Engineering an in vitro model of the mammary gland

The breast (mammary gland) is a complex, highly specialised tissue that has evolved to provide nutrition for the young. This essential life-giving role for the breast does not come without cost to the mother as this tissue is highly susceptible to cancer, with breast cancer being one of the most likely forms of death for women. The human breast is unusual amongst adult organs in that it undergoes dramatic, and cyclical, changes during the lifetime of a female animal. With each successive pregnancy, the cells of the mammary gland undergo cycles of proliferation, differentiation, secretion and programmed cell death. It is estimated that the number of epithelial cells increases by approximately 100-fold during pregnancy in response to hormones and other secreted factors. Our current knowledge of the processes involved in these complex changes in cell composition and function have been derived from the use of experimental animals, mainly mice. It is possible to genetically modify mice such that they 'lose' the function of a particular gene thereby allowing the role of this gene in breast development to be defined and studied at the molecular level. The mouse has been used extensively also for studies on tumour development, and is used as a model for breast cancer. The aim of this project is to engineer a model of the mammary gland that can be grown in culture so that the use of rodents can be dramatically reduced. If this project is successful, we will also develop a human version of this model so that studies can be carried out in the most relevant tissue for human disease. This is particularly important when testing new therapeutic drugs that may have undesired side effects or may work differently in rodents compared to humans. This project will combine the skills of two departments in Cambridge: the Department of Materials Science and Metallurgy and the Department of Pathology. This will bring together expertise in tissue engineering and in breast biology. The aim is to build a polymer scaffold in which both fat cells and breast epithelial cells can be grown and subsequently treated with a variety of reagents to induce growth and branching. Once formed, the mammopad can be treated with agents that induce or knockdown gene expression to test their function. Stem cells can also be cultured in a mammopad to investigate their properties and to investigate the contribution of stem cells to aberrant growth. Such a model has not been attempted before and there will be a number of challenges. However, should this project be successful, it may be possible to use the engineered tissue to replace surgically removed tissue or to introduce therapeutic reagents directly into the breast.

The primary aim of this proposal is to engineer a synthetic mammary gland (mammopad) that can be used in place of animals for studies on mammary epithelial cell morphogenesis, invasion and differentiation. The breast is unusual in that tissue replacement is not the main thrust of stem cell research or tissue engineering. However, there is a need for tissue replacement after breast cancer surgery, to replace the use of prosthetic devices. Therefore, while the purpose of this project will be to provide a novel resource for basic research and for drug screening that will reduce the numbers of mice used to study the role of specific genes in mammary gland developmental processes and oncogenesis, this project may provide also a suitable resource for tissue replacement. This project will bring together expertise in tissue engineering and mammary gland biology. Dr Ruth Cameron (The Cambridge Centre for Medical Materials in the Department of Materials Science and Metallurgy) has expertise in the construction of porous scaffolds and bioactive coatings. Dr Christine Watson's laboratory (Department of Pathology) has expertise in the isolation and culture of mammary epithelial cells and in the basic biology of the mammary gland. This work will be carried out in Cambridge in collaboration with Professor David Flint (University of Strathclyde) who will provide expertise and training on adipocyte co-cultures. We will construct a suitable synthetic support matrix in which cells can be embedded and grown and to use these matrices as a foundation to construct 3D blocks of similar size to a mammary fat pad (10 x 5 x 1 mm). Hormones such as estrogen and other substances can be incorporated into the scaffold. The presence of pores will allow transport of oxygen and nutrients. An in vitro fat pad will be generated by introducing adipocytes into the scaffold. These will grow into the scaffold and then mouse or human mammary epithelial cells introduced to produce a mammopad.