Inhibition of transmembrane member 16A calcium-activated chloride channels by natural flavonoids contributes to flavonoid anticancer effects

Anoctamin pharmacology

TMEM16 proteins, also known as anoctamins, are a family of ten membrane proteins with various tissue expression and subcellular localization. TMEM16A (anoctamin 1) is a plasma membrane protein that acts as a calcium-activated chloride channel. It is expressed in many types of epithelial cells, smooth muscle cells and some neurons. In airway epithelial cells, TMEM16A expression is particularly enhanced by inflammatory stimuli that also promote goblet cell metaplasia and mucus hypersecretion. Therefore, pharmacological modulation of TMEM16A could be beneficial to improve mucociliary clearance in chronic obstructive respiratory diseases. However, the correct approach to modulate TMEM16A activity (activation or inhibition) is still debated. Pharmacological inhibitors of TMEM16A could also be useful as anti-hypertensive agents given the TMEM16A role in smooth muscle contraction. In contrast to TMEM16A, TMEM16F (anoctamin 6) behaves as a calcium-activated phospholipid scramblase, responsible for the externalization of phosphatidylserine on cell surface. Inhibitors of TMEM16F could be useful as anti-coagulants and anti-viral agents. The role of other anoctamins as therapeutic targets is still unclear since their physiological role is still to be defined.

Sex and age affect depot expression of Ca2+ channels in rat white fat adipocytes

White adipose tissue (WAT) requires extracellular Ca2+ influx for lipolysis, differentiation, and expansion. This partly occurs via plasma membrane Ca2+ voltage-dependent channels (CaVs). However, WFA exists in different depots whose function varies with age, sex, and location. To explore whether their CaV expression profiles also differ we used RNAseq and qPCR on gonadal, mesenteric, retroperitoneal, and inguinal subcutaneous fat depots from rats of different ages and sex. CaV expression was found dependent on age, sex, and WFA location. In the gonadal depots of both sexes a significantly lower expression of CaV1.2 and CaV1.3 was seen for adults compared to pre-pubescent juveniles. A lower level of expression was also seen for CaV3.1 in adult male but not female gonadal WFA, the latter of whose expression remained unchanged with age. Relatively little expression of CaV3.2 and 3.2 was observed. In post-pubescent inguinal subcutaneous fat, where the third and fourth mammary glands are located, CaV3.1 was decreased in males but increased in females - thus suggesting that this channel is associated with mammogenesis; however, no difference in intracellular Ca2+ levels or adipocyte size were noted. For all adult depots, CaV3.1 expression was larger in females than males - a difference not seen in pre-pubescent rats. These observations are consistent with the changes of CaV3.1 expression seen in 3T3-L1 cell differentiation and the ability of selective CaV3.1 antagonists to inhibit adipogensis. Our results show that changes in CaV expression patterns occur in fat depots related to sexual dimorphism: reproductive tracts and mammogenesis.

Loureirin C extracted from Dracaena cochinchinensis S.C. Chen prevents rotaviral diarrhea in mice by inhibiting the intestinal Ca2+-activated Cl- channels

ETHNOPHARMACOLOGICAL RELEVANCE

Resina Draconis (RD) is the red resin of Dracaena cochinchinensis (Lour.) S.C. Chen and most used as a hemostatic drug in traditional Chinese medicine. Recent studies have reported that RD has a therapeutic effect on gastrointestinal diseases. Loureirin A, B, and C (LA, LB, and LC) are dihydrochalcone compounds isolated from RD.

AIM OF THE STUDY

Dehydration is the primary cause of death in rotaviral diarrhea. Inhibition of Ca2+-activated Cl- channels (CaCCs)-mediated Cl- secretion significantly reduced fluid secretion in rotaviral diarrhea. RD was used to treat digestive diseases such as diarrhea and abdominal pain; however, the pharmacological mechanism remains unclear. This study investigated the effects of RD and loureirin on intestinal Cl- channels and their therapeutic effects on rotavirus-induced diarrhea, aiming to reveal RD's molecular basis, targets, and mechanisms for treating rotaviral diarrhea.

MATERIALS AND METHODS

Cell-based fluorescence quenching assays were used to examine the effect of RD and loureirin on Cl- channels activity. Electrophysiological properties were tested using short-circuit current experiments in epithelial cells or freshly isolated mouse intestinal tissue. Fecal water content, intestinal peristalsis rate, and smooth muscle contraction were measured in neonatal mice infected with SA-11 rotavirus before and after LC treatment or adult mice.

RESULTS

RD, LA, LB, and LC inhibited CaCCs-mediated Cl- current in HT-29 cells and colonic epithelium. The inhibitory effect of LC on CaCCs was primarily on the apical side in epithelial cells, which may be partially produced by affecting cytoplasmic Ca2+ levels. LC significantly inhibited TMEM16A-mediated Cl- current. Characterization studies revealed that LC inhibited basolateral K+ channel activity without affecting Na+/K+-ATPase activity in the colonic epithelium. Although LC activated the cystic fibrosis transmembrane regulator in epithelial cells, its effect was not apparent in colonic epithelium. In vivo, LC significantly reduced the fecal water content, intestinal peristalsis rate, and smooth muscle contraction of mice infected with rotavirus.

CONCLUSION

RD and its active compound LC inhibit intestinal CaCCs activity, which might mediate the anti-rotaviral diarrheal effect of RD.

Three sesquiterpene lactones suppress lung adenocarcinoma by blocking TMEM16A-mediated Ca2+-activated Cl- channels

Transmembrane protein TMEM16A, which encodes calcium-activated chloride channel has been implicated in tumorigenesis. Overexpression of TMEM16A is associated with poor prognosis and low overall survival in multiple cancers including lung adenocarcinoma, making it a promising biomarker and therapeutic target. In this study, three structure-related sesquiterpene lactones (mecheliolide, costunolide and dehydrocostus lactone) were extracted from the traditional Chinese medicine Aucklandiae Radix and identified as novel TMEM16A inhibitors with comparable inhibitory effects. Their effects on the proliferation and migration of lung adenocarcinoma cells were examined. Whole-cell patch clamp experiments showed that these sesquiterpene lactones potently inhibited recombinant TMEM16A currents in a concentration-dependent manner. The half-maximal concentration (IC50) values for three tested sesquiterpene lactones were 29.9 ± 1.1 μM, 19.7 ± 0.4 μM, and 24.5 ± 2.1 μM, while the maximal effect (Emax) values were 100.0% ± 2.8%, 85.8% ± 0.9%, and 88.3% ± 4.6%, respectively. These sesquiterpene lactones also significantly inhibited the endogenous TMEM16A currents and proliferation, and migration of LA795 lung cancer cells. These results demonstrate that mecheliolide, costunolide and dehydrocostus lactone are novel TMEM16A inhibitors and potential candidates for lung adenocarcinoma therapy.

TMEM16A ion channel: A novel target for cancer treatment

Cancer draws attention owing to the high morbidity and mortality. It is urgent to develop safe and effective cancer therapeutics. The calcium-activated chloride channel TMEM16A is widely distributed in various tissues and regulates physiological functions. TMEM16A is abnormally expressed in several cancers and associate with tumorigenesis, metastasis, and prognosis. Knockdown or inhibition of TMEM16A in cancer cells significantly inhibits cancer development. Therefore, TMEM16A is considered as a biomarker and therapeutic target for some cancers. This work reviews the cancers associated with TMEM16A. Then, the molecular mechanism of TMEM16A overexpression in cancer was analyzed, and the possible signal transduction mechanism of TMEM16A regulating cancer development was summarized. Finally, TMEM16A inhibitors with anticancer effect and their anticancer mechanism were concluded. We hope to provide new ideas for pharmacological studies on TMEM16A in cancer.

New flavone-based arylamides as potential V600E-BRAF inhibitors: Molecular docking, DFT, and pharmacokinetic properties

Objectives

The V600E-BRAF protein kinase is an attractive and essential therapeutic target in melanoma and other tumors. However, because of its resistance to the known inhibitors and side effects of some identified inhibitors, new potent inhibitors need to be identified.

Methods

In the present work, in silico strategies such as the molecular docking simulation, DFT (Density-Functional-Theory) computations, and pharmacokinetic evaluation were used to determine potential V600E-BRAF inhibitors from a set of 31 synthesized novel flavone-based arylamides.

Results

The docking result demonstrated that four compounds (10, 11, 28, and 31) had acceptable docking scores (MolDock score of -167.523 kcal mol^-1, -158.168 kcal mol^-1, -160.581 kcal mol^-1,-162.302 kcal mol^-1, and a Rerank score of -124.365, -129.365, -135.878 and -117.081, respectively) appeared as most active and potent V600E-BRAF inhibitors that topped vemurafenib (-158.139 and -118.607 kcal mol^-1). The appearance of H-bonds and hydrophobic interactions with essential residues for V600E-BRAF proved the high stability of these complexes. The energy for the frontier molecular orbitals such as HOMO, LUMO, energy gap, and other reactivity parameters was computed using DFT. The frontier molecular-orbital surfaces and electrostatic potentials (EPs) were investigated to demonstrate the charge-density distributions that might be linked to anticancer activity. Similarly, the chosen compounds revealed superior pharmacological properties according to the drug-likeness rules (bioavailability) and pharmacokinetic properties.

Conclusion

The chosen compounds were recognized as potent V600E-BRAF inhibitors with superior pharmacokinetic properties and could be promising cancer drug candidates.

Identification of a druggable pocket of the calcium-activated chloride channel TMEM16A in its open state

The calcium-activated chloride channel TMEM16A is a potential drug target to treat hypertension, secretory diarrhea, and several cancers. However, all reported TMEM16A structures are either closed or desensitized, and direct inhibition of the open state by drug molecules lacks a reliable structural basis. Therefore, revealing the druggable pocket of TMEM16A exposed in the open state is important for understanding protein-ligand interactions and facilitating rational drug design. Here, we reconstructed the calcium-activated open conformation of TMEM16A using an enhanced sampling algorithm and segmental modeling. Furthermore, we identified an open state druggable pocket and screened a potent TMEM16A inhibitor, etoposide, which is a derivative of a traditional herbal monomer. Molecular simulations and site-directed mutagenesis showed that etoposide binds to the open state of TMEM16A, thereby blocking the ion conductance pore of the channel. Finally, we demonstrated that etoposide can target TMEM16A to inhibit the proliferation of prostate cancer PC-3 cells. Together, these findings provide a deep understanding of the TMEM16A open state at an atomic level and identify pockets for the design of novel inhibitors with broad applications in chloride channel biology, biophysics, and medicinal chemistry.

Drug repurposing and molecular mechanisms of the antihypertensive drug candesartan as a TMEM16A channel inhibitor

TMEM16A, a Ca²⁺-activated chloride channel (CaCC), and its pharmacological inhibitors can inhibit the growth of lung adenocarcinoma cells. However,the poor efficacy, safety, and stability of TMEM16A inhibitors limit the development of these agents. Therefore, finding new therapeutic directions from already marketed drugs is a feasible strategy to obtain safe and effective therapeutic drugs. Here, we screened a library contain more than 2400 FDA, EMA, and NMPA-approved drugs through virtual screening. We identified a drug candidate, candesartan (CDST), which showed strong inhibitory effect on the TMEM16A in a concentration-dependent manner with an IC₅₀ of 24.40 ± 3.21 μM. In addition, CDST inhibited proliferation, migration and induced apoptosis of LA795 cells targeting TMEM16A, and significantly inhibited lung adenocarcinoma tumor growth in vivo. The molecular mechanism of CDST inhibiting TMEM16A channel indicated it bound to R515/R535/E623/E624 in the drug pocket, thereby blocked the pore. In conclusion, we identified a novel TMEM16A channel inhibitor, CDST, which exhibited excellent inhibitory activity against lung adenocarcinoma. Considering that CDST has been used in clinical treatment of hypertension, it may play an important role in the combined treatment of hypertension and lung adenocarcinoma as a multi-target drug in the future.

The role of Transmembrane Protein 16A (TMEM16A) in pulmonary hypertension

Transmembrane protein 16A (TMEM16A), a member of the TMEM16 family, is the molecular basis of Ca2+-activated chloride channels (CaCCs) and is involved in a variety of physiological and pathological processes. Previous studies have focused more on respiratory-related diseases and tumors. However, recent studies have identified an important role for TMEM16A in cardiovascular diseases, especially in pulmonary hypertension. TMEM16A is expressed in both pulmonary artery smooth muscle cells and pulmonary artery endothelial cells and is involved in the development of pulmonary hypertension. This paper presents the structure and function of TMEM16A, the pathogenesis of pulmonary hypertension, and highlights the role and mechanism of TMEM16A in pulmonary hypertension, summarizing the controversies in this field and taking into account hypertension and portal hypertension, which have similar pathogenesis. It is hoped that the unique role of TMEM16A in pulmonary hypertension will be illustrated and provide ideas for research in this area.

Near-Infrared Light-Responsive Nanoinhibitors for Tumor Suppression through Targeting and Regulating Anion Channels

The gated state of anion channels is involved in the regulation of proliferation and migration of tumors. Specific regulators are urgently needed for efficacious cancer ablation. For this purpose, it is essential to understand the molecular mechanisms of interaction between the regulators and anion channels and apply this knowledge to regulate anion channels. Transmembrane 16A (TMEM16A) is the molecular basis of the calcium-activated chloride channels. It is an anion channel activated by Ca²⁺, and the inhibition of TMEM16A is associated with a decrease in tumorigenesis. Herein, we characterized a natural compound procyanidin (PC) as an efficacious and selective inhibitor of TMEM16A with an IC₅₀ of 10.6 ± 0.6 μM. Our research revealed the precise sites (D383, R535, and E624) of electrostatic interactions between PC and TMEM16A. Near-infrared (NIR)-light-responsive photothermal conjugated polymer nanoparticles encapsulating PC (CPNs-PC) were established to remotely target and regulate the TMEM16A anion channel. Upon NIR irradiation, CPNs-PC downregulated the signaling pathway downstream of TMEM16A and arrested the cell cycle progression of cancer cells and improved the bioavailability of PC. The tumor inhibition ratio of CPNs-PC was superior to PC by 13.4%. Our findings enabled the development of a strategy to accurately and remotely regulate anion channels to promote tumor regression using NIR-light-responsive conjugated polymer nanoparticles containing specific inhibitors of TMEM16A.

Multi-target tracheloside and doxorubicin combined treatment of lung adenocarcinoma

Chemotherapy is one of the main methods for malignant lung cancer treatment. However, the side effects of chemotherapy drugs are serious and it is prone to drug resistance. Therefore, multi-drug combination chemotherapy is popular in lung cancer treatment. This study found that tracheloside (TCS) was a novel inhibitor of TMEM16A which was specific high expressed in lung cancer tissues. TCS concentration dependently inhibited TMEM16A with an IC₅₀ of 3.09 ± 0.21 μM. It inhibited lung cancer cells proliferation, migration, and induced cells apoptosis targeting TMEM16A. In addition, molecular docking combined with site-directed mutagenesis confirmed that the binding sites of TCS to TMEM16A were S387, E623, E624. Subsequently, multi-target combined drug administration was conducted based on the different drug targets of TCS and doxorubicin (DOX). Both in vitro and in vivo experiments indicated that the combined administration of low concentration of TCS and DOX achieved satisfactory anticancer effect, and it offset the side effects caused by high concentration of DOX. Therefore, TCS is a safe and efficient anticancer lead compound which can enhance the effect of DOX.

Treatment of Gastrointestinal Disorders-Plants and Potential Mechanisms of Action of Their Constituents

The worldwide prevalence of gastrointestinal diseases is about 40%, with standard pharmacotherapy being long-lasting and economically challenging. Of the dozens of diseases listed by the Rome IV Foundation criteria, for five of them (heartburn, dyspepsia, nausea and vomiting disorder, constipation, and diarrhoea), treatment with herbals is an official alternative, legislatively supported by the European Medicines Agency (EMA). However, for most plants, the Directive does not require a description of the mechanisms of action, which should be related to the therapeutic effect of the European plant in question. This review article, therefore, summarizes the basic pharmacological knowledge of synthetic drugs used in selected functional gastrointestinal disorders (FGIDs) and correlates them with the constituents of medicinal plants. Therefore, the information presented here is intended as a starting point to support the claim that both empirical folk medicine and current and decades-old treatments with official herbal remedies have a rational basis in modern pharmacology.

Zafirlukast inhibits the growth of lung adenocarcinoma via inhibiting TMEM16A channel activity

Lung cancer has the highest mortality among cancers worldwide due to its high incidence and lack of the effective cures. We have previously demonstrated that the membrane ion channel TMEM16A is a potential drug target for the treatment of lung adenocarcinoma and have identified a pocket of inhibitor binding that provides the basis for screening promising new inhibitors. However, conventional drug discovery strategies are lengthy and costly, and the unpredictable side effects lead to a high failure rate in drug development. Therefore, finding new therapeutic directions for already marketed drugs may be a feasible strategy to obtain safe and effective therapeutic drugs. Here, we screened a library of over 1400 Food and Drug Administration-approved drugs through virtual screening and activity testing. We identified a drug candidate, Zafirlukast (ZAF), clinically approved for the treatment of asthma, that could inhibit the TMEM16A channel in a concentration-dependent manner. Molecular dynamics simulations and site-directed mutagenesis experiments showed that ZAF can bind to S387/N533/R535 in the nonselective inhibitor binding pocket, thereby blocking the channel pore. Furthermore, we demonstrate ZAF can target TMEM16A channel to inhibit the proliferation and migration of lung adenocarcinoma LA795 cells. In vivo experiments showed that ZAF can significantly inhibit lung adenocarcinoma tumor growth in mice. Taken together, we identified ZAF as a novel TMEM16A channel inhibitor with excellent anticancer activity, and as such, it represents a promising candidate for future preclinical and clinical studies.

Anticancer Activity of Natural and Synthetic Chalcones

Cancer is a condition caused by many mechanisms (genetic, immune, oxidation, and inflammatory). Anticancer therapy aims to destroy or stop the growth of cancer cells. Resistance to treatment is theleading cause of the inefficiency of current standard therapies. Targeted therapies are the most effective due to the low number of side effects and low resistance. Among the small molecule natural compounds, flavonoids are of particular interest for theidentification of new anticancer agents. Chalcones are precursors to all flavonoids and have many biological activities. The anticancer activity of chalcones is due to the ability of these compounds to act on many targets. Natural chalcones, such as licochalcones, xanthohumol (XN), panduretin (PA), and loncocarpine, have been extensively studied and modulated. Modification of the basic structure of chalcones in order to obtain compounds with superior cytotoxic properties has been performed by modulating the aromatic residues, replacing aromatic residues with heterocycles, and obtaining hybrid molecules. A huge number of chalcone derivatives with residues such as diaryl ether, sulfonamide, and amine have been obtained, their presence being favorable for anticancer activity. Modification of the amino group in the structure of aminochalconesis always favorable for antitumor activity. This is why hybrid molecules of chalcones with different nitrogen hetercycles in the molecule have been obtained. From these, azoles (imidazole, oxazoles, tetrazoles, thiazoles, 1,2,3-triazoles, and 1,2,4-triazoles) are of particular importance for the identification of new anticancer agents.

Targeting ion channels for the treatment of lung cancer

Lung cancer is caused by several environmental and genetic variables and is globally associated with elevated morbidity and mortality. Among these variables, membrane-bound ion channels have a key role in regulating multiple signaling pathways in tumor cells and dysregulation of ion channel expression and function is closely related to proliferation, migration, and metastasis of lung cancer. This work reviews and summarizes current knowledge about the role of ion channels in lung cancer, focusing on the changes in the expression and function of various ion channels in lung cancer and how these changes affect lung cancer cell biology both in vitro and in vivo as evidenced by both genetic and pharmacological studies. It can help understand the molecular mechanisms of various ion channels influencing the initiation and progression of lung cancer and shed new insights into their roles in the development and treatment of this deadly disease.

Cepharanthine, a novel selective ANO1 inhibitor with potential for lung adenocarcinoma therapy

Anoctamin-1 (ANO1), also known as transmembrane protein 16A (TMEM16A), is identified as a Ca²⁺-activated Cl^- channel that is expressed in many organs and tissues. It is involved in numerous major physiological functions and especially in tumor growth. By screening 530 natural compounds, we identified cepharanthine as a potent blocker of ANO1 channels with an IC₅₀ of 11.2 ± 0.9 μM and E_max of 92.7 ± 1.7%. The Lys³⁸⁴, Arg⁵³⁵, Thr⁵³⁹, and Glu⁶²⁴ in ANO1 are critical for the inhibitory effect of cepharanthine. Similar to its effect on ANO1, cepharanthine inhibits ANO2, the closest analog of TMEM16A. In contrast, up to 30 μM of cepharanthine showed limited inhibitory effects on recombinant ANO6 and bestrophin-1-encoded Ca²⁺-activated Cl^- currents, but it showed no effects on endogenous volume-regulated anion currents (VRAC). Cepharanthine could also potently suppress endogenous ANO1 currents, significantly inhibit cell proliferation and migration, and induce apoptosis in LA795 lung adenocarcinoma cells. Moreover, animal experiments have shown that cepharanthine can dramatically inhibit the growth of xenograft tumors in mice. The high specificity provided by cepharanthine could be an important foundation for future studies of the physiological role of ANO1 channels, and these findings may reveal a new mechanism of its anticancer effect.

Theaflavin binds to a druggable pocket of TMEM16A channel and inhibits lung adenocarcinoma cell viability

As a calcium-activated chloride channel regulated by the intracellular Ca²⁺ concentration and membrane potential, TMEM16A has attracted considerable attention and has been proposed as a novel anticancer drug target. We have previously reported that the pocket above the ion conductance pore could be a nonselective inhibitor-binding pocket. However, whether this pocket is druggable remains unexplored. In this study, we performed virtual screening to target the presumed inhibitor-binding pocket and identified a highly effective TMEM16A inhibitor, theaflavin (TF: a tea polyphenol in black tea). Molecular dynamics simulations revealed that theaflavin adopts a "wedge insertion mode" to block the ion conduction pore and induces pore closure. Moreover, the binding mode showed that the TF pedestal plays an important role in pore blockade, and R515, R535, T539, K603, E623, and E633 were determined to be most likely to interact directly with the pedestal. Mutagenesis experiment results corroborated the mechanism through which TF binds to this pocket. Combined with the quantitative calculation results, our data indicated that the three hydroxyl groups on the pedestal may be the most crucial pharmacophores for TMEM16A inhibition by TF. Finally, antitumor experiments revealed that TF could target TMEM16A to inhibit the proliferation and migration of LA795 cells, indicating the potential therapeutic effect of TF on the growth of lung adenocarcinoma with high TMEM16A expression. The successful application of drug screening strategies based on this binding pocket highlights new directions for discovering superior modulators and contributes to the development of novel therapeutics for lung adenocarcinoma.

Pharmacological Modulation of Ion Channels for the Treatment of Cystic Fibrosis

Cystic fibrosis (CF) is a life-shortening monogenic disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR) protein, an anion channel that transports chloride and bicarbonate across epithelia. Despite clinical progress in delaying disease progression with symptomatic therapies, these individuals still develop various chronic complications in lungs and other organs, which significantly restricts their life expectancy and quality of life. The development of high-throughput assays to screen drug-like compound libraries have enabled the discovery of highly effective CFTR modulator therapies. These novel therapies target the primary defect underlying CF and are now approved for clinical use for individuals with specific CF genotypes. However, the clinically approved modulators only partially reverse CFTR dysfunction and there is still a considerable number of individuals with CF carrying rare CFTR mutations who remain without any effective CFTR modulator therapy. Accordingly, additional efforts have been pursued to identify novel and more potent CFTR modulators that may benefit a larger CF population. The use of ex vivo individual-derived specimens has also become a powerful tool to evaluate novel drugs and predict their effectiveness in a personalized medicine approach. In addition to CFTR modulators, pro-drugs aiming at modulating alternative ion channels/transporters are under development to compensate for the lack of CFTR function. These therapies may restore normal mucociliary clearance through a mutation-agnostic approach (ie, independent of CFTR mutation) and include inhibitors of the epithelial sodium channel (ENaC), modulators of the calcium-activated channel transmembrane 16A (TMEM16, or anoctamin 1) or of the solute carrier family 26A member 9 (SLC26A9), and anionophores. The present review focuses on recent progress and challenges for the development of ion channel/transporter-modulating drugs for the treatment of CF.

Emerging Modulators of TMEM16A and Their Therapeutic Potential

Calcium-activated chloride channels (CaCCs) are widespread chloride channels which rely on calcium activation to perform their functions. In 2008, TMEM16A (also known as anoctamin1, ANO1) was identified as the molecular basis of the CaCCs, which provided the possibility to study the physiological function of CaCCs. TMEM16A is widely expressed in various cells and controls basic physiological functions, including neuronal and cardiac excitability, nerve transduction, smooth muscle contraction, epithelial Cl^- secretion and fertilization. However, the abnormal function of TMEM16A may cause a variety of diseases, including asthma, gastrointestinal motility disorder and various cancers. Therefore, TMEM16A is a putative drug target for many diseases, and it is important to determine specific and efficient modulators of TMEM16A channel. In recent years, we and others have screened several natural modulators of TMEM16A against cancers and gastrointestinal motility dysfunction. This article reviews the screening methods, efficacy of TMEM16A modulators and pharmacological effects of TMEM16A modulators on different diseases. GRAPHIC ABSTACT.

Identification of evodiamine and rutecarpine as novel TMEM16A inhibitors and their inhibitory effects on peristalsis in isolated Guinea-pig ileum

The transmembrane member 16A (TMEM16A)-encoded Ca²⁺-activated Cl^- channel (CaCC) is expressed in interstitial cells of Cajal (ICCs) and involved in the generation of the slow-wave currents of gastrointestinal (GI) smooth muscles. TMEM16A modulators have been shown to positively or negatively regulate the contraction of gastrointestinal smooth muscle. Therefore, targeting the pharmacological modulation of TMEM16A may represent a novel treatment approach for gastrointestinal dysfunctions such as constipation and diarrhoea. In this study, evodiamine and rutecarpine were extracted from the traditional Chinese medicine Evodia rutaecarpa and identified as novel TMEM16A inhibitors with comparable inhibitory effects. Their effects on intestinal peristalsis were examined. Whole-cell patch clamp results show that evodiamine and rutecarpine inhibited TMEM16A Cl^- currents in CHO cells. The half-maximal inhibition values (IC₅₀) of evodiamine and rutecarpine on TMEM16A Cl^- currents were 11.8 ± 1.3 μΜ and 9.2 ± 0.4 μM, and the maximal effect values (E_max) were 95.8 ± 5.1% and 99.1 ± 1.6%, respectively. The Lys³⁸⁴, Thr³⁸⁵, and Met⁵²⁴ in TMEM16A are critical for evodiamine and rutecarpine's inhibitory effects. Further functional studies show that both evodiamine and rutecarpine can significantly suppress the peristalsis in isolated guinea-pig ileum. These findings demonstrate that evodiamine and rutecarpine are new TMEM16A inhibitors and support the regulation effect of TMEM16A modulators on gastrointestinal motility.

Honokiol inhibits proliferation of colorectal cancer cells by targeting anoctamin 1/TMEM16A Ca2+ -activated Cl- channels

BACKGROUND AND PURPOSE

Ca²⁺ -activated Cl^- channels (Ano1 channels) contribute to the pathogenesis of colorectal cancer. Honokiol is known to inhibit cell proliferation and tumour growth in colorectal cancer. However, the molecular target of honokiol remains unclear. This study aimed to investigate whether honokiol inhibited cell proliferation of colorectal cancer by targeting Ano1 channels.

EXPERIMENTAL APPROACH

Patch-clamp techniques were performed to study the effect of honokiol on Ca²⁺ -activated Cl^- currents in HEK293 cells overexpressing Ano1- or Ano2-containing plasmids or in human colorectal carcinoma SW620 cells. Site-directed mutagenesis was used to identify the critical residues for honokiol-induced Ano1 inhibition. Proliferation of SW620 cells or human intestinal epithelial NCM460 cells by CCK-8 assays.

KEY RESULTS

Honokiol blocked Ano1 currents in Ano1-overexpressing HEK293 cells and SW620 cells. Honokiol more potently inhibited Ano1 currents than Ano2 currents. Three amino acids (R429, K430 and N435) were critical for honokiol-induced Ano1 inhibition. The R429A/K430L/N435G mutation reduced the sensitivity of Ano1 to honokiol. Honokiol inhibited SW620 cell proliferation, and this effect was reduced by Ano1-shRNAs. Furthermore, Ano1 overexpression promoted proliferation in NCM460 cells with low Ano1 endogenous expression and resulted in an increased sensitivity to honokiol. Overexpression of the R429A/K430L/N435G mutation reduced WT Ano1-induced increase in the sensitivity of NCM460 cells to honokiol.

CONCLUSION AND IMPLICATIONS

We identified a new anticancer mechanism of honokiol, through the inhibition of cell proliferation, by targeting Ano1 Ca²⁺ -activated Cl^- channels.

The Ca2+-activated chloride channel ANO1/TMEM16A: An emerging therapeutic target for epithelium-originated diseases?

Anoctamin 1 (ANO1) or TMEM16A gene encodes a member of Ca²⁺ activated Cl^– channels (CaCCs) that are critical for physiological functions, such as epithelial secretion, smooth muscle contraction and sensory signal transduction. The attraction and interest in ANO1/TMEM16A arise from a decade long investigations that abnormal expression or dysfunction of ANO1 is involved in many pathological phenotypes and diseases, including asthma, neuropathic pain, hypertension and cancer. However, the lack of specific modulators of ANO1 has impeded the efforts to validate ANO1 as a therapeutic target. This review focuses on the recent progress made in understanding of the pathophysiological functions of CaCC ANO1 and the current modulators used as pharmacological tools, hopefully illustrating a broad spectrum of ANO1 channelopathy and a path forward for this target validation.

Coronary hypercontractility to acidosis owes to the greater activity of TMEM16A/ANO1 in the arterial smooth muscle cells

BACKGROUND

Severe acidosis deteriorates cardiac injury. Rat coronary arteries (RCAs) are unusually hypercontractive to extracellular (o) acidosis (EA). TMEM16A-encoded anoctamin 1 (ANO1), a Ca²⁺-activated chloride channel (CaCC), plays an important role in regulating coronary arterial tension.

PURPOSE

We tested the possibility that the activation of CaCCs in the arterial smooth muscle cell (ASMC) contributes to EA-induced RCA constriction.

METHODS

ANO1 expression was detected with immunofluorescence staining and Western blot. TMEM16A mRNA was assessed with quantitative Real-Time PCR. Cl^- currents and membrane potentials were quantified with a patch clamp. The vascular tension was recorded with a myograph. Intracellular (i) level of Cl^- and Ca²⁺ was measured with fluorescent molecular probes.

RESULTS

ANO1 was expressed in all tested arterial myocytes, but was much more abundant in RCA ASMCs as compared with ASMCs isolated from rat cerebral basilar, intrarenal and mesenteric arteries. EA reduced [Cl^-]_i levels, augmented CaCC currents exclusively in RCA ASMCs and depolarized RCA ASMCs to a greater extent. Cl^- deprivation, which depleted [Cl^-]_i by incubating the arteries or their ASMCs in Cl^--free bath solution, decreased EA-induced [Cl^-]_i reduction, diminished EA-induced CaCC augmentation and time-dependently depressed EA-induced RCA constriction. Inhibitor studies showed that these EA-induced effects including RCA constriction, CaCC current augmentation, [Cl^-]_i reduction and/or [Ca²⁺]_i elevation were depressed by various Cl^- channel blockers, [Ca²⁺]_i release inhibitors and L-type voltage-gated Ca²⁺ channel inhibitor nifedipine. ANO1 antibody attenuated all observed changes induced by EA in RCA ASMCs.

CONCLUSION

The greater activity of RCA ASMC CaCCs complicated with an enhanced Ca²⁺ mobilization from both [Ca²⁺]_i release and [Ca²⁺]_o influx plays a pivotal role in the distinctive hypercontractility of RCAs to acidosis. Translation of these findings to human beings may lead to a new conception in our understanding and treating cardiac complications in severe acidosis.

The Calcium-Activated Chloride Channel TMEM16A is Inhibitied by Liquiritigenin

The transmembrane 16 (TMEM16) family contains 10 subtypes, and the function of each protein is different. TMEM16A is a calcium-activated chloride channel involved in physiological and pathological situations. Liquiritigenin is an aglycone derived from Glycyrrhiza glabra, and it is generated via the metabolism of enterobacterial flora. It has been known that liquiritigenin reduces pain sensation involving TMEM16A activation in primary sensory neurons. In addition, other pharmacological effects of liquiritigenin in physiological functions involving TMEM16A have been reported. However, the relationship between TMEM16A and liquiritigenin is still unknown. Therefore, we hypothesized that TMEM16A is inhibited by liquiritigenin. To confirm this hypothesis, we investigated the effect of liquiritigenin on TMEM16A currents evoked by intracellular free calcium in HEK293T cells transfected with TMEM16A. In this study, we found that liquiritigenin inhibited the mouse and human TMEM16A currents. To further confirm its selectivity, we also investigated its pharmacological effects on other ion channels, including transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1), which are non-selective cation channels involved in pain sensation. However, liquiritigenin did not inhibit the currents of TRPV1 and TRPA1 induced by capsaicin and allyl isothiocyanate, respectively. Therefore, our findings indicate that selective TMEM16A inhibition could be one molecular mechanism that explains liquiritigenin-induced pain reduction. Additionally, we also investigated the inhibitory effects of estrogens on TMEM16A because liquiritigenin reportedly binds to the estrogen receptor. In this study, a pregnancy-dependent estrogen, estriol, significantly inhibited TMEM16A. However, the efficacy was weak. Although there is a possibility that TMEM16A activity could be suppressed during pregnancy, the physiological significance seems to be small. Thus, the inhibitory effect of estrogen might not be significant under physiological conditions. Furthermore, we investigated the effect of dihydrodaidzein, which is an analog of liquiritigenin that has a hydroxyphenyl at different carbon atom of pyranose. Dihydrodaidzein also inhibited mouse and human TMEM16A. However, the inhibitory effects were weaker than those of liquiritigenin. This suggests that the efficacy of TMEM16A antagonists depends on the hydroxyl group positions. Our finding of liquiritigenin-dependent TMEM16A inhibition could connect the current fragmented knowledge of the physiological and pathological mechanisms involving TMEM16A and liquiritigenin.

[Calcium-activated chloride channels: structure, properties, role in physiological and pathological processes]

Ca2+-activated chloride channels (CaCC) are a class of intracellular calcium activated chloride channels that mediate numerous physiological functions. In 2008, the molecular structure of CaCC was determined. CaCC are formed by the protein known as anoctamine 1 (ANO1 or TMEM16A). CaCC mediates the secretion of Cl- in secretory epithelia, such as the airways, salivary glands, intestines, renal tubules, and sweat glands. The presence of CaCC has also been recognized in the vascular muscles, smooth muscles of the respiratory tract, which control vascular tone and hypersensitivity of the respiratory tract. TMEM16A is activated in many cancers; it is believed that TMEM16A is involved in carcinogenesis. TMEM16A is also involved in cancer cells proliferation. The role of TMEM16A in the mechanisms of hypertension, asthma, cystic fibrosis, nociception, and dysfunction of the gastrointestinal tract has been determined. In addition to TMEM16A, its isoforms are involved in other physiological and pathophysiological processes. TMEM16B (or ANO2) is involved in the sense of smell, while ANO6 works like scramblase, and its mutation causes a rare bleeding disorder, known as Scott syndrome. ANO5 is associated with muscle and bone diseases. TMEM16A interacts with various cellular signaling pathways including: epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPK), calmodulin (CaM) kinases, transforming growth factor TGF-β. The review summarizes existing information on known natural and synthetic compounds that can block/modulate CaCC currents and their effect on some pathologies in which CaCC is involved.

Inhibitory activities of curzerenone, curdione, furanodienone, curcumol and germacrone on Ca2+-activated chloride channels

Calcium-activated chloride channels (CaCCs) as a kind of widely expressed ion channels play crucial roles in a variety of physiological regulation. TMEM16A has been identified as the molecular basis of CaCCs in numerous cell types and is considered a new drug target for many diseases. Regulating the function of TMEM16A through small molecule modulators has become a new strategy to improve respiratory and digestive dysfunction and even tumor therapy. Herein, we obtained 5 sesquiterpenoids, named curzerenone, curdione, furanodienone, curcumol and germacrone with TMEM16A inhibition and revealed their mechanism of action by fluorescent and electrophysiological assays. Cell-based YFP fluorescence data demonstrated that 5 compounds inhibited TMEM16A-mediated I^- influx in a dose-dependent manner. To explore the mechanism of 5 compounds on CaCCs, FRT cells with high expression of TMEM16A, HBE, HT-29 and T84 cells and mouse colons were used in short-circuit current assay. Our results showed that 5 compounds inhibited the Ca²⁺-activated Cl^- currents generated by the E_act, ATP and UTP stimulation, and this inhibitory effect was related not only to the direct inhibition of channel opening, but also the inhibition of intracellular Ca²⁺ concentration and K⁺ channel activity. In addition to CaCCs, these 5 compounds also had definite inhibitory activities against cystic fibrosis transmembrane regulator (CFTR) at the cellular level. In summary, these compounds have the potential to regulate the activites of TMEM16A/CaCCs and CFTR channels in vitro, providing a new class of lead compounds for the development of drugs for diseases related to chloride channel dysfunction.

TMEM16A-encoded anoctamin 1 inhibition contributes to chrysin-induced coronary relaxation

BACKGROUND

Chrysin, a natural flavonoid available in honey, propolis and medicinal plants, has been shown to be vasorelaxant in some vascular beds. Proper intake of an alimental vasodilator as a food additive may be a promising strategy for prevention and treatment of coronary spasmodic disorders.

PURPOSE

TMEM16A-encoded anoctamin 1 (ANO1), a Ca²⁺ activated Cl^- channel (CaCC), plays an important role in the modulation of vascular tone. We tested the possibility that inhibition of CaCCs contributes to chrysin-induced coronary arterial relaxation.

METHODS

The vascular tone of the rat coronary artery (RCA) was recorded with a wire myograph. CaCC currents were assessed using whole-cell patch clamp in arterial smooth muscle cell (ASMC) freshly isolated from RCAs. An inhibitor study was performed to explore the mechanisms underlying the vasomotor and electrophysiological effects of chrysin.

RESULTS

Pre-incubation with chrysin depressed the contractions elicited by thromboxane A2 analog U46619, vasopressin (VP), depolarization and extracellular Ca²⁺ elevation/depolarization without significant preference among these vasoconstrictors. Besides, chrysin inhibited both intracellular Ca²⁺ release-dependent and extracellular Ca²⁺ influx-dependent components of contractions induced by U46619 or VP. In RCAs pre-contracted with U46619, VP or KCl, chrysin elicited concentration-dependent relaxations, which were weakened by Cl^- -deprivation. The electrophysiological study showed that chrysin reduced ANO1-antibody-sensitive CaCC currents and depressed CaCC increments induced by U46619. Inhibitor study showed that both the vasorelaxation and the CaCC current reduction induced by chrysin were attenuated by blocking CaCCs and inhibiting cAMP/PKA and NO/PKG pathways.

CONCLUSION

The present findings indicate that inhibition of RCA ASMC CaCC currents, which may be consequential following intracellular Ca²⁺ availability reduction and activation of cAMP/PKA and NO/cGMP signaling pathways, contributes to chrysin-induced RCA relaxation.

Activation of TMEM16A by natural product canthaxanthin promotes gastrointestinal contraction

Transmembrane 16A (TMEM16A), also known as anoctamin 1, is the molecular basis of the calcium-activated chloride channels. TMEM16A is present in interstitial cells of Cajal, which are the pacemaker cells that control smooth muscle contraction. TMEM16A is implicated in gastrointestinal disorders. Activation of TMEM16A is believed to promote the gastrointestinal muscle contraction. Here, we report a highly efficient, nontoxic, and selective activator of TMEM16A, canthaxanthin (CX). The study using molecular docking and site-directed mutation revealed that CX-specific binging site in TMEM16A is K769. CX was also found to promote the contraction of smooth muscle cells in gastrointestinal tract through activation of TMEM16A channels, which provides an excellent basis for development of CX as a chemical tool and potential therapeutic for gastrointestinal dysfunction.

TMEM16A-inhibitor loaded pH-responsive nanoparticles: A novel dual-targeting antitumor therapy for lung adenocarcinoma

To overcome the adverse effects of conventional chemotherapy for cancers, various nanoparticles based drug delivery systems have been developed. However, nanoparticles delivering drugs directly to kill tumor cells still faced with challenges, because tumors possessed adopt complex mechanism to resist damages, which compromised the therapeutic efficacy. TMEM16A/CaCCs (Calcium activates chloride channels) has been identified to be overexpressed in lung adenocarcinoma which can serve as a novel tumor specific drug target in our previous work. Here, we developed a novel dual-targeted antitumor strategy via designing a novel nano-assembled, pH-sensitive drug-delivery system loading with specific inhibitors of TMEM16A against lung adenocarcinoma. For validation, we assayed the novel dual-targeting therapy on xenograft mouse model which exhibited significant antitumor activity and not affect mouse body weight. The dual targeting therapy accomplished in this study will shed light on the development of advanced antitumor strategy.

Inhibition of TMEM16A Ca2+-activated Cl- channels by avermectins is essential for their anticancer effects

Transmembrane member 16A (TMEM16A) encoded Ca²⁺-activated Cl^- channels were found to be involved in tumorigenesis. Previous studies suggest the effect of TMEM16A gene amplification on tumorigenic proliferation is exerted through its channel function. TMEM16A-specific and potent small molecule inhibitors have been proposed to potentially be useful for the treatment of cancer. Thus, we screened six analogues of avermectin for their inhibitory activities on TMEM16A mediated currents. A whole-cell patch technique was used to record the currents. The IC₅₀ and E_max values for TMEM16A inhibition of five tested avermectins (avermectin B₁, ivermectin, doramectin, selamectin, and moxidectin) were 0.15-1.32 μM and 65-87 %, respectively. In addition, these avermectins significantly inhibited endogenous TMEM16A mediated currents and thus, the proliferation, migration, inducing apoptosis of LA795 cancer cells. Eprinomectin (4"-(acetylamino)-4"-deoxy-avermectin B₁) and two other important macrolides (erythromycin and azithromycin), which have minimal or no TMEM16A inhibitory effects, were used as negative control drugs. These drugs were found to have limited effects on the proliferation, migration, and apoptosis of LA795 cells. Finally, avermectin B₁ and ivermectin dramatically inhibited the growth of xenograft tumors in mice. These data demonstrate that avermectins are novel TMEM16A inhibitors and are potentially useful in specific cancer therapies. These findings also provide a new opportunity to develop TMEM16A modulators.

Arctigenin, a novel TMEM16A inhibitor for lung adenocarcinoma therapy

TMEM16A plays critical roles in physiological process and may serve as drug targets for diverse diseases. Recently, TMEM16A has started to be regarded as potential primary lung adenocarcinoma targets. Here, we identified that arctigenin, a natural compound, is a novel TMEM16A inhibitor, and it can suppress lung adenocarcinoma growth through inhibiting TMEM16A both in vitro and in vivo. Our data also showed that the IC₅₀ of actigenin to TMEM16A whole-cell current was 19.29 ± 4.69 μM, and the putative binding sites of arctigenin in TMEM16A were R515 and R535. Arctigenin concentration-dependently inhibited the proliferation and migration of LA795, however, the inhibition effect can be abolished by knockdown of the endogenous TMEM16A with shRNA. Further, we injected arctigenin on xenograft mouse model which exhibited significant antitumor activity with no adverse effect. At last, western blotting results showed the mechanism of arctigenin inhibiting lung adenocarcinoma was through inhibiting MAPK pathway. In summary, TMEM16A is a novel drug target for lung adenocarcinoma treatment. Arctigenin can be used as a lead compound for the development of lung adenocarcinoma therapy drugs.

The Molecular Mechanism of Ginsenoside Analogs Activating TMEM16A

The calcium-activated chloride channel TMEM16A is involved in many physiological processes, and insufficient function of TMEM16A may lead to the occurrence of various diseases. Therefore, TMEM16A activators are supposed to be potentially useful for treatment of TMEM16A downregulation-inducing diseases. However, the TMEM16A activators are relatively rare, and the underlying activation mechanism of them is unclear. In the previous work, we have proved that ginsenoside Rb1 is a TMEM16A activator. In this work, we explored the activation mechanism of ginsenoside analogs on TMEM16A through analyzing the interactions between six ginsenoside analogs and TMEM16A. We identified GRg2 and GRf can directly activate TMEM16A by screening five novel ginsenosids analogs (GRb2, GRf, GRg2, GRh2, and NGR1). Isolated guinea pig ileum assay showed both GRg2 and GRf increased the amplitude and frequency of ileum contractions. We explored the molecular mechanisms of ginsenosides activating TMEM16A by combining molecular simulation with electrophysiological experiments. We proposed a TMEM16A activation process model based on the results, in which A697 on TM7 and L746 on TM8 bind to the isobutenyl of ginsenosides through hydrophobic interaction to fix the spatial location of ginsenosides. N650 on TM6 and E705 on TM7 bind to ginsenosides through electrostatic interaction, which causes the inner half of α-helix 6 to form physical contact with ginsenosides and leads to the pore opening. It should be emphasized that TMEM16A can be activated by ginsenosides only when both the above two conditions are satisfied. This is the first, to our knowledge, report of TMEM16A opening process activated by small-molecule activators. The mechanism of ginsenosides activating TMEM16A will provide important clues for TMEM16A gating mechanism and for new TMEM16A activators screening.

The multifaceted role of TMEM16A in cancer

The calcium-activated chloride channel TMEM16A is intimately linked to cancers. Over decades, TMEM16A over-expression and contribution to prognosis have been widely studied for multiple cancers strengthening the idea that TMEM16A could be a valuable biomarker and a promising therapeutic target. Surprisingly, from the survey of the literature, it appears that TMEM16A has been involved in multiple cancer-related functions and a large number of molecular targets of TMEM16A have been proposed. Thus, TMEM16A appears to be an ion channel with a multifaceted role in cancers. In this review, we summarize the latest development regarding TMEM16A contribution to cancers. We will survey TMEM16A contribution in cancer prognosis, the origins of its over-expression in cancer cells, the multiple biological functions and molecular pathways regulated by TMEM16A. Then, we will consider the question regarding the molecular mechanism of TMEM16A in cancers and the possible basis for the multifaceted role of TMEM16A in cancers.

Recent advances in TMEM16A: Structure, function, and disease

TMEM16A (also known as anoctamin 1, ANO1) is the molecular basis of the calcium-activated chloride channels, with ten transmembrane segments. Recently, atomic structures of the transmembrane domains of mouse TMEM16A (mTMEM16A) were determined by single-particle electron cryomicroscopy. This gives us a solid ground to discuss the electrophysiological properties and functions of TMEM16A. TMEM16A is reported to be dually regulated by Ca²⁺ and voltage. In addition, the dysfunction of TMEM16A has been found to be involved in many diseases including cystic fibrosis, various cancers, hypertension, and gastrointestinal motility disorders. TMEM16A is overexpressed in many cancers, including gastrointestinal stromal tumors, gastric cancer, head and neck squamous cell carcinoma (HNSCC), colon cancer, pancreatic ductal adenocarcinoma, and esophageal cancer. Furthermore, overexpression of TMEM16A is related to the occurrence, proliferation, and migration of tumor cells. To date, several studies have shown that many natural compounds and synthetic compounds have regulatory effects on TMEM16A. These small molecule compounds might be novel drugs for the treatment of diseases caused by TMEM16A dysfunction in the future. In addition, recent studies have shown that TMEM16A plays different roles in different diseases through different signal transduction pathways. This review discusses the topology, electrophysiological properties, modulators and functions of TMEM16A in mediates nociception, gastrointestinal dysfunction, hypertension, and cancer and focuses on multiple regulatory mechanisms regarding TMEM16A.

[Diltiazem inhibits proliferation and motility of hepatocellular cells in vitro by downregulating calcium-activated chloride channel TMEM16A]

OBJECTIVE

To assess the inhibitory effect of diltiazem, a calcium channel inhibitor, on the proliferation and mobility of human hepatocellular carcinoma cells in vitro and explore the possible mechanism.

METHODS

Two human hepatocellular carcinoma cell lines, MHCC97H and 7402, were treated with different concentrations (0-400 μmol/L) of diltiazem for 12, 24, or 48 h, and the changes in the cell proliferation and mobility were observed with MTT assay and wound healing assay, respectively. The changes in the expressions of calcium-activated chloride channel TMEM16A at mRNA and protein levels in the treated cells were detected using RT-PCR and immunocytochemistry.

RESULTS

Treatment with diltiazem obviously inhibited the proliferation and suppressed the mobility of MHCC97H and 7402 cells in a time- and concentration-dependent manner (P < 0.05). Treatment with 100 μmol/L diltiazem for 24 h significantly inhibited the proliferation of MHCC97H cells and down-regulated the mRNA and protein levels of TMEM16A. In 7402 cells, diltiazem treatment at 50 μmol/L for 48 h resulted in the most significant inhibitory effect on the cell proliferation and TMEM16A expressions.

CONCLUSIONS

Diltiazem can transiently inhibit the invasion of hepatocellular carcinoma cells in vitro possibly by down-regulating the expression of TMEM16A at both the mRNA and protein levels.

Natural and synthetic flavonoids, novel blockers of the volume-regulated anion channels, inhibit endothelial cell proliferation

Natural flavonoids are ubiquitous in dietary plants and vegetables and have been proposed to have antiviral, antioxidant, cardiovascular protective, and anticancer effects. Volume-regulated anion channels (VRACs), which are essential for cell volume regulation, have been proposed to play a key role in cell proliferation and migration, apoptosis, transepithelial transport, and cancer development. In this study, we screened a group of 53 structurally related natural flavonoids and three synthetic flavonoids for their inhibitory activities on VRAC currents. A whole-cell patch technique was used to record VRAC currents in the human embryonic kidney (HEK) 293 and human umbilical vein endothelial (HUVEC) cells. The 5'-bromo-2-deoxyuridine (BrdU) assay technique was used to investigate cell proliferation. At 100 μM, 34 of 53 compounds significantly inhibited hypotonic extrasolution-induced VRAC currents by > 50% in HEK293 cells. Among these compounds, luteolin, baicalein, eupatorin, galangin, quercetin, fisetin, karanjin, Dh-morin, genistein, irisolidone, and prunetin exhibited the highest efficacy for VRAC blockade (the mean inhibition > 80%) with IC₅₀s of 5-13 μM and E_maxs of about 87-99%. We also studied the effects of three synthetic flavonoids on VRAC currents in HEK293 cells. Flavoxate showed high inhibition efficacy toward VRAC currents (IC₅₀ = 2.3 ± 0.3 μM; E_max = 91.8% ± 2.7%). Finally, these flavonoids inhibited endogenous VRAC currents and cell proliferation in endothelial cells. This study demonstrates that natural and synthetic flavonoids are potent VRAC current inhibitors, and VRAC inhibition by flavonoids might be responsible for their anti-angiogenic effects.

Inhibition of transmembrane member 16A calcium-activated chloride channels by natural flavonoids contributes to flavonoid anticancer effects

BACKGROUND AND PURPOSE

Natural flavonoids are ubiquitous in dietary plants and vegetables and have been proposed to have antiviral, antioxidant, cardiovascular protective and anticancer effects. Transmembrane member 16A (TMEM16A)-encoded Ca²⁺ -activated Cl^- channels play a variety of physiological roles in many organs and tissues. Overexpression of TMEM16A is also believed to be associated with cancer progression. Therefore, inhibition of TMEM16A current may be a potential target for cancer therapy. In this study, we screened a broad spectrum of flavonoids for their inhibitory activities on TMEM16A currents.

EXPERIMENTAL APPROACH

A whole-cell patch technique was used to record the currents. The BrdU assay and transwell technique were used to investigate cell proliferation and migration.

KEY RESULTS

At a concentration of 100 μM, 10 of 20 compounds caused significant (>50%) inhibition of TMEM16A currents. The four most potent compounds - luteolin, galangin, quercetin and fisetin - had IC₅₀ values ranging from 4.5 to 15 μM). To examine the physiological relevance of these findings, we also studied the effects of these flavonoids on endogenous TMEM16A currents in addition to cell proliferation and migration in LA795 cancer cells. Among the flavonoids tested, we detected a highly significant correlation between TMEM16A current inhibition and cell proliferation or reduction of migration.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that flavonoids inhibit TMEM16A currents and suggests that flavonoids could have anticancer effects via this mechanism.