As the techniques behind liquid biopsy become more advanced, we should be able to diagnose and evaluate an increasing number of cancers using simple blood tests... in theory. Unfortunately, not all forms of the disease are cooperative. Breast cancer, for instance, has long eluded detection in this manner – but it may not remain hidden for much longer. “Phosphorylation is one of the major regulation mechanisms in many diseases, including breast cancer,” says W. Andy Tao, a biochemistry professor at Purdue University. “Phosphorylation and kinases have been the major target for cancer therapy, but unfortunately not for diagnosis.” Why? Because the use of phosphorylated molecules as diagnostic biomarkers in blood is confounded by plasma-dwelling phosphatases, which remove the phosphate groups. The solution? Extracellular vesicles (EVs), according to a team of researchers led by Tao (1): “Our findings highlight that isolating EVs from plasma allows us to use blood or other liquid biopsy for potential cancer screening based on the status of protein phosphorylation – something that’s not been done before.”
The EVs found in blood plasma form a protective shell around the phosphoproteins, preventing dephosphorylation. To measure the cargo inside, the investigators broke apart the EVs and then used trypsin to create phosphopeptides ahead of analysis and identification using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Their study detected 144 phosphoproteins at higher concentration levels in breast cancer cases than in healthy controls. The findings hold significance not only because of the improved ability to measure phosphoprotein biomarker levels in blood, but also because of the abundance of EVs in plasma, which could allow the detection of thousands of phosphopeptides from a single milliliter of sample. Next, the team plan to investigate potential biomarkers in other cancers and diseases – a promising avenue, given that their initial investigation revealed over 10,000 unique plasma phosphoproteins.
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References
- IH Chen et al., “Phosphoproteins in extracellular vesicles as candidate markers for breast cancer”, Proc Natl Acad Sci USA, 114, 3175–3180 (2017). PMID: 28270605.
