Pimozide inhibits STAT5 activity. (A) Chemical structure of pimozide. (B) Reporter cell lines were treated with the indicated doses of pimozide for 2 hours, after which cytokines were added to activate the appropriate transcription factor. Luciferase activity was quantitated by luminometry 6 hours later. (C) KU812 cells were treated with vehicle or pimozide (5μM) for 18 hours, after which RNA was harvested, and expression of the indicated genes was measured using quantitative RT-PCR and normalized to the expression of β-actin. (D) KU812 cells were treated with the indicated concentrations of pimozide for 3 hours. Immunoblots were performed using antibodies specific for tyrosine phosphorylated STAT5 and total STAT5.