Ultrasound can 'see' when tumor cells turn genes on and off | Science

Ultrasound can reveal a leaking heart valve, exposes torn tendon, and gives parents an early snapshot of their baby within the womb. Now, researchers have shown that these genes are likely to be triggered by the growth of cancer cells.

Michael Kolios of Ryerson University in Toronto, Canada, who was not connected to the study, said, "It could not be connected to the study.

Cells continuously turn genes on and off. To illuminate that activity-or expression-in-cells, researchers can genetically modify them so that when they fire up particular genes, they also produce fluorescent protein (GFP). Although this approach works well for cells in culture dishes, it makes it difficult to track gene activity inside tissues and organs.

Ultrasound, which produces high-frequency, high-frequency sound waves in the body, said chemical engineer Mikhail Shapiro of the California Institute of Technology (Caltech) in Pasadena. The noninvasive technique, he adds, is "really great" at peering deep into tissues.

But individual cells are too small to distinguish with most ultrasound frequencies. That's why Shapiro and his colleagues turned to aquatic bacteria that manufacture microscopic air bubbles that reflect sound waves. Inside the cells, the bubbles boost the number of sound waves that make the host cells detectable.

Last year, a team that included Shapiro and Caltech bioengineer Arash Farhadi inserted 11 genes for producing gas-filled spheres into gut bacteria and then injected the modified microbes into the intestines of mice. Using a small ultrasound probe, the scientists could pinpoint clusters of bacteria in the animals' intestines.

Making the same technique work in mammals. Bacterial genes and their role in the treatment of mammalian cells. For instance, multiple bacterial genes often share a promoter, a DNA sequence that functions like a switch, but each mammalian gene has its own. Farhadi, Shapiro, and colleagues discovered several workarounds. They found that by stitching several of the bacterial genes together with a protein from a virus, they could coax mammalian cells into activating the genes using one promoter. Inserting nine bacterial genes could induce human kidney cells into a dish to produce gas spheres. Cells containing the capsules showed up under ultrasound Science.

To test whether the cells are visible in an animal, they are believed to be infected with viral diseases that they then injected into mice. These cells caused tumors to sprout in the rodents. When the researchers visualized the tumors with GFP, they appeared as green blobs. Ultrasound provides a more accurate image, showing that only cells at the rim of the tumors had turned on the bubble-producing genes. "You can see this beautiful expression pattern in the animals," Farhadi says.

Gregory Czarnota of the Sunnybrook Health Sciences Center in Toronto, says: "It's a good practice to test the expression of genes in cells.

But he and other scientists agree that researchers need to solve a few problems to make the technique widely useful. For example, the team's genetic engineering approach is complex, says neuroscientist Sreekanth Chalasani of the Salk Institute for Biological Studies in San Diego, California. "I would love to use this today," he says. "If there was a way to put these genes in, I'd do it."