Figure 3. (A) Effect of proline on the inhibition of STAT3. (B) Prodrugs do not inhibit EGF induced STAT5 phosphorylation or Ser473Akt phosphorylation. (C) Prodrugs do not inhibit Src phosphorylation of Tyr861 of FAK. (D) Prodrugs inhibit IFNγ-stimulated phosphorylation of STAT1 but at 10-fold higher concentration than constitutive STAT3. In (A) cells were treated with prodrug for 2 h before lysis and protein determination by western blots. In (B–D) cells were treated with prodrug for 1.5 h at which time EGF or IFNγ was added. After 30 min cells were lysed and protein levels determined by western blots.