ACTIVATED CELL-CYCLE CHECKPOINTS IN EPIRUBICIN-TREATED BREAST-CANCER CELLS STUDIED BY BRDURD-FLOW CYTOMETRY

Genetic alterations, such as p53 mutations, may affect a tumour's resp onse to chemotherapy, We have treated. two human breast cancer cell li nes that differ in p53 status with epirubicin in order to study if the re are differences Ln cell cycle kinetic response. MCF-7 cells express wild-type p53, while SK-BR-3 cells express only a mutated form of p53 . The transition of cells from one cell cycle stage to another was stu died by a bromodeoxyuridine (BrdUrd)-flow cytometry (FCM) method. MCF- 7 cells showed a block in the G(1) phase after treatment with 50 nM ep irubicin for 24 hours, in agreement with the actions of p53 at the G(1 ) checkpoint. SK-BR-S cells, on the other hand, progressed through the G(1) checkpoint and were blocked in late S and G(2) phases, presumabl y due to the activation of a later checkpoint, In addition, studies of the mRNA levels of p53 and its effector gene p21 revealed that althou gh both cell lines expressed p53 mRNA, a marked difference in the mRNA levels of p21 was seen. A dramatic increase in the level of p21 mRNA was seen in epirubicin-treated MCF-7 cells, while no such increase was seen in SK-BR-3 cells. (C) 1997 Wiley-Liss, Inc.