Glutamic Acid 709 Substitutions Highlight the Importance of the Interaction between Androgen Receptor Helices H3 and H12 for Androgen and Antiandrogen Actions

Structural analysis of the impact of a novel androgen receptor gene mutation in two adult patients with mild androgen insensitivity syndrome

Androgen receptor gene (AR) mutations are responsible for androgen insensitivity syndrome (AIS) presenting with a clinical phenotype that ranges from gynaecomastia and/ or infertility in mild AIS (MAIS) to complete testicular feminisation in complete AIS. We report a novel AR gene mutation in two unrelated adult patients with MAIS and we studied its functional impact using 3D modelling. Patient 1, referred for infertility, presented with gynaecomastia, mild hypospadias and bilateral testicular hypotrophy contrasting with high testosterone levels, an elevated FSH, an elevated androgen sensitivity index (ASI) and oligoasthenoteratospermia. In vitro fertilisation and intracytoplasmic sperm injection resulted in a successful twin pregnancy. Patient 2 referred for a decrease in athletic performance had surgically treated gynaecomastia, oligoasthenospermia, high testosterone levels and an elevated ASI. Despite his impaired spermogram, he fathered two children without assisted reproductive technology. AR gene sequencing in the two patients revealed a common novel missense mutation, Ala699Thr, in exon 4 within the ligand-binding domain. 3D modelling studies showed that this mutation may impact dimer stability upon ligand binding or may affect allosteric changes upon dimerisation. This study illustrates the value of structural analysis for the functional study of mutations and expands the database of AR gene mutations.

Functional and Structural Study of the Amino Acid Substitution in a Novel Familial Androgen Receptor Mutation (W752G) Responsible for Complete Androgen Insensitivity Syndrome

Mutations of the androgen receptor (AR) gene are the most frequent cause of 46,XY disorders of sex development. They are associated with a variety of phenotypes, ranging from phenotypic women (complete androgen insensitivity syndrome, CAIS) to milder degrees of undervirilization (partial forms) or men with only infertility (mild form). We identified a new W752G AR mutation responsible for a familial case of CAIS and performed an in vitro study and structural analysis of this mutation and the only other reported substitution affecting the same amino acid (W752R). Although sex assignment is not discussed in cases of CAIS, we show how the phenotype-genotype correlation can be refined by in vitro and structural studies according to the nature of the amino acid substitution, which in turn may have interesting impacts on the follow-up of these patients.

BAY 1024767 blocks androgen receptor mutants found in castration-resistant prostate cancer patients

Androgen receptor (AR) mutations arise in patients developing resistance to hormone deprivation therapies. Here we describe BAY 1024767, a thiohydantoin derivative with strong antagonistic activity against nine AR variants with mutations located in the AR ligand-binding domain (LBD), and against wild-type AR. Antagonism was maintained, though reduced, at increased androgen levels. Anti-tumor efficacy was evidenced in vivo in the KuCaP-1 prostate cancer model which bears the W741C bicalutamide resistance mutation and in the syngeneic prostate cancer rat model Dunning R3327-G. The prevalence of six selected AR mutations was determined in plasma DNA originating from 100 resistant patients and found to be at least 12%. Altogether the results show BAY 1024767 to be a strong antagonist for several AR mutants linked to therapy resistance, which opens the door for next-generation compounds that can benefit patients based on their mutation profile.

Partial Androgen Insensitivity Syndrome Presenting with Gynecomastia

Gynecomastia is a benign enlargement of the male breast caused by the proliferation of glandular breast tissue. Determining the various causes of gynecomastia such as physiological causes, drugs, systemic diseases, and endocrine disorders is important. Androgen insensitivity syndrome (AIS) is a rare endocrine disorder presenting with gynecomastia and is a disorder of male sexual differentiation caused by mutations within the androgen receptor gene. All individuals with AIS have the 46 XY karyotype, although AIS phenotypes can be classified as mild, partial or complete and can differ among both males and females including ambiguous genitalia or infertility in males. We experienced a case of partial AIS presenting with gynecomastia and identified the androgen receptor gene mutation.

Learning from estrogen receptor antagonism: structure-based identification of novel antiandrogens effective against multiple clinically relevant androgen receptor mutants

Current treatment strategy for advanced prostate cancer is to suppress androgen receptor (AR) by castration and antiandrogens. However, several clinically relevant AR mutations cause insensitivity to current antiandrogens and convert them into agonists. We aim to identify full AR antagonists even for AR mutants. As crystal structure of AR ligand-binding domain (LBD) at antagonistic form is not available, we decided to learn from estrogen receptor (ER) antagonism: (i) We built a structural model of wild-type AR-LBD complexed with antiandrogen bicalutamide (wild type/bicalutamide) using ERα-LBD/hydroxytamoxifen structure as the template for helix-12. (ii) By comparative structural analysis of 24 ERα-LBD complexes, we found residues D351 and L354 at helix-3 adopt unique conformations, and distance between them is a marker of ERα-LBD/antagonist complexes. The AR residues corresponding to D351 and L354 are E709 and L712, respectively. We found distance between E709 and L712 of the wild type/bicalutamide model is substantially different from that of AR-LBD/agonist complexes, suggesting this distance could be a marker of antagonistic AR-LBD, which was supported by molecular dynamics simulations. Based on the wild type/bicalutamide model, we discovered compound 3 is a novel antiandrogen effective against the wild type and T877A-, W741C-, and H874Y-mutated androgen receptors. We found compound 3 has dual functions, inhibiting androgen receptor and IKK(β) .

A new highly androgen specific yeast biosensor, enabling optimisation of (Q)SAR model approaches

Recently we constructed recombinant yeast cells that express the human androgen receptor (hAR) and yeast enhanced green fluorescent protein (yEGFP), the latter in response to androgens. When exposed to 17beta-testosterone, the concentration where half-maximal activation is reached (EC50) was 50 nM. Relative androgenic potencies (RAP), defined as the ratio between the EC50 of 17beta-testosterone and the EC50 of the compound, were 1.7, 1.2 and 0.008 for 19-nortestosterone, tetrahydrogestrinone and 17beta-estradiol respectively. Steroids representative for other hormone receptors, like estrone, 17alpha-ethynylestradiol, and diethylstilbestrol for the estrogen receptor and corticosterone and dexamethasone for the glucocorticoid receptor, showed no agonistic response. Only compounds known to exert androgenic effects give a response. Determined RAPs were in line with results obtained from optimised QSAR model calculations and demonstrated that Saccharomyces cerevisiae showed no metabolism of test compounds and displayed no crosstalk from endogenous hormone receptors. The suitability of this bioassay to verify the outcomes of (Q)SAR models to predict the activities of different steroids was further examined by studies with steroid isomers and a number of designer steroids, confirming that the 17beta-hydroxyl group, 3-keto group and 5alpha-steroidal framework are extremely important for the activity of the androgenic steroid.

Quantitative detection of the ligand-dependent interaction between the androgen receptor and the co-activator, Tif2, in live cells using two color, two photon fluorescence cross-correlation spectroscopy

Two-photon, two-color fluorescence cross-correlation spectroscopy (TPTCFCCS) was used to directly detect ligand-dependent interaction between an eCFP-fusion of the androgen receptor (eCFP-AR) and an eYFP fusion of the nuclear receptor co-activator, Tif2 (eYFP-Tif2) in live cells. As expected, these two proteins were co-localized in the nucleus in the presence of ligand. Analysis of the cross-correlation amplitude revealed that AR was on average 81% bound to Tif2 in the presence of agonist, whereas the fractional complex formation decreased to 56% in the presence of antagonist. Residual AR-Tif2 interaction in presence of antagonist is likely mediated by its ligand-independent activation function. These studies demonstrate that using TPTCFCCS it is possible to quantify ligand-dependent interaction of nuclear receptors with co-regulator partners in live cells, making possible a vast array of structure-function studies for these important transcriptional regulators.