Efficacy of combined tumor irradiation and KCa3.1-targeting with TRAM-34 in a syngeneic glioma mouse model

The intermediate-conductance calcium-activated potassium channel KCa3.1 has been proposed to be a new potential target for glioblastoma treatment. This study analyzed the effect of combined irradiation and KCa3.1-targeting with TRAM-34 in the syngeneic, immune-competent orthotopic SMA-560/VM/Dk glioma mouse model. Whereas neither irradiation nor TRAM-34 treatment alone meaningfully prolonged the survival of the animals, the combination significantly prolonged the survival of the mice. We found an irradiation-induced hyperinvasion of glioma cells into the brain, which was inhibited by concomitant TRAM-34 treatment. Interestingly, TRAM-34 did neither radiosensitize nor impair SMA-560's intrinsic migratory capacities in vitro. Exploratory findings hint at increased TGF-β1 signaling after irradiation. On top, we found a marginal upregulation of MMP9 mRNA, which was inhibited by TRAM-34. Last, infiltration of CD3+, CD8+ or FoxP3+ T cells was not impacted by either irradiation or KCa3.1 targeting and we found no evidence of adverse events of the combined treatment. We conclude that concomitant irradiation and TRAM-34 treatment is efficacious in this preclinical glioma model.

Potential of pre-operative MRI features in glioblastoma to predict for molecular stem cell subtype and patient overall survival

AIM OF THE STUDY

A molecular signature based on 10 mRNA abundances that characterizes the mesenchymal-to-proneural phenotype of glioblastoma stem(like) cells (GSCs) enriched in primary culture has been previously established. As this phenotype has been proposed to be prognostic for disease outcome the present study aims to identify features of the preoperative MR imaging that may predict the GSC phenotype of individual tumors.

MATERIAL/METHODS

Molecular mesenchymal-to-proneural mRNA signatures and intrinsic radioresistance (SF4, survival fraction at 4 Gy) of primary GSC-enriched cultures were associated with survival data and pre-operative MR imaging of the corresponding glioblastoma patients of a prospective cohort (n = 24). The analyzed imaging parameters comprised linear vectors derived from tumor volume, necrotic volume and edema as contoured manually.

RESULTS

A necrosis/tumor vector ratio and to a weaker extent the product of this ratio and the edema vector were identified to correlate with the mesenchymal-to-proneural mRNA signature and the SF4 of the patient-derived GSC cultures. Importantly, both parameter combinations were predictive for overall survival of the whole patient cohort. Moreover, the combination of necrosis/tumor vector ratio and edema vector differed significantly between uni- and multifocally recurring tumors.

CONCLUSION

Features of the preoperative MR images may reflect the molecular signature of the GSC population and might be used in the future as a prognostic factor and for treatment stratification especially in the MGMT promotor-unmethylated sub-cohort of glioblastoma patients.

Tetraploidization Increases the Motility and Invasiveness of Cancer Cells

Polyploidy and metastasis are associated with a low probability of disease-free survival in cancer patients. Polyploid cells are known to facilitate tumorigenesis. However, few data associate polyploidization with metastasis. Here, by generating and using diploid (2n) and tetraploid (4n) clones from malignant fibrous histiocytoma (MFH) and colon carcinoma (RKO), we demonstrate the migration and invasion advantage of tetraploid cells in vitro using several assays, including the wound healing, the OrisTM two-dimensional cell migration, single-cell migration tracking by video microscopy, the Boyden chamber, and the xCELLigence RTCA real-time cell migration. Motility advantage was observed despite tetraploid cell proliferation weakness. We could also demonstrate preferential metastatic potential in vivo for the tetraploid clone using the tail vein injection in mice and tracking metastatic tumors in the lung. Using the Mitelman Database of Chromosome Aberrations in Cancer, we found an accumulation of polyploid karyotypes in metastatic tumors compared to primary ones. This work reveals the clinical relevance of the polyploid subpopulation and the strategic need to highlight polyploidy in preclinical studies as a therapeutic target for metastasis.

Protein Levels of Anti-Apoptotic Mcl-1 and the Deubiquitinase USP9x Are Cooperatively Upregulated during Prostate Cancer Progression and Limit Response of Prostate Cancer Cells to Radiotherapy

BACKGROUND

Radiotherapy constitutes an important therapeutic option for prostate cancer. However, prostate cancer cells often acquire resistance during cancer progression, limiting the cytotoxic effects of radiotherapy. Among factors regulating sensitivity to radiotherapy are members of the Bcl-2 protein family, known to regulate apoptosis at the mitochondrial level. Here, we analyzed the role of anti-apoptotic Mcl-1 and USP9x, a deubiquitinase stabilizing Mcl-1 protein levels, in prostate cancer progression and response to radiotherapy.

METHODS

Changes in Mcl-1 and USP9x levels during prostate cancer progression were determined by immunohistochemistry. Neutralization of Mcl-1 and USP9x was achieved by siRNA-mediated knockdown. We analyzed Mcl-1 stability after translational inhibition by cycloheximide. Cell death was determined by flow cytometry using an exclusion assay of mitochondrial membrane potential-sensitive dye. Changes in the clonogenic potential were examined by colony formation assay.

RESULTS

Protein levels of Mcl-1 and USP9x increased during prostate cancer progression, and high protein levels correlated with advanced prostate cancer stages. The stability of Mcl-1 reflected Mcl-1 protein levels in LNCaP and PC3 prostate cancer cells. Moreover, radiotherapy itself affected Mcl-1 protein turnover in prostate cancer cells. Particularly in LNCaP cells, the knockdown of USP9x expression reduced Mcl-1 protein levels and increased sensitivity to radiotherapy.

CONCLUSION

Posttranslational regulation of protein stability was often responsible for high protein levels of Mcl-1. Moreover, we demonstrated that deubiquitinase USP9x as a factor regulating Mcl-1 levels in prostate cancer cells, thus limiting cytotoxic response to radiotherapy.

Ion channels as molecular targets of glioblastoma electrotherapy

Therapies with weak, non-ionizing electromagnetic fields comprise FDA-approved treatments such as Tumor Treating Fields (TTFields) that are used for adjuvant therapy of glioblastoma. In vitro data and animal models suggest a variety of biological TTFields effects. In particular, effects ranging from direct tumoricidal, radio- or chemotherapy-sensitizing, metastatic spread-inhibiting, up to immunostimulation have been described. Diverse underlying molecular mechanisms, such as dielectrophoresis of cellular compounds during cytokinesis, disturbing the formation of the spindle apparatus during mitosis, and perforating the plasma membrane have been proposed. Little attention, however, has been paid to molecular structures that are predestinated to percept electromagnetic fields-the voltage sensors of voltage-gated ion channels. The present review article briefly summarizes the mode of action of voltage sensing by ion channels. Moreover, it introduces into the perception of ultra-weak electric fields by specific organs of fishes with voltage-gated ion channels as key functional units therein. Finally, this article provides an overview of the published data on modulation of ion channel function by diverse external electromagnetic field protocols. Combined, these data strongly point to a function of voltage-gated ion channels as transducers between electricity and biology and, hence, to voltage-gated ion channels as primary targets of electrotherapy.

Tumoricidal, Temozolomide- and Radiation-Sensitizing Effects of KCa3.1 K+ Channel Targeting In Vitro Are Dependent on Glioma Cell Line and Stem Cell Fraction

Reportedly, the intermediate-conductance Ca²⁺-activated potassium channel K_Ca3.1 contributes to the invasion of glioma cells into healthy brain tissue and resistance to temozolomide and ionizing radiation. Therefore, K_Ca3.1 has been proposed as a potential target in glioma therapy. The aim of the present study was to assess the variability of the temozolomide- and radiation-sensitizing effects conferred by the K_Ca3.1 blocking agent TRAM-34 between five different glioma cell lines grown as differentiated bulk tumor cells or under glioma stem cell-enriching conditions. As a result, cultures grown under stem cell-enriching conditions exhibited indeed higher abundances of mRNAs encoding for stem cell markers compared to differentiated bulk tumor cultures. In addition, stem cell enrichment was paralleled by an increased resistance to ionizing radiation in three out of the five glioma cell lines tested. Finally, TRAM-34 led to inconsistent results regarding its tumoricidal but also temozolomide- and radiation-sensitizing effects, which were dependent on both cell line and culture condition. In conclusion, these findings underscore the importance of testing new drug interventions in multiple cell lines and different culture conditions to partially mimic the in vivo inter- and intra-tumor heterogeneity.

Patient-individual phenotypes of glioblastoma stem cells are conserved in culture and associate with radioresistance, brain infiltration and patient prognosis

Identification of prognostic or predictive molecular markers in glioblastoma resection specimens may lead to strategies for therapy stratification and personalized treatment planning. Here, we analyzed in primary glioblastoma stem cell (pGSC) cultures the mRNA abundances of 7 stem cell (MSI1, Notch1, nestin, Sox2, Oct4, FABP7, ALDH1A3), and 3 radioresistance or invasion markers (CXCR4, IK_Ca , BK_Ca ). From these abundances, an mRNA signature was deduced which describes the mesenchymal-to-proneural expression profile of an individual GSC culture. To assess its functional significance, we associated the GSC mRNA signature with the clonogenic survival after irradiation with 4 Gy and the fibrin matrix invasion of the GSC cells. In addition, we compared the molecular pGSC mRNA signature with the tumor recurrence pattern and the overall survival of the glioblastoma patients from whom the pGSC cultures were derived. As a result, the molecular pGSC mRNA signature correlated positively with the pGSC radioresistance and matrix invasion capability in vitro. Moreover, patients with a mesenchymal (> median) mRNA signature in their pGSC cultures exhibited predominantly a multifocal tumor recurrence and a significantly (univariate log rank test) shorter overall survival than patients with proneural (≤ median mRNA signature) pGSCs. The tumors of the latter recurred predominately unifocally. We conclude that our pGSC cultures induce/select those cell subpopulations of the heterogeneous brain tumor that determine disease progression and therapy outcome. In addition, we further postulate a clinically relevant prognostic/predictive value for the 10 mRNAs-based mesenchymal-to-proneural signature of the GSC subpopulations in glioblastoma.

Repurposing Disulfiram for Targeting of Glioblastoma Stem Cells: An In Vitro Study

Mesenchymal glioblastoma stem cells (GSCs), a subpopulation in glioblastoma that are responsible for therapy resistance and tumor spreading in the brain, reportedly upregulate aldehyde dehydrogenase isoform-1A3 (ALDH1A3) which can be inhibited by disulfiram (DSF), an FDA-approved drug formerly prescribed in alcohol use disorder. Reportedly, DSF in combination with Cu²⁺ ions exerts multiple tumoricidal, chemo- and radio-therapy-sensitizing effects in several tumor entities. The present study aimed to quantify these DSF effects in glioblastoma stem cells in vitro, regarding dependence on ALDH1A3 expression. To this end, two patient-derived GSC cultures with differing ALDH1A3 expression were pretreated (in the presence of CuSO₄, 100 nM) with DSF (0 or 100 nM) and the DNA-alkylating agent temozolomide (0 or 30 µM) and then cells were irradiated with a single dose of 0–8 Gy. As read-outs, cell cycle distribution and clonogenic survival were determined by flow cytometry and limited dilution assay, respectively. As a result, DSF modulated cell cycle distribution in both GSC cultures and dramatically decreased clonogenic survival independently of ALDH1A3 expression. This effect was additive to the impairment of clonogenic survival by radiation, but not associated with radiosensitization. Of note, cotreatment with temozolomide blunted the DSF inhibition of clonogenic survival. In conclusion, DSF targets GSCs independent of ALDH1A3 expression, suggesting a therapeutic efficacy also in glioblastomas with low mesenchymal GSC populations. As temozolomide somehow antagonized the DSF effects, strategies for future combination of DSF with the adjuvant standard therapy (fractionated radiotherapy and concomitant temozolomide chemotherapy followed by temozolomide maintenance therapy) are not supported by the present study.

ANXA7 Regulates Platelet Lipid Metabolism and Ca2+ Release in Arterial Thrombosis

[Figure: see text].

γH2AX foci assay in glioblastoma: Surgical specimen versus corresponding stem cell culture

AIM

To assess radiation response using γH2AX assay in surgical specimens from glioblastoma (GB) patients and their corresponding primary gliosphere culture. To test the hypothesis that gliospheres (stem cell enriched) are more resistant than specimens (bulky cell dominated) but that the interpatient heterogeneity is similar.

MATERIAL AND METHODS

Ten pairs of specimens and corresponding gliospheres derived from patients with IDH-wildtype GB were studied. Specimens and gliospheres were irradiated with graded doses and after 24 h the number of residual γH2AX foci was counted.

RESULTS

Gliospheres showed a higher Nestin expression than specimens and exhibited two different phenotypes: free floating (n = 7) and attached (n = 3). Slope analysis revealed an interpatient heterogeneity with values between 0.15 and 1.30 residual γH2AX foci/Gy. Free-floating spheres were more resistant than their parental specimens (median slope 0.13 foci/Gy versus 0.53) as well as than the attached spheres (2.14). The slopes of free floating spheres did not correlate with their corresponding specimens while a trend for a positive correlation was found for the attached spheres and the respective specimens. Association with MGMT did not reach statistical significance.

CONCLUSION

Consistent with the clinical phenotype and our previous experiments, GB specimens show low radiation sensitivity. Stem-cell enriched free-floating gliospheres were more resistant than specimens supporting the concept of radioresistance in stem cell-like cells. The lack of correlation between specimens and their respective gliosphere cultures needs validation and may have a profound impact on future translational studies using γH2AX as a potential biomarker for personalized radiation therapy.

Towards redox-switchable organocatalysts based on bidentate halogen bond donors

Redox-active bidentate halogen bond donors based on halopyridinium groups as halogen-bond donating units were synthesized and their structures were elucidated by X-ray diffraction analyses and DFT calculations. Via reversible twofold reduction, these dicationic species can be transformed to neutral compounds which should be much weaker Lewis acids. The corresponding electrochemical data were obtained, and CV as well as UV-vis and NMR techniques were also used to determine binding constants of these halogen bond donors to halides. While all titrations agree on the relative order of binding strengths (with chloride being bound strongest), there are marked deviations in the overall affinity constants which are discussed. In contrast to earlier azo-bridge analogues, the ethylene-linked variants presented herein do not oxidize halides, and thus the novel halogen bond donors could also be used as Lewis acidic organocatalysts in a halide abstraction benchmark reaction, yielding a performance similar to bis(haloimidazolium)-derived catalysts.

Against Repurposing Methadone for Glioblastoma Therapy

Methadone, which is used as maintenance medication for outpatient treatment of opioid dependence or as an analgesic drug, has been suggested by preclinical in vitro and mouse studies to induce cell death and sensitivity to chemo- or radiotherapy in leukemia, glioblastoma, and carcinoma cells. These data together with episodical public reports on long-term surviving cancer patients who use methadone led to a hype of methadone as an anti-cancer drug in social and public media. However, clinical evidence for a tumoricidal effect of methadone is missing and prospective clinical trials, except in colorectal cancer, are not envisaged because of the limited preclinical data available. The present article reviews the pharmacokinetics, potential molecular targets, as well as the evidence for a tumoricidal effect of methadone in view of the therapeutically achievable doses in the brain. Moreover, it provides original in vitro data showing that methadone at clinically relevant concentrations fails to impair clonogenicity or radioresistance of glioblastoma cells.

Subunits of BK channels promote breast cancer development and modulate responses to endocrine treatment in preclinical models

BACKGROUND AND PURPOSE

Pore-forming α subunits of the voltage- and Ca²⁺ -activated K⁺ channel with large conductance (BKα) promote malignant phenotypes of breast tumour cells. Auxiliary subunits such as the leucine-rich repeat containing 26 (LRRC26) protein, also termed BKγ1, may be required to permit activation of BK currents at a depolarized resting membrane potential that frequently occur in non-excitable tumour cells.

EXPERIMENTAL APPROACH

Anti-tumour effects of BKα loss were investigated in breast tumour-bearing MMTV-PyMT transgenic BKα knockout (KO) mice, primary MMTV-PyMT cell cultures, and in a syngeneic transplantation model of breast cancer derived from these cells. The therapeutic relevance of BK channels in the context of endocrine treatment was assessed in human breast cancer cell lines expressing either low (MCF-7) or high (MDA-MB-453) levels of BKα and BKγ1, as well as in BKα-negative MDA-MB-157.

KEY RESULTS

BKα promoted breast cancer onset and overall survival in preclinical models. Conversely, lack of BKα and/or knockdown of BKγ1 attenuated proliferation of murine and human breast cancer cells in vitro. At low concentrations, tamoxifen and its major active metabolites stimulated proliferation of BKα/γ1-positive breast cancer cells, independent of the genomic signalling controlled by the oestrogen receptor. Finally, tamoxifen increased the relative survival time of BKα KO but not of wild-type tumour cell recipient mice.

CONCLUSION AND IMPLICATIONS

Breast cancer initiation, progression, and tamoxifen sensitivity depend on functional BK channels thereby providing a rationale for the future exploration of the oncogenic actions of BK channels in clinical outcomes with anti-oestrogen therapy.

hERG K+ Channels Promote Survival of Irradiated Leukemia Cells

Many tumor cells express highly elevated activities of voltage-gated K⁺ channels in the plasma membrane which are indispensable for tumor growth. To test for K⁺ channel function during DNA damage response, we subjected human chronic myeloid leukemia (CML) cells to sub-lethal doses of ionizing radiation (0-8 Gy, 6 MV photons) and determined K⁺ channel activity, K⁺ channel-dependent Ca²⁺ signaling, cell cycle progression, DNA repair, and clonogenic survival by whole-cell patch clamp recording, fura-2 Ca²⁺ imaging, Western blotting, flow cytometry, immunofluorescence microscopy, and pre-plating colony formation assay, respectively. As a result, the human erythroid CML cell line K562 and primary human CML cells functionally expressed hERG1. Irradiation stimulated in both cell types an increase in the activity of hERG1 K⁺ channels which became apparent 1-2 h post-irradiation. This increase in K⁺ channel activity was paralleled by an accumulation in S phase of cell cycle followed by a G₂/M cell cycle arrest as analyzed between 8 and 72 h post-irradiation. Attenuating the K⁺ channel function by applying the hERG1 channel inhibitor E4031 modulated Ca²⁺ signaling, impaired inhibition of the mitosis promoting subunit cdc2, overrode cell cycle arrest, and decreased clonogenic survival of the irradiated cells but did not affect repair of DNA double strand breaks suggesting a critical role of the hERG1 K⁺ channels for the Ca²⁺ signaling and the cell cycle control during DNA damage response.

Irradiation enhances the therapeutic effect of the oncolytic adenovirus XVir-N-31 in brain tumor initiating cells

Virotherapy using oncolytic viruses is an upcoming therapy strategy for cancer treatment. A variety of preclinical and clinical trials have indicated that adenoviruses may be used as potent agents in the treatment of a variety of cancers, and also for the treatment of brain tumors. In these studies, it has also been shown that oncovirotherapy is safe in terms of toxicity and side effects. In addition, previous studies have presented evidence for a significant role of oncovirotherapy in the activation of anti‑tumor immune responses. With regard to oncolytic adenoviruses, we have demonstrated previously that the multifunctional protein Y‑box binding protein‑1 (YB‑1) is a potent factor that was used to develop an YB‑1‑dependent oncolytic adenovirus (XVir‑N‑31). XVir‑N‑31 provides the opportunity for tumor‑selective replication and exhibited marked oncolytic properties in a mouse glioma tumor model using therapy‑resistant brain tumor initiating cells (BTICs). In a number of, but not all, patients with glioma, YB‑1 is primarily located in the nucleus; this promotes XVir‑N‑31‑replication and subsequently tumor cell lysis. However, in certain BTICs, only a small amount of YB‑1 has been identified to be nuclear, and therefore virus replication is suboptimal. YB‑1 in BTICs was demonstrated to be translocated into the nucleus following irradiation, which was accompanied by an enhancement in XVir‑N‑31 production. R28 glioma spheres implanted in living organotypic human brain slices exhibited a significantly delayed growth rate when pre‑irradiated prior to XVir‑N‑31‑infection as compared with single treatment methods. Consistent with the in vitro data, R28 glioma‑bearing mice exhibited a prolonged mean and median survival following single tumor irradiation prior to intratumoral XVir‑N‑31 injection, compared with the single treatment methods. In conclusion, the present study demonstrated that in an experimental glioma model, tumor irradiation strengthened the effect of an XVir‑N‑31‑based oncovirotherapy.

Rationale for Combining Radiotherapy and Immune Checkpoint Inhibition for Patients With Hypoxic Tumors

In order to compensate for the increased oxygen consumption in growing tumors, tumors need angiogenesis and vasculogenesis to increase the supply. Insufficiency in this process or in the microcirculation leads to hypoxic tumor areas with a significantly reduced pO2, which in turn leads to alterations in the biology of cancer cells as well as in the tumor microenvironment. Cancer cells develop more aggressive phenotypes, stem cell features and are more prone to metastasis formation and migration. In addition, intratumoral hypoxia confers therapy resistance, specifically radioresistance. Reactive oxygen species are crucial in fixing DNA breaks after ionizing radiation. Thus, hypoxic tumor cells show a two- to threefold increase in radioresistance. The microenvironment is enriched with chemokines (e.g., SDF-1) and growth factors (e.g., TGFβ) additionally reducing radiosensitivity. During recent years hypoxia has also been identified as a major factor for immune suppression in the tumor microenvironment. Hypoxic tumors show increased numbers of myeloid derived suppressor cells (MDSCs) as well as regulatory T cells (T_regs) and decreased infiltration and activation of cytotoxic T cells. The combination of radiotherapy with immune checkpoint inhibition is on the rise in the treatment of metastatic cancer patients, but is also tested in multiple curative treatment settings. There is a strong rationale for synergistic effects, such as increased T cell infiltration in irradiated tumors and mitigation of radiation-induced immunosuppressive mechanisms such as PD-L1 upregulation by immune checkpoint inhibition. Given the worse prognosis of patients with hypoxic tumors due to local therapy resistance but also increased rate of distant metastases and the strong immune suppression induced by hypoxia, we hypothesize that the subgroup of patients with hypoxic tumors might be of special interest for combining immune checkpoint inhibition with radiotherapy.

Potential Role of CXCR4 Targeting in the Context of Radiotherapy and Immunotherapy of Cancer

Cancer immunotherapy has been established as standard of care in different tumor entities. After the first reports on synergistic effects with radiotherapy and the induction of abscopal effects-tumor shrinkage outside the irradiated volume attributed to immunological effects of radiotherapy-several treatment combinations have been evaluated. Different immunotherapy strategies (e.g., immune checkpoint inhibition, vaccination, cytokine based therapies) have been combined with local tumor irradiation in preclinical models. Clinical trials are ongoing in different cancer entities with a broad range of immunotherapeutics and radiation schedules. SDF-1 (CXCL12)/CXCR4 signaling has been described to play a major role in tumor biology, especially in hypoxia adaptation, metastasis and migration. Local tumor irradiation is a known inducer of SDF-1 expression and release. CXCR4 also plays a major role in immunological processes. CXCR4 antagonists have been approved for the use of hematopoietic stem cell mobilization from the bone marrow. In addition, several groups reported an influence of the SDF-1/CXCR4 axis on intratumoral immune cell subsets and anti-tumor immune response. The aim of this review is to merge the knowledge on the role of SDF-1/CXCR4 in tumor biology, radiotherapy and immunotherapy of cancer and in combinatorial approaches.

Abscopal effects of radiotherapy and combined mRNA-based immunotherapy in a syngeneic, OVA-expressing thymoma mouse model

BACKGROUND

Tumor metastasis and immune evasion present major challenges of cancer treatment. Radiotherapy can overcome immunosuppressive tumor microenvironments. Anecdotal reports suggest abscopal anti-tumor immune responses. This study assesses abscopal effects of radiotherapy in combination with mRNA-based cancer vaccination (RNActive®).

METHODS

C57BL/6 mice were injected with ovalbumin-expressing thymoma cells into the right hind leg (primary tumor) and left flank (secondary tumor) with a delay of 4 days. Primary tumors were irradiated with 3 × 2 Gy, while secondary tumors were shielded. RNA and combined treatment groups received mRNA-based RNActive® vaccination.

RESULTS

Radiotherapy and combined radioimmunotherapy significantly delayed primary tumor growth with a tumor control in 15 and 53% of mice, respectively. In small secondary tumors, radioimmunotherapy significantly slowed growth rate compared to vaccination (p = 0.002) and control groups (p = 0.01). Cytokine microarray analysis of secondary tumors showed changes in the cytokine microenvironment, even in the non-irradiated contralateral tumors after combination treatment.

CONCLUSION

Combined irradiation and immunotherapy is able to induce abscopal responses, even with low, normofractionated radiation doses. Thus, the combination of mRNA-based vaccination with irradiation might be an effective regimen to induce systemic anti-tumor immunity.

KCa3.1 Channels and Glioblastoma: In Vitro Studies

BACKGROUND

Several tumor entities including brain tumors aberrantly overexpress intermediate conductance Ca2+ activated KCa3.1 K+ channels. These channels contribute significantly to the transformed phenotype of the tumor cells.

METHOD

PubMed was searched in order to summarize our current knowledge on the molecular signaling upstream and downstream and the effector functions of KCa3.1 channel activity in tumor cells in general and in glioblastoma cells in particular. In addition, KCa3.1 expression and function for repair of DNA double strand breaks was determined experimentally in primary glioblastoma cultures in dependence on the abundance of proneural and mesenchymal stem cell markers.

RESULTS

By modulating membrane potential, cell volume, Ca2+ signals and the respiratory chain, KCa3.1 channels in both, plasma and inner mitochondrial membrane, have been demonstrated to regulate many cellular processes such as migration and tissue invasion, metastasis, cell cycle progression, oxygen consumption and metabolism, DNA damage response and cell death of cancer cells. Moreover, KCa3.1 channels have been shown to crucially contribute to resistance against radiotherapy. Futhermore, the original in vitro data on KCa3.1 channel expression in subtypes of glioblastoma stem(-like) cells propose KCa3.1 as marker for the mesenchymal subgroup of cancer stem cells and suggest that KCa3.1 contributes to the therapy resistance of mesenchymal glioblastoma stem cells.

CONCLUSION

The data suggest KCa3.1 channel targeting in combination with radiotherapy as promising new tool to eradicate therapy-resistant mesenchymal glioblastoma stem cells.

New roles for nuclear EGFR in regulating the stability and translation of mRNAs associated with VEGF signaling

Cell membrane-associated epidermal growth factor receptor (EGFR) translocates into a perinuclear/nuclear location upon stimulation, where it complexes with mRNAs. Treatment with radiation and cisplatin decreases the amounts of mRNAs present within this complex. Gene array analyses of mRNAs in complex with immunoprecipitated nEGFR revealed significant enrichment of different mRNA species compared to the control immunoprecipitation. Functional annotation with help of DAVID Gene Ontology Analysis identified under other terms the HIF-1A/VEGF signaling pathway as one of the top scoring KEGG pathways. RT-PCR and western blots revealed the radiation-induced expression of mRNAs and proteins involved in HIF-1A/VEGF signaling. Simultaneously, the levels of the corresponding validated miRNAs within the complex containing nEGFR and mRNAs were decreased. This finding argues that an mRNA/miRNA/nEGFR complex regulates protein expression. Indeed, we detected the GW182, AGO2, PABPC1 and cNOT1 proteins, which belong to the deadenylase complex, in a complex with nuclear EGFR. Erlotinib-mediated inhibition of EGFR kinase reduced the radiation-induced increase in mRNA expression. In this context, erlotinib reduced AGO2 phosphorylation by the EGFR kinase at residue Y393, which was associated with increased cNOT1 deadenylase activity and reduced mRNA stability. To prove the roles of miRNAs in this context, we transfected cells with an inhibitor of Hsa-mir-1180p5, which targets the NFATC4 mRNA, an mRNA associated with VEGF signaling, or pretreated cells with erlotinib. Indeed, Hsa-mir-1180p5 knockdown increased and the erlotinib treatment decreased the expression of the NFATC4 protein. The expression of the NFATC4 protein controlled the cloning efficiency and radiosensitivity of A549 and FaDu tumor cells. Thus, this study is the first to show that a membrane-located tyrosine kinase receptor, such as EGFR, is internalized to a nuclear/perinuclear location upon exposure to stress and modulates the stability and translation of miRNA-selected mRNAs. This mechanism enables cells to directly express proteins in response to EGFR activation and may contribute to treatment resistance in EGFR-overexpressing tumors.

Radiation alters the cargo of exosomes released from squamous head and neck cancer cells to promote migration of recipient cells

Radiation is a highly efficient therapy in squamous head and neck carcinoma (HNSCC) treatment. However, local recurrence and metastasis are common complications. Recent evidence shows that cancer-cell-derived exosomes modify tumour cell movement and metastasis. In this study, we link radiation-induced changes of exosomes to their ability to promote migration of recipient HNSCC cells. We demonstrate that exosomes isolated from irradiated donor cells boost the motility of the HNSCC cells BHY and FaDu. Molecular data identified enhanced AKT-signalling, manifested through increased phospho-mTOR, phospho-rpS6 and MMP2/9 protease activity, as underlying mechanism. AKT-inhibition blocked the pro-migratory action, suggesting AKT-signalling as key player in exosome-mediated migration. Proteomic analysis of exosomes isolated from irradiated and non-irradiated BHY donor cells identified 39 up- and 36 downregulated proteins. In line with the observed pro-migratory effect of exosomes isolated from irradiated cells protein function analysis assigned the deregulated exosomal proteins to cell motility and AKT-signalling. Together, our findings demonstrate that exosomes derived from irradiated HNSCC cells confer a migratory phenotype to recipient cancer cells. This is possibly due to radiation-regulated exosomal proteins that increase AKT-signalling. We conclude that exosomes may act as driver of HNSCC progression during radiotherapy and are therefore attractive targets to improve radiation therapy strategies.

Simultaneous quantification of DNA damage and mitochondrial copy number by long-run DNA-damage quantification (LORD-Q)

DNA damage and changes in the mitochondrial DNA content have been implicated in ageing and cancer development. To prevent genomic instability and tumorigenesis, cells must maintain the integrity of their nuclear and mitochondrial DNA. Advances in the research of DNA damage protection and genomic stability, however, also depend on the availability of techniques that can reliably quantify alterations of mitochondrial DNA copy numbers and DNA lesions in an accurate high-throughput manner. Unfortunately, no such method has been established yet. Here, we describe the high-sensitivity long-run real-time PCR technique for DNA-damage quantification (LORD-Q) and its suitability to simultaneously measure DNA damage rates and mitochondrial DNA copy numbers in cultured cells and tissue samples. Using the LORD-Q multiplex assay, we exemplarily show that the mitochondrial DNA content does not directly affect DNA damage susceptibility, but influences the efficacy of certain anticancer drugs. Hence, LORD-Q provides a fast and precise method to assess DNA lesions, DNA repair and mtDNA replication as well as their role in a variety of pathological settings.

The radioprotector ortho-phospho-L-tyrosine (pTyr) attenuates the side effects of fractionated irradiation in retinoblastoma mouse models but also decreases the local tumour control

BACKGROUND

Radiotherapy (RT) is used to treat retinoblastoma (Rb), the most frequent ocular tumour in children. Besides eradicating the tumour, RT can cause severe side effects including secondary malignancies. This study aimed to define whether the radioprotector ortho-phospho-L-tyrosine (pTyr) prevents RT-induced side effects and affects local tumour control in a xenograft and a genetic orthotopic Rb mouse model.

METHODS

B6;129-Rb1tm3Tyj/J (Rb^+/-) and Y79-Rb cell-xenografted nude mice were fractionated external beam irradiated (15 fractions of 5Gy 6MV photons during 3weeks) with or without pTyr pre-treatment (100mg/kg BW, 16h prior to each irradiation). One, three, six and nine months after RT, tumour control and RT toxicity were evaluated using in vivo imaging and histology. We also analysed pTyr dependant post irradiation cell survival and p53 activity in vitro.

RESULTS

In vitro pTyr pre-treatment showed no radioprotection on Y79 cells, but led to p53 stabilisation in unirradiated Y79 cells and to a facilitation of radiation-induced p21 up-regulation, confirming a modulation of p53 activity by pTyr. In both mouse models, secondary tumours were undetectable. In Rb^+/- mice, pTyr significantly lowered RT-induced greying of the fur, retinal thickness reduction and photoreceptor loss. However, in the xenografted Rb model, pTyr considerably decreased RT-mediated tumour control, which was observed in 16 out of 22 control eyes but in none of the 24 pTyr treated eyes.

CONCLUSIONS

In Rb^+/- mice pTyr significantly prevents RT-induced greying of the fur as well as retinal degeneration. However, since non-irradiated control mice were not used in our study, a formal possibility exists that the effect shown in the retina of Rb^+/- mice may be due to ageing of the animals and/or actions of pTyr alone. Unfortunately, as tested in a xenograft model, pTyr treatment reduced the control of Rb tumours.

SK4 channels modulate Ca2+ signalling and cell cycle progression in murine breast cancer

Oncogenic signalling via Ca²⁺‐activated K⁺ channels of intermediate conductance (SK4, also known as K_Ca3.1 or IK) has been implicated in different cancer entities including breast cancer. Yet, the role of endogenous SK4 channels for tumorigenesis is unclear. Herein, we generated SK4‐negative tumours by crossing SK4‐deficient (SK4 KO) mice to the polyoma middle T‐antigen (PyMT) and epidermal growth factor receptor 2 (cNeu) breast cancer models in which oncogene expression is driven by the retroviral promoter MMTV. Survival parameters and tumour progression were studied in cancer‐prone SK4 KO in comparison with wild‐type (WT) mice and in a syngeneic orthotopic mouse model following transplantation of SK4‐negative or WT tumour cells. SK4 activity was modulated by genetic or pharmacological means using the SK4 inhibitor TRAM‐34 in order to establish the role of breast tumour SK4 for cell growth, electrophysiological signalling, and [Ca²⁺]_i oscillations. Ablation of SK4 and TRAM‐34 treatment reduced the SK4‐generated current fraction, growth factor‐dependent Ca²⁺ entry, cell cycle progression and the proliferation rate of MMTV‐PyMT tumour cells. In vivo, PyMT oncogene‐driven tumorigenesis was only marginally affected by the global lack of SK4, whereas tumour progression was significantly delayed after orthotopic implantation of MMTV‐PyMT SK4 KO breast tumour cells. However, overall survival and progression‐free survival time in the MMTV‐cNeu mouse model were significantly extended in the absence of SK4. Collectively, our data from murine breast cancer models indicate that SK4 activity is crucial for cell cycle control. Thus, the modulation of this channel should be further investigated towards a potential improvement of existing antitumour strategies in human breast cancer.

Tumor-targeted IL-12 combined with local irradiation leads to systemic tumor control via abscopal effects in vivo

NHS-IL12 is an immunocytokine, a fusion protein of IL12's functional domains and a necrosis-targeting antibody, which has shown significant effects against human rhabdomyosarcoma xenografts in a humanized tumor model, including terminal growth arrest and differentiation of the tumor cells. Here, we locally irradiated the tumors, increasing necrosis and consequently intratumoral immune cytokine availability, and asked whether this effect may surmount efficacy of single treatment modality. Humanized mice bearing bilateral rhabdomyosarcoma xenografts were evaluated for tumor burden and survival after irradiation, systemic NHS-IL12 therapy or a combination of both. Intratumoral immune compartments were characterized by immunohistochemistry and molecular methods. T_H1-cytokine dependency of underlying effector mechanisms were investigated in vitro in several human tumor cell lines. NHS-IL12 when combined with irradiation terminally arrested tumor growth and significantly improved survival. Combination treatment induced dense intratumoral T-cell infiltrates, clonal epitope-specific T-cell expansions, expression of cytotoxins, decreased pro-tumorigenic cytokines and induced senescence and differentiation in the cancer cells. Senescence and differentiation were reproduced in vitro and confirmed to be dependent on T_H1 cytokines IFNγ and TNF-α. NHS-IL12 and irradiation together induced broad intratumoral T_H1 biased NK and T-cell compartments, established antitumoral cytokine profiles and irreversibly growth arrested tumor cells, leading to systemic cancer control and improved survival. For the first time, we describe immune-induced senescence as a novel mechanism resulting from a treatment regimen combining irradiation with immunotherapy.

Targeting eIF5A Hypusination Prevents Anoxic Cell Death through Mitochondrial Silencing and Improves Kidney Transplant Outcome

The eukaryotic initiation factor 5A (eIF5A), which is highly conserved throughout evolution, has the unique characteristic of post-translational activation through hypusination. This modification is catalyzed by two enzymatic steps involving deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Notably, eIF5A may be involved in regulating the lifespan of Drosophila during long-term hypoxia. Therefore, we investigated the possibility of a link between eIF5A hypusination and cellular resistance to hypoxia/anoxia. Pharmacologic targeting of DHPS by N1-guanyl-1,7-diaminoheptane (GC7) or RNA interference-mediated inhibition of DHPS or DOHH induced tolerance to anoxia in immortalized mouse renal proximal cells. Furthermore, GC7 treatment of cells reversibly induced a metabolic shift toward glycolysis as well as mitochondrial remodeling and led to downregulated expression and activity of respiratory chain complexes, features characteristic of mitochondrial silencing. GC7 treatment also attenuated anoxia-induced generation of reactive oxygen species in these cells and in normoxic conditions, decreased the mitochondrial oxygen consumption rate of cultured cells and mice. In rats, intraperitoneal injection of GC7 substantially reduced renal levels of hypusinated eIF5A and protected against ischemia-reperfusion-induced renal injury. Finally, in the preclinical pig kidney transplant model, intravenous injection of GC7 before kidney removal significantly improved graft function recovery and late graft function and reduced interstitial fibrosis after transplant. This unconventional signaling pathway offers an innovative therapeutic target for treating hypoxic-ischemic human diseases and organ transplantation.

K+ channel signaling in irradiated tumor cells

K⁺ channels crosstalk with biochemical signaling cascades and regulate virtually all cellular processes by adjusting the intracellular K⁺ concentration, generating the membrane potential, mediating cell volume changes, contributing to Ca²⁺ signaling, and directly interacting within molecular complexes with membrane receptors and downstream effectors. Tumor cells exhibit aberrant expression and activity patterns of K⁺ channels. The upregulation of highly "oncogenic" K⁺ channels such as the Ca²⁺-activated IK channel may drive the neoplastic transformation, malignant progression, metastasis, or therapy resistance of tumor cells. In particular, ionizing radiation in doses used for fractionated radiotherapy in the clinic has been shown to activate K⁺ channels. Radiogenic K⁺ channel activity, in turn, contributes to the DNA damage response and promotes survival of the irradiated tumor cells. Tumor-specific overexpression of certain K⁺ channel types together with the fact that pharmacological K⁺ channel modulators are already in clinical use or well tolerated in clinical trials suggests that K⁺ channel targeting alone or in combination with radiotherapy might become a promising new strategy of anti-cancer therapy. The present article aims to review our current knowledge on K⁺ channel signaling in irradiated tumor cells. Moreover, it provides new data on molecular mechanisms of radiogenic K⁺ channel activation and downstream signaling events.

Deubiquitylating enzyme USP9x regulates radiosensitivity in glioblastoma cells by Mcl-1-dependent and -independent mechanisms

Glioblastoma is a very aggressive form of brain tumor with limited therapeutic options. Usually, glioblastoma is treated with ionizing radiation (IR) and chemotherapy after surgical removal. However, radiotherapy is frequently unsuccessful, among others owing to resistance mechanisms the tumor cells have developed. Antiapoptotic B-cell leukemia (Bcl)-2 family members can contribute to radioresistance by interfering with apoptosis induction in response to IR. Bcl-2 and the closely related Bcl-xL and Mcl-1 are often overexpressed in glioblastoma cells. In contrast to Bcl-2 and Bcl-xL, Mcl-1 is a short-lived protein whose stability is closely regulated by ubiquitylation-dependent proteasomal degradation. Although ubiquitin ligases facilitate degradation, the deubiquitylating enzyme ubiquitin-specific protease 9x (USP9x) interferes with degradation by removing polyubiquitin chains from Mcl-1, thereby stabilizing this protein. Thus, an inability to downregulate Mcl-1 by enhanced USP9x activity might contribute to radioresistance. Here we analyzed the impact of USP9x on Mcl-1 levels and radiosensitivity in glioblastoma cells. Correlating Mcl-1 and USP9x expressions were significantly higher in human glioblastoma than in astrocytoma. Downregulation of Mcl-1 correlated with apoptosis induction in established glioblastoma cell lines. Although Mcl-1 knockdown by siRNA increased apoptosis induction after irradiation in all glioblastoma cell lines, USP9x knockdown significantly improved radiation-induced apoptosis in one of four cell lines and slightly increased apoptosis in another cell line. In the latter two cell lines, USP9x knockdown also increased radiation-induced clonogenic death. The massive downregulation of Mcl-1 and apoptosis induction in A172 cells transfected with USP9x siRNA shows that the deubiquitinase regulates cell survival by regulating Mcl-1 levels. In contrast, USP9x regulated radiosensitivity in Ln229 cells without affecting Mcl-1 levels. We conclude that USP9x can control survival and radiosensitivity in glioblastoma cells by Mcl-1-dependent and Mcl-1-independent mechanisms.

Ca2+-Activated IK K+ Channel Blockade Radiosensitizes Glioblastoma Cells

Ca(2+)-activated K(+) channels, such as BK and IK channels, have been proposed to fulfill pivotal functions in neoplastic transformation, malignant progression, and brain infiltration of glioblastoma cells. Here, the ionizing radiation (IR) effect of IK K(+) channel targeting was tested in human glioblastoma cells. IK channels were inhibited pharmacologically by TRAM-34 or genetically by knockdown, cells were irradiated with 6 MV photons and IK channel activity, Ca(2+) signaling, cell cycling, residual double-strand breaks, and clonogenic survival were determined. In addition, the radiosensitizing effect of TRAM-34 was analyzed in vivo in ectopic tumors. Moreover, The Cancer Genome Atlas (TCGA) was queried to expose the dependence of IK mRNA abundance on overall survival (OS) of patients with glioma. Results indicate that radiation increased the activity of IK channels, modified Ca(2+) signaling, and induced a G2-M cell-cycle arrest. TRAM-34 decreased the IR-induced accumulation in G2-M arrest and increased the number of γH2AX foci post-IR, suggesting that TRAM-34 mediated an increase of residual DNA double-strand breaks. Mechanistically, IK knockdown abolished the TRAM-34 effects indicating the IK specificity of TRAM-34. Finally, TRAM-34 radiosensitized ectopic glioblastoma in vivo and high IK mRNA abundance associated with shorter patient OS in low-grade glioma and glioblastoma.

IMPLICATIONS

Together, these data support a cell-cycle regulatory function for IK K(+) channels, and combined therapy using IK channel targeting and radiation is a new strategy for anti-glioblastoma therapy.

mRNA-based vaccines synergize with radiation therapy to eradicate established tumors

BACKGROUND

The eradication of large, established tumors by active immunotherapy is a major challenge because of the numerous cancer evasion mechanisms that exist. This study aimed to establish a novel combination therapy consisting of messenger RNA (mRNA)-based cancer vaccines and radiation, which would facilitate the effective treatment of established tumors with aggressive growth kinetics.

METHODS

The combination of a tumor-specific mRNA-based vaccination with radiation was tested in two syngeneic tumor models, a highly immunogenic E.G7-OVA and a low immunogenic Lewis lung cancer (LLC). The molecular mechanism induced by the combination therapy was evaluated via gene expression arrays as well as flow cytometry analyses of tumor infiltrating cells.

RESULTS

In both tumor models we demonstrated that a combination of mRNA-based immunotherapy with radiation results in a strong synergistic anti-tumor effect. This was manifested as either complete tumor eradication or delay in tumor growth. Gene expression analysis of mouse tumors revealed a variety of substantial changes at the tumor site following radiation. Genes associated with antigen presentation, infiltration of immune cells, adhesion, and activation of the innate immune system were upregulated. A combination of radiation and immunotherapy induced significant downregulation of tumor associated factors and upregulation of tumor suppressors. Moreover, combination therapy significantly increased CD4+, CD8+ and NKT cell infiltration of mouse tumors.

CONCLUSION

Our data provide a scientific rationale for combining immunotherapy with radiation and provide a basis for the development of more potent anti-cancer therapies.

Ionizing radiation, ion transports, and radioresistance of cancer cells

The standard treatment of many tumor entities comprises fractionated radiation therapy which applies ionizing radiation to the tumor-bearing target volume. Ionizing radiation causes double-strand breaks in the DNA backbone that result in cell death if the number of DNA double-strand breaks exceeds the DNA repair capacity of the tumor cell. Ionizing radiation reportedly does not only act on the DNA in the nucleus but also on the plasma membrane. In particular, ionizing radiation-induced modifications of ion channels and transporters have been reported. Importantly, these altered transports seem to contribute to the survival of the irradiated tumor cells. The present review article summarizes our current knowledge on the underlying mechanisms and introduces strategies to radiosensitize tumor cells by targeting plasma membrane ion transports.

EGFR cooperates with glucose transporter SGLT1 to enable chromatin remodeling in response to ionizing radiation

BACKGROUND AND PURPOSE

EGFR and the sodium-dependent glucose transporter, SGLT1, are found in complex after radiation treatment. The aim of this study was to elucidate the role of EGFR in glucose uptake and chromatin remodeling.

MATERIAL AND METHODS

Glucose accumulation was quantified with help of (3)H-glucose. Involvement of SGLT was detected by a specific inhibitor. Role of EGFR was proved by EGFR overexpression and siRNA driven knockdown. Functional endpoints were intracellular ATP levels, protein expression, residual DNA-damage and colony formation.

RESULTS

EGFR/SGLT1 interactions in response to ionizing radiation were associated with increased glucose uptake. Nevertheless, tumor cells exhibit ATP depletion following irradiation. Recovery from radiation-induced ATP crisis was EGFR/SGLT-dependent and associated with increased cell survival and improved DNA-repair. The blockage of either EGFR or SGLT inhibited ATP level recovery and histone H3 modifications crucial for both chromatin remodeling and DNA repair in response to irradiation. Inhibition of the acetyltransferase TIP60, which is essential for histone H3-K9 acetylation and ATM activation, prevented energy crisis and chromatin remodeling.

CONCLUSIONS

Radiation-associated interactions between SGLT1 and EGFR resulted in increased glucose uptake, which counteracts the ATP crisis in tumor cells due to chromatin remodeling. The blockage of recovery from ATP crisis led to radio-sensitization in tumor cells.

Regulation of protein translation initiation in response to ionizing radiation

Background

Proliferating tumor cells require continuous protein synthesis. De novo synthesis of most proteins is regulated through cap-dependent translation. Cellular stress such as ionizing radiation (IR) blocks cap-dependent translation resulting in shut-down of global protein translation which saves resources and energy needed for the stress response. At the same time, levels of proteins required for stress response are maintained or even increased. The study aimed to analyze the regulation of signaling pathways controlling protein translation in response to IR and the impact on Mcl-1, an anti-apoptotic and radioprotective protein, which levels rapidly decline upon IR.

Methods

Protein levels and processing were analyzed by Western blot. The assembly of the translational pre-initiation complex was examined by Immunoprecipitation and pull-down experiments with 7-methyl GTP agarose. To analyze IR-induced cell death, dissipation of the mitochondrial membrane potential and DNA fragmentation were determined by flow cytometry. Protein levels of the different initiation factors were down-regulated using RNA interference approach.

Results

IR induced caspase-dependent cleavage of the translational initiation factors eIF4G1, eIF3A, and eIF4B resulting in disassembly of the cap-dependent initiation complex. In addition, DAP5-dependent initiation complex that regulates IRES-dependent translation was disassembled in response to IR. Moreover, IR resulted in dephosphorylation of 4EBP1, an inhibitor of cap-dependent translation upstream of caspase activation. However, knock-down of eIF4G1, eIF4B, DAP5, or 4EBP1 did not affect IR-induced decline of the anti-apoptotic protein Mcl-1.

Conclusion

Our data shows that cap-dependent translation is regulated at several levels in response to IR. However, the experiments indicate that IR-induced Mcl-1 decline is not a consequence of translational inhibition in Jurkat cells.

In vitro hypoxic cytotoxicity and hypoxic radiosensitization. Efficacy of the novel 2-nitroimidazole N,N,N-tris[2-(2-nitro-1H-imidazol-1-yl)ethyl]amine

BACKGROUND AND PURPOSE

Tumor hypoxia is a major problem in radiation therapy of solid tumors because of the radiosensitizing effect of oxygen. Nitroimidazole-containing compounds are oxygen mimetics accumulating in hypoxic tumor areas. However, the broad use of 2-nitroimidazoles as a hypoxic radiosensitizer is limited by their partially low efficacy and/or high neurotoxicity.

MATERIALS AND METHODS

Here, we characterized the in vitro hypoxic cytotoxicity and hypoxic radiosensitizing efficacy of N,N,N-tris [2-(2-nitro-1H-imidazol-1-yl)ethyl]amine (PRC) in a hypoxia-sensitive lymphoma and a hypoxia-resistant glioblastoma cell line by colony formation assay and flow cytometry.

RESULTS

PRC exerted high hypoxic cytotoxic and radiosensitizing action on both cell lines at almost absent toxicity under normoxic conditions. In particular, under hypoxia, but not normoxia, PRC targeted the mitochondria resulting in oxidative stress, G(2)/M cell cycle arrest, and triggering of the intrinsic apoptosis pathway.

CONCLUSION

Our in vitro findings suggest that PRC might be a promising new 2-nitroimidazole for improving radiation therapy of hypoxic tumors in vivo.

EGFR-mediated stimulation of sodium/glucose cotransport promotes survival of irradiated human A549 lung adenocarcinoma cells

BACKGROUND AND PURPOSE

Solid tumor cells may adapt to an ischemic microenvironment by upregulation of sodium/glucose cotransport (SGLT) in the plasma membrane which supplies the tumor cell with glucose even at very low extracellular glucose concentration. Since SGLT activity has been shown to depend on the epithelial growth factor receptor (EGFR) and EGFR reportedly is activated by ionizing radiation, we tested for irradiation-induced SGLT activity.

MATERIALS AND METHODS

A549 lung adenocarcinoma and FaDu head and neck squamous cancer cells were irradiated with 0 and 4 Gy X-ray and electrogenic SGLT transport activity was recorded by patch clamp current clamp in the presence and absence of extracellular glucose (5mM), the SGLT inhibitor phlorizin (500 μM), and the inhibitor of the EGFR tyrosine kinase activity erlotinib (1 μM). In addition, the effect of phlorizin and erlotinib on glucose uptake and clonogenic survival was tested in irradiated and control cells by tracer flux and colony formation assays, respectively.

RESULTS

Irradiated A549 cells exhibited a significantly lower membrane potential 3h after irradiation than the control cells. Phlorizin, erlotinib or removal of extracellular glucose, hyperpolarized the irradiated A549 cells to a significantly higher extent than the control cells. Similarly, but less pronounced, glucose removal hyperpolarized irradiated FaDu cells. In addition, irradiated A549 cells exhibited a highly increased (3)H-glucose uptake which was sensitive to phlorizin. Finally, phlorizin radiosensitized the A549 and FaDu cells as evident from the colony formation assays.

CONCLUSIONS

Taken together, these data suggest an irradiation-stimulated and EGFR-mediated increase in SGLT-generated glucose uptake which is required for the survival of the genotoxically stressed tumor cells.

Ca2+ signaling in the regulation of dendritic cell functions

Dendritic cells (DCs) are highly versatile antigen-presenting cells critically involved in both innate and adaptive immunity as well as maintenance of self-tolerance. DC function is governed by Ca(2+) signaling, which directs the DC responses to diverse antigens, including Toll-like receptor ligands, intact bacteria, and microbial toxins. Ca(2+)-sensitive DC functions include DC activation, maturation, migration, and formation of immunological synapses with T cells. Moreover, alterations of cytosolic Ca(2+) trigger immune suppression or switch off DC activity. Ca(2+) signals are generated by the orchestration of Ca(2+) transport processes across plasma, endoplasmic reticulum, and inner mitochondrial membrane. These processes include active pumping of Ca(2+), Ca(2+)/Na(+) antiport, and electrodiffusion through Ca(2+)-permeable channels or uniporters. Ca(2+) channels in the plasma membrane such as Ca(2+) release-activated Ca(2+) or L-type Ca(2+) channels are tightly regulated by the membrane potential which in turn depends on the activity of voltage-gated K(+) or Ca(2+)-activated nonselective cation channels. The rapidly growing knowledge on the function and regulation of these membrane transport proteins provides novel insight into pathophysiological mechanisms underlying dysfunction of the immune system and opens novel therapeutic opportunity to favorably influence the function of the immune system.

Anti-apoptotic Bcl-2 fails to form efficient complexes with pro-apoptotic Bak to protect from Celecoxib-induced apoptosis

The non-steroidal anti-inflammatory drug Celecoxib is a specific inhibitor of cyclooxygenase-2. Apart from its inhibitor function, Celecoxib induces apoptosis through the intrinsic pathway which is controlled by the Bcl-2 family members. In Jurkat T lymphoma cells, treatment with Celecoxib results in a rapid decline of the anti-apoptotic Bcl-2-related protein Mcl-1. The depletion of Mcl-1 is sufficient for apoptosis induction and can be blocked by overexpression of Bcl-xL but not by the close homologue Bcl-2. The present investigation analyzed the mechanism by which Bcl-xL prevents apoptosis induction whereas Bcl-2 failed to. Our data show that the involvement of the orphan nuclear receptor Nur77/TR3 specifically targeting Bcl-2 but not Bcl-xL was not involved in Celecoxib-induced apoptosis. Surprisingly, BH3-only proteins Bid, Bim, and Puma of the Bcl-2 family were not needed either. However, unlike Bcl-2, Mcl-1, and Bcl-xL sequestered Bak preventing it from activation through a direct interaction. Thus, when abundantly expressed, Bcl-xL can substitute for the loss of Mcl-1 whereas Bcl-2, incapable of forming a high affinity complex with Bak, could not.

Non-selective cation channel-mediated Ca2+-entry and activation of Ca2+/calmodulin-dependent kinase II contribute to G2/M cell cycle arrest and survival of irradiated leukemia cells

Genotoxic stress induces cell cycle arrest and DNA repair which may enable tumor cells to survive radiation therapy. Here, we defined the role of Ca(2+) signaling in the cell cycle control and survival of chronic myeloid leukemia (CML) cells subjected to ionizing radiation (IR). To this end, K562 erythroid leukemia cells were irradiated (0-10 Gy). Tumor survival was analyzed by clonogenic survival assay and cell cycle progression via flow cytometry. Plasma membrane cation conductance was assessed by patch-clamp whole-cell recording and the cytosolic free Ca(2+) concentration ([Ca(2+)](i)) was measured by fura-2 Ca(2+) imaging. Nuclear activity of Ca(2+)/calmodulin-dependent kinase II (CaMKII) was defined by Western blotting. In addition, the effect of IR (5 Gy) on the cation conductance of primary CML cells was determined. The results indicated that IR (10 Gy) induced a G(2)/M cell cycle arrest of K562 cells within 24 h post-irradiation (p.i.) and decreased the clonogenic survival to 0.5 % of that of the control cells. In K562 cells, G(2)/M cell cycle arrest was preceded by activation of TRPV5/6-like nonselective cation channels in the plasma membrane 1-5 h p.i., resulting in an elevated Ca(2+) entry as evident from fura-2 Ca(2+) imaging. Similarly, IR stimulated a Ca(2+)-permeable nonselective cation conductance in primary CML cells within 2-4 h p.i.. Ca(2+) entry, into K562 cells was paralleled by an IR-induced activation of nuclear CaMKII. The IR-stimulated accumulation in G(2) phase was delayed upon buffering [Ca(2+)](i) with the Ca(2+) chelator BAPTA-AM or inhibiting CaMKII with KN93 (1 nM). In addition, KN93 decreased the clonogenic survival of irradiated cells but not of control cells. In conclusion, the data suggest that IR-stimulated cation channel activation, Ca(2+) entry and CaMKII activity participate in control of cell cycle progression and survival of irradiated CML cells.

Protective effect of amiodarone in malaria

According to previous observations, amiodarone triggers suicidal erythrocyte death or eryptosis, which is characterized by cell shrinkage and exposure of phosphatidylserine at the erythrocyte surface. Eryptosis may in turn accelerate the clearance of Plasmodium-infected erythrocytes. The present study tested whether amiodarone augments phosphatidylserine exposure of Plasmodium-infected erythrocytes, interferes with the development of parasitemia and thus influences the course of malaria. The in vitro infection of human erythrocytes with Plasmodium falciparum (strain BinH) increased annexin V-binding, an effect significantly augmented by amiodarone (10 microM). Amiodarone further significantly decreased intraerythrocytic DNA/RNA content (> or =5 microM) and in vitro parasitemia (> or =1 microM). Following infection of mice with Plasmodiumberghei ANKA by intraperitoneal injection of parasitized murine erythrocytes (1x10(6)) amiodarone (intraperitoneal 50mg/kg b.w.) significantly decreased the parasitemia and increased the survival of P. berghei-infected mice (from 0% to 70% 26 days after infection). Moreover, treatment with amiodarone significantly increased the percentage of PS-exposing infected erythrocytes. In conclusion, amiodarone inhibits intraerythrocytic growth of P. falciparum, enhances suicidal death of infected erythrocytes, decreases parasitemia following P. berghei infection and supports host survival during malaria.

Functional significance of the intermediate conductance Ca2+-activated K+ channel for the short-term survival of injured erythrocytes

Increased cytosolic Ca(2+) concentrations activate Gardos K(+) channels in human erythrocytes with membrane hyperpolarization, efflux of K(+), Cl⁻, and osmotically obliged H₂O resulting in cell shrinkage, a phenomenon referred to as Gardos effect. We tested whether the Gardos effect delays colloid osmotic hemolysis of injured erythrocytes from mice lacking the Ca(2+)-activated K(+) channel K(Ca)3.1. To this end, we applied patch clamp and flow cytometry and determined in vitro as well as in vivo hemolysis. As a result, erythrocytes from K(Ca)3.1-deficient (K(Ca)3.1(-/-)) mice lacked Gardos channel activity and the Gardos effect. Blood parameters, reticulocyte count, or osmotic erythrocyte resistance, however, did not differ between K(Ca)3.1(-/-) mice and their wild-type littermates, suggesting low or absent Gardos channel activity in unstressed erythrocytes. Oxidative stress-induced Ca(2+) entry and phospholipid scrambling were significantly less pronounced in K(Ca)3.1(-/-) than in wild-type erythrocytes. Moreover, in vitro treatment with α-toxin from Staphylococcus aureus, which forms pores in the cellular membrane, resulted in significantly stronger hemolysis of K(Ca)3.1(-/-) than of wild-type erythrocytes. Intravenous injection of α-toxin induced more profound hemolysis in K(Ca)3.1(-/-) than in wild-type mice. Similarly, intra-peritoneal application of the redox-active substance phenylhydrazine, an agent for the induction of hemolytic anemia, was followed by a significantly stronger decrease of hematocrit in K(Ca)3.1(-/-) than in wild-type mice. Finally, malaria infection triggered the activation of K(Ca)3.1 and transient shrinkage of the infected erythrocytes. In conclusion, K(Ca)3.1 channel activity and Gardos effect counteract hemolysis of injured erythrocytes, thus decreasing hemoglobin release into circulating blood.

Increased cation conductance in human erythrocytes artificially aged by glycation

Excessive glucose concentrations foster glycation and thus premature aging of erythrocytes. The present study explored whether glycation-induced erythrocyte aging is paralleled by features of suicidal erythrocyte death or eryptosis, which is characterized by cell membrane scrambling with subsequent phosphatidylserine exposure at the cell surface and cell shrinkage. Both are triggered by increases of cytosolic Ca(2+) concentration ([Ca(2+)](i)), which may result from activation of Ca(2+) permeable cation channels. Glycation was accomplished by exposure to high glucose concentrations (40 and 100 mM), phosphatidylserine exposure estimated from annexin binding, cell shrinkage from decrease of forward scatter, and [Ca(2+)](i) from Fluo3-fluorescence in analysis via fluorescence-activated cell sorter. Cation channel activity was determined by means of whole-cell patch clamp. Glycation of total membrane proteins, immunoprecipitated TRPC3/6/7, and immunoprecipitated L-type Ca(2+) channel proteins was estimated by Western blot testing with polyclonal antibodies used against advanced glycation end products. A 30-48-h exposure of the cells to 40 or 100 mM glucose in Ringer solution (at 37 degrees C) significantly increased glycation of membrane proteins, hemoglobin (HbA(1c)), TRPC3/6/7, and L-type Ca(2+) channel proteins, enhanced amiloride-sensitive, voltage-independent cation conductance, [Ca(2+)](i), and phosphatidylserine exposure, and led to significant cell shrinkage. Ca(2+) removal and addition of Ca(2+) chelator EGTA prevented the glycation-induced phosphatidylserine exposure and cell shrinkage after glycation. Glycation-induced erythrocyte aging leads to eryptosis, an effect requiring Ca(2+) entry from extracellular space.

Accelerated clearance of Plasmodium-infected erythrocytes in sickle cell trait and annexin-A7 deficiency

The course of malaria does not only depend on the virulence of the parasite Plasmodium but also on properties of host erythrocytes. Here, we show that infection of erythrocytes from human sickle cell trait (HbA/S) carriers with ring stages of P. falciparum led to significantly enhanced PGE(2) formation, Ca(2+) permeability, annexin-A7 degradation, phosphatidylserine (PS) exposure at the cell surface, and clearance by macrophages. P. berghei-infected erythrocytes from annexin-A7-deficient (annexin-A7(-/-)) mice were more rapidly cleared than infected wildtype cells. Accordingly, P. berghei-infected annexin-A7(-/-) mice developed less parasitemia than wildtype mice. The cyclooxygenase inhibitor aspirin decreased erythrocyte PS exposure in infected annexin-A7(-/-) mice and abolished the differences of parasitemia and survival between the genotypes. Conversely, the PGE(2)-agonist sulprostone decreased parasitemia and increased survival of wild type mice. In conclusion, PS exposure on erythrocytes results in accelerated clearance of Plasmodium ring stage-infected HbA/S or annexin-A7(-/-) erythrocytes and thus confers partial protection against malaria in vivo.

Suicide for survival--death of infected erythrocytes as a host mechanism to survive malaria

The pathogen of malaria, Plasmodium, enters erythrocytes and thus escapes recognition by the immune system. The pathogen induces oxidative stress to the host erythrocyte, which triggers eryptosis, the suicidal death of erythrocytes. Eryptosis is characterized by cell shrinkage, membrane blebbing and cell membrane phospholipid scrambling with phosphatidylserine exposure at the cell surface. Phosphatidylserine-exposing erythrocytes are identified by macrophages which engulf and degrade the eryptotic cells. To the extent that infected erythrocytes undergo eryptosis prior to exit of Plasmodiaand subsequent infection of other erythrocytes, the premature eryptosis may protect against malaria. Accordingly, any therapeutical intervention accelerating suicidal death of infected erythrocytes has the potential to foster elimination of infected erythrocytes, delay the development of parasitemia and favorably influence the course of malaria. Eryptosis is stimulated by a wide variety of triggers including osmotic shock, oxidative stress, energy depletion and a wide variety of xenobiotics. Diseases associated with accelerated eryptosis include sepsis, haemolytic uremic syndrome, malaria, sickle-cell anemia, beta-thalassemia, glucose-6-phosphate dehydrogenase (G6PD)-deficiency, phosphate depletion, iron deficiency and Wilson's disease. Among the known stimulators of eryptosis, paclitaxel, chlorpromazine, cyclosporine, curcumin, PGE2 and lead have indeed been shown to favourably influence the course of malaria. Moreover, sickle-cell trait, beta-thalassemia trait, glucose-6-phosphate dehydrogenase (G6PD)-deficiency and iron deficiency confer some protection against a severe course of malaria. Importantly, counteracting Plasmodia by inducing eryptosis is not expected to generate resistance of the pathogen, as the proteins involved in suicidal death of the host cell are not encoded by the pathogen and thus cannot be modified by mutations of its genes.

Azathioprine favourably influences the course of malaria

BACKGROUND

Azathioprine triggers suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and exposure of phosphatidylserine at the erythrocyte surface. Eryptosis may accelerate the clearance of Plasmodium-infected erythrocytes. The present study thus explored whether azathioprine influences eryptosis of Plasmodium-infected erythrocytes, development of parasitaemia and thus the course of malaria.

METHODS

Human erythrocytes were infected in vitro with Plasmodium falciparum (P. falciparum) (strain BinH) in the absence and presence of azathioprine (0.001 - 10 microM), parasitaemia determined utilizing Syto16, phosphatidylserine exposure estimated from annexin V-binding and cell volume from forward scatter in FACS analysis. Mice were infected with Plasmodium berghei (P. berghei) ANKA by injecting parasitized murine erythrocytes (1 x 106) intraperitoneally. Where indicated azathioprine (5 mg/kg b.w.) was administered subcutaneously from the eighth day of infection.

RESULTS

In vitro infection of human erythrocytes with P. falciparum increased annexin V-binding and initially decreased forward scatter, effects significantly augmented by azathioprine. At higher concentrations azathioprine significantly decreased intraerythrocytic DNA/RNA content (>or= 1 microM) and in vitro parasitaemia (>or= 1 microM). Administration of azathioprine significantly decreased the parasitaemia of circulating erythrocytes and increased the survival of P. berghei-infected mice (from 0% to 77% 22 days after infection).

CONCLUSION

Azathioprine inhibits intraerythrocytic growth of P. falciparum, enhances suicidal death of infected erythrocytes, decreases parasitaemia and fosters host survival during malaria.