Hydroxylated Polychlorinated Biphenyls (PCBs) as Estrogens and Antiestrogens: Structure–Activity Relationships

Abstract

The effects of structure on the estrogenicity and antiestrogenicity of hydroxylated polychlorinated biphenyls were investigated using the following estrogen-sensitive assays: competitive binding to the rat and mouse cytosolic estrogen receptor (ER); immature rat and mouse uterine wet weight, peroxidase and progesterone receptor (PR) levels; induction of luciferase activity in HeLa cells stably transfected with a Gal4:human ER chimera and a 17mer-regulated luciferase reporter gene; proliferation of MCF-7 human breast cancer cells; induction of chloramphenicol acetyl transferase (CAT) activity in MCF-7 cells transiently transfected with a full-length human ER expression plasmid and a plasmid containing an estrogen-responsive vitellogenin A2 promoter linked to a CAT reporter gene. The chemicals synthesized for this study contained a 4-hydroxy group in one ring, a 2- or 3-chloro substituentmetaororthoto the hydroxyl group, and variable substitution (2′,3′,4′,5′-, 2′,3′,4′,6′-, 2′,3′,5′,6′-tetrachloro and 2′,4′,6′-trichloro) in the chlorophenyl ring. The compounds included: 2,2′,3′,4′,5′- (A), 2,2′,3′,4′,6′- (B), and 2,2′,3′,5′,6′-pentachloro- (C); 2,2′,4′,6′-tetrachloro-4-biphenylol (D); 2′,3,3′,4′,5′- (E), 2′,3,3′,4′,6′- (F), and 2′,3,3′,5′,6′-pentachloro (G); and 2′,3,4′,6′-tetrachloro-4-biphenylol (H). With the exception of 2′,3,4′,6′-tetrachloro-4-biphenylol (H), all of the compounds competitively bound to the mouse and rat ER with relative binding affinities [compared to 17β-estradiol (E2)] varying from 1.4 × 10⁻³to 5.3 × 10⁻⁵. The structure–ER binding relationships for the hydroxy-PCB congeners were different in the rat and mouse, and no dose-dependent estrogenic activities were observed in the mouse or rat uterus. Several hydroxy-PCB congeners exhibited antiestrogenic activity (primarily in the mouse uterus) and two compounds, 2,2′,3′,5′,6- and 2,2′,3′,4′,6′-pentachloro-4-biphenylol, inhibited E2-induced uterine wet weight, PR binding, and peroxidase activity in the mouse uterus. 2,2′,3′,4′,5′- and 2,2′,3′,4′,6′-Pentachloro-4-biphenylol induced CAT activity in MCF-7 cells transiently transfected with the Vit-CAT plasmid; the remaining congeners did not induce CAT activity but exhibited antiestrogenic activity in MCF-7 cells cotreated with 10⁻⁹E2 plus 10⁻⁵mhydroxy-PCBs. Complementary structure–estrogenicity relationships were observed utilizing the HeLa cell luciferase induction and MCF-7 cell proliferation assays. The placement of the 2- or 3-chloro groups in the phenolic ring had minimal effects on estrogenic activity, whereas 2,4,6-trichloro- and 2,3,4,6-tetrachloro substitution in the chlorophenyl ring (B, D, F, and H) were required for this response. Substitution in the phenolic ring was also not important for structure–antiestrogenicity relationships, and the most active compounds (A, C, E, and G) contained 2′,3′,4′,5′- and 2′,3′,5′,6′-tetrachlorophenyl groups. Thus, structure–estrogenicity/antiestrogenicity relationships for this series of hydroxy-PCBs were complex and response-specific.