The development of anti-cancer drugs is a lengthy process because results obtained in vitro in the laboratory often differ from what then occurs in a living organism. A group of researchers led by Prof. Dr. Margareta Müller at the Furtwangen University of Applied Sciences is therefore developing a new cell culture model that adjusts in vitro to real conditions.
A malignant growth in the body not only consists of specialised tumour cells but also of intact blood vessels that supply the tumour and the tumour stroma, i.e. the tumour's microenvironment consisting of healthy cells, with oxygen and nutrients. This tumour-promoting environment enables abnormal tissue to grow and initiate metastasis. It has been suspected for several years that cancer grows especially well under conditions where the stroma is activated by inflammatory processes. In general, inflammation is a short-term process. Under certain conditions, however, inflammatory responses fail to resolve, resulting in chronic inflammation. This is why researchers see a causal connection between chronic, clinically barely discernable inflammatory reactions and the growth of tumours as a result of the activation of tumour stroma.
So far, however, it has not been possible to demonstrate in the cell model how these components are related to one another. This is due to the fact that cell cultures contain tumour cells, but no inflammatory cells. A new model now makes it possible to simulate the interaction of different cell types by integrating different types of cells such as tumour cells, inflammatory cells and other stromal cells into a three-dimensional tissue model.
"This helps us to pinpoint the role of the interaction between different cells for the development and progression of tumours," says Prof. Dr. Margareta Müller from the Medical and Life Sciences Faculty at the Furtwangen University of Applied Sciences. Margareta Müller is currently coordinating a Germany-wide project on breast and lung carcinomas which is focused on representing tumour growth in relation to the surrounding tissue using a three-dimensional tumour-stroma model (3D-TuMiMo).
Two-dimensional in vitro cell cultures are traditionally used in basic research and pharmaceutical industry screening systems because they are well established, controllable and can be manipulated in specific ways. However, 2D cell culture does not take into account a cell's microenvironment, so results differ considerably from the findings of in vivo experiments, for example in mice. "In vivo results deliver relevant data, but suffer from the limited ability to manipulate the system and the considerable differences between the physiology of human and animal organisms," says Prof. Müller. Therefore, scientists are increasingly using 3D cell culture systems that allow the analysis of the interaction between different human cell types and the extracelullar matrix. However, these models are primarily based on biological matrices whose composition varies from batch to batch and restricts the reproducibility of the data. "In addition, these models do not usually contain all cells that are relevant for the tumour environment. They are usually focused on the interaction of two or at most three specific cell types," explains the head of the research group.
In order to remedy this situation, Margareta Müller is working on a 3D model whose extracellular matrix contains cells from the tumour's microenvironment, including endothelial cells, inflammatory cells and fibroblasts. For the model, only chemically defined matrices - synthetically inert hydrogel matrices - are used in order to ensure reproducible results. In addition, the scientist is developing analytical methods that enable the quantification of proteases, cytokines and newly synthesised extracellular matrix proteins. The use of chemically inert hydrogels allows the researchers to eliminate disturbing factors and thus obtain much clearer results. "The combination of inert hydrogels, 3D tumour-stroma-cancer models and the multiplex, quantitative analysis of the proteins formed represents a new approach in the development of 3D in vitro tumour models. This new approach enables cell interaction in the in vitro model to be studied in greater detail," says Prof. Müller.
So far, only limited data are available on how tumour growth factors (e.g. inflammation) affect the binding of certain cell surface receptors. To analyse this, complex cell interaction models need to be established. "Such models are urgently required for the testing of anti-cancer drugs in settings that are as realistic as possible," says Prof. Müller. The project contributes to making such complex model systems accessible to tumour-stroma interactions in synthetic matrices used for basic research and pharmaceutical screening procedures.
Initial research suggests that the induction of a tumour-promoting inflammatory environment and the activation of tumour-promoting fibroblasts can also be observed in the three-dimensional tumour-stroma model. "This means that our new cell culture model is similar to a model based on a matrix made of animal collagen, or even to in vivo models like the mouse," says Prof. Müller. As a result, the number of animal experiments can be significantly reduced. However, Prof. Müller and her team have not yet achieved their ultimate goal. "We now have plans to manipulate tumour-promoting inflammatory reactions using the 3D tumour-stroma model that is easy to control, and find ways to reduce inflammatory reactions that might lead to tumours. We hope that this will reduce the invasion of the tumour cells into the surrounding tissue as well as prevent the activation of the cancer-promoting microenvironment, thus resulting in the inhibition of tumour growth and progression," concludes Prof. Müller.