Two types of behavior following treatment of human breast cancer cell lines with microtubule-depolymerizing agents. (a) After a 24-hour treatment with 1 μM nocodazole, adherent and nonadherent MDA-MB-468 or MCF-7 cells were combined, stained with Hoechst 33258, and examined by fluorescence microscopy. Note that MDA-MB-468 cells remained in interphase, whereas many MCF-7 cells arrested in mitosis. (b–d) Breast cancer cells (filled triangles, MCF-7; filled circles, HS0578T; open triangles, BT20; open circles, MDA-MB-468) were treated with 1 μM nocodazole (b), 100 nM vincristine (c), or 100 nM paclitaxel (d) for various periods of time. Alternatively, HMECs (e) were treated with these agents for 14 hours, a length of time chosen because this isolate doubled every 16 hours. After adherent and nonadherent cells were combined, the morphology of 300 or more nuclei in each sample was scored by fluorescence microscopy. In b–d, representative individual experiments are shown and the degree of variation is indicated in the text. In e, the mean and range of two experiments are shown. Ctrl, control; Pacl, paclitaxel; Noco, nocodazole; Vin, vincristine.