Synthesis and Evaluation of Aromatic A-Ring 23-Oxavitamin D3 Analogues as Hedgehog Pathway Inhibitors

The Hedgehog (Hh) signaling pathway plays a crucial role in the initiation and progression of tumors, and Hh inhibitors have been used as potential chemotherapeutic agents for the treatment of basal cell carcinomas (BCCs). Vitamin D3(VD3) and its derivatives have been identified as potent Hh inhibitors. However, the selectivity of VD3derivatives to vitamin D receptor (VDR) and the Hh signaling pathway still needs optimization. In this study, a series of aromatic A-ring mimics VD3analogues that contain a C-23 oxygen atom or incorporate C-25 hydroxyl on side chains were designed and synthesized. These compounds were tested in various cell lines for anti-Hh activity, with analogues3jand4iidentified as potent inhibitors. Mechanism studies showed their anti-Hh effects are mainly due to targeting Smoothened (Smo) without binding to the cyclopamine site. Structure-activity relationship (SAR) studies revealed that VD3-based inhibitors enhance anti-Hh activity by adding a hydroxyl group at C25 while reducing VDR activity by incorporating an oxygen atom into the side chain.