[Mechanistic study of radiosensitization by gemcitabine on human squamous carcinoma cell line of the cervix].
OBJECTIVE
To investigate whether gemcitabine (dFdC) at the non-cytotoxic concentration enhances the effect of irradiation on human squamous carcinoma cells of the uterine cervix (HeLa) in vitro, and to evaluate the mechanism by which dFdC at the non-cytotoxic concentration [24 h 10% inhibiting concentration (IC(10))] is able to enhance radiation-induced cytotoxicity to HeLa in vitro.


METHODS
The non-cytotoxic concentration (24 h IC(10)) of dFdC was determined by methyl thiazolyl tetrazolium (MTT). After exposure to the non-cytotoxic concentration (0.01 micro mol/L) for 4, 8, 12 and 24 hours followed by immediate irradiation (4, 6 and 8 Gy), the surviving fraction was counted and the radiation enhancement ratio (RER) was evaluated. Cell cycle distribution and apoptosis were analyzed by flow cytometry. The expressions of p53, bcl-2 and bax were studied by western blot.


RESULTS
After exposure to non-cytotoxic concentration (0.01 micro mol/L) for 4, 8, 12 and 24 hours followed by immediate irradiation, the RER was 1.19, 1.35, 1.72 and 1.93, respectively. After exposed to dFdC, HeLa cells showed an S phase block. The proportion of S phase cells was elevated with the increase of exposure duration (P < 0.01). The S-phase proportion increased to 51.8% at 24 hours of exposure. Meanwhile, compared with the single-agent treatments, combination of dFdC and radiation did not additionally increase the number of apoptotic cells and expression of proteins related to apoptosis such as p53, bcl-2 and bax (P > 0.05).


CONCLUSIONS
HeLa cells were radiosensitive at IC(10) concentration of dFdC. The radiosensitization effect depends on the exposure duration to dFdC. There appears a strong association between the radiosensitization and the progression of cells into S-phase after dFdC treatment. Combination of dFdC and radiation did not increase apoptosis of HeLa cells.
Miao
Jin-wei
JW
Department of Oncology, Affiliated Beijing Obstetrics and Gynecology Hospital, Capital University of Medical Sciences, Beijing 100006, China.
Kong
Wei-min
WM
Zhang
Wei-hua
WH
Niu
Ju-wei
JW
Deng
Xiao-hong
XH
D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects* / Q000528:radiation effects; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005434:Flow Cytometry; D006367:HeLa Cells; D006801:Humans; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000093542:Gemcitabine
D011838:Radiation-Sensitizing Agents; D016159:Tumor Suppressor Protein p53; D003841:Deoxycytidine; D000093542:Gemcitabine