Synthesis and evaluation of third generation vitamin D3 analogues as inhibitors of Hedgehog signaling

The Hedgehog (Hh) pathway is a developmental pathway with therapeutic potential as a target for a variety of cancers. In recent years, several vitamin D-based compounds have been identified as potent inhibitors of Hh signaling. These analogues contain aromatic phenol A-ring mimics coupled to the CD-ring side chain of vitamin D3 through modified seco-B regions. To continue structure-activity relationship studies on this class of Hh pathway inhibitors, multiple series of vitamin D-based analogues that contain an amine-based seco-B tether and/or incorporate a hydroxyl moiety on C-25 were designed and synthesized. These compounds were evaluated in multiple cell lines for their anti-Hh activity, and we identify analogues 16, 21, 22 as potent vitamin D-based Hh inhibitors (IC₅₀ values of 110-340 nM). We also performed a series of mechanism of action studies in knockout cell lines to further explore whether these analogues inhibit the Hh pathway through a known Hh pathway component or the vitamin D receptor. While the specific cellular target that mediates these effects remains elusive, our studies suggest multiple cellular targets may mediate the anti-Hh activity of this scaffold.