Quercetin enhances human α7 nicotinic acetylcholine receptor-mediated ion current through interactions with Ca2+ binding sites

The flavonoid quercetin is a low molecular weight substance found in fruits and vegetables. Aside from its anti-oxidative effect, quercetin, like other flavonoids, has a wide range of neuropharmacological actions. The α7 nicotinic acetylcholine receptor (α7 nAChR) has a Ca²⁺-binding site, is highly permeable to the Ca²⁺ ion, and plays important roles in Ca²⁺-related normal brain functions. Dysfunctions of α7 nAChR are associated with a variety of neurological disorders. In the present study, we investigated the effects of quercetin on the ACh-induced inward peak current (I _ACh ) in Xenopus oocytes that heterologously express human α7 nAChR. I _ACh was measured with the two-electrode voltage clamp technique. In oocytes injected with α7 nAChR cRNA, the effects of the co-application of quercetin on I _ACh were concentration-dependent and reversible. The ED₅₀ was 36.1 + 6.1 μM. Quercetin-mediated enhancement of I _ACh caused more potentiation when quercetin was pre-applied. The degree of I _ACh potentiation by quercetin pre-application was time-dependent and saturated after 1 min. Quercetin-mediated I _ACh enhancement was not affected by ACh concentration and was voltage-independent. However, quercetin-mediated I _ACh enhancement was dependent on extracellular Ca²⁺ concentrations and was specific to the Ca²⁺ ion, since the removal of extracellular Ca²⁺ or the addition of Ba²⁺ instead of Ca²⁺ greatly diminished quercetin enhancement of IACh. The mutation of Glu195 to Gln195, in the Ca²⁺-binding site, almost completely diminished quercetin-mediated I _ACh enhancement. These results indicate that quercetin-mediated I _ACh enhancement human α7 nAChR heterologously expressed in Xenopus oocytes could be achieved through interactions with the Ca²⁺-binding site of the receptor.     

Design and synthesis of novel series of 5-HT6 receptor ligands having indole,a central aromatic core and 1-amino-4 methyl piperazine as a positive ionizable group

The exclusive distribution of 5-HT₆ receptor in the brain regions and high affinity for antipsychotic and antidepressant drugs makes 5-HT₆ receptor a promising target in treatment of CNS diseases. Based on a pharmacophore model reported in the literature, we designed and synthesized a novel series of 5-HT₆ receptor ligands having indole as a central aromatic core and 1-amino-4-methyl piperazine as positive ionizable group. Out of 32 compounds we have successfully identified 10 new compounds as 5-HT₆ receptor antagonists. The structure–activity relationship (SAR) studies have been carried out by mapping the compounds with the 3D QSAR model.     

In vitro cytotoxicity on human ovarian cancer cells by T-type calcium channel blockers

The growth inhibition of human cancer cells via T-type Ca²⁺ channel blockade has been well known. Herein, a series of new 3,4-dihydroquinazoline derivatives were synthesized via a brief SAR study on KYS05090 template and evaluated for both T-type Ca²⁺ channel (Ca_v3.1) blockade and cytotoxicity on three human ovarian cancer cells (SK-OV-3, A2780 and A2780-T). Most of compounds except 6i generally exhibited more potent cytotoxicity on SK-OV-3 than mibefradil as a positive control regardless of the degree of T-type channel blockade. In particular, eight compounds (KYS05090, 6a and 6c–6h) showing strong channel blockade exhibited almost equal and more potent cytotoxicity on A2780 when compared to mibefradil. On A2780-T paclitaxel-resistant human ovarian carcinoma, two compounds (KYS05090 and 6d) were 20-fold more active than mibefradil. With respect to cell cycle arrest effect on A2780 and A2780-T cells, KYS05090 induced large proportion of sub-G₁ phase in the cell cycle progression of A2780 and A2780-T, meaning the induction of cancer cell death instead of cell cycle arrest via blocking T-type Ca²⁺ channel. Among new analogues, compounds 6g and 6h induced cell cycle arrest at G₁ phase of A2780 and A2780-T cells in dose-dependent manner and exhibited strong anti-proliferation effects of ovarian cancer cells by blocking T-type Ca²⁺ channel. Furthermore, 6g and 6h possessing strong cytotoxic effects could induce apoptosis of A2780 cells, which was detected by confocal micrographs using DAPI staining.     

Pharmacological studies of Cav3.1 T-type calcium channels using automated patch-clamp techniques

T-type calcium channels are involved in a variety of physiological and pathophysiological processes, and thus could be therapeutic targets. However, there is no T-type channel selective blocker for use in clinical practice, demanding a need for the development of novel drugs where a higher-throughput screening system is required. Here we present pharmacological studies on Ca(v)3.1 T-type channels using automated patch-clamp. The IC(50) values obtained from automated patch-clamp and conventional one showed a good correlation (correlation coefficient of 0.82), suggesting that the automated patch-clamp is an efficient and reliable method for ranking the drug potencies for T-type channels.