Acylthiourea, Acylurea, and Acylguanidine Derivatives with Potent Hedgehog Inhibiting Activity

The Smoothened (Smo) receptor is the major transducer of the Hedgehog (Hh) signaling pathway. On the basis of the structure of the acylthiourea Smo antagonist (MRT-10), a number of different series of analogous compounds were prepared by ligand-based structural optimization. The acylthioureas, originally identified as actives, were converted into the corresponding acylureas or acylguanidines. In each series, similar structural trends delivered potent compounds with IC(50) values in the nanomolar range with respect to the inhibition of the Hh signaling pathway in various cell-based assays and of BODIPY-cyclopamine binding to human Smo. The similarity of their biological activities, in spite of discrete structural differences, may reveal the existence of hydrogen-bonding interactions between the ligands and the receptor pocket. Biological potency of compounds 61, 72, and 86 (MRT-83) were comparable to those of the clinical candidate GDC-0449. These findings suggest that these original molecules will help delineate Smo and Hh functions and can be developed as potential anticancer agents.