Protein phosphatase 2A inhibition enhances radiation sensitivity and reduces tumor growth in chordoma

Neuro Oncol. 2018 May 18;20(6):799-809. doi: 10.1093/neuonc/nox241.


Background: Standard therapy for chordoma consists of surgical resection followed by high-dose irradiation. Protein phosphatase 2A (PP2A) is a ubiquitously expressed serine/threonine phosphatase involved in signal transduction, cell cycle progression, cell differentiation, and DNA repair. LB100 is a small-molecule inhibitor of PP2A designed to sensitize cancer cells to DNA damage from irradiation and chemotherapy. A recently completed phase I trial of LB100 in solid tumors demonstrated its safety. Here, we show the therapeutic potential of LB100 in chordoma.

Methods: Three patient-derived chordoma cell lines were used: U-CH1, JHC7, and UM-Chor1. Cell proliferation was determined with LB100 alone and in combination with irradiation. Cell cycle progression was assessed by flow cytometry. Quantitative γ-H2AX immunofluorescence and immunoblot evaluated the effect of LB100 on radiation-induced DNA damage. Ultrastructural evidence for nuclear damage was investigated using Raman imaging and transmission electron microscopy. A xenograft model was established to determine potential clinical utility of adding LB100 to irradiation.

Results: PP2A inhibition in concert with irradiation demonstrated in vitro growth inhibition. The combination of LB100 and radiation also induced accumulation at the G2/M phase of the cell cycle, the stage most sensitive to radiation-induced damage. LB100 enhanced radiation-induced DNA double-strand breaks. Animals implanted with chordoma cells and treated with the combination of LB100 and radiation demonstrated tumor growth delay.

Conclusions: Combining LB100 and radiation enhanced DNA damage-induced cell death and delayed tumor growth in an animal model of chordoma. PP2A inhibition by LB100 treatment may improve the effectiveness of radiation therapy for chordoma.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Apoptosis
  • Biomarkers, Tumor / metabolism*
  • Bridged Bicyclo Compounds, Heterocyclic / pharmacology*
  • Cell Movement
  • Cell Proliferation
  • Chordoma / drug therapy*
  • Chordoma / enzymology
  • Chordoma / pathology*
  • Female
  • Humans
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • Neoplasm Invasiveness
  • Piperazines / pharmacology*
  • Protein Phosphatase 2 / antagonists & inhibitors*
  • Radiation Tolerance / drug effects*
  • Signal Transduction
  • Tumor Cells, Cultured
  • Xenograft Model Antitumor Assays


  • Biomarkers, Tumor
  • Bridged Bicyclo Compounds, Heterocyclic
  • LB100
  • Piperazines
  • Protein Phosphatase 2