Selective androgen receptor modulators (SARMs) are androgen receptor (AR) ligands that induce anabolism while having reduced effects in reproductive tissues. In various experimental contexts SARMs fully activate, partially activate, or even antagonize the AR, but how these complex activities translate into tissue selectivity is not known. Here, we probed receptor function using >1000 synthetic AR ligands. These compounds produced a spectrum of activities in each assay ranging from 0 to 100% of maximal response. By testing different classes of compounds in ovariectomized rats, we established that ligands that transactivated a model promoter 40 -80% of an agonist, recruited the coactivator GRIP-1 <15%, and stabilized the N-/C-terminal interdomain interaction <7% induced bone formation with reduced effects in the uterus and in sebaceous glands. Using these criteria, multiple SARMs were synthesized including MK-0773, a 4-aza-steroid that exhibited tissue selectivity in humans. Thus, AR activated to moderate levels due to reduced cofactor recruitment, and N-/C-terminal interactions produce a fully anabolic response, whereas more complete receptor activation is required for reproductive effects. This bimodal activation provides a molecular basis for the development of SARMs.

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Androgen replacement therapy is a promising strategy for the treatment of frailty; however, androgens pose risks for unwanted effects including virilization and hypertrophy of reproductive organs. Selective Androgen Receptor Modulators (SARMs) retain the anabolic properties of androgens in bone and muscle while having reduced effects in other tissues. We describe two structurally similar 4-aza-steroidal androgen receptor (AR) ligands, Cl-4AS-1, a full agonist, and TFM-4AS-1, which is a SARM. TFM-4AS-1 is a potent AR ligand (IC 50 , 38 nM) that partially activates an AR-dependent MMTV promoter (55% of maximal response) while antagonizing the N-terminal/C-terminal interaction within AR that is required for full receptor activation. Microarray analyses of MDA-MB-453 cells show that whereas Cl-4AS-1 behaves like 5␣-dihydrotestosterone (DHT), TFM-4AS-1 acts as a geneselective agonist, inducing some genes as effectively as DHT and others to a lesser extent or not at all. This gene-selective agonism manifests as tissue-selectivity: in ovariectomized rats, Cl-4AS-1 mimics DHT while TFM-4AS-1 promotes the accrual of bone and muscle mass while having reduced effects on reproductive organs and sebaceous glands. Moreover, TFM-4AS-1 does not promote prostate growth and antagonizes DHT in seminal vesicles. To confirm that the biochemical properties of TFM-4AS-1 confer tissue selectivity, we identified a structurally unrelated compound, FTBU-1, with partial agonist activity coupled with antagonism of the N-terminal/C-terminal interaction and found that it also behaves as a SARM. TFM-4AS-1 and FTBU-1 represent two new classes of SARMs and will allow for comparative studies aimed at understanding the biophysical and physiological basis of tissue-selective effects of nuclear receptor ligands.Androgens, primarily testosterone (T) 7 and its more potent derivative, 5␣-dihydrotestosterone (DHT), induce male reproductive physiology and secondary sexual traits such as facial hair and deepened voice. Additionally, in both genders androgens regulate bone and muscle anabolism, adipose mass, lipoprotein metabolism, and behavior (1-3). Androgens decline with age in both men and women (4), which contributes to age-related bone and muscle loss and increases in fat mass (5). Several studies report low testosterone as a risk factor for age-related diseases including osteoporosis (6), sarcopenia (7), atherosclerosis (8), type II diabetes/metabolic syndrome and obesity (9), cognitive impairment (10), and depression (11). Restoring androgens to youthful levels could thus slow unfavorable changes in body composition and improve mood, motivation, and general health. Unfortunately, current androgens induce male secondary sexual traits such as acne and hirsutism, an effect known as virilization, (12) and pose concerns related to unwanted effects in the prostate and other reproductive organs (13-15). Therefore, androgens are limited by concerns over safety and tolerability.Androgens exert their physiological effects by activating the androgen receptor ...

Signaling by androgens and interferons (IFN) plays an important role in prostate cancer initiation and progression. Using microarray analysis, we describe here a functional cross-talk between dihydrotestosterone and interferon signaling. Glutathione S-transferase pull-down and co-immunoprecipitation experiments reveal that the androgen receptor and the interferon-activated RNase L interact with each other in a ligand-dependent manner. Furthermore, overexpression of wild type RNase L confers IFN sensitivity to a dihydrotestosterone-inducible reporter gene, whereas R462Q-mutated RNase L does not. Based on our data we hypothesize that in 22RV1 cells, activated androgen receptor (AR) contributes to the insensitivity to IFN of the cell. Accordingly, we show that AR knockdown restores responsiveness to IFN␥. Our findings support a model in which both the activation of AR and the down-regulation of IFN signaling can synergize to promote cell survival and suppress apoptosis. This model provides the molecular basis to understand how mutated RNase L can lead to early onset PCa and illustrates how inflammatory cytokines and nuclear hormone signaling contribute to tumor development.Tumors are increasingly regarded as neoplastic organs with a specific microenvironment that comprises cells of different origins. The contribution of tumor-associated fibroblasts and endothelial cells to tumor growth is now well established (1). The role of inflammatory cells has received renewed attention with two recent reports that describe the interplay between tumor cells and tumor associated immune cells (2,3).In contrast to the contribution of inflammatory cytokines and immunoglobulins to tumor growth, T-cell-produced interferons have be shown to act as tumor suppressive cytokines (4). The recent identification of the interferonactivated ribonuclease RNase L as a candidate for the hereditary prostate cancer allele HPC1 further emphasized the role of interferon signaling in preventing tumor progression (5). Activated by 2Ј-5Ј oligoadenylates, RNase L acts as an IFN 2 -inducible tumor suppressor that stimulates apoptosis in prostate cells (6, 7).Endocrine signaling through nuclear receptors is required for the progression of a number of tumors (8). Androgen signaling affects normal prostate development and maintenance as well as prostate cancer progression. Accordingly, androgen blockade is the major therapeutic approach for prostate cancer. Up-regulation of the androgen receptor activity correlates with PCa progression and resistance from hormone blockade therapies (9, 10). Furthermore, dihydrotestosterone (DHT) has been shown to affect proliferation of breast tumor derived cells (11,12). The role of androgen receptor signaling in cancer is not fully understood. Several lines of evidence suggest that AR could promote PCa progression by inhibiting apoptosis or by promoting cell survival or proliferation (13).We describe here an intracellular cross talk between interferon and androgen signaling pathways. RNA microarrays analysis revealed that...

The diverse biological actions of retinoic acid (RA) are mediated by retinoic acid receptors (RARs) and retinoid X receptors. Although it has been suggested that the ligand binding domains (LBDs) of RARs share the same novel folding pattern, many RAR subtype-specific agonists and antagonists have been synthesized demonstrating that the LBD of each RAR subtype has unique features. We have examined the role of several positively charged amino acid residues located in the LBD of RAR␣ in RA binding. These results are compared with previously published data for the homologous mutations in RAR␤.