ABSTRACT Evidence from knockout studies in male mice and from experiments in male rats,in which expression of the estrogen receptor alpha (ERα) gene was inhibited in the medial preoptic area (MPO), suggests that ERα is important in the control of male rat mating behavior. Therefore, in this experiment, we tested the hypothesis that activation of ERα in the MPO is sufficient to maintain mating behavior in castrated male rats receiving subcutaneously (s.c.) dihydrotestosterone (DHT), a non-aromatizable androgen. Accordingly, castrated rats treated with DHT s.c. received MPO implants of either: (i) propyl-pyrazole-triol (PPT) (Stauffer, et al 2000; Katzenellenbogen, et al 2000), a selective ERα agonist, (ii) E2 (positive controls) or (iii) cholesterol (negative controls)and sexual behavior was monitored. PPT was as effective as E2 at maintaining mating behavior suggesting that, in the MPO, ERα is sufficient to mediate responses to E2 that underlie male rat mating behavior.

The growth and survival of normal breast epithelial cells and breast cancer cells is promoted by estrogens. In contrast, androgens inhibit the proliferation of normal and malignant breast epithelial cells. While this effect of androgens on breast cells appears to be androgen receptor (AR) dependent, the precise mechanism of inhibition and its functional significance are unknown. The aims of this thesis were to investigate the effect of androgen signalling on growth of normal and malignant breast epithelial cells, and to assess the interactions between androgen and estrogen signalling in the breast. To investigate the role of androgen signalling in the growth and development of the normal mammary gland, female mice were treated with either the native androgen 5α- dihydrotestosterone (DHT) or the antiandrogen, flutamide. Analysis of the mammary glands at the end of the treatment period demonstrated that DHT reduced ductal branching and mammary epithelial cell proliferation when treatment commenced mid-puberty. Conversely, flutamide treatment that commenced post-puberty significantly increased ductal branching and proliferation of mammary epithelial cells. This data demonstrates that androgen signalling inhibits proliferation in the normal mammary gland, and may therefore oppose to the growth stimulatory effects of estrogen signalling to regulate breast growth and development. The antiproliferative effects of androgens on breast epithelial cells may be due in part to direct AR-mediated activation of androgen regulated genes, or alternatively, androgens could act indirectly through AR to inhibit estrogen receptor alpha (ERα) activity. Expression of fulllength AR or a truncated, constitutively active AR (AR-T707) significantly inhibited the activity of ectopically expressed ERα in MDA-MB-231 breast cancer cells (ERα- and ARnegative), in a dose-dependent manner. The functional consequences of inhibition of estrogen signalling by overexpressing AR were investigated in the T-47D breast cancer cell line (ERα- and AR-positive). Expression of AR-T707 in T-47D cells resulted in inhibition of both basal and estradiol-induced cell proliferation and a marked reduction in the steady-state protein levels of the estrogen regulated gene, PR. The final chapter investigated the mechanism by which AR inhibits ERα activity. A coimmunoprecipitation assay demonstrated an interaction between ectopically expressed AR and ERα in COS-1 cells, but not endogenous AR and ERα in a breast cancer cell line. To delineate the regions of AR required for inhibition of ERα signalling, various functional domains of the AR were mutated or deleted. Reporter gene assays showed that the inhibitory effects of AR were abrogated by deletion or mutation of the DNA binding domain (DBD). Furthermore, overexpression of the AR-DBD alone was sufficient to inhibit ERα activity. Consistent with a requirement for the DBD of AR to inhibit ERα activity, mobility shift assays demonstrated binding of AR to the Xenopus vitellogenin A2 consensus estrogen response element (cERE); however AR/ERα heterodimers were not detected on a cERE. Consistent with these findings, molecular modelling demonstrated that it is feasible for the DBD of AR to bind to a cERE and that it is unlikely that AR/ERα heterodimers could bind. Chromatin immunoprecipitation demonstrated recruitment of AR to the promoters of endogenous estrogen regulated genes. The findings suggest that the inhibitory effect of AR on ERα activity may occur either via formation of non-functional AR/ERα heterodimers that are unable to bind to EREs, or AR homodimers competing effectively for binding to EREs, in ERα target genes. The results in this thesis demonstrate an inhibitory effect of androgen signalling on growth of normal and malignant breast epithelial cells. Additionally, the inhibition of breast epithelial cell proliferation by androgen signalling can be attributed, at least in part, to inhibition of ERα activity. These studies have provided insight into androgen action in the breast, and support a model whereby androgens balance the stimulatory effects of estrogen signalling in normal and malignant breast epithelial cells. / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2008

This thesis investigates the biological activity of selected non-steroidal analogues of sex steroid hormones by examining two different effects of analogues on endogenous sex hormone activity. Non-steroidal analogues of sex hormones were synthesised to study their biological interactions with a sex steroid receptor and a sex steroid metabolising enzyme. Chapter One introduces the steroid hormones and their physiology, which leads to a review of the mechanisms by which steroids exert their effects. Their implication in disease is discussed, with particular emphasis on the sex steroids. As the biological activity of steroids is related to their chemical structure, the important features of steroid structure are identified, including the cyclopentanoperhydrophenanthrene nucleus, arrangement of ring substituents and ring junction conformation. The concept of non-steroidal analogues of steroids is introduced, and the harmful or beneficial effects analogues have on endogenous steroid activity are considered. Alteration of steroid activity and its consequences are focussed on two main areas; the potential adverse effects of environmental chemicals which mimic sex steroid activity, and the use of non-steroidal analogues in medicinal chemistry for treating sex steroid related disease. Chapter Two describes an investigation into the 17β-estradiol mimicking activity of non-steroidal analogues. Exogenous chemicals that mimic estradiol are of concern as they may alter endogenous estradiol activity and disrupt endocrine systems. Firstly, an introduction to the field of research concerned with environmental chemicals that mimic steroid hormones is given. The interaction of xenoestrogens with the estrogen receptor is described, as are the methods available for assessing the estrogen mimicking activity of xenoestrogens. The concern for insecticides mimicking estrogen activity is described by reviewing reported activities of insecticides, which leads into a discussion of work carried out as part of this thesis. Metabolites of the pyrethroid insecticides permethrin and cypermethrin, 2.14, 2.15, and 2.16 were synthesised while others were commercially obtained. The interaction of pyrethroid insecticide metabolites with the human estrogen receptor expressed in recombinant yeast (Saccharomyces cerevisiae) was studied, following the establishment and validation of the assay. Metabolites 2.11, 2.12, and 2.14 were found to weakly stimulate estrogen receptor-mediated estradiol responsive gene expression in the yeast assay (105 less active than 17β-estradiol). Since the activity of the metabolites using the yeast assay was greater than for the parent compounds, metabolic pathways need to be considered when assessing the impact of exposure to environmental estrogens. The low estrogenic activity suggests these compounds are not individually contributing significantly to the xenoestrogenic impact on humans, but will add to total xenoestrogen exposure. Chapter Three describes the inhibition of a sex steroid metabolising enzyme, steroid 5a-reductase, by novel non-steroidal compounds. Inhibitors of this enzyme are potentially useful therapeutic agents for regulating the activity of an androgen in prostate disorders. A review of the literature on non-steroidal inhibition of 5a-reductase identified three key structural features known to enhance inhibitor potency; ring substitution, position and nature of ring unsaturation and angular methyl group presence. These features were taken into account in the design of inhibitors synthesised in this thesis (3.55-3.57, 3.59, 3.61, 3.62, 3.110 and 3.111). Inhibitors consisting of non-steroidal 5- or 1-aryl pyridone scaffolds were synthesised to investigate SAR for 4'-substituents. The 5-aryl 1-methyl-2-pyridone/piperidone scaffold of compounds 3.55-3.57 and 3.59 was constructed by Suzuki cross coupling methodology, while the 1-aryl 2-methyl 2,3-dihydro-4-pyridone scaffold of 3.61 and 3.62 was constructed by aza Diels-Alder methodology. Long carbon chain olefin containing tethers 3.107 and 3.108 were synthesised for conjugation to inhibitor 3.57 by cross metathesis to give conjugates 3.110 and 3.111. Compounds 3.55-3.57, 3.59, 3.61, 3.62, 3.110 and 3.111 inhibited the type 1 5a-reductase isozyme expressed by HEK-I cells, with activities comparable to those of related literature compounds. The 1-aryl 2,3-dihydro-4-pyridone 3.62 inhibited both the type 1 and 2 isozymes (expressed by HEK-II cells) of 5a-reductase. The presence of bulky hydrophobic groups (benzoyl, long chain tethers) at the 4' position enhanced the potency of type 1 inhibition by 5-aryl pyridone type compounds in comparison to N,N-diisopropyl- and N-allylacetamide groups. This information provides further understanding of SAR within and across different classes of non-steroidal inhibitors of steroid 5a-reductase towards improved drug design.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 21, 2008) Includes bibliographical references.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Thesis (M.S.)--University of North Carolina Wilmington, 2007. / Includes bibliographical references (Leaves: 110-116)

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2006. / Härtill 4 uppsatser.