Cardenolides and cancer

The Effects of Cinobufagin on Hepatocellular Carcinoma Cells Enhanced by MRT68921, an Autophagy Inhibitor

Cinobufagin, a cardiotonic steroid derived from toad venom extracts, exhibits significant anticancer properties by inhibiting Na[Formula: see text]/K[Formula: see text]-ATPase in cancer cells. It is frequently used in clinical settings to treat advanced-stage cancer patients, improving their quality of life and survival time. However, its long-term use can result in multidrug resistance to other chemotherapy drugs, and the exact mechanism underlying this effect remains unknown. Therefore, this study explores the molecular mechanism underlying the anticancer effects of cinobufagin in hepatocellular carcinomas (HCCs), specifically in HepG2 and Huh-7 cells. As determined using transcriptome analysis, cinobufagin-triggered protective autophagy suppressed cell apoptosis in liver cancer HepG2 and Huh-7 cells by inhibiting the phosphoinositide-3-Kinase (PI3K)-AKT serine/threonine kinase (AKT)-mammalian target of rapamycin (mTOR) pathway. Cinobufagin-inhibited cell proliferation, induced apoptosis, and generated cell autophagy by upregulating the expression of MAP1 light chain 3 protein II, Beclin1, and autophagy-related protein 12-5. In addition, the autophagy inhibitor MRT68921 improved the antiproliferative and proapoptotic effects of cinobufagin in the studied cell lines. Overall, this study suggests that combining cinobufagin with an autophagy inhibitor can effectively treat HCC, providing a potential strategy for cancer therapy.

Toxicarioside O Inhibits Cell Proliferation and Epithelial-Mesenchymal Transition by Downregulation of Trop2 in Lung Cancer Cells

Toxicarioside O (TCO), a natural product derived from Antiaris toxicaria, has been identified to be a promising anticancer agent. In this study, we aimed to investigate the effect of TCO on the proliferation and epithelial-mesenchymal transition (EMT) of lung cancer cells and its molecular mechanisms. Here, we indicated that TCO inhibits the proliferation of lung cancer cells both in vitro and in vivo. Our results demonstrated that TCO induces apoptosis in lung cancer cells. Moreover, we found that TCO suppresses EMT program and inhibits cell migration in vitro. Mechanistically, TCO decreases the expression of trophoblast cell surface antigen 2 (Trop2), resulting in inhibition of the PI3K/Akt pathway and EMT program. Overexpression of Trop2 rescues TCO-induced inhibition of cell proliferation and EMT. Our findings demonstrate that TCO markedly inhibits cell proliferation and EMT in lung cancer cells and provides guidance for its drug development.

Ouabain and Digoxin Activate the Proteasome and the Degradation of the ERα in Cells Modeling Primary and Metastatic Breast Cancer

Simple Summary

Breast cancer (BC) treatment relies on the detection of the estrogen receptor α (ERα). ERα-expressing BC patients are treated with anti-estrogen drugs (i.e., tamoxifen and fulvestrant). Despite their proven efficacy, these drugs cause serious side effects in a significant fraction of the patients, including both tumor insurgence in secondary organs, and resistant phenotypes, which result in a relapsing disease with scarce treatment options. Thus, new drugs for treatment of primary and metastatic BC (MBC) are needed. Here, we report the characterization of two cardiac glycosides (CGs) (i.e., ouabain and digoxin), approved by the FDA for treatment of heart disease, as novel ‘anti-estrogen’-like drugs. We found that these drugs induce ERα degradation, and prevent the proliferation of cellular models of primary and metastatic BC cells. Remarkably, we discovered that these CGs are activators of the proteasome, and therefore may be repurposed for treatment not only of BC, but also for other proteasome-based diseases.

Abstract

Estrogen receptor α expressing breast cancers (BC) are classically treated with endocrine therapy. Prolonged endocrine therapy often results in a metastatic disease (MBC), for which a standardized effective therapy is still lacking. Thus, new drugs are required for primary and metastatic BC treatment. Here, we report that the Food and Drug Administration (FDA)-approved drugs, ouabain and digoxin, induce ERα degradation and prevent proliferation in cells modeling primary and metastatic BC. Ouabain and digoxin activate the cellular proteasome, instigating ERα degradation, which causes the inhibition of 17β-estradiol signaling, induces the cell cycle blockade in the G2 phase, and triggers apoptosis. Remarkably, these effects are independent of the inhibition of the Na/K pump. The antiproliferative effects of ouabain and digoxin occur also in diverse cancer models (i.e., tumor spheroids and xenografts). Additionally, gene profiling analysis reveals that these drugs downregulate the expression of genes related to endocrine therapy resistance. Therefore, ouabain and digoxin behave as ‘anti-estrogen’-like drugs, and are appealing candidates for the treatment of primary and metastatic BCs.

Cardenolide-rich fraction of Pergularia tomentosa as a novel Antiangiogenic agent mainly targeting endothelial cell migration

PURPOSE

Angiogenesis related abnormalities underlie several life-threatening disorders. Despite approved therapies, scientists have yet to develop highly efficient, low cost approaches with minimal side effects.

METHODS

We evaluated the antiangiogenic activity of 50% hydroalcoholic extracts of Pergularia tomentosa L. root and aerial parts along with their EtOAc and water fractions, in vivo and in vitro. Transgenic zebrafish line Tg(fli1:EGFP) was used for in vivo assay and human umbilical vein endothelial cell (HUVEC) migration test along with possibility of tube formation were performed as in vitro tests. Furthermore, microvasculature in chicken chorioallantoic membrane (CAM) was assessed under P. tomentosa treatment. The fractionation of the 50% hydroalcoholic extracts was led to the identification of the best active fraction in this study. The metabolite profiling of the active fraction was also carried out using LC-HRESIMS analysis.

RESULTS

Pergularia tomentosa markedly inhibited intersegmental vessel (ISV) formation at 48 h post-fertilization (hpf) embryos in zebrafish. The water fraction of root hydroalcoholic extract (PtR2), showed strong antiangiogenic effect with minimal adverse viability impacts. Over 80% of embryos showed more than 50% inhibition in their ISV development at 20 and 40 μg/mL. PtR2 at 20 μg/mL substantially reduced human umbilical vein endothelial cell (HUVEC) migration up to 40%, considerable destruction of the formed tubes in the tube formation and microvasculature in CAM assays. Immunocytochemistry showed a marked reduction in vascular endothelial cadherin (VE-cadherin) abundance at cell junctions concurrent with substantial reduction of phospho-Akt (p-Akt) and β-catenin protein expressions. Phytochemical profile of PtR2 showed a rich source of cardenolide structures, including ghalakinoside, calactin and calotropin derivatives.

CONCLUSION

Thus, the P. tomentosa cardenolide-rich fraction (PtR2) may hold a considerable promise for an antiangiogenic impact by impairment of endothelial cell (EC) migration and viability. Graphical abstract.

AnvirzelTMregulates cell death through inhibiting GSK-3 activity in human U87 glioma cells

Objectives: Cardiac glycosides are used as potential anti-cancer agents due to their effects on the inhibition of proliferation and induction of apoptosis and/or autophagy in cancer cells. Herein, we aimed to study the potential signaling pathways taken role in differential cell-death properties of Anvirzel^TM which is consisted of two toxic cardiac glycosides (oleandrin and oleandrigenin), in U87 human glioblastoma cells.Methods: The anti-proliferative and anti-migratory effects of Anvirzel^TM were assessed in U87 cells by WST-1 assay and wound healing assay, respectively. After treatment of Anvirzel^TMwith doses of 10, 25, 50, 100 and 250 μg/ml, expression levels of proteins related to cell death were investigated by Western blot.Results: Anvirzel™ markedly inhibited the growth of U87 cells in a time- and dose-dependent manner following 24 h and 48 h treatments (p < 0.05). In addition, it was found that Anvirzel™ inhibited GSK-3, NOS and HIF1-α expressions whereas activated ERK in U87 cells compared to vehicle (p < 0.05).Discussion: The results suggested that Anvirzel^TM regulated cell death distinctly from apoptosis in human glioblastoma cells. Further studies are required for validation of mechanistic insights about the potential signaling pathways taken role in differential cell death properties of Anvirzel^TM.

Lanatoside C Induces G2/M Cell Cycle Arrest and Suppresses Cancer Cell Growth by Attenuating MAPK, Wnt, JAK-STAT, and PI3K/AKT/mTOR Signaling Pathways

Cardiac glycosides (CGs) are a diverse family of naturally derived compounds having a steroid and glycone moiety in their structures. CG molecules inhibit the α-subunit of ubiquitous transmembrane protein Na⁺/K⁺-ATPase and are clinically approved for the treatment of cardiovascular diseases. Recently, the CGs were found to exhibit selective cytotoxic effects against cancer cells, raising interest in their use as anti-cancer molecules. In this current study, we explored the underlying mechanism responsible for the anti-cancer activity of Lanatoside C against breast (MCF-7), lung (A549), and liver (HepG2) cancer cell lines. Using Real-time PCR, western blot, and immunofluorescence studies, we observed that (i) Lanatoside C inhibited cell proliferation and induced apoptosis in cell-specific and dose-dependent manner only in cancer cell lines; (ii) Lanatoside C exerts its anti-cancer activity by arresting the G2/M phase of cell cycle by blocking MAPK/Wnt/PAM signaling pathways; (iii) it induces apoptosis by inducing DNA damage and inhibiting PI3K/AKT/mTOR signaling pathways; and finally, (iv) molecular docking analysis shows significant evidence on the binding sites of Lanatoside C with various key signaling proteins ranging from cell survival to cell death. Our studies provide a novel molecular insight of anti-cancer activities of Lanatoside C in human cancer cells.

A novel source of the cardiac glycoside digoxin from the endophytic fungus Epicoccum nigrum: isolation, characterization, production enhancement by gamma irradiation mutagenesis and anticancer activity evaluation

AIMS

Different endophytic fungi were isolated and screened for their digoxin-producing ability. Strain improvement and different culture conditions were studied for more effective production of digoxin.

METHODS AND RESULTS

Among the isolated fungi, an isolate produced digoxin in a concentration of 2·07 mg l^-1 . The digoxin-producing fungal isolate was identified as Epicoccum nigrum Link according to the morphological features and phylogenetic analyses. The potentiality of the fungal strain for production enhancement of digoxin was performed by gamma radiation mutagenesis. Gamma irradiation dose of 1000 Gy intensified the digoxin yield by five-fold. Using this dose, a stable mutant strain with improved digoxin productivity was isolated and the stability for digoxin production was followed up across four successive generations. In the effort to increase digoxin magnitude, selection of the proper cultivation medium, addition of some elicitors to the most proper medium and several physical fermentation conditions were tested. Fermentation process carried out in malt extract autolysate medium (pH 6·5) supplemented by methyl jasmonate and inoculated with 2 ml of 6-day-old culture and incubated at 25°C for 10 days stimulated the highest production of digoxin to attain 50·14 mg l^-1 . Moreover, cytotoxicity of digoxin separated from the fungal culture was tested against five different cancer cell lines. Based on the MTT assay, digoxin inhibited the proliferation of the five different cancer cell lines and the recorded 50% inhibitory concentration ranged from 10·76 to 35·14 μg ml^-1 .

CONCLUSIONS

This is the first report on the production and enhancement of digoxin using fungal fermentation as a new and alternate source with high productivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings offer new and alternate sources with excellent biotechnological potential for digoxin production by fungal fermentation. Moreover, digoxin proved to be a promising anticancer agent whose anticancer potential should be assessed in prospective cancer therapy.

Cardiotonic steroids as potential Na+/K+-ATPase inhibitors - a computational study

Cardiotonic steroids (CTS) are steroidal drugs, processed from the seeds and dried leaves of the genus Digitalis as well as from the skin and parotid gland of amphibians. The most commonly known CTS are ouabain, digoxin, digoxigenin and bufalin. CTS can be used for safer medication of congestive heart failure and other related conditions due to promising pharmacological and medicinal properties. Ouabain isolated from plants is widely utilized in in vitro studies to specifically block the sodium potassium (Na⁺/K⁺-ATPase) pump. For checking, whether ouabain derivatives are robust inhibitors of Na⁺/K⁺-ATPase pump, molecular docking simulation was performed between ouabain and its derivatives using YASARA software. The docking energy falls within the range of 8.470 kcal/mol to 7.234 kcal/mol, in which digoxigenin was found to be the potential ligand with the best docking energy of 8.470 kcal/mol. Furthermore, pharmacophore modeling was applied to decipher the electronic features of CTS. Molecular dynamics simulation was also employed to determine the conformational properties of Na⁺/K⁺-ATPase-ouabain and Na⁺/K⁺-ATPase-digoxigenin complexes with the plausible structural integrity through conformational ensembles for 100 ns which promoted digoxigenin as the most promising CTS for treating conditions of congestive heart failure patients.

Cardiac Glycoside Glucoevatromonoside Induces Cancer Type-Specific Cell Death

Cardiac glycosides (CGs) are natural compounds used traditionally to treat congestive heart diseases. Recent investigations repositioned CGs as potential anticancer agents. To discover novel cytotoxic CG scaffolds, we selected the cardenolide glucoevatromonoside (GEV) out of 46 CGs for its low nanomolar anti-lung cancer activity. GEV presented reduced toxicity toward non-cancerous cell types (lung MRC-5 and PBMC) and high-affinity binding to the Na⁺/K⁺-ATPase α subunit, assessed by computational docking. GEV-induced cell death was caspase-independent, as investigated by a multiparametric approach, and culminates in severe morphological alterations in A549 cells, monitored by transmission electron microscopy, live cell imaging and flow cytometry. This non-canonical cell death was not preceded or accompanied by exacerbation of autophagy. In the presence of GEV, markers of autophagic flux (e.g. LC3I-II conversion) were impacted, even in presence of bafilomycin A1. Cell death induction remained unaffected by calpain, cathepsin, parthanatos, or necroptosis inhibitors. Interestingly, GEV triggered caspase-dependent apoptosis in U937 acute myeloid leukemia cells, witnessing cancer-type specific cell death induction. Differential cell cycle modulation by this CG led to a G2/M arrest, cyclin B1 and p53 downregulation in A549, but not in U937 cells. We further extended the anti-cancer potential of GEV to 3D cell culture using clonogenic and spheroid formation assays and validated our findings in vivo by zebrafish xenografts. Altogether, GEV shows an interesting anticancer profile with the ability to exert cytotoxic effects via induction of different cell death modalities.

Functional characterization and anti-cancer action of the clinical phase II cardiac Na+/K+ ATPase inhibitor istaroxime: in vitro and in vivo properties and cross talk with the membrane androgen receptor

Sodium potassium pump (Na⁺/K⁺ ATPase) is a validated pharmacological target for the treatment of various cardiac conditions. Recent published data with Na⁺/K⁺ ATPase inhibitors suggest a potent anti-cancer action of these agents in multiple indications. In the present study, we focus on istaroxime, a Na⁺/K⁺ ATPase inhibitor that has shown favorable safety and efficacy properties in cardiac phase II clinical trials. Our experiments in 22 cancer cell lines and in prostate tumors in vivo proved the strong anti-cancer action of this compound. Istaroxime induced apoptosis, affected the key proliferative and apoptotic mediators c-Myc and caspase-3 and modified actin cystoskeleton dynamics and RhoA activity in prostate cancer cells. Interestingly, istaroxime was capable of binding to mAR, a membrane receptor mediating rapid, non-genomic actions of steroids in prostate and other cells. These results support a multi-level action of Na⁺/K⁺ ATPase inhibitors in cancer cells and collectively validate istaroxime as a strong re-purposing candidate for further cancer drug development.

The synthesis of cardenolide and bufadienolide aglycones, and related steroids bearing a heterocyclic subunit

Covering: early studies through to March 2016Cardenolides and bufadienolides constitute an attractive class of biologically active steroid derivatives which have been used for the treatment of heart disease in traditional remedies as well as in modern medicinal therapy. Due to their application as therapeutic agents and their unique molecular structures, bearing unsaturated 5- or 6-membered lactones (or other heterocycles) attached to the steroid core, cardio-active steroids have received great attention, which has intensified during the last decade, in the synthetic organic community. Advances in the field of cross-coupling reactions have provided a powerful tool for the attachment of lactone subunits to the steroid core. This current review covers a methodological analysis of synthetic efforts to cardenolide and bufadienolide aglycones. Special emphasis is given to cross-coupling reactions applied for the attachment of lactone subunits at sterically very hindered positions of the steroid core. The carefully selected partial and total syntheses of representative cardio-active steroids will also be presented to exemplify recent achievements (improvements) in the field.

Microbial Transformation of 14-Anhydrodigoxigenin by Alternaria alternata

The microbial transformation of 14-anhydrodigoxigenin (1) by Alternaria alternata CGMCC 3.577 led to the production of seven new metabolites, 2-8. Their structures were determined by extensive spectroscopic (CD, IR, 1D- and 2D-NMR, and HR-ESI-MS) data analyses. The reactions in the bioprocess exhibited diversity, including specific oxidation, hydroxylation, reduction, epoxidation, and dehydration. In addition, a hypothetical biocatalytic pathway is proposed.

Proscillaridin A is cytotoxic for glioblastoma cell lines and controls tumor xenograft growth in vivo

Glioblastoma is the most frequent primary brain tumor in adults. Because of molecular and cellular heterogeneity, high proliferation rate and significant invasive ability, prognosis of patients is poor. Recent therapeutic advances increased median overall survival but tumor recurrence remains inevitable. In this context, we used a high throughput screening approach to bring out novel compounds with anti-proliferative and anti-migratory properties for glioblastoma treatment. Screening of the Prestwick chemical library® of 1120 molecules identified proscillaridin A, a cardiac glycoside inhibitor of the Na⁺/K⁺ ATPase pump, with most significant effects on glioblastoma cell lines. In vitro effects of proscillaridin A were evaluated on GBM6 and GBM9 stem-like cell lines and on U87-MG and U251-MG cell lines. We showed that proscillaridin A displayed cytotoxic properties, triggered cell death, induced G₂/M phase blockade in all the glioblastoma cell lines and impaired GBM stem self-renewal capacity even at low concentrations. Heterotopic and orthotopic xenotransplantations were used to confirm in vivo anticancer effects of proscillaridin A that both controls xenograft growth and improves mice survival. Altogether, results suggest that proscillaridin A is a promising candidate as cancer therapies in glioblastoma. This sustains previous reports showing that cardiac glycosides act as anticancer drugs in other cancers.

Inhibition of Na+/K+-ATPase induces hybrid cell death and enhanced sensitivity to chemotherapy in human glioblastoma cells

Background

Glioblastoma multiforme (GBM) is very difficult to treat with conventional anti-cancer/anti-apoptotic drugs. We tested the hypothesis that inhibition of Na⁺/K⁺-ATPase causes a mixed or hybrid form of concurrent apoptosis and necrosis and therefore should enhance anti-cancer effects of chemotherapy on glioblastoma cells.

Methods

In human LN229 and drug-resistant T98G glioblastoma cell cultures, cell death and signal pathways were measured using immunocytochemistry and Western blotting. Fluorescent dyes were applied to measure intracellular Ca²⁺, Na⁺ and K⁺ changes.

Results

The specific Na⁺/K⁺-ATPase blocker ouabain (0.1 - 10 μM) induced cell death and disruption of K⁺ homeostasis in a time- and concentration-dependent manner. Annexin-V translocation and caspase-3 activation indicated an apoptotic component in ouabain cytoxicity, which was accompanied with reduced Bcl-2 expression and mitochondrial membrane potential. Ouabain-induced cell death was partially attenuated by the caspase inhibitor Z-VAD (100 μM). Consistently, the K⁺ ionophore valinomycin initiated apoptosis in LN229 cells in a K⁺ efflux-dependent manner. Ouabain caused an initial cell swell, which was followed by a sustained cell volume decrease. Electron microscopy revealed ultrastructural features of both apoptotic and necrotic alterations in the same cells. Finally, human T98G glioblastoma cells that are resistant to the chemotherapy drug temozolomide (TMZ) showed a unique high expression of the Na⁺/K⁺-ATPase α2 and α3 subunits compared to the TMZ-sensitive cell line LN229 and normal human astrocytes. At low concentrations, ouabain selectively killed T98G cells. Knocking down the α3 subunit sensitized T98G cells to TMZ and caused more cell death.

Conclusion

This study suggests that inhibition of Na⁺/K⁺-ATPase triggers hybrid cell death and serves as an underlying mechanism for an enhanced chemotherapy effect on glioblastoma cells.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-716) contains supplementary material, which is available to authorized users.

Anvirzel™ in combination with cisplatin in breast, colon, lung, prostate, melanoma and pancreatic cancer cell lines

Background

Platinum derivatives are used widely for the treatment of many cancers. However, the toxicity that is observed makes imperative the need for new drugs, or new combinations. Anvirzel™ is an extract which has been demonstrated with experimental data that displays anticancer activity. The aim of the present study is to determine whether the combination of Cisplatin and Anvirzel™ has a synergistic effect against different types of cancer.

Materials and methods

To measure the efficacy of treatment with Cisplatin and Anvirzel™, methyl-tetrazolium dye (MTT) chemosensitivity assays were used incorporating established human cancer cell lines. Measurements were performed in triplicates, three times, using different incubation times and different concentrations of the two formulations in combination or on their own. t-test was used for statistical analysis.

Results

In the majority of the cell lines tested, lower concentrations of Anvirzel™ induced a synergistic effect when combined with low concentrations of Cisplatin after an incubation period of 48 to 72 h. The combination of Anvirzel™/Cisplatin showed anti-proliferative effects against a wide range of tumours.

Conclusion

The results showed that the combination of Anvirzel™ and Cisplatin is more effective than monotherapy, even when administered at low concentrations; thus, undesirable toxic effects can be avoided.

In vitro propagation and production of cardiotonic glycosides in shoot cultures of Digitalis purpurea L. by elicitation and precursor feeding

Digitalis purpurea L. (Scrophulariaceae; Foxglove) is a source of cardiotonic glycosides such as digitoxin and digoxin which are commercially applied in the treatment to strengthen cardiac diffusion and to regulate heart rhythm. This investigation deals with in vitro propagation and elicited production of cardiotonic glycosides digitoxin and digoxin in shoot cultures of D. purpurea L. In vitro germinated seedlings were used as a primary source of explants. Multiple shoot formation was achieved for three explant types (nodal, internodal, and leaf) cultured on Murashige and Skoog (MS) medium with several treatments of cytokinins (6-benzyladenine-BA; kinetin-Kin; and thidiazuron-TDZ) and auxins (indole-3-acetic acid-IAA; α-naphthaleneacetic acid-NAA; and 2,4-dichlorophenoxy acetic acid-2,4-D). Maximum multiple shoots (12.7 ± 0.6) were produced from nodal explants on MS + 7.5 μM BA. Shoots were rooted in vitro on MS containing 15 μM IAA. Rooted plantlets were successfully acclimatized. To further maintain the multiple shoot induction, mother tissue was cut into four equal parts and repeatedly sub-cultured on fresh shoot induction liquid medium after each harvest. On adaptation of this strategy, an average of 18 shoots per explant could be produced. This strategy was applied for the production of biomass and glycosides digitoxin and digoxin in shoot cultures on MS medium supplemented with 7.5 μM BA and several treatments with plant growth regulators, incubation period, abiotic (salicylic acid, mannitol, sorbitol, PEG-6000, NaCl, and KCl), biotic (Aspergillus niger, Helminthosporium sp., Alternaria sp., chitin, and yeast extract) elicitors, and precursors (progesterone, cholesterol, and squalene). The treatment of KCl, mycelial mass of Helminthosporium sp., and progesterone were highly effective for the production of cardenolides. In the presence of progesterone (200 to 300 mg/l), digitoxin and digoxin accumulation was enhanced by 9.1- and 11.9-folds respectively.

Na+/K+-ATPase and cancer

The sodium pump, Na+/K+-ATPase, could be an important target for the development of anticancer drugs as it serves as a versatile signal transducer, plays a key role in cell adhesion and has abnormal expression and activity that are implicated in the development and progression of different cancers. Several publications have reported differing expression of Na+/K+-ATPase α- and β-subunits in malignant tissues compared with their normal tissue counterparts, thus offering a powerful diagnostic tool. A growing number of patent applications claim the invention or discovery of Na+/K+-ATPase inhibitors (e.g., cardiac glycosides) to be used to effectively treat certain cancers that are refractory to conventional chemotherapy or radiotherapy. The aims of this review are to provide an overview of the most significant patents that highlight Na+/K+-ATPase as a valuable target in anticancer therapy and which report on novel Na+/K+-ATPase inhibitors and ligands designed as potential anticancer agents.

Cardiotonic steroids attenuate ERK phosphorylation and generate cell cycle arrest to block human hepatoma cell growth

Recent studies revealed the potential of Na(+)/K(+)-ATPase as a target for anticancer therapy and showed additional modes of action of cardiotonic steroids (CSs), a diverse family of naturally derived compounds, as inhibitors of Na(+)/K(+)-ATPase. The results from epidemiological studies showed significantly lower mortality rates in cancer patients receiving CSs, which sparked interest in the anticancer properties of these drugs. The present study was designed to investigate the anticancer effect of CSs (ouabain or cinobufagin) and to elucidate the molecular mechanisms of CS activity in hepatoma cell lines (HepG2 and SMMC-7721). Ouabain and cinobufagin significantly inhibited cell proliferation by attenuating the phosphorylation of extracellular regulated kinase (ERK) and down-regulating the expression of C-myc. These CSs also induced cell apoptosis by increasing the concentration of intracellular free calcium ([Ca(2+)](i)) and induced S phase cell cycle arrest by down-regulating the expression of Cyclin A, cyclin dependent kinase 2 (CDK2) and proliferating cell nuclear antigen (PCNA) as well as up-regulating the expression of cyclin dependent kinase inhibitor 1A (p21(CIP1)). Overexpression of ERK reversed the antiproliferation effect of ouabain or cinobufagin in HepG2 and SMMC-7721 cells. Currently, the first generation of CS-based anticancer drugs (UNBS1450 and Anvirzel) are in Phase I clinical trials. These data clearly support their potential use as cancer therapies.

Ex vivo activity of cardiac glycosides in acute leukaemia

Background

Despite years of interest in the anti-cancerous effects of cardiac glycosides (CGs), and numerous studies in vitro and in animals, it has not yet been possible to utilize this potential clinically. Reports have demonstrated promising in vitro effects on different targets as well as a possible therapeutic index/selectivity in vitro and in experimental animals. Recently, however, general inhibition of protein synthesis was suggested as the main mechanism of the anti-cancerous effects of CGs. In addition, evidence of species differences of a magnitude sufficient to explain the results of many studies called for reconsideration of earlier results.

Principal Findings

In this report we identified primary B-precursor and T-ALL cells as being particularly susceptible to the cytotoxic effects of CGs. Digitoxin appeared most potent and IC₅₀ values for several patient samples were at concentrations that may be achieved in the clinic. Significant protein synthesis inhibition at concentrations corresponding to IC₅₀ was demonstrated in colorectal tumour cell lines moderately resistant to the cytotoxic effects of digoxin and digitoxin, but not in highly sensitive leukaemia cell lines.

Conclusion

It is suggested that further investigation regarding CGs may be focused on diagnoses like T- and B-precursor ALL.

A Direct Comparison of the Anticancer Activities of Digitoxin MeON-Neoglycosides and O-Glycosides: Oligosaccharide Chain Length-Dependent Induction of Caspase-9-Mediated Apoptosis

Digitoxin is a cardiac glycoside currently being investigated for potential use in oncology. While a number of structure-activity relationship studies have been conducted, an investigation of anticancer activity as a function of oligosaccharide chain length has not yet been performed. We generated mono-, di-, and tri-O-digitoxoside derivatives of digitoxin and compared their activity to the corresponding MeON-neoglycosides. Both classes of cardenolide derivatives display comparable oligosaccharide chain length-dependent cytotoxicity toward human cancer cell lines. Further investigation revealed that both classes of compounds induce caspase-9-mediated apoptosis in non-small cell lung cancer cells (NCI-H460). Since O-glycosides and MeON-neoglycosides share a similar mode of action, the convenience of MeON-neoglycosylation could be exploited in future SAR work to rapidly survey large numbers of carbohydrates to prioritize selected O-glycoside candidates for traditional synthesis.

Tanghinigenin from seeds of Cerbera manghas L. induces apoptosis in human promyelocytic leukemia HL-60 cells

Tanghinigenin, a cardiac glycoside, is isolated from the seeds of Cerbera manghas L. In this study, we demonstrated that tanghinigenin reduced the viability of human promyelocytic leukemia HL-60 cells in a time- and dose-dependent manner, and efficiently induced apoptosis in HL-60 cells as evidenced by the Annexin V/PI binding assay, DNA fragmentation and AO/EB staining studies. In addition, stimulation of HL-60 cells with tanghinigenin induced a series of intracellular events including the activation of caspase-3, -8, and -9, as well as up-regulation of Fas and FasL protein level. Taken together, caspase activation and Fas/FasL interaction was found to be involved in tanghinigenin-induced HL-60 cell apoptosis.

Cytotoxic effects of cardiac glycosides in colon cancer cells, alone and in combination with standard chemotherapeutic drugs

Cardiac glycosides have been reported to exhibit cytotoxic activity against several different cancer types, but studies against colorectal cancer are lacking. In a screening procedure aimed at identifying natural products with activity against colon cancer, several cardiac glycosides were shown to be of interest, and five of these were further evaluated in different colorectal cancer cell lines and primary cells from patients. Convallatoxin (1), oleandrin (4), and proscillaridin A (5) were identified as the most potent compounds (submicromolar IC50 values), and digitoxin (2) and digoxin (3), which are used in cardiac disease, exhibited somewhat lower activity (IC50 values 0.27-4.1 microM). Selected cardiac glycosides were tested in combination with four clinically relevant cytotoxic drugs (5-fluorouracil, oxaliplatin, cisplatin, irinotecan). The combination of 2 and oxaliplatin exhibited synergism including the otherwise highly drug-resistant HT29 cell line. A ChemGPS-NP application comparing modes of action of anticancer drugs identified cardiac glycosides as a separate cluster. These findings demonstrate that such substances may exhibit significant activity against colorectal cancer cell lines, by mechanisms disparate from currently used anticancer drugs, but at concentrations generally considered not achievable in patient plasma.

Present and potential future adjuvant issues in high-grade astrocytic glioma treatment

Despite major advances in the management of malignant gliomas of which glioblastomas represent the ultimate grade of malignancy, they remain characterized by dismal prognoses. Glioblastoma patients have a median survival expectancy of only 14 months on the current standard treatment of surgical resection to the extent feasible, followed by adjuvant radiotherapy plus temozolomide, given concomitantly with and after radiotherapy. Malignant gliomas are associated with such dismal prognoses because glioma cells can actively migrate through the narrow extra-cellular spaces in the brain, often travelling relatively long distances, making them elusive targets for effective surgical management. Clinical and experimental data have demonstrated that invasive malignant glioma cells show a decrease in their proliferation rates and a relative resistance to apoptosis (type I programmed cell death) as compared to the highly cellular centre of the tumor, and this may contribute to their resistance to conventional pro-apoptotic chemotherapy and radiotherapy. Resistance to apoptosis results from changes at the genomic, transcriptional and post-transcriptional level of proteins, protein kinases and their transcriptional factor effectors. The PTEN/ PI3K/Akt/mTOR/NF-kappaB and the Ras/Raf/MEK/ERK signaling cascades play critical roles in the regulation of gene expression and prevention of apoptosis. Components of these pathways are mutated or aberrantly expressed in human cancer, notably glioblastomas. Monoclonal antibodies and low molecular-weight kinase inhibitors of these pathways are the most common classes of agents in targeted cancer treatment. However, most clinical trials of these agents as monotherapies have failed to demonstrate survival benefit. Despite resistance to apoptosis being closely linked to tumorigenesis, tumor cells can still be induced to die by non-apoptotic mechanisms such as necrosis, senescence, autophagy (type II programmed cell death) and mitotic catastrophe. Temozolomide brings significant therapeutic benefits in glioblastoma treatment. Part of temozolomide cytotoxic activity is exerted through pro-autophagic processes and also through the induction of late apoptosis. Autophagy, type II programmed cell death, represents an alternative mechanism to overcome, at least partly, the dramatic resistance of many cancers to pro-apoptotic-related therapies. Another way to potentially overcome apoptosis resistance is to decrease the migration of malignant glioma cells in the brain, which then should restore a level of sensitivity to pro-apoptotic drugs. Recent series of studies have supported the concept that malignant gliomas might be seen as an orchestration of cross-talks between cancer cells, microenvironment, vasculature and cancer stem cells. The present chapter focuses on (i) the major signaling pathways making glioblastomas resistant to apoptosis, (ii) the signaling pathways distinctly activated by pro-autophagic drugs as compared to pro-apoptotic ones, (iii) autophagic cell death as an alternative to combat malignant gliomas, (iv) the major scientific data already obtained by researchers to prove that temozolomide is actually a pro-autophagic and pro-apoptotic drug, (v) the molecular and cellular therapies and local drug delivery which could be used to complement conventional treatments, and a review of some of the currently ongoing clinical trials, (vi) the fact that reducing the levels of malignant glioma cell motility can restore pro-apoptotic drug sensitivity, (vii) the observation that inhibiting the sodium pump activity reduces both glioma cell proliferation and migration, (viii) the brain tumor stem cells as a target to complement conventional treatment.

High-throughput screening identifies cardiac glycosides as potent inhibitors of human tissue kallikrein expression: implications for cancer therapies

PURPOSE

Human tissue kallikreins (KLK) comprise a subgroup of 15 homologous secreted serine proteases. Primarily known for their clinical use as cancer biomarkers (e.g., PSA), KLKs have recently been directly implicated in cancer-related processes, including invasion, angiogenesis, and tumor growth regulation. Therefore, the identification of compounds that would modulate expression of KLKs might be of considerable therapeutic value.

EXPERIMENTAL DESIGN

A cell-based high-throughput screening (HTS) of three small molecule libraries ( approximately 4,500 compounds) was undertaken; KLK expression in the breast cancer cell line MDA-MB-468 was assessed with sensitive ELISAs.

RESULTS

The initial screening resulted in 66 "putative hits" that decreased KLK5 expression by at least 50% over control. Secondary screening and mini-dose-response assays resulted in 21 "validated hits." These 21 compounds were clustered in only three distinct functional families and were further analyzed in vitro to determine their effectiveness (IC(50)s). Hits that failed to show dose-responsiveness or interfered with the viability of the cells were excluded. Multiple members of the cardiac glycoside family were found to be novel inhibitors of KLK expression, acting at low concentrations (10-50 nmol/L). Furthermore, members of the same family induced marked decreases in c-MYC and c-FOS expression, in a dose-dependent manner that correlated the KLK inhibition, suggesting a transcriptional mechanism of regulation of KLK expression.

CONCLUSIONS

We conclude that cardiac glycosides can dramatically suppress the transcription of KLKs and that these effects may be linked to proto-oncogene (c-myc/fos) expression. These findings may partially explain the recently realized antineoplastic actions of cardiac glycosides.

Modifying the glycosidic linkage in digitoxin analogs provides selective cytotoxins

A chemoselective reaction between oxyamines and unprotected, unactivated reducing sugars was used to construct for the first time a panel of linkage-diversified neoglycosides. This panel of digitoxin analogs included potent and selective tumor cytotoxins; cytotoxicity was dependent on the structure of the glycosidic linkage. These results validate linkage diversification through neoglycosylation as a unique and simple strategy to powerfully complement existing methods for the optimization of glycoconjugates.

Targeting the alpha 1 subunit of the sodium pump to combat glioblastoma cells

OBJECTIVE

Ion transporters play pivotal roles in cancer cell migration in general and in glioblastomas (GBMs) in particular. However, the specific role of Na/K-ATPase (the sodium pump) and, in particular, its alpha1 subunit, has remained unexplored in GBMs.

MATERIALS AND METHODS

The expression of Na+/K+ -ATPase alpha1 in GBM clinical samples, normal brain tissue, and a human GBM cell line has been investigated. Using the novel cardenolide UNBS1450 (Unibioscreen, Brussels, Belgium), which is a ligand of the sodium pump, we have characterized the effects of inhibiting Na+/K+ -ATPase alpha1 in human GBM cells with respect to cell proliferation; morphology; impact on intracellular Na+, Ca2+, and adenosine triphosphate; and changes in the actin cytoskeleton. We have investigated the mechanism by which UNBS1450 overcomes the apoptosis resistance of GBMs and determined its anti-tumor effects in comparative studies in vitro in GBM cell viability assays and in vivo using an orthotopic human GBM xenograft model.

RESULTS

Overall, the alpha1 subunit of Na+/K+ -ATPase is highly expressed in a majority of glioblastomas compared with normal brain tissues, and by binding to this subunit in human U373-MG GBM cells, UNBS1450 impairs cell proliferation and migration via an intracellular adenosine triphosphate decrease-mediated disorganization of the actin cytoskeleton and cytotoxic proautophagic effects. UNBS1450 also significantly increases the in vivo survival of mice orthotopically grafted with U373-MG GBM cells.

CONCLUSION

Inhibition of the Na+/K+ -ATPase alpha1 subunit in human GBM cells impairs both cell migration and cell proliferation.

The sodium pump alpha1 subunit as a potential target to combat apoptosis-resistant glioblastomas

PURPOSE

To review the involvement of the ion transporter Na+/K+-ATPase (NaK) in the migration and proliferation of glioma cells. Preliminary studies indicate that NaK alpha1 subunits seem to be upregulated in a proportion of glioblastomas but not in normal brain tissues.

DESIGN

The present review focuses on (1) the natural resistance of migrating malignant glioma cells to apoptosis, (2) autophagic cell death as an alternative to combat malignant gliomas, (3) the fact that reducing the levels of malignant glioma cell motility can restore proapoptotic drug sensitivity,and (4) on the observation that inhibiting the NaK activity reduces both glioma cell proliferation and migration.

RESULTS

The natural ligands of the NaK are the cardiotonic steroids. A hemisynthetic derivative of 2"-oxovoruscharin (UNBS1450), a novel cardenolide, displays unique structural features, making its binding affinity to NaK alpha subunits (including alpha1) 10 to 100 times higher than that of other cardenolides. UNBS1450 markedly decreases intracellular ATP concentration in glioma cells, disorganizes the actin cytoskeleton, and leads to autophagic cell death in NaK alpha1 over-expressing glioma cells.

CONCLUSIONS

Glioblastoma patients who do not respond to chemotherapy and whose tumors over-express NaK alpha1 subunits could benefit from a treatment using ligands with marked binding affinity for the NaK alpha1 subunit.

Digitoxin as an anticancer agent with selectivity for cancer cells: possible mechanisms involved

Accumulating preclinical and clinical data suggest that the cardiac drug digitoxin might be used in cancer therapy. Recent reports have shown that digitoxin can inhibit the growth and induce apoptosis in cancer cells at concentrations commonly found in the plasma of cardiac patients treated with this drug. Several mechanisms have been associated with the anticancer activity of digitoxin, yet at present it is unknown why malignant cells are more susceptible to this cardiac glycoside than non-malignant cells. This report analyses the possible anticancer mechanisms of digitoxin and proposes that the inhibition of glycolysis may be a key mechanism by which this natural product selectively targets cancer cells. Finally, whether or not there is enough evidence to support the clinical evaluation of digitoxin in patients with cancer is discussed.

Cardiotonic steroids on the road to anti-cancer therapy

The sodium pump, Na(+)/K(+)-ATPase, could be an important target for the development of anti-cancer drugs as it serves as a versatile signal transducer, it is a key player in cell adhesion and its aberrant expression and activity are implicated in the development and progression of different cancers. Cardiotonic steroids, known ligands of the sodium pump have been widely used for the treatment of heart failure. However, early epidemiological evaluations and subsequent demonstration of anti-cancer activity in vitro and in vivo have indicated the possibility of developing this class of compound as chemotherapeutic agents in oncology. Their development to date as anti-cancer agents has however been impaired by a narrow therapeutic margin resulting from their potential to induce cardiovascular side-effects. The review will thus discuss (i) sodium pump structure, function, expression in diverse cancers and its chemical targeting and that of its sub-units, (ii) reported in vitro and in vivo anti-cancer activity of cardiotonic steroids, (iii) managing the toxicity of these compounds and the limitations of existing preclinical models to adequately predict the cardiotoxic potential of new molecules in man and (iv) the potential of chemical modification to reduce the cardiovascular side-effects and improve the anti-cancer activity of new molecules.

The alpha1 subunit of the sodium pump could represent a novel target to combat non-small cell lung cancers

With an overall 5 year survival rate as low as 15% for non-small cell lung cancer (NSCLC), even with surgical intervention and the use of newer molecules in adjuvant chemotherapy, there is an urgent need for new biological targets and associated novel anti-cancer agents. The present study was undertaken to evaluate the potential of the Na(+)/K(+)-ATPase alpha1 subunit as a novel target in NSCLC and revealed that alpha1 expression is markedly higher in a significant proportion of NSCLC clinical samples compared to normal lung tissue. Furthermore, reduction in alpha1 expression in A549 NSCLC cells by anti-alpha1 siRNA resulted in markedly impaired proliferation and migration of these cancer cells. Finally, of three cardenolides investigated, UNBS1450, which is known to bind to Na(+)/K(+)-ATPase and displays potent anti-tumour activity in vivo in experimental models of human NSCLCs, is the most potent inhibitor of Na(+)/K(+)-ATPase isozymes (alpha1beta1, alpha2beta1 and alpha3beta1), most strikingly of alpha1beta1. This was reflected in the compound's more potent anti-proliferative activity in all NSCLC cell lines evaluated (A549, Cal-12T, NCI-H727 and A427); the first three of which over-express alpha1. The marked impairment in A549 NSCLC cell proliferation and migration, and resulting similar morphology following anti-alpha1 siRNA or UNBS1450 treatment, was associated with features of abnormal cytokinesis, mediated in the case of UNBS1450 by disorganization of the actin cytoskeleton. Collectively these data strongly suggest that targeting the Na(+)/K(+)-ATPase alpha1 using specific cardenolides could represent a novel means to combat certain NSCLCs.

Endogenous and exogenous cardiac glycosides: their roles in hypertension, salt metabolism, and cell growth

Cardiotonic steroids (CTS), long used to treat heart failure, are endogenously produced in mammals. Among them are the hydrophilic cardenolide ouabain and the more hydrophobic cardenolide digoxin, as well as the bufadienolides marinobufagenin and telecinobufagin. The physiological effects of endogenous ouabain on blood pressure and cardiac activity are consistent with the "Na(+)-lag" hypothesis. This hypothesis assumes that, in cardiac and arterial myocytes, a CTS-induced local increase of Na(+) concentration due to inhibition of Na(+)/K(+)-ATPase leads to an increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) via a backward-running Na(+)/Ca(2+) exchanger. The increase in [Ca(2+)](i) then activates muscle contraction. The Na(+)-lag hypothesis may best explain short-term and inotropic actions of CTS. Yet all data on the CTS-induced alteration of gene expression are consistent with another hypothesis, based on the Na(+)/K(+)-ATPase "signalosome," that describes the interaction of cardiac glycosides with the Na(+) pump as machinery activating various signaling pathways via intramembrane and cytosolic protein-protein interactions. These pathways, which may be activated simultaneously or selectively, elevate [Ca(2+)](i), activate Src and the ERK1/2 kinase pathways, and activate phosphoinositide 3-kinase and protein kinase B (Akt), NF-kappaB, and reactive oxygen species. A recent development indicates that new pharmaceuticals with antihypertensive and anticancer activities may be found among CTS and their derivatives: the antihypertensive rostafuroxin suppresses Na(+) resorption and the Src-epidermal growth factor receptor-ERK pathway in kidney tubule cells. It may be the parent compound of a new principle of antihypertensive therapy. Bufalin and oleandrin or the cardenolide analog UNBS-1450 block tumor cell proliferation and induce apoptosis at low concentrations in tumors with constitutive activation of NF-kappaB.

Role of homologous ASP334 and GLU319 in human non-gastric H,K- and Na,K-ATPases in cardiac glycoside binding

Cardiac steroids inhibit Na,K-ATPase and the related non-gastric H,K-ATPase, while they do not interact with gastric H,K-ATPase. Introducing an arginine, the residue present in the gastric H,K-ATPase, in the second extracellular loop at the corresponding position 334 in the human non-gastric H,K-ATPase (D334R mutation) rendered it completely resistant to 2mM ouabain. The corresponding mutation (E319R) in alpha1 Na,K-ATPase produced a approximately 2-fold increase of the ouabain IC(50) in the ouabain-resistant rat alpha1 Na,K-ATPase and a large decrease of the ouabain affinity of human alpha1 Na,K-ATPase, on the other hand this mutation had no effect on the affinity for the aglycone ouabagenin. These results provide a strong support for the orientation of ouabain in its biding site with its sugar moiety interacting directly with the second extracellular loop.

The cardenolide UNBS1450 is able to deactivate nuclear factor kappaB-mediated cytoprotective effects in human non-small cell lung cancer cells

Non-small cell lung cancers (NSCLC) are associated with very dismal prognoses, and adjuvant chemotherapy, including irinotecan, taxanes, platin, and Vinca alkaloid derivatives, offers patients only slight clinical benefits. Part of the chemoresistance of NSCLCs results from the constitutive or anticancer drug-induced activation of the nuclear factor-kappaB (NF-kappaB) signaling pathways. The present study shows that human A549 NSCLC cells display highly activated cytoprotective NF-kappaB signaling pathways. UNBS1450, which is a cardenolide belonging to the same class of chemicals as ouabain and digitoxin, affected the expression and activation status of different constituents of the NF-kappaB pathways in these A549 tumor cells. The modifications brought about by UNBS1450 led to a decrease in both the DNA-binding capacity of the p65 subunit and the NF-kappaB transcriptional activity. Using the 3-(4,5-dimethylthiazol-2yl)-dephenyltetrazolium bromide colorimetric assay, we observed in vitro that UNBS1450 was as potent as taxol and SN38 (the active metabolite of irinotecan) in reducing the overall growth levels of the human A549 NSCLC cell line, and was more efficient than platin derivatives, including cisplatin, carboplatin, and oxaliplatin. The chronic in vivo i.p. and p.o. UNBS1450 treatments of human A549 orthotopic xenografts metastasizing to the brains and the livers of immunodeficient mice had a number of significant therapeutic effects on this very aggressive model.

Cardenolide-induced lysosomal membrane permeabilization demonstrates therapeutic benefits in experimental human non-small cell lung cancers

Non-small cell lung cancers (NSCLCs) are the leading cause of cancer deaths in most developed countries. Targeting heat shock protein 70 (Hsp70) expression and function, together with the induction of lysosomal membrane permeabilization (LMP), could overcome the multiple anti-cell death mechanisms evidenced in NSCLCs that are responsible for the failure of currently used chemotherapeutic drugs. Because cardenolides bind to the sodium pump, they affect multiple signaling pathways and thus have a number of marked effects on tumor cell behavior. The aim of the present study was to characterize in vitro and in vivo the antitumor effects of a new cardenolide (UNBS1450) on experimental human NSCLCs. UNBS1450 is a potent source of in vivo antitumor activity in the case of paclitaxel-and oxaliplatin-resistant subcutaneous human NCI-H727 and orthotopic A549 xenografts in nude mice. In vitro UNBS1450-mediated antitumor activity results from the induction of nonapoptotic cell death. UNBS1450 mediates the decrease of Hsp70 at both mRNA and protein levels, and this is at least partly due to UNBS1450-induced downregulation of NFAT5/TonEBP (a factor responsible for the transcriptional control of Hsp70). These effects were paralleled by the induction of LMP, as evidenced by acridine orange staining and immunofluorescence analysis for cathepsin B accumulation.

Neoglycorandomization and chemoenzymatic glycorandomization: two complementary tools for natural product diversification

In an effort to explore the contribution of the sugar constituents of pharmaceutically relevant glycosylated natural products, chemists have developed glycosylation methods that are amenable to the generation of libraries of analogues with a broad array of glycosidic attachments. Recently, two complementary glycorandomization strategies have been described, namely, neoglycorandomization, a chemical approach based on a one-step sugar ligation reaction that does not require any prior sugar protection or activation, and chemoenzymatic glycorandomization, a biocatalytic approach that relies on the substrate promiscuity of enzymes to activate and attach sugars to natural products. Since both methods require reducing sugars, this review first highlights recent advances in monosaccharide generation and then follows with an overview of recent progress in the development of neoglycorandomization and chemoenzymatic glycorandomization.

Enhancing the anticancer properties of cardiac glycosides by neoglycorandomization

Glycosylated natural products are reliable platforms for the development of many front-line drugs, yet our understanding of the relationship between attached sugars and biological activity is limited by the availability of convenient glycosylation methods. When a universal chemical glycosylation method that employs reducing sugars and requires no protection or activation is used, the glycorandomization of digitoxin leads to analogs that display significantly enhanced potency and tumor specificity and suggests a divergent mechanistic relationship between cardiac glycoside-induced cytotoxicity and Na+/K+-ATPase inhibition. This report highlights the remarkable advantages of glycorandomization as a powerful tool in glycobiology and drug discovery.

Possible future issues in the treatment of glioblastomas: special emphasis on cell migration and the resistance of migrating glioblastoma cells to apoptosis

PURPOSE

The present review aims to emphasize that malignant gliomas are characterized by the diffuse invasion of distant brain tissue by a myriad of single migrating cells that exhibit decreased levels of apoptosis (programmed cell death type I), thus a resistance to cytotoxic insult.

METHODS

The present review surveys the molecular mechanisms of migration in malignant gliomas and potential issues arising from treatments, in addition to relationships between glioma cell migration and resistance to apoptosis in terms of the molecular signaling pathways.

RESULTS

Clinical and experimental data demonstrate that glioma cell migration is a complex combination of multiple molecular processes, including the alteration of tumor cell adhesion to a modified extracellular matrix, the secretion of proteases by the cells, and modifications to the actin cytoskeleton. Intracellular signaling pathways involved in the acquisition of resistance to apoptosis by migrating glioma cells concern PI3K, Akt, mTOR, NF-kappaB, and autophagy (programmed cell death type II).

CONCLUSION

A number of signaling pathways can be constitutively activated in migrating glioma cells, thus rendering these cells resistant to cytotoxic insults. However, these pathways are not all constitutively activated at the same time in any one glioma. Particular inhibitors should therefore only be chosen if the target is present in the tumor tissue, but this is only possible if individual patients are submitted to the molecular profiling of their tumors before undergoing any treatment to combat their migratory glioma cells. Specific antimigratory compounds should be added to conventional radio- and/or chemotherapy.

Identification of a novel cardenolide (2''-oxovoruscharin) from Calotropis procera and the hemisynthesis of novel derivatives displaying potent in vitro antitumor activities and high in vivo tolerance: structure-activity relationship analyses

Analysis of the methanolic extract of Calotropis procera root barks enabled the identification of a novel cardenolide (2''-oxovoruscharin) to be made. Of the 27 compounds that we hemisynthesized, one (23) exhibited a very interesting profile with respect to its hemisynthetic chemical yield, its in vitro antitumor activity, its in vitro inhibitory influence on the Na+/K+-ATPase activity, and its in vivo tolerance. Compound 23 displayed in vitro antitumor activity on a panel of 57 human cancer cell lines similar to taxol, and higher than SN-38 (the active metabolite of irinotecan), two of the most potent drugs used in hospitals to combat cancer.