Characterizing the role of Thr352 in the inhibition of the large conductance Ca2+-activated K+ channels by 1-[1-hexyl-6-(methyloxy)-1H-indazol-3-yl]-2-methyl-1-propanone.

Large conductance Ca(2+)-activated K(+) (BK) channels are known to be regulated by both intracellular Ca(2+) and voltage. Although BK channel modulators have been identified, there is a paucity of information regarding the molecular entities of this channel that govern interaction with blockers and activators. Using both whole-cell and single-channel electrophysiological studies we have characterized the possible role that a threonine residue in the pore region of the channel has on function and interaction with BK channel modulators. A threonine-to-serine substitution at position 352 (T352S) resulted in a 59-mV leftward shift in the voltage-dependent activation curve. Single-channel conductance was 236 pS for the wild-type channel and 100 pS for the T352S mutant, measured over the range -80 mV to +80 mV. In addition, there was an almost 10-fold reduction in the potency of the BK channel inhibitor 1-[1-hexyl-6-(methyloxy)-1H-indazol-3-yl]-2-methyl-1-propanone (HMIMP), the IC(50) values being 4.3 +/- 0.3 and 38.2 +/- 3.3 nM for wild-type and mutant channel, respectively. There was no significant difference between wild type and the mutant channel in response to inhibition by iberiotoxin. The IC(50) was 8.1 +/- 0.3 nM for the wild type and 7.7 +/- 0.3 nM for the mutant channel. Here, we have identified a residue in the pore region of the BK channel that alters voltage sensitivity and reduces the potency of the blocker HMIMP.

2-[2-(3,4-dichloro-phenyl)-2,3-dihydro-1H-isoindol-5-ylamino]-nicotinic acid (PD-307243) causes instantaneous current through human ether-a-go-go-related gene potassium channels.

Long and short QT syndromes associated with loss and gain of human ether-a-go-go-related gene (hERG) channel activity, respectively, can cause life-threatening arrhythmias. As such, modulation of hERG channel activity is an important consideration in the development of all new therapeutic agents. In the present study, we investigated the mechanisms of action of 2-[2-(3,4-dichloro-phenyl)-2,3-dihydro-1H-isoindol-5-ylamino]-nicotinic acid (PD-307243), a known hERG channel activator, on hERG channels stably expressed in Chinese hamster ovary (CHO) cells using the patch-clamp technique. In the whole-cell recordings, the extracellular application of PD-307243 concentration-dependently increased the hERG current and markedly slowed hERG channel deactivation and inactivation. PD-307243 had no effect on the selectivity filter of hERG channels. The activity of PD-307243 was use-dependent. PD-307243 (3 and 10 muM) induced instantaneous hERG current with little decay at membrane potentials from -120 to -40 mV. At more positive voltages, PD-307243 induced an I(to)-like upstroke of hERG current. The actions of PD-307243 on the rapid component of delayed rectifier K(+) current (I(Kr)) in rabbit ventricular myocytes were similar to those observed in hERG channel-transfected CHO cells. Inside-out patch experiments revealed that PD-307243 increased hERG tail currents by 2.1 +/- 0.6 (n = 7) and 3.4 +/- 0.3-fold (n = 4) at 3 and 10 muM, respectively, by slowing the channel deactivation but had no effect on channel activation. During a voltage-clamp protocol using a prerecorded cardiac action potential, 3 muM PD-307243 increased the total potassium ions passed through hERG channels by 8.8 +/- 1.0-fold (n = 5). Docking studies suggest that PD-307243 interacts with residues in the S5-P region of the channel.

Development of dihydropyridone indazole amides as selective Rho-kinase inhibitors.

Rho kinase (ROCK1) mediates vascular smooth muscle contraction and is a potential target for the treatment of hypertension and related disorders. Indazole amide 3 was identified as a potent and selective ROCK1 inhibitor but possessed poor oral bioavailability. Optimization of this lead resulted in the discovery of a series of dihydropyridones, exemplified by 13, with improved pharmacokinetic parameters relative to the initial lead. Indazole substitution played a critical role in decreasing clearance and improving oral bioavailability.

Discovery of aminofurazan-azabenzimidazoles as inhibitors of Rho-kinase with high kinase selectivity and antihypertensive activity.

The discovery, proposed binding mode, and optimization of a novel class of Rho-kinase inhibitors are presented. Appropriate substitution on the 6-position of the azabenzimidazole core provided subnanomolar enzyme potency in vitro while dramatically improving selectivity over a panel of other kinases. Pharmacokinetic data was obtained for the most potent and selective examples and one (6n) has been shown to lower blood pressure in a rat model of hypertension.

A critical assessment of docking programs and scoring functions.

Docking is a computational technique that samples conformations of small molecules in protein binding sites; scoring functions are used to assess which of these conformations best complements the protein binding site. An evaluation of 10 docking programs and 37 scoring functions was conducted against eight proteins of seven protein types for three tasks: binding mode prediction, virtual screening for lead identification, and rank-ordering by affinity for lead optimization. All of the docking programs were able to generate ligand conformations similar to crystallographically determined protein/ligand complex structures for at least one of the targets. However, scoring functions were less successful at distinguishing the crystallographic conformation from the set of docked poses. Docking programs identified active compounds from a pharmaceutically relevant pool of decoy compounds; however, no single program performed well for all of the targets. For prediction of compound affinity, none of the docking programs or scoring functions made a useful prediction of ligand binding affinity.

Perspectives on the discovery of small-molecule modulators for epigenetic processes.

Epigenetic gene regulation is a critical process controlling differentiation and development, the malfunction of which may underpin a variety of diseases. In this article, we review the current landscape of small-molecule epigenetic modulators including drugs on the market, key compounds in clinical trials, and chemical probes being used in epigenetic mechanistic studies. Hit identification strategies for the discovery of small-molecule epigenetic modulators are summarized with respect to writers, erasers, and readers of histone marks. Perspectives are provided on opportunities for new hit discovery approaches, some of which may define the next generation of therapeutic intervention strategies for epigenetic processes.

Potent, selective and orally bioavailable dihydropyrimidine inhibitors of Rho kinase (ROCK1) as potential therapeutic agents for cardiovascular diseases.

Recent studies using known Rho-associated kinase isoform 1 (ROCK1) inhibitors along with cellular and molecular biology data have revealed a pivotal role of this enzyme in many aspects of cardiovascular function. Here we report a series of ROCK1 inhibitors which were originally derived from a dihydropyrimidinone core 1. Our efforts focused on the optimization of dihydropyrimidine 2, which resulted in the identification of a series of dihydropyrimidines with improved pharmacokinetics and P450 properties.