Why did we fund this project?
This award aims to expand the chick embryo chorioallantoic membrane model (CAM) to studies of malignant pleural mesothelioma (MPM) to replace the use of mouse xenograft models.
New therapies for MPM are first identified using in vitro immortalised MPM cells. Candidate drugs then undergo preclinical testing in mouse xenograft models. These xenografts use either MPM cell lines or tissue derived from a patient’s tumour. The severity of these studies is classified as moderate under the Animals (Scientific Procedures) Act 1986 due to the level of suffering caused. CAM has previously been validated for breast and pancreatic cancers by Dr Anne Herrmann (Co-Investigator) as part of her NC3Rs David Sainsbury Fellowship. Cells are implanted into the CAM, a highly vascular extraembryonic membrane, where they form a small tumour that can be extracted and used in a number of functional studies to study tumorigenesis, angiogenesis and metastasis. Chick embryos are immunodeficient and could avoid some of the issues of xenograft rejection seen in mouse models, which are reported to have a 40% engraftment rate, creating a bias of MPM cancers that are studied.
Professor Judy Coulson is collaborating with Anne to optimise the CAM for use in MPM research. They will establish robust protocols for engrafting and culturing MPM cell lines and generate standard operating procedures to enable uptake by other researchers. Judy and colleagues will also use CAM in functional studies to screen the effectiveness of therapeutics against MPM and investigate the role of BAP1 – a tumour suppressor with loss-of-function mutations in more than half of all mesotheliomas.
Mesothelioma is an aggressive and largely untreatable cancer of the lung lining, mainly caused by environmental exposure to asbestos. New treatments, or new approaches to treatment, are urgently required. We can now read detailed information about genetic changes from a small sample of a patient's cancer, which can then be used to make decisions about the most effective anti-cancer drugs to give to an individual patient as "precision medicine". Recent studies have revealed the type and frequency of genetic changes that occur in mesothelioma, which may help in predicting new treatments.
In many cancers, genetic changes switch on "oncogenes", which accelerate the speed with which cancer cells divide into two, driving tumour growth. Many cancer treatments use drugs that directly block the activity of oncogenes to prevent this uncontrolled tumour growth. However, mesothelioma is unusual, as there are no common oncogene mutations. Instead, genetic changes mostly occur in "tumour suppressor" genes, disabling proteins that would normally apply a brake to slow down dividing cells and so prevent tumour growth. This presents a difficult challenge for finding ways to treat mesothelioma, as we need to fully understand how each specific tumour suppressor mutation alters the cancerous behaviour of mesothelioma cells, in order to find an Achilles' heel that we might be able to target with drugs. Ultimately, we also need to develop the best laboratory models in which to test the drugs, before they can be given to mesothelioma patients.
Disabling mutations of the tumour suppressor BAP1 are found in more than half of all mesotheliomas. Normally, BAP1 controls the production and destruction of other proteins within the cell. Therefore, in mesothelioma without BAP1, there are potentially changes in the amounts of many different proteins that could affect cancerous behaviour. Using cells with gene-edited mutations of BAP1, we identified many of these protein changes. We found that BAP1 mutation not only affects proteins that alter the growth of cancer cells, but also proteins that control how they move, gain access to blood vessels, and spread around the body. We are currently evaluating which of these proteins make mesothelioma cells more sensitive to specific anti-cancer drugs. However, we need to test these drugs in models that can provide a good replica of human mesothelioma growth and spread.
To do this, we will develop a chick embryo model of mesothelioma, as a replacement for currently used mouse models. The chick embryo model is classified as non-protected under the Animals Scientific Procedures Act, and so is a useful technique to replace testing in animals. It has many additional advantages over mouse models, including cost effectiveness, accessibility and speed. It is an excellent model to study the growth and spread of tumour cells, as they can be easily engrafted onto the "chorioallantoic membrane". This is an accessible surface, located outside the chick embryo directly beneath the eggshell, with a good supply of blood vessels. Within a few days, a small tumour develops, which can spread across and into the membrane, potentially accessing blood vessels to spread to specific organs. Importantly, new drug treatments can be readily tested in the chick embryo model, and the tumour cells imaged over time to assess their survival and behaviour.
We will use the chick embryo model to grow mesothelioma cells, with and without BAP1 mutation, and evaluate therapeutic responses to our candidate drugs. Successful
outcomes will suggest new drugs for inclusion in precision medicine trials in mesothelioma patients. During the project, we will develop the first standard operating procedures to generate and monitor mesothelioma tumours in this model. We will make these protocols, and key reagents, available to the mesothelioma research community, encouraging widespread replacement of murine models.