the hope of developing a PDE4 inhibitor without this adverse effect.

Phosphodiesterase 4 inhibitors and the treatment of asthma: where are we now and where do we go from here?

Research conducted over the last 20 years has established that inflammation of the airways is central to the airway dysfunction that characterises asthma. Typically, the airway wall is infiltrated by a variety of cells including mast cells, eosinophils and T lymphocytes, which have deviated towards a T(H)2 phenotype. Together, these cells release a plethora of mediators including interleukin (IL)-4, IL-5, granulocyte/macrophage colony-stimulating factor and eotaxin which ultimately cause the histopathology and symptoms of asthma. Glucocorticosteroids are the only drugs currently available that effectively impact upon this inflammation and resolve, to a greater or lesser extent, compromised lung function. However, steroids are nonselective and generally unsuitable for paediatric use. New drugs are clearly required. One group of potential therapeutic agents for asthma are inhibitors of cyclic AMP-specific phosphodiesterase (PDE), of which theophylline may be considered a prototype. It is now known that PDE is a generic term which refers to at least 11 distinct enzyme families that hydrolyse cAMP and/or cGMP. Over the last decade, inhibitors of PDE4 (a cAMP-specific family that negatively regulates the function of almost all pro-inflammatory and immune cells, and exerts widespread anti-inflammatory activity in animal models of asthma) have been developed with the view to reducing the adverse effects profile associated with non-selective inhibitors such as theophylline. Such is the optimism regarding PDE4 as a viable therapeutic target that more than 100 PDE4 inhibitor patent applications have been filed since 1996 by 13 major pharmaceutical companies. This article reviews the progress of PDE4 inhibitors as anti-inflammatory agents, and identifies problems that have been encountered by the pharmaceutical industry in the clinical development of these drugs and what strategies are being considered to overcome them.

Phosphodiesterase 4 (PDE4) inhibitors in asthma and chronic obstructive pulmonary disease (COPD)

Phosphodiesterases (PDE) are a family of enzymes responsible for the metabolism of the intracellular second messengers cyclic AMP and cyclic GMP. PDE4 is a cyclic AMP specific PDE that is the major if not sole cyclic AMP metabolizing enzymes found in inflammatory and immune cells, and contributes significantly to cyclic AMP metabolism in smooth muscles. Based on its cellular and tissue distribution and the demonstration that selective inhibitors of this isozyme reduce bronchoconstriction in animals and suppress the activation of inflammatory cells, PDE4 has become an important molecular target for the development of novel therapies for asthma and COPD. This chapter will review the evidence demonstrating the ability of PDE4 inhibitors to modify airway obstruction, airway inflammation and airway remodelling and hyperreactivity, will present some preliminary findings obtained with theses compounds in clinical trials and and will discuss experimental approaches designed to identify novel compounds that maintain the beneficial activity of the initial selective PDE4 inhibitors but with a reduced tendency of elicit the gastrointestinal side effects observed with this class of compounds.

Suppression of human inflammatory cell function by subtype-selective PDE4 inhibitors correlates with inhibition of PDE4A and PDE4B

1. Of the four major phosphodiesterase 4 (PDE4) subtypes, PDE4A, PDE4B and PDE4D are widely expressed in human inflammatory cells, including monocytes and T lymphocytes. We explored the functional role of these subtypes using ten subtype-selective PDE4 inhibitors, each belonging to one of two classes: (i) dual PDE4A/PDE4B inhibitors or (ii) PDE4D inhibitors. 2. These compounds were evaluated for their ability to inhibit antigen-stimulated T-cell proliferation and bacterial lipopolysaccharide (LPS)-stimulated tumour necrosis factor alpha (TNFalpha) release from peripheral blood monocytes. 3. All compounds inhibited T-cell proliferation in a concentration-dependent manner; with IC50 values distributed over an approximately 50 fold range. These compounds also inhibited TNFalpha release concentration-dependently, with a wider ( approximately 1000 fold) range of IC50 values. 4. In both sets of experiments, mean IC50 values were significantly correlated with compound potency against the catalytic activity of recombinant human PDE4A or PDE4B when analysed by either linear regression of log IC50 values or by Spearman's rank-order correlation. The correlation between inhibition of inflammatory cell function and inhibition of recombinant PDE4D catalytic activity was not significant in either analysis. 5. These results suggest that PDE4A and/or PDE4B may play the major role in regulating these two inflammatory cell functions but do not rule out PDE4D as an important mediator of other activities in mononuclear leukocytes and other immune and inflammatory cells. Much more work is needed to establish the functional roles of the PDE4 subtypes across a broader range of cellular functions and cell types.

Suppression of anti-CD3-induced interleukin-4 and interleukin-5 release from splenocytes of Mesocestoides corti-infected BALB/c mice by phosphodiesterase 4 inhibitors

We investigated the suppressive effects of rolipram, RP 73401 (piclamilast), and other structurally diverse inhibitors of adenosine 3'5'-cyclic monophosphate (cAMP)-specific phosphodiesterase (PDE4) on anti-CD3-stimulated interleukin (IL)-4 and IL-5 generation by splenocytes from BALB/c mice infected with Mesocestoides (M) corti. RP 73401 (IC40: 0.011 +/- 0.004 microM) was a very potent inhibitor of anti-CD3-induced IL-4 release, being approximately 40-fold more potent than (+/-)-rolipram (IC40: 0.43 +/- 0.09 microM). A maximal inhibition of 60-70% of the response was achieved at the top concentrations of RP 73401 (1 microM) and rolipram (100 microM). These PDE inhibitors also suppressed IL-5 generation over the same concentration ranges, but the maximal suppression achieved was only 30-40%. R-(-)-rolipram (IC40: 0.39 +/- 0.09 microM) was approximately 6-fold more potent than S-(+)- rolipram (IC40: 2.6 +/- 0.95 microM) in inhibiting IL-4 release. A close correlation (r2 = 0.82) was observed between suppression of IL-4 release by PDE inhibitors and inhibition of CTLL cell PDE4, a form against which R-(-)-rolipram displayed relatively weak inhibitory potency. A poorer correlation (r2 = 0.26) was observed between suppression of IL-4 release and affinities of cAMP PDE inhibitors for the high-affinity rolipram binding site in mouse brain membranes. The cGMP-inhibited PDE (PDE3) inhibitor, siguazodan, had little or no effect (IC40 > 100 microM) on anti-CD3-stimulated release of either IL-4 or IL-5 and did not significantly enhance the inhibitory action of RP 73401 on the release of either of these cytokines. Finally, RP 73401 (IC50: 0.41 +/- 0.19 nM) inhibited anti-CD3-stimulated DNA synthesis in splenocyte preparations from M. corti-infected mice and siguazodan (10 microM) had no effect on this response, either alone or in combination with the PDE4 inhibitor. The results show that PDE4 inhibitors suppress the release of Th2 cytokines from anti-CD3-stimulated murine spenocytes and that this effect is correlated with inhibition of a low-affinity PDE4 form.

Caspase-3-like activity is necessary for IL-2 release in activated Jurkat T-cells

The caspase family of proteases has previously been implicated in the biochemical cascade leading to apoptotic cell death. Recently caspase-3 was reported to be cleaved into its catalytically active subunits (17 and 13 kDa) following phytohemagglutinin (PHA) activation of peripheral blood mononuclear cells (C. Miossec et al., J. Biol. Chem. 272, 13459-13462). More recently, J. M. Zapata and colleagues (J. Biol. Chem. 273, 6916-6920, 1998), however, proposed that caspase-3 activity detected during T-cell activation was due to a methodological artifact related to the composition of the cell lysis buffer. Here we show that in PHA-activated Jurkat T-cells using the recommended lysis buffer detailed by Zapata et al., a caspase-3-like protease is activated and is accompanied by cleavage of PARP and alpha-spectrin into cleavage products suggestive of caspase-3 proteolytic activation. LDH release did not increase following PHA stimulation in this paradigm. Two caspase inhibitors, carbobenzoxy-Asp-CH2OC(O)-2,6-dichlorobenzene (Z-D-DCB) and acetyl-Asp-Glu-Val-Asp-CHO, blocked IL-2 release in a dose-dependent manner. Caspase-3-like protease-generated PARP and alpha-spectrin breakdown product formation was also reduced by Z-D-DCB. In addition, Jurkat T-cells costimulated with anti-CD3 plus anti-CD28 produced significant levels of IL-2 that were also blocked by these caspase inhibitors. Importantly, IL-2 was determined in cell culture supernatants, thus avoiding a cell lysis step that might have enabled activation of caspase-3 by granzyme B. Collectively, these data support the role of caspase-3-like protease activity in Jurkat T-cell activation and demonstrate that caspase-3 like activity is necessary for IL-2 release in PHA-activated and anti-CD3/anti-CD28 costimulated Jurkat T-cells.