Addition of a single methyl group to a small molecule sodium channel inhibitor introduces a new mode of gating modulation

Synthesis and biological activities of local anesthetics

Local anesthetics are mainly used in stomatology, ophthalmology, gynecology and surgery to temporarily relieve pain. Local anesthetics act on nerve endings or around nerve trunks, and are combined with specific sodium ion (Na⁺) channel sites on the nerve membrane. They can affect the membrane potential by reducing Na⁺ passage through sodium ion channels, thus blocking the generation and conduction of nerve impulses, reversibly blocking the generation and conduction of sensory nerve impulses. Local anesthetics are used for convenience in local surgical operations and treatments. Herein, we mainly review the research progress on local anesthetics and discuss the important aspects of design, synthesis and biological activity of various new compounds.

Local anesthetics are mainly used in stomatology, ophthalmology, gynecology and surgery to temporarily relieve pain.

Activation of voltage-gated sodium current and inhibition of erg-mediated potassium current caused by telmisartan, an antagonist of angiotensin II type-1 receptor, in HL-1 atrial cardiomyocytes

Telmisartan (TEL) is a non-peptide blocker of angiotensin II type-1 (AT₁ ) receptor. However, the mechanisms through which this drug interacts directly with ion currents in hearts remain largely unclear. Herein, we aim to investigate the effects of TEL the on ionic currents and membrane potential of murine HL-1 cardiomyocytes. In whole-cell recordings, addition of TEL stimulated the peak and late components of voltage-gated Na⁺ currents (I_Na ) with different potencies. The EC₅₀ values required to achieve the stimulatory effect of this drug on peak and late I_Na were 0.2 and 1.2 μmol/L, respectively, and the current-voltage relationship of peak I_Na shifted toward less-depolarized potentials during exposure to TEL. Telmisartan not only increased peak I_Na but also prolonged the inactivation time course of late I_Na . Amiodarone (Amio) or ranolazine (Ran), but not angiotensin II, could reverse TEL-mediated effects. The drug enhanced the recovery rate of I_Na inactivation and exerted an inhibitory effect on erg-mediated K⁺ and L-type Ca²⁺ currents. In whole-cell current-clamp recordings, addition of the drug resulted in prolongation of the duration of action potentials (APs) in a dose-dependent manner in HL-1 cells; Amio or Ran could reverse this increase in AP durations. Telmisartan-mediated prolongation of AP was attenuated in KCNH2 siRNA-transfected HL-1 cells. In cultured smooth muscle cells of the human coronary artery, TEL enhanced I_Na amplitudes and slowed current inactivation. Stimulation by TEL of I_Na in HL-1 cells did not simply increase current magnitude but altered current kinetics, thereby suggesting state-dependent activation. Telmisartan may have greater affinity to the open/inactivated state than to the resting state residing in Na_V channels. Collectively, TEL-mediated stimulation of I_Na and inhibition of I_K(erg) could be an important ionic mechanism underlying the increased cell excitability of HL-1 cells; these actions, however, cannot be entirely explained by its blockade of AT₁ receptor.

The discovery of a potent Nav1.3 inhibitor with good oral pharmacokinetics

In this article, we describe the discovery of an aryl ether series of potent and selective Na_v1.3 inhibitors. Based on structural analogy to a similar series of compounds we have previously shown bind to the domain IV voltage sensor region of Na_v channels, we propose this series binds in the same location. We describe the development of this series from a published starting point, highlighting key selectivity and potency data, and several studies designed to validate Na_v1.3 as a target for pain.

Addition of a single methyl group to a small molecule sodium channel inhibitor introduces a new mode of gating modulation

BACKGROUND AND PURPOSE

Aryl sulfonamide Nav 1.3 or Nav 1.7 voltage-gated sodium (Nav ) channel inhibitors interact with the Domain 4 voltage sensor domain (D4 VSD). During studies to better understand the structure-activity relationship of this interaction, an additional mode of channel modulation, specifically slowing of inactivation, was revealed by addition of a single methyl moiety. The objective of the current study was to determine if these different modulatory effects are mediated by the same or distinct interactions with the channel.

EXPERIMENTAL APPROACH

Electrophysiology and site-directed mutation were used to compare the effects of PF-06526290 and its desmethyl analogue PF-05661014 on Nav channel function.

KEY RESULTS

PF-05661014 selectively inhibits Nav 1.3 versus Nav 1.7 currents by stabilizing inactivated channels via interaction with D4 VSD. In contrast, PF-06526290, which differs from PF-05661014 by a single methyl group, exhibits a dual effect. It greatly slows inactivation of Nav channels in a subtype-independent manner. However, upon prolonged depolarization to induce inactivation, PF-06526290 becomes a Nav subtype selective inhibitor similar to PF-05661014. Mutation of the D4 VSD modulates inhibition of Nav 1.3 or Nav 1.7 by both PF-05661014 and PF-06526290, but has no effect on the inactivation slowing produced by PF-06526290. This finding, along with the absence of functional inhibition of PF-06526290-induced inactivation slowing by PF-05661014, suggests that distinct interactions underlie the two modes of Nav channel modulation.

CONCLUSIONS AND IMPLICATIONS

Addition of a methyl group to a Nav channel inhibitor introduces an additional mode of gating modulation, implying that a single compound can affect sodium channel function in multiple ways.