title: Loss of G2/M arrest correlates with radiosensitization in two human sarcoma cell lines with mutant p53.
abstract: 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.
authors: Department of Radiotherapy, Martin-Luther-University of Halle-Wittenberg, Halle/Saale, Germany.
authors: M
authors: M
authors: Bache
authors: S
authors: S
authors: Pigorsch
authors: J
authors: J
authors: Dunst
authors: P
authors: P
authors: Würl
authors: A
authors: A
authors: Meye
authors: F
authors: F
authors: Bartel
authors: H
authors: H
authors: Schmidt
authors: F W
authors: FW
authors: Rath
authors: H
authors: H
authors: Taubert
mesh_terms: 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
chemical_list: 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