Substituted 4-phenyl-2-aminoimidazoles and 4-phenyl-4,5-dihydro-2-aminoimidazoles as voltage-gated sodium channel modulators.

Voltage-gated sodium channels play an integral part in neurotransmission and their dysfunction is frequently a cause of various neurological disorders. On the basis of the structure of marine alkaloid clathrodin, twenty eight new analogs were designed, synthesized and tested for their ability to block human NaV1.3, NaV1.4 and NaV1.7 channels, as well as for their selectivity against human cardiac isoform NaV1.5, using automated patch clamp electrophysiological assay. Several compounds exhibited promising activities on different NaV channel isoforms in the medium micromolar range and some of the compounds showed also moderate isoform selectivities. The most promising results were obtained for the NaV1.3 channel, for which four compounds were found to possess IC50 values lower than 15 µM. All of the active compounds bind to the open-inactivated states of the channels and therefore act as state-dependent modulators. The obtained results validate the approach of using natural products driven chemistry for drug discovery starting points and represent a good foundation for future design of selective NaV modulators.

Ligand- and structure-based virtual screening for clathrodin-derived human voltage-gated sodium channel modulators.

Voltage-gated sodium channels (VGSC) are attractive targets for drug discovery because of the broad therapeutic potential of their modulators. On the basis of the structure of marine alkaloid clathrodin, we have recently discovered novel subtype-selective VGSC modulators I and II that were used as starting points for two different ligand-based virtual screening approaches for discovery of novel VGSC modulators. Similarity searching in the ZINC database of drug-like compounds based on compound I resulted in five state-dependent Na(v)1.3 and Na(v)1.7 modulators with improved activity compared to I (IC50 < 20 µM). Compounds 2 and 16 that blocked sodium permeation in Na(v)1.7 with IC50 values of 7 and 9 µM, respectively, are among the most potent clathrodin analogs discovered so far. In the case of compound II, 3D similarity searching in the same database was followed by docking of an enriched compound library into our human Na(v)1.4 open-pore homology model. Although some of the selected compounds, e.g., 31 and 32 displayed 21% and 22% inactivated state I(peak) block of Na(v)1.4 at 10 µM, respectively, none showed better Na(v)1.4 modulatory activity than compound II. Taken together, virtual screening yielded compounds 2 and 16, which represent novel scaffolds for the discovery of human Na(v)1.7 modulators.

Novel state-dependent voltage-gated sodium channel modulators, based on marine alkaloids from Agelas sponges.

Clathrodin, alkaloid isolated from Agelas sponges, was reported in 1995 as a voltage-gated sodium channel modulator. Here we describe the design and synthesis of conformationally restricted clathrodin analogues incorporating the 4,5,6,7-tetrahydrobenzo[d]thiazol-2-amine moiety and evaluation of their modulatory activities on human voltage-gated sodium channel isoforms Na(v)1.3, Na(v)1.4 and Na(v)1.7, as well as their selectivity against cardiac isoform Na(v)1.5. Compounds were shown to act as state-dependent modulators of Na(v)1.3, Na(v)1.4 and Na(v)1.7 with IC50 values in the lower micromolar range for the open-inactivated state of the channels. Preliminary structure-activity relationship studies have revealed the importance of hydrophobic interactions for binding to all three tested isoforms. Compound 4e with IC50 value of 8 µM against Na(v)1.4 represents a novel selective state-dependent Na(v)1.4 channel modulator.

New pharmacological approaches to atrial fibrillation.

Atrial fibrillation (AF) is the most common cardiac arrhythmia facing physicians, afflicting 13% of men and 11% of women over 85 years of age. Epidemiological studies estimate that there are ≥ 11 million AF sufferers in the seven major economies and that its prevalence will increase two- to threefold over the next 50 years. Current strategies for treating AF involve either sinus rhythm (SR) maintenance or heart rate control, combined with anticoagulation therapy. Although SR control is the preferred and most effective treatment of AF, none of the SR control drugs currently available are able to maintain rhythm without significant side effects. In this article we discuss some of the recent advancements in developing new antiarrhythmic drugs for AF.

The role of sodium channels in neuropathic pain.

Our knowledge of the ion channels, receptors and signalling mechanisms involved in pain pathophysiology, and which specific channels play a role in subtypes of pain such as neuropathic and inflammatory pain, has expanded considerably in recent years. It is now clear that in the neuropathic state the expression of certain channels is modified, and that these changes underlie the plasticity of responses that occur to generate inappropriate pain signals from normally trivial inputs. Pain is modulated by a subset of the voltage-gated sodium channels, including Nav1.3, Nav1.7, Nav1.8 and Nav1.9. These isoforms display unique expression patterns within specific tissues, and are either up- or down-regulated upon injury to the nervous system. Here we describe our current understanding of the roles of sodium channels in pain and nociceptive information processing, with a particular emphasis on neuropathic pain and drugs useful for the treatment of neuropathic pain that act through mechanisms involving block of sodium channels. One of the future challenges in the development of novel sodium channel blockers is to design and synthesise isoform-selective channel inhibitors. This should provide substantial benefits over existing pain treatments.

A comparative study of sildenafil, NCX-911 and BAY41-2272 on the anococcygeus muscle of diabetic rats.

We compared the effects of a nitric oxide (NO)-releasing sildenafil (NCX-911), NO-independent soluble guanylate cyclase activator (BAY41-2272) and sildenafil on the anococcygeus muscle from streptozotocin-induced 16-weeks diabetic rats. NCX-911, BAY41-2272 and sildenafil reduced the phenylephrine-induced tone in the control group (EC50=1088.8+/-165.0, 151.6+/-9.3 and 827.1+/-167.3 nM, respectively). The potencies of NCX-911 and BAY41-2272 were not altered, but that of sildenafil was significantly reduced in the diabetic group. EC50 values for NCX-911, BAY41-2272 and sildenafil in the diabetic group were 1765.9+/-303.5, 209.7+/-27.3 and 2842.2+/-640.3 nM, respectively (P<0.05 for sildenafil). Nitrergic relaxation responses were significantly decreased in the diabetic group. The remaining nitrergic relaxation responses were potentiated by BAY41-2272 but not by sildenafil or NCX-911. These results confirm that endogenous NO derived from nitrergic nerves is significantly decreased in diabetes, and suggest that NO-releasing PDE5 inhibitors and NO-independent soluble guanylate cyclase activators could be more useful than PDE5 inhibitors in the treatment of ED in long-term diabetes.

Synthesis and analysis of conjugates of the major vitamin E metabolite, alpha-CEHC.

Glucuronide and sulphate conjugates of 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), the major metabolite of alpha-tocopherol (vitamin E), have been synthesized and used for the first direct analysis of conjugated urinary vitamin E metabolites. The metabolites of vitamin E (alpha-tocopherol) could be useful as markers of the function(s) of vitamin E in vivo. A number of methods have been described for the analysis of urinary vitamin E metabolites but these have relied on either acid or enzymatic deconjugation of the metabolites prior to analysis by high performance liquid chromatography or gas chromatography/mass spectrometry. These methods have provided useful information about the amount and types of metabolites excreted in the urine but suffer from a number of disadvantages. Deconjugation has been shown to produce artifacts as a result of the conversion of alpha-CEHC to alpha-tocopheronolactone and the efficiency of deconjugation is also difficult to assess. Methods that allow the direct measurement of the conjugated metabolites would overcome these problems and would also substantially reduce the preparation and analysis time. Here we describe the use of conjugated standards to characterize alpha-CEHC conjugates in human urine by tandem mass spectrometry (MS-MS). The future use of MS-MS to measure urinary vitamin E metabolites is also discussed.