The crystal structure of the AR LBD was first described by Matiaset al

The crystal structure of the AR LBD was first described by Matiaset al.in PF-06424439 methanesulfonate 2000 in a complex with the synthetic steroid, R1881 [Matias et al., 2000]. to multiple disorders such as hypogonadism, muscle wasting, cachexia, osteoporosis, loss of reproductive function, prostate cancer and others [Araujo et al., 2007;Brooke et al., 2008;Leder, 2007;Morley et al., 2005]. The ubiquitous expression of AR and the steroidal backbone of the natural ligands limit their use for therapeutic purposes, factors which encourage the pursuit of nonsteroidal tissue-selective androgen receptor modulators (SARMs). The first SARMs were reported in 1998 [Dalton et al., 1998;Edwards et al., 1998]. Since then, SARMs with a variety of structural scaffolds and a range of tissue selectivity and specificity have been discovered [Allan et al., 2007b;Manfredi et al., 2007]. The concept of tissue selective receptor modulators (SRMs) PF-06424439 methanesulfonate evolved from selective estrogen receptor modulators (SERMs), which have been clinically used for over two decades to replenish the diminishing circulating estrogens in postmenopausal conditions [Ward, 1973]. Efforts among the pharmaceutical and academic communities to discover SRMs for other receptors such as glucocorticoid receptor (SGRM) [Link et al., 2005;Mohler, 2007a;Mohler, 2007b], progesterone receptor (SPRM) [Tabata et al., 2003] and others are in progress. == Structure and function of androgen receptor (AR) == AR belongs to the largest class of DNA binding transcription factors, called nuclear receptors, comprised of 48 members [Evans, 1988;Tsai and O’Malley, 1994]. Each member of this family has a crucial nonredundant role and regulates critical biological functions in vertebrates and non-vertebrates [Escriva et al., 1997;Lu et PF-06424439 methanesulfonate al., 2006;Owen and Zelent, 2000]. Phylogenetic studies indicate that the members are highly conserved from the earliest metazoan [Owen and Zelent, 2000]. Of the 48 receptors, 24-27 bind ligand with a characterized ligand binding domain (LBD). The members of this family are divided into three classes, with class I containing receptors for estrogen, progesterone, mineralocorticoids, glucocorticoids and androgens. Receptors for vitamin D, retinoids and thyroids are categorized into PF-06424439 methanesulfonate class II. Class III receptors are those for which ligands have not yet been identified, and are hence classified as orphans. However, in recent years, natural and synthetic ligands for many of these orphan receptors have been uncovered [Blumberg and Evans, 1998;Tsai and O’Malley, 1994]. The AR DNA sequence is present in the X chromosome, which has 8 exons spanning 90 kb sequences encoding a 919 A.A. protein [Lu et al., CTLA1 2006]. Like the PR and ER, AR exists as 2 isoforms, AR and AR-A, formed by an alternate translation start. Similar to PR-A, which lacks the first 164 amino acids of PR-B, AR-A lacks the first 187 amino acids PF-06424439 methanesulfonate of AR. However, this isoform is not as well characterized as PR or ER isoforms and its functions remain unknown [Wilson and McPhaul, 1994;Wilson and McPhaul, 1996]. AR, similar to the other members of the class, contains four structural domains, with each performing exclusive functions. The complete function of the N-terminal domain (NTD) is still under investigation. However, the activation function (AF-1) located in the NTD plays a pivotal role in AR function. Unlike other receptors, the NTD of AR is the major transactivation domain and deletion of AF-1 leads to a significant loss of AR function [Alen et al., 1999;Bevan et al., 1999;Gao et al., 1996;Jenster et al., 1991;Simental et al., 1991]. In addition, the NTD.