Diphyllin, a novel and naturally potent V-ATPase inhibitor, abrogates acidification of the osteoclastic resorption lacunae and bone resorption

Novel SERCA2 inhibitor Diphyllin displays anti-tumor effect in non-small cell lung cancer by promoting endoplasmic reticulum stress and mitochondrial dysfunction

Abnormal calcium signaling is associated with non-small cell lung cancer (NSCLC) malignant progression, poor survival and chemotherapy resistance. Targeting endoplasmic reticulum (ER) Ca2+ channels or pumps to block calcium uptake in the ER induces ER stress and concomitantly promotes mitochondrial calcium uptake, leading to mitochondrial dysfunction and ultimately inducing cell death. Here, we identified Diphyllin was a potential specific inhibitor of endoplasmic reticulum (ER) calcium-importing protein sarco/endoplasmic-reticulum Ca2+ ATPase 2 (SERCA2). In vitro and in vivo studies showed that Diphyllin increased NSCLC cell apoptosis, along with inhibition of cell proliferation and migration. Mechanistically, Diphyllin promoted ER stress by directly inhibiting SERCA2 activity and decreasing ER Ca2+ levels. At the same time, the accumulated Ca2+ in cytoplasm flowed into mitochondria to increase reactive oxygen species (ROS) and decrease mitochondrial membrane potential (MMP), leading to cytochrome C (Cyto C) release and mitochondrial dysfunction. In addition, we found that Diphyllin combined with cisplatin could have a synergistic anti-tumor effect in vitro and in vivo. Taken together, our results suggested that Diphyllin, as a potential novel inhibitor of SERCA2, exerts anti-tumor effects by blocking ER Ca2+ uptake and thereby promoting ER stress and mitochondrial dysfunction.

Nanoformulation of the Broad-Spectrum Hydrophobic Antiviral Vacuolar ATPase Inhibitor Diphyllin in Human Recombinant H-ferritin

Background

As highlighted by recent pandemic outbreaks, antiviral drugs are crucial resources in the global battle against viral diseases. Unfortunately, most antiviral drugs are characterized by a plethora of side effects and low efficiency/poor bioavailability owing to their insolubility. This also applies to the arylnaphthalide lignin family member, diphyllin (Diph). Diph acts as a vacuolar ATPase inhibitor and has been previously identified as a promising candidate with broad-spectrum antiviral activity. However, its physicochemical properties preclude its efficient administration in vivo, complicating preclinical testing.

Methods

We produced human recombinant H- ferritin (HsaFtH) and used it as a delivery vehicle for Diph encapsulation through pH-mediated reversible reassembly of HsaFtH. Diph nanoformulation was subsequently thoroughly characterized and tested for its non-target cytotoxicity and antiviral efficiency using a panel of pathogenic viral strain.

Results

We revealed that loading into HsaFtH decreased the undesired cytotoxicity of Diph in mammalian host cells. We also confirmed that encapsulated Diph exhibited slightly lower antiviral activity than free Diph, which may be due to the differential uptake mechanism and kinetics of free Diph and Diph@HsaFtH. Furthermore, we confirmed that the antiviral effect was mediated solely by Diph with no contribution from HsaFtH.

Conclusion

It was confirmed that HsaFtH is a suitable vehicle that allows easy loading of Diph and production of highly homogeneous nanoparticles dispersion with promising broad-spectrum antiviral activity.

Structure-Activity Relationships of Natural and Semisynthetic Plecomacrolides Suggest Distinct Pathways for HIV-1 Immune Evasion and Vacuolar ATPase-Dependent Lysosomal Acidification

The human immunodeficiency virus (HIV)-encoded accessory protein Nef enhances pathogenicity by reducing major histocompatibility complex I (MHC-I) cell surface expression, protecting HIV-infected cells from immune recognition. Nef-dependent downmodulation of MHC-I can be reversed by subnanomolar concentrations of concanamycin A (1), a well-known inhibitor of vacuolar ATPase, at concentrations below those that interfere with lysosomal acidification or degradation. We conducted a structure-activity relationship study that assessed 76 compounds for Nef inhibition, 24 and 72 h viability, and lysosomal neutralization in Nef-expressing primary T cells. This analysis demonstrated that the most potent compounds were natural concanamycins and their derivatives. Comparison against a set of new, semisynthetic concanamycins revealed that substituents at C-8 and acylation of C-9 significantly affected Nef potency, target cell viability, and lysosomal neutralization. These findings provide important progress toward understanding the mechanism of action of these compounds and the identification of an advanced lead anti-HIV Nef inhibitory compound.

Bioactives and Biomaterial Construction for Modulating Osteoclast Activities

Bone tissue constitutes 15-20% of human body weight and plays a crucial role in supporting the body, coordinating movement, regulating mineral homeostasis, and hematopoiesis. The maintenance of bone homeostasis relies on a delicate balance between osteoblasts and osteoclasts. Osteoclasts, as the exclusive "bone resorbers" in the human skeletal system, are of paramount significance yet often receive inadequate attention. When osteoclast activity becomes excessive, it frequently leads to various bone metabolic disorders, subsequently resulting in secondary bone injuries, such as fractures. This not only reduces life quality of patients, but also imposes a significant economic burden on society. In response to the pressing need for biomaterials in the treatment of osteoclast dysregulation, there is a surge of research and investigations aimed at osteoclast regulation. Promising progress is achieved in this domain. This review seeks to provide a comprehensive understanding of how to modulate osteoclast activities. It summarizes bioactive substances that influence osteoclasts and elucidates strategies for constructing related biomaterial systems. It offers practical insights and ideas for the development and application of biomaterials and tissue engineering, with the hope of guiding the clinical treatment of osteoclast-related bone diseases using biomaterials in the future.

Discovery of Novel Isoquinoline Analogues as Dual Tubulin Polymerization/V-ATPase Inhibitors with Immunogenic Cell Death Induction

Cancer immunotherapy has revolutionized clinical advances in a variety of cancers. Due to the low immunogenicity of the tumor, only a few patients can benefit from it. Specific microtubule inhibitors can effectively induce immunogenic cell death and improve immunogenicity of the tumor. A series of isoquinoline derivatives based on the natural products podophyllotoxin and diphyllin were designed and synthesized. Among them, F10 showed robust antiproliferation activity against four human cancer cell lines, and it was verified that F10 exerted antiproliferative activity by inhibiting tubulin and V-ATPase. Further studies indicated that F10 is able to induce immunogenic cell death in addition to apoptosis. Meanwhile, F10 inhibited tumor growth in an RM-1 homograft model with enhanced T lymphocyte infiltration. These results suggest that F10 may be a promising lead compound for the development of a new generation of microtubule drugs.

Bioactivities and Mechanisms of Action of Diphyllin and Its Derivatives: A Comprehensive Systematic Review

Natural products are treasure houses for modern drug discovery. Diphyllin is a natural arylnaphthalene lignan lactone isolated from the leaf of Astilboides tabularis. Studies have found that it possesses plenty of bioactivity characteristics. In this paper, we reviewed the structure, bioactivity, and mechanism of action of diphyllin and its derivatives. The references were obtained from PubMed, Web of Science, and Science Direct databases up to August 2023. Papers without a bio-evaluation were excluded. Diphyllin and its derivatives have demonstrated V-ATPase inhibition, anti-tumor, anti-virus, anti-biofilm, anti-inflammatory, and anti-oxidant activities. The most studied activities of diphyllin and its derivatives are V-ATPase inhibition, anti-tumor activities, and anti-virus activities. Furthermore, V-ATPase inhibition activity is the mechanism of many bioactivities, including anti-tumor, anti-virus, and anti-inflammatory activities. We also found that the galactosylated modification of diphyllin is a common phenomenon in plants, and therefore, galactosylated modification is applied by researchers in the laboratory to obtain more excellent diphyllin derivatives. This review will provide useful information for the development of diphyllin-based anti-tumor and anti-virus compounds.

Vacuolar ATPase Is a Possible Therapeutic Target in Acute Myeloid Leukemia: Focus on Patient Heterogeneity and Treatment Toxicity

Vacuolar ATPase (V-ATPase) is regarded as a possible target in cancer treatment. It is expressed in primary acute myeloid leukemia cells (AML), but the expression varies between patients and is highest for patients with a favorable prognosis after intensive chemotherapy. We therefore investigated the functional effects of two V-ATPase inhibitors (bafilomycin A1, concanamycin A) for primary AML cells derived from 80 consecutive patients. The V-ATPase inhibitors showed dose-dependent antiproliferative and proapoptotic effects that varied considerably between patients. A proteomic comparison of primary AML cells showing weak versus strong antiproliferative effects of V-ATPase inhibition showed a differential expression of proteins involved in intracellular transport/cytoskeleton functions, and an equivalent phosphoproteomic comparison showed a differential expression of proteins that regulate RNA processing/function together with increased activity of casein kinase 2. Patients with secondary AML, i.e., a heterogeneous subset with generally adverse prognosis and previous cytotoxic therapy, myeloproliferative neoplasia or myelodysplastic syndrome, were characterized by a strong antiproliferative effect of V-ATPase inhibition and also by a specific mRNA expression profile of V-ATPase interactome proteins. Furthermore, the V-ATPase inhibition altered the constitutive extracellular release of several soluble mediators (e.g., chemokines, interleukins, proteases, protease inhibitors), and increased mediator levels in the presence of AML-supporting bone marrow mesenchymal stem cells was then observed, especially for patients with secondary AML. Finally, animal studies suggested that the V-ATPase inhibitor bafilomycin had limited toxicity, even when combined with cytarabine. To conclude, V-ATPase inhibition has antileukemic effects in AML, but this effect varies between patients.

2, 4, 5-Trideoxyhexopyranosides derivatives of diphyllin: Synthesis and anticancer activity

Diphyllin and its natural derivatives were identified as potent vacuolar H⁺ -ATPase (V-ATPase) inhibitors. In this study, twelve 2, 4, 5-trideoxyhexopyranosides derivatives of diphyllin were synthesized. Most of these compounds showed potent abilities to inhibit the growth of HT-29, MCF-7, HepG2 cancer cells with IC₅₀ values at submicromolar concentration. The compounds 5c3 and 5c4 showed the best inhibitory activity on breast cancer cell lines MCF-7 with IC₅₀ values of 0.09 and 0.10 μM. Compounds 5c3 and 5c4 showed similar V-ATPase inhibitory potency to diphyllin. Molecular docking showed that a hydrogen bond was found between the hydroxyl of 5c3 and SerA534 in the pocket of the V-ATPase receptor.

Recent advances in natural anti-obesity compounds and derivatives based on in vivo evidence: A mini-review

Obesity is not only viewed as a chronic aggressive disorder but is also associated with an increased risk for various diseases. Nonetheless, new anti-obesity drugs are an urgent need since few pharmacological choices are available on the market. Natural compounds have served as templates for drug discovery, whereas modified molecules from the leads identified based on in vitro models often reveal noncorresponding bioactivity between in vitro and in vivo studies. Therefore, to provide inspiration for the exploration of innovative anti-obesity agents, recent discoveries of natural anti-obesity compounds with in vivo evidence have been summarized according to their chemical structures, and the comparable efficacy of these compounds is categorized using animal models. In addition, several synthetic derivatives optimized from the phytochemicals are also provided to discuss medicinal chemistry achievements guided by natural sources.

Multinucleated Giant Cells: Current Insights in Phenotype, Biological Activities, and Mechanism of Formation

Monocytes and macrophages are innate immune cells with diverse functions ranging from phagocytosis of microorganisms to forming a bridge with the adaptive immune system. A lesser-known attribute of macrophages is their ability to fuse with each other to form multinucleated giant cells. Based on their morphology and functional characteristics, there are in general three types of multinucleated giant cells including osteoclasts, foreign body giant cells and Langhans giant cells. Osteoclasts are bone resorbing cells and under physiological conditions they participate in bone remodeling. However, under pathological conditions such as rheumatoid arthritis and osteoporosis, osteoclasts are responsible for bone destruction and bone loss. Foreign body giant cells and Langhans giant cells appear only under pathological conditions. While foreign body giant cells are found in immune reactions against foreign material, including implants, Langhans giant cells are associated with granulomas in infectious and non-infectious diseases. The functionality and fusion mechanism of osteoclasts are being elucidated, however, our knowledge on the functions of foreign body giant cells and Langhans giant cells is limited. In this review, we describe and compare the phenotypic aspects, biological and functional activities of the three types of multinucleated giant cells. Furthermore, we provide an overview of the multinucleation process and highlight key molecules in the different phases of macrophage fusion.

Lonafarnib Inhibits Farnesyltransferase via Suppressing ERK Signaling Pathway to Prevent Osteoclastogenesis in Titanium Particle-Induced Osteolysis

Wear debris after total joint arthroplasty can attract the recruitment of macrophages, which release pro-inflammatory substances, triggering the activation of osteoclasts, thereby leading to periprosthetic osteolysis (PPOL) and aseptic loosening. However, the development of pharmacological strategies targeting osteoclasts to prevent periprosthetic osteolysis has not been fruitful. In this study, we worked toward researching the effects and mechanisms of a farnesyltransferase (FTase) inhibitor Lonafarnib (Lon) on receptor activator of nuclear factor κB (NF-κB) ligand (RANKL)-induced osteoclastogenesis and bone resorption, as well as the impacts of Lon on titanium particle-induced osteolysis. To investigate the impacts of Lon on bone resorption and osteoclastogenesis in vitro, bone marrow macrophages were incubated and stimulated with RANKL and macrophage colony-stimulating factor (M-CSF). The influence of Lon on osteolysis prevention in vivo was examined utilizing a titanium particle-induced mouse calvarial osteolysis model. The osteoclast-relevant genes expression was explored by real-time quantitative PCR. Immunofluorescence was used to detect intracellular localization of nuclear factor of activated T cells 1 (NFATc1). SiRNA silence assay was applied to examine the influence of FTase on osteoclasts activation. Related signaling pathways, including NFATc1 signaling, NF-κB, mitogen-activated protein kinases pathways were identified by western blot assay. Lon was illustrated to suppress bone resorptive function and osteoclastogenesis in vitro, and it also reduced the production of pro-inflammatory substances and prevented titanium particle-induced osteolysis in vivo. Lon decreased the expression of osteoclast-relevant genes and suppressed NFATc1 nuclear translocation and auto-amplification. Mechanistically, Lon dampened FTase, and inhibition of FTase reduced osteoclast formation by suppressing ERK signaling. Lon is a promising treatment option for osteoclast-related osteolysis diseases including periprosthetic osteolysis by targeted inhibition of FTase through suppressing ERK signaling.

Multitarget-Based Virtual Screening for Identification of Herbal Substances toward Potential Osteoclastic Targets

Osteoporosis is a complex bone disease indicating porous bone with low bone mass density and fragility. Cathepsin K, V-ATPase, and αVβ3 integrin are exhibited as novel targets for osteoporosis treatment. Our preliminary study uses a state-of-the-art method, including target-based virtual screening and clustering methods to determine promising candidates with multitarget properties. Phytochemicals with osteoprotective properties from the literature are used to elucidate the molecular interactions toward three targets. The binding scores of compounds are normalized and rescored. The K-means and hierarchical clustering methods are applied to filter and define the promising compounds, and the silhouette analysis is supposed to validate the clustering method. We explore 108 herbal compounds by virtual screening and the cluster approach, and find that rutin, sagittatoside A, icariin, and kaempferitrin showed strong binding affinities against Cathepsin K, V-ATPase, and αVβ3 integrin. Dockings of candidates toward three targets also provide the protein-ligand interactions and crucial amino acids for binding. Our study provides a straightforward and less time-consuming approach to exploring the new multitarget candidates for further investigations, using a combination of in silico methods.

Diphyllin Shows a Broad-Spectrum Antiviral Activity against Multiple Medically Important Enveloped RNA and DNA Viruses

Diphyllin is a natural arylnaphtalide lignan extracted from tropical plants of particular importance in traditional Chinese medicine. This compound has been described as a potent inhibitor of vacuolar (H⁺)ATPases and hence of the endosomal acidification process that is required by numerous enveloped viruses to trigger their respective viral infection cascades after entering host cells by receptor-mediated endocytosis. Accordingly, we report here a revised, updated, and improved synthesis of diphyllin, and demonstrate its antiviral activities against a panel of enveloped viruses from Flaviviridae, Phenuiviridae, Rhabdoviridae, and Herpesviridae families. Diphyllin is not cytotoxic for Vero and BHK-21 cells up to 100 µM and exerts a sub-micromolar or low-micromolar antiviral activity against tick-borne encephalitis virus, West Nile virus, Zika virus, Rift Valley fever virus, rabies virus, and herpes-simplex virus type 1. Our study shows that diphyllin is a broad-spectrum host cell-targeting antiviral agent that blocks the replication of multiple phylogenetically unrelated enveloped RNA and DNA viruses. In support of this, we also demonstrate that diphyllin is more than just a vacuolar (H⁺)ATPase inhibitor but may employ other antiviral mechanisms of action to inhibit the replication cycles of those viruses that do not enter host cells by endocytosis followed by low pH-dependent membrane fusion.

Antiviral, Anticancer and Hypotensive Potential of Diphyllin Glycosides and their Mechanisms of Action

Diphyllin glycosides (DG) are the type of arylnaphthalene lignans isolated from different plants and their synthetic derivatives have shown effective antiviral, cytotoxic, hypotensive and diuretic effects at very low concentrations similar to standard drugs that are under clinical use. The biological activities of the DG interfere with signaling pathways of viral infection and cancer induction. The sugar moieties of DG enhance bioavailability and pharmacological activities. The promising results of DG at nanomolar concentrations under in vitro and in vivo conditions should be explored further with clinical trials to determine its toxic effects, pharmacokinetics and pharmacodynamics. This may identify suitable antiviral and anticancer drugs in the near future. Considering all these activities, the present review is focused on the chemical aspects of DG with a detailed account on the mechanisms of action of DG. An attempt is also made to comment on the status of clinical trials of DG along with the possible limitations in studies based on available literature through September 2020.

PHY34 inhibits autophagy through V-ATPase V0A2 subunit inhibition and CAS/CSE1L nuclear cargo trafficking in high grade serous ovarian cancer

PHY34 is a synthetic small molecule, inspired by a compound naturally occurring in tropical plants of the Phyllanthus genus. PHY34 was developed to have potent in vitro and in vivo anticancer activity against high grade serous ovarian cancer (HGSOC) cells. Mechanistically, PHY34 induced apoptosis in ovarian cancer cells by late-stage autophagy inhibition. Furthermore, PHY34 significantly reduced tumor burden in a xenograft model of ovarian cancer. In order to identify its molecular target/s, we undertook an unbiased approach utilizing mass spectrometry-based chemoproteomics. Protein targets from the nucleocytoplasmic transport pathway were identified from the pulldown assay with the cellular apoptosis susceptibility (CAS) protein, also known as CSE1L, representing a likely candidate protein. A tumor microarray confirmed data from mRNA expression data in public databases that CAS expression was elevated in HGSOC and correlated with worse clinical outcomes. Overexpression of CAS reduced PHY34 induced apoptosis in ovarian cancer cells based on PARP cleavage and Annexin V staining. Compounds with a diphyllin structure similar to PHY34 have been shown to inhibit the ATP6V0A2 subunit of V(vacuolar)-ATPase. Therefore, ATP6V0A2 wild-type and ATP6V0A2 V823 mutant cell lines were tested with PHY34, and it was able to induce cell death in the wild-type at 246 pM while the mutant cells were resistant up to 55.46 nM. Overall, our data demonstrate that PHY34 is a promising small molecule for cancer therapy that targets the ATP6V0A2 subunit to induce autophagy inhibition while interacting with CAS and altering nuclear localization of proteins.

Ring Expansion of 1-Indanones to 2-Halo-1-naphthols as an Entry Point to Gilvocarcin Natural Products

Herein, we describe a two-step ring expansion of 1-indanones to afford 2-chloro/bromo-1-naphthols (32 examples). The developed method shows broad functional group tolerance, benefits from mild reaction conditions, and enables rapid access to the tetracyclic core of gilvocarcin natural products. The orthogonally functionalized products allow for selective postmodifications as exemplified in the total synthesis of defucogilvocarcin M. For the selective oxidation of the chromene, a mild and regioselective oxidation protocol (DDQ and TBHP) was developed.

Small molecule probes for targeting autophagy

Autophagy is implicated in a wide range of (patho)physiological processes including maintenance of cellular homeostasis, neurodegenerative disorders, aging and cancer. As such, small molecule autophagy modulators are in great demand, both for their ability to act as tools to better understand this essential process and as potential therapeutics. Despite substantial advances in the field, major challenges remain in the development and comprehensive characterization of probes that are specific to autophagy. In this Review, we discuss recent developments in autophagy-modulating small molecules, including the specific challenges faced in the development of activators and inhibitors, and recommend guidelines for their use. Finally, we discuss the potential to hijack the process for targeted protein degradation, an area of great importance in chemical biology and drug discovery.

Leaves of Cleome amblyocarpa Barr. And Murb. And Cleome arabica L.: Assessment of nutritional composition and chemical profile (LC-ESI-MS/MS), anti-inflammatory and analgesic effects of their extracts

ETHNOPHARMACOLOGICAL RELEVANCE

The Cleomaceae family is known for its richness in secondary metabolites and different Cleome species are used in folk medicine. Cleome amblyocarpa and Cleome arabica are medicinal herbs used in Tunisia and other North Africa countries to treat various diseases such as diabetes, rheumatism, colic, pain and digestive disorders.

AIM OF THE STUDY

To our knowledge, few data are available about the nutritional value, phytochemical components and biological effects of C. arabica and C. amblyocarpa cultivated in Tunisia. For this reason, the present survey aimed to determine the nutritional value, bioactive compounds and pharmacological properties of the leaves of these two species of Cleome.

MATERIALS AND METHODS

To characterize and determine the bioactive compounds in both extracts of leaves of Cleome species, ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) was used. The various nutritional parameters were analyzed, in particular the amounts of protein, carbohydrates, ash, fiber, and total lipids. Vitamin E and fatty acid profiles were also evaluated by HPLC-DAD-FLD and GC-FID, respectively. The acute toxic effects of leaf extracts in mice at concentrations of 100, 500 and 800 mg/kg body weight have been investigated. The anti-inflammatory effect of leaves extracts was examined by means of the in vitro and in vivo models. The in vivo anti-inflammatory test was assessed by means of the carrageenan induced paw edema in rats. For the in vitro anti-inflammatory assay, the red blood cells membrane stabilization and protein denaturation methods were employed. The analgesic effect of hydroalcoholic extracts of leaves was also assessed by acetic acid induced writhing model in mice.

RESULTS

The phytochemical composition and the nutritional values of the leaves of C. amblyocarpa and C. arabica were determined. Our results revealed that the leaves of C. amblyocarpa are rich in flavonoids and glucosinolates. On the other hand, these latter metabolites are not present in the C. arabica extract and the leaves are characterized by the presence of flavones, methoxyflavones and their glycosides. Our findings revealed that the leaves of the two species contain a potential quantity of vitamins; proteins, carbohydrates and dietary fiber, and their hydroalcoholic extracts indicated substantial anti-inflammatory and antinociceptive activities in all the tests. Additionally, the data from the acute toxicity test proved that the leaf extracts did not cause any mortality or signs of toxicity in animals at doses up to 800 mg/kg CONCLUSIONS: The results obtained in this investigation demonstrated that the leaves of C. arabica and C. amblyocarpa are a valuable source of nutrients and active substances. Our observations support the traditional utilize of these two Cleome species for the treatment of painful diseases and as a source of natural anti-inflammatory agents.

Medicinal Plants, Phytochemicals, and Herbs to Combat Viral Pathogens Including SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome corona virus-2 (SARS-CoV-2), is the most important health issue, internationally. With no specific and effective antiviral therapy for COVID-19, new or repurposed antiviral are urgently needed. Phytochemicals pose a ray of hope for human health during this pandemic, and a great deal of research is concentrated on it. Phytochemicals have been used as antiviral agents against several viruses since they could inhibit several viruses via different mechanisms of direct inhibition either at the viral entry point or the replication stages and via immunomodulation potentials. Recent evidence also suggests that some plants and its components have shown promising antiviral properties against SARS-CoV-2. This review summarizes certain phytochemical agents along with their mode of actions and potential antiviral activities against important viral pathogens. A special focus has been given on medicinal plants and their extracts as well as herbs which have shown promising results to combat SARS-CoV-2 infection and can be useful in treating patients with COVID-19 as alternatives for treatment under phytotherapy approaches during this devastating pandemic situation.

Gene therapy for infantile malignant osteopetrosis: review of pre-clinical research and proof-of-concept for phenotypic reversal

Infantile malignant osteopetrosis is a devastating disorder of early childhood that is frequently fatal and for which there are only limited therapeutic options. Gene therapy utilizing autologous hematopoietic stem and progenitor cells represents a potentially advantageous therapeutic alternative for this multisystemic disease. Gene therapy can be performed relatively rapidly following diagnosis, will not result in graft versus host disease, and may also have potential for reduced incidences of other transplant-related complications. In this review, we have summarized the past sixteen years of research aimed at developing a gene therapy for infantile malignant osteopetrosis; these efforts have culminated in the first clinical trial employing lentiviral-mediated delivery of TCIRG1 in autologous hematopoietic stem and progenitor cells.

Membrane Transport Proteins in Osteoclasts: The Ins and Outs

During bone resorption, the osteoclast must sustain an extraordinarily low pH environment, withstand immense ionic pressures, and coordinate nutrient and waste exchange across its membrane to sustain its unique structural and functional polarity. To achieve this, osteoclasts are equipped with an elaborate set of membrane transport proteins (pumps, transporters and channels) that serve as molecular ‘gatekeepers’ to regulate the bilateral exchange of ions, amino acids, metabolites and macromolecules across the ruffled border and basolateral domains. Whereas the importance of the vacuolar-ATPase proton pump and chloride voltage-gated channel 7 in osteoclasts has long been established, comparatively little is known about the contributions of other membrane transport proteins, including those categorized as secondary active transporters. In this Special Issue review, we provide a contemporary update on the ‘ins and outs’ of membrane transport proteins implicated in osteoclast differentiation, function and bone homeostasis and discuss their therapeutic potential for the treatment of metabolic bone diseases.

Antiviral Activity of Vacuolar ATPase Blocker Diphyllin against SARS-CoV-2

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a causative agent of the pandemic coronavirus disease 2019 (COVID-19), which has resulted in over two million deaths worldwide to date. Diphyllin and diphyllinosides are known as natural blockers of cellular vacuolar ATPases, and so can act as inhibitors of the pH-dependent fusion of viral envelopes with host cell endosomal membranes. Such pH-dependent fusion is a critical early step during the SARS-CoV-2 replication cycle. Accordingly, the anti-SARS-CoV-2 profiles and cytotoxicities of diphyllin, diphyllinoside cleistanthin B, and two structurally related compounds, helioxanthin 8-1 and helioxanthin 5-4-2, are evaluated here using in vitro cell-based assay systems. Neither helioxanthin exhibits any obvious anti-SARS-CoV-2 effects in vitro. By contrast diphyllin and cleistanthin B do exhibit anti-SARS-CoV-2 effects in Vero cells, with respective 50% effective concentrations (EC₅₀) values of 1.92 and 6.51 µM. Diphyllin displays anti-SARS-CoV-2 effect also in colorectal adenocarcinoma (CaCo-2) cells. Moreover, when diphyllin is added at various times post infection, a significant decrease in viral titer is observed in SARS-CoV-2-infected Vero cells, even at high viral multiplicities of infection. Importantly, neither diphyllin nor cleistanthin B are found cytotoxic to Vero cells in concentrations up to 100 µM. However, the cytotoxic effect of diphyllin is more pronounced in Vero E6 and CaCo-2 cells. Overall, our data demonstrate that diphyllin and diphyllin analogues might be perfected as anti-SARS-CoV-2 agents in future preclinical studies, most especially if nanomedicine approaches may be invoked to optimize functional drug delivery to virus infected cells.

Synthesis, Cytotoxicity, Anti-migration and Anti-invasion Activity of Diphyllin Heterocyclic Derivatives

BACKGROUND

Diphyllin, an arylnaphthalene lignan lactone, isolated from many traditional medicinal plants, has been reported to possess anticancer and antiviral activities. Natural diphyllin and its glycosides were identified as potent vacuolar H+ -ATPase (V-ATPase) inhibitors.

OBJECTIVE

The aim of this study was to design and synthesize a series of heterocyclic derivatives of diphyllin as novel anticancer agents.

METHODS

The targeted heterocyclic derivatives of diphyllin were synthesized from diphyllin employing etherification reaction and N-substitution reaction. Cytotoxicity of these compounds on four cancer cells was assessed by MTT assay. The inhibitory activity of V-ATPase of compound 3n was measured on MGC-803 cells. Anti-migration and anti-invasion abilities were assessed by transwell invasion assay and scratch wound assay.

RESULTS

Most of these derivatives displayed potent cytotoxicity on four cancer cells at submicromolar concentrations. The most potent derivative 3n has been shown to inhibited V-ATPase activity, migration and invasion abilities on MGC-803 cells at 0.75 mM.

CONCLUSION

The collective results clearly indicate that heterocyclic derivatives of diphyllin inhibit the viability, V-ATPase activity, migration and invasion of the MGC803 cells. The current findings provide valuable insights for the future development of novel diphyllin derivatives as anticancer agents.

Diphyllin Improves High-Fat Diet-Induced Obesity in Mice Through Brown and Beige Adipocytes

Brown adipose tissue (BAT) and beige adipose tissue dissipate metabolic energy and mediate nonshivering thermogenesis, thereby boosting energy expenditure. Increasing the browning of BAT and beige adipose tissue is expected to be a promising strategy for combatting obesity. Through phenotype screening of C3H10-T1/2 mesenchymal stem cells, diphyllin was identified as a promising molecule in promoting brown adipocyte differentiation. In vitro studies revealed that diphyllin promoted C3H10-T1/2 cell and primary brown/beige preadipocyte differentiation and thermogenesis, which resulted increased energy consumption. We synthesized the compound and evaluated its effect on metabolism in vivo. Chronic experiments revealed that mice fed a high-fat diet (HFD) with 100 mg/kg diphyllin had ameliorated oral glucose tolerance and insulin sensitivity and decreased body weight and fat content ratio. Adaptive thermogenesis in HFD-fed mice under cold stimulation and whole-body energy expenditure were augmented after chronic diphyllin treatment. Diphyllin may be involved in regulating the development of brown and beige adipocytes by inhibiting V-ATPase and reducing intracellular autophagy. This study provides new clues for the discovery of anti-obesity molecules from natural products.

Herbal Medication to Enhance or Modulate Viral Infections

Viral infections and their emergence continue to pose a threat to human lives. Up to the present, there are limited numbers of vaccines that effectively work and few antivirals licensed for use in clinical practice. Added to this is the increase in antiviral resistance, meaning that drugs that do work are at risk of reduced efficacy. The recent global pandemic of coronavirus 2019 has provided evidence for the risk of a preventative vaccination and effective treatment of viruses' subsequent consequences. The aim of this article is to review traditional and herbal treatments for infections, specifically addressing gastrointestinal and respiratory viral infections.

Lignans from linseed (Linum usitatissimum L.) and its allied species: Retrospect, introspect and prospect

Lignans are complex diphenolic compounds representing phytoestrogens and occur widely across the plant kingdom. Formed by the coupling of two coniferyl alcohol residues, lignans constitute major plant "specialized metabolites" with exceptional biological attributes that aid in plant defence and provide health benefits in humans by reducing the risk of ailments such as cancer, diabetes etc. Linseed (Linum usitatissimum L.) is one of the richest sources of lignans followed by cereals and legumes. Among the various types of lignans, secoisolariciresinol diglucoside (SDG) is considered as the essential and nutrient rich lignan in linseed. Lignans exhibit established antimitotic, antiviral and anti-tumor properties that contribute to their medicinal value. The present review seeks to provide a holistic view of research in the past and present times revolving around lignans from linseed and its allied species. This review attempts to elucidate sources, structures and functional properties of lignans, along with detailed biosynthetic mechanisms operating in plants. It summarizes various methods for the determination of lignan content in plants. Biotechnological interventions (in planta and in vitro) aimed at enriching lignan content and adoption of integrative approaches that might further enhance lignan content and medicinal and nutraceutical value of Linum spp. have also been discussed.

Patent highlights, August-September 2019

A snapshot of recent noteworthy developments in the patent literature of relevance to pharmaceutical and medical research and development.

Lignans and Their Derivatives from Plants as Antivirals

Lignans are widely produced by various plant species; they are a class of natural products that share structural similarity. They usually contain a core scaffold that is formed by two or more phenylpropanoid units. Lignans possess diverse pharmacological properties, including their antiviral activities that have been reported in recent years. This review discusses the distribution of lignans in nature according to their structural classification, and it provides a comprehensive summary of their antiviral activities. Among them, two types of antiviral lignans—podophyllotoxin and bicyclol, which are used to treat venereal warts and chronic hepatitis B (CHB) in clinical, serve as examples of using lignans for antivirals—are discussed in some detail. Prospects of lignans in antiviral drug discovery are also discussed.

Glycosylated diphyllin as a broad-spectrum antiviral agent against Zika virus

Background

Flaviviruses such as Zika cause sporadic pandemic outbreaks worldwide. There is an urgent need for anti-Zika virus (ZIKV) drugs to prevent mother-to-child transmission of ZIKV, new infections in high-risk populations, and the infection of medical personnel in ZIKV-affected areas.

Methods

Here, we showed that the small molecule 6-deoxyglucose-diphyllin (DGP) exhibited anti-ZIKV activity both in vitro and in vivo. DGP potently blocked ZIKV infection across all human and monkey cell lines tested. DGP also displayed broad-spectrum antiviral activity against other flaviviruses. Remarkably, DGP prevented ZIKV-induced mortality in mice lacking the type I interferon receptor (Ifnar1^−/−). Cellular and virological experiments showed that DGP blocked ZIKV at a pre-fusion step or during fusion, which prevented the delivery of viral contents into the cytosol of the target cell. Mechanistic studies revealed that DGP prevented the acidification of endosomal/lysosomal compartments in target cells, thus inhibiting ZIKV fusion with cellular membranes and infection.

Findings

These investigations revealed that DGP inhibits ZIKV infection in vitro and in vivo.

Interpretation

The small molecule DGP has great potential for preclinical studies and the ability to inhibit ZIKV infection in humans.

Small molecules for modulating the localisation of the water channel aquaporin-2-disease relevance and perspectives for targeting local cAMP signalling

The tight spatial and temporal organisation of cyclic adenosine monophosphate (cAMP) signalling plays a key role in arginine-vasopressin (AVP)-mediated water reabsorption in renal collecting duct principal cells and in a plethora of other processes such as in the control of cardiac myocyte contractility. This review critically discusses in vitro- and cell-based screening strategies for the identification of small molecules that interfere with AVP/cAMP signalling in renal principal cells; it features phenotypic screening and approaches for targeting protein-protein interactions of A-kinase anchoring proteins (AKAPs), which organise local cAMP signalling hubs. The discovery of novel chemical entities for the modulation of local cAMP will not only provide tools for elucidating molecular mechanisms underlying cAMP signalling. Novel chemical entities can also serve as starting points for the development of novel drugs for the treatment of human diseases. Examples illustrate how screening for small molecules can pave the way to novel approaches for the treatment of certain forms of diabetes insipidus, a disease caused by defects in AVP-mediated water reabsorption.

A novel potent autophagy inhibitor ECDD-S27 targets vacuolar ATPase and inhibits cancer cell survival

Autophagy is a conserved lysosomal-dependent cellular degradation process and its dysregulation has been linked to numerous diseases including neurodegeneration, infectious diseases, and cancer. Modulation of autophagy is therefore considered as an attractive target for disease intervention. We carried out a high-content image analysis screen of natural product-derived compounds to discover novel autophagy modulating molecules. Our screen identified ECDD-S27 as the most effective compound for increasing the number of autophagic vacuoles inside cells. The structure of ECDD-S27 revealed that it is a derivative of cleistanthin A, a natural arylnaphthalene lignan glycoside found in plants. ECDD-S27 increases the number of autophagic vacuoles by inhibiting the autophagic flux and is able to restrict the survival of different cancer cells at low nanomolar concentrations. Molecular docking and SERS analysis showed that ECDD-S27 may potentially target the V-ATPase. Upon treatment of various cancer cells with ECDD-S27, the V-ATPase activity is potently inhibited thereby resulting in the loss of lysosomal acidification. Taken together, these data indicated that ECDD-S27 retards the autophagy pathway by targeting the V-ATPase and inhibits cancer cell survival. The observed antitumor activity without cytotoxicity to normal cells suggests the therapeutic potential warranting further studies on lead optimization of the compound for cancer treatment.

Previously Uncharacterized Vacuolar-type ATPase Binding Site Discovered from Structurally Similar Compounds with Distinct Mechanisms of Action

Using a comprehensive chemical genetics approach, we identified a member of the lignan natural product family, HTP-013, which exhibited significant cytotoxicity across various cancer cell lines. Correlation of compound activity across a panel of reporter gene assays suggested the vacuolar-type ATPase (v-ATPase) as a potential target for this compound. Additional cellular studies and a yeast haploinsufficiency screen strongly supported this finding. Competitive photoaffinity labeling experiments demonstrated that the ATP6V0A2 subunit of the v-ATPase complex binds directly to HTP-013, and further mutagenesis library screening identified resistance-conferring mutations in ATP6V0A2. The positions of these mutations suggest the molecule binds a novel pocket within the domain of the v-ATPase complex responsible for proton translocation. While other mechanisms of v-ATPase regulation have been described, such as dissociation of the complex or inhibition by natural products including bafilomycin A1 and concanamycin, this work provides detailed insight into a distinct binding pocket within the v-ATPase complex.

Phenotypic Prioritization of Diphyllin Derivatives That Block Filoviral Cell Entry by Vacuolar (H+ )-ATPase Inhibition

Many viruses use endosomal pathways to gain entry into cells and propagate infection. Sensing of endosomal acidification is a trigger for the release of many virus cores into the cell cytosol. Previous efforts with inhibitors of vacuolar ATPase have been shown to block endosomal acidification and affect viral entry, albeit with limited potential for therapeutic selectivity. In this study, four novel series of derivatives of the vacuolar ATPase inhibitor diphyllin were synthesized to assess their potential for enhancing potency and anti-filoviral activity over cytotoxicity. Derivatives that suitably blocked cellular entry of Ebola pseudotyped virus were further evaluated as inhibitors of endosomal acidification and isolated human vacuolar ATPase activity. Several compounds with significant increases in potency over diphyllin in these assays also separated from cytotoxic doses in human cell models by >100-fold. Finally, three derivatives were shown to be inhibitors of replication-competent Ebola viral entry into primary macrophages with similar potencies and enhanced selectivity toward antiviral activity.

V-ATPases and osteoclasts: ambiguous future of V-ATPases inhibitors in osteoporosis

Vacuolar ATPases (V-ATPases) play a critical role in regulating extracellular acidification of osteoclasts and bone resorption. The deficiencies of subunit a3 and d2 of V-ATPases result in increased bone density in humans and mice. One of the traditional drug design strategies in treating osteoporosis is the use of subunit a3 inhibitor. Recent findings connect subunits H and G1 with decreased bone density. Given the controversial effects of ATPase subunits on bone density, there is a critical need to review the subunits of V-ATPase in osteoclasts and their functions in regulating osteoclasts and bone remodeling. In this review, we comprehensively address the following areas: information about all V-ATPase subunits and their isoforms; summary of V-ATPase subunits associated with human genetic diseases; V-ATPase subunits and osteopetrosis/osteoporosis; screening of all V-ATPase subunits variants in GEFOS data and in-house data; spectrum of V-ATPase subunits during osteoclastogenesis; direct and indirect roles of subunits of V-ATPases in osteoclasts; V-ATPase-associated signaling pathways in osteoclasts; interactions among V-ATPase subunits in osteoclasts; osteoclast-specific V-ATPase inhibitors; perspective of future inhibitors or activators targeting V-ATPase subunits in the treatment of osteoporosis.

Phyllanthusmin Derivatives Induce Apoptosis and Reduce Tumor Burden in High-Grade Serous Ovarian Cancer by Late-Stage Autophagy Inhibition

High-grade serous ovarian cancer (HGSOC) is a lethal gynecological malignancy with a need for new therapeutics. Many of the most widely used chemotherapeutic drugs are derived from natural products or their semi-synthetic derivatives. We have developed potent synthetic analogues of a class of compounds known as phyllanthusmins, inspired by natural products isolated from Phyllanthus poilanei Beille. The most potent analogue, PHY34, had the highest potency in HGSOC cell lines in vitro and displayed cytotoxic activity through activation of apoptosis. PHY34 exerts its cytotoxic effects by inhibiting autophagy at a late stage in the pathway, involving the disruption of lysosomal function. The autophagy activator, rapamycin, combined with PHY34 eliminated apoptosis, suggesting that autophagy inhibition may be required for apoptosis. PHY34 was readily bioavailable through intraperitoneal administration in vivo where it significantly inhibited the growth of cancer cell lines in hollow fibers, as well as reduced tumor burden in a xenograft model. We demonstrate that PHY34 acts as a late-stage autophagy inhibitor with nanomolar potency and significant antitumor efficacy as a single agent against HGSOC in vivo This class of compounds holds promise as a potential, novel chemotherapeutic and demonstrates the effectiveness of targeting the autophagic pathway as a viable strategy for combating ovarian cancer. Mol Cancer Ther; 17(10); 2123-35. ©2018 AACR.

Advancements in Host-Based Interventions for Influenza Treatment

Influenza is a major acute respiratory infection that causes mortality and morbidity worldwide. Two classes of conventional antivirals, M2 ion channel blockers and neuraminidase inhibitors, are mainstays in managing influenza disease to lessen symptoms while minimizing hospitalization and death in patients with severe influenza. However, the development of viral resistance to both drug classes has become a major public health concern. Vaccines are prophylaxis mainstays but are limited in efficacy due to the difficulty in matching predicted dominant viral strains to circulating strains. As such, other potential interventions are being explored. Since viruses rely on host cellular functions to replicate, recent therapeutic developments focus on targeting host factors involved in virus replication. Besides controlling virus replication, potential targets for drug development include controlling virus-induced host immune responses such as the recently suggested involvement of innate lymphoid cells and NADPH oxidases in influenza virus pathogenesis and immune cell metabolism. In this review, we will discuss the advancements in novel host-based interventions for treating influenza disease.

Osteoclasts degrade bone and cartilage knee joint compartments through different resorption processes

Background

Osteoclasts have been strongly implicated in osteoarthritic cartilage degradation, at least indirectly via bone resorption, and have been shown to degrade cartilage in vitro. The osteoclast resorption processes required to degrade subchondral bone and cartilage—the remodeling of which is important in the osteoarthritic disease process—have not been previously described, although cathepsin K has been indicated to participate. In this study we profile osteoclast-mediated degradation of bovine knee joint compartments in a novel in vitro model using biomarkers of extracellular matrix (ECM) degradation to assess the potential of osteoclast-derived resorption processes to degrade different knee joint compartments.

Methods

Mature human osteoclasts were cultured on ECMs isolated from bovine knees—articular cartilage, cortical bone, and osteochondral junction ECM (a subchondral bone-calcified cartilage mixture)—in the presence of inhibitors: the cystein protease inhibitor E-64, the matrix metalloproteinase (MMP) inhibitor GM6001, or the vacuolar-type H⁺-ATPase (V-ATPase) inhibitor diphyllin. Biomarkers of bone (calcium and C-terminal type I collagen (CTX-I)) and cartilage (C2M) degradation were measured in the culture supernatants. Cultures without osteoclasts were used as background samples. Background-subtracted biomarker levels were normalized to the vehicle condition and were analyzed using analysis of variance with Tukey or Dunnett’s T3 post hoc test, as applicable.

Results

Osteochondral CTX-I release was inhibited by E-64 (19% of vehicle, p = 0.0008), GM6001 (51% of vehicle, p = 0.013), and E-64/GM6001 combined (4% of vehicle, p = 0.0007)—similarly to bone CTX-I release. Diphyllin also inhibited osteochondral CTX-I release (48% of vehicle, p = 0.014), albeit less than on bone (4% of vehicle, p < 0.0001). Osteochondral C2M release was only inhibited by E-64 (49% of vehicle, p = 0.07) and GM6001 (14% of vehicle, p = 0.006), with complete abrogation when combined (0% of vehicle, p = 0.004). Cartilage C2M release was non-significantly inhibited by E-64 (69% of vehicle, p = 0.98) and was completely abrogated by GM6001 (0% of vehicle, p = 0.16).

Conclusions

Our study supports that osteoclasts can resorb non-calcified and calcified cartilage independently of acidification. We demonstrated both MMP-mediated and cysteine protease-mediated resorption of calcified cartilage. Osteoclast functionality was highly dependent on the resorbed substrate, as different ECMs required different osteoclast processes for degradation. Our novel culture system has potential to facilitate drug and biomarker development aimed at rheumatic diseases, e.g. osteoarthritis, where pathological osteoclast processes in specific joint compartments may contribute to the disease process.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1564-5) contains supplementary material, which is available to authorized users.

Effects of diphyllin as a novel V-ATPase inhibitor on TE-1 and ECA-109 cells

Diphyllin is a natural component of traditional Chinese medicine, which effectively inhibits V-ATPase activity and affects the progression of cancer. However, few studies have been conducted on esophageal cancer, and the mechanisms remain to be elucidated. The present study revealedthat diphyllin inhibited proliferation and induced S arrest in esophageal cancer cell lines TE-1 and ECA-109. Further experiments revealed that diphyllin inhibited V-ATPase activity and decreased the mRNA expression of mammalian target of rapamycin complex 1 (mTORC1), hypoxia-inducible factor-1α (HIF-1α), and vascular endothelial growth factor (VEGF). The present study also revealed that diphyllin inhibited proliferation and reduced the formation of new blood vessels. Diphyllin inhibited blood metastasis by regulating the mTORC1/HIF-1α-/VEGF pathway, therefore it could be considered as a new V-ATPase inhibitor to treat esophageal cancer.

The Search for Anticancer Agents from Tropical Plants

Many of the clinically used anticancer agents in Western medicine are derived from secondary metabolites found in terrestrial microbes, marine organisms, and higher plants, with additional compounds of this type being currently in clinical trials. If plants are taken specifically, it is generally agreed that the prospects of encountering enhanced small organic-molecule chemical diversity are better if tropical rather than temperate species are investigated in drug discovery efforts. Plant collection in tropical source countries requires considerable preparation and organization to conduct in a responsible manner that abides by the provisions of the 1992 Rio Convention of Biological Diversity and the 2010 Nagoya Protocol on Access to Genetic Resources. Correct taxonomic identifications and enhanced procedures for processing and documenting plant samples when collected in often difficult terrain are required. Phytochemical aspects of the work involve solvent fractionation, known compound dereplication, preliminary in vitro testing, and prioritization, leading to "activity-guided fractionation", compound structure determination, and analog development. Further evaluation of lead compounds requires solubility, formulation, preliminary pharmacokinetics, and in vivo testing in suitable models. Covering the work of the authors carried out in two sequential multidisciplinary, multi-institutional research projects, examples of very promising compounds discovered from plants acquired from Africa, Southeast Asia, the Americas, and the Caribbean region, and with potential anticancer activity will be mentioned. These include plant secondary metabolites of the diphyllin lignan, cyclopenta[b]benzofuran, triterpenoid, and tropane alkaloid types.

Key Triggers of Osteoclast-Related Diseases and Available Strategies for Targeted Therapies: A Review

Osteoclasts, the only cells with bone resorption functions in vivo, maintain the balance of bone metabolism by cooperating with osteoblasts, which are responsible for bone formation. Excessive activity of osteoclasts causes many diseases such as osteoporosis, periprosthetic osteolysis, bone tumors, and Paget's disease. In contrast, osteopetrosis results from osteoclast deficiency. Available strategies for combating over-activated osteoclasts and the subsequently induced diseases can be categorized into three approaches: facilitating osteoclast apoptosis, inhibiting osteoclastogenesis, and impairing bone resorption. Bisphosphonates are representative molecules that function by triggering osteoclast apoptosis. New drugs, such as tumor necrosis factor and receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitors (e.g., denosumab) have been developed for targeting the receptor activator of nuclear factor kappa-B /RANKL/osteoprotegerin system or CSF-1/CSF-1R axis, which play critical roles in osteoclast formation. Furthermore, vacuolar (H⁺)-ATPase inhibitors, cathepsin K inhibitors, and glucagon-like peptide 2 impair different stages of the bone resorption process. Recently, significant achievements have been made in this field. The aim of this review is to provide an updated summary of the current progress in research involving osteoclast-related diseases and of the development of targeted inhibitors of osteoclast formation.

Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments

Vacuolar H⁺-ATPases (V-ATPases) are multi-subunit enzymes that play housekeeping roles in eukaryotic cells by acidifying lysosomes, late endosomes, Golgi, and other membrane-bounded compartments. Beyond that, V-ATPases have specialized functions in certain cell types linked to diseases including osteoporosis and cancer. Efforts to identify strategies to develop inhibitors selective for V-ATPases that are involved in disease progression have been ongoing for more than two decades, but so far have not yielded a therapeutic agent that has been translated to the clinic. Recent basic science studies have identified unexpected roles for V-ATPases in nutrient and energy sensing, and renin/angiotensin signaling, which offer additional incentives for considering V-ATPases as therapeutic targets. This article briefly reviews efforts to utilize inhibitors of V-ATPases as drugs. Primary focus is on recent "rational" efforts to identify small molecule inhibitors of the V-ATPases that are selectively expressed in osteoclasts and cancer cells. Enoxacin and bis-enoxacin are two molecules that emerged from these efforts. These molecules block a binding interaction between V-ATPases and microfilaments that occurs in osteoclasts, but not most other cell types, which relates to the specialized function of V-ATPases in bone resorption. Enoxacin and bis-enoxacin have proven useful in the treatment of bone diseases and cancer in animal models and display therapeutic effects that are different, and perhaps better, than current drugs. These results provide evidence that agents targeting subsets of V-ATPases may prove useful in the clinic.

Vacuolar ATPase as a possible therapeutic target in human acute myeloid leukemia

INTRODUCTION

V-ATPase is a proton pump expressed both in the membrane of intracellular organelles (e.g. endosomes, lysosomes, Golgi structures) and the plasma membrane. It is an important regulator of organellar functions, intracellular molecular trafficking, intercellular communication and intracellular signaling. It is therefore considered as a possible therapeutic target in the treatment of human malignancies. Areas covered: Relevant publications were identified through literature searches in the PubMed database. We searched for original articles and reviews describing the possible importance of V-ATPase for leukemogenesis and chemosensitivity in human myeloid cells, especially acute myeloid leukemia (AML) cells. Expert commentary: The expression of V-ATPase in the primary human AML cells varies between patients, and high levels are associated with high constitutive release of a wide range of soluble mediators. Several of the molecules included in the V-ATPase interactome may also be important in leukemogenesis and/or development of chemoresistance in human AML. Therapeutic targeting of V-ATPase should therefore be regarded as a possible therapeutic strategy in human AML, but the efficiency of such targeting will probably differ between patients. The possibility of toxicity, especially hematological toxicity and immunosuppression, also has to be clarified.

Nanoparticulate vacuolar ATPase blocker exhibits potent host-targeted antiviral activity against feline coronavirus

Feline infectious peritonitis (FIP), caused by a mutated feline coronavirus, is one of the most serious and fatal viral diseases in cats. The disease remains incurable, and there is no effective vaccine available. In light of the pathogenic mechanism of feline coronavirus that relies on endosomal acidification for cytoplasmic entry, a novel vacuolar ATPase blocker, diphyllin, and its nanoformulation are herein investigated for their antiviral activity against the type II feline infectious peritonitis virus (FIPV). Experimental results show that diphyllin dose-dependently inhibits endosomal acidification in fcwf-4 cells, alters the cellular susceptibility to FIPV, and inhibits the downstream virus replication. In addition, diphyllin delivered by polymeric nanoparticles consisting of poly(ethylene glycol)-block-poly(lactide-co-glycolide) (PEG-PLGA) further demonstrates an improved safety profile and enhanced inhibitory activity against FIPV. In an in vitro model of antibody-dependent enhancement of FIPV infection, diphyllin nanoparticles showed a prominent antiviral effect against the feline coronavirus. In addition, the diphyllin nanoparticles were well tolerated in mice following high-dose intravenous administration. This study highlights the therapeutic potential of diphyllin and its nanoformulation for the treatment of FIP.

Identification of Novel Bisbenzimidazole Derivatives as Anticancer Vacuolar (H⁺)-ATPase Inhibitors

The vacuolar (H⁺)-ATPases (V-ATPases) are a family of ATP-driven proton pumps and they have been associated with cancer invasion, metastasis, and drug resistance. Despite the clear involvement of V-ATPases in cancer, the therapeutic use of V-ATPase-targeting small molecules has not reached human clinical trials to date. Thus, V-ATPases are emerging as important targets for the identification of potential novel therapeutic agents. We identified a bisbenzimidazole derivative (V) as an initial hit from a similarity search using four known V-ATPase inhibitors (I–IV). Based on the initial hit (V), we designed and synthesized a focused set of novel bisbenzimidazole analogs (2a–e). All newly prepared compounds have been screened for selected human breast cancer (MDA-MB-468, MDA-MB-231, and MCF7) and ovarian cancer (A2780, Cis-A2780, and PA-1) cell lines, along with the normal breast epithelial cell line, MCF10A. The bisbenzimidazole derivative (2e) is active against all cell lines tested. Remarkably, it demonstrated high cytotoxicity against the triple-negative breast cancer (TNBC) cell line, MDA-MB-468 (IC₅₀ = 0.04 ± 0.02 μM). Additionally, it has been shown to inhibit the V-ATPase pump that is mainly responsible for acidification. To the best of our knowledge the bisbenzimidazole pharmacophore has been identified as the first V-ATPase inhibitor in its class. These results strongly suggest that the compound 2e could be further developed as a potential anticancer V-ATPase inhibitor for breast cancer treatment.

Cleistanthin A inhibits the invasion and metastasis of human melanoma cells by inhibiting the expression of matrix metallopeptidase-2 and -9

It has been demonstrated that numerous types of metastatic cancer overexpress vacuolar-type H⁺ (V)-ATPases. It may be possible to inhibit the growth and metastasis of human cancer cells by inhibiting V-ATPases. It was previously reported that diphyllin, a novel V-ATPase inhibitor, can inhibit the migration and invasion of SGC7901 human gastric cancer cells; however, the effects of cleistanthin A (CA), a diphyllin glycoside, on melanoma cells has not been demonstrated. The present study aimed to investigate the effect of CA as a V-ATPase inhibitor and its effects on the invasion and metastasis of A375 cells. The results of an MTT assay in the present study indicated that the growth inhibition of A375 cells by CA was induced in a dose- and time-dependent manner; however, A375 cell viability was not significantly affected by low concentrations (0.03, 0.1 and 0.3 µM) after 24 h. Similar results were obtained by viable cell counting with trypan blue. Therefore, these concentrations of CA were selected for the treatment of A375 cells in further experiments. It was demonstrated that CA inhibited the expression of V-ATPases in a dose-dependent manner and decreased the internal pH level of A375 cells. Alterations to the lysosomal pH were associated with the CA concentration. Furthermore, CA treatment induced a significant decrease in cell migration and invasion, as demonstrated with wound-healing and Transwell assays. Gelatin zymography and western blot analysis demonstrated that the expression levels of matrix metallopeptidase (MMP)-2 and -9 decreased following CA treatment. Therefore, CA can be characterized as a novel V-ATPase inhibitor for the treatment of melanoma that may inhibit invasion and metastasis by downregulating the expression of MMP-2 and -9.

Vacuolar ATPase in phago(lyso)some biology

Many eukaryotic cells ingest extracellular particles in a process termed phagocytosis which entails the generation of a new intracellular compartment, the phagosome. Phagosomes change their composition over time and this maturation process culminates in their fusion with acidic, hydrolase-rich lysosomes. During the maturation process, degradation and, when applicable, killing of the cargo may ensue. Many of the events that are pathologically relevant depend on strong acidification of phagosomes by the 'vacuolar' ATPase (V-ATPase). This protein complex acidifies the lumen of some intracellular compartments at the expense of ATP hydrolysis. We discuss here the roles and importance of V-ATPase in intracellular trafficking, its distribution, inhibition and activities, its role in the defense against microorganisms and the counteractivities of pathogens.

Inhibiting clathrin-mediated endocytosis of the leucine-rich G protein-coupled receptor-5 diminishes cell fitness

The leucine-rich G protein-coupled receptor-5 (LGR5) is expressed in adult tissue stem cells of many epithelia, and its overexpression is negatively correlated with cancer prognosis. LGR5 potentiates WNT/β-catenin signaling through its unique constitutive internalization property that clears negative regulators of the WNT-receptor complex from the membrane. However, both the mechanism and physiological relevance of LGR5 internalization are unclear. Therefore, a natural product library was screened to discover LGR5 internalization inhibitors and gain mechanistic insight into LGR5 internalization. The plant lignan justicidin B blocked the constitutive internalization of LGR5. Justicidin B is structurally similar to more potent vacuolar-type H⁺-ATPase inhibitors, which all inhibited LGR5 internalization by blocking clathrin-mediated endocytosis. We then tested the physiological relevance of LGR5 internalization blockade in vivo A LGR5-rainbow (LBOW) mouse line was engineered to express three different LGR5 isoforms along with unique fluorescent protein lineage reporters in the same mouse. In this manner, the effects of each isoform on cell fate can be simultaneously assessed through simple fluorescent imaging for each lineage reporter. LBOW mice express three different forms of LGR5, a wild-type form that constitutively internalizes and two mutant forms whose internalization properties have been compromised by genetic perturbations within the carboxyl-terminal tail. LBOW was activated in the intestinal epithelium, and a year-long lineage-tracing course revealed that genetic blockade of LGR5 internalization diminished cell fitness. Together these data provide proof-of-concept genetic evidence that blocking the clathrin-mediated endocytosis of LGR5 could be used to pharmacologically control cell behavior.

Regulation and Function of Lentiviral Vector-Mediated TCIRG1 Expression in Osteoclasts from Patients with Infantile Malignant Osteopetrosis: Implications for Gene Therapy

Infantile malignant osteopetrosis (IMO) is a rare, recessive disorder characterized by increased bone mass caused by dysfunctional osteoclasts. The disease is most often caused by mutations in the TCIRG1 gene encoding a subunit of the V-ATPase involved in the osteoclasts capacity to resorb bone. We previously showed that osteoclast function can be restored by lentiviral vector-mediated expression of TCIRG1, but the exact threshold for restoration of resorption as well as the cellular response to vector-mediated TCIRG1 expression is unknown. Here we show that expression of TCIRG1 protein from a bicistronic TCIRG1/GFP lentiviral vector was only observed in mature osteoclasts, and not in their precursors or macrophages, in contrast to GFP expression, which was observed under all conditions. Thus, vector-mediated TCIRG1 expression appears to be post-transcriptionally regulated, preventing overexpression and/or ectopic expression and ensuring protein expression similar to that of wild-type osteoclasts. Codon optimization of TCIRG1 led to increased expression of mRNA but lower levels of protein and functional rescue. When assessing the functional rescue threshold in vitro, addition of 30 % CB CD34⁺ cells to IMO CD34⁺ patient cells was sufficient to completely normalize resorptive function after osteoclast differentiation. From both an efficacy and a safety perspective, these findings will clearly be of benefit during further development of gene therapy for osteopetrosis.