A recent discovery approximately the process of evasion by cancer cells has led researchers towards a new approach to treat the disease.
Cancer cells are known for spreading genetic chaos. As cancer cells divide, DNA segments and even whole chromosomes may also be duplicated, mutated, or missing altogether. This is known as chromosomal instability, and scientists at Memorial Sloan Kettering have learned that it is associated with cancer’s aggressiveness.
The more unstable chromosomes are, the much more likely that bits of DNA from these chromosomes will end up where they don’t belong: out of doors of a cell’s central nucleus and floating in the cytoplasm.
Cells interpret these rogue bits of DNA as evidence of viral invaders, which sets off their internal alarm bells and results in inflammation. Immune cells trip to the site of the tumour and churn out defensive chemicals. A mystery has been why this immune reaction, triggered by the cancer cells, does not spell their downfall.
“The elephant in the room is that we didn’t in point of fact know how cancer cells were in a position to live to tell the tale and thrive in this inflammatory surroundings,” said Samuel Bakhoum, a physician-scientist at MSK and a member of the Human Oncology and Pathogenesis Program.
According to the new study from Dr. Bakhoum’s lab in the publication Cancer Discovery, the reason has to do, in part, with a molecule sitting on the out of doors of the cancer cells that destroys the warning signals before they ever reach neighbouring immune cells.
The findings help to provide an explanation for why some tumours do not respond to immunotherapy, and — equally important — propose ways to sensitize them to immunotherapy.
Detecting Dangerous DNA
The warning system Dr. Bakhoum studies is known as cGAS-STING. When DNA from a virus (or an unstable cancer chromosome) lands in a cell’s cytoplasm, cGAS binds to it, forming a compound molecule called cGAMP, which serves as a warning sign. Within the cell, this warning sign activates an immune response called STING, which addresses the instant problem of a potential viral invader.
Moreover, much of the cGAMP also travels out of doors the cell where it serves as a warning sign to neighbouring immune cells. It activates their STING pathway and unleashes an immune attack against the virally infected cell.
Preceding work from the Bakhoum lab had shown that cGAS-STING signalling within of cancer cells causes them to adopt features of immune cells — in specific, the capacity to crawl and migrate — which aids their ability to metastasize. This given a part of the answer to the question of how cancer cells live to tell the tale inflammation and aid metastasis in the process.
The new research shows how the cancer cells cope with the warning signals that activated cGAS-STING releases into the surroundings. A scissor-like protein shreds the signals, providing a second way the cells can thwart the specter of immune destruction.
The scissor-like protein that coats cancer cells is known as ENPP1. When cGAMP finds its way out of doors the cell, ENPP1 chops it up and prevents the sign from reaching immune cells. At the same time, this chopping releases an immune-suppressing molecule called adenosine, which also quells inflammation.
Through a battery of experiments conducted in mouse models of breast, lung, and colorectal cancers, Dr. Bakhoum and his colleagues showed that ENPP1 acts like a regulate switch for immune suppression and metastasis. Turning it on suppresses immune responses and increases metastasis; turning it off enables immune responses and reduces metastasis.
The scientists also looked at ENPP1 in samples of human cancers. ENPP1 expression correlated with both increased metastasis and resistance to immunotherapy.
From a remedy perspective, possibly the most notable finding of the study is that flipping the ENPP1 switch off could increase the sensitivity of several different cancer types to immunotherapy drugs called checkpoint inhibitors. The researchers showed that this approach used to be effective in mouse models of cancer.
Several companies — including one that Dr. Bakhoum and colleagues founded — are now developing drugs to inhibit ENPP1 on cancer cells.
Dr. Bakhoum says it’s lucky that ENPP1 is located on the surface of cancer cells since this makes it an easier target for drugs designed to block it.
It’s also slightly particular. Since most other tissues in a healthy individual don’t seem to be inflamed, drugs targeting ENPP1 primarily have an effect on cancer.
After all, targeting ENPP1 undercuts cancer in two separate ways: “You’re concurrently increasing cGAMP levels out of doors the cancer cells, which activates STING in neighbouring immune cells, while you’re also preventing the production of the immune-suppressive adenosine. So, you’re hitting two birds with one stone,” Dr. Bakhoum explains.
The pace of the research has been incredibly fast, he says. “Probably the most things I would be in point of fact prou
(This story has been published from a wire agency feed without modifications to the text.)
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