Page 392 - Read Online

Darbre. J Cancer Metastasis Treat 2019;5:58 I http://dx.doi.org/10.20517/2394-4722.2019.22 Page 5 of 13

n-propylparaben, n-butylparaben and isobutylparaben) 99% of the human breast tissues were found to
[26]
contain at least one of the esters, and 60% contained all five esters . Although the parabens bind more
weakly to estrogen receptors than do the endogenous estrogens, their efficacy is not weak provided
[27]
sufficient concentration is present . It is therefore noteworthy that the concentrations of parabens
[26]
measurable to human breast tissues are considerably higher (in the micromolar range) than the levels of
endogenous 17b-estradiol (in the nanomolar range) [2,28] . Previous work has demonstrated that parabens can
increase proliferation of estrogen-responsive human breast cancer cells in cell culture at concentrations
[29]
[27]
measurable in some human breast tissue samples through estrogen receptor-mediated mechanisms .
However, parabens have now been found to also increase migratory and invasive activity of human breast
cancer cells in culture . Migratory activity was measured using scratch assays, time-lapse microscopy
[30]
[30]
and xCELLigence technology . Invasive activity was measured using matrix degradation assays and
invasion through matrigel on the xCELLigence system . Unlike the proliferative effects which were
[30]
measurable within days of addition of the parabens [27,29] , the increased migratory and invasive properties
[30]
only developed in the cells after long-term exposure (20 weeks) . Western immunoblotting showed an
associated downregulation of E-cadherin and b-catenin in the long-term paraben-exposed cells, which
[30]
could be consistent with a mechanism involving EMT .
One technology which has been particularly useful in determining adhesion, migration and invasion
of breast cells following exposure to estrogen disrupting chemicals has been the ACEA BioSciences
xCELLigence technology, and the increased cell migration following long-term exposure of MCF-7 human
breast cancer cells to paraben which was measured using this technology is shown in Figure 1A. This
technology works on the basis of a modified Boyden chamber in which two chambers are separated by a
membrane. Migration of cells through the membrane on the base of the upper chamber can be monitored
in real time at any pre-determined time interval as the cells move onto the undersurface of this membrane
located at the top of the lower chamber. The CIM-plate-16 contains 16 wells which can be monitored
independently but simultaneously to measure cell migration/invasion in real time through 8 mm pores
in the membrane onto gold electrodes on the underside of the membrane using the ACEA BioSciences
xCELLigence analyser system. Cell movement onto the gold electrodes is measured as electrical impedance
(cell index). Collated traces of cell index are shown in Figure 1A for cell migration through uncoated
-5
-4
membranes following 20 weeks of prior treatment with or without 5 × 10 M methylparaben or 10 M
n-butylparaben (conditions as published in reference 30).
UV filters
Chemicals which can absorb UV light (UVA and/or UVB) are added to consumer products either to
protect the skin of the user from UV damage (sunscreen products) or to protect the product itself from UV
[31]
[32]
damage during storage . They are also used in textiles marketed as UV protective clothing . Widespread
use of benzophenone-3 (BP-3), octylmethoxycinnamate (OMC) and 4-methylbenzilidenecamphor (4-MBC)
[33]
has led to their detection in environmental water and soil samples and they have been recently also
[34]
measured as present in human breast tissues . One or more of these UV filters were quantifiable in 84% of
the breast tissue samples and in at least one breast region of 95% of the women . BP-3, OMC and 4-MBC
[34]
all possess estrogenic activity in reporter gene assays in estrogen-responsive MCF-7 human breast cancer
cells [31,35] . Long-term exposure (23 weeks) to any one of these three compounds has now also been found to
increase migratory activity in MCF-7 cells using scratch assays, time-lapse microscopy and xCELLigence
technology, and to increase invasion through matrigel as measured using xCELLigence technology .
[35]
The increased cell migration following long-term treatment (23 weeks) of the MCF-7 cells with or without
-5
10 M of BP-3 or OMC is shown in Figure 1B using xCELLigence technology (conditions as published in
reference 35). However, increased motility of estrogen‐unresponsive MDA‐MB‐231 human breast cancer
cells was also observed after long-term exposure to each of the three compounds, implying the increased
[35]
migratory activity was not confined to estrogen responsive cells . Furthermore, molecular mechanisms