Human skin can be morphed into genetically modified, cancer-killing brain stem cells, according to a new study. This latest advance has only been tested in mice — but eventually, it’s possible that it could be translated into a personalized treatment for people with a deadly form of brain cancer.
The study builds on an earlier discovery that brain stem cells have a weird affinity for cancers. So researchers, led by Shawn Hingtgen, a professor at University of North Carolina at Chapel Hill, created genetically engineered brain stem cells out of human skin. Then they armed the stem cells with drugs to squirt directly onto the tumors of mice that had been given a human form of brain cancer. The treatment shrank the tumors and extended survival of the mice, according to results recently published in the journal Science Translational Medicine.
Usually we think about stem cell therapy in the context of rebuilding or regrowing a broken body part — like a spinal cord. But if they could be modified to become cancer-fighting homing missiles, it would give patients with a deadly and incurable brain cancer called glioblastoma a better chance at survival. Glioblastomas typically affect adults, and are highly fatal because they send out a web of cancerous threads. Even when the main mass is removed, those threads remain despite chemotherapy and radiation treatment. This cancer has caused a number of high-profile deaths including Senator Edward (Ted) Kennedy in 2009, and possibly Beau Biden more recently. Approximately 12,000 new cases of glioblastoma are estimated to be diagnosed in 2017.
“We really have no drugs, no new treatment options in years to even decades,” Hingtgen says. “[We] just really want to create new therapy that can stand a chance against this disease.”
But there’s a problem: brain stem cells aren’t exactly easy to get. Brain stem cells, more properly known as neural stem cells, hang out in the walls of the brain’s irrigation canals — areas filled with cerebrospinal fluid, called ventricles. They generate the cells of the nervous system, like neurons and glial cells, throughout our lives.
A research group at the City of Hope in California conducted a clinical trial to make sure it was safe to treat glioblastoma patients with genetically engineered neural stem cells. But they used a neural stem cell line that they’d obtained from fetal tissue. Since the stem cells weren’t the patients’ own, people who were genetically more likely to reject the cells couldn’t receive the treatment at all. For the people who could, treatment with the neural stem cells turned out to be relatively safe — although at this phase of clinical trials, it hasn’t been particularly effective.
More personalized treatments have been held up by the challenge of getting enough stem cells out of the patients’ own brains, which is “virtually impossible,” says stem cell scientist Frank Marini at the Wake Forest School of Medicine, who was not involved in this study. “You can’t really generate a bank of neural stem cells from anybody because you have to go in and resect the brain.”
So instead, Hingtgen and his colleagues figured out a way to generate neural stem cells from skin — which in the future, could let them make neural stem cells personalized to each patient. For this study, though, Hingtgen and his colleagues extracted the skin cells from chunks of human flesh leftover as surgical waste. “That really is the magic piece here,” Marini says. “Now, all of a sudden we have a neural stem cell that can be used as a tumor-homing vehicle.”
Using a disarmed virus to infect the cells with a cocktail of new genes, the researchers morphed the skin cells into something in between a skin cell and a neural stem cell. People have turned skin cells back into a more generalized type of stem cell before. But then turning those basic stem cells into stem cells for a certain organ like the brain takes another couple of steps, which takes more time. That’s something that people with glioblastoma don’t have.
The breakthrough here is that Hingtgen’s team figured out how to go straight from skin cells to something resembling a neural stem cell in just four days. The researchers then genetically engineered these induced neural stem cells to arm them with one of two different weapons: One group was equipped with an enzyme that could convert an anti-fungal drug into chemotherapy, right at the cancer’s location. The other was armed with a protein that binds to the cancer cells and makes them commit suicide in an orderly process called apoptosis.
The researchers tested these engineered neural stem cells in mice that had been injected with human glioblastoma cells, which multiplied out of control to create a human cancer in a mouse body. Both of the weaponized stem cell groups were able to significantly shrink the tumors and keep the mice alive by about an extra 30 days (for scale, mice usually live an average of two years).
But injecting the cells directly into the tumor doesn’t really reflect how the therapy would be used in humans. It’s more likely that a person with glioblastoma would get the bulk of the tumor surgically removed. Then, the idea is that these neural stem cells, generated from the patient’s own skin, will be inserted into the hole left in the brain. So, the researchers tried this out in mice, and the tumors that regrew after surgery were more than three times smaller in the mice treated with the neural stem cells.
It’s a promising start, but it could take a few years still before it’s in the clinic, Hingtgen says. He and his colleagues started a company called Falcon Therapeutics to drive this new therapy forward. “We’re working as fast as we can,” Hingtgen says. “We probably can’t help the patients today. Hopefully in a year or two, we’ll be able to help those patients.”
One of the things they’ll have to figure out first is whether the neural stem cells can travel the much bigger distances in human brains, and whether they’ll be able to eliminate every remaining cancer cell. “The caveats on this are that, of course, it’s a mouse study, and whether or not that directly converts to humans is unclear,” Marini says. Still, he adds, “There’s a very high probability in this case.”