Synthesis, molecular modeling, and K+ channel-blocking activity of dequalinium analogues having semirigid linkers

Bis-Quinolinium Cyclophane Blockers of SK Potassium Channels Are Antagonists of M3 Muscarinic Acetylcholine Receptors

Dequalinium is used as an antimicrobial compound for oral health and other microbial infections. Derivatives of dequalinium, the bis-quinolinium cyclophanes UCL 1684 and UCL 1848, are high affinity SK potassium channel antagonists. Here we investigated these compounds as M3 muscarinic receptor (mACHR) antagonists. We used the R-CEPIAer endoplasmic reticulum calcium reporter to functionally assay for Gq-coupled receptor signaling, and investigated the bis-quinolinium cyclophanes as antagonists of M3 mACHR activation in transfected CHO cells. Given mACHR roles in airway smooth muscle (ASM) contractility, we also tested the ability of UCL 1684 to relax ASM. We find that these compounds antagonized M3 mACHRs with an IC₅₀ of 0.27 μM for dequalinium chloride, 1.5 μM for UCL 1684 and 1.0 μM for UCL 1848. UCL 1684 also antagonized M1 (IC₅₀ 0.12 μM) and M5 (IC₅₀ 0.52 μM) mACHR responses. UCL 1684 was determined to be a competitive antagonist at M3 receptors as it increased the EC₅₀ for carbachol without a reduction in the maximum response. The Ki for UCL1684 determined from competition binding experiments was 909 nM. UCL 1684 reduced carbachol-evoked ASM contractions (>90%, IC₅₀ 0.43 μM), and calcium mobilization in rodent and human lung ASM cells. We conclude that dequalinium and bis-quinolinium cyclophanes antagonized M3 mACHR activation at sub- to low micromolar concentrations, with UCL 1684 acting as an ASM relaxant. Caution should be taken when using these compounds to block SK potassium channels, as inhibition of mACHRs may be a side-effect if excessive concentrations are used.

Quaternary ammonium salts and their antimicrobial potential: targets or nonspecific interactions?

For more than 50 years dequalinium chloride has been used successfully as an antiseptic drug and disinfectant, particularly for clinical purposes. Given the success of dequalinium chloride, several series of mono- and bisquaternary ammonium compounds have been designed and reported to have improved antimicrobial activity. Furthermore, many of them exhibit high activity against mycobacteria and protozoa, especially against plasmodia. This review discusses the structure-activity relationships and the modes of action of the various series of (bis)quaternary ammonium compounds.

Identification of a pharmacophore of SKCa channel blockers

Small conductance calcium-activated potassium channels (SK) are widely expressed throughout the central nervous system (CNS) and the periphery. Three subtypes of SK channels have so far been identified in different parts of the brain. Activation of the SK channels by a rise in intracellular calcium leads to the hyperpolarisation of the membrane, reducing cell excitability. Blocking the SK channels might be beneficial in the treatment of depression, Parkinson's disease and cognitive disorders. However, few blockers of SK channels have been characterized. In this study, a pharmacophoric model of SK channels blockers is presented. It is based on a series of nonpeptidic compounds and apamin, a peptidic blocker. To create the pharmacophore model, the conformational space of nonpeptidic blockers was investigated to generate a series of distance constraints applied to a simulated annealing study of apamin. The resulting conformation was superimposed with the nonpeptidic blockers to give a pharmacophore.

Synthesis and pharmacological testing of polyaminoquinolines as blockers of the apamin-sensitive Ca2+-activated K+ channel (SK(Ca))

The synthesis and pharmacological testing of a series of non-peptidic blockers of the SK(Ca) (SK-3) channel is described. Target compounds were designed to mimic the spatial relationships of selected key residues in the energy-minimised structure of the octadecapeptide apamin, which are a highly potent blocker of this channel. Structures consist of a central unit, either a fumaric acid or an aromatic ring, to which are attached two alkylguanidine or two to four alkylaminoquinoline substituents. Potency was tested by the ability to inhibit the SK(Ca) channel-mediated after-hyperpolarization (AHP) in cultured rat sympathetic neurones. It was found that bis-aminoquinoline derivatives are significantly more potent as channel blockers than are the corresponding guanidines. This adds to the earlier evidence that delocalisation of positive charge through the more extensive aminoquinolinium ring system is important for effective channel binding. It was also found that an increase in activity can be gained by the addition of a third aminoquinoline residue to give non-quaternized amines which have submicromolar potencies (IC(50)=0.13-0.36 microM). Extension to four aminoquinoline residues increased the potency to IC(50)=93 nM.

Symmetrical Bis-Quinolinium Compounds: New Human Choline Kinase Inhibitors with Antiproliferative Activity against the HT-29 Cell Line

Studies have been aimed at the establishment of structure-activity relationships that define choline kinase inhibitory and antiproliferative activities of 40 bisquinolinium compounds. These derivatives have electron-releasing groups at position 4 of the quinolinium ring. It is found that the enzymatic inhibition is closely related to the size of the linker, the 3,3'-biphenyl moiety being the most suitable. On the other hand, the antiproliferative activity against the HT-29 cancer cell line is less influenced by the linker type and by substituent R(4). The corresponding QSAR equation was obtained for the whole set of compounds for the antiproliferative activity, the electronic parameter sigma(R) of R(4), the molar refractivity of R(8), and the lipophilic parameters clog P and pi(linker). The most potent antiproliferative agent so far described is 40 for which an IC(50) = 0.45 microM was predicted by the QSAR equation, while its experimental value is IC(50) = 0.20 microM.

Quantitative structure-activity relationships for a series of symmetrical bisquaternary anticancer compounds

56 biscationic dibromides with distinct polar heads [bis(4-substituted)pyridinium, bis(4-aminoquinolinium), bisquinolinium, and bisisoquinolinium moieties] and several spacers between the two charged nitrogen atoms were synthesised. This oriented synthesis produced 45 inhibitors of choline kinase with antitumour activity against the HT-29 cell line. In an attempt to understand the antiproliferative activity, a quantitative structure-activity relationship was developed. The unknown sigma(R) and sigma(R)(+) descriptors for the diallylamino, pyrrolidino, piperidino and perhydroazepino groups and sigma(R) for the N-methylanilino moiety, were estimated by (13)C NMR spectroscopy in a simple, fast and reproducible manner. The electron characteristic of the substituent at position 4 of the heterocycle and the theoretical lipophilic character of the whole molecule were found to significantly affect the antitumour activity. 1,1'-[Ethylenebis(benzene-1,4-diylmethylene)]bis[4-(N-methylanilino)pyridinium] dibromide is the most active compound of the series so far described and shows a reasonable agreement between predicted and observed antiproliferative data (predicted pIC(50)=6.50, experimental pIC(50)=6.46).

Synthesis, molecular modeling, and pharmacological testing of bis-quinolinium cyclophanes: potent, non-peptidic blockers of the apamin-sensitive Ca(2+)-activated K(+) channel

The synthesis and pharmacological testing of two series of novel bis-quinolinium cyclophanes as blockers of the apamin-sensitive Ca(2+)-activated K(+) (SK(Ca)) channel are presented. In these cyclophanes the two 4-aminoquinolinium groups are joined at the ring N atoms (linker L) and at the exocyclic N atoms (linker A). In those cases where A and L contain two or more aromatic rings each, the activity of the compound is not critically dependent upon the nature of the linkers. When A and L each have only one benzene ring, the blocking potency changes dramatically with simple structural variations in the linkers. One of these smaller cyclophanes having A = benzene-1,4-diylbis(methylene) and L = benzene-1, 3-diylbis(methylene) (3j, 6,10-diaza-1,5(1,4)-diquinolina-3(1,3),8(1, 4)-dibenzenacyclodecaphanedium tritrifluoroacetate, UCL 1684) has an IC(50) of 3 nM and is the most potent non-peptidic SK(Ca) channel blocker described to date. Conformational analysis on the smaller cyclophanes using molecular modeling techniques suggests that the differences in the blocking potencies of the compounds may be attributable to their different conformational preferences.