TCDD and PCBs inhibit breast cancer cell proliferation in vitro

The effects on cell proliferation of arylhydrocarbon receptor (AhR) agonists in estrogen-responsive T47D and ZR-75-1 cells were investigated. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and the non-ortho-substituted polychlorinated biphenyl (PCB) congeners, PCB 77, PCB 81, PCB 126, and PCB 169 each inhibited 17β-estradiol (E₂)-stimulated cell proliferation in a dose-responsive manner. In the absence of added E₂, TCDD, PCB 77, PCB 81, and PCB 169 had no significant effect on cell proliferation, while PCB 126 at high concentrations caused slight elevations. The order of effective inhibition of E₂-stimulated cell proliferation by the PCB congeners was: PCB 81>PCB 126≃PCB 169>PCB 77. In the comparative literature, mammalian TEFs for these congeners toxic potency are in the order: PCB 126>PCB 169>PCB 81≃PCB 77 [Organohalogen Compd. 34 (1997) 237]. Our results thus show an unexpected different pattern for the inhibitory effects of PCBs congeners on E₂-mediated cell proliferation.