Washington investigators develop a new tool for high-res live cancer imaging

Deep-tissue in vivo photoacoustic genetic imaging of reversibly switchable bacterial phytochrome BphP1--Courtesy of Wash. U. in St. Louis

Photoacoustic tomography (PAT) of genetically encoded probes allows for good penetration of tissue at high spatial resolution; however, high background signals from the blood have limited the use of this technique for the live imaging of mammalian tissue.

Now in a novel study conducted by researchers at Washington University in St. Louis, they combine the use of a nonfluorescent bacterial phytochrome with PAT imaging in cancerous tissue, resulting in high spatial resolution, increased penetration depth, and crucially, enhanced detection sensitivity with significantly reduced background signals. The impact of such work may have translational value especially in certain tissue that is rich in blood which would otherwise confound PAT imaging analysis.

Lead author Lihong Wang, a professor of biomedical engineering at the university's School of Engineering, together with his postdoctoral researcher, Junjie Yao, published their findings in Nature Methods this month.

By leveraging off a novel protein called BphP1 found in the Rhodopseudomonas palustris bacterium, the group found that by genetically altering an aggressive cancer cell line to express this protein they were able to visualise the cancerous cells at greater resolution at up to 1 cm deep.

The sensitivity of this imaging technique works well since the BphP1 protein can respond to different types of light by shifting its absorption properties. This reversible switch in the protein means the researchers can "flip the switch" when they shine the second light onto the tissue, deducing unwanted background signals which may come from blood cells.

One of the difficulties in imaging cancer has been the detection sensitivity in early cancerous tissue. Now, Yao believes this technology will be adopted in the lab for imaging tissue with genetic specificity, drug screening in real time, as well as other highly vascularized tissue including the heart.

"This technology provides a promising new tool to biologists for high resolution, deep imaging of cancer with genetic specificity as well as for drug screening in living tissue," Wang says.

- here's the release
- read the research abstract

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