The frequency of micronuclei in lung cancer cell lines and their correlation to intrinsic radiation sensitivity.

BACKGROUND: Micronuclei arise from chromosomal, acentric, fragments or whole chromosomes that are not incorporated into the daughter nuclei at mitosis. The micronuclei assay is technically simple and requires only one mitosis in order to obtain information concerning the amount of micronuclei. This study was performed to investigate whether the formation of micronuclei could be used as a marker for intrinsic radiation sensitivity in lung cancer patients. MATERIALS AND METHODS: Two human lung cancer cell lines, a non-small cell lung cancer (NSCLC) cell line (U-1810) and a small cell lung cancer (SCLC) cell line (U-1906L), were used. Radiosensitivity data on the survival fraction at 2 Gy were obtained from the clonogenic assay. Radiation was delivered as one-fraction doses: 0, 1, 2, 4, 10 and 20 Gy. After irradiation, the cells were incubated for 0, 24, 48, 60, 72 and 96 hours before fixation and staining. RESULTS: The frequency of micronuclei in U-1906L was clearly elevated after 96 hours in the 20 Gy fraction. The frequency of micronuclei reached 5.5%. For U-1810 the micronuclei had a peak clearly different than the other settings after 48 hours in the 10 Gy fraction. The frequency of micronuclei was 1.2%. CONCLUSION: Counting micronuclei is not sensitive enough for estimation of radiosensitivity in clinical doses. However, our results demonstrated a distinct difference between NSCLC and SCLC cell lines at higher doses. This difference might be due to different repair fidelity, so future studies with this assay should aim to investigate this hypothesis.

The in vivo dose rate effect of chronic gamma radiation in mice: translocation and micronucleus analyses.

The in vivo effects of chronic, ultra low dose rates of gamma radiation in mice were evaluated using fluorescence in situ hybridization and the in vivo micronucleus test. SWRxC57BL/6 mice were divided into nine exposure groups and continuously exposed to 0.5, 2.0 or 4.0cGy 137Cs per day for 30, 60 or 90 days; unexposed control mice were also included. Following exposure, blood samples were taken from each animal and the frequencies of micronucleated polychromatic erythrocytes (MPCE) and micronucleated normochromatic erythrocytes (MNCE) were determined using flow cytometry. Peripheral blood lymphocytes were cultured and analyzed by chromosome painting to determine translocation frequencies. A significant dose rate response was seen in translocations and both MPCE and MNCE. Comparisons were made between the three chronic dose rates and it was determined that there was no significant difference among translocation frequencies for each rate. However, a significant difference was found between the chronic exposures reported here and the fractionated daily exposures reported previously. Dose rate reduction effects, ranging from 3 at low doses to 14 at high doses, were found for chronic versus acute exposures. The possibility of gender effects was investigated in both micronucleus and translocation data. No gender effect was found in translocation induction, but a slight effect was suggested in micronucleus induction.