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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.

Background Despite aggressive treatment regimens comprising surgery and radiochemotherapy, glioblastoma (GBM) remains a cancer entity with very poor prognosis. The development of novel, combined modality approaches necessitates adequate preclinical model systems and therapy regimens that closely reflect the clinical situation. So far, image-guided, fractionated radiotherapy of orthotopic GBM models represents a major limitation in this regard. Methods GL261 mouse GBM cells were inoculated into the right hemispheres of C57BL/6 mice. Tumor growth was monitored by contrast-enhanced conebeam CT (CBCT) scans. When reaching an average volume of approximately 7 mm3, GBM tumors were irradiated with daily fractions of 2 Gy up to a cumulative dose of 20 Gy in different beam collimation settings. For treatment planning and tumor volume follow-up, contrast-enhanced CBCT scans were performed twice per week. Daily repositioning of animals was achieved by alignment of bony structures in native CBCT scans. When showing neurological symptoms, mice were sacrificed by cardiac perfusion. Brains, livers, and kidneys were processed into histologic sections. Potential toxic effects of contrast agent administration were assessed by measurement of liver enzyme and creatinine serum levels and by histologic examination. Results Tumors were successfully visualized by contrast-enhanced CBCT scans with a detection limit of approximately 2 mm3, and treatment planning could be performed. For daily repositioning of the animals, alignment of bony structures in native CT scans was well feasible. Fractionated irradiation caused a significant delay in tumor growth translating into significantly prolonged survival in clear dependence of the beam collimation setting and margin size. Brain sections revealed tumors of similar appearance and volume on the day of euthanasia. Importantly, the repeated contrast agent injections were well tolerated, as liver enzyme and creatinine serum levels were only subclinically elevated, and liver and kidney sections displayed normal histomorphology. Conclusions Contrast-enhanced, CT-based, fractionated radiation of orthotopic mouse GBM represents a versatile preclinical technique for the development and evaluation of multimodal radiotherapeutic approaches in combination with novel therapeutic agents in order to accelerate translation into clinical testing.

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 xeno graft and a genetic orthotopic Rb mouse model. Methods B6;129-Rb1tm3Tyj/J (Rb +/− ) and Y79-Rb cell- xeno grafted nude mice were fractionated external beam irradiated (15 fractions of 5 Gy 6 MV photons during 3 weeks) with or without pTyr pre-treatment (100 mg/kg BW, 16 h 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 xeno grafted 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 xeno graft model, pTyr treatment reduced the control of Rb tumours.

Oncogenic signalling via Ca2+-activated K+ channels of intermediate conductance (SK4, also known as KCa3.1 or IK) has been implicated in different cancer entities including breast cancer. Yet, the role of endogenous SK4 channels for tumourigenesis 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 promotor MMTV. Survival parameters and tumour progression were studied in cancer-prone SK4 KO in comparison to wildtype (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 tumourigenesis 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 anti-tumour strategies in human breast cancer.

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.

// Lena Edalat 1, 2, * , Benjamin Stegen 2, * , Lukas Klumpp 2, 5 , Erik Haehl 2 , Karin Schilbach 3 , Robert Lukowski 1 , Matthias Kuhnle 4 , Gunther Bernhardt 4 , Armin Buschauer 4 , Daniel Zips 2 , Peter Ruth 1 , Stephan M. Huber 2 1 Department of Pharmacology, Toxicology and Clinical Pharmacy, University of Tubingen, Tubingen, Germany 2 Department of Radiation Oncology, University of Tubingen, Tubingen, Germany 3 Department of General Pediatrics, Oncology/Hematology, University of Tubingen, Tubingen, Germany 4 Department of Pharmaceutical/Medicinal Chemistry II, University of Regensburg, Regensburg, Germany 5 Dr. Margarete Fischer-Bosch-Institute of Clinical Pharmacology, University of Tubingen, Tubingen, Germany * These authors contributed equally to this work Correspondence to: Peter Ruth, e-mail: peter.ruth@uni-tuebingen.de Stephan M. Huber, e-mail: stephan.huber@uni-tuebingen.de Keywords: glioma, radiation therapy, patch-clamp recording, fura-2 Ca2 + imaging, transfilter migration Received: October 20, 2015 Accepted: January 29, 2016 Published: February 16, 2016 ABSTRACT Infiltration of the brain by glioblastoma cells reportedly requires Ca 2+ signals and BK K + channels that program and drive glioblastoma cell migration, respectively. Ionizing radiation (IR) has been shown to induce expression of the chemokine SDF-1, to alter the Ca 2+ signaling, and to stimulate cell migration of glioblastoma cells. Here, we quantified fractionated IR-induced migration/brain infiltration of human glioblastoma cells in vitro and in an orthotopic mouse model and analyzed the role of SDF-1/CXCR4 signaling and BK channels. To this end, the radiation-induced migratory phenotypes of human T98G and far-red fluorescent U-87MG-Katushka glioblastoma cells were characterized by mRNA and protein expression, fura-2 Ca 2+ imaging, BK patch-clamp recording and transfilter migration assay. In addition, U-87MG-Katushka cells were grown to solid glioblastomas in the right hemispheres of immunocompromised mice, fractionated irradiated (6 MV photons) with 5 × 0 or 5 × 2 Gy, and SDF-1, CXCR4, and BK protein expression by the tumor as well as glioblastoma brain infiltration was analyzed in dependence on BK channel targeting by systemic paxilline application concomitant to IR. As a result, IR stimulated SDF-1 signaling and induced migration of glioblastoma cells in vitro and in vivo . Importantly, paxilline blocked IR-induced migration in vivo . Collectively, our data demonstrate that fractionated IR of glioblastoma stimulates and BK K + channel targeting mitigates migration and brain infiltration of glioblastoma cells in vivo . This suggests that BK channel targeting might represent a novel approach to overcome radiation-induced spreading of malignant brain tumors during radiotherapy.

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Neoadjuvant, adjuvant or definitive fractionated radiation therapy are implemented in first line anti-cancer treatment regimens of many tumor entities. Ionizing radiation kills the tumor cells mainly by causing double strand breaks of their DNA through formation of intermediate radicals. Survival of the tumor cells depends on both, their capacity of oxidative defense and their efficacy of DNA repair. By damaging the targeted cells, ionizing radiation triggers a plethora of stress responses. Among those is the modulation of ion channels such as Ca2+-activated K+ channels or Ca2+-permeable nonselective cation channels belonging to the super-family of transient receptor potential channels. Radiogenic activation of these channels may contribute to radiogenic cell death as well as to DNA repair, glucose fueling, radiogenic hypermigration or lowering of the oxidative stress burden. The present review article introduces these channels and summarizes our current knowledge on the mechanisms underlying radiogenic ion channel modulation. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

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.