Cell cycle effect of gemcitabine and its role in the radiosensitizing mechanism in vitro.
OBJECTIVE
The mechanism of radiosensitization by gemcitabine is still unclear. It has been hypothesized that the accumulation of cells in early S phase may play a role in enhancing radiosensitivity.


METHODS
The schedule dependency of the radiosensitizing effect was studied in ECV304, human bladder cancer cells, and H292, human lung cancer cells, by varying the incubation time and time interval between gemcitabine and radiation treatment. To determine the role of cell cycle perturbations in the radiosensitization, the influence of gemcitabine on the cell cycle at the moment of radiation was investigated by flow cytometry.


RESULTS
The radiosensitizing effect increased with a longer incubation period: Dose enhancement factors varied from 1.30 to 2.82 in ECV304 and from 1.04 to 1.78 in H292 after treatment during 8-32 h, respectively. Radiosensitization decreased with an increasing interval: Dose enhancement factors varied from 2.26 to 1.49 in ECV304 and from 1.45 to 1.11 in H292 after an interval 0-24 h, respectively. Cells were blocked in the early S phase of the cell cycle by gemcitabine. The highest percentage S-phase cells was observed after treatment with the schedules that resulted in the highest radiosensitizing effect.


CONCLUSIONS
We observed a clear schedule-dependent radiosensitization by gemcitabine. Our findings demonstrated a correlation between gemcitabine-induced early S-phase block and the radiosensitizing effect.
Laboratory of Cancer Research and Clinical Oncology, Department of Medical Oncology, University of Antwerp (UIA/UZA), Wilrijk, Belgium. pauwels@ua.ac.be
Bea
B
Pauwels
Annelies E C
AE
Korst
Greet G O
GG
Pattyn
Hilde A J
HA
Lambrechts
Dirk R
DR
Van Bockstaele
Katrien
K
Vermeulen
Marc
M
Lenjou
Christel M J
CM
de Pooter
Jan B
JB
Vermorken
Filip
F
Lardon
D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D016196:S Phase; D013997:Time Factors; D000093542:Gemcitabine
D011838:Radiation-Sensitizing Agents; D003841:Deoxycytidine; D000093542:Gemcitabine