SAG (Synonyms: Smoothened Agonist)

SAG is a synthetic chlorobenzothiophene-containing Hh pathway agonist that regulates smo activity. It is a SMO agonist at EC50 of 3 nM and but inhibits hedgehog signaling at >1 μM. [1]

Smoothened (SMO) is a GPCR-like receptor that mediates hedgehog signaling with Patched to regulate gene expression through the Gli transcription factors. It is plays an important role for embryogenesis and adults tissue homeostasis

In a mouse cultured cell assay (Shh-LIGHT2), SAG induces pathway activation (EC50 ≈3 nM). It differs in that pathway activity decreases dramatically as SAG concentration surpasses 1 μM. [1] SAG binds directly to the SMO heptahelical bundle. SAG dose dependently blocks this association and produces apparent dissociation constant (KD) of 59 nM for the SAG/SMO complex. [2]

SAG also antagonizes GC’s antiproliferative effects in CGNP P4 wild-type mice primary cultures. At 15-240 nM, SAG prevents the neurotoxic effects of glucocorticoids without interfering with the beneficial effects of glucocorticoids on lung maturation. [2]

References:
1.  Chen JK, Taipale J, Young KE et al. Small molecule modulation of Smoothened activity. Proc Natl Acad Sci U S A. 2002 Oct 29;99(22):14071-6.
2.  Heine VM, Griveau A, Chapin C et al. A small-molecule smoothened agonist prevents glucocorticoid-induced neonatal cerebellar injury. Sci Transl Med. 2011 Oct 19;3(105):105ra104.