Radiation rendered more cytotoxic by fludarabine monophosphate in a human oropharynx carcinoma cell-line than in fetal lung fibroblasts.
OBJECTIVE
Fludarabine monophosphate (fludarabine-P) is a relatively new drug in the treatment of different haematological diseases. The mechanism of action also implies a possible role of this drug as a radiosensitizer. Up to now no in vitro investigations dealing with radiosensitizing effects of fludarabine-P in carcinoma cell lines and fibroblasts have been published. The aim of our studies was to analyse the cytotoxic and radiosensitizing effects of different dosages and application schedules of fludarabine-P in a human squamous carcinoma cell line of the oropharynx (ZMK-1) and of fetal lung fibroblasts (MRC-5) in vitro. Possible mechanisms of interaction of fludarabine-P and radiation were investigated.


METHODS
ZMK-1 and MRC-5 cells were cultured under standard conditions with different concentrations of fludarabine-P in combination with escalating doses of radiation. Cytotoxic effects were measured by colony-forming assays. Induction and rejoining of radiation-induced DNA double-strand breaks after incubation with fludarabine-P were measured using constant-field gel electrophoresis. Incubation times for rejoining varied from 0 h to 24 h.


RESULTS
Fludarabine-P showed a radiosensitizing activity in ZMK-1 tumour cells and MRC-5 fibroblasts. The observed effects depended on the concentration and the incubation time. The largest effect was demonstrable for an incubation of 5 days, which started shortly before irradiation, whereas an incubation solely before irradiation did not have a clear effect on the cellular survival. The sensitizer enhancement ratio, at the 10% survival level, in the ZMK-1 cells was 2.2 in comparison to 1.6 in MRC-5 cells. The analysis of the interaction of fludarabine-P and ionising radiation by means of the isobologram approach, revealed an overadditive effect in the tumour cell line and an additive effect in the lung fibroblasts. Fludarabine-P did not modify the rejoining of radiation-induced DNA double-strand breaks in either cell line.


CONCLUSIONS
We conclude that fludarabine-P in clinically attainable doses is a strong radiosensitizer in ZMK-1 cells and has a lower activity in the MRC-5 fibroblasts in vitro. The radiosensitization of fludarabine-P seems to be over additive in the malignant cells and additive in normal fetal fibroblasts. This would indicate that fludarabine-P might enhance the therapeutic ratio of radiation. Further investigations are warranted to identify the potential of this drug as a radiosensitizer in vivo and to elucidate the mechanism of interaction of the drug and radiation.
Laurent
D
D
Department of Radiotherapy and Radiooncology, University Clinic of Göttingen, Germany.
Pradier
O
O
Schmidberger
H
H
Rave-Fränk
M
M
Frankenberg
D
D
Hess
C F
CF
D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000532:radiotherapy; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005333:Fetus / Q000166:cytology; D005347:Fibroblasts / Q000187:drug effects* / Q000528:radiation effects*; D006801:Humans; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D009959:Oropharyngeal Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects; D001084:Vidarabine Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology
D011838:Radiation-Sensitizing Agents; D001084:Vidarabine Phosphate; C042382:fludarabine phosphate