An investigation of the interactions of the androgen receptor with a non-steroidal compound and two synthetic progestins

[摘要] ENGLISH ABSTRACT:The aim of this thesis was to define the interactions of the androgen receptor(AR) with an analog of a non-steroidal plant compound, Compound A (CpdA), aswell as two synthetic progestins, medroxyprogesterone acetate (MPA) andnorethindrone acetate (NET-A). The data presented indicates that CpdA has antiandrogenicproperties, as it represses androgen-induced activation of both specific andnon-specific androgen-responsive reporter constructs. It was found that CpdA exertsthese effects by a mechanism other than competition with androgen for binding to theligand-binding domain (LBD) of the receptor. On the other hand, it is demonstratedthat both MPA and NET-A compete with androgen for binding to the AR and inducepartial agonist activity via the receptor. Using mammalian two-hybrid assays it wasrevealed that CpdA, similar to anti-androgenic compounds that are able to competewith androgens for binding to the receptor, represses the androgen-induced interactionbetween the NH2- and COOH-terminals of the AR (N/C-interaction) withoutcompeting for binding to the LBD. Furthermore, it was shown that CpdA slightlyrepresses the androgen-dependent recruitment of steroid receptor co-activator 1(SRC1) to the activation function (AF2) domain of the AR. When the effects of MPAand NET-A on the N/C-interaction were studied, intriguing results were obtained.NET-A, as expected, induced this AR agonist-induced interaction. MPA, however,repressed this AR agonist-induced interaction, an effect previously associated withanti-androgenic activity, despite displaying partial agonist activity in transctivationexperiments. On the other hand, both MPA and NET-A induced the interactionbetween SRC1 and the AF2 domain. In additional experiments with CpdA, it wasfound that CpdA did not affect the recruitment of SRC1 to the AF1 domain of thereceptor; neither did it influence the constitutive activity of the NH2-terminal domain.The anti-androgenic activities of CpdA were confirmed by the toxic effect that thiscompound had on the androgen-dependent lymph node carcinoma of the prostate(LNCaP) cell-line as well as its ability to repress the androgen-induced expression ofthe prostate specific antigen (PSA) protein. Taken together, the results presented inthis thesis, in combination with the knowledge available on AR function, contribute toan improved understanding of AR function. Furthermore, the importance of definingthe precise mechanism by which individual compounds exert their effects ishighlighted. In this regard it is demonstrated that two compounds (MPA and NET-A)that display partial agonist activity, can exert their effects via different mechanisms atthe molecular level. Detecting such differences in the molecular mechanisms of actioncould facilitate the improved design of progestins as well as aid clinicians and theirpatients in selecting the best method of contraception. Lastly, the insights gained intothe mechanisms of the anti-androgenic action of CpdA could be useful in therapeuticdrug design for diseases, such as prostate cancer, that have an androgen-dependentetiology.

[发布机构] Stellenbosch University