Ramesh Narayanan

Nonsteroidal Selective Androgen Receptor Modulators (SARMs): Dissociating the anabolic and androgenic activities of the androgen receptor for therapeutic benefit

Interest in the development and therapeutic potential of nonsteroidal tissue-selective androgen receptor modulators (SARMs) has increased dramatically within the past decade. Rapidly expanding knowledge of nuclear hormone receptor structure and function and successful proof-of-principle clinical trials with SARMs have revived an almost dormant search for improved androgens. This Award Address attempts to chronicle the landmark discoveries (with emphasis on our work), organize the SARM landscape into clinically relevant bins, and provide insight into the clinical prospects for SARMs. 1.1. Origins of Androgen Use. An early (1889) and unusual experiment in androgen therapy was performed by Charles Edouard Brown-Sequard, age 72. He administered a testicular extract to himself and reported that he felt “increased vigor and capacity for work”. Despite retrospective suggestions that any effect was purely placebo, this report resulted in widespread use of testicular extracts throughout Europe and North America for several decades. Attempts to isolate the active components of testicular extract failed until 1935 when testosterone (17 hydroxy-4-andosten-3-one) was isolated from bull testes. Shortly thereafter, its synthesis was reported. In the same year, extracts of urine from males were shown to cause nitrogen retention, an indicator of anabolic metabolism. Testosterone was the first anabolic androgen to be used clinically, but its use is limited by its androgenicity and pharmacokinetic (PK) issues. 1 In the latter half of the 20th century, the chemical scaffold of testosterone was modified extensively, producing many

Cyclin-dependent kinase activity is required for progesterone receptor function: novel role for cyclin A/Cdk2 as a progesterone receptor coactivator.

ABSTRACT Our studies examining the role of the cell cycle-regulated kinase cyclin A/Cdk2 in progesterone receptor (PR) action have demonstrated that cyclin-dependent kinase activity is required for PR function and that cyclin A/Cdk2 functions as a PR coactivator. Although Cdk2 can phosphorylate PR, elimination of these phosphorylation sites has little effect on the ability of cyclin A/Cdk2 to stimulate PR activity. PR interacts with cyclin A and recruits cyclin A/Cdk2 to progestin-responsive promoters, stimulating transcription. Inhibition of Cdk2 activity abolishes progesterone-dependent activation of PR target genes in part through inhibition of PR-dependent recruitment of steroid receptor coactivator 1 (SRC-1) and subsequent histone H4 acetylation at the target promoter. In vitro studies revealed that the interaction between SRC-1 and PR is dependent upon phosphorylation of SRC-1. This heretofore-unknown mechanism provides a potential means for integrating the regulation of PR activity with cell cycle progression. Moreover, the ability of PR to recruit cyclin A/Cdk2 to target promoters provides locally elevated levels of kinase, which can preferentially facilitate phosphorylation-dependent interactions and enzymatic activities of coactivators at the target promoter.

Selective androgen receptor modulators in preclinical and clinical development

Androgen receptor (AR) plays a critical role in the function of several organs including primary and accessory sexual organs, skeletal muscle, and bone, making it a desirable therapeutic target. Selective androgen receptor modulators (SARMs) bind to the AR and demonstrate osteo- and myo-anabolic activity; however, unlike testosterone and other anabolic steroids, these nonsteroidal agents produce less of a growth effect on prostate and other secondary sexual organs. SARMs provide therapeutic opportunities in a variety of diseases, including muscle wasting associated with burns, cancer, or end-stage renal disease, osteoporosis, frailty, and hypogonadism. This review summarizes the current standing of research and development of SARMs, crystallography of AR with SARMs, plausible mechanisms for their action and the potential therapeutic indications for this emerging class of drugs.

Selective Androgen Receptor Modulator (SARM) Treatment Prevents Bone Loss and Reduces Body Fat in Ovariectomized Rats

PurposeThis study was conducted to examine the bone and body composition effects of S-4, an aryl-propionamide derived Selective Androgen Receptor Modulator (SARM) in an ovariectomy induced model of accelerated bone loss.MethodsOne hundred twenty female Sprague–Dawley rats aged to twenty-three weeks were randomly assigned to twelve treatment groups. Drug treatment was initiated immediately following ovariectomy and continued for one hundred twenty days. Whole body bone mineral density (BMD), body composition, and lumbar vertebrae BMD were measured by dual energy x-ray absorptiometry. More stringent regional pQCT and biomechanical strength testing was performed on excised femurs.ResultsWe found that S-4 treatment maintained whole body and trabecular BMD, cortical content, and increased bone strength while decreasing body fat in these animals.ConclusionsThe data presented herein show the protective skeletal effects of S-4. Our previous reports have shown the tissue selectivity and muscle anabolic activity of S-4. Together these data suggest that S-4 could reduce the incidence of fracture via two different mechanisms (i.e., via direct effects in bone and reducing the incidence of falls through increased muscle strength). This approach to fracture reduction would be advantageous over current therapies in these patients which are primarily antiresorptive in nature.

Estrogen Receptor-β-selective Ligands Alleviate High-fat Diet- and Ovariectomy-induced Obesity in Mice

Obesity is an epidemic problem affecting millions of people in the Western hemisphere and costs the United States economy more than

Human Progesterone Receptor Displays Cell Cycle-Dependent Changes in Transcriptional Activity

200 billion annually. Currently, there are no effective treatments to combat obesity. Recent studies have implicated the constitutive activity of estrogen receptor (ER) β as an important regulator of metabolic diseases. However, the potential of ER-β-selective ligands to offset obesity is not clear. We evaluated the pharmacological effect of ER-β-selective ligands (β-LGNDs) in animal models of high-fat diet- and ovariectomy-induced obesity. Ligand binding, transactivation, and uterotrophic studies with β-LGNDs demonstrated selectivity for ER-β over ER-α. Animals fed a high-fat diet showed a significant increase in body weight, and this weight gain was attenuated by β-LGNDs. High-fat diet-mediated increases in serum cholesterol, leptin, glucose, and fat accumulation in organs were also reduced by β-LGNDs. In addition, MRI scanning indicated that β-LGNDs altered body composition by reducing fat mass and increasing lean body mass. Organ weights and gene expression analyses demonstrated that adipose tissue is the center of action for β-LGNDs, and the reduction in body weight is likely due to increased energy expenditure. In vitro and in vivo mechanistic studies indicated that the anti-obesity effects of β-LGNDs were due to indirect peroxisome proliferator-activated receptor γ antagonistic actions requiring the ligand binding domain of ER-β and through abrogation of the ability of PGC-1 to coactivate peroxisome proliferator-activated receptor γ. In conclusion, these studies indicate that ligand-activated ER-β is a potential therapeutic target to combat obesity and obesity-related metabolic diseases.

TMPRSS2:ERG Gene Fusion Predicts Subsequent Detection of Prostate Cancer in Patients With High-Grade Prostatic Intraepithelial Neoplasia

ABSTRACT The human progesterone receptor (PR) contains multiple Ser-Pro phosphorylation sites that are potential substrates for cyclin-dependent kinases, suggesting that PR activity might be regulated during the cell cycle. Using T47D breast cancer cells stably transfected with an mouse mammary tumor virus (MMTV) chloramphenicol acetyltransferase reporter (Cat0) synchronized in different phases of the cell cycle, we found that PR function and phosphorylation is remarkably cell cycle dependent, with the highest activity in S phase. Although PR expression was reduced in the G2/M phase, the activity per molecule of receptor was markedly reduced in both G1 and G2/M phases compared to the results seen with the S phase of the cell cycle. Although PR is recruited to the MMTV promoter equivalently in the G1 and S phases, recruitment of SRC-1, SRC-3, and, consequently, CBP is reduced in G1 phase despite comparable expression levels of SRC-1 and SRC-3. In G2/M phase, site-specific phosphorylation of PR at Ser162 and at Ser294, a site previously reported to be critical for transcriptional activity and receptor turnover, was abolished. Treatment with the histone deacetylase inhibitor trichostatin A elevated G1 and G2/M activity to that of the S phase, indicating that the failure to recruit sufficient levels of active histone acetyltransferase is the primary defect in PR-mediated transactivation.

c-Jun N-Terminal Kinase Contributes to Aberrant Retinoid Signaling in Lung Cancer Cells by Phosphorylating and Inducing Proteasomal Degradation of Retinoic Acid Receptor α

PURPOSE High-grade prostatic intraepithelial neoplasia (HGPIN) is considered a precursor lesion of prostate cancer (PCa). The predictive value of ERG gene fusion in HGPIN for PCa was interrogated as a post hoc analysis in the context of a randomized clinical trial. PATIENTS AND METHODS The GTx Protocol G300104 randomly assigned 1,590 men with biopsy-diagnosed HGPIN to receive toremifene or placebo for 3 years or until a diagnosis of PCa was made on prostate biopsy. As part of this phase III clinical trial, a central pathologist evaluated biopsies of patients with isolated HGPIN at baseline and 12, 24, and 36 months of follow-up. ERG immunohistochemistry was performed on biopsies from 461 patients and evaluated for protein overexpression. RESULTS ERG expression was detected in 11.1% of patients (51 of 461 patients) with isolated HGPIN. In the first year and during the 3-year clinical trial, 14.7% and 36.9% of 461 patients were diagnosed with PCa, respectively. Patients with ERG expression were more likely to develop PCa, with 27 (53%) of 51 ERG-positive and 143 (35%) of 410 ERG-negative patients experiencing progression to PCa (P = .014, Fishers exact test). ERG expression was not associated with age, baseline PSA, Gleason score, or tumor volume. CONCLUSION This study underscores the necessity of more stringent follow-up for men with HGPIN that is also positive for ERG overexpression. Clinicians should consider molecular characterization of HGPIN as a means to improve risk stratification.

Steroidal androgens and nonsteroidal, tissue-selective androgen receptor modulator, S-22, regulate androgen receptor function through distinct genomic and nongenomic signaling pathways

ABSTRACT Retinoic acid (RA) is the ligand for nuclear RA receptors (RARs and RXRs) and is crucial for normal epithelial cell growth and differentiation. During malignant transformation, human bronchial epithelial cells acquire a block in retinoid signaling caused in part by a transcriptional defect in RARs. Here, we show that activation of c-Jun N-terminal kinase (JNK) contributes to RAR dysfunction by phosphorylating RARα and inducing degradation through the ubiquitin-proteasomal pathway. Analysis of RARα mutants and phosphopeptide mapping revealed that RARα residues Thr181, Ser445, and Ser461 are phosphorylated by JNK. Mutation of these residues to alanines prevented efficient ubiquitination of RARα and increased the stability of the protein. We investigated the importance of RARα phosphorylation by JNK as a mediator of retinoid resistance in lung cancer. Mice that develop lung cancer from activation of a latent K-ras oncogene had high intratumoral JNK activity and low RARα levels and were resistant to treatment with an RAR ligand. JNK inhibition in a human lung cancer cell line enhanced RARα levels, ligand-induced activity of RXR-RAR dimers, and growth inhibition by RA. These findings point to JNK as a key mediator of aberrant retinoid signaling in lung cancer cells.

MicroRNAs are mediators of androgen action in prostate and muscle.

Androgen receptor (AR) ligands are important for the development and function of several tissues and organs. However, the poor oral bioavailability, pharmacokinetic properties, and receptor cross-reactivity of testosterone, coupled with side effects, place limits on its clinical use. Selective AR modulators (SARMs) elicit anabolic effects in muscle and bone, sparing reproductive organs like the prostate. However, molecular mechanisms underlying the tissue selectivity remain ambiguous. We performed a variety of in vitro studies to compare and define the molecular mechanisms of an aryl propionamide SARM, S-22, as compared with dihydrotestosterone (DHT). Studies indicated that S-22 increased levator ani muscle weight but decreased the size of prostate in rats. Analysis of the upstream intracellular signaling events indicated that S-22 and DHT mediated their actions through distinct pathways. Modulation of these pathways altered the recruitment of AR and its cofactors to the PSA enhancer in a ligand-dependent fashion. In addition, S-22 induced Xenopus laevis oocyte maturation and rapid phosphorylation of several kinases, through pathways distinct from steroids. These studies reveal novel differences in the molecular mechanisms by which S-22, a nonsteroidal SARM, and DHT mediate their pharmacological effects.