Figure 6. Combined effects of Chk1 inhibition and cisplatin on tetraploid tumor cells in vitro and in vivo.

A. Cytotoxic effects of Chk1 depletion in combination with cisplatin. Diploid (D) and tetraploid (T) HCT116 cells were knocked down for Chk1 (or transfected with control siRNA SCR) for 24 h and then cultured in absence or presence of cisplatin (20 µM) for further 48 h. Finally, the frequency of dying (DiOC₆(3)^low PI⁻) or dead (DiOC₆(3)^low PI⁺) cells was monitored by DiOC₆(3)/PI staining. B. Cell killing by pharmacological inhibition of Chk1 plus cisplatin. Cells were cultured with cisplatin (20 µM), UCN-01 (500 nM) and/or SD1825 (500 nM) for 48 h, and dead and dying cells were determined as in A. C–E. Combined effects of Chk1 inhibition and cisplatin on tetraploid tumors established in vivo. Diploid or tetraploid HCT116 tumors were established in vivo and their growth was monitored continuously from day 18 (when tumors measured 125 to 250 mm³), when animals were injected with PBS alone (controls in C), cisplatin (D), UCN-01 (E), or with a combination of both (F). Asterisks indicate significant differences between diploid and tetraploid cells (p<0.05, unpaired Student t test). The results shown in Fig. 6C–E are representative for three different experiments.