A low-temperature 'plasma blowtorch' triggers death of diseased cells
Patients battling the blood cancer leukemia could one day receive a new type of treatment that uses a plasma -- a gas of electrically charged particles -- to kill cancer cells while keeping the healthy cells intact, according to new research.
"We have a really amazing device," said Mounir Laroussi, director of the laser and plasma engineering institute at Old Dominion University in Norfolk, Va., "We can generate a beam of plasma that is around room temperature. It doesn't burn anything; it doesn't destroy or poke holes. You can touch it with your hand."
After 10 minutes of treatment with the cold-plasma blowtorch, over 90 percent of leukemia cells were destroyed, according to the study published by Laroussi and research scientist Nazir Barekzi in October in the Journal of Physics D: Applied Physics
Leukemia is the most common childhood cancer and is responsible for almost one-third of all cancer-related deaths in children, according to the Leukemia and Lymphoma Society. Currently, leukemia survivors can lead healthy lives but long-term side-effects of the treatments, including chemotherapy, radiation therapy and bone marrow transplants, remain serious, said Laroussi.
Cold plasma, on the other hand, is made from near room-temperature nontoxic gases and is not believed to have negative long-term side effects.
Scientists create cold plasma by sending super-speedy electrons through gasses like helium and air. These electrons hit the atoms and molecules with so much energy that they pull off the outermost electrons of the atoms and molecules in the gas, creating a soupy mixture of free electrons and free ions. The gas remains at around room temperature, Laroussi explained, because the energy required to separate the electrons from their atoms quickly dissipates, leaving the gas ions cool.
When leukemia cells were treated with the cold-plasma plume, the scientists found something unexpected: the cells did not die right away.
"Rather, right after the experiment -- in the zeroth hour -- the cells are still okay. But after four to eight hours, they start dying," said Laroussi.
Laroussi believes that the delayed effect of the plasma treatment indicates that it triggers a biochemical reaction that provokes the cancer cell to kill itself. He said that targeting cancer cells to induce cell-death while leaving healthy cells unharmed is the key to developing effective leukemia treatments with plasma.
Laroussi's view is shared by Michael Keidar, associate professor of Mechanical and Aerospace Engineering at George Washington University, who was not involved in the study but whose laboratory also researches plasma for cancer therapy.
One of the molecules in cold plasma is an especially reactive oxygen molecule made of three oxygen atoms, known as ozone, rather than the two atoms of oxygen molecules in the air. Scientists have known since the early twentieth century that ozone acts as a disinfectant and recent research has demonstrated that ozone kills bacterial infections, an important innovation in treating wounds and drug-resistant bacterial infections.
Keidar's laboratory has identified that this ozone is a key player in targeting cancer cells. The molecule is a natural byproduct of a cell's metabolic cycle, Keidar said. Cancer cells have higher metabolisms than healthy cells, which leads to naturally elevated levels of ozone. Adding the right amount of extra ozone to the cancer cells can push their already elevated levels over the threshold and trigger cell-suicide, or apoptosis. Healthy cells, with their slower metabolisms, have ozone levels beneath this threshold and remain unscathed.
In addition to further work in leukemia treatment, Laroussi said that there are many future applications for low-temperature plasma. Laroussi's laboratory has studied cold plasma treatments for leukemia, bacterial infections, and even as a potential treatment for the plaques that cause Parkinson's and Alzheimer's diseases.
As more is understood about how the plasma initiates cell death, Keidar said that scientists might develop different kinds of plasmas and adapt the way they deliver the plasma to the tissue for each disease. His lab is currently developing new ways of tailoring plasma doses for skin, lung, and brain cancers.
"We are also looking into a detection mechanism that can determine where the cancer is, treat it with cold plasma, and then check if the treatment works. It’s very exciting," said Keidar.
-Halleh B. Balch, Inside Science News Service
Halleh B. Balch is a physics researcher and science writer currently based in Washington D.C. She has written for a wide range of publications covering physics, technology, and the biomedical sciences.