title: Ca2+-Activated IK K+ Channel Blockade Radiosensitizes Glioblastoma Cells.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiation Oncology, University of Tübingen, Tübingen, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Stegen
authors.affiliation: Department of Radiation Oncology, University of Tübingen, Tübingen, Germany. Department of Pharmacology, Toxicology and Clinical Pharmacy, Institute of Pharmacy, University of Tübingen, Tübingen, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Butz
authors.affiliation: Department of Radiation Oncology, University of Tübingen, Tübingen, Germany. Dr. Margarete Fischer-Bosch-Institute of Clinical Pharmacology, Stuttgart, Germany.
authors.forename: Lukas
authors.initials: L
authors.lastname: Klumpp
authors.affiliation: Department of Radiation Oncology, University of Tübingen, Tübingen, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Zips
authors.affiliation: Division of Radiobiology and Molecular Environmental Research, Department of Radiation Oncology, University of Tübingen, Tübingen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittmann
authors.affiliation: Department of Pharmacology, Toxicology and Clinical Pharmacy, Institute of Pharmacy, University of Tübingen, Tübingen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Ruth
authors.affiliation: Department of Radiation Oncology, University of Tübingen, Tübingen, Germany. stephan.huber@uni-tuebingen.de.
authors.forename: Stephan M
authors.initials: SM
authors.lastname: Huber
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D018572:Disease-Free Survival; D005260:Female; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D055785:Gene Knockdown Techniques; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D005910:Glioma / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D000077204:Temozolomide
chemical_list: C468783:H2AX protein, human; D006657:Histones; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D011720:Pyrazoles; D012333:RNA, Messenger; D011838:Radiation-Sensitizing Agents; C411671:TRAM 34; D003606:Dacarbazine; D002118:Calcium; D000077204:Temozolomide