Novel imidazophenoxazine-4-sulfonamides: Their synthesis and evaluation as potential inhibitors of PDE4

A number of novel imidazophenoxazine-4-sulfonamides have been designed as potential inhibitors of PDE4. All these compounds were readily prepared via an elegant multi-step method involving the initial construction of 1-nitro-10H-phenoxazine ring and then fused imidazole ring as key steps. Some of these compounds showed promising PDE4B and D inhibition when tested in vitro and good interactions with these proteins in silico. Three of these compounds showed dose dependent inhibition of PDE4B with IC₅₀ value of 3.31 ± 0.62, 1.23 ± 0.18 and 0.53 ± 0.18 μM.     

Phosphodiesterase types 3 and 4 regulate the phasic contraction of neonatal rat bladder smooth myocytes via distinct mechanisms

Activation of the cyclic AMP (cAMP) pathway reduces bladder contractility. However, the role of phosphodiesterase (PDE) families in regulating this function is poorly understood. Here, we compared the contractile function of the cAMP hydrolyzing PDEs in neonatal rat bladder smooth myocytes. RT-PCR and Western blotting analysis revealed that several isoforms of PDE1–4 were expressed in neonatal rat bladder. While 8-methoxymethyl-3-isobutyl-1-methylxanthine (a PDE1 inhibitor) and BAY-60-7550 (a PDE2 inhibitor) had no effect on the carbachol-enhanced phasic contractions of bladder strips, cilostamide (Cil, a PDE3 inhibitor) and Ro-20-1724 (Ro, a PDE4 inhibitor) significantly reduced these contractions. This inhibitory effect of Ro was blunted by the PKA inhibitor H-89, while the inhibitory effect of Cil was strongly attenuated by the PKG inhibitor KT 5823. Application of Ro in single bladder smooth myocytes resulted in an increase in Ca^2 + spark frequency but a decrease both in Ca^2 + transients and in sarcoplasmic reticulum (SR) Ca^2 + content. In contrast, Cil had no effect on these events. Furthermore, Ro-induced inhibition of the phasic contractions was significantly blocked by ryanodine and iberiotoxin. Taken together, PDE3 and PDE4 are the main PDE isoforms in maintaining the phasic contractions of bladder smooth myocytes, with PDE4 being functionally more active than PDE3. However, their roles are mediated through different mechanisms.     

Synthesis and biological evaluation of nimesulide based new class of triazole derivatives as potential PDE4B inhibitors against cancer cells

A new class of 1,2,3-triazol derivatives derived from nimesulide was designed as potential inhibitors of PDE4B. Synthesis of these compounds was carried out via a multi-step sequence consisting of copper-catalyzed azide–alkyne cycloaddition (CuAAC) as a key step in aqueous media. The required azide was prepared via the reaction of aryl amine (obtained from nimesulide) with α-chloroacetyl chloride followed by displacing the α-chloro group by an azide. Some of the synthesized compounds showed encouraging PDE4B inhibitory properties in vitro that is >50% inhibition at 30 μM that were supported by the docking studies of these compounds at the active site of PDE4B enzyme (dock scores ～ ?28.6 for a representative compound). Two of these PDE4 inhibitors showed promising cytotoxic properties against HCT-15 human colon cancer cells in vitro with IC₅₀ ～ 21–22 μg/mL.     

The increase in rat ventricular automaticity induced by salbutamol is mediated through β(1)- but not β(2)-adrenoceptors: role of phosphodiesterases

AimsWhile β₂-adrenoceptor (AR) agonists are useful bronchodilators, they also produce cardiac arrhythmias. These agents are not fully selective and also activate β₁-AR, but the involvement of β₁-AR and β₂-AR in the observed pro-arrhythmic effect has not been established. We studied the effect of β₁-AR and β₂-AR activation on ventricular automaticity and the role of phosphodiesterases (PDE) in regulating this effect.Main methodsExperiments were performed in the spontaneously beating isolated right ventricle of the rat heart. We also measured cAMP production in this tissue.Key findingsThe β₂-AR agonist salbutamol (1-100 μM) produced a concentration-dependent increase in ventricular automaticity that was not affected by 50 nM of the β₂-AR antagonist ICI 118551. This effect was enhanced by the non-selective PDE inhibitor theophylline (100 μM) and by the selective PDE4 inhibitors rolipram (1 μM) and Ro 201724 (2 μM), but not modified by the selective PDE3 inhibitors cilostamide (0.3 μM) or milrinone (0.2 μM). The effects of salbutamol alone and in the presence of either theophylline or rolipram were virtually abolished by 0.1 μM β₁-AR antagonist CGP20712A. Salbutamol (10 μM) increased the cAMP concentration, and this effect was abolished by CGP 20712A (0.1 μM) but enhanced by theophylline (100 μM) or rolipram (1 μM). Cilostamide (0.3 μM) failed to modify the effect of salbutamol on cAMP concentration.SignificanceThese results indicate that the increase of ventricular automaticity elicited by salbutamol was exclusively mediated through β₁-AR and enhanced by non-selective PDE inhibition with theophylline or selective PDE4 inhibition. However, PDE3 did not appear to regulate this effect.     

Cyclic GMP catabolism up-regulation in MRL/lpr lupus-prone mice is associated with organ remodeling

Production of high titer of antibodies against nuclear components is a hallmark of systemic lupus erythematosus, an autoimmune disease characterized by the progressive chronic inflammation of multiple joints and organs. Organ damage and dysfunction such as renal failure are typical clinical features in lupus. Cell hypermetabolism and hypertrophy can accelerate organ dysfunction. In this study we focus on a specific murine model of lupus, the MRL/lpr strain, and investigated the role of cyclic guanosine monophosphate (cGMP) catabolism in organ remodeling of main target tissues (kidney, spleen and liver) in comparison with age-matched control mice. In MRL/lpr-prone mice, the cGMP-phosphodiesterase (PDE) activities were significantly increased in the kidney (3-fold, P < 0.001), spleen (2-fold, P < 0.001) and liver (1.6-fold, P < 0.05). These raised activity levels were paralleled by both an increased activity of PDE1 in the kidney (associated with nephromegaly) and in the liver, and PDE2 in the spleen of lupus-prone mice. The up-regulation of PDE1 and PDE2 activities were associated with a decrease in intracellular cGMP levels. This underlines an alteration of cGMP-PDE signaling in the kidney, spleen and liver targeting different PDEs according to organs. In good agreement with these findings, a single intravenous administration to MRL/lpr mice of nimodipine (PDE1 inhibitor) but not of EHNA (PDE2 inhibitor) was able to significantly lower peripheral hypercellularity (P = 0.0401), a characteristic feature of this strain of lupus-prone mice. Collectively, our findings are important for generating personalized strategies to prevent certain forms of the lupus disease as well as for understanding the role of PDEs and cGMP in the pathophysiology of lupus.     

Role of AKAP 149–PKA–PDE4A complex in cell survival and cell differentiation processes

The cellular localization of A-kinase anchoring proteins (AKAPs), protein kinase A (PKAs) and phosphodiesterases (PDEs) is a key step to the spatiotemporal regulation of the second messenger adenosine 3′,5′-cyclic monophosphate (cAMP). In this paper the cellular distribution of the mitochondrial AKAP 149–PKA–PDE4A complex and its implications in the cell death induced by YTX treatment, a known PDE modulator, was studied. K-562 cell line was incubated with YTX for 24 or 48 h. Under these conditions AKAP 149, PKA and type-4A PDE (PDE4A) levels were measured in the cytosol, in the plasma membrane and in the nucleus. Apoptotic hallmarks were also measured after the same conditions. In addition, YTX effect on cell viability was checked after AKAP 149 and PDE4A silencing. The results obtained show a decrease in AKAP 149–PKA–PDE4A levels in cytosol after YTX exposure. 24 h after the toxin addition, the complex expression increased in the plasma membrane and after 48 h in the nucleus domain. Furthermore Bcl-2 levels were decreased and the expression of caspase 3 together with caspase 8 activity were increased after 24 h of toxin incubation but not after 48 h. These results suggest apoptotic cell death at 24 h and a non-apoptotic cell death after 48 h. When AKAP 149 and PDE4A were silenced YTX did not induce cellular death. In summary, AKAP 149–PKA–PDE4A complex localization is related with YTX effect in K-562 cell line. When this complex is mainly located in the plasma membrane apoptosis is activated while when the complex is in the nuclear domain non-apoptotic cellular death or cellular differentiation is activated. Therefore AKAP 149–PKA–PDE4A distribution and integrity have a key role in cellular survival.     

Design,synthesis and biological evaluation of 6-(benzyloxy)-4-methylquinolin-2(1H)-one derivatives as PDE3 inhibitors

Selective PDE3 (phosphodiesterase 3) inhibitors improve cardiac contractility and may be used in congestive heart failure. However, their proarrhythmic potential is the most important side effect. In this work ten new synthetic compounds (3-[(4-methyl-2-oxo-1,2-dihydro-6-quinolinyl)oxy]methylbenzamide analogs: 4a–j) were designed, synthesized and tested for the inhibitory activity against human PDE3A and PDE3B. The strategy of the design was based on the structure of vesnarinone (a selective PDE3 inhibitor) and its docking analysis results. The synthetic compounds showed better PDE3 inhibitory activity in comparison with vesnarinone. Using docking analysis, a common binding model of each compound toward PDE3 was suggested. In the next step the potential cardiotonic activity of the best PDE3A inhibitors (4b, IC₅₀ = 0.43 ± 0.04 μM) was evaluated by using the spontaneously beating atria model. In the experiment, atrium of reserpine-treated rat was isolated and the contractile and chronotropic effects of the synthetic compound were assessed. That was carried out in comparison with vesnarinone. The best pharmacological profile was obtained for the compound 4b, which displayed selectivity for increasing the force of contraction (46 ± 3% change over the control) rather than the frequency rate (16 ± 4% change over the control) at 100 μM.     

Design and synthesis of novel 5-(3,4,5-trimethoxybenzoyl)-4-aminopyrimidine derivatives as potent and selective phosphodiesterase 5 inhibitors: Scaffold hopping using a pseudo-ring by intramolecular hydrogen bond formation

5-(3,4,5-Trimethoxybenzoyl)-4-amimopyrimidine derivatives were found as a novel chemical class of potent and highly selective phosphodiesterase 5 inhibitors. A pseudo-ring formed by an intramolecular hydrogen bond constrained the conformation of 3-chloro-4-methoxybenzylamino and 3,4,5-trimethoxybenzoyl substituents and led to the discovery of T-6932 (19a) with a potent PDE5 inhibitory activity (IC₅₀ = 0.13 nM) and a high selectivity over PDE6 (IC₅₀ ratio: PDE6/PDE5 = 2400). Further modification at the 2-position of T-6932 resulted in the finding of 26, which exhibited potent relaxant effects on isolated rabbit corpus cavernosum (EC₃₀ = 11 nM) with a high PDE5 selectivity over PDE6 (IC₅₀ ratio: PDE6/PDE5 = 2800).     

Design,synthesis and biological evaluation of dual acetylcholinesterase and phosphodiesterase 5A inhibitors in treatment for Alzheimer’s disease

With the recent research advances in molecular biology and technology, multiple credible hypotheses about the progress of Alzheimer’s disease (AD) have been proposed; multi-target drugs have emerged as an innovative therapeutic approach for AD. Current clinical therapy for AD patients is mainly palliative treatment targeting acetylcholinesterase (AChE). Inhibition of phosphodiesterase 5A (PDE5A) has recently been validated as a potentially novel therapeutic approach for Alzheimer’s disease (AD). In this work, series of new compounds were designed, synthesized and evaluated as dual cholinesterase and PDE5A inhibitor. Biological results revealed that some of these compounds display good biological activities against AChE with IC₅₀ values about 44.67–169.80 nM (donepezil IC₅₀ 50.12 nM). Notably, compound 12 presented potent activities against PDE5A with IC₅₀ values about 50 μM (sildenafil IC₅₀ 12.59 μM), and some of these compounds showed low cell toxicity to A549 cells in vitro.     

Identification of the fused bicyclic 4-amino-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors

2-Phenyl-4-piperidinyl-6,7-dihydrothieno[3,4-d]pyrimidine derivative (2) was found to be a new PDE4 inhibitor with moderate PDE4B activity (IC₅₀ = 150 nM). A number of derivatives with a variety of 4-amino substituents and fused bicyclic pyrimidines were synthesized. Among these, 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivative (18) showed potent PDE4B inhibitory activity (IC₅₀ = 25 nM). Finally, N-propylacetamide derivative (31b) was determined as a potent inhibitor for both PDE4B (IC₅₀ = 7.5 nM) and TNF-α production in mouse splenocytes (IC₅₀ = 9.8 nM) and showed good in vivo anti-inflammatory activity in the LPS-induced lung inflammation model in mice (ID₅₀ = 18 mg/kg). The binding mode of the new inhibitor (31e) in the catalytic site of PDE4B is presented based on an X-ray crystal structure of the ligand–enzyme complex.     

Design,synthesis and biological evaluation of novel pyridine derivatives as anticancer agents and phosphodiesterase 3 inhibitors

Two series of 4,6-diaryl-2-imino-1,2-dihydropyridine-3-carbonitriles and their isosteric 4,6-diaryl-2-oxo-1,2-dihydropyridine-3-carbonitriles were synthesized through a combinatorial approach. The prepared analogues were evaluated for their in vitro capacity to inhibit PDE3A and the growth of the human HT-29 colon adenocarcinoma tumor cell line. Compound 6-(4-bromophenyl)-4-(2-ethoxyphenyl)-2-imino-1,2-dihydropyridine-3-carbonitrile (Id) exhibited the strongest PDE3 inhibition when cGMP but not cAMP is the substrate with a IC₅₀of 27 μM, which indicates a highly selective mechanism of enzyme inhibition. On the other hand, compound 6-(1,3-benzodioxol-5-yl)-4-(2-ethoxyphenyl)-2-imino-1,2-dihydropyridine-3-carbonitrile (Ii) was the most active in inhibiting colon tumor cell growth with a IC₅₀ of 3 μM. The electronic effects, steric effects and conformational aspects of Id seem to be the most crucial for the PDE3 inhibition. Meanwhile, steric factors and the H-bonding capability seem to be the most important factors for tumor cell growth inhibitory activity. Conversely, there is no direct correlation between PDE3 inhibition and anticancer activity for the prepared compounds. An in silico docking experiment indicates the potential involvement of other potential molecular targets such as PIM-1 kinase to explain its tumor cell growth inhibitory activity.     

Improvement of Sleep Disturbance and Neurocognitive Function after Parathyroidectomy in Patients with Primary Hyperparathyroidism

ObjectiveTo investigate the frequency of the nontraditional symptoms of sleep disturbance and impaired cognitive functioning in patients with primary hyperparathyroidism (PHPT) and to assess changes in such patients after parathyroidectomy.MethodsIn this study, we used formal neurocognitive assessment of patients undergoing parathyroidectomy for PHPT. The Brief Sleep Disturbance Inventory assessed sleep disturbance, and Stroop tests evaluated for cognitive impairment. Study patients underwent preoperative and postoperative neurocognitive testing.ResultsFifty-five patients underwent neurocognitive evaluation; the 43 women and 12 men had a mean age of 63 years. Sleep disturbance was assessed in all 55 patients, whereas evaluation for cognitive impairment was performed in 47. Sleep disturbance was identified preoperatively in 24 (44%) of the 55 patients. This disorder affected 17 (31%) of 55 patients postoperatively (P < 0.01). Impaired executive functioning was found at baseline in 6 (13%) of 47 patients and decreased to 1 (2%) of 47 postoperatively (P < 0.01), whereas impaired cognitive processing speed was detected in 12 (26%) of 47 patients at baseline and decreased to 3 (6%) of 47 after parathyroidectomy (P < 0.01). Eight patients did not meet the National Institutes of Health consensus statement criteria for parathyroidectomy; 4 of these patients had preoperative impairment of sleep or cognitive functioning, 3 of whom showed improvement postoperatively.ConclusionSleep disturbance and neurocognitive impairment occur in patients with PHPT, and these disorders improve after parathyroidectomy. Further objective evaluation of nontraditional symptoms in patients diagnosed as having PHPT is warranted. (Endocr Pract. 2007;13:338-344)     

Synthesis and biological evaluation of 5-carbamoyl-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors

5-Carbamoyl-2-phenylpyrimidine derivative 2 has been identified as a phosphodiesterase 4 (PDE4) inhibitor with moderate PDE4B inhibitory activity (IC₅₀ = 200 nM). Modification of the carboxylic acid moiety of 2 gave N-neopentylacetamide derivative 10f, which had high in vitro PDE4B inhibitory activity (IC₅₀ = 8.3 nM) and in vivo efficacy against lipopolysaccharide (LPS)-induced pulmonary neutrophilia in mice (ID₅₀ = 16 mg/kg, ip). Furthermore, based on the X-ray crystallography of 10f bound to the human PDE4B catalytic domain, we designed 7,8-dihydro-6H-pyrido[4,3-d]pyrimidin-5-one derivative 39 which has a fused bicyclic lactam scaffold. Compound 39 exhibited excellent inhibitory activity against LPS-induced tumor necrosis factor alpha (TNF-α) production in mouse splenocytes (IC₅₀ = 0.21 nM) and in vivo anti-inflammatory activity against LPS-induced pulmonary neutrophilia in mice (41% inhibition at a dose of 1.0 mg/kg, i.t.).     

Synthesis of 2,2,4-trimethyl-1,2-dihydroquinolinyl substituted 1,2,3-triazole derivatives: Their evaluation as potential PDE 4B inhibitors possessing cytotoxic properties against cancer cells

The 2,2,4-trimethyl-1,2-dihydroquinolinyl substituted 1,2,3-triazole derivatives were designed as potential inhibitors of PDE4B. These compounds were synthesized via a multi-step sequence consisting of copper-catalyzed azide-alkyne cycloaddition (CuAAC) as a key step in aqueous media. The required alkynes were prepared from nimesulide via N-propargylation and then nitro group reduction followed by a CAN mediated modified Skraup reaction of the resulting amine. All the synthesized compounds showed PDE4B inhibitory properties in vitro at 30 μM with two compounds showing >50% inhibition that were supported by the in silico docking results of these compounds at the active site of PDE4B. Three of these PDE4 inhibitors showed promising cytotoxic properties against A549 human lung cancer cells in vitro with IC₅₀ ∼8–9 μM.     

Select 3′,5′-cyclic nucleotide phosphodiesterases exhibit altered expression in the aged rodent brain

3′,5′-cyclic nucleotide phosphodiesterases (PDEs) are the only known enzymes to compartmentalize cAMP and cGMP, yet little is known about how PDEs are dynamically regulated across the lifespan. We mapped mRNA expression of all 21 PDE isoforms in the adult rat and mouse central nervous system (CNS) using quantitative polymerase chain reaction (qPCR) and in situ hybridization to assess conservation across species. We also compared PDE mRNA and protein in the brains of old (26 months) versus young (5 months) Sprague–Dawley rats, with select experiments replicated in old (9 months) versus young (2 months) BALB/cJ mice. We show that each PDE isoform exhibits a unique expression pattern across the brain that is highly conserved between rats, mice, and humans. PDE1B, PDE1C, PDE2A, PDE4A, PDE4D, PDE5A, PDE7A, PDE8A, PDE8B, PDE10A, and PDE11A showed an age-related increase or decrease in mRNA expression in at least 1 of the 4 brain regions examined (hippocampus, cortex, striatum, and cerebellum). In contrast, mRNA expression of PDE1A, PDE3A, PDE3B, PDE4B, PDE7A, PDE7B, and PDE9A did not change with age. Age-related increases in PDE11A4, PDE8A3, PDE8A4/5, and PDE1C1 protein expression were confirmed in hippocampus of old versus young rodents, as were age-related increases in PDE8A3 protein expression in the striatum. Age-related changes in PDE expression appear to have functional consequences as, relative to young rats, the hippocampi of old rats demonstrated strikingly decreased phosphorylation of GluR1, CaMKIIα, and CaMKIIβ, decreased expression of the transmembrane AMPA regulatory proteins γ2 (a.k.a. stargazin) and γ8, and increased trimethylation of H3K27. Interestingly, expression of PDE11A4, PDE8A4/5, PDE8A3, and PDE1C1 correlate with these functional endpoints in young but not old rats, suggesting that aging is not only associated with a change in PDE expression but also a change in PDE compartmentalization.     

Exploration of the 5-bromopyrimidin-4(3H)-ones as potent inhibitors of PDE5

The substituents both at the 6-position of the 5-bromopyrimidinone ring and at the 5′-position of the phenyl ring of 5-bromopyrimidin-4(3H)-ones were explored. 5-Bromo-6-isopropyl-2-(2-propoxy-phenyl)pyrimidin-4(3H)-one was identified as a new scaffold for potent PDE5 inhibitors. The crystal structures of PDE5/2e and PDE5/10a complexes provided a structural basis for the inhibition of 5-bromopyrimidinones to PDE5. In addition, it was also found that there is a great tolerance for the substitution at the 5′-position of the phenyl ring of 5-bormopyrimidinones and the resulted compound 13a has the highest inhibition activity to PDE5 (IC₅₀, 1.7 nM).     

Discovery of potent selective bioavailable phosphodiesterase 2 (PDE2) inhibitors active in an osteoarthritis pain model. Part II: Optimization studies and demonstration of in vivo efficacy

Selective phosphodiesterase 2 (PDE2) inhibitors are shown to have efficacy in a rat model of osteoarthritis (OA) pain. We identified potent, selective PDE2 inhibitors by optimizing residual PDE2 activity in a series of phosphodiesterase 4 (PDE4) inhibitors, while minimizing PDE4 inhibitory activity. These newly designed PDE2 inhibitors bind to the PDE2 enzyme in a cGMP-like binding mode orthogonal to the cAMP-like binding mode found in PDE4. Extensive structure activity relationship studies ultimately led to identification of pyrazolodiazepinone, 22, which was >1000-fold selective for PDE2 over recombinant, full length PDEs 1B, 3A, 3B, 4A, 4B, 4C, 7A, 7B, 8A, 8B, 9, 10 and 11. Compound 22 also retained excellent PDE2 selectivity (241-fold to 419-fold) over the remaining recombinant, full length PDEs, 1A, 4D, 5, and 6. Compound 22 exhibited good pharmacokinetic properties and excellent oral bioavailability (F = 78%, rat). In an in vivo rat model of OA pain, compound 22 had significant analgesic activity 1 and 3 h after a single, 10 mg/kg, subcutaneous dose.     

Sildenafil is a strong activator of mammalian carbonic anhydrase isoforms I–XIV

Sildenafil citrate, a phosphodiesterase-5 (PDE5) inhibitor widely used for the treatment of erectile dysfunction was investigated for its interaction with the zinc-enzyme carbonic anhydrase (CA, EC 4.2.1.1), as it has in its molecule a piperazine moiety also found in some CA activators (CAAs). Sildenafil was a potent, low micromolar activator of several CA isozymes, such as CA I, VA and VI (K_As in the range of 1.08–6.54 μM), and activated slightly less the isoforms CA III, IV and VA (K_As of 13.4–16.8 μM). CA isozymes II, IX, XIII and XIV showed activation constants in the range of 27.5–34.0 μM, whereas the least activated isoforms were CA VII and XII (K_As of 72.9–73.0 μM). Sildenafil citrate was also given orally to Sprague-Dawley rats at 1 mg/kg body weight. Red blood cell CA activity was inhibited in the treated animals at 3–5 h post-administration (in the range of 60–85%), probably due to NO/nitrite formed by PDE5 inhibition or by another, unknown mechanism. Whether CA activation by sildenafil has clinical consequences in humans is beyond the scope of the present work and warrants further studies.     

Design,synthesis and evaluation of dual pharmacology β2-adrenoceptor agonists and PDE4 inhibitors

A novel series of formoterol–phthalazinone hybrids were synthesised and evaluated as dual pharmacology β₂-adrenoceptor agonists and PDE4 inhibitors. Most of the hybrids displayed high β₂-adrenoceptor agonist and moderate PDE4 inhibitory activities. The most potent compound, (R,R)-11c, exhibited agonist (EC₅₀ = 1.05 nM, pEC₅₀ = 9.0) and potent PDE4B2 inhibitory activities (IC₅₀ = 0.092 μM).