Prostate cancer is one of the most common forms of cancer in men, and the second most deadly cancer in Western society. While many men get prostate cancer when they are older, it is usually benign and becomes deadly when it metastasizes to bone.
Prostate cancer only naturally occurs in significant numbers in humans and dogs. While the cancer in dogs shares characteristics with humans, there are differences in the likelihood of the cancer metastasizing and the tissue of the prostate . However, by studying the prostate gland in dogs, Charles Huggins discovered that the growth of tumours was dependant on the natural hormones of the body. Reducing male sex hormones or increasing female hormones could treat prostate cancer. Even patients with only a short time to live showed improvement from this new type of treatment, which had fewer side effects than other therapies. For his work and the treatments he helped to develop, Charles Huggins was awarded a Nobel Prize in 1966.
Efforts have been made to produce prostate cancer models in rats and mice. These have included xenograft models, transgenic models and knockout gene models. The models each have different strengths in their similarity to the human disease, including structure and behaviour. However, there is not yet a standard model used for a range of studies.
Cancer models in mice were used to develop Cabozantinib, a drug that targets two mechanisms that cancer cells use to survive . By blocking VEGF receptors on the surface of the cells, the cancer cells are starved of oxygen but this leads to them migrating to a new area and spreading through the body. By targeting another receptor (c-MET) as well, Cabozantinib prevents the spreading and reduces the ability of the cancer to grow. In tests on 108 men with prostate cancer that had spread to bone, which is usually untreatable, the tumours grew in just 3 of them and two-thirds reported less pain.
Rodent studies of the drug goserelin, originally being investigated as a possible fertility treatment, showed that it suppresses the body's release of hormones that increase prostate tumour growth . This effect was unexpected and was unlikely to have been recognised except through experiments on animals. Further animal studies were needed to work out the best way for people to be given this medicine, since it is inactivated in the stomach when taken by mouth. A long-lasting injection, which gradually releases the medicine over 28 days, was developed in rats. As a result of this research, not only has an effective medicine against prostate cancer been developed, but also an important new drug delivery system.
- The Ethics of Research Involving Animals, Nuffield Council on Bioethics