Radiosensitization of pancreatic cancer cells by 2',2'-difluoro-2'-deoxycytidine.
OBJECTIVE
We have reported that the deoxycytidine analog 2',2'difluoro-2'-deoxycytidine (dFdCyd) is a potent radiosensitizer of HT29 human colon cancer cells probably through its effects on intracellular deoxyribonucleotide (dNTP) pools. Because dFdCyd has activity against pancreatic cancer in clinical trials, we wished to determine if dFdCyd would radiosensitize human pancreatic cancer cells.


METHODS
We assessed the effect of dFdCyd on radiation sensitivity of two human pancreatic cancer cell lines, Panc-1 and BxPC-3. To begin to investigate the mechanism of sensitization, we determined the effect of dFdCyd on dNTP pools and cell cycle distribution.


RESULTS
We found that dFdCyd produced radiation enhancement ratios of 1.7-1.8 under noncytotoxic conditions in both cell lines. Sensitization was not associated with intracellular levels of 2',2'-difluoro-2'-deoxycytidine triphosphate, the cytotoxic metabolite of dFdCyd, but occurred when dATP pools were depleted below the level of approximately 1 micromolar. Although both cell lines showed substantial cell cycle redistribution after drug treatment, the flow cytogram of the BxPC-3 cells would not, by itself, be anticipated to result in increased radiation sensitivity.


CONCLUSIONS
These findings demonstrate that dFdCyd is a potent radiation sensitizer of human pancreatic cancer cells and support the development of a clinical protocol using combined dFdCyd and radiation therapy in the treatment of pancreatic cancer.
Lawrence
T S
TS
Department of Radiation Oncology, The University of Michigan Medical Center, Ann Arbor, MI 48109-0582, USA.
Chang
E Y
EY
Hahn
T M
TM
Hertel
L W
LW
Shewach
D S
DS
D000255:Adenosine Triphosphate / Q000378:metabolism; D002453:Cell Cycle / Q000528:radiation effects; D002470:Cell Survival; D003570:Cytidine Triphosphate / Q000378:metabolism; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000627:therapeutic use; D004354:Drug Screening Assays, Antitumor; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D011838:Radiation-Sensitizing Agents / Q000378:metabolism / Q000627:therapeutic use*; D013942:Thymine Nucleotides / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000093542:Gemcitabine
D011838:Radiation-Sensitizing Agents; D013942:Thymine Nucleotides; D003841:Deoxycytidine; D003570:Cytidine Triphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; C024157:thymidine 5'-triphosphate; D000093542:Gemcitabine