A scanning electron micrograph (top) shows human lymphoma cells inside hydrogel microwells. When the cells produce a protease, the enzyme cleaves a peptide in the hydrogel to release a quencher molecule, causing a fluorescent molecule remaining in the gel to glow green (bottom). Scale bar in bottom image is 50 μm.
Credit: Anal. Chem.
Cancer cells often leave a molecular calling card. They secrete an active version of the enzyme matrix metalloproteinase 9 (MM9) at higher levels than healthy cells do. With a new microfluidic technique, scientists can see if cancer cells are present by detecting MM9 (Anal. Chem. 2013, DOI: 10.1021/ac402660z). The method lets scientists detect as few as 11 cancer cells in a fluid sample.
MM9’s actions play a part in tumor cell invasion and metastasis. Because of the enzyme’s crucial role, researchers have developed other methods to measure protease concentration in cells but not in a real-time, high-throughput manner, says Dong-Sik Shin, a postdoctoral fellow in biomedical engineering at the University of California, Davis. In addition to speeding up cancer diagnostics, this would allow researchers to study how protease secretion by cancer cells changes in response to drugs.
Shin, working with UC Davis professor Alexander Revzin and colleagues, designed a peptide that is cleaved by MM9. They attached a pair of molecules to each end of the peptide: one that fluoresces and another that quenches that fluorescence. The team placed the hydrogel in 100-µm-diameter circular wells in a microfluidic device, then attached the peptide to the gel with a thiol group. Cells from a liquid sample flow over the wells and get captured by an antibody in the hydrogel, Shin says.
When a cell producing MM9 lands in the well, the protease cleaves the peptide, and the quencher molecule floats away from the hydrogel, allowing the fluorescent molecule to glow. Higher levels of fluorescence mean greater amounts of protease, indicating the presence of cancer cells. The method is sensitive enough that the researchers can detect as few as 11 human lymphoma cells per well.
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