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=Breast Cancer Cell Lines=

Breast cancer cell lines are permanently established, immortalized cultures of cells that differentiate and proliferate indefinitely through random mutation or modification when subjected to a suitable medium and space. They are extensively cultivated and used to study breast cancer biology in hopes of contributing to the ongoing discovery of breast cancer therapies developed by analyzing gene function. These cell lines are activated from a range of tumor types, from primary to metastatic. Depending on the tumor source that the cells are isolated from, the different types of cell lines will have varying antigenic expression profiles. Common types of breast cancer cell lines include MCF-7, SK-BR-3, MDA-MB-231, and T-47D. They are easy to handle and have the potential to grow in infinite quantities.

Cell Culture Techniques
Among the many cell culture techniques for the culturing and engineering of stable cell lines, two are widely used, the spillage technique (originally described in 1958) and the enzyme dispersal technique. Scientists choose a particular technique depending on its relevance to their experiment, their accessibility to certain materials, and the precision of their method. In the spillage technique the tumor is cut open, the cancer cells are allowed to spill out and are collected. In the enzymatic dispersal technique, the breast cancer tissue from the tumor is collected, cut into small fragments, washed and treated with collagenase lll enzyme allowing the enzyme to mechanically digest the tumor cell fragments. To separate organoid, epithelial and stromal breast cells depending on their density, the fragmented tissue are centrifuged by a process called differential centrifugation. Other techniques rely on sedimentation rates for cells of differing sizes that are also separated using differential centrifugation. After the cell lines are constructed and allowed to grow in selective media, they can be used in vivo or in vitro depending on the purpose of the experiment.

MCF-7
In 1970, a 69-year-old Caucasian woman isolated the MCF-7 breast cancer cell line. Later in 1973, Dr. Herbert Soule along with his coworkers then established the cell line at the Michigan Cancer Foundation in Detroit. The MCF-7 cell line is usually found in invasive breast ductal carcinoma and is the most commonly used cell line in experiments today. MCF-7 was derived from a pleural effusion extracted from a patient with metastatic breast cancer. Antiestrogen is a substance that inhibits the production and use of estrogen in cells, therefore, the ability of pure antiestrogens to control the growth of tamoxifen-stimulated MCF-7 tumors presented strong evidence that progressed to clinical trials. The cells were found to contain estrogen and progesterone receptors and cause tumorigenicity in mice.



SK-BR-3
Discovered in the late 1970s, the breast cancer cell line SK-BR-3 was derived from a pleural effusion in an invasive ductal carcinoma found in a patient’s breast. Most breast cancer cells tend to over express the human epidermal growth factor receptor 2 HER2. Most studies use SK-BR-3 cell line to investigate the issue of overcoming the resistance of Herceptin in those breast cancer cells. Additionally, SK-BR-3 breast cancer cells have a high potential of invasion and migration as shown in the study including up regulation of the membrane protein GPR30 in SK-BR-3 breast cancer cells by Heregulin-B1 derived from tumor cells.

MDA-MB
A range of MDA-MB cell lines was discovered in 1978. All were found to have metastatic origin and located in the primary tumor invasive ductal carcinoma. The nineteen different types exhibited varying growth rates and patterns. MDA-MB 134, 453, 468, and 469 were shown to be single cells or groups of loosely attached cells which are easily shaken off, MDA-MB 175, 309, 331, 390, and 416 are very tightly stuck to each other, and MDA-MB 415, 431, and 435 are flat and have clear cut figures. MD-MB 231 and 436 cells grow randomly and are spindle-shaped, and MDA-MB 175 and 330 have been shown to stick to one another and to other larger and smaller types to form a single colony. The cells within the colony have potential to grow and differentiate into different specialized cells with varying functions. Factors like Pinolenic acid and methotrexate proline prodrug are known to inhibit the human breast cancer MDA-MB-231 cells.

T-47D
T-47D cells form tight cohesive structures between cells and express the estrogen receptor naturally. Similar to MCF-7, T-47D have high tumorigenicity potential and can be inhibited by anti-estrogen therapy. A study examined a specific and receptive estrogen-responsive gene expression assay, that can be used for the screening of potential anti-estrogenic chemicals using T-47D cells. There are multiple advantages and disadvantages in working with cell lines and with primary cell cultures in comparison to distant metastatic cultures.

Advantages
Advantages of using cell lines in experimentation and therapy development include their ability to grow infinitely, their ease of use, their moderately high levels of homogeneity, and their ability to be replaced by frozen cultures when contaminated. Furthermore, cell-to-cell interactions are lost in tissues cultured in vitro, therefore, experiments have shown that isolated primary cells have been demonstrating the maintenance of those interactions in vitro.

Disadvantages
The main disadvantage of using cell lines is that they have a continuous growing culture and are prone to genetic and phenotypic drift as seen with cell line MCF-7. Despite the fact that cells of a particular type exhibit the same morphology, sometimes cells in an established cell line can be found to have varying hormone receptor content and cellular growth rates. This gives rise to challenges when scientists are trying to grow and use cells of identical biological content. The most important limitation of a primary culture is its slow cellular population doubling time. Because tumors are heterogeneous, the desired isolated epithelial cells might be contaminated by the normal epithelial cells. Therefore, choosing the appropriate cell culture for a specific cell line and experiment is vital to maximize their usage and to take advantage of their distinct properties.