A) Cabozantinib acutely increased caspase-3 staining within 24–48 hours of treatment in established murine PTEN/p53-deficient prostate tumors. Mice were treated with cabozantinib for the indicated times, and prostate tumor tissues were stained with caspase-3 antibody by IHC. Images show representative sections from n=3 mice per timepoint. B) PTEN/p53 deficient prostate tumor-derived cell lines treated with cabozantinib showed only modest cell death. SC1, AC1 and AC3 cells were treated with 30 μM cabozantinib for the indicated times, followed by apoptosis analysis with Annexin V staining (n=3 experiments). *p < 0.05, **p < 0.01, ***p < 0.001.