AKT activity in myr-AKT-transfected U266 cells. (A) Expression of total and phosphorylated AKT (Ser473) was determined in U266 cells transfected with myr-AKT or empty vector (EV) control cells, as described in “Materials and methods.” (B) AKT activity regulates tumor sensitivity to CCI-779. Mice (8 per group) were challenged subcutaneously with 3 × 10⁷ myr-AKT transfected U266 or EV-transfected U266 cells, as described in Figure 2. When tumor size reached 200 mm³, mice were randomly assigned to receive vehicle alone (▪) or 20 mg/kg CCI-779 (□) intraperitoneally for 10 days, as described in “Materials and methods.” Results indicate the mean ± SEM volume (mm³) of CCI-779-treated tumors compared with vehicle control tumors assayed on days 8 and 13 of treatment.