National Antivisection Society
Progress in brain tumour project
Posted: 22 April 2010. Updated: 7 October 2010
With 25% of cancers found in the body spreading to the brain and worsening patient prognosis, it is vital to understand the mechanisms by which cancerous cells metastasise (move) into the brain, thereby spreading the cancer.
In vitro constructions generally use animal tissues, such as rat and mice cells, to model the blood-brain barrier (BBB), the layer which covers and protects the brain. However, these animal models do not reflect the situation in humans. Those models which do use human cells are often grown in media which include foetal calf serum, a product which is ethically unsound.
Exciting new progress has been made however, in the development of an all-human tissue model of the BBB at Portsmouth University, where Professor Geoffrey Pilkington and his team have been testing various permutations of cell cultures in the Transwell® model. The researchers are using astrocytes (supporting cells) from two different areas of the brain; endothelial cells, which line the blood vessels, and pericytes. Pericytes are a less well known component of the BBB and are thought to regulate proliferation and differentiation of endothelial cells. Many other researchers do not include pericytes in in vitro models due to the difficulties involved by introducing them into the BBB model. However, the team at Portsmouth has persevered with this element as they believe their inclusion is needed to produce a true reflection of the in vivo situation.
The Transwell® model is set up by adding the human astrocytes and endothelial cells to either side of a membrane filter. This membrane is coated with extracellular matrices (ECM) and the whole model is grown in human serum supplement.
The initial stages of the study were performed to analyse the components of the BBB model, to aid the development of the Transwell® model. In these first stages, different cancer cells were added to various cultures of brain cells. Results found lung cancer cells, which were observed over 48 hours, to move through an endothelial cell mono-culture, demonstrating the cancer’s high metastatic potential.
Aspects of the cells were measured and observed using state of the art techniques such as ECIS™, which uses electrical currents to measure the resistance of cells and cell behaviour, treatment with immunoflorescence and time lapse microscopy.
Recent preliminary results have revealed that co-cultures of astrocytes and endothelial cells have shown better formation of ‘tight junctions’ (TJs) than endothelial cell mono-cultures. TJs make the BBB a highly effective biological barrier so these results indicate that astrocytes improve the TJ formation.
Currently, the addition of pericytes to create a tri-culture has not improved tight junction formation. However, this is possibly due to the pericytes blocking the endothelial cells, preventing them from producing a monolayer. The team intend to repeat the experiment, with the pericytes at the bottom of the Transwell® so that they are not in direct contact with the endothelial cells.
It is hoped the model will identify the pathways malignant cells take to cross the BBB and, once fully developed, could be used to study metastases. In addition, because of the importance of the BBB in conditions of the Central Nervous System, such as stroke and brain trauma, this model has the potential to improve the treatment of these conditions. Excitingly the model could also be used as a tool by drug companies to discover if, and how, therapeutic agents pass through the BBB.
