Potent inhibitor of Src-family tyrosine kinases. Inhibits p56lck and p59fynT (IC50 values are 5 and 6 nM respectively). Displays > 8000-fold selectivity over ZAP-70 and JAK2. Also moderately inhibits p38, CSK, PDGF receptors, RET-derived oncoproteins, c-Kit and Bcr-Abl.