New imaging technique could harness nanoparticles to track cancer-cell changes

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A new imaging technology could give scientists the capability to simultaneously measure as many as 100 or more distinct features in or on a single cell, which in a disease such as cancer, would provide a much better picture of what's going on in individual tumor cells, according to a study published April 15 in the online journal PLoS-ONE.

A team from Stanford University School of Medicine in Stanford, Calif., led by Cathy Shachaf, PhD, an instructor in microbiology and immunology, has used specially designed dye-containing nanoparticles to simultaneously image two features within single cells. Although current single-cell flow cytometry technologies can do up to 17 simultaneous visualizations, the new method has the potential to do far more. The new technology works by enhancing the detection of ultra-specific but very weak patterns, or Raman signals, that molecules emit in response to light.

The researchers simultaneously monitor changes in two intracellular proteins that play crucial roles in the development of cancer. Development of the new technique may improve scientists' ability not only to diagnose cancers--for example, by determining how aggressive tumors' constituent cells are--but to eventually separate living, biopsied cancer cells from one another based on characteristics indicating their stage of progression or their degree of resistance to chemotherapeutic drugs.

That would expedite the testing of treatments targeting a tumor's most recalcitrant cells, said Shachaf, a cancer researcher who works in a laboratory run by the study's senior author Garry Nolan, PhD, associate professor of microbiology and immunology and a member of Stanford's Cancer Center.

Two intracellular proteins, Stat1 and Stat6, play crucial roles in the development of cancer. The investigators were able to simultaneously monitor changes in phosphorylation levels of both proteins in lab-cultured myeloid leukemia cells. The changes in Stat1 and Stat6 closely tracked those demonstrated with existing visualization methods, establishing proof of principle for the new approach.

While the new technology so far has been used only to view cells on slides, it could eventually be used in a manner similar to flow cytometry, the current technology, which lets scientists visualize single cells in motion. In flow cytometry, cells are bombarded with laser light as they pass through a scanning chamber. The cells can then be analyzed and, based on their characteristics, sorted and routed to different destinations within the cytometer.

Still, flow cytometry has its limits, as it involves tethering fluorescent dye molecules to antibodies, with different colors tied to antibodies that target different molecules. The dye molecules respond to laser light by fluorescing-echoing light at exactly the same wavelength, or color, with which they were stimulated. The fluorescence's strength indicates the abundance of the cell-surface features to which those dyes are now attached. But at some point, the light signals given off by multiple dyes begin to interfere with one another. It is unlikely that the number of distinct features flow cytometry can measure simultaneously will exceed 20 or so.

The new high-tech dye-containing particles used by the Stanford team go a step further. They give off not just single-wavelength fluorescent echoes but also more-complex fingerprints comprising wavelengths slightly different from the single-color beams that lasers emit. These patterns, or Raman signals, occur when energy levels of electrons are just barely modified by weak interactions among the constituent atoms in the molecule being inspected.