TY - JOUR
T1 - Improvement of esophageal adenocarcinoma cell and xenograft responses to radiation by targeting cyclin-dependent kinases
AU - Raju, Uma
AU - Ariga, Hisanori
AU - Koto, Masashi
AU - Lu, Xueguan
AU - Pickett, Jessica
AU - Valdecanas, David
AU - Mason, Kathryn A.
AU - Milas, Luka
N1 - Funding Information:
This work was supported by Esophageal Cancer MRP grant, The University of Texas M.D. Anderson Cancer Center and Aventis Pharmaceuticals.
PY - 2006/8
Y1 - 2006/8
N2 - Background and Purpose: Concurrent chemo-radiotherapy before surgery is standard treatment protocol for esophageal cancer with a less than 30% complete response due to resistance to therapy. The aim of this study was to determine whether molecular targeting approach using an inhibitor of cyclin-dependent kinases, flavopiridol, can help overcome the resistance to radiotherapy. Materials and Methods: SEG-1 cells (human esophageal adenocarcinoma) were exposed to γ-rays with and without flavopiridol treatment and assayed for clonogenic survival, apoptosis, cell cycle distribution, and Western blot analysis. Efficacy of flavopiridol in enhancing tumor response to radiation was determined by tumor growth delay assay using SEG-1 tumor xenografts generated in nude mice. Results: The clonogenic cell survival assay data showed that flavopiridol (300 nM, 24 h), when given either before or after radiation, significantly enhanced the radiosensitivity of SEG-1 cells. The cells were accumulated at G1 phase of the cell cycle by flavopiridol that was associated with downregulation of p-cdk-1, p-cdk-2, cyclin D1 and p-Rb expression. Flavopiridol by itself induced apoptosis in SEG-1 cells and also enhanced the radiation-induced apoptosis, associated with an increase in cleaved poly ADP-ribose polymerase. Reduction in phosphorylation of RNA polymerase II by flavopiridol suggested that flavopiridol inhibited the transcriptional activity. In vivo studies with SEG-1 tumor xenografts showed that flavopiridol, either given before or after radiation, greatly enhanced the effect of tumor irradiation. Conclusions: Flavopiridol treatment significantly enhanced SEG-1 cell radiosensitivity as well as the radioresponse of SEG-1 tumor xenografts. The underlying mechanisms are multiple, including cell cycle redistribution, apoptosis, and transcriptional inhibition. These preclinical data suggest that flavopiridol has the potential to increase the radioresponse of esophageal adenocarcinomas.
AB - Background and Purpose: Concurrent chemo-radiotherapy before surgery is standard treatment protocol for esophageal cancer with a less than 30% complete response due to resistance to therapy. The aim of this study was to determine whether molecular targeting approach using an inhibitor of cyclin-dependent kinases, flavopiridol, can help overcome the resistance to radiotherapy. Materials and Methods: SEG-1 cells (human esophageal adenocarcinoma) were exposed to γ-rays with and without flavopiridol treatment and assayed for clonogenic survival, apoptosis, cell cycle distribution, and Western blot analysis. Efficacy of flavopiridol in enhancing tumor response to radiation was determined by tumor growth delay assay using SEG-1 tumor xenografts generated in nude mice. Results: The clonogenic cell survival assay data showed that flavopiridol (300 nM, 24 h), when given either before or after radiation, significantly enhanced the radiosensitivity of SEG-1 cells. The cells were accumulated at G1 phase of the cell cycle by flavopiridol that was associated with downregulation of p-cdk-1, p-cdk-2, cyclin D1 and p-Rb expression. Flavopiridol by itself induced apoptosis in SEG-1 cells and also enhanced the radiation-induced apoptosis, associated with an increase in cleaved poly ADP-ribose polymerase. Reduction in phosphorylation of RNA polymerase II by flavopiridol suggested that flavopiridol inhibited the transcriptional activity. In vivo studies with SEG-1 tumor xenografts showed that flavopiridol, either given before or after radiation, greatly enhanced the effect of tumor irradiation. Conclusions: Flavopiridol treatment significantly enhanced SEG-1 cell radiosensitivity as well as the radioresponse of SEG-1 tumor xenografts. The underlying mechanisms are multiple, including cell cycle redistribution, apoptosis, and transcriptional inhibition. These preclinical data suggest that flavopiridol has the potential to increase the radioresponse of esophageal adenocarcinomas.
KW - Cdks
KW - Flavopiridol
KW - Radiosensitization
KW - SEG-1
KW - Tumor xenografts
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U2 - 10.1016/j.radonc.2006.07.027
DO - 10.1016/j.radonc.2006.07.027
M3 - Article
C2 - 16905211
AN - SCOPUS:33748048523
SN - 0167-8140
VL - 80
SP - 185
EP - 191
JO - Radiotherapy and Oncology
JF - Radiotherapy and Oncology
IS - 2
ER -