RADIATION-INDUCED DNA-DAMAGE AND DAMAGE REPAIR IN 3 HUMAN TUMOR-CELL LINES

Three human tumour cell lines (HX142, RT112 and MGH-U1) with different radiosensitivities were tested for differences in the rate and/or ext ent of DNA unwinding in alkali as well as for differences in the induc tion of DNA double strand breaks by means of the pulsed field gel elec trophoresis, after X-irradiation. Unlike that which has been found usi ng the non-denaturing filter elution technique (NDE, McMillan et al., 1990), no differences in initial DNA damage (the extent of alkaline un winding and the induction of double strand breaks) were found for the three cell lines. These data suggest that rather than a different numb er of DNA lesions per Da per Gy between these cell lines, structural d ifferences in chromatin structure (related to radiosensitivity) might impair the detectability of lesions in some assays like the NDE. The n ature of such structure differences remains unclear. However, the diff erences did not affect alkaline unwinding profiles, as all three cell lines showed identical rates of DNA unwinding after exposure to X-rays . Furthermore, the three cell lines did not show significant differenc es in the kinetics of DNA strand break rejoining nor in the amounts of damage remaining after 24 h repair. The results obtained in this stud y, together with other findings, suggest that the three cell lines may differ in their 'presentation' of DNA damage.