HPI-1 is a Hedgehog pathway inhibitor acting downstream of Smo and independently of PKA, PI3K and MAPK. It can suppress Hh pathway activation induced by loss of Su(fu) or Gli overexpression. Inhibits both endogenous and exogenous Gli1/Gli2 activity. IC₅₀’s range from 0.2 to 6 µM for various cell-based assays.