Figure 4. HDACis and spindle checkpoint activation in PCa cells. Simultaneous inhibition of PCa cells with HDACis and colcemid leads to accumulation of cells in mitosis in PC3 cells, but to a time-dependent increase of a sub-G0 population in DU-145 cells. (A) DU-145 and PC3 cells were treated for 18 h with colcemid at a final concentration of 0.1 µg/ml after being released from S-phase (M3). This resulted in mitotic accumulation of PC3 cells (M2), but DU-145 cells exhibited an increased sub-G0 population (M4), indicating cytotoxicity. DU-145 cells were successfully arrested in mitosis with low toxicity at a final concentration of 0.04 µg/ml colcemid. (B) PC3 cells were treated for variable periods with either 9 µM vorinostat alone or a combination of 0.1 µg/ml colcemid with 4 µM vorinostat or 4 mM VPA. Combining HDACis with colcemid resulted in mitotic accumulation of PC3 cells. (C) DU-145 cells were treated for variable periods with either 9 µM vorinostat alone or a combination of 0.04 µg/ml colcemid with 4 µM vorinostat or 4 mM VPA. Combining HDACis with colcemid resulted in a time-dependent increase of a sub-G0 population in DU-145 cells.