Tatjana Mijatovic

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

OBJECTIVEIon 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 α1 subunit, has remained unexplored in GBMs. MATERIALS AND METHODSThe expression of Na+/K+-ATPase α1 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 α1 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. RESULTSOverall, the α1 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. CONCLUSIONInhibition of the Na+/K+-ATPase α1 subunit in human GBM cells impairs both cell migration and cell proliferation.

Interleukin-4 and -13 inhibit tumor necrosis factor-alpha mRNA translational activation in lipopolysaccharide-induced mouse macrophages.

The production of tumor necrosis factor-α (TNF-α) by lipopolysaccharide (LPS)-stimulated macrophages can be markedly inhibited by the two closely related cytokines, interleukin (IL)-4 and IL-13. To investigate the molecular mechanism of this inhibition, we analyzed the effect of the two cytokines on TNF-α production and TNF-α mRNA accumulation in the mouse macrophage cell lines RAW 264.7 and J774 stimulated by LPS. Whereas LPS-induced TNF-α production is strongly suppressed by both cytokines, TNF-α mRNA accumulation is not significantly affected, indicating that IL-4 and IL-13 induce a translational repression of TNF-α mRNA. Transfection of reporter gene constructs containing different regions of the TNF-α gene revealed that the inhibitory action of IL-4 and IL-13 is mediated by the UA-rich sequence present in the TNF-α mRNA 3′-untranslated region.

Naphthalimides and azonafides as promising anti-cancer agents.

Naphthalimides, a class of compounds which bind to DNA by intercalation, have shown high anti-cancer activity against a variety of murine and more notably human cancer cell lines. Azonafide derivatives are also potential anti-tumor agents which are structurally related to the naphthalimides. Derivatives of azonafide have shown enhanced activity against various cancer models, especially leukemias, breast cancer and melanoma. Naphthalimides in general and amonafide in particular, are most probably the agents which have been involved in the greatest number of clinical trials without ever acceding to the market because of dose-limiting toxicity. This statement also reflects the immense interest that oncologists have paid to this class of compounds with respect to their anti-cancer potential. While the first generation of naphthalimides were mainly topoisomerse II poisons, some new compounds display novel mechanism of action. In contrast to the most widely used topo II poisons, including etoposide, adriamycin and their analogues, which often induce multi-drug resistance, several naphthalimide-related compounds have been reported not to be affected by this phenomenon. Multi-disciplinary approaches including medicinal chemistry, early toxicology and DMPK, in vivo activity assessment in diverse preclinical models and in-depth mechanism of action deciphering, along with the lessons learnt from previous and currently ongoing clinical trials, have resulted in the generation of a number of novel promising naphthalimide derivatives. It is thus reasonable to expect that members of this class of compounds will reach the oncology market in the near future.

Evidence of galectin-1 involvement in glioma chemoresistance.

Glioblastomas (GBMs) are resistant to apoptosis but less so to autophagy; a fact that may at least partly explain the therapeutic benefits of the pro-autophagic drug temozolomide in the treatment of GBM patients. Galectin-1 (Gal1) whose expression is stimulated by hypoxia is a potent modulator of GBM cell migration and a pro-angiogenic molecule. Hypoxia is also known to confer cancer cells with resistance to chemotherapy and radiotherapy and to modulate the unfolded protein response (UPR) during endoplasmic reticulum (ER) stress. The present study investigates whether decreasing Gal1 expression (by means of a siRNA approach) in human Hs683 GBM cells increases their sensitivity to pro-autophagic or pro-apoptotic drugs. The data reveal that temozolomide, the standard treatment for glioma patients, increases Gal1 expression in Hs683 cells both in vitro and in vivo. However, reducing Gal1 expression in these cells by siRNA increases the anti-tumor effects of various chemotherapeutic agents, in particular temozolomide both in vitro and in vivo. This decrease in Gal1 expression in Hs683 cells does not induce apoptotic or autophagic features, but is found to modulate p53 transcriptional activity and decrease p53-targeted gene expression including DDIT3/GADD153/CHOP, DUSP5 ATF3 and GADD45A. The decrease in Gal1 expression also impairs the expression levels of seven other genes implicated in chemoresistance: ORP150, HERP, GRP78/Bip, TRA1, BNIP3L, GADD45B and CYR61, some of which are located in the ER and whose expression is also known to be modified by hypoxia. This novel facet of Gal1 involvement in glioblastoma biology may be amenable to therapeutic manipulation.

The cardenolide UNBS1450 is able to deactivate nuclear factor κB–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-κB (NF-κB) signaling pathways. The present study shows that human A549 NSCLC cells display highly activated cytoprotective NF-κB 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-κB 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-κB 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. [Mol Cancer Ther 2006;5(2):391–9]

The sodium pump α1 sub-unit: a disease progression–related target for metastatic melanoma treatment

Melanomas remain associated with dismal prognosis because they are naturally resistant to apoptosis and they markedly metastasize. Up‐regulated expression of sodium pump α sub‐units has previously been demonstrated when comparing metastatic to non‐metastatic melanomas. Our previous data revealed that impairing sodium pump α1 activity by means of selective ligands, that are cardiotonic steroids, markedly impairs cell migration and kills apoptosis‐resistant cancer cells. The objective of this study was to determine the expression levels of sodium pump α sub‐units in melanoma clinical samples and cell lines and also to characterize the role of α1 sub‐units in melanoma cell biology. Quantitative RT‐PCR, Western blotting and immunohistochemistry were used to determine the expression levels of sodium pump α sub‐units. In vitro cytotoxicity of various cardenolides and of an anti‐α1 siRNA was evaluated by means of MTT assay, quantitative videomicroscopy and through apoptosis assays. The in vivo activity of a novel cardenolide UNBS1450 was evaluated in a melanoma brain metastasis model. Our data show that all investigated human melanoma cell lines expressed high levels of the α1 sub‐unit, and 33% of human melanomas displayed significant α1 sub‐unit expression in correlation with the Breslow index. Furthermore, cardenolides (notably UNBS1450; currently in Phase I clinical trials) displayed marked anti‐tumour effects against melanomas in vitro. This activity was closely paralleled by decreases in cMyc expression and by increases in apoptotic features. UNBS1450 also displayed marked anti‐tumour activity in the aggressive human metastatic brain melanoma model in vivo. The α1 sodium pump sub‐unit could represent a potential novel target for combating melanoma.

Knocking down galectin 1 in human hs683 glioblastoma cells impairs both angiogenesis and endoplasmic reticulum stress responses.

Galectin (Gal) 1 is a hypoxia-regulated proangiogenic factor that also directly participates in glioblastoma cell migration. To determine how Gal-1 exerts its proangiogenic effects, we investigated Gal-1 signaling in the human Hs683 glioblastoma cell line. Galectin 1 signals through the endoplasmic reticulum transmembrane kinase/ribonuclease inositol-requiring 1&agr;, which regulates the expression of oxygen-regulated protein 150. Oxygen-regulated protein 150 controls vascular endothelial growth factor maturation. Galectin 1 also modulates the expression of 7 other hypoxia-related genes (i.e. CTGF, ATF3, PPP1R15A, HSPA5, TRA1, and CYR61) that are implicated in angiogenesis. Decreasing Gal-1 expression in Hs683 orthotopic xenografts in mouse brains by siRNA administration impaired endoplasmic reticulum stress and enhanced the therapeutic benefits of the proautophagic drug temozolomide. These results suggest that decreasing Gal-1 expression (e.g. through brain delivery of nonviral infusions of anti-Gal-1 siRNA in patients) can represent an additional therapeutic strategy for glioblastoma.

Na+/K+-ATPase alpha subunits as new targets in anticancer therapy.

Background: The sodium pump (Na+/K+-ATPase) could be a target for the development of anticancer drugs as it serves as a signal transducer, it is a player in cell adhesion and its aberrant expression and activity are implicated in the development and progression of different cancers. Cardiotonic steroids (CS) are the natural ligands and inhibitors of the sodium pump and this supports the possibility of their development as anticancer agents targeting overexpressed Na+/K+-ATPase α subunits. Objectives: To highlight and further develop the concept of using Na+/K+-ATPase α1 and α3 subunits as targets in anticancer therapy and to address the question of the actual usefulness of further developing CS as anticancer agents. Conclusions: Targeting overexpressed Na+/K+-ATPase α subunits using novel CS might open a new era in anticancer therapy and bring the concept of personalized medicine from aspiration to reality. Clinical data are now needed to further support this proposal. Furthermore, future medicinal chemistry should optimize new anticancer CS to target Na+/K+-ATPase α subunits with the aim of rendering them more potent and less toxic.

7-((4-Substituted)piperazin-1-yl) derivatives of ciprofloxacin: synthesis and in vitro biological evaluation as potential antitumor agents

Ciprofloxacin (CP), an antibiotic has been shown to have antiproliferative and apoptotic activities in several cancer cell lines. Moreover, several reports have highlighted the interest of increasing the lipophilicity to improve the antitumor efficacy. These studies have led us to synthesize new CP derivatives of various lipophilicities and to evaluate their activity in five human cancer cell lines. With an easy and cost-efficient procedure, 31 7-((4-substituted)piperazin-1-yl) derivatives of CP were prepared that displayed IC(50) values ranging from microM to mM concentrations and are non-toxic in vivo in healthy mice as shown by their maximal tolerated dose (MTD) indices >80 mg/kg. Several derivatives displayed higher in vitro antitumor activity than parent CP however this was not dependent on the lipophilicity of the substituent. Among all synthesized derivatives, the most potent were 2 and 6h whose IC(50) values were 10 microM in three (derivative 2) or four (derivative 6h) cancer cell lines.

Cardiotonic steroids-mediated Na+/K+-ATPase targeting could circumvent various chemoresistance pathways.

Many cancer patients fail to respond to chemotherapy because of the intrinsic resistance of their cancer to pro-apoptotic stimuli or the acquisition of the multidrug resistant phenotype during chronic treatment. Previous data from our groups and from others point to the sodium/potassium pump (the Na+/K+-ATPase, i.e., NaK) with its highly specific ligands (i.e., cardiotonic steroids) as a new target for combating cancers associated with dismal prognoses, including gliomas, melanomas, non-small cell lung cancers, renal cell carcinomas, and colon cancers. Cardiotonic steroid-mediated Na+/K+-ATPase targeting could circumvent various resistance pathways. The most probable pathways include the involvement of Na+/K+-ATPase β subunits in invasion features and Na+/K+-ATPase α subunits in chemosensitisation by specific cardiotonic steroid-mediated apoptosis and anoïkis-sensitisation; the regulation of the expression of multidrug resistant-related genes; post-translational regulation, including glycosylation and ubiquitinylation of multidrug resistant-related proteins; c-Myc downregulation; hypoxia-inducible factor downregulation; NF-κB downregulation and deactivation; the inhibition of the glycolytic pathway with a reduction of intra-cellular ATP levels and an induction of non-apoptotic cell death. The aims of this review are to examine the various molecular pathways by which the NaK targeting can be more deleterious to biologically aggressive cancer cells than to normal cells.