In vitro activity: SIS3 completely diminishes the constitutive phosphorylation of Smad3 as well as the up-regulated type I collagen expression in scleroderma fibroblasts, thus abolishes the ECM overexpression in the TGF-β1-treated normal dermal fibroblasts and scleroderma fibroblasts in vitro.

Kinase Assay: SIS3 is a potent and selective inhibitor of Smad3 with an IC50 of 3 μM for Smad3 phosphorylation. (E)-SIS3 inhibits the myofibroblast differentiation of fibroblasts by TGF-β1

Cell Assay: Normal human dermal fibroblasts are plated at a density of 105 cells/well in six-well culture plates and grown until subconfluence in MEM containing 10% FCS. Cells are quiesced by 24-h incubation in serum-free MEM, followed by incubation in serum-free medium in the presence or absence of SIS3 before the collection of cells for 72 h. Then, the cells are detached from the wells by trypsin treatment and counted using a Coulter counter.