March 12, 2020 -- A new protein has been identified on tumor-derived extracellular vesicles that indicates if a lung tumor is likely to metastasize, according to research published in Science Advances on March 11. A minimally invasive biomarker test to catch cancer early could significantly improve patient outcomes.
Lung cancer is among the deadliest cancers in men and women worldwide, with the most prevalent form of lung cancer being non-small cell lung cancer (NSCLC). More than half of NSCLC patients die after developing metastases.
NSCLC tumors are heterogeneous, making them notoriously difficult to treat. The identification of relevant biomarkers would therefore be extremely useful in facilitating treatment choice to reduce patient risk of metastasis development.
"The goal of any cancer diagnosis and treatment is to catch it early," said Tony Hu, PhD, Weatherhead Presidential Chair in Biotechnology Innovation at Tulane University School of Medicine, in a statement. "This information could help diagnose patients who are at high risk for having their cancer metastasize, and treatment could be tailored to account for that. Not all patients have the same type of tumor, and if you can target therapy to address a particular tumor, you can improve outcomes."
Researchers from Tulane explored if extracellular vesicles (EVs) could be used as diagnostic biomarkers for metastatic NSCLC. They used mass spectrometry to detect EV proteins in two mouse lines with metastatic and nonmetastatic phenotypes.
EVs are secreted by all cancer cell subsets within tumors and can reflect heterogeneous features present in tumors. They can be obtained safely and repeatedly via blood samples. The abundance of EVs in the bloodstream makes them excellent candidates for biomarkers to predict metastasis or early detection of metastasis. This is based on the "seed and soil" theory, in which tumor-derived EVs migrate to distant organs and condition sites for initiation of metastasis.
Upon isolating extracellular vesicles from both metastatic and nonmetastatic cell lines, the researchers identified proteins that were differentially expressed. Mass spectrometry revealed that 196 proteins were shared in EVs, 234 were present in metastatic EVs, and 188 were present only in nonmetastatic EVs.
Then, proteins in metastatic EVs were filtered for high expression, which resulted in 10 candidate proteins. Tetraspanin 8 (Tspan8) was selected as a potential prognostic biomarker for NSCLC metastasis. This protein mediates signal transduction events in the regulation of cell development, growth, and motility. The gene for Tspan8 is expressed in a number of carcinomas.
To understand how Tspan8 is associated with metastasis, the researchers measured gene expression of proteins associated with internalization and recovery of Tspan8. They found that intersectin-2 (ITSN2) expression was greatly increased in metastatic cell lines, indicating that it has an important role in recruiting Tspan8 to EVs in metastatic tumor cells. The study findings suggest that EV-Tspan8 progression and metastasis of NSCLC may be under the regulation of ITSN2.
Lastly, measuring Tspan8 expression of archived serum samples from patients with NSCLC showed that serum EV-Tspan8 concentrations predicted future metastasis. For example, high serum EV-Tspan8 expression in patients with stage III NSCLC is an independent predictor for distant metastasis (when tumor spreads to distant organs).
With this knowledge in hand, Hu and his team plan to incorporate the biomarker profiling into their nanoplasmonic detection assay for rapid clinical translation.
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