Cell cycle perturbations in cisplatin-sensitive and resistant human ovarian carcinoma cells following treatment with cisplatin and low dose rate irradiation.

Abstract

To investigate cell cycle pertubations in plateau-phase human ovarian carcinoma cells following treatment with cisplatin, low dose-rate irradiation (LDRI), or combined cisplatin and LDRI, in order to understand cell cycle mechanisms by which these two treatment modalities interact. Human ovarian carcinoma cells sensitive (A2780) and resistant (2780CP) to cisplatin were grown to plateau phase and given protracted cisplatin treatments (A2780 0.7 and 2 microg/ml; 2780CP 5 and 15 microg/ml) and/or LDRI (0.41 cGy/min). Cell cycle distribution following treatment was determined by two-parameter flow cytometry, based on bromodeoxyuridine (BrdU) uptake and DNA content using propidium iodide staining. The cisplatin-sensitive A2780 cells exposed to cisplatin alone for up to 28 h showed depletion of the G1 fraction and accumulation in S-phase, although the percentage of S-phase cells actively incorporating BrdU dropped to almost zero. The cisplatin-resistant 2780CP cells exposed to cisplatin alone showed a G1 arrest when exposed to 15 microg/ml, but not when exposed to 5 microg/ml. LDRI alone caused little cell cycle redistribution different from controls in either cell line. When LDRI was combined with cisplatin, no significant cell cycle redistribution was observed, apart from a decline in the actively incorporating S-phase fraction. Cisplatin caused A2780 cells to accumulate in nonincorporating S-phase, with no evidence of G1 arrest. Cisplatin-resistant 2780CP cells showed a G1 block when exposed to a high enough cisplatin concentration. This could indicate a mechanism of cisplatin resistance in these cells. LDRI alone or in combination with cisplatin did not result in significant cell cycle redistribution.