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Cancer is one of the leading causes of death in the U.S., second only to heart disease. But a new cancer treatment method from CU ������ý���� researchers uses sound waves to soften tumors and could be a potent tool against the disease.

Chemotherapy can help treat many types of cancer. Chemo drugs aim to disrupt or destroy cancer cells, which tend to grow and divide quickly. But the drugs aren’t always effective, partly because tumor tissue can be so dense that drugs can’t penetrate the inner layers of cells. Chemo drugs can also damage healthy cells and cause unpleasant side effects.

Shane Curry

In a new study in the journal , a team of researchers led by former CU ������ý���� graduate engineering student Shane Curry used two tools to soften tumors. They paired high-frequency ultrasound waves with a type of sound-responsive particle to reduce the protein content of tumors.

Andrew Goodwin, senior author of the study and associate professor in the Department of Chemical and Biological Engineering at CU ������ý����, said softening tumors this way could make chemotherapy more likely to work.

“Tumors are kind of like a city. There are highways running through, but it's not laid out very well, so it's hard to get through,” he said. “Are there ways we can improve these lines of transport so the drugs can do their job?”

Ultrasound can also treat cancer by breaking down tumor tissue, but like chemo, the sound waves can also be damaging to the body. The researchers’ particles could make it easier to treat tumors with less intense sound waves, making the procedure safer for patients.

"A major limitation in many tumor treatments is delivering sufficient therapeutic doses without damaging healthy tissue,” said Curry. “My hope is that these particles can expand the applications and increase the potency of a variety of treatments."

Changing body tissue through sound

Sound creates physical waves that move through air, liquid and solid objects. Goodwin said the sounds we hear are essentially small packets of fluctuating pressure moving through the space around us.

“When a packet of high pressure and low pressure pushes your eardrum, the pressure makes it vibrate, and these vibrations are interpreted by your brain,” he said.

Ultrasound imaging, like the kind pregnant women undergo, uses this principle to visualize what’s inside the body. It sends sound waves into the body, and as those sound waves bounce off internal organs and tissues, the echoes are converted into live images and videos.

A microscopic image of the researchers' sound-responsive particles. (Credit: Andrew Goodwin)

Doctors also sometimes use ultrasound to treat cancer. Ultrasound waves can destroy tumor cells and tissue, but the sound waves are strong enough to also damage healthy tissue and disrupt blood vessels. They can also heighten the risk of the cancer spreading, or metastasizing, to another part of the body.

To solve that problem, Goodwin and his research team developed a type of microscopic particle that vibrates and pulses in response to sound waves. High-frequency ultrasound waves make the particles vibrate so fast they vaporize the water surrounding them, creating tiny bubbles—a process called cavitation.

These particles, which measure about 100 nanometers across, are made from silica and coated in a layer of fatty molecules.

In the new study, the researchers added these particles into both 2D and 3D cultures of tumor tissue. When they applied ultrasound, the particles changed the structure of both the 2D and 3D tumor cultures, but in slightly different ways.

In the 2D cultures, which consisted of a layer of cells grown on a plastic dish, the particles destroyed the tumor tissue. But in the 3D cultures, which were more lifelike, the particles simply reduced the amounts of certain proteins surrounding the tumor cells, which made the tissue softer.

The fact that the cells in the 3D culture didn’t break down is a good sign, Goodwin said. It means the treatment softened, but didn’t destroy, the tumor tissue, so it’s also less likely to damage healthy tissue.

Possibilities for the future

Goodwin believes this type of cancer treatment would work well for prostate, bladder, ovarian, breast and other cancers that have tumors located in a specific part of the body. Other cancers, such as those that affect the blood and bones, can be more spread out and harder to treat in this way.

Currently, Goodwin and his team are using similar sound-responsive particles to treat tumors in mice, but eventually, the researchers hope to administer the particles inside the human body.

Goodwin thinks it could be possible to attach the particles to antibodies—immune system proteins that bind to bacteria, viruses and other invaders—and then add those antibodies to the bloodstream, where they could travel to a tumor. Once the particles have arrived, the researchers could apply ultrasound and test the treatment.

Although that day could still be a ways off, Goodwin said he’s excited about the possibilities this treatment could unlock.

“The technology for focused ultrasound has come a really long way in the last decade,” he said. “I'm hoping that the particles we build in the lab can start to meld with the acoustic, imaging and therapy technologies that are part of the clinical regimen.”