Loss of the CaSR in colorectal tumourigenesis

The cancer of the large bowel is, to a great extent, preventable. Calcium was identified as a probable chemopreventive agent. In order to strengthen the evidence for the role of calcium in prevention of bowel cancer we propose to investigate the role of a special molecule that is able to bind calcium, called the calcium-sensing receptor (CaSR) for the cancer-protective effect of calcium. The CaSR plays a key role in maintaining blood calcium levels and regulates the fate of the intestinal cells. The CaSR is present in the whole gut and is important for regulating fluid secretion, and stimulating proper development of the cells. The CaSR expression is lost in some cancers, such as those of the parathyroid and large bowel, suggesting that it plays a tumour-suppressive role in these tissues. We hypothesise that loss of CaSR provides growth advantage to large bowel cancer cells, conferring them resistance to calcium-mediated growth regulation. The aim of the project is to assess whether the CaSR has the anti-tumour effects. We will evaluate the impact of clinically relevant CaSR variants in large bowel cancer cells, in order to understand whether persons bearing these variants have increased risk to develop intestinal cancer. We will determine, whether drugs modulating the CaSR level or function can potentiate the effect of known medications in the treatment of intestinal tumours. Novelty: This proposal will show, whether too low CaSR levels confer growth advantage to cancerous cells, revealing one possible mechanism that links calcium to intestinal cancer development. The CaSR could become the marker that distinguishes between responders and non- responders to calcium in the intestine. We might find new potential for CaSR modulators, opening a new field for therapeutic strategies directed at restoring normal intestinal CaSR function.

In our project, we planned to test if a molecule, called the calcium-sensing receptor (CaSR), could prevent the development of cancers of the large intestine. Receptors are molecules that can bind other molecules, called ligands, and then perform different roles as "switches" in the cells and tissues. Interestingly, the CaSR is able to bind not only calcium but also other ligands. The main role of the CaSR is the regulation of calcium levels in the blood. For this, the CaSR is present in all organs involved in the regulation of blood calcium levels. However, it is known that it can be present in other, non-calcium related organs as well, where it regulates other processes, such as the development of tumours or inflammation. Our results have now shown that the CaSR or its activation with natural or pharmacological ligands (drugs) was not able to influence large intestinal tumour development. Interestingly, the CaSR has been shown to be involved in inflammatory diseases, such as asthma. Chronic (long lasting) inflammation of the intestine, called inflammatory bowel disease (IBD), is a highly debilitating disease and it can even lead to the development of intestinal cancer. Therefore, we wanted to examine the role of the CaSR role in IBD. Because there are no "normal" intestinal cell lines that can be used in the laboratory, we had to work with colon cancer cells. The CaSR is not present in colon cancer cells; therefore, we had to genetically modify the cells to have high amounts of the CaSR, to be used as a model system. We used then these cells to test if the CaSR affects inflammation and found that presence of the CaSR by itself already leads to a higher production of inflammatory factors. When we stimulated the cells with ligands of the receptor, then even more inflammatory factors were produced. We then tested if the receptor is also involved in intestinal inflammation and if we could target it with specific drugs. In a mouse model of intestinal inflammation, we could show that drugs inhibiting the CaSR reduced the severity of the inflammation, while drugs activating the receptor worsened the symptoms. As there is no known cure for IBD and surgical removal of the damaged portions of the bowel is often necessary, finding drugs that could postpone the development of the disease or even lead to cure is an unmet necessity. The results of our project offer an important rationale to investigate further if drugs targeting the CaSR could be repurposed for the treatment of intestinal inflammation, which is also key risk factor for colorectal cancer.