EZH2 Downregulation Augments the Effect of Irradiation in Reducing Pancreatic Cancer Cell Proliferation in vitro

Ann Clin Lab Sci. 2020 Jan;50(1):45-56.


Objective: Pancreatic ductal carcinoma has a 5-year survival rate of 9%. This makes it the 4th leading cause of cancer-related death in the United States. Advanced-stage diagnosis and limited treatment options contribute to poor prognosis. Thus, there is an urgent need for new approaches to treatment. Enhancer of Zeste 2 (EZH2), a catalytic subunit of the multi-protein histone methyltransferase, known as the polycomb repressive complex, has been implicated in carcinogenesis. E2H2's downregulation has been shown to have a therapeutic effect in B cell lymphomas.

Materials and methods: We examined the effect of EZH2 downregulation in combination with irradiation on the proliferation and apoptosis of pancreatic cancer cells (PANC-1 and MIA PaCa-2) in vitro. EZH2 downregulation was accomplished by treatment of cells with small interfering RNA (siRNA) or EPZ. To do this, cell survival was assessed over a 96 hr (short-term) by ATP measurement and immunohistochemical assessment of Phosphohistone 3 (PHH3), Ki-67 and CC3 over two weeks (long-term) by clonogenic assay.

Results: EZH2 downregulation resulted in the decreased proliferation of PANC-1 and MIA PaCa-2 cells within short-term assays with maximal reduction at 72 hr. Irradiation reduced cell proliferation beginning at 96 hr and continued over the long-term. Irradiation with EZH2 downregulation reduced cell proliferation between 48 and 72 hr. This combined treatment reduced cell proliferation by 3 to 14% as compared to those treated with irradiation alone at two weeks. PANC-1 and MIA PaCa-2 cells exhibited similar responses to EZH2 downregulation and irradiation, but to different degrees. siRNA or EPZ were equally effective in EZH2 downregulation.

Conclusions: EZH2 downregulation in combination with irradiation reduces PANC-1 and MIA PaCa-2 cell proliferation more than irradiation alone. This study affirms the role of EZH2 downregulation for radiosensitization in pancreatic cancer treatment.

Keywords: EPZ-6438; EZH2; MIA PaCa-2; PANC-1; irradiation; pancreatic cancer; siRNA.

MeSH terms

  • Apoptosis
  • Cell Proliferation*
  • Enhancer of Zeste Homolog 2 Protein / antagonists & inhibitors*
  • Enhancer of Zeste Homolog 2 Protein / genetics
  • Enhancer of Zeste Homolog 2 Protein / metabolism
  • Gamma Rays
  • Humans
  • In Vitro Techniques
  • Pancreatic Neoplasms / metabolism
  • Pancreatic Neoplasms / pathology
  • Pancreatic Neoplasms / radiotherapy*
  • RNA, Small Interfering / genetics*
  • Tumor Cells, Cultured


  • RNA, Small Interfering
  • EZH2 protein, human
  • Enhancer of Zeste Homolog 2 Protein