TGFB1 and glioblastoma: To further show the role of the TGF-β pathway for inducing a mesenchymal shift and migration/invasion in GBM, we employed A8301, a potent small-molecule blocker of the TGF-β type I receptors activin-like kinase 4 (ALK4, ALK5) and ALK7.29 The inhibitor was effective in blocking TGF-β-induced phosphorylation of SMAD2 and the upregulation of Fibronectin in U87 and U251 cells (Figure 3a).