(A and C) MB231, MB453, MB468, and CAL148 cells were treated with palbociclib and/or MLN0128 for 120 h. The X axis shows palbociclib concentration. (B) Combination index (CI) was calculated in MB231 and in MB453. CI > 1 means antagonistic effect, = 1 means additive effect, and < 1 means synergistic effect. (D) MB231 and MB453 cells were treated with palbociclib and/or everolimus at the indicated concentrations. Results of MTT assay are expressed as the ratio of control, and are mean ± SD at each treatment concentration, from triplicate measurements for each treatment.