Fibroblasts from breast carcinomas promote the growth of cancer cells more significantly than normal mammary fibroblasts, suggesting co-evolution of cancer and surrounding fibroblasts. Ĭontrary to the preventive effect of the microenvironment, once cancer cells override the self-defense mechanisms and begin to form a tumour, the surrounding cells such as fibroblasts acquire the ability to aid further growth of cancer cells. These examples represent the preventive effect of the normal cellular microenvironment on the early stages of tumour growth and may explain why the chance of a small number of tumour cells successfully establishing a colony or forming secondary tumours in a new location is extremely low. In mammary ducts in vivo, myoepithelial cells surround luminal cells on their basal side and secrete anti-invasive and anti-angiogenic factors. In this context, pro-apoptotic factors secreted by the normal epithelial cells are responsible for the attenuation of cancer cell growth. In another example, normal breast epithelial cells or their conditioned media attenuate the growth of co-cultured breast cancer cells. For example, when a single epithelial cell is transformed by an oncogene and is surrounded by normal epithelial cells, the transformed cell is, in many cases, apically extruded and thus eliminated from the epithelium. The effect of normal cells on cancer cells provides a fascinating mechanism for self-defense against cancer. The microenvironment comprises extracellular matrix, growth factors, cytokines, oxygen and vasculature as well as the cells that provide them, such as fibroblasts, adjacent cancer cells and/or normal cells. The tumour microenvironment has a strong influence on cancer cell growth, motility and gene expression. The method can be useful for various aspects such as different combinations of cancer and non-cancer cell types, addressing the organ-specific affinity of cancer cells to host cells, and monitoring the cellular response to anti-cancer drugs. This culture method is a powerful technique to investigate cancer cell dynamics and cellular changes in response to the microenvironment. A decreased level of gelatin-digesting ability as well as reduced production of matrix metaroproteinase-2 was also observed. MDA-MB-231 cells co-cultured with a large number of normal epithelial cells showed reduced expression of monocarboxylate transporter-1, suggesting a change in the cell metabolism. However, when there was a relatively large population of normal epithelial cells, the MDA-MB-231 cells did not engulf the epithelial spheres effectively, despite repeated contacts. The surrounded epithelial cells were eventually destroyed, becoming debris, and were taken into the MDA-MB-231 cells.
When co-cultured with epithelial cells, the MDA-MB-231 cells displayed a strong attraction to the epithelial spheres, and proceeded to surround and engulf the epithelial cell mass. The single MDA-MB-231 cells exhibited both round and spindle shapes, with dynamic changes from one shape to the other, visible within a matter of hours. In contrast to the 2D culture system, whereby most MDA-MB-231 cells exhibit spindle-shaped morphology as single cells, in the 3D culture the MDA-MB-231 cells were found to be single cells or else formed aggregates, both of which were motile. Ultrastructural, immunocytochemical and protein expression analyses were also performed following the time-lapse study. Cell movement was monitored using time-lapse analyses. In the 3D culture, the epithelial cells establish a spherical morphology (epithelial sphere) thus providing cancer cells with accessibility to the basal surface of epithelia, similar to the in vivo condition. GFP-labelled breast cancer cells, MDA-MB-231, were co-cultured with mCherry-labelled non-cancerous epithelial cells, MDCK, in a gel matrix. This work aims to establish a method to reveal the interaction of cancer and normal epithelial cells using 3D time-lapse.
Conventional 2D culture systems, however, do not reflect in vivo conditions, impeding detailed studies of cancer cell dynamics. The cancer microenvironment has a strong impact on the growth and dynamics of cancer cells.