Fig 2.

Effect of erlotinib and gemcitabine treatment schedule on parental A-431 cells. A. Cells were treated with 0 or 3.5 nM gemcitabine for 72 h and then with 0.125-16 μM erlotinib for 72 h. A synergistic effect was observed. B. In contrast, a synergistic effect was not observed when cells were treated with 0 or 10 μM erlotinib for 72 h and then with 0.4375-56 nM gemcitabine for 72 h. Note that the concentration along the x-axis scale in each graph doubles at each tick mark.