Abstract/Summary

Breast cancer is a major health problem and exposure to oestrogen is a main risk factor. Many environmental chemicals with oestrogenic activity are known to enter the human breast from exposure through diet, the domestic environment and personal care products. In this study, six chemicals, used to absorb ultraviolet light (UV screens) in consumer products and known to be detectable in human milk, have been studied for their effects on proliferation and migration of MCF-7, T-47-D and MDA-MB-231 human breast cancer cells. The six chemicals were benzophenone-1 (Bp1), benzophenone-2 (Bp2), benzophenone-3 (Bp3), octylmethoxycinnamate (OMC), 3-(4-methylbenzilidene) camphor (4MBC) and homosalate (HS). All six of these UV screens at 10-5M could induce luciferase activity from an ERELUC reporter gene stably transfected into MCF-7 cells. Dose-response experiments on proliferation of oestrogen-responsive MCF-7 and T-47-D cells showed increased proliferation following the exposure to the UV screens but not OMC, which had no effect on proliferation of MCF-7 cells except when cells are seeded on a laminin matrix. No effect on MDA-MB- 231 cell proliferation was recorded. Although the oestrogenic activity of these chemicals has been shown to influence proliferation, this is only one of the hallmarks of cancer cells. Another important hallmark is activation of invasion and metastasis which is relevant for breast cancer where mortality arises not from growth of the primary tumour but from metastatic tumour spread. Effects of these UV screens have therefore been studied on migration and invasion of MCF-7, T-47-D and MDA-MB-231 cells following prior (2 weeks) or (up to 30 weeks) exposure using a wound healing assay, time-lapse microscopy or xCELLigence technology. 2 weeks of exposure to10-5M OMC, 4MBC and HS increased the motility of MCF-7 cells as determined by xCELLigence technology or time-lapse microscopy. 21 weeks of exposure to 10-5 M Bp1, Bp3, to 10-7M concentrations of OMC, 4MBC and HS increased the motility of MCF-7 cells. Results using western immunoblotting suggest a decrease in E-cadherin mRNA levels by 10-5 M Bp1, Bp3, OMC, 4MBS and HS and protein levels of cells exposed to 10-5 M Bp1 and HS.10-5M Bp1 also increased the secretion of MMP-9 as measured by zymography and the protein levels of pro-MMP-14 as measured by western immunoblotting. β-catenin protein was reduced in MCF-7 cells following the exposure to 10-5M OMC, which also reduced the mRNA levels of other two molecular markers of motility (PIK3R1 and BMP7). T-47-D cells exposed to 10-5M of the UV screens have shown an increase in motility as determined by xCELLigence but only Bp1 increased the migration as determined by wound healing. MDA-MB-231 cells showed no increase in motility following 2 weeks of exposure to the UV screens. However, 8 weeks of exposure to 10-7 M Bp2, Bp3, 4MBC and HS increased the cells motility as determined by the xCELLigence and 15 weeks of exposure to 10-7 M of the UV screens increased the motility of MDA-MB-231 cell as measured by the time-lapse microscopy. OMC and 4MBC increased the secretion of MMP-2 by MDA-MB-231 cells. Overall, these results demonstrate for the first time that these six UV screens can influence not only proliferation but also migration of human breast cancer cells.