Phenotype-dependent apoptosis signalling in mesothelioma cells after selenite exposure

Intravenous Infusion of High Dose Selenite in End-Stage Cancer Patients: Analysis of Systemic Exposure to Selenite and Seleno-Metabolites

Cancer is one of the main causes of human death globally and novel chemotherapeutics are desperately required. As a simple selenium oxide, selenite is a very promising chemotherapeutic because of pronounced its dose-dependent tumor-specific cytotoxicity. We previously published a first-in-man systematic phase I clinical trial in patients with cancer (from IV to end-stage) (the SECAR trial) showing that selenite is safe and tolerable with an unexpectable high maximum tolerated dose (MTD) and short half-life. In the present study, we analyzed the selenium species in plasma samples, from the patients participating in the SECAR trial and from various time points and dose cohorts using LC-ICP-MS. In conclusion, selenite, selenosugars, and 1-2 unidentified peaks that did not correspond to any standard, herein denoted ui-selenium, were detected in the plasma. However, trimethylated selenium (trimethylselenonoium) was not detected. The unidentified ui-selenium was eluting close to the selenium-containing amino acids (selenomethionine and selenocysteine) but was not part of a protein fraction. Our data demonstrate that the major metabolite detected was selenosugar. Furthermore, the identification of selenite even long after the administration is remarkable and unexpected. The kinetic analysis did not support that dosing per the body surface area would reduce interindividual variability of the systemic exposure in terms of trough concentrations.

Suppression of CXCL-1 Could Restore Necroptotic Pathway in Chronic Lymphocytic Leukemia

Purpose

To clarify the role of different cytokines and selenite in the defective necroptotic pathway of chronic lymphocytic leukemia (CLL).

Patients and Methods

We randomly collected the peripheral blood samples of 11 untreated CLL patients and 10 healthy volunteers, and then separated B lymphocytes from peripheral blood. Then, real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA) and Western Blot were performed to detect the expression of different cytokines, including CXC-motif chemokine ligand 1 (CXCL-1). Finally, we used flow cytometry to analyze the percentage of surviving cells to figure out whether CLL cells or normal B lymphocytes underwent necroptosis.

Results

1) The high expression of CXCL-1 was seen in CLL cells compared with normal B lymphocytes (p = 0.0001, adjusted p =0.0012); 2) The downregulation of CXCL-1 was shown in normal B lymphocytes after induction by TNF-α and z-VAD; 3) CLL cells could restore necroptosis induced by TNF-α and z-VAD after knockdown of CXCL-1; 4) The transcriptional and translational expression of LEF-1 were downregulated after the knockdown of CXCL-1 in CLL cells; 5. 3.2μM selenite could help CLL cells restore necroptosis (p = 0.0102) and inhibit the transcriptional and translational expression of CXCL-1.

Conclusion

CXCL-1 played an important role in the defective necroptosis of CLL cells and regulated the expression of LEF-1. Selenite could inhibit the expression of CXCL-1 and help CLL cells restore necroptosis together with TNF-α and z-VAD. Selenite might be the potential medication of CLL in the future.

Suppression of proliferation and activation of cell death by sodium selenite involves mitochondria and lysosomes in chemoresistant bladder cancer cells

The specific effects of sodium selenite (selenite) on a chemoresistant human bladder cancer cell line RT-112/D21 were investigated during 72 h. Selenite at low concentration of 2.5 μmol (otherwise tolerated in normal urothelial cells UROtsa) suppressed growth and proliferation of the tested cancer cells via induced oxidative stress. Selenite further altered mitochondrial functions (i.e. decreased mitochondrial membrane potential, increased production of superoxide and reduced ATP synthesis), disrupted lysosomal membranes and activated autophagy. These changes in selenite-exposed cells ultimately resulted in their demise via necrosis and other cell death modality displaying heterotypic apoptotic and autophagic features.

Apoptosis by [Pt(O,O'-acac)(γ-acac)(DMS)] requires PKC-δ mediated p53 activation in malignant pleural mesothelioma

Mesothelioma cancer cells have epithelioid or sarcomatoid morphology. The worst prognosis is associated with sarcomatoid phenotype and resistance to therapy is affected by cells heterogeneity. We recently showed that in ZL55 mesothelioma cell line of epithelioid origin [Pt(O,O'-acac)(γ-acac)(DMS)] (Ptac2S) has an antiproliferative effect in vitro and in vivo. Aim of this work was to extend the study on the effects of Ptac2S on ZL34 cell line, representative of sarcomatoid mesothelioma. ZL34 cells were used to assay the antitumor activity of Ptac2S in a mouse xenograft model in vivo. Then, both ZL34 and ZL55 cells were used in order to assess the involvement of p53 protein in (a) the processes underlying the sensitivity to chemotherapy and (b) the activation of various transduction proteins involved in apoptosis/survival processes. Ptac2S increases ZL34 cell death in vivo compared with cisplatin and, in vitro, Ptac2S was more efficacious than cisplatin in inducing apoptosis. In Ptac2S-treated ZL34 and ZL55 cells, p53 regulated gene products of apoptotic BAX and anti-apoptotic Bcl-2 proteins via transcriptional activation. Ptac2S activated PKC-δ and PKC-ε; their inhibition by PKC-siRNA decreased the apoptotic death of cells. PKC-δ was responsible for JNK1/2 activation that has a role in p53 activation. In addition, PKC-ε activation provoked phosphorylation of p38MAPK, concurring to apoptosis. In ZL34 cells, Ptac2S also activated PKC-α thus provoking ERK1/2 activation; inhibition of PKC-α, or ERK1/2, increased Ptac2S cytotoxicity. Results confirm that Ptac2S is a promising therapeutic agent for malignant mesothelioma, giving a substantial starting point for its further validation.

Chemosensitivity and resistance testing in malignant effusions with focus on primary malignant mesothelioma and metastatic adenocarcinoma

Cell based chemosensitivity and resistance testing is an attractive approach that offers functional measurement of drug response ex vivo with the ultimate goal to guide the choice of chemotherapy for various cancers. Thus, it has a great potential to select patients for the optimal treatment option, thereby offering a tool for personalized cancer therapy. Despite several decades of intensive scientific efforts ex-vivo tests are still not incorporated in the standard of care. Limited access to fresh tumor tissue, unsatisfactory models and single readout as endpoint constitute major hindrance. Thus, establishing and validating clinically useful and reliable model systems still remains a major challenge. Here we present malignant effusions as valuable sources for ex-vivo chemosensitivity and resistance testing. Accumulation of a malignant effusion in the pleura, peritoneum or pericardium is often the first diagnostic material for both primary malignant mesothelioma and a broad spectrum of metastatic adenocarcinoma originating from lung-, breast-, ovary- and gastro-intestinal organs as well as lymphoma. In contrast to biopsies, in these effusions malignant cells are easily accessible and often abundant. Effusion derived cells can occur dissociated or forming three-dimensional papillary structures that authentically recapitulate the biology of the corresponding tumor tissue and offer models for ex vivo testing. In addition, effusions have the advantage of being available prior to or concurrent with the pathological review, thus constituting an excellent source of viable cells for simultaneous molecular profiling, biomarker analysis and for establishing primary cells for studying tumor biology and resistance mechanisms. For a reliable test, however, a careful validation is needed, taking into account the inherited heterogeneity of malignant tumors, but also the complex interplay between malignant and benign cells, which are always present in this setting.

Selenium compounds as therapeutic agents in cancer

BACKGROUND

With cancer cells encompassing consistently higher production of reactive oxygen species (ROS) and with an induced antioxidant defense to counteract the increased basal ROS production, tumors have a limited reserve capacity resulting in an increased vulnerability of some cancer cells to ROS. Based on this, oxidative stress has been recognized as a tumor-specific target for the rational design of new anticancer agents. Among redox modulating compounds, selenium compounds have gained substantial attention due to their promising chemotherapeutic potential.

SCOPE OF REVIEW

This review aims in summarizing and providing the recent developments of our understanding of the molecular mechanisms that underlie the potential anticancer effects of selenium compounds.

MAJOR CONCLUSIONS

It is well established that selenium at higher doses readily can turn into a prooxidant and thereby exert its potential anticancer properties. However, the biological activity of selenium compounds and the mechanism behind these effects are highly dependent on its speciation and the specific metabolic pathways of cells and tissues. Conversely, the chemical properties and the main molecular mechanisms of the most relevant inorganic and organic selenium compounds as well as selenium-based nanoparticles must be taken into account and are discussed herein.

GENERAL SIGNIFICANCE

Elucidating and deepening our mechanistic knowledge of selenium compounds will help in designing and optimizing compounds with more specific antitumor properties for possible future application of selenium compounds in the treatment of cancer. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Characterization and drug sensitivity profiling of primary malignant mesothelioma cells from pleural effusions

Background

Patients with malignant mesothelioma have a poor prognosis and only 40% respond to first line treatment; a combination of pemetrexed and cisplatin or carboplatin. We used primary malignant mesothelioma cells and an ex vivo chemosensitivity assay with future purpose to predict best choice of treatment. The clinical outcome of these patients might be predicted by measuring drug sensitivity.

Methods

Pleural effusions containing primary malignant mesothelioma cells were received from the diagnostic routine. We characterized and tested the chemosensitivity of 18 malignant samples and four benign samples from 16 different patients with pleural effusions. Cells were seeded in a 384-well plate for a robotized ex vivo testing of drug sensitivity to 32 different drugs. The primary cells were further characterized by immunocytochemistry to evaluate the proportion of malignant cells and to study the RRM1 and ERCC1 reactivity, two proteins associated with drug resistance.

Results

We observed great individual variability in the drug sensitivity. Primary cell isolates were affected by between one and ten drugs, and resistant to the remaining tested drugs. Actinomycin D and daunorubicin were the two drugs effective in most cases. Adjusting efficiency of individual drugs for varying proportion of tumor cells and to the average effect on benign cells correlated with effect of pemetrexed, cisplatin and survival time. General drug sensitivity, proportion of malignant cells and reactivity to RRM1 correlated to each other and to survival time of the patients.

Conclusions

The proportion of malignant cells and RRM1 reactivity in the pleural effusions correlate to drug sensitivity and survival time. The variability in response to the commonly used chemotherapies emphasizes the need for tests that indicate best individual choice of cytotoxic drugs. The efficiency of the obtained results should preferably be corrected for admixture of benign cells and effects of given drugs on benign cells.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-709) contains supplementary material, which is available to authorized users.

Selenium induces a multi-targeted cell death process in addition to ROS formation

Selenium compounds inhibit neoplastic growth. Redox active selenium compounds are evolving as promising chemotherapeutic agents through tumour selectivity and multi-target response, which are of great benefit in preventing development of drug resistance. Generation of reactive oxygen species is implicated in selenium-mediated cytotoxic effects on cancer cells. Recent findings indicate that activation of diverse intracellular signalling leading to cell death depends on the chemical form of selenium applied and/or cell line investigated. In the present study, we aimed at deciphering different modes of cell death in a single cell line (HeLa) upon treatment with three redox active selenium compounds (selenite, selenodiglutathione and seleno-DL-cystine). Both selenite and selenodiglutathione exhibited equipotent toxicity (IC₅₀ 5 μM) in these cells with striking differences in toxicity mechanisms. Morphological and molecular alterations provided evidence of necroptosis-like cell death in selenite treatment, whereas selenodiglutathione induced apoptosis-like cell death. We demonstrate that selenodiglutathione efficiently glutathionylated free protein thiols, which might explain the early differences in cytotoxic effects induced by selenite and selenodiglutathione. In contrast, seleno-DL-cystine treatment at an IC₅₀ concentration of 100 μM induced morphologically two distinct different types of cell death, one with apoptosis-like phenotype, while the other was reminiscent of paraptosis-like cell death, characterized by induction of unfolded protein response, ER-stress and occurrence of large cytoplasmic vacuoles. Collectively, the current results underline the diverse cytotoxic effects and variable potential of redox active selenium compounds on the survival of HeLa cells and thereby substantiate the potential of chemical species-specific usage of selenium in the treatment of cancers.

Variation in drug sensitivity of malignant mesothelioma cell lines with substantial effects of selenite and bortezomib, highlights need for individualized therapy

Background

Malignant mesothelioma cells have an epithelioid or sarcomatoid morphology, both of which may be present in the same tumor. The sarcomatoid phenotype is associated with worse prognosis and heterogeneity of mesothelioma cells may contribute to therapy resistance, which is often seen in mesothelioma. This study aimed to investigate differences in sensitivity between mesothelioma cell lines to anti-cancer drugs. We studied two novel drugs, selenite and bortezomib and compared their effect to four conventional drugs. We also investigated the immunoreactivity of potential predictive markers for drug sensitivity; Pgp, MRP-1, ERCC1, RRM1, TS, xCT and proteasome 20S subunit.

Materials and methods

We treated six mesothelioma cell lines with selenite, bortezomib, carboplatin, pemetrexed, doxorubicin or gemcitabine as single agents and in combinations. Viability was measured after 24 and 48 hours. Immunocytochemistry was used to detect predictive markers.

Results

As a single agent, selenite was effective on four out of six cell lines, and in combination with bortezomib yielded the greatest response in the studied mesothelioma cell lines. Cells with an epithelioid phenotype were generally more sensitive to the different drugs than the sarcomatoid cells. Extensive S-phase arrest was seen in pemetrexed-sensitive cell lines. MRP-1 predicted sensitivity of cell lines to treatment with carboplatin and xCT predicted pemetrexed effect.

Conclusions

The observed heterogeneity in sensitivity of mesothelioma cell lines with different morphology highlights the need for more individualized therapy, requiring development of methods to predict drug sensitivity of individual tumors. Selenite and bortezomib showed a superior effect compared to conventional drugs, motivating clinical testing of these agents as future treatment regime components for patients with malignant mesothelioma.

Inhibition of sphingosine kinase 1 enhances cytotoxicity, ceramide levels and ROS formation in liver cancer cells treated with selenite

High doses of selenite have been shown to induce cell death in acute myeloid leukemia and lung cancer cells. In this study, we combined selenite treatment with modulators of sphingolipid metabolism in the hepatocellular carcinoma cell line Huh7. Treatment with 20 μM of selenite reduced the viability of Huh7 cells by half and increased the levels of long chain C14-, C16-, C18- and C18:1- ceramides by two-fold. Inhibition of neutral sphingomyelinase with 3-O-methylsphingosine significantly reduced the cytotoxic effect of selenite. In line with this result, selenite caused a 2.5-fold increase in the activity of neutral sphingomyelinase. The sphingosine kinase 1 (SK1) inhibitor 2-(p-hydroxyanilino)-4-(p-chlorophenyl)thiazole (SK1-II) sensitized the cells to the cytotoxic effects of selenite. Preincubation with 10 μM of SK1-II prior to treatment with 10 μM of selenite caused induction of apoptosis and gave rise to a 2.5-fold increase in C14-, C16-, C18- and C18:1- ceramides. Instead, 50 μM of SK1-II combined with 10 μM of selenite caused accumulation of cells in G1/S phases, but less apoptosis and accumulation of ceramides. The formation of reactive oxygen species (ROS) after treatment with 10 μM of selenite was maximally enhanced by 1 μM of SK1-II. Moreover, combined treatment with SK1-II and 10 μM of selenite synergistically reduced the number of viable Huh7 cells, while the non-tumorigenic hepatocyte cell line MIHA remained unaffected by the same treatment. These results raise the possibility that a combination of selenite and SK1 inhibitors could be used to treat liver cancer cells, that are regarded as drug resistant, at doses that are non-toxic to normal liver cells.

Selenite-induced apoptosis and autophagy in colon cancer cells

Sodium selenite (Se) is known to induce diverse stress responses in malignant cells which may lead to various types of cell death including apoptosis and/or autophagy. In colon cancer cells, Se activates several signaling pathways whose interactions and ultimate endpoints may vary in individual study models. In our previous work we showed differences in Se-dependent growth inhibition, cell cycle alterations and apoptosis in colon cancer cells with functional (HCT-116) and deleted (HCT-116-p53KO) p53. Moreover, detailed morphological and biochemical analyses revealed the presence of autophagy in Se-treated cells. Thus the aim of this study was to investigate in detail mechanisms, relationship and crosstalk between apoptosis and autophagy in Se-treated HCT-116 cancer cells differing in p53 status since p53 has been shown to play a well-known role in apoptosis but dichotomous role in autophagy. We report that the absence of p53 in malignant colonocytes changes patterns of response to Se-induced stress which include differential activation of MAP kinases (p38 - HCT-116 and JNK - HCT-116 p53KO) including their respective roles in the process of apoptosis and autophagy as well as the involvement of mTOR or PI3K signaling. Our results seem to suggest that deletion of p53 inevitably leads to a higher level of instability and delays in an individual cell decision in the face of stress whether to activate apoptosis or autophagy which may consequently occur simultaneously with mutual dichotomous relationship.

Rat mesothelioma cell proliferation requires p38δ mitogen activated protein kinase and C/EBP-α

Pleural malignant mesothelioma is a rare but deadly tumour mainly induced by asbestos inhalation. Despite the ban of asbestos in 1990 in 52 countries, mesothelioma cases still increase worldwide. In pleural mesothelioma, p38 mitogen activated protein kinases (MAPK) have been suggested to play a major role in carcinogenesis and aggressiveness of tumours. The aim of this study was to determine the role of the different four p38 MAPK isoforms and their effect on proliferation together with the underlying signalling pathways in a rat pleural mesothelioma cell line. Rat pleural mesothelioma cells were stimulated with platelet-derived growth factor (PDGF)-BB and/or transforming growth factor beta (TGF)-β. MAPK and transcription factor expression and activation was monitored in the cytosol and nucleus by immuno-blotting. Proliferation was determined by manual cell count and siRNAs were used to control MAPK and transcription factor expression and action. Only PDGF-BB, but not TGF-β1 induced proliferation via activated Erk1/2 and p38 MAPK. The p38α and δ isoforms were expressed in the cytosol, and upon activation p38δ translocated into the nucleus, while p38α remained in the cytosol. No other p38 isoform was expressed by rat mesothelioma cells. C/EBP-α was found in both the cytosol and the nucleus, while C/EBP-β was not expressed at all. PDGF-BB induced proliferation was suppressed by down-regulation of either Erk1/2, or p38δ MAPK, or C/EBP-α. Furthermore, TGF-β inhibited PDGF-BB induced proliferation by interruption of p38 MAPK signalling. From this rat model, we conclude that in pleural mesothelioma, p38δ in C/EBP-α mediate proliferation and thus may represent new targets in mesothelioma therapy.

Selenium and the selenoprotein thioredoxin reductase in the prevention, treatment and diagnostics of cancer

Selenium is an essential element that is specifically incorporated as selenocystein into selenoproteins. It is a potent modulator of eukaryotic cell growth with strictly concentration-dependant effects. Lower concentrations are necessary for cell survival and growth, whereas higher concentrations inhibit growth and induce cell death. It is well established that selenium has cancer preventive effects, and several studies also have shown that it has strong anticancer effects with a selective cytotoxicity on malignant drug-resistant cells while only exerting marginal effects on normal and benign cells. This cancer-specific cytotoxicity is likely explained by high affinity selenium uptake dependent on proteins connected to multidrug resistance. One of the most studied selenoproteins in cancer is thioredoxin reductase (TrxR) that has important functions in neoplastic growth and is an important component of the resistant phenotype. Several reports have shown that TrxR is induced in tumor cells and pre-neoplastic cells, and several commonly used drugs interact with the protein. In this review, we summarize the current knowledge of selenium as a potent preventive and tumor selective anticancer drug, and we also discuss the potential of using the expression and modulation of the selenoprotein TrxR in the diagnostics and treatment of cancer.