Gene regulatory potential of 1 alpha,25-dihydroxyvitamin D-3 analogues with two side chains

The nuclear hormone 1 alpha ,25-dihydroxyvitamin D-3 (1 alpha ,25(OH)(2)D-3 ) acts through the transcription factor vitamin D receptor (VDR) via combin ed contact with the retinoid X receptor (RXR), coactivator proteins, and sp ecific DNA binding sites (VDREs). Ligand-mediated conformational changes of the VDR are the core of the molecular switch of nuclear 1 alpha ,25(OH)2D3 signalling. Studying the interaction of 1 alpha ,25(OH)(2)D-3 analogues wi th this molecular switch should al low the characterization of their potent ial selective biological profile. A 1 alpha ,25(OH)(2)D-3 analogue with two side chains (Ro27-2310 or Gemini) was found to stabilize functional VDR co nformations and VDR-RXR heterodimers on a VDRE with a slightly lower sensit ivity than the natural hormone. A 19-nor derivative of Gemini (Ro27-5646) s howed similar sensitivity whereas 5,6-trans (Ro27-6462) 3-epi (Ro27-5840) a nd 1 alpha -fluoro (Ro27-3752) derivatives were equal to each other, but ap proximately 30-times less sensitive than Gemini. A des-C,D derivative or Ge mini (Ro28-1909) showed only residual activity at maximal concentrations. I n contrast to 1 alpha ,25(OH)(2)D-3, Gemini and its derivatives showed a di fferential preference in stabilizing VDR conformations which was found to b e modulated by DNA coactivator and corepressor proteins. an analysis of the gene regulatory potential of the VDR agonists in cellular reporter gene sy stems demonstrated the same ranking as in the in vitro systems, bur Gemini and its 19-nor derivative were found to be more sensitive than 1 alpha ,25( OH)(2)D-3 which indicates that the natural hormone is selectively metaboliz ed. This study used straightforward methods for the in vitro and ex vivo ev aluation of the gene regulatory potential of 1 alpha ,25(OH)(2)D-3 analogue s. Gemini was highlighted as an interesting drug candidate which could not be optimized through obvious chemical modifications in its A-ring. (C) 2001 Wiley-Liss, Inc.