Experimental Studies in Cells (In Vitro)
Definition: Studies of human or animal cells outside the living body and maintained in an artificial environment
Much of the basic biology of breast cancer cells has been studied in isolated cell systems in which normal human breast cells or human breast cancer cells have been removed by biopsy and then allowed to grow and proliferate (sometimes for hundreds or even thousands of generations of daughter cells) in containers in the laboratory. These cell systems have been studied extensively, and thus are well-understood. Studies of cell lines have allowed scientists to compare susceptibility and behavior of the cells under a variety of conditions, and to monitor carefully the cellular and molecular events that characterize the processes by which normal cells are transformed into cancerous cells.
Cell lines can represent a variety of biomarker profiles (genes or proteins that are identifiable and related to risk for breast cancer).For example, some cell lines are ER+ and PR+, while others are receptor negative (Lacroix, 2004).
The MCF-7 human breast tumor cell line is ER+ (has estrogen receptors) and is dependent on estrogenic stimulation for cell proliferation. It has been critical for characterizing many environmental chemicals as endocrine disruptors with estrogenic effects. Among the many chemicals identified as being estrogenic using this system are alkylphenols, phthalates, BPA and several pesticides (Soto, 2006).
On the other hand, one line of normal (non-cancerous) breast epithelial cells, the MCF-10A, is ER- (does not have estrogen receptors). Studies have compared the effects of various chemicals including known endocrine disruptors like phthalates, on cell responses in both MCF-7 and MCF-10A cells (Wrobel, 2013). Sometimes scientists are able to add the estrogen receptor into the MCF-10A cells, making them more similar to their MCF-7 cancer cell counterparts for comparisons of these sorts. This then allows them to test specifically for the role of estrogen receptors in modifying mammary cell responses to environmental exposures (Sreeja, 2012).
Not all studies of cells in culture use these so-called “immortalized” cell lines, or lines of cells that have been grown for tens or hundreds of generations. Cell-culture studies can also test the effects of exposures on newly collected cells from breasts that are either cancerous or noncancerous at the time the cells are gathered.
Dairkee and colleagues (2008) used fine-needle biopsies of the unaffected breast from patients undergoing surgery for cancer in the other breast. The combined cells from biopsies from eight women were grown in culture, and the effects of exposure to estradiol and/or BPA on gene expression was examined. In this way the scientists were able to use newly collected human breast cells of different sorts (epithelial and stromal cells) from healthy breast tissue to examine the effects of an environmental exposure under controlled conditions. The researchers found evidence that some exposures can lead normal cells to begin to behave more like cancerous cells, which may help explain part of the process of carcinogenesis.
Because multiple tests of initially identical cells can be run concurrently under different conditions, effects can be observed relatively easily and rapidly, without requiring the use of live animals. By adding other factors that mimic living breast tissue, such as stromal (supporting)cells and nutrients, more complex processes in breast tumor cells can now be studied (Dewan, 2006; Heneweer, 2005).
The major limitation to cell-culture or in vitro studies is simply that they are run under such artificial conditions. No matter how many cell types and nutrients are added, the complexity of a living biological system, with its various intricacies and feedback loops, is not met. These cell studies are run in the absence of normal feedback from all of the other cells and physiological systems of the body. Proper development and function of mammary cells in culture only occurs in the presence of the full range of cells, extra-cellular matrix and support enzymes normally present in intact mammary tissue (Nelson, 2006).