Potent Antagonist for the Vitamin D Receptor: Vitamin D Analogues with Simple Side Chain Structure

Abstract

We previously reported that 22S-butyl-25,26,27-trinor-1alpha,24-dihydroxyvitamin D(3) 2 was a potent VDR antagonist. The X-ray crystal structure of the ligand binding domain of VDR complexed with 2 indicated that this ligand induces an extra cavity within the ligand-binding pocket. The structure also showed that the ligand forms only poor hydrophobic interactions with helix 12 of the protein. Here, to study the effects of the induction of the extra cavity and of insufficient interactions with helix 12 on antagonism, we designed and synthesized a series of vitamin D(3) analogues with or without a 22-alkyl substituent and evaluated their biological potency. We found that the 22-butyl analogues 3c and 5c act as full antagonists, the 22-ethyl analogues 3b, 4b, 5b, and 22-butyl analogue 4c act as partial agonists, and the others (3a, 4a, 5a, 6a, 6b, and 6c) act as full agonists for VDR. It is intriguing that 6c is a potent agonist for VDR, whereas its 26,27-dinor analogue 5c is a potent antagonist. Analogue 6c recruited coactivator SRC-1 well, but 5c did not. These results indicate that a combination of induction of the extra cavity and insufficient hydrophobic interactions with helix 12 is important for VDR antagonism in this class of ligands.

A 20S Combined with a 22R Configuration Markedly Increases both in Vivo and in Vitro Biological Activity of 1α,25-Dihydroxy-22-methyl-2-methylene-19-norvitamin D3

“…11 In contrast to similar synthetic approaches, independently proposed by Fujishima 12 and Mouriño, 13 we used crystallization, avoiding the expensive separation of the C,D-ring isomers by flash chromatography or HPLC. Since only a few 22-alkyl-19-nor-1α,25-dihydroxyvitamin D 3 analogues have been synthesized to the date, 9 we have also decided to prepare and test the analogues double-substituted at C-22 (Scheme 1). …”

“…7,8 Recently, Yamamoto et al described 2-methylene-19-norvitamin D compounds bearing a 22 S -butyl and 22 S -ethyl group and discovered that they can act as agonists or antagonists for the VDR. 9 …”

Butyl Pocket Formation in the Vitamin D Receptor Strongly Affects the Agonistic or Antagonistic Behavior of Ligands

“…28 We found that these synthetic ligands show strong antagonist, partial agonist, or full agonist activities, depending on the primary or tertiary alcohol at the side chain terminus and on the length of the 22-alkyl group. The results suggested that both the induction of a butyl pocket and insufficient hydrophobic interactions with the VDR C-terminus are necessary for VDR antagonism.…”

“…12 The results are shown in Figure 1, together with the results for 3a−c and 4a−c. 28 New analogues 5a−c showed concentration-dependent transcriptional activity and acted as potent agonists. Of the 22-butyl analogues, new analogue 5c completely restored full agonistic activity.…”

Inhibitors for the Vitamin D Receptor–Coregulator Interaction

“…However, in the presence of 1,25-(OH) 2 D 3 , both interactions were inhibited by compound 4 at a concentration of 1 μM (161). Elongation of compound 4’s carbon chain by one CH 2 unit resulted in a slightly more potent antagonist (162). Introduction of a methyl or an ethyl substituent in the 24 position increased the agonist activity of these ligands determined by a luciferase reporter assay (163).…”