Researchers at MedUni Vienna's Center for Pathobiochemistry and Genetics have shown that a protein called mTORC2, which is the target of newly developed cancer drugs, is not even active in colorectal cancer. mTORC2 activity was only found in certain immune cells, which actually need this protein to fight cancer cells. The results were published in the paper, ‘Inactivation of mTORC2 in macrophages is a signature of colorectal cancer that promotes tumorigenesis’, featured in JCI Insight.
In addition to cancer cells, tumours also contain a large number of different types of immune cells, which normally fight against the cancer cells. However, many tumours have developed strategies to reprogram immune cells so that they actually assist tumour growth. In the age of immunotherapy, which is very successful in reactivating the immune system, research into how tumour cells and immune cells interact is of major importance.
The mTORC2 protein plays an important role in tumorigenesis and is currently the target of a series of new drugs that can successfully inhibit the growth of cancer cells in a test tube. In the future, mTORC2 inhibitors could be effective in many types of cancer, including colorectal cancer. A MedUni Vienna research team centred around Thomas Weichhart's group has now discovered that mTORC2 is actually not active in colorectal cancer cells, but only in certain immune cells, so-called macrophages, which normally fight cancer cells. These findings have now been published in the Journal of Clinical Investigation Insight.
Together with their colleagues, the three lead authors, Karl Katholnig, Birgit Schütz and Stephanie Fritsch, have shown that a high level of mTORC2 activity is important in macrophages to suppress the growth of colorectal cancer in an animal model.
"When we deactivated mTORC2 specifically in macrophages in an animal model, the growth of the colorectal tumour accelerated in these mice," said Katholnig.
The researchers now want to find out how the tumour cells deactivate mTORC2 in macrophages. If that can be prevented, it may comprise a new immunotherapy approach. In any case, it appears that in order to have a full understanding of drug efficacy, it is also necessary to consider the immune system, and an efficient cancer treatment must also include the immune system.
"Surprisingly, an mTORC2 inhibitor also had the same effect in this colorectal cancer model,” added Schütz. The researchers discovered that in colorectal cancer patients, high mTORC2 activity in macrophages is associated with a favourable course. These results indicate that it could be therapeutically useful to maintain mTORC2 activity in colorectal cancer, rather than inhibiting it.
"In order to safeguard their own survival, the cancer cells even try to deactivate mTORC2 in macrophages as soon as these cells penetrate into the tumour mass," said Weichhart.