Role of nuclear receptors in lipid dysfunction and obesity-related diseases.

This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the Experimental Biology 12 meeting in San Diego, CA. The presentations discussed the roles of a number of nuclear receptors in regulating glucose and lipid homeostasis, the pathophysiology of obesity-related disease states, and the promise associated with targeting their activities to treat these diseases. While many of these receptors (in particular, constitutive androstane receptor and pregnane X receptor) and their target enzymes have been thought of as regulators of drug and xenobiotic metabolism, this symposium highlighted the advances made in our understanding of the endogenous functions of these receptors. Similarly, as we gain a better understanding of the mechanisms underlying bile acid signaling pathways in the regulation of body weight and glucose homeostasis, we see the importance of using complementary approaches to elucidate this fascinating network of pathways. The observation that some receptors, like the farnesoid X receptor, can function in a tissue-specific manner via well defined mechanisms has important clinical implications, particularly in the treatment of liver diseases. Finally, the novel findings that agents that selectively activate estrogen receptor ß can effectively inhibit weight gain in a high-fat diet model of obesity identifies a new role for this member of the steroid superfamily. Taken together, the significant findings reported during this symposium illustrate the promise associated with targeting a number of nuclear receptors for the development of new therapies to treat obesity and other metabolic disorders.

Estrogen receptor-{beta}-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 $200 billion annually. Currently, there are no effective treatments to combat obesity. Recent studies have implicated the constitutive activity of estrogen receptor (ER) ß as an important regulator of metabolic diseases. However, the potential of ER-ß-selective ligands to offset obesity is not clear. We evaluated the pharmacological effect of ER-ß-selective ligands (ß-LGNDs) in animal models of high-fat diet- and ovariectomy-induced obesity. Ligand binding, transactivation, and uterotrophic studies with ß-LGNDs demonstrated selectivity for ER-ß over ER-α. Animals fed a high-fat diet showed a significant increase in body weight, and this weight gain was attenuated by ß-LGNDs. High-fat diet-mediated increases in serum cholesterol, leptin, glucose, and fat accumulation in organs were also reduced by ß-LGNDs. In addition, MRI scanning indicated that ß-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 ß-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 ß-LGNDs were due to indirect peroxisome proliferator-activated receptor γ antagonistic actions requiring the ligand binding domain of ER-ß 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-ß is a potential therapeutic target to combat obesity and obesity-related metabolic diseases.

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

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.

Selective androgen receptor modulators (SARMs) negatively regulate triple-negative breast cancer growth and epithelial:mesenchymal stem cell signaling.

INTRODUCTION: The androgen receptor (AR) is the most highly expressed steroid receptor in breast cancer with 75-95% of estrogen receptor (ER)-positive and 40-70% of ER-negative breast cancers expressing AR. Though historically breast cancers were treated with steroidal androgens, their use fell from favor because of their virilizing side effects and the emergence of tamoxifen. Nonsteroidal, tissue selective androgen receptor modulators (SARMs) may provide a novel targeted approach to exploit the therapeutic benefits of androgen therapy in breast cancer. MATERIALS AND METHODS: Since MDA-MB-453 triple-negative breast cancer cells express mutated AR, PTEN, and p53, MDA-MB-231 triple-negative breast cancer cells stably expressing wildtype AR (MDA-MB-231-AR) were used to evaluate the in vitro and in vivo anti-proliferative effects of SARMs. Microarray analysis and epithelial:mesenchymal stem cell (MSC) co-culture signaling studies were performed to understand the mechanisms of action. RESULTS: Dihydrotestosterone and SARMs, but not bicalutamide, inhibited the proliferation of MDA-MB-231-AR. The SARMs reduced the MDA-MB-231-AR tumor growth and tumor weight by greater than 90%, compared to vehicle-treated tumors. SARM treatment inhibited the intratumoral expression of genes and pathways that promote breast cancer development through its actions on the AR. SARM treatment also inhibited the metastasis-promoting paracrine factors, IL6 and MMP13, and subsequent migration and invasion of epithelial:MSC co-cultures. CONCLUSION: 1. AR stimulation inhibits paracrine factors that are important for MSC interactions and breast cancer invasion and metastasis. 2. SARMs may provide promise as novel targeted therapies to treat AR-positive triple-negative breast cancer.

Steroidogenic enzyme AKR1C3 is a novel androgen receptor-selective coactivator that promotes prostate cancer growth.

PURPOSE: Castration-resistant prostate cancer (CRPC) may occur by several mechanisms including the upregulation of androgen receptor (AR), coactivators, and steroidogenic enzymes, including aldo keto reductase 1C3 (AKR1C3). AKR1C3 converts weaker 17-keto androgenic precursors to more potent 17-hydroxy androgens and is consistently the major upregulated gene in CRPC. The studies in the manuscript were undertaken to examine the role of AKR1C3 in AR function and CRPC. EXPERIMENTAL DESIGN: LNCaP cells stably transfected with AKR1C3 and VCaP cells endogenously expressing AKR1C3 were used to understand the effect of AKR1C3 on prostate cancer cell and tumor growth in nude mice. Chromatin immunoprecipitation, confocal microscopy, and co-immunoprecipitation studies were used to understand the recruitment of AKR1C3, intracellular localization of AKR1C3 and its interaction with AR in cells, tumor xenograft, and in Gleason sum 7 CRPC tissues. Cells were transiently transfected for AR transactivation. Novel small-molecule AKR1C3-selective inhibitors were synthesized and characterized in androgen-dependent prostate cancer and CRPC models. RESULTS: We identified unique AR-selective coactivator- and prostate cancer growth-promoting roles for AKR1C3. AKR1C3 overexpression promotes the growth of both androgen-dependent prostate cancer and CRPC xenografts, with concomitant reactivation of androgen signaling. AKR1C3 interacted with AR in prostate cancer cells, xenografts, and in human CRPC samples and was recruited to the promoter of an androgen-responsive gene. The coactivator and growth-promoting functions of AKR1C3 were inhibited by an AKR1C3-selective competitive inhibitor. CONCLUSIONS: AKR1C3 is a novel AR-selective enzymatic coactivator and may represent the first of more than 200 known nuclear hormone receptor coactivators that can be pharmacologically targeted.

Discovery and preclinical characterization of novel small molecule TRK and ROS1 tyrosine kinase inhibitors for the treatment of cancer and inflammation.

Receptor tyrosine kinases (RTKs), in response to their growth factor ligands, phosphorylate and activate downstream signals important for physiological development and pathological transformation. Increased expression, activating mutations and rearrangement fusions of RTKs lead to cancer, inflammation, pain, neurodegenerative diseases, and other disorders. Activation or over-expression of ALK, ROS1, TRK (A, B, and C), and RET are associated with oncogenic phenotypes of their respective tissues, making them attractive therapeutic targets. Cancer cDNA array studies demonstrated over-expression of TRK-A and ROS1 in a variety of cancers, compared to their respective normal tissue controls. We synthesized a library of small molecules that inhibit the above indicated RTKs with picomolar to nanomolar potency. The lead molecule GTx-186 inhibited RTK-dependent cancer cell and tumor growth. In vitro and in vivo growth of TRK-A-dependent IMR-32 neuroblastoma cells and ROS1-overexpressing NIH3T3 cells were inhibited by GTx-186. GTx-186 also inhibited inflammatory signals mediated by NFκB, AP-1, and TRK-A and potently reduced atopic dermatitis and air-pouch inflammation in mice and rats. Moreover, GTx-186 effectively inhibited ALK phosphorylation and ALK-dependent cancer cell growth. Collectively, the RTK inhibitor GTx-186 has a unique kinase profile with potential to treat cancer, inflammation, and neuropathic pain.

ß-LGND2, an ERß selective agonist, inhibits pathologic retinal neovascularization.

PURPOSE: The goal of our study was to evaluate the in vitro and in vivo anti-angiogenic effects of ERß selective agonist, ß-LGND2, using human retinal microvascular endothelial cell (HRMVEC) cultures and a mouse model for oxygen-induced retinopathy (OIR). METHODS: The selectivity of ß-LGND2 was determined using binding and transactivation assays. The effects of ß-LGND2 on pathologic neovascularization were evaluated in OIR mice by histology and retinal mounts stained with isolectin B4 to quantify aberrant angiogenesis. Gene expression and protein levels were evaluated using Q-PCR, angiogenesis protein array, and Western blotting. A cell death detection ELISA kit was used to evaluate HRMVECs following hypoxic and hyperoxic conditions. In vitro angiogenesis was evaluated by growth factor-induced proliferation, tube formation, and cell migration assays. RESULTS: ß-LGND2-treated OIR mice had a reduced number of neovascular tufts compared to vehicle-treated animals and a significant amount of normal blood vessel maturation similar to normoxia controls. ß-LGND2 inhibited in vitro hypoxia- or hyperoxia-induced cell death and the formation of endothelial tubular structures in an ERß-specific mechanism. However, ß-LGND2 did not inhibit significantly growth factor-induced HRMVEC proliferation and migration. Gene and protein studies revealed that OIR mice treated with ß-LGND2 had lower levels of pro-angiogenic factors, like VEGF and HIF1α. CONCLUSIONS: ß-LGND2 inhibited in vitro and in vivo pathologic neovascularization in the retina in an ERß-specific mechanism. These results show that ß-LGND2, a non-steroidal ERß selective agonist, could be a useful therapeutic for ocular diseases involving aberrant angiogenesis, like ROP, wet-AMD, and diabetic retinopathy.

17-ß estradiol protects ARPE-19 cells from oxidative stress through estrogen receptor-ß.

PURPOSE: To elucidate the mechanism of 17-ß estradiol (17ß-E(2))-mediated protection of retinal pigment epithelium (RPE) from oxidative stress. METHODS: Cultured ARPE-19 cells were subjected to oxidative stress with t-butyl hydroxide or hydrogen peroxide in the presence or absence of 17ß-E(2). Reactive oxygen species (ROS) were measured using H(2)DCFDA fluorescence. Apoptosis was evaluated by cell-death ELISA kit and Hoechst-3486 staining. Mitochondrial membrane potential was measured using the JC-1 assay. Cellular localization of estrogen receptor (ER) was evaluated by confocal microscopy. Gene expression and protein expression was quantified using qRT-PCR and western blotting. Superoxide dismutase and ATP levels were measured using commercial kits. RESULTS: ARPE-19 cells expressed significant amounts of ERα and ERß. Pretreatment with 17ß-E2 protected ARPE-19 cells from oxidative stress and apoptosis. 17ß-E(2) reduced the ROS levels and mitochondrial depolarization. The 17ß-E(2)-mediated cytoprotection was inhibited by ER antagonists ICI (ERα and ERß) and THC (ERß) but not by tamoxifen (ERα). Knockdown of ERß expression by siRNA abolished the protective effects of 17ß-E(2). Further, qRT-PCR analysis revealed that 17ß-E(2) pretreatment upregulated the expression of ERß and phase II cellular antioxidant genes. CONCLUSIONS: These results indicate that 17ß-E(2) protects ARPE-19 cells from oxidative stress through an ERß-dependent mechanism. 17ß-E(2)-mediated cytoprotection occurred through the preservation of mitochondrial function, reduction of ROS production, and induction of cellular antioxidant genes.

Discovery and mechanistic characterization of a novel selective nuclear androgen receptor exporter for the treatment of prostate cancer.

Despite the success of medical strategies to reduce androgen levels in the treatment of prostate cancer, this disease invariably relapses to a castrate-resistant state that is generally fatal. Although it had been thought that androgen-insensitive cancers no longer relied on the androgen receptor (AR) for growth and survival, it is now clear that this is not the case. Because relapses are known to occur by many mechanisms that keep the AR functionally active, strategies to block AR accumulation in the nucleus may be therapeutically useful. Here, we report the discovery of a selective nuclear androgen receptor exporter (SNARE) that functions to exclude AR from the nucleus. SNARE-1 binds wild-type and mutant ARs and efficiently inhibits their transactivation activity and ability to induce PSA gene expression. SNARE-1 inhibits the androgen-sensitive growth of LNCaP cells and tumor xenografts. Quantitative subcellular localization studies suggest that SNARE-1 inhibits nuclear translocation of AR, but also facilitates export of nuclear AR that has been translocated by an agonist. Mechanistic studies indicate that SNARE-1 rapidly phosphorylates p38 mitogen-activated protein kinase (MAPK) and Ser(650) of the AR. Additionally, SNARE-1 was found to promote ubiquitination of AR in LNCaP cells. Lastly, SNARE-1 functions as a tissue-selective AR inhibitor, as it fails to phosphorylate p38 MAPK in U2OS bone cells that are stably transfected with AR. In summary, SNARE-1 inhibits AR function by a mechanism that is distinct from clinically available antiandrogens, such that it might inform novel methods to block AR function in androgen-independent prostate cancer.