[Potentiation of radiosensitivity by staurosporine associated with abrogation of G2 phase arrest].
OBJECTIVE
To investigate the radiosensitizing effect and mechanism of action of staurosporine (STP) in human colon carcinoma HT-29 and breast cancer MCF-7/ADR cells.


METHODS
The effect of STP on the cytotoxicity of X-ray was determined by clonogenic assay. The effect of STP on cell cycle arrest induced by X irradiation was studied in two cell lines by using flow cytometry, Western Blotting was performed to indicate the changes of cyclin B1 and cdc2 protein levels.


RESULTS
STP sensitized the two cell lines to X-ray by clonogenic assay. STP potentiated the cytotoxicity of X-ray by 2.10- and 2.09-fold in HT-29 and MCF-7/ADR cells. Flow cytometry assay showed that exposure of HT-29 and MCF-7/ADR cells to X-ray caused cells arrest in G2 phase. The percentage of arrest G2 phase cells were 56% and 52.7%, respectively. The addition of STP after irradiation resulted in a dose-dependent reduction of G2 phase arrest induced by X-ray. Furthermore, the results showed that STP blocked decrease of cyclin B1 expression induced by X-ray, while mitotic index measurement indicated that X-ray-irradiated cells treated with STP entered mitosis. The data suggested that the potentiation of cytotoxicity of X-ray by STP is associated with the suppression of cyclin B1 expression, which result in the abrogation of G2 arrest, before the cells entered into M phase, they had not enough time to repair.


CONCLUSIONS
STP is a potent G2 checkpoint abrogator and markedly enhanced the cytotoxicity of X irradiation in the p53 mutant cancer cells.
Sun
Xin-chen
XC
Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100050, China.
Wang
Jun-jie
JJ
Zhen
Yong-su
YS
Shao
Rong-guang
RG
D001943:Breast Neoplasms / Q000473:pathology; D019926:Cyclin B / Q000096:biosynthesis; D056744:Cyclin B1; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D016195:G2 Phase / Q000187:drug effects*; D019073:HT29 Cells; D006801:Humans; D008940:Mitotic Index; D010315:Particle Accelerators; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D019311:Staurosporine / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; D004791:Enzyme Inhibitors; D011838:Radiation-Sensitizing Agents; D019311:Staurosporine