Evaluating the cancer therapeutic potential of cardiac glycosides

The Madagascar palm genome provides new insights on the evolution of Apocynaceae specialized metabolism

Specialized metabolites possess diverse interesting biological activities and some cardenolides- and monoterpene indole alkaloids- (MIAs) derived pharmaceuticals are currently used to treat human diseases such as cancers or hypertension. While these two families of biocompounds are produced by specific subfamilies of Apocynaceae, one member of this medicinal plant family, the succulent tree Pachypodium lamerei Drake (also known as Madagascar palm), does not produce such specialized metabolites. To explore the evolutionary paths that have led to the emergence and loss of cardenolide and MIA biosynthesis in Apocynaceae, we sequenced and assembled the P. lamerei genome by combining Oxford Nanopore Technologies long-reads and Illumina short-reads. Phylogenomics revealed that, among the Apocynaceae whose genomes have been sequenced, the Madagascar palm is so far the species closest to the common ancestor between MIA producers/non-MIA producers. Transposable elements, constituting 72.48% of the genome, emerge as potential key players in shaping genomic architecture and influencing specialized metabolic pathways. The absence of crucial MIA biosynthetic genes such as strictosidine synthase in P. lamerei and non-Rauvolfioideae species hints at a transposon-mediated mechanism behind gene loss. Phylogenetic analysis not only showcases the evolutionary divergence of specialized metabolite biosynthesis within Apocynaceae but also underscores the role of transposable elements in this intricate process. Moreover, we shed light on the low conservation of enzymes involved in the final stages of MIA biosynthesis in the distinct MIA-producing plant families, inferring independent gains of these specialized enzymes along the evolution of these medicinal plant clades. Overall, this study marks a leap forward in understanding the genomic dynamics underpinning the evolution of specialized metabolites biosynthesis in the Apocynaceae family, with transposons emerging as potential architects of genomics restructuring and gene loss.

The ethnomedicine, phytochemistry, and pharmacological properties of the genus Bersama: current review and future perspectives

Bersama (Melianthaceae) has been used in traditional medicine for a wide range of ailments, including blood purifier, immune booster, psychotropic medication, and treatment for malaria, hepatitis, infertility, diabetes, impotency, meningitis, and stroke. This review gathers fragmented information from the literature on ethnomedicinal applications, phytochemistry, pharmacology, and toxicology of the Bersama genus. It also explores the therapeutic potential of the Bersama genus in ethnophytopharmacology, allowing for further investigation. All the available information published in the English language on Bersama genus was compiled from electronic databases such as Academic Journals, Ethnobotany, Google Scholar, PubMed, Science Direct, Web of Science, and library search using the following keywords: "Bersama genus," "traditional use," "phytochemistry," "pharmacological effects," and "toxicology". The ethnomedical applications of the Bersama genus have been recorded, and it has been used traditionally for more than 30 different types of ailments. Thus far, more than 50 compounds have been isolated from the genus. Cardiac glycosides and terpenoids are the main compounds isolated from the Bersama genus. Different plant parts of Bersama genus extracts demonstrated a wide range of pharmacological properties, including antioxidant, antimalarial, antidiabetic, antiviral, anti-inflammatory, and cytotoxic activity. Exemplary drug leads from the genus include mangiferin and quercetin-3-O-arabinopyranoside, both of which have antioxidant activities. Bersama genus has long been used to cure a wide range of ailments. Bersama genus extracts and phytochemicals have been found to have promising pharmacological activities. Further study on promising crude extracts and compounds is required to develop innovative therapeutic candidates.

Cardenolide Increase in Foxglove after 2,1,3-Benzothiadiazole Treatment Reveals a Potential Link between Cardenolide and Phytosterol Biosynthesis

Cardenolides are steroidal metabolites in Digitalis lanata with potent cardioactive effects on animals. In plants, cardenolides are likely involved in various stress responses. However, the molecular mechanism of cardenolide increase during stresses is mostly unknown. Additionally, cardenolides are proposed to arise from cholesterol, but indirect results show that phytosterols may also be substrates for cardenolide biosynthesis. Here, we show that cardenolides increased after methyl jasmonate (MJ), sorbitol, potassium chloride (KCl) and salicylic acid analog [2,1,3-benzothiadiazole (BTH)] treatments. However, the expression of three known genes for cardenolide biosynthesis did not correlate well with these increases. Specifically, the expression of progesterone-5β-reductases (P5βR and P5βR2) did not correlate with the cardenolide increase. The expression of 3β-hydroxysteroid dehydrogenase (3βHSD) correlated with changes in cardenolide levels only during the BTH treatment. Mining the D. lanata transcriptome identified genes involved in cholesterol and phytosterol biosynthesis: C24 sterol sidechain reductase 1 (SSR1), C4 sterol methyl oxidase 1, and 3 (SMO1 and SMO3). Surprisingly, the expression of all three genes correlated well with the cardenolide increase after the BTH treatment. Phylogenetic analysis showed that SSR1 is likely involved in both cholesterol and phytosterol biosynthesis. In addition, SMO1 is likely specific to phytosterol biosynthesis, and SMO3 is specific to cholesterol biosynthesis. These results suggest that stress-induced increase of cardenolides in foxglove may correlate with cholesterol and phytosterol biosynthesis. In summary, this work shows that cardenolides are important for stress responses in D. lanata and reveals a potential link between phytosterol and cardenolide biosynthesis.

Bufalin inhibits epithelial-mesenchymal transition and increases radiosensitivity of non-small cell lung cancer via inhibition of the Src signaling

Background

Epithelial-mesenchymal transition (EMT) is a biological process involved in tumor migration, invasion, and radiotherapy resistance. Bufalin can affect the proliferation, apoptosis and invasion of tumor cells by regulating multiple signaling pathways. Whether bufalin can increase radiosensitivity through EMT deserves further investigation.

Methods

In this study, we investigated the effect of bufalin on the EMT and radiosensitivity of non-small cell lung cancer (NSCLC) and the underlying molecular mechanism. NSCLC cells were treated with bufalin (at a dose of 0-100 nM) or irradiated with 6 MV X-rays (4 Gy/min). The effects of bufalin on cell survival, cell cycle, radiosensitivity, cell migration, and invasion were detected. Western blot was used to analyze the gene expression changes of Src signaling in NSCLC cell induced by Bufalin.

Results

Bufalin significantly inhibited cell survival, migration, and invasion and induced G2/M arrest and apoptosis. Cells co-treated with bufalin and radiation manifested a higher inhibitory effect compared to those treated with radiation or bufalin alone. Furthermore, the levels of p-Src and p-STAT3 were considerably reduced following bufalin treatment. Interestingly, elevated p-Src and p-STAT3 were observed in cells treated with radiation. Bufalin inhibited radiation-induced p-Src and p-STAT3, whereas the knockdown of Src abrogated the effects of bufalin on cell migration, invasion, EMT, and radiosensitivity.

Conclusions

Bufalin inhibits EMT and enhances radiosensitivity through targeting Src signaling in NSCLC.

The botanical drug PBI-05204, a supercritical CO2 extract of Nerium oleander, sensitizes alveolar and embryonal rhabdomyosarcoma to radiotherapy in vitro and in vivo

Treatment of rhabdomyosarcoma (RMS), the most common a soft tissue sarcoma in childhood, provides intensive multimodal therapy, with radiotherapy (RT) playing a critical role for local tumor control. However, since RMS efficiently activates mechanisms of resistance to therapies, despite improvements, the prognosis remains still largely unsatisfactory, mainly in RMS expressing chimeric oncoproteins PAX3/PAX7-FOXO1, and fusion-positive (FP)-RMS. Cardiac glycosides (CGs), plant-derived steroid-like compounds with a selective inhibitory activity of the Na+/K+-ATPase pump (NKA), have shown antitumor and radio-sensitizing properties. Herein, the therapeutic properties of PBI-05204, an extract from Nerium oleander containing the CG oleandrin already studied in phase I and II clinical trials for cancer patients, were investigated, in vitro and in vivo, against FN- and FP-RMS cancer models. PBI-05204 induced growth arrest in a concentration dependent manner, with FP-RMS being more sensitive than FN-RMS, by differently regulating cell cycle regulators and commonly upregulating cell cycle inhibitors p21Waf1/Cip1 and p27Cip1/Kip1. Furthermore, PBI-05204 concomitantly induced cell death on both RMS types and senescence in FN-RMS. Notably, PBI-05204 counteracted in vitro migration and invasion abilities and suppressed the formation of spheroids enriched in CD133+ cancer stem cells (CSCs). PBI-05204 sensitized both cell types to RT by improving the ability of RT to induce G2 growth arrest and counteracting the RT-induced activation of both Non‐Homologous End‐Joining and homologous recombination DSBs repair pathways. Finally, the antitumor and radio-sensitizing proprieties of PBI-05204 were confirmed in vivo. Notably, both in vitro and in vivo evidence confirmed the higher sensitivity to PBI-05204 of FP-RMS. Thus, PBI-05204 represents a valid radio-sensitizing agent for the treatment of RMS, including the intrinsically radio-resistant FP-RMS.

Ononitol Monohydrate-A Glycoside Potentially Inhibit HT-115 Human Colorectal Cancer Cell Proliferation through COX-2/PGE-2 Inflammatory Axis Regulations

We aimed to inhibit HT-115 human colorectal cancer cell proliferation using ononitol monohydrate (OMH), a bioactive principle isolated from Cassia tora (L.). The cytotoxicity of OMH has been assayed using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide), cell and nuclear morphology, and apoptosis mechanisms have been analyzed using real-time PCR. Higher doses of OMH potentially inhibit 84% of HT-115 cell viability; we observed that the IC₅₀ level was 3.2 µM in 24 h and 1.5 µM in 48 h. The treatment with 3.2 µM of OMH for 48 h characteristically showed 64% apoptotic cells and 3% necrotic cells, confirmed by propidium iodide and acridine orange/ethidium bromide (AO/ErBr) staining. We found the overexpression of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE-2) in the control HT-115 cells, which was directly associated with colorectal tumorigenesis. However, 3.2 µM of OMH treatment to HT-115 cells for 48 h significantly reduced inflammatory genes, such as TNF-α/IL-1β and COX-2/PGE-2. The downregulation of COX-2 and PGE-2 was more significant with the 3.2 µM dose when compared to the 1.5 µM dose of OMH. Additionally, the protein levels of COX-2 and PGE-2 were decreased in the 3.2 µM OMH-treated cells compared to the control. We found significantly (p ≤ 0.01) increased mRNA expression levels of tumor-suppressor genes, such as pRb2, Cdkn1a, p53, and caspase-3, and decreased Bcl-2, mdm2, and PCNA after 48 h was confirmed with apoptotic stimulation. In conclusion, the antiproliferative effect of OMH via the early suppression of protumorigenic inflammatory agents TNF-α/IL-1β, COX-2/PGE-2 expression, and the increased expression levels of tumor-suppressor genes Cdkn1a and pRb2, which enhanced the activation of Bax and p53.

Glycosides and Vascular Complications of Diabetes

Diabetes is linked with various microvascular and macrovascular complications. Nephropathy, neuropathy and retinopathy are important microvascular complications of diabetes. Different types of secondary metabolites including glycosides have been studied for their effects in diabetic complications. Various glycosides such as flavanoid glycosides and saponin glycosides are reported for their beneficial effects in diabetic nephropathy, neuropathy, retinopathy and cardiomyopathy by action on various pathways involved in the progression of these complications. Coumarin glycosides and cryanogenic glycosides have been studied for their effective role in diabetic nephropathy. Phenolic glycosides and anthraquinone glycosides also have beneficial role in diabetic neuropathy. The present review focuses on various classes of glycosides and their role in the prevention and treatment of vascular complications of diabetes.

Drug screening and genome editing in human pancreatic cancer organoids identifies drug-gene interactions and candidates for off-label treatment

Pancreatic cancer (PDAC) is a highly aggressive malignancy for which the identification of novel therapies is urgently needed. Here, we establish a human PDAC organoid biobank from 31 genetically distinct lines, covering a representative range of tumor subtypes, and demonstrate that these reflect the molecular and phenotypic heterogeneity of primary PDAC tissue. We use CRISPR-Cas9 genome editing and drug screening to characterize drug-gene interactions with ARID1A and BRCA2. We find that missense- but not frameshift mutations in the PDAC driver gene ARID1A are associated with increased sensitivity to the kinase inhibitors dasatinib (p < 0.0001) and VE-821 (p < 0.0001). We conduct an automated drug-repurposing screen with 1,172 FDA-approved compounds, identifying 26 compounds that effectively kill PDAC organoids, including 19 chemotherapy drugs currently approved for other cancer types. We validate the activity of these compounds in vitro and in vivo. The in vivo validated hits include emetine and ouabain, compounds which are approved for non-cancer indications and which perturb the ability of PDAC organoids to respond to hypoxia. Our study provides proof-of-concept for advancing precision oncology and identifying candidates for drug repurposing via genome editing and drug screening in tumor organoid biobanks.

Cardiac glycosides from Digitalis lanata and their cytotoxic activities

Cardiac glycosides (CGs) are good candidates as drug leads in the treatment of cancer because of their structural diversities and potent biological activities. In this study, fifteen CGs including three new ones (1–3) were isolated from Digitalis lanata Ehrh. Their structures were elucidated by HRESIMS, NMR spectroscopic methods, including homonuclear and heteronuclear coupling constant analysis, and acid-catalyzed hydrolysis and derivatization analysis of the sugar chain. The cytotoxic activities of these CGs were evaluated against three human cancer cell lines (A549, HeLa and MCF-7 cell lines), and all of them showed strong activities at nanomolar scale. The flow cytometric analysis indicated that compound 1 induced cell cycle arrest in the G2/M phase. Transcriptome analysis revealed a panel of possible targets for compound 1. RT-PCR and western blot experiments showed that 1 significantly inhibited the expression of vasohibin-2 (VASH2). Moreover, compound 1 restrained angiogenesis in a concentration-dependent manner in the chick embryo chorioallantoic membrane (CAM) model.

Cardiac glycosides (CGs) are good candidates as drug leads in the treatment of cancer because of their structural diversities and potent biological activities.

Screening for Selective Anticancer Activity of 65 Extracts of Plants Collected in Western Andalusia, Spain

Finding cytotoxic drugs with a high selectivity towards cancer cells is crucial to improve the low survival rates of patients diagnosed with metastatic cancers. Since plants are an important source of anticancer drugs, we have screened 65 extracts from 45 plants collected in several areas of Western Andalusia (Spain) for cytotoxic activity on lung cancer cells versus lung normal cells. An extract from the leaves of Tetraclinis articulata (Vahl) Mast. (Cupressaceae) showed a marked cytotoxicity (IC50 = 0.37 ± 0.03 μg/mL) and selectivity (selectivity index = 378.3) against the lung cancer cells; cisplatin, 5-fluorouracil, and an extract from the leaves of Taxus baccata L. (Taxaceae) were less cytotoxic and selective. Extracts from Cascabela thevetia (L.) Lippold (Apocynaceae), Frangula alnus Mill. (Rhamnaceae), Iberis ciliata subsp. contracta (Pers.) Moreno (Brassicaceae), Juniperus macrocarpa Sm (Cupressaceae), and Pancratium maritimum L. (Amaryllidaceae) also showed selective cytotoxicity (selectivity index > 10). Active extracts were also tested against a panel of cancer cell lines from a variety tissues. The plants identified in this work are potential sources of natural compounds with selective toxicity towards cancer cells.

Antitumour effect of odoroside A and its derivative on human leukaemia cells through the ROS/JNK pathway

Oleandrigenin-3-O-β-D-diginoside (a derivative of odoroside A), isolated and purified by our group, has seldom been explored for its pharmacological activity. This study aimed at clarifying the mechanisms towards the leukaemia-suppressive role of odoroside A (compound #1) and its derivative, oleandrigenin-3-O-β-D-diginoside (compound #2) isolated from Nerium oleander. Viability and nuclear morphology change were assessed by CCK-8 assay and fluorescence microscope, respectively. Then, the cell apoptosis and autophagy induced by the compounds were detected by flow cytometry and Western blot. Xenograft model of nude mice was also applied to measure the leukaemia-suppressive effects of compound #2 in vivo. The result displayed that compound #1 and compound #2 inhibited the proliferation of HL60 and K562 cells and stronger effects were found in HL60 than K562 cells. Both of the compounds induced a dose-dependent apoptosis and autophagy in HL60 cells, where compound #2 was more potent than compound #1. Compound #2 also demonstrated a time-dependent apoptosis and autophagy in HL60 cells. Furthermore, ROS generation and JNK phosphorylation occurred in a dose-dependent manner in the cells treated with compound #2. Mitochondria also played critical role, proved by the decrease of Bcl-2, the release of cyto c to cytosol and the activation of caspase-3 and caspase-9. Moreover, the antitumour effects of compound #2 were validated in the nude mouse xenograft model in vivo. Odoroside A and its derivative inhibited the growth of leukaemia by inducing apoptosis and autophagy through the activation of ROS/JNK pathway. These results suggest that the compounds can serve as potential antitumour agents against leukaemia, especially acute myeloid leukaemia (AML).

Bulbous Plants Drimia: "A Thin Line between Poisonous and Healing Compounds" with Biological Activities

Drimia (synonym Urginea) plants are bulbous plants belonging to the family Asparagaceae (formerly the family Hyacinthaceae) and are distinctive, powerful medicinal plants. Just some species are indigenous to South Africa and have been traditionally utilized for centuries to cure various diseases and/or ailments. They have been recognized among the most famous and used medicinal plants in South Africa. Traditionally, the plants are used for various illnesses such as dropsy, respiratory disease, bone and joint complications, skin disorders, epilepsy and cancer. A number of studies have reported biological properties such as antiviral, antibacterial, antioxidant and anti-inflammatory, immunomodulatory, and anticancer activities. Their bulbs are a popular treatment for colds, measles, pneumonia, coughs, fever and headaches. However, some plant species are regarded as one of the six most common poisonous plants in Southern Africa that are toxic to livestock and humans. Due to the therapeutic effects of the Drimia plant bulb, research has focused on the phytochemicals of Drimia species. The principal constituents isolated from this genus are cardiac glycosides. In addition, phenolic compounds, phytosterols and other phytochemical constituents were identified. This study constitutes a critical review of Drimia species' bioactive compounds, toxicology, biological properties and phytochemistry, advocating it as an important source for effective therapeutic medicine. For this purpose, various scientific electronic databases such as ScienceDirect, Scopus, Google Scholar, PubMed and Web of Science were researched and reviewed to conduct this study. Despite well-studied biological investigations, there is limited research on the toxic properties and the toxic compounds of certain Drimia species. Searching from 2017 to 2021, Google Scholar search tools retrieved 462 publications; however, only 3 investigated the toxicity and safety aspects of Drimia. The aim was to identify the current scientific research gap on Drimia species, hence highlighting a thin line between poisonous and healing compounds, dotted across numerous publications, in this review paper.

Emergence of Cardiac Glycosides as Potential Drugs: Current and Future Scope for Cancer Therapeutics

Cardiac glycosides are natural sterols and constitute a group of secondary metabolites isolated from plants and animals. These cardiotonic agents are well recognized and accepted in the treatment of various cardiac diseases as they can increase the rate of cardiac contractions by acting on the cellular sodium potassium ATPase pump. However, a growing number of recent efforts were focused on exploring the antitumor and antiviral potential of these compounds. Several reports suggest their antitumor properties and hence, today cardiac glycosides (CG) represent the most diversified naturally derived compounds strongly recommended for the treatment of various cancers. Mutated or dysregulated transcription factors have also gained prominence as potential therapeutic targets that can be selectively targeted. Thus, we have explored the recent advances in CGs mediated cancer scope and have considered various signaling pathways, molecular aberration, transcription factors (TFs), and oncogenic genes to highlight potential therapeutic targets in cancer management.

Anticancer potential of cardiac glycosides and steroid-azole hybrids

Steriods are well-known scaffolds that have a widespread occurrence in different compounds characterized by extensive biological properties including anticancer activity. Structural modifications on steroids always generate potential lead compounds with superior bioactivity, and creation of steroid hybrids by combining steroid with other anticancer pharmacophores in one molecule, which can exert the anticancer activity through different mechanisms, is one of the most promising strategies to enhance efficiency, overcome drug resistance and reduce side effects. Sugars and azoles, can act on diverse receptors, proteins and enzymes in cancer cells, are pharmacologically significant scaffolds in the development of novel anticancer agents. Therefore, steroid-sugar hybrids cardiac glycosides and steroid-azole hybrids are privileged scaffolds for the discovery of novel anticancer candidates. This review emphasized on the development, the structure-activity relationship and the mechanism of action of cardiac glycosides and steroid-azole hybrids with potential application for fighting against various cancers including drug-resistant forms to facilitate further rational design of novel drug candidates covering articles published between 2015 and 2020.

Implications of Synthetic Modifications of the Cardiotonic Steroid Lactone Ring on Cytotoxicity

Na,K-ATPase (NKA) and cardiotonic steroids (CTS) have shown potent cytotoxic and anticancer effects. Here, we have synthesized a series of CTS digoxin derivatives (γ-benzylidene) with substitutions in the lactone ring and evaluated the cytotoxicity caused by digoxin derivatives in tumor and non-tumor cells lines, as well as their effects on NKA. The cytotoxicity assay was determined in HeLa, A549, and WI-26 VA4 after they were treated for 48 h with increased concentrations of CTS. The effects of CTS on NKA activity and immunoblotting of α1 and β1 isoforms were evaluated at IC₅₀ concentrations in A549 cell membrane. NKA activity from mouse brain cortex was also measured. The majority of CTS exhibited low cytotoxicity in tumor and non-tumor cells, presenting IC₅₀ values at micromolar concentrations, while digoxin showed cytotoxicity at nanomolar concentrations. BD-15 presented the lowest IC₅₀ value (8 µM) in A549 and reduced its NKA activity in 28%. In contrast, BD-7 was the compound that most inhibited NKA (56% inhibition) and presented high IC₅₀ value for A549. In mouse cortex, only BD-15 modulated the enzyme activity in a concentration-dependent inhibition curve. These results demonstrate that the cytotoxicity of these compounds is not related to NKA inhibition. The substitutions in the lactone ring of digoxin led to an increase in the cytotoxic concentration in tumor cells, which may not be interesting for cancer, but it has the advantage of increasing the therapeutic margin of these molecules when compared to classic CTS, and can be used safely in research for other diseases.

The Cardenolide Glycoside Acovenoside A Interferes with Epidermal Growth Factor Receptor Trafficking in Non-Small Cell Lung Cancer Cells

Cardenolide glycosides are natural compounds known to inhibit the ion pumping function of the Na+/K+-ATPase in cellular systems. Interestingly, various cancer cell types are highly susceptible to cardenolide glycosides. Herein, we explore the cardenolide glycoside Acovenoside A (AcoA) with respect to its influences on human A549 non-small cell lung cancer (NSCLC) cells. We found that exposure to AcoA, digoxin and ouabain increases intracellular sodium and ATP levels indicating that the ion pumping function of the transmembrane Na+/K+-ATPase is effectively inhibited. Like digoxin and ouabain, AcoA inhibits transcription factor NF-κB activation and induces apoptotic cell death in NSCLC cells. This was confirmed by a preclinical in vivo model in which AcoA treatment of NSCLC xenografts grown on chick chorioallantoic membranes inhibited the expression of proliferation antigen Ki-67 and induced apoptotic DNA strand breaks. We aimed to elucidate the underlying mechanisms. The Na+/K+-ATPase transmembrane complex contains Src kinase and epidermal growth factor receptor (EGFR). Indeed, we found that AcoA activates Src kinase in A549 cells, but not in a cell-free assay using recombinant Src kinase. Src kinase is a downstream target of EGFR, and correlation analysis using the NCI60 database pointed to a role of EGFR in cardenolide glycoside-induced cancer cell death. Accordingly, NSCLC cells expressing hyperphosphorylated EGFRmut exhibited resistance to AcoA. To investigate the interaction between cardenolide glycosides and EGFR in detail, we performed immunoblotting studies: Whereas ligand binding and EGFR phosphorylation were not significantly affected, ubiquitinated EGFR accumulated after prolonged incubation with AcoA. To visualize EGFR trafficking we used A549 cells transfected with a fluorescent biosensor which binds to activated EGFR. Pretreatment with AcoA and digoxin induced accumulation of EGFR in endosomal compartments thus inhibiting EGF-induced EGFR degradation comparable to the Na+ ionophore monensin, a known inducer of EGFR endosomal arrest. Intracellular Na+ concentrations regulate EGFR trafficking and signaling. Na+ homeostasis is maintained by the Na+/K+-ATPase, which might account for its close interaction with the EGFR. Cardenolide glycosides inhibit the ATP-dependent Na+/K+ exchange through the Na+/K+-ATPase resulting in higher intracellular Na+ levels. Our data provide first evidence that this impedes efficient EGFR trafficking at the endosomal compartment.

Survival of detached cancer cells is regulated by movement of intracellular Na+,K+-ATPase

Beginning of metastasis, cancer cells detach from the primary tumor and they can survive even under loss of anchorage; however, the detachment-elicited mechanisms have remained unknown. Here, we found that Na⁺,K⁺-ATPase α3-isoform (α3NaK) in human cancer cells is dynamically translocated from intracellular vesicles to the plasma membrane when the attached cells are detached and that this mechanism contributes to the survival of the detached (floating) cancer cells. α3NaK was detected in the plasma membrane of floating cancer cells in peritoneal fluids of patients, while it was in the cytoplasm of the cells in primary tumor tissues. On cancer cell detachment, we also found the focal-adhesion-kinase-dependent Ca²⁺ response that induces the α3NaK translocation via nicotinic acid adenine dinucleotide phosphate pathway. Activation of AMP-activated protein kinase was associated with the translocated α3NaK in the plasma membrane. Collectively, our study identifies a unique mechanism for survival of detached cancer cells, opening up new opportunities for development of cancer medicines.

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Na⁺,K⁺-ATPase α3-isoform (α3NaK) is localized in cytoplasm of attached cancer cells

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Intracellular α3NaK is moved to plasma membrane (PM) upon the cell detachment

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FAK and NAADP-dependent Ca²⁺ response is involved in the translocation of α3NaK

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Activation of AMPK associated with the PM-α3NaK contributes to the cell survival

Oleandrin, a cardiac glycoside, induces immunogenic cell death via the PERK/elF2α/ATF4/CHOP pathway in breast cancer

Chemotherapeutic agents have been linked to immunogenic cell death (ICD) induction that is capable of augmenting anti-tumor immune surveillance. The cardiac glycoside oleandrin, which inhibits Na⁺/K⁺-ATPase pump (NKP), has been shown to suppress breast cancer growth via inducing apoptosis. In the present study, we showed that oleandrin treatment triggered breast cancer cell ICD by inducing calreticulin (CRT) exposure on cell surface and the release of high-mobility group protein B1 (HMGB1), heat shock protein 70/90 (HSP70/90), and adenosine triphosphate (ATP). The maturation and activation of dendritic cells (DCs) were increased by co-culturing with the oleandrin-treated cancer cells, which subsequently enhanced CD8⁺ T cell cytotoxicity. Murine breast cancer cell line EMT6 was engrafted into BALB/c mice, and tumor-bearing mice were administered with oleandrin intraperitoneally every day. Oleandrin inhibited tumor growth and increased tumor infiltrating lymphocytes including DCs and T cells. Furthermore, the differential mRNA expression incurred by oleandrin was investigated by mRNA sequencing and subsequently confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. Mechanistically, oleandrin induced endoplasmic reticulum (ER) stress-associated, caspase-independent ICD mainly through PERK/elF2α/ATF4/CHOP pathway. Pharmacological and genetic inhibition of protein kinase R-like ER kinase (PERK) suppressed oleandrin-triggered ICD. Taken together, our findings showed that oleandrin triggered ER stress and induced ICD-mediated immune destruction of breast cancer cells. Oleandrin combined with immune checkpoint inhibitors might improve the efficacy of immunotherapy.

Proscillaridin A inhibits hepatocellular carcinoma progression through inducing mitochondrial damage and autophagy

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths globally. At present, drug options for systemic treatment of HCC are very limited. There is an urgent need to develop additional effective drugs for HCC treatment. In the present study, we found that proscillaridin A (ProA), a cardiac glycoside, exerted a strong anticancer effect on multiple HCC cell lines. ProA significantly inhibited the cell proliferation, migration, and invasion of HCC cells. ProA also had a marked inhibitory effect on the progression of HCC in the MHCC97H xenograft nude mouse model. ProA-mediated suppression of HCC was closely related to cell apoptosis. ProA-treated HCC cells displayed significant mitochondrial damage and elevated reactive oxygen species production, resulting in profound cell apoptosis. Meanwhile, ProA also played a role in autophagy induction in HCC cells. Defects in autophagy partially relieved ProA's anticancer effect in HCC cells. Our findings demonstrate that ProA can effectively inhibit HCC progression and may serve as a potential therapeutic agent for HCC treatment.

Prospects and Therapeutic Applications of Cardiac Glycosides in Cancer Remediation

Active metabolites from natural sources are the predominant molecular targets in numerous biological studies owing to their appropriate compatibility with biological systems and desirable selective toxicities. Thus, their potential for therapeutic development could span a broad scope of disease areas, including pathological and neurological dysfunctions. Cardiac glycosides are a unique class of specialized metabolites that have been extensively applied as therapeutic agents for the treatment of numerous heart conditions, and more recently, they have also been explored as probable antitumor agents. They are a class of naturally derived compounds that bind to and inhibit Na⁺/K⁺-ATPase. This study presents cardiac glycosides and their analogues with highlights on their applications, challenges, and prospects as lead compounds for cancer treatment.

Semisynthetic Cardenolides Acting as Antiviral Inhibitors of Influenza A Virus Replication by Preventing Polymerase Complex Formation

Influenza virus infections represent a major public health issue by causing annual epidemics and occasional pandemics that affect thousands of people worldwide. Vaccination is the main prophylaxis to prevent these epidemics/pandemics, although the effectiveness of licensed vaccines is rather limited due to the constant mutations of influenza virus antigenic characteristics. The available anti-influenza drugs are still restricted and there is an increasing viral resistance to these compounds, thus highlighting the need for research and development of new antiviral drugs. In this work, two semisynthetic derivatives of digitoxigenin, namely C10 (3β-((N-(2-hydroxyethyl)aminoacetyl)amino-3-deoxydigitoxigenin) and C11 (3β-(hydroxyacetyl)amino-3-deoxydigitoxigenin), showed anti-influenza A virus activity by affecting the expression of viral proteins at the early and late stages of replication cycle, and altering the transcription and synthesis of new viral proteins, thereby inhibiting the formation of new virions. Such antiviral action occurred due to the interference in the assembly of viral polymerase, resulting in an impaired polymerase activity and, therefore, reducing viral replication. Confirming the in vitro results, a clinically relevant ex vivo model of influenza virus infection of human tumor-free lung tissues corroborated the potential of these compounds, especially C10, to completely abrogate influenza A virus replication at the highest concentration tested (2.0 µM). Taken together, these promising results demonstrated that C10 and C11 can be considered as potential new anti-influenza drug candidates.

Cardiac glycosides inhibit cancer through Na/K-ATPase-dependent cell death induction

Successful drug repurposing relies on the understanding of molecular mechanisms of the target compound. Cardiac glycosides have demonstrated potent anticancer activities; however, the pharmacological mechanisms underlying their anticancer effects remained elusive, which has restricted their further development in cancer treatment. A bottleneck is the lack of comprehensive understanding about genes and signaling pathways that are altered at the early stage of drug treatment, which is key to understand how they inhibit cancer. To address this issue, we first investigated the anticancer effects of a panel of 68 naturally isolated cardiac glycosides. Our results illustrate critical structure activity relationship of these compounds on cancer cell survival. We confirmed the anticancer effect of cardiac glycoside in mouse tumor xenografts. Through RNA sequencing, quantitative PCR and immunoblotting, we show that cardiac glycoside first activated autophagy and then induced apoptosis. Further activating autophagy by rapamycin or inhibiting apoptosis by caspase inhibitor mitigated cardiac glycoside-induced cell death, whereas inhibiting autophagy by RNA interference-mediated depletion of critical autophagy genes enhanced cell death. While depletion of Na/K-ATPase, the protein target of cardiac glycosides, by RNA interference inhibited both autophagy activation and apoptosis induction by cardiac glycoside, expression of human, but not rodent Na/K-ATPase, increased cell sensitivity to cardiac glycoside. In conclusion, our analyses reveal sequential activation of autophagy and apoptosis during early stages of cardiac glycoside treatment and indicate the importance of Na/K-ATPase in their anticancer effects.

Bufalin attenuates triple-negative breast cancer cell stemness by inhibiting the expression of SOX2/OCT4

Triple-negative breast cancer (TNBC) has the poorest prognosis among all types of breast cancer and there is yet no effective therapy. Chemotherapy is the traditional standard of care for patients with TNBC; however, treatment of TNBC with chemotherapy may lead to the enrichment of cancer stem cells (CSCs), which exhibitan enhanced capacity for self-renewal, tumor initiation and metastasis. The present study demonstrated that bufalin, a small molecular compound used in traditional Chinese medicine, exerted anticancer effects on a wide range of cancer cell lines, inhibited cell proliferation through inducing G2/M cell cycle arrest, and triggered apoptosis in the TNBC cell lines MDA-MB-231 and HCC-1937. Consistently, bufalin markedly suppressed TNBC growth in a cell line-derived xenograft model. More importantly, unlike common chemotherapeutic drugs, bufalin reduced the stemness of TNBC stem cells. A mechanistic study suggested that bufalin may suppress the proliferation of TNBC stem cells by inhibiting the expression of octamer-binding transcription factor 4 (OCT4) and sex determining region Y-box 2 (SOX2) in MDA-MB-231 and HCC-1937 cells. These results indicated that bufalin may hold promise as a therapeutic agent in TNBC, and its effects may be mediated through the SOX2/OCT4 axis.

Inhibition of JNK-Mediated Autophagy Promotes Proscillaridin A- Induced Apoptosis via ROS Generation, Intracellular Ca+2 Oscillation and Inhibiting STAT3 Signaling in Breast Cancer Cells

Breast cancer is the most heterogenous cancer type among women across the world. Despite concerted efforts, breast cancer management is still unsatisfactory. Interplay between apoptosis and autophagy is an imperative factor in categorizing therapeutics for cancer treatment. Proscillaridin A (PSD-A), a well-known cardiac glycoside used for cardiac arrest and arrythmias, has been unveiled in many cancer types but the underlying mechanism for apoptosis and autophagy in breast cancer is not fully understood. In our study, PSD-A restricted cell growth, inhibited STAT3 activation and induced apoptosis and autophagy in breast cancer cells via ROS generation and Ca⁺² oscillation. Pretreatment of NAC and BAPTA-AM restored PSD-A induced cellular events in breast cancer cells. PSD-A induced apoptosis via DNA fragmentation, caspase-cascade activation, PARP cleavage, mitochondrial dysfunction, Bax/Bcl-2 proteins modulation and ER chaperone GRP78 inhibition along with decreased phosphorylation of ERK1/2. Inhibition of STAT3 activation was found to be associated with decreased phosphorylation of SRC. Moreover, PSD-A induced events of autophagy i.e. conversion of LC3-I to LC3-II, and Atg3 expression via JNK activation and decreased mTOR and AKT phosphorylation. In this study, pretreatment of SP600125, a JNK inhibitor, reduced autophagy and enhanced STAT3 inhibition and apoptosis. Additionally, SB203580, a commercial p38 inhibitor, stimulated STAT3 activation and improved autophagic events rate in breast cancer cells, displaying the role of the MAPK signaling pathway in interplay between apoptosis and autophagy. Our data suggest that the rate of apoptotic cell death is improved by blocking JNK-induced autophagy in PSD-A treated MCF-7 and MDA-MB-231 breast cancer cells.

Anticancer and Antiviral Properties of Cardiac Glycosides: A Review to Explore the Mechanism of Actions

Cardiac glycosides (CGs) have a long history of treating cardiac diseases. However, recent reports have suggested that CGs also possess anticancer and antiviral activities. The primary mechanism of action of these anticancer agents is by suppressing the Na+/k+-ATPase by decreasing the intracellular K+ and increasing the Na+ and Ca2+. Additionally, CGs were known to act as inhibitors of IL8 production, DNA topoisomerase I and II, anoikis prevention and suppression of several target genes responsible for the inhibition of cancer cell proliferation. Moreover, CGs were reported to be effective against several DNA and RNA viral species such as influenza, human cytomegalovirus, herpes simplex virus, coronavirus, tick-borne encephalitis (TBE) virus and Ebola virus. CGs were reported to suppress the HIV-1 gene expression, viral protein translation and alters viral pre-mRNA splicing to inhibit the viral replication. To date, four CGs (Anvirzel, UNBS1450, PBI05204 and digoxin) were in clinical trials for their anticancer activity. This review encapsulates the current knowledge about CGs as anticancer and antiviral drugs in isolation and in combination with some other drugs to enhance their efficiency. Further studies of this class of biomolecules are necessary to determine their possible inhibitory role in cancer and viral diseases.

21-Benzylidene digoxin decreases proliferation by inhibiting the EGFR/ERK signaling pathway and induces apoptosis in HeLa cells

Cardiotonic steroids (CTS) are agents traditionally known for their capacity to bind to the Na,K-ATPase (NKA), affecting the ion transport and the contraction of the heart. Natural CTS have been shown to also have effects on cell signaling pathways. With the goal of developing a new CTS derivative, we synthesized a new digoxin derivative, 21-benzylidene digoxin (21-BD). Previously, we have shown that this compound binds to NKA and has cytotoxic actions on cancer, but not on normal cells. Here, we further studied the mechanisms of actions of 21-BD. Working with HeLa cells, we found that 21-BD decreases the basal, as well as the insulin stimulated proliferation. 21-BD reduces phosphorylation of the epidermal growth factor receptor (EGFR) and extracellular-regulated kinase (ERK), which are involved in pathways that stimulate cell proliferation. In addition, 21-BD promotes apoptosis, which is mediated by the translocation of Bax from the cytosol to mitochondria and the release of mitochondrial cytochrome c to the cytosol. 21-BD also activated caspases-8, -9 and -3, and induced the cleavage of poly (ADP-ribose) polymerase-1 (PARP-1). Altogether, these results show that the new compound that we have synthesized exerts cytotoxic actions on HeLa cells by inhibition of cell proliferation and the activation of both the extrinsic and intrinsic apoptotic pathways. These results support the relevance of the cardiotonic steroid scaffold as modulators of cell signaling pathways and potential agents for their use in cancer.

Oleandrin induces apoptosis via activating endoplasmic reticulum stress in breast cancer cells

BACKGROUND

Breast cancer is the most common malignant tumor in women. Due to limited treatment outcome and high rate of metastasis, the prognosis is especially poor for triple-negative breast cancer. It is urgent to discover and develop novel agents for treatment of breast cancer. Herein, we investigated the potential mechanisms of Oleandrin's (a cardiac glycoside) cytotoxic activity against breast cancer cells.

METHODS

Cell proliferation was assessed by xCELLigence Real-Time Cell Analyzer (RTCA)-MP system. Apoptotic cells were detected by using Annexin V/PI staining and nuclear fragments observation. The effect of oleandrin on ATP1B3 expression and markers of ER stress were determined by western blot. A primary cell sensitivity assay was performed via a collagen gel droplet-embedded culture drug sensitivity method (CD-DST).

RESULTS

Oleandrin suppressed cell proliferation and colony formation in the three breast cancer cell lines but did not affect normal mammary epithelial cells. Additionally, the expression of ATP1B3 was higher in the three breast cancer cell lines compared to MCF10A cells. Treatment with oleandrin increased the number of apoptotic cells and led to nuclear pyknosis, fragmentation, and apoptotic body formation in breast cancer cells. Furthermore, oleandrin treatment increased expression of Bax and Bim but decreased that of Bcl-2. Treatment with oleandrin also upregulated the expression of endoplasmic reticulum stress associated proteins, including eIF2α, ATF4, and CHOP, but not PERK. oleandrin treatment also induced the phosphorylation of PERK and eIF2α. Of note, oleandrin exhibited antitumor effects on patient-derived breast cancer cells under three-dimensional culture conditions.

CONCLUSIONS

Taken together, our results suggest that oleandrin induces mitochondrial-mediated apoptosis by activating endoplasmic reticulum stress in breast cancer. Moreover, oleandrin may be an effective strategy for the treatment of breast cancer.

New 99mTc-Labeled Digitoxigenin Derivative for Cancer Cell Identification

In recent years, cardiac glycosides (CGs) have been investigated as potential antiviral and anticancer drugs. Digitoxigenin (DIG) and other CGs have been shown to bind and inhibit Na⁺/K⁺-adenosinetriphosphatase (ATPase). Tumor cells show a higher expression rate of the Na⁺/K⁺-ATPase protein or a stronger affinity towards the binding of CGs and are therefore more prone to CGs than non-tumor cells. Cancer imaging techniques using radiotracers targeted at specific receptors have yielded successful results. Technetium-99m (^99mTc) is one of the radionuclides of choice to radiolabel pharmaceuticals because of its favorable physical and chemical properties along with reasonable costs. Herein, we describe a new Na⁺/K⁺-ATPase targeting radiotracer consisting of digitoxigenin and diethylenetriaminepentaacetic acid (DTPA), a bifunctional chelating ligand used to prepare ^99mTc-labeled complexes, and its evaluation as an imaging probe. We report the synthesis and characterization of the radiolabeled compound including stability tests, blood clearance, and biodistribution in healthy mice. Additionally, we investigated the binding of the compound to A549 human non-small-cell lung cancer cells and the inhibition of the Na⁺/K⁺-ATPase by the labeled compound in vitro. The ^99mTc-labeled DTPA-digitoxigenin (^99mTc-DTPA-DIG) compound displayed high stability in vitro and in vivo, a fast renal excretion, and a specific binding towards A549 cancer cells in comparison to non-tumor cells. Therefore, ^99mTc-DTPA-DIG could potentially be used for non-invasive visualization of tumor lesions by means of scintigraphic imaging.

Drug Repurposing for Retinoblastoma: Recent Advances

Retinoblastoma is the intraocular malignancy that occurs during early childhood. The current standard of care includes chemotherapy followed by focal consolidative therapies, and enucleation. Unfortunately, these are associated with many side and late effects. New drugs and/or drug combinations need to be developed for safe and effective treatment. This compelling need stimulated efforts to explore drug repurposing for retinoblastoma. While conventional drug development is a lengthy and expensive process, drug repurposing is a faster, alternate approach, where an existing drug, not meant for treating cancer, can be repurposed to treat retinoblastoma. The present article reviews various attempts to test drugs approved for different purposes such as calcium channels blockers, non-steroidal antiinflammatory drugs, cardenolides, antidiabetic, antibiotics and antimalarial for treating retinoblastoma. It also discusses other promising candidates that could be explored for repurposing for retinoblastoma.

The effects of extraction techniques and quantitative determination of oxalates in Nerium oleander and feeds

Shrubs represent the most affordable and accessible form of feed that livestock can rely on to acquire both essential and non-essential elements of life. In addition to their inherent toxins, they contain endogenous substances commonly referred to as 'antinutritive factors' (ANFs) that often interfere with the utilisation of nutrients. Their abundance may lead to severe clinical trauma. Hence, the objective of the study was to investigate the effects of different extraction techniques on Nerium oleander L. and animal feeds as well as to quantify oxalates. Organic (hexane, acetone and methanol) sequential and aqueous (infusion and decoction) extractions were explored. Qualitative and quantitative analyses were conducted to determine the presence of various phytochemicals and oxalate contents as putative ANFs, respectively. The results showed higher extraction yields of 22.6% and 43.1% in the decoction and infusion of N. oleander, respectively. The quantification methods were validated for linearity, accuracy and precision. Oxalate contents of 6.76 ± 0.245 (0.65%) mg/g and 5.74 ± 0.236 mg/g dry weight (0.55%) were obtained in N. oleander and feeds, respectively. This difference was statistically significant with p < 0.05. Percentage recoveries of 98.5 (percent relative standard deviation [% RSD] = 2.3), 85.7 (% RSD = 1.03) and 80.3 (% RSD = 1.22) at 76%, 95% and 112% fortifications were obtained, respectively. Relative standard deviation for precision was 0.99% and 1.13% at 0.33 mg and 0.39 mg fortifications, respectively, while reproducibility showed 2.21% RSD. Therefore, these methods can be used to provide a valuable basis for qualitative determination of ANFs, particularly in shrub foliage.

New therapeutic aspects of steroidal cardiac glycosides: the anticancer properties of Huachansu and its main active constituent Bufalin

Aim of the review

In the past decade, increasing research attention investigated the novel therapeutic potential of steroidal cardiac glycosides in cancer treatment. Huachansu and its main active constituent Bufalin have been studied in vitro, in vivo and clinical studies. This review aims to summarize the multi-target and multi-pathway pharmacological effects of Bufalin and Huachansu in the last decade, with the aim of providing a more comprehensive view and highlighting the recently discovered molecular mechanisms.

Results

Huachansu and its major derivative, Bufalin, had been found to possess anti-cancer effects in a variety of cancer cell lines both in vitro and in vivo. The underlying anti-cancer molecular mechanisms mainly involved anti-proliferation, apoptosis induction, anti-metastasis, anti-angiogenesis, epithelial-mesenchymal transition inhibition, anti-inflammation, Na⁺/K⁺-ATPase activity targeting, the steroid receptor coactivator family inhibitions, etc. Moreover, the potential side-effects and toxicities of the toad extract, Huachansu, and Bufalin, including hematological, gastrointestinal, mucocutaneous and cardiovascular adverse reactions, were reported in animal studies and clinic trails.

Conclusions

Further research is needed to elucidate the potential drug-drug interactions and multi-target interaction of Bufalin and Huachansu. Large-scale clinical trials are warranted to translate the knowledge of the anticancer actions of Bufalin and Huachansu into clinical applications as effective and safe treatment options for cancer patients in the future.

The anticancer effects of cinobufagin on hepatocellular carcinoma Huh‑7 cells are associated with activation of the p73 signaling pathway

The Na⁺/K⁺-ATPase inhibitor cinobufagin exhibits numerous anticancer effects on hepatocellular carcinoma (HCC) cells expressing wild-type p53 via inhibition of aurora kinase A (AURKA) and activation of p53 signaling. However, the effects of cinobufagin on HCC cells expressing mutant p53 remain unclear. In the present study, the anticancer effects of cinobufagin were investigated on HCC Huh-7 cells with mutant p53, and the effects of AURKA overexpression or inhibition on the anticancer effects of cinobufagin were analyzed. Viability, cell cycle progression and apoptosis of cells were determined using an MTT assay, flow cytometry and Hoechst 33342 staining, respectively. The expression levels of p53 and p73 signaling-associated proteins were investigated via western blot analysis. The results demonstrated that the expression levels of AURKA, B-cell lymphoma 2 (Bcl-2), cyclin-dependent kinase 1, cyclin B1, proliferating cell nuclear antigen and heterogeneous nuclear ribonucleoprotein K, as well as the phosphorylation of p53 and mouse double minute 2 homolog, were significantly decreased in Huh-7 cells treated with 5 µmol/l cinobufagin for 24 h. Conversely, the expression levels of Bcl-2-associated X protein, p21, p53 upregulated modulator of apoptosis and phorbol-12-myristate-13-acetate-induced protein 1, were significantly increased by cinobufagin treatment. Overexpression or inhibition of AURKA suppressed or promoted the anticancer effects of cinobufagin on Huh-7 cells, respectively. These results indicated that cinobufagin may induce anticancer effects on Huh-7 cells via the inhibition of AURKA and p53 signaling, and via the activation of p73 signaling, in an AURKA-dependent manner.

Cardiac glycoside cerberin exerts anticancer activity through PI3K/AKT/mTOR signal transduction inhibition

Natural products possess a significant role in anticancer therapy and many currently-used anticancer drugs are of natural origin. Cerberin (CR), a cardenolide isolated from the fruit kernel of Cerbera odollam, was found to potently inhibit cancer cell growth (GI₅₀ values < 90 nM), colony formation and migration. Significant G2/M cell cycle arrest preceded time- and dose-dependent apoptosis-induction in human cancer cell lines corroborated by dose-and time-dependent PARP cleavage and caspase 3/7 activation, in addition to reduced Bcl-2 and Mcl-1 expression. CR potently inhibited PI3K/AKT/mTOR signalling depleting polo-like kinase 1 (PLK-1), c-Myc and STAT-3 expression. Additionally, CR significantly increased the generation of reactive oxygen species (ROS) producing DNA double strand breaks. Preliminary in silico biopharmaceutical assessment of CR predicted >60% bioavailability and rapid absorption; doses of 1-10 mg/kg CR were predicted to maintain efficacious unbound plasma concentrations (>GI₅₀ value). CR's potent and selective anti-tumour activity, and its targeting of key signalling mechanisms pertinent to tumourigenesis support further preclinical evaluation of this cardiac glycoside.

Antagonistic anticancer effect of paclitaxel and digoxin combination

Despite the growing interest in the antitumor effect of cardiotonic steroids, combination treatments with well-established chemotherapy drugs like paclitaxel have been rarely investigated. Moreover, paclitaxel has been suggested as a Na⁺ /K⁺ -ATPase inhibitor. Here we investigated the effect of paclitaxel and digoxin alone or in combination on the viability of human lung (A549) and cervical cancer (HeLa) cell lines and the inhibitory effect of paclitaxel on several mammalian Na⁺ /K⁺ -ATPases. Although the viability of both tumor cell lines was concentration-dependently affected by digoxin treatment after 48 hours (A549 IC₅₀  = 31 nM and HeLa IC₅₀  = 151 nM), a partial effect was observed for paclitaxel, with a maximal inhibitory effect of 45% at 1000 nM with A549 and around 70% with HeLa cells (IC₅₀  = 1 nM). Although the two drugs were cytotoxic, their combined effect in HeLa cells was revealed to be antagonistic, as estimated by the combination index. No direct inhibitory effect of paclitaxel was detected in human, pig, rat, and mouse Na⁺ /K⁺ -ATPase enzymes, but high concentrations of paclitaxel decreased the Na⁺ /K⁺ -ATPase activity in HeLa cells after 48 hours without affecting protein expression. Our findings demonstrate that, under our conditions, paclitaxel and digoxin cotreatment produce antagonistic cytotoxic effects in HeLa cells, and the mechanism of action of paclitaxel does not involve a direct inhibition of Na⁺ /K⁺ -ATPase. More studies shall be designed to evaluate the consequences of the interaction of cardiotonic steroids and chemotherapy drugs.

Modular Total Synthesis and Cell-Based Anticancer Activity Evaluation of Ouabagenin and Other Cardiotonic Steroids with Varying Degrees of Oxygenation

A Cu(II)-catalyzed diastereoselective Michael/aldol cascade approach is used to accomplish concise total syntheses of cardiotonic steroids with varying degrees of oxygenation including cardenolides ouabagenin, sarmentologenin, 19-hydroxysarmentogenin, and 5- epi-panogenin. These syntheses enabled the subsequent structure activity relationship (SAR) studies on 37 synthetic and natural steroids to elucidate the effect of oxygenation, stereochemistry, C3-glycosylation, and C17-heterocyclic ring. Based on this parallel evaluation of synthetic and natural steroids and their derivatives, glycosylated steroids cannogenol-l-α-rhamnoside (79a), strophanthidol-l-α-rhamnoside (92), and digitoxigenin-l-α-rhamnoside (97) were identified as the most potent steroids demonstrating broad anticancer activity at 10-100 nM concentrations and selectivity (nontoxic at 3 μM against NIH-3T3, MEF, and developing fish embryos). Further analyses indicate that these molecules show a general mode of anticancer activity involving DNA-damage upregulation that subsequently induces apoptosis.

New knowledge about old drugs; a cardenolide type glycoside with cytotoxic effect and unusual secondary metabolites from Digitalis grandiflora Miller

Phytochemical investigation of the aerial parts of Digitalis grandiflora Miller (Plantaginaceae) led to the isolation of an undescribed cardenolide type glycoside digigrandifloroside (1) along with five known compounds, rengyoside A (2), rengyoside B (3), cleroindicin A (4), salidroside (5), and cornoside (6), from its aqueous fraction of methanolic extract. Structures of the isolated compounds were determined by means of spectroscopic techniques. 1-6 were isolated for the first time from D. grandiflora. 2 and 3 are being reported for the first time from Digitalis genus and Plantaginaceae family with this study. This is the second report for occurrence of 4 from a Digitalis species. Cytotoxic activity of the aqueous fraction was also tested against HEp-2 (Human larynx epidermoid carcinoma) and HepG2 (Human hepatocellular carcinoma) cancer cell lines and L929 (Mouse fibroblast cell) non-cancerous cell line. Aqueous fraction showed stronger cytotoxicity on HEp-2 cells than HepG2. Therefore, the cytotoxic activity of 1, 2, 4, and 6 were tested against HEp-2 and L929 cell lines. 3 and 5 couldn't be tested due to their insufficient amount. 1 showed the highest cytotoxicity against HEp-2 cells with IC₅₀ value 10.1 μM when compared with the positive control, etoposide and 2-6 (IC₅₀ of etoposide; 39.5 μM).

A review of cardiac glycosides: Structure, toxicokinetics, clinical signs, diagnosis and antineoplastic potential

Cardiac glycosides (CGs) are secondary compounds found in plants and amphibians and are widely distributed in nature with potential cardiovascular action. Their mechanism is based on the blockage of the heart's sodium potassium ATPase, with a positive inotropic effect. Some of the most well-known CGs are digoxin, ouabain, oleandrin, and bufalin. They have similar chemical structures: a lactone ring, steroid ring, and sugar moiety. Digoxin, ouabain, and oleandrin are classified as cardenolides, consisting of a lactone ring with five carbons, while bufalin is classified as bufodienolides, with a six-carbon ring. Small structural differences determine variations in the toxicokinetics and toxicodynamics of such substances. Most case reports of poisoning caused by CGs are associated with cardiovascular toxicity, causing a variety of arrhythmias and lesions in the heart tissue. Experimental studies also describe important similarities among different CGs, especially regarding species sensitivity. Recent studies furthermore focus on their antineoplastic potential, with controversial results. Data from research studies and case reports were reviewed to identify the main characteristics of the CGs, including toxicokinetics, toxicodynamics, clinical signs, electrocardiographic, pathological findings, antineoplastic potential and the main techniques used for diagnostic purposes.

Oleandrin and Its Derivative Odoroside A, Both Cardiac Glycosides, Exhibit Anticancer Effects by Inhibiting Invasion via Suppressing the STAT-3 Signaling Pathway

The cardiac glycosides oleandrin and odoroside A, polyphenolic monomer compounds extracted from Nerium oleander, have been found to have antitumor effects on various tumors at low doses. However, the mechanisms of anticancer effects of oleandrin and odoroside A are not well known. Therefore, in this study, we aimed to investigate the anticancer effects of oleandrin and odoroside A and their associated mechanisms in highly metastatic MDA-MB-231 breast cancer cells and radiotherapy-resistant (RT-R) MDA-MB-231 cells. Our results showed that oleandrin and odoroside A dose-dependently decreased the colony formation and the invasion of both cell lines at nanomolar ranges. Furthermore, oleandrin (50 nM) and odoroside A (100 nM) reduced octamer-binding transcription factor 3/4 (OCT3/4) and β-catenin levels and matrix metalloproteinase-9 (MMP-9) activity. Finally, we found that phospho-STAT-3 levels were increased in MDA-MB-231 and RT-R-MDA-MB-231, but not in endothelial cells (ECs), and that the levels were significantly decreased by oleandrin (50 nM) and odoroside A (100 nM). Inhibition of phospho-signal transducer and activator of transcription (STAT)-3 significantly reduced OCT3/4 and β-catenin levels and MMP-9 activity, ultimately resulting in reduced invasion. These results suggest that the anticancer effects of oleandrin and odoroside A might be due to the inhibition of invasion through of phospho-STAT-3-mediated pathways that are involved in the regulation of invasion-related molecules.

Metabolic profiling and correlation analysis for the determination of killer compounds of proliferating and clonogenic HRT-18 colon cancer cells from Lafoensia pacari

ETHNOPHARMACOLOGICAL RELEVANCE

Lafoensia pacari A. St.-Hil., belonging to the family Lythraceae and popularly known as 'dedaleira' and 'mangava-brava,' is a native tree of the Brazilian Cerrado, and its barks have been traditionally used as a tonic to treat inflammatory conditions, particularly related to gastric ulcers, wounds or fevers and various types of cancer.

AIM OF THE STUDY

We have previously demonstrated the apoptogenic effects of the methanolic extract of L. pacari using various cancer cell lines. In the present study, this extract has been partitioned into fractions to identify the components that might be responsible for the apoptogenic effects using HRT-18 cells, which have been previously demonstrated to be sensitive to this extract.

MATERIALS AND METHODS

A standard methanolic extract was prepared and fractionated by centrifugal partition chromatography. The fractions were submitted to cytotoxicity and clonogenic assays to monitor the effects in parallel with LC-DAD-MS and statistical analyses to suggest the potential bioactive compounds.

RESULTS

Besides ellagic acid, the primary constituent of the plant and also the biomarker of the species, punicalin, pedunculagin and punicalagin isomers, catechin and ellagic acid derivatives were putatively identified.

CONCLUSIONS

The barks of L. pacari are rich in ellagic acid and various hydrolysable tannins, some of which were reported for the first time in this species, such as punicalagin and ellagitannins. This mixture of substances had the ability to kill proliferating cells and abrogate the growth of clonogenic cells in a similar manner shown by the methanolic extract of our previous study. The collective data reported herein suggest that the biological activities of the L. pacari barks used by population to treat cancer conditions are due to the apoptogenic effects promoted by a mixed content of ellagitannins.

Leukemic stem cell signatures identify novel therapeutics targeting acute myeloid leukemia

Therapy for acute myeloid leukemia (AML) involves intense cytotoxic treatment and yet approximately 70% of AML are refractory to initial therapy or eventually relapse. This is at least partially driven by the chemo-resistant nature of the leukemic stem cells (LSCs) that sustain the disease, and therefore novel anti-LSC therapies could decrease relapses and improve survival. We performed in silico analysis of highly prognostic human AML LSC gene expression signatures using existing datasets of drug–gene interactions to identify compounds predicted to target LSC gene programs. Filtering against compounds that would inhibit a hematopoietic stem cell (HSC) gene signature resulted in a list of 151 anti-LSC candidates. Using a novel in vitro LSC assay, we screened 84 candidate compounds at multiple doses and confirmed 14 drugs that effectively eliminate human AML LSCs. Three drug families presenting with multiple hits, namely antihistamines (astemizole and terfenadine), cardiac glycosides (strophanthidin, digoxin and ouabain) and glucocorticoids (budesonide, halcinonide and mometasone), were validated for their activity against human primary AML samples. Our study demonstrates the efficacy of combining computational analysis of stem cell gene expression signatures with in vitro screening to identify novel compounds that target the therapy-resistant LSC at the root of relapse in AML.

Drug Repositioning for Effective Prostate Cancer Treatment

Drug repositioning has gained attention from both academia and pharmaceutical companies as an auxiliary process to conventional drug discovery. Chemotherapeutic agents have notorious adverse effects that drastically reduce the life quality of cancer patients so drug repositioning is a promising strategy to identify non-cancer drugs which have anti-cancer activity as well as tolerable adverse effects for human health. There are various strategies for discovery and validation of repurposed drugs. In this review, 25 repurposed drug candidates are presented as result of different strategies, 15 of which are already under clinical investigation for treatment of prostate cancer (PCa). To date, zoledronic acid is the only repurposed, clinically used, and approved non-cancer drug for PCa. Anti-cancer activities of existing drugs presented in this review cover diverse and also known mechanisms such as inhibition of mTOR and VEGFR2 signaling, inhibition of PI3K/Akt signaling, COX and selective COX-2 inhibition, NF-κB inhibition, Wnt/β-Catenin pathway inhibition, DNMT1 inhibition, and GSK-3β inhibition. In addition to monotherapy option, combination therapy with current anti-cancer drugs may also increase drug efficacy and reduce adverse effects. Thus, drug repositioning may become a key approach for drug discovery in terms of time- and cost-efficiency comparing to conventional drug discovery and development process.

Risk of cancer in patients with heart failure who use digoxin: a 10-year follow-up study and cell-based verification

Heart failure (HF) is the leading cause of death in the world and digoxin remains one of the oldest therapies for HF. However, its safety and efficacy have been controversial since its initial use and there is uncertainty about its long-term efficacy and safety. Recently, the repositioning of cardiac glycosides is to function in anti-tumor activity via multiple working pathways. It is interesting to compare the potential effects of digoxin in clinical patients and cell lines. First, we analyze patient information retrieved from the National Health Insurance Research database of Taiwan between January 1, 2000 and December 31, 2000. This retrospective study included a study cohort (1,219 patients) and a comparison cohort. Our analytical data suggested that patients taking digoxin are at an increased risk of cancers, including breast, liver, and lung cancers, during the 10-year follow-up period. In contrast to the anti-tumor function of digoxin, we further examined the potential pathway of digoxin via the cell-based strategy using several breast cancer cell lines, including MCF-7, BT-474, MAD-MB-231, and ZR-75-1. Digoxin consistently exerted its cytotoxicity to these four cell lines with various range of concentration. However, the proliferation of ZR-75-1 cells was the only cell lines induced by digoxin and the others were dramatically suppressed by digoxin. The responsiveness of SRSF3 to digoxin might be involved with cell-type differences. In summary, we combined a cohort study for digoxin treatment for HF patients with a cell-based strategy that addresses the translation issue, which revealed the complexity of personalized medicine.

Influence of auxin and its polar transport inhibitor on the development of somatic embryos in Digitalis trojana

The present study reports the role of auxin and its transport inhibitor during the establishment of an efficient and optimized protocol for the somatic embryogenesis in Digitalis trojana Ivan. Hypocotyl segments (5 mm long) were placed vertically in the Murashige and Skoog medium supplemented with three sets [indole-3-acetic acid (IAA) alone or 2,3,5-triiodobenzoic acid (TIBA) alone or IAA-TIBA combination] of formulations of plant growth regulators, to assess their differential influence on induction and proliferation of somatic embryos (SEs). IAA alone was found to be the most effective, at a concentration of 0.5 mg/l, inducing ~ 10 SEs per explant with 52% induction frequency. On the other hand, the combination of 0.5 mg/l of IAA and 1 mg/l of TIBA produced significantly fewer (~ 3.6 SEs) and abnormal (enlarged, oblong, jar and cup-shaped) SEs per explant with 24% induction frequency in comparison to that in the IAA alone. The explants treated with IAA-TIBA exhibited a delayed response along with the formation of abnormal SEs. Our study revealed that IAA induces high-frequency SE formation when used singly, but the frequency gradually declines when IAA was coupled with increasing levels of TIBA. Eventually, our findings bring new insights into the roles of auxin and its polar transport in somatic embryogenesis of D. trojana.

Proscillaridin A Promotes Oxidative Stress and ER Stress, Inhibits STAT3 Activation, and Induces Apoptosis in A549 Lung Adenocarcinoma Cells

Cardiac glycosides are natural compounds used for the treatment of cardiovascular disorders. Although originally prescribed for cardiovascular diseases, more recently, they have been rediscovered for their potential use in the treatment of cancer. Proscillaridin A (PSD-A), a cardiac glycoside component of Urginea maritima, has been reported to exhibit anticancer activity. However, the cellular targets and anticancer mechanism of PSD-A in various cancers including lung cancer remain largely unexplored. In the present study, we found that PSD-A inhibits growth and induces apoptosis in A549 lung adenocarcinoma cells. The anticancer activity of PSD-A was found to be associated with the activation of JNK, induction of ER stress, mitochondrial dysfunction, and inhibition of STAT3 activation. PSD-A induces oxidative stress as evidenced from ROS generation, GSH depletion, and decreased activity of TrxR1. PSD-A-mediated ER stress was verified by increased phosphorylation of eIF2α and expression of its downstream effector proteins ATF4, CHOP, and caspases-4. PSD-A triggered apoptosis by inducing JNK (1/2) activation, increasing bax/bcl-2 ratio, dissipating mitochondrial membrane potential, and inducing cleavage of caspases and PARP. Further study revealed that PSD-A inhibits both constitutive and inducible STAT3 activations and decreases STAT3 DNA-binding activity. Moreover, PSD-A-mediated inhibition of STAT3 activation was found to be associated with increased SHP-1 expression, decreased phosphorylation of Src, and binding of PSD-A with STAT3 SH2 domain. Finally, STAT3 knockdown by shRNA inhibited growth and enhanced apoptotic efficacy of PSD-A. Taken together, the data suggest that PSD-A could be developed into a potential therapeutic agent against lung adenocarcinoma.

Clinically Observed Estrogen Receptor Alpha Mutations within the Ligand-Binding Domain Confer Distinguishable Phenotypes

OBJECTIVE

Twenty to fifty percent of estrogen receptor-positive (ER+) metastatic breast cancers express mutations within the ER ligand-binding domain. While most studies focused on the constitutive ER signaling activity commonly engendered by these mutations selected during estrogen deprivation therapy, our study was aimed at investigating distinctive phenotypes conferred by different mutations within this class.

METHODS

We examined the two most prevalent mutations, D538G and Y537S, employing corroborative genome-edited and lentiviral-transduced ER+ T47D cell models. We used a luciferase-based reporter and endogenous phospho-ER immunoblot analysis to characterize the estrogen response of ER mutants and determined their resistance to known ER antagonists.

RESULTS

Consistent with their selection during estrogen deprivation therapy, these mutants conferred constitutive ER activity. While Y537S mutants showed no estrogen dependence, D538G mutants demonstrated an enhanced estrogen-dependent response. Both mutations conferred resistance to ER antagonists that was overcome at higher doses acting specifically through their ER target.

CONCLUSIONS

These observations provide a tenable hypothesis for how D538G ESR1-expressing clones can contribute to shorter progression-free survival observed in the exemestane arm of the BOLERO-2 study. Thus, in those patients with dominant D538G-expressing clones, longitudinal analysis for this mutation in circulating free DNA may prove beneficial for informing more optimal therapeutic regimens.