Structural refinement of seco-steroidal skeleton and the biological activity through nuclear receptors

Abstract

1α,25-Dihydroxyvitamin D3 (1) regulates a variety of biological actions through vitamin D receptor (VDR), including calcium and phosphorus homeostasis, bone remodeling, cellular proliferation and differentiation and many other functions. To enhance its potency and to study the structure/function relationship, we synthesized a series of analogs of 1 with a modification at the C-2α position. Introducing 2α-methyl, 2α-(3-hydroxypropyl), or 2α-(3-hydroxypropoxy) group increased its binding affinity for the VDR 2- to 4-fold compared to 1. The crystal structures of the VDR bound to these analogs provide a molecular explanation for the interaction between the 2α-substituents and water molecules exist in the VDR-ligand binding domain. Based on the accumulated knowledge in VDR agonists, we synthesized 2-substituted analogs of 'double side chain' (gemini), 19-norvitamin D3 (MART-10), TEI-9647 (VDR antagonist), 1-alkylated vitamin D3, 14-epi-previtamin D3 etc. Gemini analogs showed potent HL-60 cell differentiation activity (13-38 times compared to 1), and MART-10 exhibited remarkable antiproliferative activity on PZ-HPV-7 cells even at 10-10 M. (24S)-2α-(3-Hydroxypropoxy)-24-propyl-TEI-9647 showed potent VDR antagonism, and its IC50 value was 7.4 pM against 10 nM of 1. 1α-Methyl-2α-(3-hydroxypropyl)-25-hydroxyvitamin D 3 improved the binding affinity for the mutant VDR (Arg274Leu), which causes hereditary vitamin D resistant rickets. 1α,25-Dihydroxy-2α- methyl-14-epi-previtamin D3 showed moderate osteocalcin transcriptional activity on HOS cells. We theorize that modification at A-ring alone and in combination with functionalization of the other parts of the vitamin D molecule would provide important new information on the mechanism of vitamin D actions that could lead to the development of new therapeutic regimes for the treatment of various diseases. © 2008 The Pharmaceutical Society of Japan.