Flavopiridol potentiates the cytotoxic effects of radiation in radioresistant tumor cells in which p53 is mutated or Bcl-2 is overexpressed.
OBJECTIVE
Loss of the cell-cycle regulatory protein p53 or overexpression of the antiapoptotic protein Bcl-2 is associated with resistance to radiation in several types of cancer cells. Flavopiridol, a synthetic flavone, inhibits the growth of malignant tumors cells in vitro and in vivo through multiple mechanisms. The purpose of the present study is to clarify whether flavopiridol enhances the cytotoxic effects of radiation in tumor cells that contain dysfunction p53 or that overexpress Bcl-2.


METHODS
A human glioma cell line (A172/mp53) stably transfected with a plasmid containing mutated p53 and a human cervical cancer cell line (HeLa/bcl-2) transfected with a bcl-2 expression plasmid were used. Cells were incubated with flavopiridol for 24 h after radiation, and then cell viability was determined by a colony formation assay. Foci of phosphorylated histone H2AX were also evaluated as a sensitive indicator of DNA double-strand breaks.


RESULTS
Compared with the parental wild-type cells, both transfected cell lines were more resistant to radiation. Post-treatment with flavopiridol increased the cytotoxic effects of radiation in both transfected cell lines, but not in their parental wild-type cell lines. Post-treatment with flavopiridol inhibited sublethal damage repair as well as the repair of DNA double-strand breaks in response to radiation.


CONCLUSIONS
Flavopiridol enhanced the cytotoxic effect of radiation in radioresistant tumor cells that harbor p53 dysfunction or Bcl-2 overexpression. A combination treatment of flavopiridol with radiation has the potential to conquer the radioresistance of malignant tumors induced by the genetic alteration of p53 or bcl-2.
Hara
Takamitsu
T
Department of Radiology, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama City, Japan.
Omura-Minamisawa
Motoko
M
Kang
Yun
Y
Cheng
Chao
C
Inoue
Tomio
T
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D005419:Flavonoids / Q000494:pharmacology*; D019254:Genes, bcl-2; D016158:Genes, p53 / Q000235:genetics; D005910:Glioma / Q000378:metabolism / Q000532:radiotherapy; D006367:HeLa Cells; D006801:Humans; D010880:Piperidines / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011836:Radiation Tolerance / Q000187:drug effects* / Q000235:genetics; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014162:Transfection; D014410:Tumor Stem Cell Assay; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D002583:Uterine Cervical Neoplasms / Q000378:metabolism / Q000532:radiotherapy
D000970:Antineoplastic Agents; D005419:Flavonoids; D010880:Piperidines; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D016159:Tumor Suppressor Protein p53; C077990:alvocidib