Researchers have been looking for years for a way to use oxygen to fight cancer. Now, they may finally have one.
A new study finds that giving high-dose oxygen may help efforts to stimulate the immune system against tumors. The study's only been done in mice and hasn't been shown safe in people yet — but it does open some possibilities, the researchers report in the journal Science Translational Medicine.
"This is exciting work," said Susanna Greer, director of clinical research and immunology for the American Cancer Society. "This is the kind of data that definitely makes you catch your breath a little bit."
It could be a simple approach to making cancer therapies work better, especially immunotherapy, said Greer, who was not involved with the study.
"I was looking to solve the problem of existence of tumors and anti-tumor killer cells in the same patient," said Michail Sitkovsky of Northeastern University in Boston, who led the study.
Most people do produce immune system cells that can kill tumors, and most cancer experts believe they actually do a good job of it, taking out tumors long before they can ever cause symptoms. But, clearly, not always, or else cancer would not be the No. 2 killer, after heart disease.
Sitkovsky and colleagues looked at one particular property of tumors. They can live without much oxygen, in what are known as hypoxic environments.
"Since the root of all problems is the lack of oxygen in tumors, a simple solution is to give tumors more oxygen," Sitkovsky told NBC News.
This approach has been tried in many different ways and so far it hasn't worked. It's been such a failure that the American Cancer Society has a specific and detailed explanation.
"Available scientific evidence does not support claims that putting oxygen-releasing chemicals into a person's body is effective in treating cancer," the organization says. "Some types of oxygen treatment may even be dangerous; there have been reports of serious illness and death from hydrogen peroxide. Ozone is a strong oxidant that can damage cells, and has also caused deaths."
Sitkovsky's team wanted to try a non-toxic approach, giving a 60 percent oxygen mix — similar to what a patient gets in the hospital through an oxygen mask.
He found an important missing element in oxygen therapy — an immune response.
"If you give the oxygen and there are no tumor killer cells, then nothing happens to the tumor," he said. "Nobody understood that before. You must have killer cells. This is why oxygen until now was not successful in cancer," he added.
The tumors use a compound called adenosine to slow down the immune cells. "When killer cells come to kill tumors, they are met with adenosine and it puts killer cells to sleep. They do not enter the tumor microenvironment," said Sitkovsky.
"If you make a party in your house and guests don't come, then you don't have a party."
So enriching the oxygen levels wakes the cells back up and allows them to get inside the tumors, the researchers found.
So how do you get the killer cells there? That's where immunotherapy comes in, stimulating the immune system to attack tumors. It's an approach being tried against several types of tumors — but it cannot work if the tumors fight back. Adding oxygen to the mix might give the immune system the advantage it needs.
"This is something that could easily be combined with other clinically approved immunotherapies," said Greer.
"To test this hypothesis, tumor-bearing mice were placed in chambers with well-controlled gas composition (60 percent oxygen) to mimic protocols of supplemental oxygen delivery to humans," they wrote in their report.
The treatment shrank lung tumors in mice, and the killer cells went after tumors that had spread, or metastasized, in mice with a hard-to-treat type of breast tumor.
"It is exciting that these cells show up, that they do what they are supposed to do," said Greer.
The next step will be to try out the approach in humans.
"We have all learned that the mouse system is not the same as human system, that inoculating a tumor is not the same as tumor that grows from the outset in a human," Greer said. "But these are exciting results."