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We have prepared three alkaloids from the Agelas sponges, clathrodin, hymenidin and oroidin, and a series of their synthetic analogues, and evaluated their inhibitory effect against six isoforms of the K v 1 subfamily of voltage-gated potassium channels, K v 1.1-K v 1.6, expressed in Chinese Hamster ovary (CHO) cells using automated patch clamp electrophysiology assay. The most potent inhibitor was the ( E )- N -(3-(2-amino-1 H -imidazol-4-yl)allyl)-4,5-dichloro-1 H -pyrrole-2-carboxamide ( 6g ) with IC 50 values between 1.4 and 6.1 μM against K v 1.3, K v 1.4, K v 1.5 and K v 1.6 channels. All compounds tested displayed selectivity against K v 1.1 and K v 1.2 channels. For confirmation of their activity and selectivity, compounds were additionally evaluated in the second independent system against K v 1.1-K v 1.6 and K v 10.1 channels expressed in Xenopus laevis oocytes under voltage clamp conditions where IC 50 values against K v 1.3-K v 1.6 channels for the most active analogues (e.g. 6g ) were lower than 1 μM. Because of the observed low sub-micromolar IC 50 values and fairly low molecular weights, the prepared compounds represent good starting points for further optimisation towards more potent and selective voltage-gated potassium channel inhibitors.

We synthesized and evaluated a series of compounds for their allosteric modulation at the Kv11.1 (hERG) channel. Most compounds were negative allosteric modulators of [(3)H]dofetilide binding to the channel, in particular 7f, 7h-j and 7p. Compounds 7f and 7p were the most potent negative allosteric modulators amongst all ligands, significantly increasing the dissociation rate of dofetilide in the radioligand kinetic binding assay, while remarkably reducing the affinities of dofetilide and astemizole in a competitive displacement assay. Additionally, both 7f and 7p displayed peculiar displacement characteristics with Hill coefficients significantly distinct from unity as shown by e.g., dofetilide, further indicative of their allosteric effects on dofetilide binding. Our findings in this investigation yielded several promising negative allosteric modulators for future functional and clinical research with respect to their antiarrhythmic propensities, either alone or in combination with known Kv11.1 blockers.

The hERG voltage-gated potassium channel mediates the cardiac I(Kr) current, which is crucial for the duration of the cardiac action potential. Undesired block of the channel by certain drugs may prolong the QT interval and increase the risk of malignant ventricular arrhythmias. Although the molecular determinants of hERG block have been intensively studied, not much is known about its stereoselectivity. Levo-(S)-bupivacaine was the first drug reported to have a higher affinity to block hERG than its enantiomer. This study strives to understand the principles underlying the stereoselectivity of bupivacaine block with the help of mutagenesis analyses and molecular modeling simulations. Electrophysiological measurements of mutated hERG channels allowed for the identification of residues involved in bupivacaine binding and stereoselectivity. Docking and molecular mechanics simulations for both enantiomers of bupivacaine and terfenadine (a non-stereoselective blocker) were performed inside an open-state model of the hERG channel. The predicted binding modes enabled a clear depiction of ligand-protein interactions. Estimated binding affinities for both enantiomers were consistent with electrophysiological measurements. A similar computational procedure was applied to bupivacaine enantiomers towards two mutated hERG channels (Tyr652Ala and Phe656Ala). This study confirmed, at the molecular level, that bupivacaine stereoselectively binds the hERG channel. These results help to lay the foundation for structural guidelines to optimize the cardiotoxic profile of drug candidates in silico.

The amine position of the K+ channel blocker 4-aminopyridine was functionalized to form amide, carbamate and urea derivatives in an attempt to identify novel compounds which restore conduction in injured spinal cord. Eight derivatives were tested in vitro, using a double sucrose gap chamber, for the ability to restore conduction in isolated, injured guinea pig spinal cord. The methyl, ethyl and t-butyl carbamates of 4-aminopyridine induced an increase in the post injury compound action potential. The methyl and ethyl carbamates were further tested in an in vivo model of spinal cord injury. These results represent the first time that 4-aminopyridine has been derivatized without losing its ability to restore function in injured spinal cord tissue.