Loss of caspase-8 sensitizes mouse colon tumors to SMAC mimetic. (A–C) Tumors and tumor-adjacent colon tissues were collected from 14-wk-old ApcMin/+ mice. (A) Quantitative RT-PCR analysis of gene expression indicated on the x axis. Gene expression was normalized to Hprt. Group sizes: n = 11; NS, P > 0.05; ***, P < 0.001. (B) Immunoblots of tissue extracts. (C) Immunostaining of colon cross sections with a RIP3 antibody. (D) Immunoblots of tumor tissue extracts from ApcMin/+ mice and ApcMin/+ Casp8ΔIEC mice. (B and D) β-Actin served as a loading control. (E) Tumor cross-sections from indicated mice were subjected to staining of H&E (left), cleaved caspase-3 (middle), and TUNEL (right). (F–H) ApcMin/+ mice and ApcMin/+ Casp8ΔIEC mice bearing size 4 tumors were intratumorally injected with LCL161 (100 µg/tumor). (F and G) The size of tumors was scored by colonoscopy every second day for 6 d. Group size: n = 5. (G) Representative colonoscopy imaging of tumors. (H) 2 d after injection of LCL161, tumors were collected for staining of H&E, mouse β-catenin (quantification is shown on the right), and TUNEL (quantification is shown on the right). **, P < 0.01; ***, P < 0.001. Results from at least three biological replicates are presented unless otherwise specified. Data derived from two independent animal experiments are shown (F–H). Bars: (C) 500 µm; (E and H) 75 µm. Error bars indicate ±SD.