Figure 4.

Mcl-1 inhibition overcomes intrinsic and acquired resistance to regorafenib in xenograft tumors. (A) Nude mice were injected s.c. with 4 × 10⁶ parental HCT116, Mcl-1-KI or HCT116-R cells. After tumor volume reached ~60 mm³, mice were treated with regorafenib (oral gavage; 20 mg/kg) alone or in combination with S63845 (i.p.; 20 mg/kg) as indicated. Tumor volume at indicated time points after treatment was calculated and plotted (n=6 in each group). (B) Representative pictures of tumors at the end of the experiment in A. (C) Xenograft tumors established and treated as in A for 4 consecutive days were randomly selected and analyzed for Mcl-1 by Western blotting. (D) and (E), Paraffin-embedded sections of tumor tissues from C were analyzed by (D) TUNEL and (E) active caspase 3 staining. Left, representative staining pictures with nuclear counterstaining by DAPI; right, quantification of positive cells. In D and E, arrows indicate example cells with positive staining. Results were expressed as means ± s.d. of three independent experiments. *, P < 0.05; **, P <0.01; ***, P <0.001.