Towards the design and synthesis of small molecule antagonists of nuclear receptor liver receptor homologue-1

Nuclear receptors (NRs) are a large family of mammalian transcription factors that have the particularity of binding directly to DNA and regulating the expression of adjacent genes. Liver receptor homologue-1 (LRH-1) is a NR from the subfamily 5 (steroidogenic factor-like) and plays a prominent role in development, reverse cholesterol transport, bile-acid homeostasis and steroidogenesis, as well as being implicated in the control of aromatase expression. In addition, Ali et al. showed that LRH-1 acts as a key regulator of the estrogen response in breast cancer cells through the regulation of estrogen receptor-α (ERα) expression. As a crystal structure of LRH-1 was available, the design of new potential LRH-1 antagonists was based on a computer-aided drug design (CADD) approach. It was believed that virtual agonist and antagonist analogues would bind at the same site within the core of the ligand-binding domain (LBD) but demonstrate different binding modes. Binding of an antagonist would induce a conformational change within the LBD of LRH-1, involving a rotation of helix 12 (H12) by direct steric clashes between this helix and the ligand and as a consequence, prevent co-activator recruitment. The LRH-1 LBD was identified as mainly hydrophobic and as one of the largest in the NR family. Three series of analogues have been designed. Steroid-based compounds bearing a challenging C-2 ether linkage were initially synthesized followed by analogues structurally related to anti-estrogen agents tamoxifen and raloxifene (Scheme 0). [diagram included in print copy, unable to reproduce electronically] Scheme 0 – Three series of virtual LRH-1 antagonists from our CADD approach [diagram label