Screening of 397 Chemicals and Development of a Quantitative Structure-Activity Relationship Model for Androgen Receptor Antagonism Anne Marie Vinggaard,* Jay Niemelä,* Eva Bay Wedebye, and Gunde Egeskov Jensen National Food Institute, Department of Toxicology and Risk Assessment, Technical UniVersity of Denmark, Mørkhøj Bygade 19, DK-2860 Søborg, Denmark ReceiVed July 3, 2007 We have screened 397 chemicals for human androgen receptor (AR) antagonism by a sensitive reporter gene assay to generate data for the development of a quantitative structure-activity relationship (QSAR) model. A total of 523 chemicals comprising data on 292 chemicals from our laboratory and data on 231 chemicals from the literature constituted the training set for the model. The chemicals were selected with the purpose of representing a wide range of chemical structures (e.g., organochlorines and polycyclic aromatic hydrocarbons) and various functions (e.g., natural hormones, pesticides, plastizicers, plastic additives, brominated flame retardants, and roast mutagens). In addition, the intention was to obtain an equal number of positive and negative chemicals. Among our own data for the training set, 45.7% exhibited inhibitory activity against the transcriptional activity induced by the synthetic androgen R1881. The MultiCASE expert system was used to construct a QSAR model for AR antagonizing potential. A “5 Times, 2-Fold 50% Cross Validation” of the model showed a sensitivity of 64%, a specificity of 84%, and a concordance of 76%. Data for 102 chemicals were generated for an external validation of the model resulting in a sensitivity of 57%, a specificity of 98%, and a concordance of 92% of the model. The model was run on a set of 176103 chemicals, and 47% were within the domain of the model. Approximately 8% of chemicals was predicted active for AR antagonism. We conclude that the predictability of the global QSAR model for this end point is good. This most comprehensive QSAR model may become a valuable tool for screening large numbers of chemicals for AR antagonism. Introduction There is increasing evidence that a variety of chemicals have the potential to disrupt the endocrine system by mimicking or inhibiting endogenous hormones such as estrogens and andro- gens. Many endocrine-disrupting chemicals (EDCs) have a potential to adversely affect development and/or reproductive function in wildlife, experimental animals, and humans. Among the many biological mechanisms that can result in endocrine disruption, one important is the expression of an antiandrogenic response. Chemicals with antiandrogenic activity counteract the effect of the male sex steroid hormones either by affecting their synthesis or metabolism or by blocking the effects of androgens. Androgens such as testosterone and dihydrotestosterone play a crucial role at several stages of male development and in the maintenance of the male phenotype. The development of the male phenotype during gestation is totally dependent on the action of androgens (1), and interference with AR action at this point of development is hypothesized as being linked to the increased frequency of male reproductive disorders such as testicular dysgenesis syndrome (2). The blocking of androgen action may be exerted by antagonism of the androgen receptor (AR), that is, by direct interaction of the chemical with AR. The AR is a member of the nuclear receptor superfamily, a class of receptors that function through ligand-dependent transcription of specific genes (3). Receptor binding is the primary intracel- lular step, and transactivation of the receptor is the critical step for androgen-dependent gene expression in vitro and in vivo (4, 5). The structural diversity of chemicals, which can bind to and affect transactivation of AR, is very broad. Chemicals from several different categories including steroids, synthetic hor- mones, polycyclic aromatic hydrocarbons (PAHs) (6), poly- chlorinated biphenyls (PCBs) (7), plastic additives (8), diphenyl derivatives, pesticides (9-19), pharmaceuticals, and a number of other miscellaneous chemicals interact with AR. It is conceivable that many other chemicals with antiandrogenic activity still have to be identified. In response to scientific and public concerns on EDCs, strategies are needed for screening and testing of a large number of chemicals that are present in our food, environment, consumer products, etc. In vivo assays for the detection of antiandrogenic action are time-consuming, costly, and labor intensive, which makes them impractical for routine screening and testing of a large number of chemicals. Although in vitro data for AR antagonism alone are not sufficient to characterize a compound as an EDC, information on the ability of a chemical to antagonize AR provides an important piece of information for priority setting of chemicals for more elaborate in vivo assays. Because of the high cost and time associated with screening and testing of EDCs, it is crucial that priorities be set to ensure that chemicals with the highest predicted probabilities or measured activities are given first priority for entry into the screening procedure. The challenge of evaluating a very large number of chemicals for their antiandrogenic activity is offset by the ability to construct quantitative structure-activity * To whom correspondence should be addressed. (A.M.V.) E-mail: rie.vinggaard@leo-pharma.com. (J.N.) E-mail: jayni@food.dtu.dk. Chem. Res. Toxicol. 2008, 21, 813–823 813 10.1021/tx7002382 CCC: $40.75  2008 American Chemical Society Published on Web 03/07/2008