Effect of Halogenated Pyrimidines on Radiosensitivity of Mouse Strain L Cells and Their Radioresistant Variant

Incorporation of halogen analogs of pyrimidine into DNA of the mouse strain L cells enhanced their sensitivity to X-ray irradiation. The maximal radiosensitization was obtained either with 72 hours, incubation in the presence of BUdR alone or 24 hours' incubation in the presence of BUdR and aminopterin before X-ray irradiation. The replacement of thymidine by BUdR in these optimal conditions was approximately 30 %, and a further increase of the replacement up to 50% did not intensify the radio-sensitization. These results may support the view that BU-labeling of single strand of DNA double helix is sufficient to confer significant radiosensitization. The radiosensitivity of the resistant Lγ cells was restored by BUdR incorporation up to the same level as that of untreated original cells. These observations would contribute to some extent towards the improvement of radiation therapy.