Loss of G2/M arrest correlates with radiosensitization in two human sarcoma cell lines with mutant p53.
We have examined the modulation of radiosensitivity by using caffeine in two human sarcoma cell lines both with a p53 mutation (US8-93 and LMS6-93). In both cell lines a strong irradiation-induced G2/M arrest was coupled with a low rate of apoptosis. Incubation with caffeine resulted in a low percentage of S and G2/M cells, associated with an accumulation in G1. With a higher caffeine concentration, we detected a lower clonogenic survival with IC(50) at 2 mM. In both cell lines incubation with caffeine completely prevents the irradiation-induced G2/M arrest. This was connected to radiosensitization, but without direct correlation to an induction of apoptosis. The effect of radiosensitization rose with higher irradiation doses. However, in comparison with LMS6-93, it was stronger in cell line US8-93. A higher radiosensitization in US8-93 correlated with the prevention of strong irradiation-induced G2/M response and higher initial DNA damage. Results of Western hybridization reveal a p53-independent mechanism of radiosensitization caused by caffeine. Our findings suggest that modulation in G2/M regulation may affect a common checkpoint for tumor cells with defective p53 function. Furthermore, our results show that the enhancer effect of caffeine is dependent on a strong reduction in the number of G2/M arrested cells and on an inhibition of DNA damage repair after irradiation.
Bache
M
M
Department of Radiotherapy, Martin-Luther-University of Halle-Wittenberg, Halle/Saale, Germany.
Pigorsch
S
S
Dunst
J
J
Würl
P
P
Meye
A
A
Bartel
F
F
Schmidt
H
H
Rath
F W
FW
Taubert
H
H
D000230:Adenocarcinoma / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D000483:Alleles; D017209:Apoptosis; D015153:Blotting, Western; D002110:Caffeine / Q000494:pharmacology; D002470:Cell Survival; D003131:Combined Modality Therapy; D020552:Comet Assay; D004249:DNA Damage / Q000528:radiation effects; D018572:Disease-Free Survival; D004307:Dose-Response Relationship, Radiation; D016195:G2 Phase; D016158:Genes, p53; D006801:Humans; D020128:Inhibitory Concentration 50; D008297:Male; D008938:Mitosis; D009154:Mutation; D009687:Nuclear Proteins; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D017430:Prostate-Specific Antigen / Q000096:biosynthesis; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D011836:Radiation Tolerance; D011878:Radiotherapy / Q000379:methods*; D012008:Recurrence; D012307:Risk Factors; D016879:Salvage Therapy; D012509:Sarcoma / Q000235:genetics* / Q000532:radiotherapy*; D012680:Sensitivity and Specificity; D013997:Time Factors; D014407:Tumor Cells, Cultured
D009687:Nuclear Proteins; D010726:Phosphodiesterase Inhibitors; D011518:Proto-Oncogene Proteins; D002110:Caffeine; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D017430:Prostate-Specific Antigen