CD-ring modified vitamin D 3 analogs and their superagonistic action

Abstract

Non-steroidal analogs of 1,25-dihydroxyvitamin D 3 [1,25(OH) 2D 3] represent a most particular class of analogs because they are either not directly derived from the core 1,25(OH) 2D 3-structure or they have modifications in the core structure that are so drastic that the steroidal structure is lost. Non-steroidal CD-ring analogs of 1,25(OH) 2D 3 have been developed to study the role of the central rigid CD-ring system in the biological activity of 1,25(OH) 2D 3. Here we review the different classes of CD-ring analogs and highlight some representative analogs such as the fluorinated D-ring analogs CD578, WU515 and WY1113 which show markedly increased differentiating activity on human SW480-ADH colon cancer cells, characterized by a stronger induction of the invasion suppressor E-cadherin and a stronger repression of the β-catenin/TCF target oncogene c-Myc. Correspondingly, CD578, WU515 and WY1113 are more potent inhibitors of β-catenin/TCF signaling than 1,25(OH) 2D 3 and induce stronger VDR–coactivator interactions. Underlying the increased biological potency of analog CD578 are additional contacts between the side chain fluorine atoms of the analog with specific residues of helix 12 (H12) of the Vitamin D Receptor (VDR) and subsequent stronger VDR–coactivator interactions.