| Popis: |
The human ovarian carcinoma cell line, A2780s, and its variant, A2780cp, provide an isogenic tumour model for examining factors which determine intrinsic radiosensitivity. A2780s demonstrates sensitivity to ionization radiation while A2780cp is relatively radioresistant (surviving fraction following a 2 Gy dose is 0.083 and 0.43, respectively). The increased radioresistance of A2780cp can not be explained by greater cellular recovery, neither from sublethal nor potentially lethal damage. Moreover, A2780s demonstrates significantly greater (P < 0.05) sublethal and potentially lethal damage recovery than A2780cp. The induction of double strand breaks (dsb), as measured by asymmetric field inversion gel electrophoresis (AFIGE), is identical in these cell lines. Dsb rejoining efficiency is similar between A2780s and A2780cp. Initially, rejoining kinetic experiments reveal that A2780s is deficient in the slow phase of rejoining, while A2780cp is not (80% of dsb remain for A2780s vs 29% A2780cp) (P < 0.01). This deficiency however, is not reproduced in residual dsb experiments and further analysis reveals that it may be an artifact of the normalization process. When the level of residual dsb as a function of dose is examined, the slopes are similar for both cell lines and the only significant difference is seen for the highest dose used, 150 Gy (50% for A2780s and 33% for A2780cp) (P < 0.05). Finally, the cell-free fidelity assay demonstrates that for blunt-cut plasmid, no differences exist in the rejoining efficiency of nuclear extracts. The ligation infidelity of blunt-cut plasmid however, is significantly less (P < 0.05) in A2780cp extracts (0.021 for A2780s vs 0.0030 for A2780cp). Therefore, neither the induction of dsb, nor the efficiency of dsb repair can explain observed differences in radiosensitivity. The fidelity of rejoining however, is significantly greater in the resistant variant and may, in part, explain these differences. |
