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

GZ17-6.02 kills PDX isolates of uveal melanoma

GZ17-6.02 has undergone phase I evaluation in patients with solid tumors (NCT03775525). The RP2D is 375 mg PO BID, with an uveal melanoma patient exhibiting a 15% reduction in tumor mass for 5 months at this dose. Studies in this manuscript have defined the biology of GZ17-6.02 in PDX isolates of uveal melanoma cells. GZ17-6.02 killed uveal melanoma cells through multiple convergent signals including enhanced ATM-AMPK-mTORC1 activity, inactivation of YAP/TAZ and inactivation of eIF2α. GZ17-6.02 significantly enhanced the expression of BAP1, predictive to reduce metastasis, and reduced the levels of ERBB family RTKs, predicted to reduce growth. GZ17-6.02 interacted with doxorubicin or ERBB family inhibitors to significantly enhance tumor cell killing which was associated with greater levels of autophagosome formation and autophagic flux. Knock down of Beclin1, ATG5 or eIF2α were more protective than knock down of ATM, AMPKα, CD95 or FADD, however, over-expression of FLIP-s provided greater protection compared to knock down of CD95 or FADD. Expression of activated forms of mTOR and STAT3 significantly reduced tumor cell killing. GZ17-6.02 reduced the expression of PD-L1 in uveal melanoma cells to a similar extent as observed in cutaneous melanoma cells whereas it was less effective at enhancing the levels of MHCA. The components of GZ17-6.02 were detected in tumors using a syngeneic tumor model. Our data support future testing GZ17-6.02 in uveal melanoma as a single agent, in combination with ERBB family inhibitors, in combination with cytotoxic drugs, or with an anti-PD1 immunotherapy.

Emergence of SGLT2 Inhibitors as Powerful Antioxidants in Human Diseases

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a new class of oral glucose-lowering agents. Apart from their glucose-lowering effects, large clinical trials assessing certain SGLT2 inhibitors have revealed cardiac and renal protective effects in non-diabetic patients. These excellent outcomes motivated scientists and clinical professionals to revisit their underlying mechanisms. In addition to the heart and kidney, redox homeostasis is crucial in several human diseases, including liver diseases, neural disorders, and cancers, with accumulating preclinical studies demonstrating the therapeutic benefits of SGLT2 inhibitors. In the present review, we aimed to update recent advances in the antioxidant roles of SGLT2 inhibitors in common but debilitating human diseases. We anticipate that this review will guide new research directions and novel therapeutic strategies for diabetes, cardiovascular diseases, nephropathies, liver diseases, neural disorders, and cancers in the era of SGLT2 inhibitors.

Metabolic Rewiring in Radiation Oncology Toward Improving the Therapeutic Ratio

To meet the anabolic demands of the proliferative potential of tumor cells, malignant cells tend to rewire their metabolic pathways. Although different types of malignant cells share this phenomenon, there is a large intracellular variability how these metabolic patterns are altered. Fortunately, differences in metabolic patterns between normal tissue and malignant cells can be exploited to increase the therapeutic ratio. Modulation of cellular metabolism to improve treatment outcome is an emerging field proposing a variety of promising strategies in primary tumor and metastatic lesion treatment. These strategies, capable of either sensitizing or protecting tissues, target either tumor or normal tissue and are often focused on modulating of tissue oxygenation, hypoxia-inducible factor (HIF) stabilization, glucose metabolism, mitochondrial function and the redox balance. Several compounds or therapies are still in under (pre-)clinical development, while others are already used in clinical practice. Here, we describe different strategies from bench to bedside to optimize the therapeutic ratio through modulation of the cellular metabolism. This review gives an overview of the current state on development and the mechanism of action of modulators affecting cellular metabolism with the aim to improve the radiotherapy response on tumors or to protect the normal tissue and therefore contribute to an improved therapeutic ratio.

Potassium Channels in Cancer

Neoplastic transformation is reportedly associated with alterations of the potassium transport across plasma and intracellular membranes. These alterations have been identified as crucial elements of the tumourigenic reprogramming of cells. Potassium channels may contribute to cancer initiation, malignant progression and therapy resistance of tumour cells. The book chapter focusses on (oncogenic) potassium channels frequently upregulated in different tumour entities, upstream and downstream signalling of these channels, their contribution to the maintenance of cancer stemness and the formation of an immunosuppressive tumour microenvironment. In addition, their role in adaptation to tumour hypoxia, metabolic reprogramming, as well as tumour spreading and metastasis is discussed. Finally, we discuss how (oncogenic) potassium channels may confer treatment resistance of tumours against radiation and chemotherapy and thus might be harnessed for new therapy strategies, for instance, by repurposing approved drugs known to target potassium channels.

Effects of radiotherapy and short-term starvation combination on metastatic and non-tumor cell lines

BACKGROUND

Since its discovery in the late 19^th century, radiotherapy has been one of the most important medical treatments in oncology. Recently, fasting or short-term starvation (STS) in cancer patients undergoing chemotherapy has been studied to determine its potential for enhancing the therapeutic index and for preventing side- effects, but no data are available in the radiotherapy setting. We thus decided to investigate the effects in vitro of STS in combination with radiotherapy in metastatic cancer cells and non-cancer cells.

METHODS

Cells were incubated in short-term starvation medium (STS medium, 0·5 g/L glucose + 1% FBS) or in control medium (CM medium, 1 g/L glucose + 10 % FBS) for 24 h and then treated with single high-dose radiation. A plexiglass custom-built phantom was used to irradiate cells. DNA damage was evaluated using alkaline comet assay and theCometAnalyser software. The cell surviving fraction was assessed by clonogenic assay.

FINDING

STS followed by single high-dose radiation significantly increased DNA damage in metastatic cancer cell lines but not in normal cells. Furthermore, STS reduced the surviving fraction of irradiated tumor cells, indicating a good radio-sensitizing effect on metastatic cell lines. This effect was not observed in non-tumor cells.

INTERPRETATION

Our results suggest that STS may alter cellular processes, enhancing the efficacy of radiotherapy in metastatic cancer cellsin vitro. Interestingly, STS has radioprotective effect on the survival of healthy cells.

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.

KCa3.1 Channels Confer Radioresistance to Breast Cancer Cells

K_Ca3.1 K⁺ channels reportedly contribute to the proliferation of breast tumor cells and may serve pro-tumor functions in the microenvironment. The putative interaction of K_Ca3.1 with major anti-cancer treatment strategies, which are based on cytotoxic drugs or radiotherapy, remains largely unexplored. We employed K_Ca3.1-proficient and -deficient breast cancer cells derived from breast cancer-prone MMTV-PyMT mice, pharmacological K_Ca3.1 inhibition, and a syngeneic orthotopic mouse model to study the relevance of functional K_Ca3.1 for therapy response. The K_Ca3.1 status of MMTV-PyMT cells did not determine tumor cell proliferation after treatment with different concentrations of docetaxel, doxorubicin, 5-fluorouracil, or cyclophosphamide. K_Ca3.1 activation by ionizing radiation (IR) in breast tumor cells in vitro, however, enhanced radioresistance, probably via an involvement of the channel in IR-stimulated Ca²⁺ signals and DNA repair pathways. Consistently, K_Ca3.1 knockout increased survival time of wildtype mice upon syngeneic orthotopic transplantation of MMTV-PyMT tumors followed by fractionated radiotherapy. Combined, our results imply that K_Ca3.1 confers resistance to radio- but not to chemotherapy in the MMTV-PyMT breast cancer model. Since K_Ca3.1 is druggable, K_Ca3.1 targeting concomitant to radiotherapy seems to be a promising strategy to radiosensitize breast tumors.

SLC5A1 promotes growth and proliferation of pancreatic carcinoma via glucose-dependent AMPK/mTOR signaling

Background: Accumulating studies have reported that aberrant expression of SLC5A1 is a negative prognostic factor to various cancer patients.

Purpose: Pancreatic cancer tissue has also shown to harbor higher expression of SLC5A1, however how SLC5A1 mediates pancreatic cancer cells growth remains unclear.

Methods: In this study, we examined the mRNA and protein expressions of SLC5A1 in human pancreatic tissue and various cell lines. The in vitro and in vivo roles of SLC5A1 in pancreatic cancer were investigated through stably transfected pancreatic cells with shRNA plasmid targeting SLC5A1.

Results: Our results observed SLC5A1 was over-expressed in human pancreatic cancer tissues as well as most pancreatic cancer cell lines. Both in vitro and in vivo inhibition of SLC5A1 retarded pancreatic cancer cell growth and progression. The SLC5A1 knockdown mediated growth suppression is mainly regulated by reduced cellular glucose uptake by pancreatic cancer cells. Our further mechanistic observation showed that inhibition of SLC5A1 induced AMPK-dependent mTOR suppression and pharmacological inhibition of AMPK rescued the effect of SLC5A1 blockade. Further protein-protein interaction analysis showed association of SLC5A1 with EGFR and knockdown of EGFR also showed decreased cellular survival and glucose uptake by pancreatic cancer cells.

Conclusion: Our findings postulated SLC5A1/EGFR as the potential therapeutic target of pancreatic cancer patients.

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.

Beyond EGFR inhibition: multilateral combat strategies to stop the progression of head and neck cancer

Epidermal growth factor receptor (EGFR) overexpression is common in head and neck squamous cell carcinoma. Targeted therapy specifically directed towards EGFR has been an area of keen interest in head and neck cancer research, as EGFR is potentially an integration point for convergent signaling. Despite the latest advancements in cancer diagnostics and therapeutics against EGFR, the survival rates of patients with advanced head and neck cancer remain disappointing due to anti-EGFR resistance. This review article will discuss recent multilateral efforts to discover and validate actionable strategies that involve signaling pathways in heterogenous head and neck cancer and to overcome anti-EGFR resistance in the era of precision medicine. Particularly, this review will discuss in detail the issue of cancer metabolism, which has recently emerged as a novel mechanism by which head and neck cancer may be successfully controlled according to different perspectives.

South Korean researchers propose novel combination strategies for overcoming drug resistance and halting the progression of head and neck cancer (HNC). Although high levels of epidermal growth factor receptor (EGFR) protein in HNC correlate with reduced survival, patients’ response to the EGFR inhibitor cetuximab often declines rapidly after a short period of effectiveness. Hyung Kwon Byeon at Korea University College of Medicine in Seoul and colleagues review current knowledge of the mechanisms underlying cetuximab resistance. They suggest that evaluating a patient’s genetic profile and combining cetuximab with drugs that enhance the effects of inhibiting EGFR signaling pathways (with inhibitors of other EGFR family members or proteins that mediate EGFR entry to the cell nucleus, for example) as well as with agents that inhibit cancer cell metabolism could be a more effective approach for treating HNC.

Glucose transporters in cancer - from tumor cells to the tumor microenvironment

Solute carriers of the glucose transporter (GLUT) family mediate the first step for cellular glucose usage. The upregulation of GLUTs has been reported in numerous cancer types as a result of perturbation of gene expression or protein relocalization or stabilization. Because they enable to sustain the energy demand required by tumor cells for various biochemical programs, they are promising targets for the development of anticancer strategies. Recently, important biological insights have come from the fine crystal structure determination of several GLUTs; these advances will likely catalyze the development of new selective inhibitory compounds. Furthermore, deregulated glucose metabolism of nontumor cells in the tumor mass is beginning to be appreciated and could have major implications for our understanding of how glucose uptake by specific cell types influences the behavior of neighboring cells in the same microenvironment. In this review, we discuss some of the deregulation mechanisms of glucose transporters, their genetic and pharmacological targeting in cancer, and new functions they may have in nontumor cells of the tumor environment or beyond glucose uptake for glycolysis.

Effects of Aptamer to U87-EGFRvIII Cells on the Proliferation, Radiosensitivity, and Radiotherapy of Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most prevalent and lethal malignant intracranial tumor in the brain, with very poor prognosis and survival. The epidermal growth factor receptor variant III (EGFRvIII) contributes to increased oncogenicity that does not occur through binding EGFR ligands and instead occurs through constitutive activation, which enhances glioma tumorigenicity and resistance to targeted therapy. Aptamers are nucleic acids with high affinity and specificity to targets selected by systematic evolution of ligands by exponential enrichment (SELEX), and are usually developed as antagonists of disease-associated factors. Herein, we generated a DNA aptamer U2, targeting U87-EGFRvIII cells, and demonstrated that U2 alters the U87-EGFRvIII cell growth, radiosensitivity, and radiotherapy of glioblastoma cells. We detected U2 and U87-EGFRvIII cells by flow cytometry and confocal microscopy to explore the binding ability of U2 to U87-EGFRvIII cells. Then, we found that aptamer U2 inhibits the proliferation, migration, invasion, and downstream signaling of U87-EGFRvIII cells. Moreover, the U2 aptamer can increase the radiosensitivity of U87-EGFRvIII in vitro and has a better antitumor effect on 188Re-U2 in vivo. Therefore, the results revealed the promising potential of the U2 aptamer to be a new type of drug candidate and aptamer-targeted drug delivery system for glioblastoma therapy.

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.

Glucose starvation impairs DNA repair in tumour cells selectively by blocking histone acetylation

BACKGROUND AND PURPOSE

Tumour cells are characterized by aerobic glycolysis and thus have high glucose consumption. Because repairing radiation-induced DNA damage is an energy-demanding process, we hypothesized that glucose starvation combined with radiotherapy could be an effective strategy to selectively target tumour cells.

MATERIAL AND METHODS

We glucose-starved tumour cells (A549, FaDu) in vitro and analysed their radiation-induced cell responses compared to normal fibroblasts (HSF7).

RESULTS

Irradiation depleted intracellular ATP levels preferentially in cancer cells. Consequently, glucose starvation impaired DNA double-strand break (DSB) repair and radiosensitized confluent tumour cells but not normal fibroblasts. In proliferating tumour cells glucose starvation resulted in a reduction of proliferation, but failed to radiosensitize cells. Glucose supply was indispensable during the late DSB repair in confluent tumour cells starting approximately 13 h after irradiation, and glucose starvation inhibited radiation-induced histone acetylation, which is essential for chromatin relaxation. Sirtinol - an inhibitor of histone deacetylases - reverted the effects of glucose depletion on histone acetylation and DNA DSB repair in tumour cells. Furthermore, a glucose concentration of 2.8 mmol/L was sufficient to impair DSB repair in tumour cells and reduced their clonogenic survival under a fractionated irradiation regimen.

CONCLUSIONS

In resting tumour cells, glucose starvation combined with irradiation resulted in the impairment of late DSB repair and the reduction of clonogenic survival, which was associated with disrupted radiation-induced histone acetylation. However, in normal cells, DNA repair and radiosensitivity were not affected by glucose depletion.

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.

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.

Transcriptional co-factor Transducin beta-like (TBL) 1 acts as a checkpoint in pancreatic cancer malignancy

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer fatalities in Western societies, characterized by high metastatic potential and resistance to chemotherapy. Critical molecular mechanisms of these phenotypical features still remain unknown, thus hampering the development of effective prognostic and therapeutic measures in PDAC. Here, we show that transcriptional co-factor Transducin beta-like (TBL) 1 was over-expressed in both human and murine PDAC. Inactivation of TBL1 in human and mouse pancreatic cancer cells reduced cellular proliferation and invasiveness, correlating with diminished glucose uptake, glycolytic flux, and oncogenic PI3 kinase signaling which in turn could rescue TBL1 deficiency-dependent phenotypes. TBL1 deficiency both prevented and reversed pancreatic tumor growth, mediated transcriptional PI3 kinase inhibition, and increased chemosensitivity of PDAC cells in vivo. As TBL1 mRNA levels were also found to correlate with PI3 kinase levels and overall survival in a cohort of human PDAC patients, TBL1 was identified as a checkpoint in the malignant behavior of pancreatic cancer and its expression may serve as a novel molecular target in the treatment of human PDAC.

Targeting TRPM2 Channels Impairs Radiation-Induced Cell Cycle Arrest and Fosters Cell Death of T Cell Leukemia Cells in a Bcl-2-Dependent Manner

Messenger RNA data of lymphohematopoietic cancer lines suggest a correlation between expression of the cation channel TRPM2 and the antiapoptotic protein Bcl-2. The latter is overexpressed in various tumor entities and mediates therapy resistance. Here, we analyzed the crosstalk between Bcl-2 and TRPM2 channels in T cell leukemia cells during oxidative stress as conferred by ionizing radiation (IR). To this end, the effects of TRPM2 inhibition or knock-down on plasma membrane currents, Ca²⁺ signaling, mitochondrial superoxide anion formation, and cell cycle progression were compared between irradiated (0–10 Gy) Bcl-2-overexpressing and empty vector-transfected Jurkat cells. As a result, IR stimulated a TRPM2-mediated Ca²⁺-entry, which was higher in Bcl-2-overexpressing than in control cells and which contributed to IR-induced G₂/M cell cycle arrest. TRPM2 inhibition induced a release from G₂/M arrest resulting in cell death. Collectively, this data suggests a pivotal function of TRPM2 in the DNA damage response of T cell leukemia cells. Apoptosis-resistant Bcl-2-overexpressing cells even can afford higher TRPM2 activity without risking a hazardous Ca²⁺-overload-induced mitochondrial superoxide anion formation.

Nuclear EGFR renders cells radio-resistant by binding mRNA species and triggering a metabolic switch to increase lactate production

BACKGROUND AND PURPOSE

EGFR is translocated into the cell nucleus in response to irradiation, where it is involved in regulation of radio-sensitivity. The aim of this study is to elucidate the functional role of nuclear EGFR.

MATERIAL AND METHODS

To identify EGFR-bound nuclear proteins and mRNAs, Maldi-TOF analysis and mRNA gene arrays were used. Complex formation of proteins was shown by confocal microscopy, immunoprecipitation and Western blotting. The effect of EGFR binding to mRNAs was exhibited by quantitative RT-PCR. Cellular endpoints were shown by Western blotting, mitochondrial mass quantification, lactate quantification and clonogenic survival assays.

RESULTS

Maldi-TOF analysis of proteins bound to nuclear EGFR in response to irradiation showed colocalization with Lamin A and heterogeneous nuclear ribonucleoproteins. Confocal microscopy and Western blotting confirmed this colocalization. Both Lamin A and heterogeneous nuclear ribonucleoproteins are involved in mRNA processing. To support a role of nEGFR in this context after irradiation, we isolated EGFR-bound mRNA and observed an EGFR kinase-dependent mRNA stabilizing effect. With the help of DNA microarrays, we identified mRNAs associated with the Warburg effect that were bound to nuclear EGFR. In this context, we observed radiation-induced HIF1α expression, which triggers inhibition of pyruvate dehydrogenase and blocks the tricarboxylic acid cycle. Consequently, we detected mitophagy and increased lactate production, which is associated with increased treatment resistance. Reduction of nEGFR decreased radiation-induced expression of Hif1α and lactate production.

CONCLUSIONS

We showed that nuclear EGFR selectively binds and stabilizes mRNA involved in the Warburg effect in response to irradiation. As a consequence, cells switch from aerobic to anaerobic glucose metabolism, which can be prevented by HIF1α inhibitor BAY87-2243, Dasatinib, Erlotinib or EGFR siRNA.

UCP-3 uncoupling protein confers hypoxia resistance to renal epithelial cells and is upregulated in renal cell carcinoma

Tumor cells can adapt to a hostile environment with reduced oxygen supply. The present study aimed to identify mechanisms that confer hypoxia resistance. Partially hypoxia/reoxygenation (H/R)-resistant proximal tubular (PT) cells were selected by exposing PT cultures to repetitive cycles of H/R. Thereafter, H/R-induced changes in mRNA and protein expression, inner mitochondrial membrane potential (ΔΨ_m), formation of superoxide, and cell death were compared between H/R-adapted and control PT cultures. As a result, H/R-adapted PT cells exhibited lower H/R-induced hyperpolarization of ΔΨ_m and produced less superoxide than the control cultures. Consequently, H/R triggered ΔΨ_m break-down and DNA degradation in a lower percentage of H/R-adapted than control PT cells. Moreover, H/R induced upregulation of mitochondrial uncoupling protein-3 (UCP-3) in H/R-adapted PT but not in control cultures. In addition, ionizing radiation killed a lower percentage of H/R-adapted as compared to control cells suggestive of an H/R-radiation cross-resistance developed by the selection procedure. Knockdown of UCP-3 decreased H/R- and radioresitance of the H/R-adapted cells. Finally, UCP-3 protein abundance of PT-derived clear cell renal cell carcinoma and normal renal tissue was compared in human specimens indicating upregulation of UCP-3 during tumor development. Combined, our data suggest functional significance of UCP-3 for H/R resistance.

Opportunities and challenges of radiotherapy for treating cancer

The past 20 years have seen dramatic changes in the delivery of radiation therapy, but the impact of radiobiology on the clinic has been far less substantial. A major consideration in the use of radiotherapy has been on how best to exploit differences between the tumour and host tissue characteristics, which in the past has been achieved empirically by radiation-dose fractionation. New advances are uncovering some of the mechanistic processes that underlie this success story. In this Review, we focus on how these processes might be targeted to improve the outcome of radiotherapy at the individual patient level. This approach would seem a more productive avenue of treatment than simply trying to increase the radiation dose delivered to the tumour.

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.

EGFR-dependent mechanisms in glioblastoma: towards a better therapeutic strategy

Glioblastoma is a particularly resilient cancer, and while therapies may be able to reach the brain by crossing the blood-brain barrier, they then have to deal with a highly invasive tumor that is very resistant to DNA damage. It seems clear that in order to kill aggressive glioma cells more efficiently and with fewer side effects on normal tissue, there must be a shift from classical cytotoxic chemotherapy to more targeted therapies. Since the epidermal growth factor receptor (EGFR) is altered in almost 50% of glioblastomas, it currently represents one of the most promising therapeutic targets. In fact, it has been associated with several distinct steps in tumorigenesis, from tumor initiation to tumor growth and survival, and also with the regulation of cell migration and angiogenesis. However, inhibitors of the EGFR kinase have produced poor results with this type of cancer in clinical trials, with no clear explanation for the tumor resistance observed. Here we will review what we know about the expression and function of EGFR in cancer and in particular in gliomas. We will also evaluate which are the possible molecular and cellular escape mechanisms. As a result, we hope that this review will help improve the design of future EGFR-targeted therapies for glioblastomas.

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 overexpressing cells and tumors are dependent on autophagy for growth and survival

BACKGROUND AND PURPOSE

The epidermal growth factor receptor (EGFR) is overexpressed, amplified or mutated in various human epithelial tumors, and is associated with tumor aggressiveness and therapy resistance. Autophagy activation provides a survival advantage for cells in the tumor microenvironment. In the current study, we assessed the potential of autophagy inhibition (using chloroquine (CQ)) in treatment of EGFR expressing tumors.

MATERIAL AND METHODS

Quantitative PCR, immunohistochemistry, clonogenic survival, proliferation assays and in vivo tumor growth were used to assess this potential.

RESULTS

We show that EGFR overexpressing xenografts are sensitive to CQ treatment and are sensitized to irradiation by autophagy inhibition. In HNSSC xenografts, a correlation between EGFR and expression of the autophagy marker LC3b is observed, suggesting a role for autophagy in EGFR expressing tumors. This observation was substantiated in cell lines, showing high EGFR expressing cells to be more sensitive to CQ addition as reflected by decreased proliferation and survival. Surprisingly high EGFR expressing cells display a lower autophagic flux.

CONCLUSIONS

The EGFR high expressing cells and tumors investigated in this study are highly dependent on autophagy for growth and survival. Inhibition of autophagy may therefore provide a novel treatment opportunity for EGFR overexpressing tumors.