17-AAG induces rapid and durable inactivation of ErbB and Akt signaling, as compared to ErbB TKIs. (A) Timecourse of gefitinib, 17-AAG and combination treatments in the human breast cancer cell line SKBR3. Cells were plated in 10 cm dishes and treated for the indicated times with 1 μM gefitinib, 1 μM 17-AAG, or their combination, and examined for the expression and phosphorylation of the indicated proteins. (B) ErbB3 reactivation in the presence of gefitinib occurs independently of serum growth factors. SKBR3 cells were plated in 6-well plates, serum starved for 24 hours and treated for the indicated times with 1 μM gefitinib. (C) Role for a non-ErbB receptor in the activation of ErbB3. SKBR3 cells were plated in a 6-well plate, treated with 1.5 μM CI-1033 for the indicated times and assayed for the expression and phosphorylation of the indicated proteins.