Targeting PBK/TOPK decreases growth and survival of glioma initiating cells in vitro and attenuates tumor growth in vivo

Mol Cancer. 2015 Jun 17:14:121. doi: 10.1186/s12943-015-0398-x.


Background: Glioblastomas are invasive therapy resistant brain tumors with extremely poor prognosis. The Glioma initiating cell (GIC) population contributes to therapeutic resistance and tumor recurrence. Targeting GIC-associated gene candidates could significantly impact GBM tumorigenicity. Here, we investigate a protein kinase, PBK/TOPK as a candidate for regulating growth, survival and in vivo tumorigenicity of GICs.

Methods: PBK is highly upregulated in GICs and GBM tissues as shown by RNA and protein analyses. We knocked down PBK using shRNA vectors and inhibited the function of PBK protein with a pharmacological PBK inhibitor, HITOPK-032. We assessed viability, tumorsphere formation and apoptosis in three patient derived GIC cultures.

Results: Gene knockdown of PBK led to decreased viability and sphere formation and in one culture an increase in apoptosis. Treatment of cells with inhibitor HITOPK-032 (5 μM and 10 μM) almost completely abolished growth and elicited a large increase in apoptosis in all three cultures. HI-TOPK-032 treatment (5 mg/kg and 10 mg/kg bodyweight) in vivo resulted in diminished growth of experimentally induced subcutaneous GBM tumors in mice. We also carried out multi-culture assays of cell survival to investigate the relative effects on GICs compared with the normal neural stem cells (NSCs) and their differentiated counterparts. Normal NSCs seemed to withstand treatment slightly better than the GICs.

Conclusion: Our study of identification and functional validation of PBK suggests that this candidate can be a promising molecular target for GBM treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Apoptosis / genetics
  • Cell Line, Tumor
  • Cell Proliferation
  • Cell Survival / drug effects
  • Disease Models, Animal
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Gene Knockdown Techniques
  • Glioblastoma / drug therapy
  • Glioblastoma / genetics
  • Glioblastoma / metabolism*
  • Glioblastoma / pathology*
  • Humans
  • Indolizines / pharmacology
  • Mice
  • Mitogen-Activated Protein Kinase Kinases / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase Kinases / genetics
  • Mitogen-Activated Protein Kinase Kinases / metabolism*
  • Neoplastic Stem Cells / metabolism*
  • Protein Kinase Inhibitors / pharmacology
  • Quinoxalines / pharmacology
  • RNA, Small Interfering / genetics
  • Signal Transduction / drug effects
  • Spheroids, Cellular
  • Tumor Cells, Cultured
  • Xenograft Model Antitumor Assays
  • p38 Mitogen-Activated Protein Kinases / metabolism


  • Indolizines
  • N-(12-cyanoindolizino(2,3-b)quinoxalin-2-yl)thiophene-2-carboxamide
  • Protein Kinase Inhibitors
  • Quinoxalines
  • RNA, Small Interfering
  • Extracellular Signal-Regulated MAP Kinases
  • p38 Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinase Kinases
  • PDZ-binding kinase