Discovery of a brain-sparing GIRK1/4 inhibitor for pharmacological cardioversion of atrial fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and a significant risk factor for ischemic stroke and heart failure. Marketed anti-arrhythmic drugs can restore sinus rhythm, but with limited efficacy and significant toxicities, including potential to induce ventricular arrhythmia. Atrial-selective ion channel drugs are expected to restore and maintain sinus rhythm without risk of ventricular arrhythmia. One such atrial-selective channel target is GIRK1/4 (G-protein regulated inwardly rectifying potassium channel 1/4). Here we describe 14b, a potent GIRK1/4 inhibitor developed to cardiovert AF to sinus rhythm while minimizing central nervous system exposure - an issue with preceding GIRK1/4 clinical candidates.

Hepatic glycogen cycling contributes to glucose lowering effects of the glucokinase activator LCZ960.

Glucokinase (GK) acts as a glucose sensor by facilitating glucose phosphorylation into glucose-6-phosphate (G6P) in the liver and pancreas, the two key target tissues. LCZ960, a glucokinase activator exerts a stimulatory effect on GK activity in hepatocytes in vitro. This study aimed to verify in vivo that LCZ960 stimulates glucose uptake primarily through a mechanism involving hepatic GK activation. Acute and chronic LCZ960 treatment-induced changes in glycemia and hepatic glucose turnover were measured in high fat diet-induced obese (DIO) mice and rats. G6P production and glycogen cycling were quantified by (13)C-MR spectroscopy during a [1-(13)C]glucose infusion, followed by a pulse-chase with [(12)C]glucose to mimic postprandial conditions in rats. Acute treatment with LCZ960 dose-dependently reduced blood glucose without causing hypoglycemia in DIO mice. Chronic LCZ960 treatment maintained normoglycemia and improved glucose tolerance without increased insulin secretion in DIO mice and rats. In rats, LCZ960 stimulated a 240% increase (P<0.05) in the glycogen synthase flux. However, due to a much higher glycogen breakdown (LCZ960: 48 ± 15 vs control: 4 ± 1µmol/kg/min, P<0.05), this translated to only a 46% (ns) increase in glycogen storage (Vsyn net, LCZ960: 64±26 vs control: 43 ± 6 µmol/kg/min). Despite a 4-fold increase in hepatic glycogen turnover (LCZ960: 36.0 ± 5.5% vs control: 8.3 ± 2.0%), LCZ960 did not impact glucose-stimulated G6P accumulation. LCZ960 did not cause hypoglycemia in DIO rodents. Under hyperglycemic conditions, LCZ960 induced a robust increase in hepatic glycogen cycling. Since net hepatic glycogen storage is diminished in type 2 diabetes patients, stimulation of glycogen synthesis may contribute to the anti-hyperglycemic properties of glucokinase activation.

Avoidance of the Ames test liability for aryl-amines via computation.

Aryl-amines are commonly used synthons in modern drug discovery, however a minority of these chemical templates have the potential to cause toxicity through mutagenicity. The toxicity mostly arises through a series of metabolic steps leading to a reactive electrophilic nitrenium cation intermediate that reacts with DNA nucleotides causing mutation. Highly detailed in silico calculations of the energetics of chemical reactions involved in the metabolic formation of nitrenium cations have been performed. This allowed a critical assessment of the accuracy and reliability of using a theoretical formation energy of the DNA-reactive nitrenium intermediate to correlate with the Ames test response. This study contains the largest data set reported to date, and presents the in silico calculations versus the in vitro Ames response data in the form of beanplots commonly used in statistical analysis. A comparison of this quantum mechanical approach to QSAR and knowledge-based methods is also reported, as well as the calculated formation energies of nitrenium ions for thousands of commercially available aryl-amines generated as a watch-list for medicinal chemists in their synthetic optimization strategies.

Investigation of functionally liver selective glucokinase activators for the treatment of type 2 diabetes.

Type 2 diabetes is a polygenic disease which afflicts nearly 200 million people worldwide and is expected to increase to near epidemic levels over the next 10-15 years. Glucokinase (GK) activators are currently under investigation by a number of pharmaceutical companies with only a few reaching early clinical evaluation. A GK activator has the promise of potentially affecting both the beta-cells of the pancreas, by improving glucose sensitive insulin secretion, as well as the liver, by reducing uncontrolled glucose output and restoring post-prandial glucose uptake and storage as glycogen. Herein, we report our efforts on a sulfonamide chemotype with the aim to generate liver selective GK activators which culminated in the discovery of 3-cyclopentyl-N-(5-methoxy-thiazolo[5,4-b]pyridin-2-yl)-2-[4-(4-methyl-piperazine-1-sulfonyl)-phenyl]-propionamide (17c). This compound activated the GK enzyme (alphaK(a) = 39 nM) in vitro at low nanomolar concentrations and significantly reduced glucose levels during an oral glucose tolerance test in normal mice.

The impact of fatty acid oxidation on energy utilization: targets and therapy.

Utilization of fat as a long-term energy storage vehicle is crucial for the maintenance of cellular metabolism and is under intricate and many times redundant control mechanisms. Aberrations in the control of energy metabolism is apparent in diseases such as diabetes and obesity and is evident early on in patients with impaired glucose tolerance. Insulin resistance has been observed at the level of muscle, liver and adipose tissue. Hyperglycemia is the hallmark of diabetes and is characterized by decreased glucose disposal and increased glucose production, driven by enhanced and uncontrolled fatty acid oxidation (FAO). Mechanisms aimed at limiting the availability of substrates or the activity of processes involved in FAO should provide an immediate reduction in undesired glucose production in these individuals. Numerous targets are available which influence directly the metabolism of fat, including limiting availability of substrate to FAO, inhibiting oxidation of the fatty acid per se, and uncoupling the energy obtained during the oxidation of the fatty acid. These include antilipolytic agents which limit the availability of substrate, FAO inhibitors which limit fatty acid transport (carnitine palmitoyl transferase, CoA sequestration), FAO per se (beta oxidation), and agents which uncouple the energy of FAO (uncoupling proteins, beta3 agonists). These other targets which affect fatty acid metabolism indirectly will be discussed in this review with 184 references.