The Bcl-2 inhibitor Obatoclax overcomes resistance to histone deacetylase inhibitors SAHA and LBH589 as radiosensitizers in patient-derived glioblastoma stem-like cells
Lotte M.E. Berghauser Pont1, Jochem K.H. Spoor1, Subramanian Venkatesan1, Sigrid Swagemakers2, Jenneke J. Kloezeman1, Clemens M.F. Dirven1, Peter J. van der Spek2, Martine L.M. Lamfers1 and Sieger Leenstra1,3
1 Department of Neurosurgery, Brain Tumor Center, Erasmus MC, Rotterdam, The Netherlands
2 Department of Bio-informatics, Erasmus MC, Rotterdam, The Netherlands
3 Department of Neurosurgery, Elisabeth Medical Hospital, Tilburg, The Netherlands
Correspondence:
Sieger Leenstra, email:
Correspondence:
Martine L.M. Lamfers, email:
Keywords: Bcl-2, Bcl-XL, HDAC inhibitor , SAHA, LBH589, radiation, Obatoclax
Received: August 14, 2014 Accepted: November 22, 2014 Published: November 23, 2014
Abstract
Glioblastoma has shown resistance to histone deacetylase inhibitors (HDACi) as radiosensitizers in cultures with Bcl-XL over-expression. We study the efficacy of SAHA/RTx and LBH589/RTx when manipulating Bcl-2 family proteins using the Bcl-2 inhibitor Obatoclax in patient-derived glioblastoma stem-like cell (GSC) cultures. GSC cultures in general have a deletion in phosphatase and tensin homolog (PTEN). Synergy was determined by the Chou Talalay method. The effects on apoptosis and autophagy were studied by measuring caspase-3/7, Bcl-XL, Mcl-1 and LC3BI/II proteins. The relation between treatment response and O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation status, recurrence and gene expression levels of the tumors were studied. Obatoclax synergized with SAHA and LBH589 and sensitized cells to HDACi/RTx. Over 50% of GSC cultures were responsive to Obatoclax with either single agent. Combined with HDACi/RTx treatment, Obatoclax increased caspase-3/7 and inhibited Bcl-2 family proteins Bcl-XL and Mcl-1 more effectively than other treatments. Genes predictive for treatment response were identified, including the F-box/WD repeat-containing protein-7, which was previously related to Bcl-2 inhibition and HDACi sensitivity. We emphasize the functional relation between Bcl-2 proteins and radiosensitization by HDACi and provide a target for increasing responsiveness in glioblastoma by using the Bcl-2 inhibitor Obatoclax.
