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

The nuclear hormone 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) acts through the transcription factor vitamin D receptor (VDR) via combined contact with the retinoid X receptor (RXR), coactivator proteins, and specific DNA binding sites (VDREs). Ligand-mediated conformational changes of the VDR are the core of the molecular switch of nuclear 1alpha,25(OH)(2)D(3) signalling. Studying the interaction of 1alpha,25(OH)(2)D(3) analogues with this molecular switch should allow the characterization of their potential selective biological profile. A 1alpha,25(OH)(2)D(3) analogue with two side chains (Ro27-2310 or Gemini) was found to stabilize functional VDR conformations and VDR-RXR heterodimers on a VDRE with a slightly lower sensitivity than the natural hormone. A 19-nor derivative of Gemini (Ro27-5646) showed similar sensitivity whereas 5,6-trans (Ro27-6462) 3-epi (Ro27-5840) and 1alpha-fluoro (Ro27-3752) derivatives were equal to each other, but approximately 30-times less sensitive than Gemini. A des-C,D derivative of Gemini (Ro28-1909) showed only residual activity at maximal concentrations. In contrast to 1alpha,25(OH)(2)D(3), Gemini and its derivatives showed a differential preference in stabilizing VDR conformations which was found to be modulated by DNA coactivator and corepressor proteins. An analysis of the gene regulatory potential of the VDR agonists in cellular reporter gene systems demonstrated the same ranking as in the in vitro systems, but Gemini and its 19-nor derivative were found to be more sensitive than 1alpha,25(OH)(2)D(3) which indicates that the natural hormone is selectively metabolized. This study used straightforward methods for the in vitro and ex vivo evaluation of the gene regulatory potential of 1alpha,25(OH)(2)D(3) analogues. Gemini was highlighted as an interesting drug candidate which could not be optimized through obvious chemical modifications in its A-ring. J. Cell. Biochem. Suppl. 36: 179-190, 2001. Copyright 2001 Wiley-Liss, Inc.