Structure Activity Relationship of Carboxylic Ester Antagonists of the Vitamin D3 Receptor
- 1Institut für Physiologische Chemie I and Biomedizinisches Forschungszentrum, Heinrich-Heine-Universität, Düsseldorf, Germany (Y.B., C.C.); and 2Medicinal Chemistry, Schering AG, Berlin, Germany (A.S.)
Abstract
A 25-carboxylic ester analog of 1α,25-dihydroxyvitamin D3[1α,25(OH)2D3], ZK159222 (compound 1), was recently described as a novel type of antagonist of 1α,25(OH)2D3 signaling. In this study five derivatives of compound 1 (compounds 2–6) were selected because of their sensitivity in facilitating complex formation between the 1α,25(OH)2D3 receptor (VDR) and the retinoid X receptor on a 1α,25(OH)2D3 response element that was comparable to that of the natural hormone (0.2–0.9 nM). Most derivatives of compound 1 reacted as typical agonists, because they were able to promote ligand-dependent interaction of the VDR with the coactivator TIF2, stabilized the VDR preferentially in its agonistic conformation c1LPD, and stimulated VDR-dependent gene activity with a potency similar to 1α,25(OH)2D3. In contrast, only compound 2 showed the antagonistic profile of compound 1, which includes the incompetence to induce a VDR-TIF2 contact, the stabilization of the antagonistic conformation c2LPD, and only a very weak and insensitive functional activity. Accordingly, only compounds 1 and 2, but not compounds 3 to 6, showed prominent antagonistic effects in cellular systems. The comparison of the structures of the compounds indicates that the essential requirements for an antagonistic function are a cyclopropyl ring at carbon 25, a hydroxy group at carbon 24, and at least a butylester. Interestingly, compound 2 was an approximately 3 times more sensitive antagonist than compound 1 and even displayed a lower residual agonistic activity. In conclusion, only a very limited number of structural variations of compound 1 are possible to keep its antagonistic profile, but the tools presented here for their in vitro evaluation allow an accurate prediction of the effects and are suited to screening for even more potent 1α,25(OH)2D3 antagonists.
Footnotes
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Send reprint requests to: Dr. Carsten Carlberg, Institut für Physiologische Chemie I, Heinrich-Heine-Universität Düsseldorf, Postfach 10 10 07, D-40001 Düsseldorf, Germany. E-mail: carlberg{at}uni-duesseldorf.de
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This work was supported by the Sonderforschungsbereich 503, project A6, DFG Grant Ca229/1, the Fonds der Chemischen Industrie, and the Wilhelm Sander Foundation (all to C.C.).
- Abbreviations:
- 1α,25(OH)2D3
- 1α,25-dihydroxyvitamin D3
- AF-2
- (trans)activation function 2
- ANF
- atrial natriuretic factor
- DBD
- DNA-binding domain
- DR3
- direct repeat spaced by three nucleotides
- EC50
- half-maximal activation
- GST
- glutathione S-transferase
- RXR
- retinoid X receptor
- LBD
- ligand-binding domain
- TIF2
- transcriptional intermediary factor 2
- VDR
- 1α,25(OH)2D3 receptor
- VDRE
- 1α,25(OH)2D3 response element
- DMSO
- dimethyl sulfoxide
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- Received June 8, 2000.
- Accepted August 10, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
