Researchers are attempting to re-educate the immune system so that it attacks tumours rather than helps them, the National Cancer Research Institute (NCRI) Conference in Birmingham was told today.
Cancer tumours "hijack" macrophages so that they promote rather than prevent tumour growth, but Cancer Research UK scientists have found that by modifying a chemical pathway in macrophages they can make them attack tumour cells and encourage the rest of the immune system to do the same.
Using this process the researchers have been able to significantly reduce the rate of tumour growth in mice with ovarian cancer.
Lead researcher Dr Hagemann from the Institute of Cancer, Barts and the London, Queen Mary's School of Medicine and Dentistry, said: "Macrophages that are supposed to fight infections typically end up helping cancers by releasing chemical messages that promote tumour growth.
"In fact, 50% or more of a typical cancer will be made up of 'normal' body cells, hijacked by the cancer to aid its survival and growth.
"But re-educating the macrophages turned them into effective cancer killers. It also encouraged the rest of the immune system to start acting against the tumour."
Macrophages release chemical messages that activate the protein NF-kB in cells, stopping cell death and promoting cell growth and spread. The researchers found that by modifying the chemical signalling pathways in macrophages, they could inhibit the function of NF-kB, stopping it from promoting tumour growth.
When these modified macrophages were exposed to ovarian cancer cells, they produced nitric oxide, a toxin which prompted the cancer cells to commit suicide. The macrophages also signalled other immune system cells to begin attacking the cancer.
Tumour growth was significantly reduced when the modified macrophages were injected into mice with established ovarian cancer.
Dr Lilian Clark, Cancer Research UK's executive director of science operations and funding, said: "Getting the immune system to attack the tumour itself is a hugely promising approach in the development of new cancer treatments."