Synthesis and structure-activity relationships of cetiedil analogues as blockers of the Ca(2+)-activated K+ permeability of erythrocytes

New Insights on KCa3.1 Channel Modulation

The human intermediate conductance calcium-activated potassium channel, KCa3.1, is involved in several pathophysiological conditions playing a critical role in cell secretory machinery and calcium signalling. The recent cryo-EM analysis provides new insights for understanding the modulation by both endogenous and pharmacological agents. A typical feature of this channel is the low open probability in saturating calcium concentrations and its modulation by potassium channel openers (KCOs), such as benzo imidazolone 1-EBIO, without changing calcium-dependent activation. In this paper, we proposed a model of KCOs action in the modulation of channel activity. The KCa3.1 channel has a very rich pharmacological profile with several classes of molecules that selectively interact with different binding sites of the channel. Among them, benzo imidazolones can be openers (positive modulators such as 1-EBIO, DC-EBIO) or blockers (negative modulators such as NS1619). Through computation modelling techniques, we identified the 1,4-benzothiazin-3-one as a promising scaffold to develop new KCa3.1 channel modulators. Further studies are needed to explore the potential use of 1-4 benzothiazine- 3-one in KCa3.1 modulation and its pharmacological application.

Chemoselective Carbonyl Allylations with Alkoxyallylsiletanes

Alkoxyallylsiletanes are capable of highly chemo- and diastereoselective carbonyl allylsilylations. Reactive substrates include salicylaldehydes and glyoxylic acids. Chemoselectivity in these reactions is thought to arise from a mechanism involving first exchange of the alkyoxy group on silicon with a substrate hydroxyl followed by activation of a nearby carbonyl by the Lewis acidic siletane and intramolecular allylation. In this way, substrates containing multiple reactive carbonyl groups (e.g., dialdehyde or triketone) can be selectively monoallylated, even overcoming inherent electrophilicity bias.

Expression and Role of the Intermediate-Conductance Calcium-Activated Potassium Channel KCa3.1 in Glioblastoma

Glioblastomas are characterized by altered expression of several ion channels that have important consequences in cell functions associated with their aggressiveness, such as cell survival, proliferation, and migration. Data on the altered expression and function of the intermediate-conductance calcium-activated K (KCa3.1) channels in glioblastoma cells have only recently become available. This paper aims to (i) illustrate the main structural, biophysical, pharmacological, and modulatory properties of the KCa3.1 channel, (ii) provide a detailed account of data on the expression of this channel in glioblastoma cells, as compared to normal brain tissue, and (iii) critically discuss its major functional roles. Available data suggest that KCa3.1 channels (i) are highly expressed in glioblastoma cells but only scantly in the normal brain parenchima, (ii) play an important role in the control of glioblastoma cell migration. Altogether, these data suggest KCa3.1 channels as potential candidates for a targeted therapy against this tumor.

Genetic neural network modeling of the selective inhibition of the intermediate-conductance Ca2+-activated K+ channel by some triarylmethanes using topological charge indexes descriptors

Selective inhibition of the intermediate-conductance Ca(2+)-activated K(+ )channel (IK (Ca)) by some clotrimazole analogs has been successfully modeled using topological charge indexes (TCI) and genetic neural networks (GNNs). A neural network monitoring scheme evidenced a highly non-linear dependence between the IK (Ca) blocking activity and TCI descriptors. Suitable subsets of descriptors were selected by means of genetic algorithm. Bayesian regularization was implemented in the network training function with the aim of assuring good generalization qualities to the predictors. GNNs were able to yield a reliable predictor that explained about 97% data variance with good predictive ability. On the contrary, the best multivariate linear equation with descriptors selected by linear genetic search, only explained about 60%. In spite of when using the descriptors from the linear equations to train neural networks yielded higher fitted models, such networks were very unstable and had relative low predictive ability. However, the best GNN BRANN 2 had a Q ( 2 ) of LOO of cross-validation equal to 0.901 and at the same time exhibited outstanding stability when calculating 80 randomly constructed training/test sets partitions. Our model suggested that structural fragments of size three and seven have relevant influence on the inhibitory potency of the studied IK (Ca) channel blockers. Furthermore, inhibitors were well distributed regarding its activity levels in a Kohonen self-organizing map (KSOM) built using the inputs of the best neural network predictor.

Inhibition of the antigen-induced activation of RBL-2H3 cells by cetiedil and some of its analogues

Our previous studies on rat basophilic leukaemia (RBL-2H3) cells suggested that IK(Ca) channels similar to those in red blood cells (RBC) may be involved in the antigen-induced beta-hexosaminidase release. Since cetiedil blocks these channels in both cell types, we studied the inhibition by a selection of the synthetic analogues of cetiedil (UCL compounds) of antigen-induced beta-hexosaminidase release and 86Rb(+)-efflux from RBL-2H3 cells. We tested the (+)- and (-)-enantiomers of cetiedil (UCL 1348 and UCL 1349), the more lipophilic triphenylacetic acid derivatives (UCL 1495 and UCL 1617) and (9-benzyl-fluoren)-9-yl derivatives (UCL 1608 and UCL 1710). They all inhibited antigen-induced beta-hexosaminidase release and 86Rb(+)-efflux. Their relative potency in inhibiting antigen-induced beta-hexosaminidase release was UCL 1608>1710>1617>1348>1349>1495, with IC(50) values of 9.6+/-0.6, 14.4+/-2.2, 23.4+/-1.4, 29.8+/-1.1, 77.5+/-11.8 and 104.6+/-14.7 (microM), respectively. These IC(50)s suggest some dissimilarity between IK(Ca) in RBL-2H3 cells and RBC. Lipophilicity and potency were well correlated in RBC, but not in RBL-2H3 cells.

Use of ab initio calculations to predict the biological potency of carboxylesterase inhibitors

Carboxylesterases are important enzymes responsible for the hydrolysis and metabolism of numerous pharmaceuticals and xenobiotics. These enzymes are potently inhibited by trifluoromethyl ketone containing (TFK) inhibitors. We demonstrated that the ketone hydration state was affected by the surrounding chemical moieties and was related to inhibitor potency, with inhibitors that favored the gem-diol conformation exhibiting greater potency. Ab initio calculations were performed to determine the energy of hydration of the ketone, and the values were correlated with esterase inhibition data for a series of carboxylesterase inhibitors. This system was examined in three different mammalian models (human liver microsomes, murine liver microsomes, and commercial porcine liver esterase) and in an insect enzyme preparation (juvenile hormone esterase). In all cases, the extent of ketone hydration was strongly correlated with biological potency. Our results showed a very strong correlation with the extent of hydration, accounting for 94% of activity for human liver microsome esterase inhibition (p < 0.01). The atomic charge on the carbon atom of the carbonyl group in the TFK also strongly correlated with inhibitor potency, accounting for 94% of inhibition activity in human liver microsomes (p < 0.01). In addition, we provide crystallographic evidence of intramolecular hydrogen bonding in sulfur-containing inhibitors and relate these data to gem-diol formation. This study provides insight into the mechanism of carboxylesterase inhibition and raises the possibility that inhibitors that too strongly favor the gem-diol configuration have decreased potency due to low rate of ketone formation.

The Ca2+-activated K+ channel of intermediate conductance:a possible target for immune suppression

The intermediate conductance Ca2+-activated K+ (IK) channel is distinguished from the functionally related Ca2+-activated K+ channels of smaller and larger unitary conductance by its molecular structure, pharmacology, tissue distribution and physiology. Like many K+ channels, IK is an assembly of four identical subunits each spanning the membrane six times and each contributing equally to the K+ selectivity pore positioned centrally in the complex. The IK channel gains its high sensitivity to intracellular Ca2+ from tightly bound calmodulin, and its activity is independent of the membrane potential. Several toxins including charybdotoxin and the more selective mutant, Glu32-charybdotoxin, maurotoxin and stichodactyla toxin potently block IK channels. Among blockers of the IK channel are also several small organic molecules including the antimycotic clotrimazole and the close analogues TRAM-34 and ICA-17043, as well as the antihypertensive, nitrendipine. The IK channel is distributed in peripheral tissues, including secretory epithelia and blood cells, but it appears absent from neuronal and muscle tissue. An important physiological role of the IK channel is to help maintain large electrical gradients for the sustained transport of ions such as Ca2+ influx that controls T lymphocyte (T cell) proliferation. In this review, special attention is given to an analysis of the use of IK blockers as potential immunosuppressants for the treatment of autoimmune disorders such as rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis.