Current Medicinal Chemistry - Volume 12, Issue 9, 2005

Nuclear receptors (NRs) are ligand-dependent transcription factors that play a central role in various physiological processes. The pharmaceutical industry has great interest in this gene-family for the discovery of novel or improved drugs for treatment of, for example, cancer, infertility, or diabetes. The usage of threedimensional coordinates of protein structures to analyse and predict interactions with ligands is an important aspect of this process. All NR ligand-binding domains have a similar fold, which allows for comparison of the structures of their three main functional sites: the ligand-binding pocket, the cofactor-binding groove, and the dimerization interface. We performed an analysis of nearly one hundred NR ligand-binding domain structures, and identified the functionally important residues. The combined knowledge about the shape of the binding sites and the residues involved in the binding is important for drug design in two ways. First, knowledge about the location of residues that interact with a ligand in all crystal structures or in certain subfamilies assists in the design and docking of drugs. Second, similarities and differences in the residue types of the most frequent ligand- and cofactor-binding residues provide insight about potential cross-reactivity of ligands or cofactors.

The last ten years much attention has been focused on the finding of non-steroidal ligands for steroidal nuclear receptors for reasons such as diminishing cross-reactivity to eliminate side effect profiles, changing physicochemical properties which might cause different tissue distribution profiles and altering binding modes which influence the binding of cofactors. Compounds with a selective functionality profile are referred to as selective nuclear receptor modulators (e.g., SARMs or SPRMs). In the following paragraphs nonsteroidal ligands which have full or partial agonistic activity will be described for the following receptors: PR, GR, AR, LXR and FXR.

The biological effects of estrogens are thought to be mediated by two receptors referred to as ERα and ERβ. In recent years significant efforts have been devoted to the design of subtype selective ligands. These ligands are valuable tools to establish the precise biological role of each of the subtypes and to develop new generations of therapeutics. The first part of this review briefly summarizes the biology behind the estrogen receptors. The second part addresses the structure-activity relationship of the subtype selective ER ligands that were reported up to now. In the third part, the current insights in the therapeutic prospects of the subtype selective estrogens will be discussed.