Stereoselective effects of the enantiomers of a new local anaesthetic, IQB-9302, on a human cardiac potassium channel (Kv1.5)

A New Strategy for Multitarget Drug Discovery/Repositioning Through the Identification of Similar 3D Amino Acid Patterns Among Proteins Structures: The Case of Tafluprost and its Effects on Cardiac Ion Channels

The identification of similar three-dimensional (3D) amino acid patterns among different proteins might be helpful to explain the polypharmacological profile of many currently used drugs. Also, it would be a reasonable first step for the design of novel multitarget compounds. Most of the current computational tools employed for this aim are limited to the comparisons among known binding sites, and do not consider several additional important 3D patterns such as allosteric sites or other conserved motifs. In the present work, we introduce Geomfinder2.0, which is a new and improved version of our previously described algorithm for the deep exploration and discovery of similar and druggable 3D patterns. As compared with the original version, substantial improvements that have been incorporated to our software allow: (i) to compare quaternary structures, (ii) to deal with a list of pairs of structures, (iii) to know how druggable is the zone where similar 3D patterns are detected and (iv) to significantly reduce the execution time. Thus, the new algorithm achieves up to 353x speedup as compared to the previous sequential version, allowing the exploration of a significant number of quaternary structures in a reasonable time. In order to illustrate the potential of the updated Geomfinder version, we show a case of use in which similar 3D patterns were detected in the cardiac ions channels NaV1.5 and TASK-1. These channels are quite different in terms of structure, sequence and function and both have been regarded as important targets for drugs aimed at treating atrial fibrillation. Finally, we describe the in vitro effects of tafluprost (a drug currently used to treat glaucoma, which was identified as a novel putative ligand of NaV1.5 and TASK-1) upon both ion channels’ activity and discuss its possible repositioning as a novel antiarrhythmic drug.

Chiral Aspects of Local Anesthetics

Thanks to the progress made in chemical technology (particularly in the methodologies of stereoselective syntheses and analyses) along with regulatory measures, the number of new chiral drugs registered in the form of pure enantiomers has increased over the past decade. In addition, the pharmacological and pharmacokinetic properties of the individual enantiomers of already-introduced racemic drugs are being re-examined. The use of the pure enantiomer of a drug that has been used to date in the form of a racemate is called a "chiral switch". A re-examination of the properties of the pure enantiomers of racemates has taken place for local anesthetics, which represent a group of drugs which have long been used. Differences in (R) and (S)-enantiomers were found in terms of pharmacodynamic and pharmacokinetic activity as well as in toxicity. Levobupivacaine and robivacaine were introduced into practice as pure (S)-(-)-enantiomers, exhibiting more favorable properties than their (R)-(+)-stereoisomers or racemates. This overview focuses on the influence of chirality on the pharmacological and toxicological activity of local anesthetics as well as on individual HPLC and capillary electrophoresis (CE) methods used for enantioseparation and the pharmacokinetic study of individual local anesthetics with a chiral center.

Tuning of EAG K(+) channel inactivation: molecular determinants of amplification by mutations and a small molecule

Ether-à-go-go (EAG) and EAG-related gene (ERG) K⁺ channels are close homologues but differ markedly in their gating properties. ERG1 channels are characterized by rapid and extensive C-type inactivation, whereas mammalian EAG1 channels were previously considered noninactivating. Here, we show that human EAG1 channels exhibit an intrinsic voltage-dependent slow inactivation that is markedly enhanced in rate and extent by 1–10 µM 3-nitro-N-(4-phenoxyphenyl) benzamide, or ICA105574 (ICA). This compound was previously reported to have the opposite effect on ERG1 channels, causing an increase in current magnitude by inhibition of C-type inactivation. The voltage dependence of 2 µM ICA-induced inhibition of EAG1 current was half-maximal at −73 mV, 62 mV negative to the half-point for channel activation. This finding suggests that current inhibition by the drug is mediated by enhanced inactivation and not open-channel block, where the voltage half-points for current inhibition and channel activation are predicted to overlap, as we demonstrate for clofilium and astemizole. The mutation Y464A in the S6 segment also induced inactivation of EAG1, with a time course and voltage dependence similar to that caused by 2 µM ICA. Several Markov models were investigated to describe gating effects induced by multiple concentrations of the drug and the Y464A mutation. Models with the smallest fit error required both closed- and open-state inactivation. Unlike typical C-type inactivation, the rate of Y464A- and ICA-induced inactivation was not decreased by external tetraethylammonium or elevated [K⁺]_e. EAG1 channel inactivation introduced by Y464A was prevented by additional mutation of a nearby residue located in the S5 segment (F359A) or pore helix (L434A), suggesting a tripartite molecular model where interactions between single residues in S5, S6, and the pore helix modulate inactivation of EAG1 channels.

The comparative hemodynamic effects of intravenous IQB-9302 and bupivacaine in anesthetized rats

BACKGROUND

The new local anesthetic IQB-9302 is an amide derivative bearing a cyclopropyl group, with remarkable long duration of action and relative low toxicity. In trying to characterize further its safety profile, the current study compared the hemodynamic effects of different concentrations of bupivacaine and IQB-9302 with saline.

METHODS

Two groups of eight anesthetized Sprague-Dawley rats were given 0.1, 0.3, 1, 3, and 10 mg/kg of intravenous (i.v.) IQB-9302 or bupivacaine at 20-min intervals; control animals received saline only. Arterial blood pressure and heart rate were monitored during the following 20 min.

RESULTS

Both bupivacaine and IQB-9302 reduced heart rate: for bupivacaine, -73.8 beats per min (bpm) (SD: 103.8) and -132.5 bpm (SD: 140.7) at 1 and 3 mg/kg, respectively; for IQB-9302, the reduction amounted to -40.8 bpm (SD: 14.2) and -113.5 bpm (SD: 94.2) at 1 and 3 mg/kg, respectively (baseline range, 318.7-438.2 bpm). The two drugs also produced a comparable increase in the mean arterial blood pressure; bupivacaine increased it by 8.7 mmHg (SD: 6.6) and 12.6 mmHg (SD: 15.4) at 1 and 3 mg/kg, respectively, and IQB-9302, 18.7 mmHg (SD: 21.1) and 20.7 mmHg (SD: 20.5) at 1 and 3 mg/kg, respectively (baseline range, 47.4-134.1 mmHg). All rats treated with 10 mg/kg of either drug died after a drop in heart rate and mean arterial blood pressure.

CONCLUSION

IQB-9302 had hemodynamic effects similar to those of bupivacaine in anesthetized rats. The clinical relevance of these effects warrants further investigation.

Amide local anesthetics potently inhibit the human tandem pore domain background K+ channel TASK-2 (KCNK5)

Blockade of voltage-gated sodium (Na+) channels by local anesthetics represents the main mechanism for inhibition of impulse propagation. Local anesthetic-induced potassium (K+) channel inhibition is also known to influence transmission of sensory impulses and to potentiate inhibition. K+ channels involved in this mechanism may belong to the emerging family of background tandem pore domain K+ channels (2P K+ channels). To determine more precisely the effects of local anesthetics on members of this ion channel family, we heterologously expressed the 2P K+ channels TASK-2 (KCNK5), TASK-1 (KCNK3), and chimeric TASK-1/TASK-2 channels in oocytes of Xenopus laevis. TASK-2 cDNA-transfected HEK 293 cells were used for single-channel recordings. Local anesthetic inhibition of TASK-2 was dose-dependent, agent-specific, and stereoselective. The IC50 values for R-(+)-bupivacaine and S-(-)-bupivacaine were 17 and 43 micro M and for R-(+)-ropivacaine and S-(-)-ropivacaine, 85 and 236 micro M. Lidocaine (1 mM) inhibited TASK-2 currents by 55 +/- 4%, whereas its quaternary positively charged analog N-ethyl lidocaine (QX314) had no effect. Bupivacaine (100 micro M) decreased channel open probability from 20.8 +/- 1.6% to 5.6 +/- 2.2%. Local anesthetics [300 micro M R-(+)-bupivacaine] caused significantly greater depolarization of the resting membrane potential of TASK-2-expressing oocytes compared with water-injected control oocytes (15.8 +/- 2.5 mV versus 0.1 +/- 0.05 mV; p < 0.001). Chimeric TASK-1/TASK-2 2P K+ channel subunits that retained pH sensitivity demonstrated that the carboxy domain of TASK-2 mediates the greater local anesthetic sensitivity of TASK-2. These results show that clinically achievable concentrations of local anesthetics inhibit background K+ channel function and may thereby enhance conduction blockade.

Effects of levobupivacaine, ropivacaine and bupivacaine on HERG channels: stereoselective bupivacaine block

1 Levobupivacaine and ropivacaine are the pure S(-) enantiomers of N-butyl- and N-propyl-2',6'-pipecoloxylidide, developed as less cardiotoxic alternatives to bupivacaine. In the present study, we have analysed the effects of levobupivacaine, ropivacaine and bupivacaine on HERG channels stably expressed in CHO cells. 2 The three drugs blocked HERG channels in a concentration-, time- and state-dependent manner. Block measured at the end of 5 s pulses to -10 mV induced by 20 microM bupivacaine (52.7+/-2.0%, n=15) and ropivacaine (55.5+/-2.7%, n=13) was similar (P>0.05) and both lower than that induced by levobupivacaine (67.5+/-4.2%, n=11) (P<0.05). 3 Dextrobupivacaine (20 microM) was less potent (47.2+/-5.2%, n=10) than levobupivacaine (P<0.05), indicating stereoselective HERG channel block. 4. Block induced by the three local anaesthetics exhibited a steep voltage dependence in the range of channel activation. In all cases, block measured at the maximum peak current at a test potential of 0 mV after promoting recovery from inactivation (I-->O) was lower than that observed at the end of 5-s pulses (I+O). 5. Levobupivacaine, ropivacaine and bupivacaine accelerated HERG inactivation kinetics, slowed the recovery from inactivation and shifted the inactivation curve towards more negative membrane potentials. The three local anaesthetics induced a rapid time-dependent decline after using a protocol that quickly activates HERG channels. 6. All these results suggest that: (1) these drugs bind to the open and the inactivated states of HERG channels, (2) they stabilize HERG channels in the inactivated state, and (3) block induced by bupivacaine enantiomers is stereoselective.