by Sharon Beder
Dr Vivienne Reeve and Scott Menzies at the Department of Veterinary Pathology and Gavin Greenoak at the Department of Animal Science at the University of Sydney use mice to study how skin cancer is caused and the way in which it develops. Using mice they are able to experiment to determine the role of various factors such as the immune system, diet and the use of sunscreens in determining incidence of cancer.
The Veterinary Pathology laboratory has several strains of mutant hairless mice which have been bred and inbred since being imported from the United States in 1981. The hairless mouse has the advantage over other mice that it has bare skin that is just like human skin. The albino mice form the basis for most of the experiments. They don't tan because they don't have any pigment in their skin and they are highly susceptible to skin cancer. However, they are thought to be a good model for what happens when human skin is damaged by UV light and it is thought that similar biochemical changes happen in the mouse skin as happen in human skin.
Most of the experiments involve exposing the mice to artificial UV radiation. They are exposed 5 days a week to the UV light source at quite a low dose rate for perhaps 10 minutes a day. They get what is called a minimum erythemal dose of UV radiation every day. It is just enough to give them a visible pink colour to the skin but never enough to cause a sunburn.
The lights that are used are about twice as intense as sunlight is in Sydney so where it would take normal human skin 20 minutes to go just pink the mice only take 10 minutes. The dose has to be increased by about 20% each week as the mice develop some protective responses and it takes longer to get an erythemal dose. This is continued for 10 weeks. After 10 weeks the exposure is stopped and the mice are left until tumours start to appear which can happen from then onwards.These tumours are counted as they appear. They usually look like warts and as they grow a proportion of them will progress into cancers called malignant sqamous cell carcinomas.
These experiments are usually carried out on groups of 20-40 mice at a time together with a similar sized group which are not irradiated. It takes 12 months and several factors are varied such as dietary intake and the use of sunscreens to work out what effect they have or what protection they give.