Modelling breast cancer in a three-dimensional heterotypic culture system

Microenvironmental factors are fundamental in the regulation of normal and tumour breast tissue. Two cell types have been implicated in having opposing effects on breast tumour cell behaviour: myoepithelial cells exhibit broad tumour-suppressor activity, whilst fibroblasts frequently promote tumour growth and invasion. Previous work has described the development of a physiologically relevant three-dimensional heterotypic culture system containing tumour, myoepithelial and fibroblast cells. The data showed organisation of the cells into co-unit structures recapitulating ductal carcinoma in situ breast, with homing of myoepithelial cells around luminal cells, and highlighted a central role for tumour-associated fibroblasts in disrupting ductal carcinoma in situ structures. This study describes further manipulation of the model to include tumour cells that represent the heterogeneity of breast cancer.

MCF-7 (ER⁺), MDA-MB-468, MDA-MB-231 (basal) and MDA-MB-453 (Her2⁺) were cultured in collagen for 7 days in the presence or absence of normal myoepithelial cells. Gels were fixed in formalin, paraffin embedded and immunohistochemistry was performed for a series of markers recognising the cell types along with basal polarity and basement membrane proteins.

Initial morphological analysis of the cultures has been performed to assess the degree of co-unit formation, based on a visual description of the size and shape of the co-units. Co-unit formation has been employed as a representative measure of tumour progression as it is known to be a key feature in early breast cancer invasion. When cultured alone, MCF-7 and MDA-MB-468 cells formed spherical co-unit structures and this was maintained in the presence of myoepithelial cells. In contrast, MDA-MB-231 and MDA-MB-453 cells show a more scattered appearance. The presence of myoepithelial cells induced polarity in the MDA-MB-231 cells and a more ordered appearance.

This study is the first time that the co-culture of tumour cell populations with myoepithelial cells has been investigated in three-dimensional collagen gels showing differences in morphology that may relate to tumour progression.