Protein tyrosine kinase (PTK) inhibitors are potential antiproliferative agents for diseases caused by the hyperactivity of PTKs. Tyrphostins are a class of antiproliferative compounds which act as PTK blockers. PTK inhibitors specific for platelet-derived growth factor (PDGF) receptor kinase could help in the treatment of atherosclerosis, restenosis, pulmonary fibrosis, and gliomas. AG-1296 is a potent and selective inhibitor of PDGF receptor kinase with an IC50 value of about 0.4 µM both in vitro and in cells (Swiss 3T3 cells). It inhibits ligand-stimulated DNA synthesis in platelet-derived growth factor receptor and stem cell factor/kit receptor transfected cells with an IC50 values of 1.5 and 1.8 µM, respectively.  Treatment of sis oncogene transfected NIH3T3 cells with AG-1296 reverses the transformed phenotype.