A 83-01 is a selective inhibitor of TGF-β type I receptor ALK5 kinase, type I activin/nodal receptor ALK4 and type I nodal receptor ALK7 (IC50 values are 12, 45 and 7.5 nM respectively). A 83-01 blocks phosphorylation of Smad2 and inhibits TGF-β-induced epithelial-to-mesenchymal transition. A 83-01 lonly weakly inhibits ALK-1, -2, -3, -6 and MAPK activity. A 83-01 is more potent than SB 431542. Fibroblasts can be reprogrammed by A 83-01 into alternative lineages.