Funded Grants

Investigation of non-targeted effects of radiation in gliomas and normal brain cells

Compared to common adult tumours such as lung and breast cancer, primary malignant cerebral tumours are uncommon, accounting for only 2-5% of all malignancies. However, malignant brain tumours are second only to stroke as a cause of death from neurological disorders and deserve attention because of their remarkable resistance to available treatments. The prognosis for high-grade malignant brain tumours, the commonest type in adults, has remained very poor with typical median survival of only 9-12 months despite optimum management. Although these tumours are most common in older people with a peak age at presentation of 65-75 years they also occur in childhood and in both age groups cause very significant disability, distress and morbidity to patients, families and carers.

The primary treatment modalities for these tumours are surgery and post-operative radiotherapy. Truly curative surgery is rarely possible because of diffuse infiltration of tumour cells in to normal brain tissue. Post operative radiotherapy improves survival in high-grade tumours by 5-6 months and may improve disability in up to one third of patients. However, long term disease control is rarely achieved. Chemotherapy (drug) treatments may further improve survival but probably has a minor impact for the majority of patients.

Because of the disappointing results of conventional treatments many new approaches have been tried in these patients. Many have focussed on using new methods to increase the dose of radiotherapy that can be given to the tumour, using radio-active sources that can be implanted directly to the tumour site or very accurately targeted beams of radiation from conventional radiotherapy machines. Unfortunately these approaches, while improving tumour control in some instances have commonly led to increased damage to surrounding normal brain and have not yet been shown to improve the outlook for most patients.

It is clear then that new approaches to treating these tumours are needed. In order to develop these it is necessary to improve our understanding of how brain tumours respond to treatment, particularly what allows them to survive toxic treatments like radiotherapy that can cure tumours at many other sites. New ways of studying the way that both normal and tumour cells react to radiation may allow us to do this. In particular it is becoming clear that, especially in the brain, the individual cells do not react simply as individuals when they are attacked by toxic agents. The different cell populations interact with each other, even at some distance from the site of the original toxin or injury. This means that simply looking at how individual cells are killed by radiation will not allow us to understand how some cells survive better than we would expect, we need to look at how cells communicate with each other and how they may help each other to survive, or encourage each other to die. This may be important for normal brain cells as well as tumour cells. Until recently it has been difficult to answer this sort of question because in order to do so it is necessary to study in detail the effects of radiation on cells that are hit directly by a radiation beam and those that are not. Most experimental systems cannot distinguish between the two.

This study has been designed to try to begin to address some of these issues. We think we can do this because of evidence that has been reported recently that supports the idea that cells communicate with each other after radiation and that this influences which cells die. In some experiments this communication happens when the fluid surrounding irradiated cells is transferred to non-irradiated cells and causes damage to the non-irradiated ones. In other experiments the cells next to irradiated cells have been shown to be damaged even if they have not been hit by the X-ray beam. We do not know how these effects are transferred between cells or whether similar effects occur in brain tumour cells and normal brain cells. However if this is the case, changing these responses could be a completely new way of altering how tumours and normal brain react to radiation.

At The Gray Cancer Institute we have a very long history in investigating the effects of radiation on cells and tissues. We have studied the effects of radiation on human tumour cells grown in the laboratory and grown as tumours in experimental animals in detail. It is clear that these systems do not always reflect what happens in a real tumour. This may be partly because of cell-cell interactions that we have never taken in to account.

In this study we want to look very carefully for these sorts of cell-cell interactions. We will be able to do this in several different ways. We will look at the effects of irradiation on surrounding cells in populations where all the cells are the same, for example they are all the same tumour cells or all the same normal brain cells. We will also look at what happens when there is a mixture of different cells in the same experiment, for example brain tumour cells surrounded by normal brain cells. We will investigate these effects in two main ways. The first will be to transfer the fluid from around irradiated cells onto unirradiated cells and measure the effects on cell survival and chromosome (gene) damage. The second will be to use the unique facility of the 'micro-beam' that is available at The Gray Cancer Institute to target only certain cells with a highly focussed radiation beam. This means that we will know which cells in an experimental dish have been hit with a radiation beam and which have not. We can therefore compare the damage in hit and nonhit cells. This is possible because of the ability of the micro-beam to target individual cells to be irradiated.

For the results of these experiments to be useful we also need to identify how these cells are communicating with each other. We already know some of the ways that cells can do this. Often it is by production of molecules - usually proteins that are secreted from the cell and act as messengers to surrounding cells. Several of these proteins have already been identified and are known to affect cell survival in the brain. They are called cytokines. Since we know what some of these proteins are, we will be able to test for levels of these proteins around cells that have been irradiated to see if they are part of the cell messenger system that occurs after radiation. We will also be able to test the effects of blocking the action of some of these proteins using drugs that are known to stop them acting on the cell. W e may therefore start to get an idea of drugs or types of drugs that could be used to influence whether tumour cells and normal brain cells die after radiation or not.

Most of the work in this study will be carried out using human cells that can be grown in the laboratory in dishes or flasks. These systems will be able to tell us quite a lot about how the cells communicate but still will not be strictly the same as a tumour or normal brain cell in an animal. The final part of this project will be to begin to develop animal models that may be useful to test for these effects in systems that are closer to the real situation. This will involve testing new ways of targeting X-ray beams very specifically in animals, for example by using implantable X-ray sources or a system similar to the microbeam that could accurately target a very small X-ray beam on specific areas of tumour or normal brain. We would then be able to test the effects of targeted irradiation on the molecules that we think may change cell survival in a more realistic model and, conversely test how blocking the effects of these proteins affects the tumour or brain response to radiation.

This study represents a completely novel approach to understanding what makes cells sensitive to radiation. It may therefore provide new means of enhancing the response of tumours to radiation or of protecting normal brain tissue.