In vitro bioassay for dioxinlike activity based on alterations in epithelial cell proliferation and morphology

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been shown to induce changes in morphology and proliferation characteristics of a nonkeratinizing derivative (XBF) of a keratinizing epithelial cell line (XB), cloned from a mouse teratoma, when cocultured with irradiated feeder cells. Polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), polynuclear aromatic hydrocarbons (PAHs), and pesticides (24 compounds in total) were tested for their ability to induce these effects. The results indicated that, for the representative compounds tested, these changes are relatively specific for-and that the XBF cells are extremely sensitive to--PCDDs and PCDFs. TCDD was the most potent congener tested, capable of inducing the effects at a concentration as low as 10(-11) M. The activities of other tested PCDDs and PCDFs ranged from 10(-1) to 10(-3) of TCDD activity. The PCBs, PAHs, and pesticides had lower activities ranging from 10(-3) to 10(-6) that of TCDD. This assay system using XBF cells cocultured with irradiated 3T3 fibroblast feeder cells was examined as a possible in vitro screening assay for dioxinlike activity by testing benzene extracts of soot from a fire involving a PCB-containing transformer. The results were compared to a high-resolution gas chromatographic/mass spectrometric analysis for total PCDFs in the same samples. This comparison showed a good correlation, suggesting that the XBF-3T3 system has potential for use as a semiquantitative assay for dioxinlike activity.