Drug Repurposing: The Anthelmintics Niclosamide and Nitazoxanide Are Potent TMEM16A Antagonists That Fully Bronchodilate Airways

TMEM16 proteins: Ca2+‑activated chloride channels and phospholipid scramblases as potential drug targets (Review)

TMEM16 proteins, which function as Ca2+‑activated Cl‑ channels are involved in regulating a wide variety of cellular pathways and functions. The modulators of Cl‑ channels can be used for the molecule‑based treatment of respiratory diseases, cystic fibrosis, tumors, cancer, osteoporosis and coronavirus disease 2019. The TMEM16 proteins link Ca2+ signaling, cellular electrical activity and lipid transport. Thus, deciphering these complex regulatory mechanisms may enable a more comprehensive understanding of the physiological functions of the TMEM16 proteins and assist in ascertaining the applicability of these proteins as potential pharmacological targets for the treatment of a range of diseases. The present review examined the structures, functions and characteristics of the different types of TMEM16 proteins, their association with the pathogenesis of various diseases and the applicability of TMEM16 modulator‑based treatment methods.

Protein nanoparticles induce the activation of voltage-dependent non-selective ion channels to modulate biological osmotic pressure in cytotoxic cerebral edema

Introduction

Cytotoxic cerebral edema is a serious complication associated with cerebral ischemic stroke and is widely treated using the hypertonic dehydrant. Here, we propose, for the first time, the decrease of intracellular osmosis as a treatment strategy for alleviating cytotoxic cerebral edema.

Methods

We established a fluorescence resonance energy transfer-based intermediate filament tension probe for the study and in situ evaluation of osmotic gradients, which were examined in real-time in living cells from primary cultures as well as cell lines. The MCAO rat model was used to confirm our therapy of cerebral edema.

Results

Depolymerization of microfilaments/microtubules and the production of NLRP3 inflammasome resulted in an abundance of protein nanoparticles (PNs) in the glutamate-induced swelling of astrocytes. PNs induced changes in membrane potential and intracellular second messengers, thereby contributing to hyper-osmosis and the resultant astrocyte swelling via the activation of voltage-dependent nonselective ion channels. Therefore, multiple inhibitors of PNs, sodium and chloride ion channels were screened as compound combinations, based on a decrease in cell osmosis and astrocyte swelling, which was followed by further confirmation of the effectiveness of the compound combination against alleviated cerebral edema after ischemia.

Discussion

The present study proposes new pathological mechanisms underlying "electrophysiology-biochemical signal-osmotic tension," which are responsible for cascade regulation in cerebral edema. It also explores various compound combinations as a potential treatment strategy for cerebral edema, which act by multi-targeting intracellular PNs and voltage-dependent nonselective ion flux to reduce astrocyte osmosis.

Niclosamide potentiates TMEM16A and induces vasoconstriction

The TMEM16A calcium-activated chloride channel is a promising therapeutic target for various diseases. Niclosamide, an anthelmintic medication, has been considered a TMEM16A inhibitor for treating asthma and chronic obstructive pulmonary disease (COPD) but was recently found to possess broad-spectrum off-target effects. Here, we show that, under physiological Ca2+ (200-500 nM) and voltages, niclosamide acutely potentiates TMEM16A. Our computational and functional characterizations pinpoint a putative niclosamide binding site on the extracellular side of TMEM16A. Mutations in this site attenuate the potentiation. Moreover, niclosamide potentiates endogenous TMEM16A in vascular smooth muscle cells, triggers intracellular calcium increase, and constricts the murine mesenteric artery. Our findings advise caution when considering clinical applications of niclosamide as a TMEM16A inhibitor. The identification of the putative niclosamide binding site provides insights into the mechanism of TMEM16A pharmacological modulation and provides insights into developing specific TMEM16A modulators to treat human diseases.

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.

Benzbromarone as adjuvant therapy for cystic fibrosis lung disease: a pilot clinical trial

OBJECTIVE

Cystic fibrosis (CF) affects multiple organs, the most severe consequences being observed in the lungs. Despite significant progress in developing CF transmembrane conductance regulator-specific treatments for CF lung disease, exploring alternative CF-targeted medications seems reasonable. We sought to evaluate the potential beneficial effects of oral benzbromarone as an adjuvant therapy in CF patients with reduced lung function.

METHODS

This was a prospective open-label pilot study of oral benzbromarone (100 mg/day) administered once daily for 90 days. Patients were followed at a tertiary referral center in southern Brazil. Safety was assessed by the number of reported adverse events. Secondary objectives included percent predicted FEV1 (FEV1%) and pulmonary exacerbations.

RESULTS

Ten patients were enrolled. Benzbromarone was found to be safe, with no serious drug-related adverse events. Eight patients completed the study; the median relative change in FEV1% tended to increase during the treatment, showing an 8% increase from baseline at the final visit. However, a nonparametric test showed that the change was not significant (p = 0.06). Of a total of ten patients, only one experienced at least one pulmonary exacerbation during the study.

CONCLUSIONS

Oral benzbromarone appears to be safe, and improved FEV1% has been observed in patients with CF. Further assessment in larger trials is warranted to elucidate whether oral benzbromarone can be a potential adjuvant therapy for CF.

The anoctamins: Structure and function

When activated by increase in intracellular Ca2+, anoctamins (TMEM16 proteins) operate as phospholipid scramblases and as ion channels. Anoctamin 1 (ANO1) is the Ca2+-activated epithelial anion-selective channel that is coexpressed together with the abundant scramblase ANO6 and additional intracellular anoctamins. In salivary and pancreatic glands, ANO1 is tightly packed in the apical membrane and secretes Cl-. Epithelia of airways and gut use cystic fibrosis transmembrane conductance regulator (CFTR) as an apical Cl- exit pathway while ANO1 supports Cl- secretion mainly by facilitating activation of luminal CFTR and basolateral K+ channels. Under healthy conditions ANO1 modulates intracellular Ca2+ signals by tethering the endoplasmic reticulum, and except of glands its direct secretory contribution as Cl- channel might be small, compared to CFTR. In the kidneys ANO1 supports proximal tubular acid secretion and protein reabsorption and probably helps to excrete HCO3-in the collecting duct epithelium. However, under pathological conditions as in polycystic kidney disease, ANO1 is strongly upregulated and may cause enhanced proliferation and cyst growth. Under pathological condition, ANO1 and ANO6 are upregulated and operate as secretory channel/phospholipid scramblases, partly by supporting Ca2+-dependent processes. Much less is known about the role of other epithelial anoctamins whose potential functions are discussed in this review.

Predicting lung exposure of intramuscular niclosamide as an antiviral agent: Power-law based pharmacokinetic modeling

Niclosamide, a potent anthelmintic agent, has emerged as a candidate against COVID-19 in recent studies. Its formulation has been investigated extensively to address challenges related to systemic exposure. In this study, niclosamide was formulated as a long-acting intramuscular injection to achieve systemic exposure in the lungs for combating the virus. To establish the dose-exposure relationship, a hamster model was selected, given its utility in previous COVID-19 infection studies. Pharmacokinetic (PK) analysis was performed using NONMEM and PsN. Hamsters were administered doses of 55, 96, 128, and 240 mg/kg with each group comprising five animals. Two types of PK models were developed, linear models incorporating partition coefficients and power-law distributed models, to characterize the relationship between drug concentrations in the plasma and lungs of the hamsters. Numerical and visual diagnostics, including basic goodness-of-fit and visual predictive checks, were employed to assess the models. The power-law-based PK model not only demonstrated superior numerical performance compared with the linear model but also exhibited better agreement in visual diagnostic evaluations. This phenomenon was attributed to the nonlinear relationship between drug concentrations in the plasma and lungs, reflecting kinetic heterogeneity. Dose optimization, based on predicting lung exposure, was conducted iteratively across different drug doses, with the minimum effective dose estimated to be ~1115 mg/kg. The development of a power-law-based PK model proved successful and effectively captured the nonlinearities observed in this study. This method is expected to be applicable for investigating the drug disposition of specific formulations in the lungs.

Inhibition of mucus secretion by niclosamide and benzbromarone in airways and intestine

The Ca2+ activated Cl- channel TMEM16A (anoctamin 1; ANO1) is expressed in secretory epithelial cells of airways and intestine. Previous studies provided evidence for a role of ANO1 in mucus secretion. In the present study we investigated the effects of the two ANO1-inhibitors niclosamide (Niclo) and benzbromarone (Benz) in vitro and in vivo in mouse models for cystic fibrosis (CF) and asthma. In human CF airway epithelial cells (CFBE), Ca2+ increase and activation of ANO1 by adenosine triphosphate (ATP) or ionomycin was strongly inhibited by 200 nM Niclo and 1 µM Benz. In asthmatic mice airway mucus secretion was inhibited by intratracheal instillation of Niclo or Benz. In homozygous F508del-cftr mice, intestinal mucus secretion and infiltration by CD45-positive cells was inhibited by intraperitoneal injection of Niclo (13 mg/kg/day for 7 days). In homozygous F508del-cftr rats intestinal mucus secretion was inhibited by oral application of Benz (5 mg/kg/day for 60 days). Taken together, well tolerated therapeutic concentrations of niclosamide and benzbromarone corresponding to plasma levels of treated patients, inhibit ANO1 and intracellular Ca2+ signals and may therefore be useful in inhibiting mucus hypersecretion and mucus obstruction in airways and intestine of patients suffering from asthma and CF, respectively.

Function and Regulation of the Calcium-Activated Chloride Channel Anoctamin 1 (TMEM16A)

Various human tissues express the calcium-activated chloride channel Anoctamin 1 (ANO1), also known as TMEM16A. ANO1 allows the passive chloride flux that controls different physiological functions ranging from muscle contraction, fluid and hormone secretion, gastrointestinal motility, and electrical excitability. Overexpression of ANO1 is associated with pathological conditions such as hypertension and cancer. The molecular cloning of ANO1 has led to a surge in structural, functional, and physiological studies of the channel in several tissues. ANO1 is a homodimer channel harboring two pores - one in each monomer - that work independently. Each pore is activated by voltage-dependent binding of two intracellular calcium ions to a high-affinity-binding site. In addition, the binding of phosphatidylinositol 4,5-bisphosphate to sites scattered throughout the cytosolic side of the protein aids the calcium activation process. Furthermore, many pharmacological studies have established ANO1 as a target of promising compounds that could treat several illnesses. This chapter describes our current understanding of the physiological roles of ANO1 and its regulation under physiological conditions as well as new pharmacological compounds with potential therapeutic applications.

Structure and Function of Calcium-Activated Chloride Channels and Phospholipid Scramblases in the TMEM16 Family

The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated chloride channels and phospholipid scramblases. Ten mammalian TMEM16 proteins, TMEM16A-K (with no TMEM16I), and several non-mammalian TMEM16 proteins, such as afTMEM16 and nhTMEM16, have been discovered. All known TMEM16 proteins are homodimeric proteins containing two subunits. Each subunit consists of ten transmembrane helices with Ca2+-binding sites and a single ion-permeation/phospholipid transport pathway. The ion-permeation pathway and the phospholipid transport pathway of TMEM16 proteins have a wide intracellular vestibule, a narrow neck, and a smaller extracellular vestibule. Interestingly, the lining wall of the ion-permeation/phospholipid transport pathway may be formed, at least partially, by membrane phospholipids, though the degree of pore-wall forming by phospholipids likely varies among TMEM16 proteins. Thus, the biophysical properties and activation mechanisms of TMEM16 proteins could differ from each other accordingly. Here we review the current understanding of the structure and function of TMEM16 molecules.

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.

Rare variants in ANO1, encoding a calcium-activated chloride channel, predispose to moyamoya disease

Moyamoya disease, a cerebrovascular disease leading to strokes in children and young adults, is characterized by progressive occlusion of the distal internal carotid arteries and the formation of collateral vessels. Altered genes play a prominent role in the aetiology of moyamoya disease, but a causative gene is not identified in the majority of cases. Exome sequencing data from 151 individuals from 84 unsolved families were analysed to identify further genes for moyamoya disease, then candidate genes assessed in additional cases (150 probands). Two families had the same rare variant in ANO1, which encodes a calcium-activated chloride channel, anoctamin-1. Haplotype analyses found the families were related, and ANO1 p.Met658Val segregated with moyamoya disease in the family with an LOD score of 3.3. Six additional ANO1 rare variants were identified in moyamoya disease families. The ANO1 rare variants were assessed using patch-clamp recordings, and the majority of variants, including ANO1 p.Met658Val, displayed increased sensitivity to intracellular Ca2+. Patients harbouring these gain-of-function ANO1 variants had classic features of moyamoya disease, but also had aneurysm, stenosis and/or occlusion in the posterior circulation. Our studies support that ANO1 gain-of-function pathogenic variants predispose to moyamoya disease and are associated with unique involvement of the posterior circulation.

Pathogenic Relationships in Cystic Fibrosis and Renal Diseases: CFTR, SLC26A9 and Anoctamins

The Cl--transporting proteins CFTR, SLC26A9, and anoctamin (ANO1; ANO6) appear to have more in common than initially suspected, as they all participate in the pathogenic process and clinical outcomes of airway and renal diseases. In the present review, we will therefore concentrate on recent findings concerning electrolyte transport in the airways and kidneys, and the role of CFTR, SLC26A9, and the anoctamins ANO1 and ANO6. Special emphasis will be placed on cystic fibrosis and asthma, as well as renal alkalosis and polycystic kidney disease. In essence, we will summarize recent evidence indicating that CFTR is the only relevant secretory Cl- channel in airways under basal (nonstimulated) conditions and after stimulation by secretagogues. Information is provided on the expressions of ANO1 and ANO6, which are important for the correct expression and function of CFTR. In addition, there is evidence that the Cl- transporter SLC26A9 expressed in the airways may have a reabsorptive rather than a Cl--secretory function. In the renal collecting ducts, bicarbonate secretion occurs through a synergistic action of CFTR and the Cl-/HCO3- transporter SLC26A4 (pendrin), which is probably supported by ANO1. Finally, in autosomal dominant polycystic kidney disease (ADPKD), the secretory function of CFTR in renal cyst formation may have been overestimated, whereas ANO1 and ANO6 have now been shown to be crucial in ADPKD and therefore represent new pharmacological targets for the treatment of polycystic kidney disease.

Identification of a drug binding pocket in TMEM16F calcium-activated ion channel and lipid scramblase

The dual functions of TMEM16F as Ca2+-activated ion channel and lipid scramblase raise intriguing questions regarding their molecular basis. Intrigued by the ability of the FDA-approved drug niclosamide to inhibit TMEM16F-dependent syncytia formation induced by SARS-CoV-2, we examined cryo-EM structures of TMEM16F with or without bound niclosamide or 1PBC, a known blocker of TMEM16A Ca2+-activated Cl- channel. Here, we report evidence for a lipid scrambling pathway along a groove harboring a lipid trail outside the ion permeation pore. This groove contains the binding pocket for niclosamide and 1PBC. Mutations of two residues in this groove specifically affect lipid scrambling. Whereas mutations of some residues in the binding pocket of niclosamide and 1PBC reduce their inhibition of TMEM16F-mediated Ca2+ influx and PS exposure, other mutations preferentially affect the ability of niclosamide and/or 1PBC to inhibit TMEM16F-mediated PS exposure, providing further support for separate pathways for ion permeation and lipid scrambling.

Niclosamide potentiates TMEM16A and induces vasoconstriction

The TMEM16A calcium-activated chloride channel is a promising therapeutic target for various diseases. Niclosamide, an anthelmintic medication, has been considered as a TMEM16A inhibitor for treating asthma and chronic obstructive pulmonary disease, but was recently found to possess broad-spectrum off-target effects. Here we show that, under physiological conditions, niclosamide acutely potentiates TMEM16A without having any inhibitory effect. Our computational and functional characterizations pinpoint a putative niclosamide binding site on the extracellular side of TMEM16A. Mutations in this site attenuate the potentiation. Moreover, niclosamide potentiates endogenous TMEM16A in vascular smooth muscle cells, triggers intracellular calcium increase, and constricts the murine mesenteric artery. Our findings advise caution when considering niclosamide as a TMEM16A inhibitor to treat diseases such as asthma, COPD, and hypertension. The identification of the putative niclosamide binding site provides insights into the mechanism of TMEM16A pharmacological modulation, shining light on developing specific TMEM16A modulators to treat human diseases.

Repurposing Niclosamide as a Novel Anti-SARS-CoV-2 Drug by Restricting Entry Protein CD147

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the global coronavirus disease 2019 (COVID-19) pandemic, and the search for effective treatments has been limited. Furthermore, the rapid mutations of SARS-CoV-2 have posed challenges to existing vaccines and neutralizing antibodies, as they struggle to keep up with the increased viral transmissibility and immune evasion. However, there is hope in targeting the CD147-spike protein, which serves as an alternative point for the entry of SARS-CoV-2 into host cells. This protein has emerged as a promising therapeutic target for the development of drugs against COVID-19. Here, we demonstrate that the RNA-binding protein Human-antigen R (HuR) plays a crucial role in the post-transcriptional regulation of CD147 by directly binding to its 3'-untranslated region (UTR). We observed a decrease in CD147 levels across multiple cell lines upon HuR depletion. Furthermore, we identified that niclosamide can reduce CD147 by lowering the cytoplasmic translocation of HuR and reducing CD147 glycosylation. Moreover, our investigation revealed that SARS-CoV-2 infection induces an upregulation of CD147 in ACE2-expressing A549 cells, which can be effectively neutralized by niclosamide in a dose-dependent manner. Overall, our study unveils a novel regulatory mechanism of regulating CD147 through HuR and suggests niclosamide as a promising therapeutic option against COVID-19.

A Novel Role of Uricosuric Agent Benzbromarone in BK Channel Activation and Reduction of Airway Smooth Muscle Contraction

The uricosuric drug benzbromarone, widely used for treatment of gout, hyperpolarizes the membrane potential of airway smooth muscle cells, but how it works remains unknown. Here we show a novel role of benzbromarone in activation of large conductance calcium-activated K⁺ channels. Benzbromarone results in dose-dependent activation of macroscopic big potassium (BK) currents about 1.7- to 14.5-fold with an EC₅₀ of 111 μM and shifts the voltage-dependent channel activation to a more hyperpolarizing direction about 10 to 54 mV in whole-cell patch clamp recordings. In single-channel recordings, benzbromarone decreases single BKα channel closed dwell time and increases the channel open probability. Coexpressing β1 subunit also enhances BK activation by benzbromarone with an EC₅₀ of 67 μM and a leftward shift of conductance-voltage (G-V) curve about 44 to 138 mV. Site-directed mutagenesis reveals that a motif of three amino acids ³²⁹RKK³³¹ in the cytoplasmic linker between S6 and C-terminal regulator of potassium conductance (RCK) gating ring mediates the pharmacological activation of BK channels by benzbromarone. Further ex vivo assay shows that benzbromarone causes reduction of tracheal strip contraction. Taken together, our findings demonstrate that uricosuric benzbromarone activates BK channels through molecular mechanism of action involving the channel RKK motif of S6-RCK linker. Pharmacological activation of BK channel by benzbromarone causes reduction of tracheal strip contraction, holding a repurposing potential for asthma and pulmonary arterial hypertension or BK channelopathies. SIGNIFICANCE STATEMENT: We describe a novel role of uricosuric agent benzbromarone in big potassium (BK) channel activation and relaxation of airway smooth muscle contraction. In this study, we find that benzbromarone is an activator of the large-conductance Ca²⁺- and voltage-activated K⁺ channel (BK channel), which serves numerous cellular functions, including control of smooth muscle contraction. Pharmacological activation of BK channel by the FDA-approved drug benzbromarone may hold repurposing potential for treatment of asthma and pulmonary arterial hypertension or BK channelopathies.

The TMEM16A blockers benzbromarone and MONNA cause intracellular Ca2+-release in mouse bronchial smooth muscle cells

We investigated effects of TMEM16A blockers benzbromarone, MONNA, CaCC_inhA01 and Ani9 on isometric contractions in mouse bronchial rings and on intracellular calcium in isolated bronchial myocytes. Separate concentrations of carbachol (0.1-10 μM) were applied for 10 min periods to bronchial rings, producing concentration-dependent contractions that were well maintained throughout each application period. Benzbromarone (1 μM) markedly reduced the contractions with a more pronounced effect on their sustained component (at 10 min) compared to their initial component (at 2 min). Iberiotoxin (0.3 μM) enhanced the contractions, but they were still blocked by benzbromarone. MONNA (3 μM) and CaCC_inhA01 (10 μM) had similar effects to benzbromarone, but were less potent. In contrast, Ani9 (10 μM) had no effect on carbachol-induced contractions. Confocal imaging revealed that benzbromarone (0.3 μM), MONNA (1 μM) and CaCC_inhA01 (10 μM) increased intracellular calcium in isolated myocytes loaded with Fluo-4AM. In contrast, Ani9 (10 μM) had no effect on intracellular calcium. Benzbromarone and MONNA also increased calcium in calcium-free extracellular solution, but failed to do so when intracellular stores were discharged with caffeine (10 mM). Caffeine was unable to cause further discharge of the store when applied in the presence of benzbromarone. Ryanodine (100 μM) blocked the ability of benzbromarone (0.3 μM) to increase calcium, while tetracaine (100 μM) reversibly reduced the rise in calcium induced by benzbromarone. We conclude that benzbromarone and MONNA caused intracellular calcium release, probably by opening ryanodine receptors. Their ability to block carbachol contractions was likely due to this off-target effect.

Analysis of inhibitors of the anoctamin-1 chloride channel (transmembrane member 16A, TMEM16A) reveals indirect mechanisms involving alterations in calcium signalling

BACKGROUND AND PURPOSE

Pharmacological inhibitors of TMEM16A (ANO1), a Ca²⁺ -activated Cl^- channel, are important tools of research and possible therapeutic agents acting on smooth muscle, airway epithelia and cancer cells. We tested a panel of TMEM16A inhibitors, including CaCC_inh -A01, niclosamide, MONNA, Ani9 and niflumic acid, to evaluate their possible effect on intracellular Ca²⁺ .

EXPERIMENTAL APPROACH

We recorded cytosolic Ca²⁺ increase elicited with UTP, ionomycin or IP₃ uncaging.

KEY RESULTS

Unexpectedly, we found that all compounds, except for Ani9, markedly decreased intracellular Ca²⁺ elevation induced by stimuli acting on intracellular Ca²⁺ stores. These effects were similarly observed in cells with and without TMEM16A expression. We investigated in more detail the mechanism of action of niclosamide and CaCC_inh -A01. Acute addition of niclosamide directly increased intracellular Ca²⁺ , an activity consistent with inhibition of the SERCA pump. In contrast to niclosamide, CaCC_inh -A01 did not elevate intracellular Ca²⁺ , thus implying a different mechanism of action, possibly a block of inositol triphosphate receptors.

CONCLUSIONS AND IMPLICATIONS

Most TMEM16A inhibitors are endowed with indirect effects mediated by alteration of intracellular Ca²⁺ handling, which may in part preclude their use as TMEM16A research tools.

Solithromycin inhibits IL-13-induced goblet cell hyperplasia and MUC5AC, CLCA1, and ANO1 in human bronchial epithelial cells

Solithromycin is a novel fluoroketolide antibiotic belonging to the class of macrolide antibiotics. Activation of the interleukin (IL)-13 receptor leads to STAT6 activation and subsequent induction of SAM pointed domain containing ETS transcription factor (SPDEF), chloride channel accessory 1 (CLCA1), and anoctamin-1 (ANO1), all of which are associated with the induction of MUC5AC. We examined the effects of solithromycin on mucin production led by IL-13 signaling. Normal human bronchial epithelial cells were grown at the air-liquid interface with IL-13 with/without solithromycin for 14 days. Histochemical analysis was performed using hematoxylin and eosin staining and MUC5AC immunostaining. MUC5AC, SPDEF, CLCA1, and ANO1 mRNA expressions were examined using real-time polymerase chain reaction. Western blot analysis was performed to assess CLCA1 and ANO1 proteins, and phosphorylation of STAT6 and ERK. Solithromycin attenuated IL-13 induction of goblet cell hyperplasia and MUC5AC, CLCA1 and ANO1 mRNA and protein expression induced by IL-13, but had no effect on the phosphorylation of STAT6 and ERK. Our results indicate that solithromycin could attenuate goblet cell hyperplasia and MUC5AC induced by IL-13 through inhibition of CLCA1 and ANO1 mRNA and protein expression. However, much more information is required to clarify the molecular mechanisms underlying the inhibition of CLCA1 and ANO1 by solithromycin.

SARS-CoV-2 Spike protein activates TMEM16F-mediated platelet procoagulant activity

Thrombosis of the lung microvasculature is a characteristic of COVID-19 disease, which is observed in large excess compared to other forms of acute respiratory distress syndrome and thus suggests a trigger for thrombosis that is endogenous to the lung. Our recent work has shown that the SARS-CoV-2 Spike protein activates the cellular TMEM16F chloride channel and scramblase. Through a screening on >3,000 FDA/EMA approved drugs, we identified Niclosamide and Clofazimine as the most effective molecules at inhibiting Spike-induced TMEM16 activation. As TMEM16F plays an important role in stimulating the procoagulant activity of platelets, we investigated whether Spike directly affects platelet activation and pro-thrombotic function and tested the effect of Niclosamide and Clofazimine on these processes. Here we show that Spike, present either on the virion envelope or on the cell plasma membrane, promotes platelet activation, adhesion and spreading. Spike was active as a sole agonist or, even more effectively, by enhancing the function of known platelet activators. In particular, Spike-induced a marked procoagulant phenotype in platelets, by enhancing Ca²⁺ flux, phosphatidylserine externalization on the platelet outer cell membrane, and thrombin generation. Eventually, this increased thrombin-induced clot formation and retraction. Both Niclosamide and Clofazimine blocked this Spike-induced procoagulant response. These findings provide a pathogenic mechanism to explain lung thrombosis-associated with severe COVID-19 infection. We propose that Spike, present in SARS-CoV-2 virions or exposed on the surface of infected cells in the lungs, enhances the effects of inflammation and leads to local platelet stimulation and subsequent activation of the coagulation cascade. As platelet TMEM16F is central in this process, these findings reinforce the rationale of repurposing Niclosamide for COVID-19 therapy.

Niclosamide does not modulate airway epithelial function through blocking of the calcium activated chloride channel, TMEM16A

Niclosamide and benzbromarone have been described as inhibitors of the calcium activated chloride channel, TMEM16A, and on this basis have been considered and tested as clinical candidates for the treatment of airway diseases. However, both compounds have previously demonstrated activity on a range of additional biological targets and it is unclear from the literature to what extent any activity on TMEM16A may contribute to efficacy in these models of airway disease. The aim of the present study was therefore to examine the pharmacology and selectivity of these clinical candidates together with a structurally unrelated TMEM16A blocker, Ani9, in a range of functional assays to better appreciate the putative role of TMEM16A in the regulation of both epithelial ion transport and the development of an airway epithelial mucus secretory phenoptype. Benzbromarone and Ani9 both attenuated recombinant TMEM16A activity in patch clamp studies, whereas in contrast, niclosamide induced a paradoxical potentiation of the TMEM16A-mediated current. Niclosamide and benzbromarone were also demonstrated to attenuate receptor-dependent increases in intracellular Ca²⁺ levels ([Ca²⁺]_i) which likely contributed to their concomitant attenuation of the Ca²⁺-stimulated short-circuit current responses of FRT-TMEM16A and primary human bronchial epithelial (HBE) cells. In contrast, Ani9 attenuated the Ca²⁺-stimulated short-circuit current responses of both cell systems without influencing [Ca²⁺]_i which supports a true channel blocking mechanism for this compound. Additional studies using HBE cells revealed effects of both niclosamide and benzbromarone on global ion transport processes (absorptive and secretory) as well as signs of toxicity (elevated LDH levels, loss of transepithelial resistance) that were not shared by Ani9. Ani9 also failed to influence the IL-13 induced differentiation of HBE towards a goblet cell rich, mucus hypersecreting epithelium, whereas niclosamide and benzbromarone attenuated numbers of both goblet and multiciliated cells, that would be consistent with cellular toxicity. Together these data challenge the description of niclosamide as a TMEM16A blocker and illustrate a range of off-target effects of both niclosamide and benzbromarone which may contribute to the reported activity in models of airway function.

Extraction of niclosamide from commercial approved tablets into aqueous buffered solution creates potentially approvable oral and nasal sprays against COVID-19 and other respiratory infections

Motivation

The low solubility, weak acid drug, niclosamide is a host cell modulator with broad-spectrum anti-viral cell-activity against many viruses, including stopping the SARS-CoV-2 virus from infecting cells in cell culture. As a result, a simple universal nasal spray preventative was proposed and investigated in earlier work regarding the dissolution of niclosamide into simple buffers. However, starting with pharmaceutical grade, niclosamide represents a new 505(b)(2) application. The motivation for this second paper in the series was therefore to explore if and to what extent niclosamide could be extracted from commercially available and regulatory-approved niclosamide oral tablets that could serve as a preventative nasal spray and an early treatment oral/throat spray, with possibly more expeditious testing and regulatory approval.

Experimental

Measurements of supernatant niclosamide concentrations were made by calibrated UV-Vis for the dissolution of niclosamide from commercially available Yomesan crushed into a powder for dissolution into Tris Buffer (TB) solutions. Parameters tested were as follows: time (0-2 days), concentration (300 µM to -1 mM), pH (7.41 to 9.35), and anhydrous/hydrated state. Optical microscopy was used to view the morphologies of the initial crushed powder, and the dissolving and equilibrating undissolved excess particles to detect morphologic changes that might occur.

Results

Concentration dependence: Niclosamide was readily extracted from powdered Yomesan at pH 9.34 TB at starting Yomesan niclosamide equivalents concentrations of 300 µM, 600 µM, and 1 mM. Peak dissolved niclosamide supernatant concentrations of 264 µM, 216 µM, and 172 µM were achieved in 1 h, 1 h, and 3 h respectively. These peaks though were followed by a reduction in supernatant concentration to an average of 112.3 µM ± 28.4 µM after overnight stir on day 2. pH dependence: For nominal pHs of 7.41, 8.35, 8.85, and 9.35, peak niclosamide concentrations were 4 µM, 22.4 µM, 96.2 µM, and 215.8 µM, respectively. Similarly, the day 2 values all reduced to 3 µM, 12.9 µM, 35.1 µM, and 112.3 µM. A heat-treatment to 200 °C dehydrated the niclosamide and showed a high 3 h concentration (262 µM) and the least day-2 reduction (to 229 µM). This indicated that the presence, or formation during exposure to buffer, of lower solubility polymorphs was responsible for the reductions in total solubilities. These morphologic changes were confirmed by optical microscopy that showed initially featureless particulate-aggregates of niclosamide could grow multiple needle-shaped crystals and form needle masses, especially in the presence of Tris-buffered sodium chloride, where new red needles were rapidly made. Scale up: A scaled-up 1 L solution of niclosamide was made achieving 165 µM supernatant niclosamide in 3 h by dissolution of just one fifth (100 mg niclosamide) of a Yomesan tablet.

Conclusion

These comprehensive results provide a guide as to how to utilize commercially available and approved tablets of niclosamide to generate aqueous niclosamide solutions from a simple dissolution protocol. As shown here, just one 4-tablet pack of Yomesan could readily make 165 L of a 20 µM niclosamide solution giving 16,500 10 mL bottles. One million bottles, from just 60 packs of Yomesan, would provide 100 million single spray doses for distribution to mitigate a host of respiratory infections as a universal preventative-nasal and early treatment oral/throat sprays throughout the world.

Graphical Abstract

pH dependence of niclosamide extraction from crushed Yomesan tablet material into Tris buffer (yellow-green in vial) and Tris-buffered saline solution (orange-red in vial). Initial anhydrous dissolution concentration is reduced by overnight stirring to likely monohydrate niclosamide; and is even lower if in TBSS forming new niclosamide sodium needle crystals grown from the original particles.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41120-023-00072-x.

Translational potential of targeting Anoctamin-1-Encoded Calcium-Activated chloride channels in hypertension

Calcium-activated chloride channels (CaCC) provide a depolarizing stimulus to a variety of tissues through chloride efflux in response to a rise in internal Ca²⁺ and voltage. One of these channels, Anoctamin-1 (ANO1 or TMEM16A) is now recognized to play a central role in promoting smooth muscle tone in various types of blood vessels. Its role in hypertension, and thus the therapeutic promise of targeting ANO1, is less straightforward. This review gives an overview of our current knowledge about the potential role ANO1 may play in hypertension within the systemic, portal, and pulmonary vascular systems and the importance of this information when pursuing potential treatment strategies. While the role of ANO1 is well-established in several forms of pulmonary hypertension, its contributions to both the generation of vascular tone and its role in hypertension within the systemic and portal systems are much less clear. This, combined with ANO1's various roles throughout a multitude of tissues throughout the body, command caution when targeting ANO1 as a therapeutic target and may require tissue-selective strategies.

Anoctamins and Calcium Signalling: An Obstacle to EGFR Targeted Therapy in Glioblastoma?

Glioblastoma is the most common form of high-grade glioma in adults and has a poor survival rate with very limited treatment options. There have been no significant advancements in glioblastoma treatment in over 30 years. Epidermal growth factor receptor is upregulated in most glioblastoma tumours and, therefore, has been a drug target in recent targeted therapy clinical trials. However, while many inhibitors and antibodies for epidermal growth factor receptor have demonstrated promising anti-tumour effects in preclinical models, they have failed to improve outcomes for glioblastoma patients in clinical trials. This is likely due to the highly plastic nature of glioblastoma tumours, which results in therapeutic resistance. Ion channels are instrumental in the development of many cancers and may regulate cellular plasticity in glioblastoma. This review will explore the potential involvement of a class of calcium-activated chloride channels called anoctamins in brain cancer. We will also discuss the integrated role of calcium channels and anoctamins in regulating calcium-mediated signalling pathways, such as epidermal growth factor signalling, to promote brain cancer cell growth and migration.

Nitazoxanide and COVID-19: A review

Coronavirus disease 2019 (COVID-19) is a current global illness triggered by severe acute respiratory coronavirus 2 (SARS-CoV-2) leading to acute viral pneumonia, acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and cytokine storm in severe cases. In the COVID-19 era, different unexpected old drugs are repurposed to find out effective and cheap therapies against SARS-CoV-2. One of these elected drugs is nitazoxanide (NTZ) which is an anti-parasitic drug with potent antiviral activity. It is effectively used in the treatment of protozoa and various types of helminths in addition to various viral infections. Thus, we aimed to elucidate the probable effect of NTZ on SARS-CoV-2 infections. Findings of the present study illustrated that NTZ can reduce SARS-CoV-2-induced inflammatory reactions through activation of interferon (IFN), restoration of innate immunity, inhibition of the release of pro-inflammatory cytokines, suppression of the mammalian target of rapamycin (mTOR), and induction of autophagic cell death. Moreover, it can inhibit the induction of oxidative stress which causes cytokine storm and is associated with ALI, ARDS, and multi-organ damage (MOD). This study concluded that NTZ has important anti-inflammatory and immunological properties that may mitigate SARS-CoV-2 infection-induced inflammatory disorders. Despite broad-spectrum antiviral properties of NTZ, the direct anti-SARS-CoV-2 effect was not evident and documented in recent studies. Then, in silico and in vitro studies in addition to clinical trials and prospective studies are needed to confirm the beneficial impact of NTZ on the pathogenesis of SARS-CoV-2 infection.

Paneth Cell Secretion in vivo Requires Expression of Tmem16a and Tmem16f

Background and Aims

Paneth cells play a central role in intestinal innate immune response. These cells are localized at the base of small intestinal crypts of Lieberkuhn. The calcium-activated chloride channel TMEM16A and the phospholipid scramblase TMEM16F control intracellular Ca2+ signaling and exocytosis. We analyzed the role of TMEM16A and TMEM16F for Paneth cells secretion.

Methods

Mice with intestinal epithelial knockout of Tmem16a (Tmem16a-/-) and Tmem16f (Tmem16f-/-) were generated. Tissue structures and Paneth cells were analyzed, and Paneth cell exocytosis was examined in small intestinal organoids in vitro. Intracellular Ca2+ signals were measured and were compared between wild-type and Tmem16 knockout mice. Bacterial colonization and intestinal apoptosis were analyzed.

Results

Paneth cells in the crypts of Lieberkuhn from Tmem16a-/- and Tmem16f-/- mice demonstrated accumulation of lysozyme. Tmem16a and Tmem16f were localized in wild-type Paneth cells but were absent in cells from knockout animals. Paneth cell number and size were enhanced in the crypt base and mucus accumulated in intestinal goblet cells of knockout animals. Granule fusion and exocytosis on cholinergic and purinergic stimulation were examined online. Both were strongly compromised in the absence of Tmem16a or Tmem16f and were also blocked by inhibition of Tmem16a/f. Purinergic Ca2+ signaling was largely inhibited in Tmem16a knockout mice. Jejunal bacterial content was enhanced in knockout mice, whereas cellular apoptosis was inhibited.

Conclusion

The present data demonstrate the role of Tmem16 for exocytosis in Paneth cells. Inhibition or activation of Tmem16a/f is likely to affect microbial content and immune functions present in the small intestine.

The pharmacology of the TMEM16A channel: therapeutic opportunities

The TMEM16A Ca²⁺-gated Cl^- channel is involved in a variety of vital physiological functions and may be targeted pharmacologically for therapeutic benefit in diseases such as hypertension, stroke, and cystic fibrosis (CF). The determination of the TMEM16A structure and high-throughput screening efforts, alongside ex vivo and in vivo animal studies and clinical investigations, are hastening our understanding of the physiology and pharmacology of this channel. Here, we offer a critical analysis of recent developments in TMEM16A pharmacology and reflect on the therapeutic opportunities provided by this target.

Niclosamide-A promising treatment for COVID-19

Vaccines have reduced the transmission and severity of COVID-19, but there remains a paucity of efficacious treatment for drug-resistant strains and more susceptible individuals, particularly those who mount a suboptimal vaccine response, either due to underlying health conditions or concomitant therapies. Repurposing existing drugs is a timely, safe and scientifically robust method for treating pandemics, such as COVID-19. Here, we review the pharmacology and scientific rationale for repurposing niclosamide, an anti-helminth already in human use as a treatment for COVID-19. In addition, its potent antiviral activity, niclosamide has shown pleiotropic anti-inflammatory, antibacterial, bronchodilatory and anticancer effects in numerous preclinical and early clinical studies. The advantages and rationale for nebulized and intranasal formulations of niclosamide, which target the site of the primary infection in COVID-19, are reviewed. Finally, we give an overview of ongoing clinical trials investigating niclosamide as a promising candidate against SARS-CoV-2.

Antiparasitic Drugs against SARS-CoV-2: A Comprehensive Literature Survey

More than two years have passed since the viral outbreak that led to the novel infectious respiratory disease COVID-19, caused by the SARS-CoV-2 coronavirus. Since then, the urgency for effective treatments resulted in unprecedented efforts to develop new vaccines and to accelerate the drug discovery pipeline, mainly through the repurposing of well-known compounds with broad antiviral effects. In particular, antiparasitic drugs historically used against human infections due to protozoa or helminth parasites have entered the main stage as a miracle cure in the fight against SARS-CoV-2. Despite having demonstrated promising anti-SARS-CoV-2 activities in vitro, conflicting results have made their translation into clinical practice more difficult than expected. Since many studies involving antiparasitic drugs are currently under investigation, the window of opportunity might be not closed yet. Here, we will review the (controversial) journey of these old antiparasitic drugs to combat the human infection caused by the novel coronavirus SARS-CoV-2.

TMEM16A blockers T16Ainh-A01 and benzbromarone do not modulate the regulation of sweating and cutaneous vasodilatation in humans in vivo

NEW FINDINGS

What is the central question of this study? Do transmembrane member 16A (TMEM16A) blockers modulate the activation of heat loss responses of sweating and cutaneous vasodilatation? What are the main finding and its importance? Relative to the vehicle control site, TMEM16A blockers T16Ainh-A01 and benzbromarone had no effect on sweat rate or cutaneous vascular conductance during whole-body heating inducing a 1.1 ± 0.1°C increase in core temperature above baseline resting levels. These results suggest that TMEM16A blockers T16Ainh-A01 and benzbromarone do not modulate the regulation of sweating and cutaneous vasodilatation during whole-body heat stress.

ABSTRACT

Animal and in vitro studies suggest that transmembrane member 16A (TMEM16A), a Ca²⁺ -activated Cl^- channel, contributes to regulating eccrine sweating. However, direct evidence supporting this possibility in humans is lacking. We assessed the hypothesis that TMEM16A blockers attenuate sweating during whole-body heating in humans. Additionally, we assessed the associated changes in the heat loss response of cutaneous vasodilatation to determine if a functional role of TMEM16A may exist. Twelve young (24 ± 2 years) adults (six females) underwent whole-body heating using a water-perfused suit to raise core temperature 1.1 ± 0.1°C above baseline. Sweat rate and cutaneous vascular conductance (normalized to maximal conductance via administration of sodium nitroprusside) were evaluated continuously at four forearm skin sites treated continuously by intradermal microdialysis with (1) lactated Ringer's solution (control), (2) 5% dimethyl sulfoxide (DMSO) serving as a vehicle control, or (3) TMEM16A blockers 1 mM T16Ainh-A01 or 2 mM benzbromarone dissolved in 5% DMSO solution. All drugs were administered continuously via intradermal microdialysis. Whole-body heating increased core temperature progressively and this was paralleled by an increase in sweat rate and cutaneous vascular conductance at all skin sites. However, sweat rate (all P > 0.318) and cutaneous vascular conductance (all P ≥ 0.073) did not differ between the vehicle control site relative to the TMEM16A blocker-treated sites. Collectively, our findings indicate that TMEM16A blockers T16Ainh-A01 and benzbromarone do not modulate the regulation of sweating and cutaneous vasodilatation during whole-body heating in young adults in vivo.

TMEM16A as a potential treatment target for head and neck cancer

Transmembrane protein 16A (TMEM16A) forms a plasma membrane-localized Ca²⁺-activated Cl- channel. Its gene has been mapped to an area on chromosome 11q13, which is amplified in head and neck squamous cell carcinoma (HNSCC). In HNSCC, TMEM16A overexpression is associated with not only high tumor grade, metastasis, low survival, and poor prognosis, but also deterioration of clinical outcomes following platinum-based chemotherapy. Recent study revealed the interaction between TMEM16A and transforming growth factor-β (TGF-β) has an indirect crosstalk in clarifying the mechanism of TMEM16A-induced epithelial-mesenchymal transition. Moreover, human papillomavirus (HPV) infection can modulate TMEM16A expression along with epidermal growth factor receptor (EGFR), whose phosphorylation has been reported as a potential co-biomarker of HPV-positive cancers. Considering that EGFR forms a functional complex with TMEM16A and is a co-biomarker of HPV, there may be crosstalk between TMEM16A expression and HPV-induced HNSCC. EGFR activation can induce programmed death ligand 1 (PD-L1) synthesis via activation of the nuclear factor kappa B pathway and JAK/STAT3 pathway. Here, we describe an interplay among EGFR, PD-L1, and TMEM16A. Combination therapy using TMEM16A and PD-L1 inhibitors may improve the survival rate of HNSCC patients, especially those resistant to anti-EGFR inhibitor treatment. To the best of our knowledge, this is the first review to propose a biological validation that combines immune checkpoint inhibition with TMEM16A inhibition.

Inhibition mechanism of the chloride channel TMEM16A by the pore blocker 1PBC

TMEM16A, a calcium-activated chloride channel involved in multiple cellular processes, is a proposed target for diseases such as hypertension, asthma, and cystic fibrosis. Despite these therapeutic promises, its pharmacology remains poorly understood. Here, we present a cryo-EM structure of TMEM16A in complex with the channel blocker 1PBC and a detailed functional analysis of its inhibition mechanism. A pocket located external to the neck region of the hourglass-shaped pore is responsible for open-channel block by 1PBC and presumably also by its structural analogs. The binding of the blocker stabilizes an open-like conformation of the channel that involves a rearrangement of several pore helices. The expansion of the outer pore enhances blocker sensitivity and enables 1PBC to bind at a site within the transmembrane electric field. Our results define the mechanism of inhibition and gating and will facilitate the design of new, potent TMEM16A modulators.

Role of ANO1 in tumors and tumor immunity

Dysregulation of gene amplification, cell-signaling-pathway transduction, epigenetic and transcriptional regulation, and protein interactions drives tumor-cell proliferation and invasion, while ion channels also play an important role in the generation and development of tumor cells. Overexpression of Ca²⁺-activated Cl- channel anoctamin 1 (ANO1) is shown in numerous cancer types and correlates with poor prognosis. However, the mechanisms involved in ANO1-mediated malignant cellular transformation and the role of ANO1 in tumor immunity remain unknown. In this review, we discuss recent studies to determine the role of ANO1 in tumorigenesis and provide novel insights into the role of ANO1 in the context of tumor immunity. Furthermore, we analyze the roles and potential mechanisms of ANO1 in different types of cancers, and provide novel notions for the role of ANO1 in the tumor microenvironment and for potential use of ANO1 in clinical applications. Our review shows that ANO1 is involved in tumor immunity and microenvironment, and may, therefore, be an effective biomarker and therapeutic drug target.

Can anti-parasitic drugs help control COVID-19?

Novel COVID-19 is a public health emergency that poses a serious threat to people worldwide. Given the virus spreading so quickly, novel antiviral medications are desperately needed. Repurposing existing drugs is the first strategy. Anti-parasitic drugs were among the first to be considered as a potential treatment option for this disease. Even though many papers have discussed the efficacy of various anti-parasitic drugs in treating COVID-19 separately, so far, no single study comprehensively discussed these drugs. This study reviews some anti-parasitic recommended drugs to treat COVID-19, in terms of function and in vitro as well as clinical results. Finally, we briefly review the advanced techniques, such as artificial intelligence, that have been used to find effective drugs for the treatment of COVID-19.

Autosomal Dominant Polycystic Kidney Disease: From Pathophysiology of Cystogenesis to Advances in the Treatment

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, with an estimated prevalence between 1:1000 and 1:2500. It is mostly caused by mutations of the PKD1 and PKD2 genes encoding polycystin 1 (PC1) and polycystin 2 (PC2) that regulate cellular processes such as fluid transport, differentiation, proliferation, apoptosis and cell adhesion. Reduction of calcium ions and induction of cyclic adenosine monophosphate (sAMP) promote cyst enlargement by transepithelial fluid secretion and cell proliferation. Abnormal activation of MAPK/ERK pathway, dysregulated signaling of heterotrimeric G proteins, mTOR, phosphoinositide 3-kinase, AMPK, JAK/STAT activator of transcription and nuclear factor kB (NF-kB) are involved in cystogenesis. Another feature of cystic tissue is increased extracellular production and recruitment of inflammatory cells and abnormal connections among cells. Moreover, metabolic alterations in cystic cells including defective glucose metabolism, impaired beta-oxidation and abnormal mitochondrial activity were shown to be associated with cyst expansion. Although tolvaptan has been recently approved as a drug that slows ADPKD progression, some patients do not tolerate tolvaptan because of frequent aquaretic. The advances in the knowledge of multiple molecular pathways involved in cystogenesis led to the development of animal and cellular studies, followed by the development of several ongoing randomized controlled trials with promising drugs. Our review is aimed at pathophysiological mechanisms in cystogenesis in connection with the most promising drugs in animal and clinical studies.

An Open Label, Adaptive, Phase 1 Trial of High-Dose Oral Nitazoxanide in Healthy Volunteers: An Antiviral Candidate for SARS-CoV-2

Repurposing approved drugs may rapidly establish effective interventions during a public health crisis. This has yielded immunomodulatory treatments for severe coronavirus disease 2019 (COVID-19), but repurposed antivirals have not been successful to date because of redundancy of the target in vivo or suboptimal exposures at studied doses. Nitazoxanide is a US Food and Drug Administration (FDA) approved antiparasitic medicine, that physiologically-based pharmacokinetic (PBPK) modeling has indicated may provide antiviral concentrations across the dosing interval, when repurposed at higher than approved doses. Within the AGILE trial platform (NCT04746183) an open label, adaptive, phase I trial in healthy adult participants was undertaken with high-dose nitazoxanide. Participants received 1,500 mg nitazoxanide orally twice-daily with food for 7 days. Primary outcomes were safety, tolerability, optimum dose, and schedule. Intensive pharmacokinetic (PK) sampling was undertaken day 1 and 5 with minimum concentration (Cmin ) sampling on days 3 and 7. Fourteen healthy participants were enrolled between February 18 and May 11, 2021. All 14 doses were completed by 10 of 14 participants. Nitazoxanide was safe and with no significant adverse events. Moderate gastrointestinal disturbance (loose stools or diarrhea) occurred in 8 participants (57.1%), with urine and sclera discoloration in 12 (85.7%) and 9 (64.3%) participants, respectively, without clinically significant bilirubin elevation. This was self-limiting and resolved upon drug discontinuation. PBPK predictions were confirmed on day 1 but with underprediction at day 5. Median Cmin was above the in vitro target concentration on the first dose and maintained throughout. Nitazoxanide administered at 1,500 mg b.i.d. with food was safe with acceptable tolerability a phase Ib/IIa study is now being initiated in patients with COVID-19.

Identification of a conserved drug binding pocket in TMEM16 proteins

The TMEM16 family of calcium-activated membrane proteins includes ten mammalian paralogs (TMEM16A-K) playing distinct physiological roles with some implicated in cancer and airway diseases. Their modulators with therapeutic potential include 1PBC, a potent inhibitor with anti-tumoral properties, and the FDA-approved drug niclosamide that targets TMEM16F to inhibit syncytia formation induced by SARS-CoV-2 infection. Here, we report cryo-EM structures of TMEM16F associated with 1PBC and niclosamide, revealing that both molecules bind the same drug binding pocket. We functionally and computationally validate this binding pocket in TMEM16A as well as TMEM16F, thereby showing that drug modulation also involves residues that are not conserved between TMEM16A and TMEM16F. This study establishes a much-needed structural framework for the development of more potent and more specific drug molecules targeting TMEM16 proteins.

The oral drug nitazoxanide restricts SARS-CoV-2 infection and attenuates disease pathogenesis in Syrian hamsters

A well-tolerated and cost-effective oral drug that blocks SARS-CoV-2 growth and dissemination would be a major advance in the global effort to reduce COVID-19 morbidity and mortality. Here, we show that the oral FDA-approved drug nitazoxanide (NTZ) significantly inhibits SARS-CoV-2 viral replication and infection in different primate and human cell models including stem cell-derived human alveolar epithelial type 2 cells. Furthermore, NTZ synergizes with remdesivir, and it broadly inhibits growth of SARS-CoV-2 variants B.1.351 (beta), P.1 (gamma), and B.1617.2 (delta) and viral syncytia formation driven by their spike proteins. Strikingly, oral NTZ treatment of Syrian hamsters significantly inhibits SARS-CoV-2-driven weight loss, inflammation, and viral dissemination and syncytia formation in the lungs. These studies show that NTZ is a novel host-directed therapeutic that broadly inhibits SARS-CoV-2 dissemination and pathogenesis in human and hamster physiological models, which supports further testing and optimization of NTZ-based therapy for SARS-CoV-2 infection alone and in combination with antiviral drugs.

Efficacy of Niclosamide vs Placebo in SARS-CoV-2 Respiratory Viral Clearance, Viral Shedding, and Duration of Symptoms Among Patients With Mild to Moderate COVID-19: A Phase 2 Randomized Clinical Trial

IMPORTANCE

Oral anthelmintic niclosamide has potent in vitro antiviral activity against SARS-CoV-2. Repurposed niclosamide could be a safe and efficacious COVID-19 therapy.

OBJECTIVE

To investigate whether niclosamide decreased SARS-CoV-2 shedding and duration of symptoms among patients with mild to moderate COVID-19.

DESIGN, SETTING, AND PARTICIPANTS

This randomized, placebo-controlled clinical trial enrolled individuals testing positive for SARS-CoV-2 by polymerase chain reaction with mild to moderate symptoms of COVID. All trial participants, investigators, staff, and laboratory personnel were kept blind to participant assignments. Enrollment was among individuals reporting at Tufts Medical Center and Wellforce Network in Massachusetts for outpatient COVID-19 testing. The trial opened to accrual on October 1, 2020; the last participant enrolled on April 20, 2021. Trial exclusion criteria included hospitalization at time of enrollment or use of any experimental treatment for COVID-19, including vaccination. Enrollment was stopped before attaining the planned sample size when COVID-19 diagnoses decreased precipitously in Massachusetts. Data were analyzed from July through September 2021.

INTERVENTIONS

In addition to receiving current standard of care, participants were randomly assigned on a 1:1 basis to receive niclosamide 2 g by mouth daily for 7 days or identically labeled placebo at the same dosing schedule.

MAIN OUTCOMES AND MEASURES

Oropharyngeal and fecal samples were self-collected for viral shedding measured by reverse-transcriptase-polymerase-chain-reaction on days 3, 7, 10, and 14, and an additional fecal sample was collected on day 21. A telehealth platform was developed to conduct remote study visits, monitor symptoms, and coordinate sample collection via couriers. The primary end point was the proportion of participants with viral clearance in respiratory samples at day 3 based on the intention-to-treat sample. Mean times to viral clearance and symptom resolution were calculated as restricted mean survival times and accounted for censored observations.

RESULTS

Among 73 participants, 36 individuals were enrolled and randomized to niclosamide and 37 individuals to placebo. Participant characteristics were similar across treatment groups; among 34 patients receiving placebo and 33 patients receiving niclosamide in the intention-to-treat sample, mean (SD) age was 36.0 (13.3) years vs 36.8 (12.9) years and there were 21 (61.8%) men vs 20 (60.6%) men. The overall mean (SD) age was 36.4 (13.0) years. For the primary end point, 66.67% (95% CI, 50.74% to 81.81%) of participants receiving niclosamide and 55.88% (95% CI, 40.27% to 72.73%) of participants receiving placebo had oropharyngeal SARS-CoV-2 clearance at day 3 (P = .37). Among 63 participants with symptoms, niclosamide did not significantly shorten symptom duration, which was 12.01 (95% CI, 8.82 to 15.2) days in the niclosamide group vs 14.61 (95% CI, 11.25 to 17.96) days in the placebo group (mean difference, -2.6 [95% CI, -7.23 to 2.03] days). Niclosamide was well-tolerated; the most commonly reported adverse events in the placebo and niclosamide groups were headaches (11 patients [32.4%] vs 7 patients [21.2%]; P = .31) and cough (8 patients [23.5%] vs 7 patients [21.2%]; P = .82).

CONCLUSIONS AND RELEVANCE

In this randomized clinical trial, there was no significant difference in oropharyngeal clearance of SARS-CoV-2 at day 3 between placebo and niclosamide groups. Confirmation in larger studies is warranted.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04399356.

Polymodal Control of TMEM16x Channels and Scramblases

The TMEM16A/anoctamin-1 calcium-activated chloride channel (CaCC) contributes to a range of vital functions, such as the control of vascular tone and epithelial ion transport. The channel is a founding member of a family of 10 proteins (TMEM16x) with varied functions; some members (i.e., TMEM16A and TMEM16B) serve as CaCCs, while others are lipid scramblases, combine channel and scramblase function, or perform additional cellular roles. TMEM16x proteins are typically activated by agonist-induced Ca2+ release evoked by Gq-protein-coupled receptor (GqPCR) activation; thus, TMEM16x proteins link Ca2+-signalling with cell electrical activity and/or lipid transport. Recent studies demonstrate that a range of other cellular factors—including plasmalemmal lipids, pH, hypoxia, ATP and auxiliary proteins—also control the activity of the TMEM16A channel and its paralogues, suggesting that the TMEM16x proteins are effectively polymodal sensors of cellular homeostasis. Here, we review the molecular pathophysiology, structural biology, and mechanisms of regulation of TMEM16x proteins by multiple cellular factors.

Computational Screening Strategy for Drug Repurposing Identified Niclosamide as Inhibitor of Vascular Calcification

Vascular calcification is a cardiovascular disorder with no therapeutic options. We recently reported that o-octanoyltransferase (CROT) suppression can inhibit vascular calcification in vivo and in vitro through amelioration of mitochondrial function and fatty acid metabolism. Inhibiting calcification with a small molecule compound targeting CROT-associated mechanisms will be a promising non-invasive treatment of vascular calcification. Here we used a computational approach to search for existing drugs that can inhibit vascular calcification through the CROT pathway. For screening of the compounds that reduce CROT expression, we utilized the Connectivity Map encompassing the L1000 computational platform that contains transcription profiles of various cell lines and perturbagens including small molecules. Small molecules (n = 13) were identified and tested in human primary smooth muscle cells cultured in osteogenic media to induce calcification. Niclosamide, an FDA-improved anthelmintic drug, markedly inhibited calcification along with reduced alkaline phosphatase activity and CROT mRNA expression. To validate this compound in vivo, LDL receptor (Ldlr)-deficient mice fed a high fat diet were given oral doses of niclosamide (0 or 750 ppm admixed with diet) for 10 weeks. Niclosamide treatment decreased aortic and carotid artery calcification as determined by optical near infrared molecular imaging (OsteoSense680) and histological analysis. In addition, niclosamide improved features of fatty liver, including decreased cholesterol levels along with decreased Crot expression, while plasma total cholesterol levels did not change. Proteomic analysis of aortic samples demonstrated that niclosamide affected wingless/integrated (Wnt) signaling pathway and decreased runt-related transcription factor 2 (Runx2) expression, an essential factor for calcification. Our target discovery strategy using a genetic perturbation database with existing drugs identified niclosamide, that in turn inhibited calcification in vivo and in vitro, indicating its potential for the treatment of vascular calcification.

Airway Delivery of Hydrogel-Encapsulated Niclosamide for the Treatment of Inflammatory Airway Disease

Repurposing of the anthelminthic drug niclosamide was proposed as an effective treatment for inflammatory airway diseases such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease. Niclosamide may also be effective for the treatment of viral respiratory infections, such as SARS-CoV-2, respiratory syncytial virus, and influenza. While systemic application of niclosamide may lead to unwanted side effects, local administration via aerosol may circumvent these problems, particularly when the drug is encapsulated into small polyethylene glycol (PEG) hydrospheres. In the present study, we examined whether PEG-encapsulated niclosamide inhibits the production of mucus and affects the pro-inflammatory mediator CLCA1 in mouse airways in vivo, while effects on mucociliary clearance were assessed in excised mouse tracheas. The potential of encapsulated niclosamide to inhibit TMEM16A whole-cell Cl- currents and intracellular Ca2+ signalling was assessed in airway epithelial cells in vitro. We achieved encapsulation of niclosamide in PEG-microspheres and PEG-nanospheres (Niclo-spheres). When applied to asthmatic mice via intratracheal instillation, Niclo-spheres strongly attenuated overproduction of mucus, inhibited secretion of the major proinflammatory mediator CLCA1, and improved mucociliary clearance in tracheas ex vivo. These effects were comparable for niclosamide encapsulated in PEG-nanospheres and PEG-microspheres. Niclo-spheres inhibited the Ca2+ activated Cl- channel TMEM16A and attenuated mucus production in CFBE and Calu-3 human airway epithelial cells. Both inhibitory effects were explained by a pronounced inhibition of intracellular Ca2+ signals. The data indicate that poorly dissolvable compounds such as niclosamide can be encapsulated in PEG-microspheres/nanospheres and deposited locally on the airway epithelium as encapsulated drugs, which may be advantageous over systemic application.

Nitazoxanide and related thiazolides induce cell death in cancer cells by targeting the 20S proteasome with novel binding modes

Nitazoxanide and related thiazolides are a novel class of anti-infectious agents against protozoan parasites, bacteria and viruses. In recent years, it is demonstrated thatthiazolides also can induced cell cycle arrest and apoptotic cell death in cancer cells. Due to their fast proliferating nature, cancer cells highly depend on the proteasome system to remove aberrant proteins. Many of these aberrant proteins are regulators of cell cycle progression and apoptosis, such as the cyclins, BCL2 family members and nuclear factor of κB (NF-κB). Here, we demonstrate at both molecular and cellular levels that the 20S proteasome is a direct target of NTZ and other thiazolides. By concurrently inhibiting the multiple catalytic subunits of 20S proteasome, NTZ promotes cell cycle arrest and triggers cell death in colon cancer cells, either directly or a sensitizer to other anti-tumor agents, especially doxorubicin. We further show that the binding mode of NTZ in the β5 subunit of the 20S proteasome is different from that of bortezomib and other existing proteasome inhibitors. These findings provide new insights in the design of novel small molecular proteasome inhibitors as anti-tumor agents suitable for solid tumor treatment in an oral dosing form.

A determination of pan-pathogen antimicrobials?

While antimicrobial drug development has historically mitigated infectious diseases that are known, COVID-19 revealed a dearth of ‘in-advance’ therapeutics suitable for infections by pathogens that have not yet emerged. Such drugs must exhibit a property that is antithetical to the classical paradigm of antimicrobial development: the ability to treat infections by any pathogen. Characterisation of such ‘pan-pathogen’ antimicrobials requires consolidation of drug repositioning studies, a new and growing field of drug discovery. In this review, a previously-established system for evaluating repositioning studies is used to highlight 4 therapeutics which exhibit pan-pathogen properties, namely azithromycin, ivermectin, niclosamide, and nitazoxanide. Recognition of the pan-pathogen nature of these antimicrobials is the cornerstone of a novel paradigm of antimicrobial development that is not only anticipatory of pandemics and bioterrorist attacks, but cognisant of conserved anti-infective mechanisms within the host-pathogen interactome which are only now beginning to emerge. Ultimately, the discovery of pan-pathogen antimicrobials is concomitantly the discovery of a new class of antivirals, and begets significant implications for pandemic preparedness research in a world after COVID-19.

The pH Dependence of Niclosamide Solubility, Dissolution, and Morphology: Motivation for Potentially Universal Mucin-Penetrating Nasal and Throat Sprays for COVID19, its Variants and other Viral Infections

Motivation

With the coronavirus pandemic still raging, prophylactic-nasal and early-treatment throat-sprays could help prevent infection and reduce viral load. Niclosamide has the potential to treat a broad-range of viral infections if local bioavailability is optimized as mucin-penetrating solutions that can reach the underlying epithelial cells.

Experimental

pH-dependence of supernatant concentrations and dissolution rates of niclosamide were measured in buffered solutions by UV/Vis-spectroscopy for niclosamide from different suppliers (AK Sci and Sigma), as precipitated material, and as cosolvates. Data was compared to predictions from Henderson-Hasselbalch and precipitation-pH models. Optical-microscopy was used to observe the morphologies of original, converted and precipitated niclosamide.

Results

Niclosamide from the two suppliers had different polymorphs resulting in different dissolution behavior. Supernatant concentrations of the “AKSci-polymorph” increased with increasing pH, from 2.53μM at pH 3.66 to 300μM at pH 9.2, reaching 703μM at pH 9.63. However, the “Sigma-polymorph” equilibrated to much lower final supernatant concentrations, reflective of more stable polymorphs at each pH. Similarly, when precipitated from supersaturated solution, or as cosolvates, niclosamide also equilibrated to lower final supernatant concentrations. Polymorph equilibration though was avoided by using a solvent-exchange technique to make the solutions.

Conclusions

Given niclosamide’s activity as a host cell modulator, optimized niclosamide solutions could represent universal prophylactic nasal and early treatment throat sprays against COVID19, its more contagious variants, and other respiratory viral infections. They are the simplest and potentially most effective formulations from both an efficacy standpoint as well as manufacturing and distribution, (no cold chain). They now just need testing.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-021-03112-x.