Discovery of fused bicyclic derivatives of 1H-pyrrolo[1,2-c]imidazol-1-one as VDR signaling regulators.

The modulation of VDR signaling is important in regulating tumor-related signal transduction and protecting from microorganismal infection. In this study we discovered by luciferase reporter assay that several fused bicyclic derivatives of 1H-pyrrolo[1,2-c]imidazol-1-one with the assistance of calcitriol result in up to three-fold increases of VDR promoter activity. Preliminary SAR results from 20 compounds disclose that ideal VDR signaling regulators of these compounds are built up by the optimal combination of multiple factors. Western blot analysis indicates that compounds of ZD-3, ZD-4 and ZD-5 not only significantly upregulate p62 and LC3-II but also elevate the ratio of LC3-II/LC3-I, which possibly leads to activated autophagy. All of five compounds also significantly downregulate p65 and upregulate p-p65 and ZD-3 is the most active one to NF-κB signaling, suggesting a possible induction of apoptosis through the regulation of NF-κB signal transduction mediated by VDR signaling. Compounds of ZD-3, ZD-4 and ZD-5 significantly counteract the interference by VDR shRNA, in which ZD-3 gets the highest compensation of VDR expression and the highest ratio of LC3-II/LC3-I, indicating that ZD-3 very likely activates VDR-mediated autophagy. Taken together, these 1H-pyrrolo[1,2-c]imidazol-1-one derivatives can modulate VDR signaling, possibly resulting in the regulation of some signal pathways to induce autophagy and apoptosis.