The Hole Story:
The Mouse Model of Cancer ctd.
The Use of Animal Tests
The question of whether the results of experiments on mice apply to humans is a continual and endless problem, says Reeve. However, it does seem that the capacity of sunscreens to protect hairless mice from sunburn matches up amazingly well with what is found when the same sunscreens are tested on human skin. Biochemical changes that happen in the mouse skin also seem to match what happens in human skin. So mouse skin is thought to be a reasonably good model of human skin at this stage. However, the amount of UV radiation that is required to induce a cancer or immune suppression is dependent on the individual stain of mouse and therefore will be be different for humans.
In the experiments with mice, they have to be exposed for longer and longer periods throughout the course of an experiment because they develop a protective response. For example, the skin thickens and so the distance between the susceptible cells and the skin surface is greater and this contributes largely to the protection. Whether humans have the same response is somewhat controversial. In some instances the reverse of it has been observed. In other words repeated doses in a single area might tend to increase the susceptibility of the skin to further UV damage.
It is not possible, of course, to experiment directly on people by inducing skin cancers. All that is possible is to look at skin cancers that have already developed in people and do epidemiological studies, that is studies of the disease in communities. Reeve tries to keep up to date with epidemiological studies that are being carried out elsewhere.
There is a study in America that I heard about recently, at a conference in Vancouver, she says. In this study they are actually using human subjects that have had one skin cancer and they are endeavouring to change the dietary habits of these people so that they are eating less polyunsaturated fat. The experiment was based on the prediction that, within 12 months of having had their first basal cell carcinoma, the majority of patients will have a second cancer appear. So by taking people who have had one cancer, a basal cell carcinoma, and by changing their dietary fat intake they are hoping to be able to change what would be the predicted number of second basal cell carcinomas to appear. So you can do that kind of experiment with humans and that is actually happening in the States. But that is about the limit to what we can to do with humans.
Apart from the various groups researching into UV effects on health at the University of Sydney there is also a group in the University of Newcastle and also a major group in Flinders University in Adelaide. Various other labs around the country have an interest as well. But in terms of the dietary effects there is currently nobody else in Australia carrying out research. In fact there is only one other major laboratory in the world, located in Houston, Texas, that is interested in dietary fat and its effects on skin cancer.
Reeve thinks the reason why there is not more research being carried out in this area is because of the problems that are associated with working with animals. Research using animals has become unpopular firstly because of protests over animal research from animal liberation groups. She argues however that experiments with mice might be considered cruel by some people but do we really have options? We need this information because it is going to save lives in the future. Reeve describes her experiments as gentle and says that although 90-100% of the mice develop skin cancer by the end of the year, the mice don’t suffer. We don't let the tumours grow large. We terminate every experiment before the mouse is debilitated in any way at all. We are conscious of this.
Reeve says that the other major reason why research using animals is decreasing it because it has simply become very expensive. There are now many restrictions on how animal work can be carried out and how the animals must be housed. Reeve thinks these developments are generally a good thing but finds the requirements laborious to carry out. The other possible dampener to this kind of research that she cites is the long wait for an answer to a hypothesis. These days when scientists have to publish or perish it has become quite an unpopular route for a research career, she says.
The reason why her research takes so long is that she only exposes the mice to low amounts of radiation over a long period because she wants to reproduce the sunlight exposure in the average Australian. She is not researching for the benefit of the kind of person who is baking themselves on the beach every weekend, sporting a fantastic suntan, because she considers that kind of behaviour to be over-exposure to the sun. That is not the kind of person who makes up two thirds of the Australian population who are going to have skin cancer in middle age. Instead she is just trying to reproduce sunlight exposure as a day to day hazard of living in Australia. So that is the reason she doesn’t over-expose the animals.