Structural basis for specificity of TGFβ family receptor small molecule inhibitors

Transforming growth factor-beta (TGF beta) receptor kinase inhibitors have a great therapeutic potential. 513431542 is one of the mainly used kinase inhibitors of the TGF beta/Activin pathway receptors, but needs improvement of its EC50 (EC50 = 1 mu M) to be translated to clinical use. A key feature of SB431542 is that it specifically targets receptors from the TGF beta/Activin pathway but not the closely related receptors from the bone morphogenic proteins (BMP) pathway. To understand the mechanisms of this selectivity, we solved the crystal structure of the TGF beta type I receptor (T beta RI) kinase domain in complex with SB431542. We mutated T beta RI residues coordinating SB431542 to their counterparts in activin-receptor like kinase 2 (ALK2), a BMP receptor kinase, and tested the kinase activity of mutated T beta RI. We discovered that a Ser280Thr mutation yielded a T beta RI variant that was resistant to 513431542 inhibition. Furthermore, the corresponding Thr283Ser mutation in ALK2 yielded a BMP receptor sensitive to SB431542. This demonstrated that Ser280 is the key determinant of selectivity for SB431542. This work provides a framework for optimising the SB431542 scaffold to more potent and selective inhibitors of the TGF beta/Activin pathway. (C) 2011 Elsevier Inc. All rights reserved.