3 In vitro, GW6604 inhibited autophosphorylation of ALK5 with an IC(50) of 140 nM and in a cellular assay inhibited TGF-beta-induced transcription of PAI-1 (IC(50): 500 nM).In vivo, GW6604 (40 mg kg(-1) p.o.) increased liver regeneration in TGF-beta-overexpressing mice, which had undergone partial hepatectomy.