Remove hidden cancer messengers: How extracellular vesicles help spread tumors

Most cells in the body send out small messengers called extracellular vesicles that carry proteins, lipids, and other biologically active molecules to other cells, playing an important role in cell-cell communication. However, healthy cells are not the only ones that rely on extracellular vesicles. The same goes for cancer cells. Small extracellular vesicles that run out of tumor cells contribute to how cancer spreads to healthy tissue.

These small messengers could be key to developing drugs and treatments to combat new cancers, but it was unclear how recipient cells could accurately absorb extracellular vesicles and their cargo. Recent studies used state-of-the-art imaging to observe the uptake of small extracellular vesicles from tumors by target cells. The results were published on Nature Communications on March 12, 2025.

“In recent years, extracellular vesicles have attracted attention as carriers of intercellular signaling. However, the mechanisms of internalization by target cells are not well understood. We wanted to elucidate the pathways and mechanisms of internalization of extracellular vesicles by target cells.” Advanced Bioimaging, National Cancer Center Research Institute, Tokyo, Japan.

The researchers focused on small extracellular vesicles derived from two different tumor cell lines. Using a high-tech imaging technique, single-particle imaging with single-molecule detection sensitivity, we were able to classify small extracellular vesicles into distinct subtypes. We then tracked the internalization pathways of extracellular vesicles, or how the vesicles were absorbed by recipient cells.

Most small extracellular vesicles were internalized to target cells through a process called endocytosis. Previously, researchers suspected that the main mechanism was a fusion. During endocytosis, the membrane of the target cell completely surrounds the extracellular vesicles, creating a kind of bubble around the vesicles. This allows the cargo to be absorbed through the membrane so that it can be deposited on the target cell.

The researchers did not observe any examples of fusion when the membranes of the extracellular vesicles fuse together until the vesicles can enter the target cell.

Endocytosis is usually promoted by a protein called clathrin, but clathrin was not involved in the absorption of small extracellular vesicles into target cells. Instead, it was a protein pair called galectin-3 and LAMP-2C found on the membrane surface of small extracellular vesicles.

“Our findings revealed that extracellular vesicles derived from several cancer cells are classified into different subtypes,” Suzuki said. “All subtypes of extracellular vesicles were internalized primarily by galectin-3-mediated clathrin-independent endocytosis, which was facilitated by an increase in intracellular calcium concentration induced by the binding of extracellular vesicles to target cells.”

This process in which cells secrete proteins that help absorb from different cell lines into recipient cells is called paracrine binding or paracrine adhesion signaling. This contrasts with autocrine binding, a cell that secretes proteins, allowing it to bind to cells from the same cell line.

By better understanding the process of bringing small extracellular vesicles into target cells, researchers hope to be able to use vesicles to modify recipient cells and develop new cancer-fighting drugs.

“Extracellular vesicles are used as biomarkers, but they are trying to use extracellular vesicles as therapeutic agents. As we have clarified the mechanism by which extracellular vesicles are taken up by target cells, we hope that a mechanism will contribute to the study of extracellular vesicles, such as therapeutic agents.

Other contributors include hirosawa, eeriko yamaguchi, komura Nagayo, hiromune ando and Yasunari Yokota. Sato Yumi from Tohoku University. Rinshi S. Kasai from the National Cancer Center Research Institute; Hoshino Kiyoshi from the University of Tokyo.