(S)-bicalutamide and bicalutamide

Androgen receptors (AR) are overexpressed in most primary and metastatic prostate cancers. To develop a nonsteroidal AR-mediated imaging agent, we synthesized and radiolabeled several analogs of the potent antiandrogen bicalutamide: [18F]bicalutamide, 4-[76Br]bromobicalutamide, and [76Br]bromo-thiobicalutamide. Two of these analogs, 4-[76Br]bromobicalutamide and [76Br]bromo-thiobicalutamide, were found to have a substantially increased affinity for the androgen receptor (AR) compared to that of bicalutamide. The synthesis of [18F]bicalutamide utilized a pseudocarrier approach to effect addition of a carbanion generated from tracer-level amounts of a radiolabeled precursor to an unlabeled carbonyl precursor. 4-[76Br]Bromobicalutamide and [76Br]bromo-thiobicalutamide were labeled through electrophilic bromination of a tributylstannane precursor. The former could be prepared in high specific activity, and its tissue distribution was tested in vivo. Androgen target tissue uptake was evident in castrated adult male rats; however, in DES-treated, AR-positive, tumor-bearing male mice, tumor uptake was low.

Topics: Androgen Antagonists; Anilides; Animals; Bromine Radioisotopes; Fluorine Radioisotopes; Isotope Labeling; Ligands; Male; Mice; Neoplasm Transplantation; Nitriles; Prostatic Neoplasms; Radioligand Assay; Radionuclide Imaging; Radiopharmaceuticals; Rats; Rats, Sprague-Dawley; Receptors, Androgen; Stereoisomerism; Structure-Activity Relationship; Tissue Distribution; Tosyl Compounds

We studied the three-dimensional quantitative structure-activity relationships (3D QSAR) of 70 structurally and functionally diverse androgen receptor (AR) binding compounds using the comparative molecular similarity indices analysis (CoMSIA) method. The compound set contained 67 nonsteroidal analogues of flutamide, nilutamide, and bicalutamide whose binding mode to AR was unknown. Docking was used to identify the preferred binding modes for the nonsteroidal compounds within the AR ligand-binding pocket (LBP) and to generate the ligand alignment for the 3D QSAR analysis. The alignment produced a statistically significant and predictive model, validated by random group cross-validation and external test sets (q(2)(LOO) = 0.656, SDEP = 0.576, r(2) = 0.911, SEE = 0.293; q(2)(10) = 0.612, q(2)(5) = 0.571; pred-r(2) = 0.800). Additional model validation comes from the CoMSIA maps that were interpreted with respect to the LBP structure. The model takes into account and links the AR LBP structure, docked ligand structures, and the experimental binding activities. The results provide valuable information on intermolecular interactions between nonsteroidal ligands and the AR LBP.

Topics: Anilides; Binding Sites; Flutamide; Imidazolidines; Ligands; Models, Molecular; Nitriles; Quantitative Structure-Activity Relationship; Receptors, Androgen; Tosyl Compounds

We examined the three-dimensional quantitative structure-activity relationship (QSAR) of a group of endogenous and synthetic compounds for the androgen receptor (AR) using comparative molecular field analysis (CoMFA). The goal of these studies was to identify structural features necessary for high binding affinity and optimization of selective androgen receptor modulators (SARMs). A homology model of the AR was used as a scaffold to align six lead compounds that served as templates for alignment of the remaining 116 structures prior to CoMFA modeling. The conventional r(2) and cross-validated q(2) relating observed and predicted relative binding affinity (RBA) were 0.949 and 0.593, respectively. Comparison of predicted and observed RBA for a test set of 10 compounds resulted in an r(2) of 0.954, demonstrating the excellent predictive ability of the model. These integrated homology modeling and CoMFA studies identified critical amino acids for SARM interactions and provided QSAR data as the basis for mechanistic studies of AR structure, function, and design of optimized SARMs.

Topics: Anilides; Heterocyclic Compounds, 3-Ring; Ligands; Models, Molecular; Molecular Conformation; Molecular Structure; Nitriles; Quantitative Structure-Activity Relationship; Quinolines; Receptors, Androgen; Static Electricity; Steroids; Tosyl Compounds

A series of chiral analogues of bicalutamide bearing electrophilic groups (isothiocyanate, N-chloroacetyl, and N-bromoacetyl) on aromatic ring B of the parent molecule were synthesized. These compounds were designed as affinity ligands for the androgen receptor (AR). We prepared the (R)- and (S)-optical isomers of these compounds as pure enantiomers. The AR binding affinities of these compounds were measured in a competitive binding assay with the radiolabeled high-affinity AR ligand, [(3)H]mibolerone. In accordance with our previous results for the enantiomers of bicalutamide, we found that all (R)-isomers demonstrated much higher binding affinity to the AR as compared to their corresponding (S)-isomers. The para-substituted affinity ligands in ring B bound the AR with higher affinities than the corresponding meta-substituted analogues. Oxidation of thioester affinity ligands to their sulfonyl analogues for the para-substituted compounds decreased AR binding affinities and similar modification increased binding affinities for corresponding meta-analogues. The least potent para-substituted sulfonyl compounds had higher AR binding affinities than the most potent meta-substituted sulfonyl compounds. Overall, the para-substituted unoxidized molecules demonstrated the highest AR binding affinity. Subsequent research using AR exchange assays and Scatchard analyses showed that the isothiocyanate affinity ligands (R)-7, (R)-9, and (R)-10 reported herein are the first specific chemoaffinity ligands for the AR.

Topics: Androgen Antagonists; Androgen Receptor Antagonists; Anilides; Animals; Disulfides; In Vitro Techniques; Isothiocyanates; Ligands; Male; Nitriles; Prostate; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Androgen; Stereoisomerism; Structure-Activity Relationship; Sulfones; Tosyl Compounds

The nonsteroidal antiandrogen 4'-cyano-3-[(4-fluorophenyl)sulfonyl]-2- hydroxy-2-methyl-3'-(trifluoromethyl)-propionanilide (1) (ICI 176334) has been resolved by chromatographic separation of the diastereomeric (R)-camphanyl esters of the precursor thioether 2 followed by hydrolysis and oxidation of the isolated enantiomers. In addition, an asymmetric synthesis of (S)-3-bromo-2-hydroxy-2-methylpropanoic acid (11) and subsequent conversion into the (S)-sulfone 6a has established that the more potent enantiomer of 1 has the R absolute configuration.

Topics: Androgen Antagonists; Anilides; Animals; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; Isomerism; Male; Nitriles; Rats; Seminal Vesicles; Tosyl Compounds