Chronic liver disease is characterized by an exacerbated accumulation of matrix, causing progressive fibrosis, which may lead to cirrhosis. Transforming growth factor beta (TGF‐β), a well‐known profibrotic cytokine, transduces its signal through the ALK5 ser/thr kinase receptor, and increases transcription of different genes including PAI‐1 and collagens. The identification of GW6604 (2‐phenyl‐4‐(3‐pyridin‐2‐yl‐1H‐pyrazol‐4‐yl)pyridine), an ALK5 inhibitor, allowed us to evaluate the therapeutic potential of inhibiting TGF‐β pathway in different models of liver disease.A cellular assay was used to identify GW6604 as a TGF‐β signaling pathway inhibitor. This ALK5 inhibitor was then tested in a model of liver hepatectomy in TGF‐β‐overexpressing transgenic mice, in an acute model of liver disease and in a chronic model of dimethylnitrosamine (DMN)‐induced liver fibrosis.In vitro, GW6604 inhibited autophosphorylation of ALK5 with an IC50 of 140 nM and in a cellular assay inhibited TGF‐β‐induced transcription of PAI‐1 (IC50: 500 nM). In vivo, GW6604 (40 mg kg−1 p.o.) increased liver regeneration in TGF‐β‐overexpressing mice, which had undergone partial hepatectomy. In an acute model of liver disease, GW6604 reduced by 80% the expression of collagen IA1. In a chronic model of DMN‐induced fibrosis where DMN was administered for 6 weeks and GW6604 dosed for the last 3 weeks (80 mg kg−1 p.o., b.i.d.), mortality was prevented and DMN‐induced elevations of mRNA encoding for collagen IA1, IA2, III, TIMP‐1 and TGF‐β were reduced by 50–75%. Inhibition of matrix genes overexpression was accompanied by reduced matrix deposition and reduction in liver function deterioration, as assessed by bilirubin and liver enzyme levels.Our results suggest that inhibition of ALK5 could be an attractive new approach to treatment of liver fibrotic diseases by both preventing matrix deposition and promoting hepatocyte regeneration.British Journal of Pharmacology (2005) 145, 166–177. doi:10.1038/sj.bjp.0706172
