A) p53ER/MYC cells were treated with CHIR99021 as indicated. Western blotting was performed for markers of GSK-3β inhibition. B) p53ER/MYC cells were grown without 4-OHT (p53-inactive). Cells were treated with DMSO or 3 μM CHIR99021 for 2 hours followed by doxorubicin as indicated. Western blotting was performed for markers of GSK-3β inhibition, apoptosis, and loading controls. C) F1 hybrid B6129PF1/J mice bearing p53ER/MYC subcutaneous grafts were intraperitoneally injected with vehicle, vehicle + 8 mg/kg doxorubicin, 100 mg/kg CHIR99021, or 100 mg/kg CHIR99021 + 8 mg/kg doxorubicin. Tumors were harvested after 18 hours for immunohistochemistry (IHC). Representative images of cleaved caspase-3 stains (brown) are shown for each treatment group.