Screening and identification of a novel class of TGF-β type 1 receptor kinase inhibitor.

Transforming growth factor beta (TGF-beta) type I receptor (activin receptor-like kinase 5, ALK5) has been identified as a promising target for fibrotic diseases. To find a novel inhibitor of ALK5, the authors performed a high-throughput screen of a library of 420 000 compounds using dephosphorylated ALK5. From primary hits of 1521 compounds, 555 compounds were confirmed. In total, 124 compounds were then selected for follow-up based on their unique structures and other properties. Repeated concentration-response testing and final interference assays of the above compounds resulted in the discovery of a structurally novel ALK5 inhibitor (compound 8) (N-(thiophen 2-ylmethyl)-3-(3,4,5 trimethoxyphenyl) imidazo[1,2 beta] pyridazin 6-amine) with a low IC(50) value of 0.7 mu M. Compound 8 also inhibited the TGF-beta-induced nuclear translocation of SMAD with an EC(50) value of 0.8 mu M. Kinetic analysis revealed that compound 8 inhibited ALK5 via mixed-type inhibition, suggesting that it may bind to ALK5 differently than other published adenosine triphosphate site inhibitors. (Journal of Biomolecular Screening 2011; 16: 724-733)