A systematic examination of the tumor and the tissue surrounding it; particularly normal cells in that tissue; called fibroblasts — has revealed a new treatment target; that could potentially prevent the rapid dissemination; and poor prognosis associated with high-grade serous carcinoma (HGSC); a tumor type that primarily originates in the fallopian tubes or ovaries and spreads throughout the abdominal cavity.
Stroma has a major impact on cancer cells
But given the lack of progress with that approach; and the fact the tumors are complex organs; comprised of different tumor-supporting cell types (stroma), “we thought; it might be better to focus less on the cancer and more on the stroma, the supporting tissue that surrounds the cancer and enables its growth.”In the issue of Nature, the researchers show that the stroma has a major impact on cancer cells. “In this case,” Lengyel said, “it makes them more malignant, more aggressive and more invasive. The stroma is often bigger than the cancer itself.”
In close collaboration with Fabian Coscia, PhD, and Matthias Mann, the researchers profiled the expression of more than 5,000 proteins in both normal and cancerous tissues derived from minute amounts of patient biobank material. “For the first time, we were able to distinguish the molecular changes in the cancer cells from the ones happening in the adjacent stroma throughout disease progression,” explained Coscia. “When we then got our data, we were; fascinated to find; that the metastatic stroma was; characterized by a highly conserved protein signature, as opposed to the cancer cells.”
The tumor-promoting effects of cancer-associated fibroblasts
So, these metastatic changes were; seen in all analyzed patients. The researchers are now trying to understand their functional role during metastasis with the goal of finding novel therapeutic targets. However, in the process, they discovered a metabolic enzyme, nicotinamide N-methyltransferase (NNMT), highly expressed in the stroma surrounding metastatic cancer cells. They found that NNMT causes widespread gene expression changes in the tumor stroma, converting normal fibroblasts to cancer-associated fibroblasts that support and accelerate tumor growth.
Stromal NNMT expression encouraged ovarian cancer progression and metastasis. It was associated with very poor patient outcomes. The researchers are now using high-throughput screening to find novel ways to inhibit this enzyme. “One method looked promising,” said Mark Eckert. “We have a backbone for several candidate inhibitors. So, we know our target, we know the structure, we know how to apply this and we have a sense of the direction. We are starting to understand how a normal fibroblast is converted into a cancer-associated fibroblast by this metabolic enzyme.
“They also found that inhibition of NNMT activity reduced or even reversed many of the tumor-promoting effects of cancer-associated fibroblasts. So, this suggests, they note, that the stroma should be explored as a new treatment target. Coscia added that “this method may be used to discover other proteins that are important for metastasis and to identify early changes during disease development.””When we put it all together,” Lengyel said in conclusion, “it gave us exciting results. We have linked high-end technology, including proteomics and metabolomics, to improve our understanding of the stroma.”