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Oncotarget. 2018 Jan 8;9(12):10497-10509. doi: 10.18632/oncotarget.24041. eCollection 2018 Feb 13.

The polo-like kinase 1 inhibitor volasertib synergistically increases radiation efficacy in glioma stem cells.

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Department of Neuro-Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Institute of Biosciences and Technology, Texas A&M Health Science Center at Houston, Center for Translational Cancer Research, Houston, TX, USA.
Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Department of Genomic Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Department of Bioinformatics and Computational Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
The Jackson Laboratory for Genomic Medicine, Farmington, CT, USA.
Contributed equally



Despite the availability of hundreds of cancer drugs, there is insufficient data on the efficacy of these drugs on the extremely heterogeneous tumor cell populations of glioblastoma (GBM).


The PKIS of 357 compounds was initially evaluated in 15 different GSC lines which then led to a more focused screening of the 21 most highly active compounds in 11 unique GSC lines using HTS screening for cell viability. We further validated the HTS result with the second-generation PLK1 inhibitor volasertib as a single agent and in combination with ionizing radiation (IR). In vitro studies showed that volasertib inhibited cell viability, and high levels of the anti-apoptotic protein Bcl-xL expression were highly correlated with volasertib resistance. Volasertib sensitized GSCs to radiation therapy by enhancing G2/M arrest and by inducing apoptosis. Colony-formation assay demonstrated that volasertib plus IR synergistically inhibited colony formation. In intracranial xenograft mouse models, the combination of volasertib and radiation significantly inhibited GSC tumor growth and prolonged median survival compared with radiation treatment alone due to inhibition of cell proliferation, enhancement of DNA damage, and induction of apoptosis.


Our results reinforce the potential therapeutic efficacy of volasertib in combination with radiation for the treatment of GBM.


We used high-throughput screening (HTS) to identify drugs, out of 357 compounds in the published Protein Kinase Inhibitor Set, with the greatest efficacy against a panel of glioma stem cells (GSCs), which are representative of the classic cancer genome atlas (TCGA) molecular subtypes.


glioblastoma; polo-like kinase 1; radiation; sensitization; volasertib

Conflict of interest statement

CONFLICTS OF INTEREST John de Groot is consulting/advisory board member for Genentech, Novartis, Celldex, VBL Therapeutics, Celldex, Deciphera Pharmaceuticals and MundiPharma.

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