Inactivation of p53 in a human ovarian cancer cell line increases the sensitivity to paclitaxel by inducing G2/M arrest and apoptosis

Paclitaxel-induced cytotoxicity, cell cycle perdurbation, and apoptosis were determined in a human ovarian cancer cell Line expressing wt p53 (A2780) and in a subclone (A2780/E6) obtained upon transfection with the product of the E6 gene of the human papilloma virus HPV16. The inactivation of wt p53 in A2780/E6 was verified by measuring the inability of the clone to induce p53 and p21 expression after paclitaxel treatment. The p53-negative clone (A2780/E6) was approximately 50-fold more sensitive to paclitaxel than wt p53-expressing A2780 cells. This increased sensitivity was related to the ability of paclitaxel to induce a strong arrest of cells in the G2/M phase of the cell cycle in A2780/E6 but not in A2780 cells. This different cell cycle arrest was accompanied by increased frequency of paclitaxel-induced p53-independent apoptosis, Initial studies on proteases activation tend to exclude a direct role of ICE: and CPP32 in the induction of apoptosis in these cells and show a paclitaxel-dependent increase in FLICE levels, whose biological relevance is however at present not defined. (C) 1998 Academic Press.