Investigation of the pyrazinones as PDE5 inhibitors: evaluation of regioisomeric projections into the solvent region.

We describe the design, synthesis and profiling of a novel series of PDE5 inhibitors. We take advantage of an alternate projection into the solvent region to identify compounds with excellent potency, selectivity and pharmacokinetic profiles.

Design, synthesis, and biological evaluation of 3-[4-(2-hydroxyethyl)piperazin-1-yl]-7-(6-methoxypyridin-3-yl)-1-(2-propoxyethyl)pyrido[3,4-b]pyrazin-2(1H)-one, a potent, orally active, brain penetrant inhibitor of phosphodiesterase 5 (PDE5).

We recently described a novel series of aminopyridopyrazinones as PDE5 inhibitors. Efforts toward optimization of this series culminated in the identification of 3-[4-(2-hydroxyethyl)piperazin-1-yl]-7-(6-methoxypyridin-3-yl)-1-(2-propoxyethyl)pyrido[3,4-b]pyrazin-2(1H)-one, which possessed an excellent potency and selectivity profile and demonstrated robust in vivo blood pressure lowering in a spontaneously hypertensive rat (SHR) model. Furthermore, this compound is brain penetrant and will be a useful agent for evaluating the therapeutic potential of central inhibition of PDE5. This compound has recently entered clinical trials.

Genetic association of the CCR5 region with lipid levels in at-risk cardiovascular patients.

BACKGROUND: There is mounting evidence to suggest that chemokine receptor 5 (CCR5) plays an important role in the development and progression of atherosclerosis. A naturally occurring variant of the CCR5 gene CCR532, exists at allele frequencies of typically 10% in European populations and results in a nonfunctional CCR5 receptor. METHODS AND RESULTS: The CCR5Delta32 deletion and 26 other variants within the chemokine receptor 2-CCR5-chemokine receptor-like protein 2 (CCRL2) gene cluster spanning 59 kilobases of chromosome 3 were genotyped in 5748 subjects from the Treating to New Targets atorvastatin trial to determine whether genetic associations could be identified with circulating lipid values and cardiovascular disease. Our results demonstrate an association between the CCR5Delta32 deletion and increased plasma high-density lipoprotein cholesterol and decreased plasma triglycerides, both of which are beneficial from a cardiovascular perspective. Three single-nucleotide polymorphisms (rs1154428, rs6808835, and rs6791599) in CCRL2 in linkage disequilibrium (r(2)> or =0.65) with CCR5Delta32 and located up to 45 kilobases distal to it were associated with high-density lipoprotein cholesterol. The high-density lipoprotein cholesterol and triglycerides findings were replicated in an additional set of >6000 individuals from the Incremental Decrease in Endpoints through Aggressive Lipid Lowering atorvastatin trial. CONCLUSIONS: Our study provides evidence that a locus within the region of the genome encompassing the CCR5-CCRL2 region is associated with lipid levels and suggests that chemokine activity influences lipid levels in populations with preexisting cardiovascular disease. CLINICAL TRIAL REGISTRATION- clinicaltrials.gov. Identifier: TNT, NCT00327691; IDEAL, NCT00159835.

Optimization of the aminopyridopyrazinones class of PDE5 inhibitors: discovery of 3-[(trans-4-hydroxycyclohexyl)amino]-7-(6-methoxypyridin-3-yl)-1-(2-propoxyethyl)pyrido[3,4-b]pyrazin-2(1H)-one.

We describe efforts to improve the pharmacokinetic profile of the aminopyridopyrazinone class of PDE5 inhibitors. These efforts led to the discovery of 3-[(trans-4-hydroxycyclohexyl)amino]-7-(6-methoxypyridin-3-yl)-1-(2-propoxyethyl)pyrido[3,4-b]pyrazin-2(1H)-one, a potent and selective inhibitor of PDE5 with an excellent PK profile.

Investigation of aminopyridiopyrazinones as PDE5 inhibitors: Evaluation of modifications to the central ring system.

Efforts to improve the potency and physical properties of the aminopyridiopyrazinone class of PDE5 inhibitors through modification of the core ring system are described. Five new ring systems are evaluated and features that impart improved potency and improved solubility are delineated.

Identification, synthesis and SAR of amino substituted pyrido[3,2b]pyrazinones as potent and selective PDE5 inhibitors.

A new class of potent and selective PDE5 inhibitors is disclosed. Guided by X-ray crystallographic data, optimization of an HTS lead led to the discovery of a series of 2-aryl, (N8)-alkyl substituted-6-aminosubstituted pyrido[3,2b]pyrazinones which show potent inhibition of the PDE5 enzyme. Synthetic details and some structure-activity relationships are also presented.

The experimental type 2 diabetes therapy glycogen phosphorylase inhibition can impair aerobic muscle function during prolonged contraction.

Glycogen phosphorylase inhibition represents a promising strategy to suppress inappropriate hepatic glucose output, while muscle glycogen is a major source of fuel during contraction. Glycogen phosphorylase inhibitors (GPi) currently being investigated for the treatment of type 2 diabetes do not demonstrate hepatic versus muscle glycogen phosphorylase isoform selectivity and may therefore impair patient aerobic exercise capabilities. Skeletal muscle energy metabolism and function are not impaired by GPi during high-intensity contraction in rat skeletal muscle; however, it is unknown whether glycogen phosphorylase inhibitors would impair function during prolonged lower-intensity contraction. Utilizing a novel red cell-perfused rodent gastrocnemius-plantaris-soleus system, muscle was pretreated for 60 min with either 3 micromol/l free drug GPi (n=8) or vehicle control (n=7). During 60 min of aerobic contraction, GPi treatment resulted in approximately 35% greater fatigue. Muscle glycogen phosphorylase a form (P<0.01) and maximal activity (P<0.01) were reduced in the GPi group, and postcontraction glycogen (121.8 +/- 16.1 vs. 168.3 +/- 8.5 mmol/kg dry muscle, P<0.05) was greater. Furthermore, lower muscle lactate efflux and glucose uptake (P<0.01), yet higher muscle Vo(2), support the conclusion that carbohydrate utilization was impaired during contraction. Our data provide new confirmation that muscle glycogen plays an essential role during submaximal contraction. Given the critical role of exercise prescription in the treatment of type 2 diabetes, it will be important to monitor endurance capacity during the clinical evaluation of nonselective GPi. Alternatively, greater effort should be devoted toward the discovery of hepatic-selective GPi, hepatic-specific drug delivery strategies, and/or alternative strategies for controlling excess hepatic glucose production in type 2 diabetes.

Metabolic adaptations to repeated periods of contraction with reduced blood flow in canine skeletal muscle.

BACKGROUND: Patients suffering from Intermittent Claudication (IC) experience repeated periods of muscle contraction with low blood flow, throughout the day and this may contribute to the hypothesised skeletal muscle abnormalities. However, no study has evaluated the consequences of intermittent contraction with low blood flow on skeletal muscle tissue. Our aim was to generate this basic physiological data, determining the 'normal' response of healthy skeletal muscle tissue. We specifically proposed that the metabolic responses to contraction would be modified under such circumstances, revealing endogenous strategies engaged to protect the muscle adenine nucleotide pool. Utilizing a canine gracilis model (n = 9), the muscle was stimulated to contract (5 Hz) for three 10 min periods (separated by 10 min rest) under low blood flow conditions (80% reduced), followed by 1 hr recovery and then a fourth period of 10 min stimulation. Muscle biopsies were obtained prior to and following the first and fourth contraction periods. Direct arterio-venous sampling allowed for the calculation of muscle metabolite efflux and oxygen consumption. RESULTS: During the first period of contraction, [ATP] was reduced by approximately 30%. During this period there was also a 10 fold increase in muscle lactate concentration and a substantial increase in muscle lactate and ammonia efflux. Subsequently, lactate efflux was similar during the first three periods, while ammonia efflux was reduced by the third period. Following 1 hr recovery, muscle lactate and phosphocreatine concentrations had returned to resting values, while muscle [ATP] remained 20% lower. During the fourth contraction period no ammonia efflux or change in muscle ATP content occurred. Despite such contrasting metabolic responses, muscle tension and oxygen consumption were identical during all contraction periods from 3 to 10 min. CONCLUSION: repeated periods of muscle contraction, with low blood flow, results in cessation of muscle ammonia production which is suggestive of a dramatic reduction in flux through AMP deaminase.

The antianginal agent trimetazidine does not exert its functional benefit via inhibition of mitochondrial long-chain 3-ketoacyl coenzyme A thiolase.

Trimetazidine acts as an effective antianginal clinical agent by modulating cardiac energy metabolism. Recent published data support the hypothesis that trimetazidine selectively inhibits long-chain 3-ketoacyl CoA thiolase (LC 3-KAT), thereby reducing fatty acid oxidation resulting in clinical benefit. The aim of this study was to assess whether trimetazidine and ranolazine, which may also act as a metabolic modulator, are specific inhibitors of LC 3-KAT. We have demonstrated that trimetazidine and ranolazine do not inhibit crude and purified rat heart or recombinant human LC 3-KAT by methods that both assess the ability of LC 3-KAT to turnover specific substrate, and LC 3-KAT activity as a functional component of intact cellular beta-oxidation. Furthermore, we have demonstrated that trimetazidine does not inhibit any component of beta-oxidation in an isolated human cardiomyocyte cell line. Ranolazine, however, did demonstrate a partial inhibition of beta-oxidation in a dose-dependent manner (12% at 100 micromol/L and 30% at 300 micromol/L). Both trimetazidine (10 micromol/L) and ranolazine (20 micromol/L) improved the recovery of cardiac function after a period of no flow ischemia in the isolated working rat heart perfused with a buffer containing a relatively high concentration (1.2 mmol/L) of free fatty acid. In summary, both trimetazidine and ranolazine were able to improve ischemic cardiac function but inhibition of LC 3-KAT is not part of their mechanism of action. The full text of this article is available online at http://www.circresaha.org.