Variation in sensitizing effect of caffeine in human tumour cell lines after gamma-irradiation.
OBJECTIVE
We have investigated whether the protective role of the G2 checkpoint has increasing importance when the p53-dependent G1 checkpoint is inactivated.


METHODS
We have studied the differential effect of caffeine by clonogenic assays and flow cytometry in three human tumour cell lines with different functionality of p53 protein.


RESULTS
The radiosensitizing effect of caffeine (2 mM) expressed itself as a significant decrease in surviving fraction at 2 Gy and a significant increase in alpha-values in RT112 and TE671, both with non-functional p53. However, no radiosensitizing effect was seen in cells with a normal p53 function (MCF-7 BUS). Two millimoles of caffeine also caused important changes in the cell cycle progression after irradiation. MCF-7 BUS showed a G1 arrest after irradiation and an early G2 arrest but those cells that reached the second G2 did not arrest significantly. In contrast, TE671 exhibited radiosensitization by caffeine, no G1 arrest, a G2 arrest in those cells irradiated in G2, no significant accumulation in the second G2 but an overall delay in release from the first cell cycle, which could be abrogated by caffeine. RT112 was similar to TE671 except that the emphasis in a G2 arrest was shifted from the block in cells irradiated in G2 to those irradiated at other cell cycle phases.


CONCLUSIONS
The data presented confirm that p53 status can be a significant determinant of the efficacy of caffeine as radiosensitizer in these tumour cell lines, and document the importance of the G2 checkpoint in this effect.
Valenzuela
M T
MT
Laboratoio de Investigaciones Médicas y Biología Tumoral, Departamento de Radiología y Medicina Física, Facultad de Medicina, Universidad de Granada, 18071, Granada, Spain.
Mateos
S
S
Ruiz de Almodóvar
J M
JM
McMillan
T J
TJ
D001943:Breast Neoplasms / Q000473:pathology; D002110:Caffeine / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D016193:G1 Phase / Q000187:drug effects / Q000528:radiation effects; D016195:G2 Phase / Q000187:drug effects / Q000528:radiation effects; D005720:Gamma Rays; D006801:Humans; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D012208:Rhabdomyosarcoma / Q000473:pathology; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000473:pathology
D011838:Radiation-Sensitizing Agents; D016159:Tumor Suppressor Protein p53; D002110:Caffeine