Table I.

Characteristics of small molecule inhibitors of activin receptor-like kinase.

Authors, year	Name	Molecular structure	Target	Function	(Refs.)
Laping et al, 2002 Inman et al, 2002 Halder et al, 2005 Matsuyama et al, 2003 Sato et al, 2015	SB-431542		Selective inhibitor for ALK4, 5 and 7, and weak effect on ALK3	SB-431542 as a selective inhibitor of activin/TGF-β signaling can reduce nuclear accumulation of Smads and inhibit collagen I and fibronectin expression. Additionally, SB-431542 can also attenuate TGF-β tumor-promoting effects, EMT, cell motility, migration and invasion, and inhibit proliferation of osteosarcoma cells and lung metastasis of breast cancer.	(110,111,115–117)
Kim et al, 2017 Wang et al, 2018	SB-505124		ALK4, 5, 7	SB-505124 can offer protection of the neocortex, hippocampus, and thalamus with enhancing cerebral autophagy contributing to the decrease in the extent of progressive neuronal cell death, and up-regulate the expression of nephrin and synaptopodin, providing a novel therapeutic target for diabetic nephropathy.	(118,119)
Grygielko et al, 2005	SB-525334		ALK4, 5, 7	SB-525334 has been demonstrated to block phosphorylation and Smad2/3 nuclear translocation, and inhibits renal fibrosis by reducing procollagen and PAI-1 expression.	(120)
Xu et al, 2012 Gauger et al, 2012 Kimura-Kuroda et al, 2010	LY-364947		ALK4, 5, 7	LY-364947 has an anti-fibrotic role by inhibiting fibroblasts proliferation and epithelium cell transdifferentiation, and prevents proliferative vitreoretinopathy and subsequent tractional retinal detachment in vivo.	(121–123)
Tojo et al, 2005	A-83-01		Selective inhibitor for ALK4, 5 and 7, and weak effect on ALK1, 2, 3 and 6	A-83-01 can inhibit the activities of ALK4, 5 and 7. For other ALK receptors such as ALK1, 2, 3 and 6, A-83-01 showed weak inhibition. A-83-01 was proved to reduce EMT.	(112)
Giannelli et al, 2014 Bueno et al, 2008	LY-2157299		ALK4, 5, 7	LY-2157299 is now under phase II clinical studies of its anti-carcinoma activities against glioblastoma and hepatocellular carcinoma, and has also been reported that it inhibits the tumor growth in human lung anaplastic carcinoma cells and breast carcinoma cells.	(124,125)
de Gouville et al, 2005	GW-6604		ALK4, 5, 7	GW-6604 can prevent matrix deposition and promote hepatocyte regeneration as anti-cancer drug development.	(126)
Leung et al, 2006	SD-208		ALK4, 5, 7	SD-208 inhibits growth and invasiveness and enhances immunogenicity of murine and human glioma cells.	(127)

ALK, Activin receptor like kinases; EMT, epithelial to mesenchymal transition; PAI-1, plasminogen activator inhibitor-1.