Exosomes regulate intercellular communication in cancers, and are drawing attention as a potential cancer biomarker.

A Japanese research group has developed a highly sensitive method for detecting these exosomes that could potentially contribute to early detection of cancer.

The findings were published in the international edition of the Angewandte Chemie journal.

Exosomes are membrane vesicles consisting of lipid bilayer that measure only about 100 nanometers and are discharged from various cells.

Exosomes secreted from cancer cells are closely linked to cancer migration, invasion, and metastasis.

By examining these cancer-secreted exosomes, we may be able to develop a new method for early detection of cancer.

Current exosome analysis methods involve complicated and time-consuming procedures, including a combination of ultracentrifugation and affinity separation.

If we could differentiate cancer-secreted exosomes from other exosomes in body fluids without complicated pretreatments, this would enable a simple test for early detection of cancer.

Using molecular imprinting technology, the team prepared an artificial polymer film of about 30 nanometers possessing cavities the size of an exosome on top of the glass substrate (a exosome-binding cavity).

Then, using their own post-imprinting technology, the researchers selectively introduced antibodies that can recognise membrane proteins on the surface of exosomes and fluorescent molecules that can report exosome binding information.

This resulted in an exosome-sensing chip, a groundbreaking, highly-sensitive fluorescence detection chip combining antibodies and artificial materials.

It recognises the membrane proteins on exosomes, captures the exosomes and reports the information via changes in fluorescence.

To simplify exosome analysis using this fluorescence-based sensing platform, the team also created a device that automatises the whole analysis process.

This instrument is a highly sensitive CMOS camera-mounted fluorescence microscope equipped with a 3D robot arm.

With a custom-made flat type pipette tip inserted with the exosome sensing substrate, it can automatically carry out suction, discharge, fluorescence detection and substrate cleaning of samples.

Using this equipment, with no pretreatment and within 10 minutes, the team achieved unprecedented high-sensitivity detection of 6 picograms per millilitre.

This technology enables us to detect about 150 exosomes in 10 microlitres, a level of sensitivity that far surpasses previously reported measuring techniques.

For early detection of cancer, pre-checks are necessary before the disease takes hold, but currently the complexity of these checks means that only a small proportion of people are screened.

The instrument developed in this study makes it easier to analyse the exosomes in bodily fluids.

"Going forward, we will collect clinical samples on a large scale and carry out exosome analysis," said Prof Takeuchi. "If it can be verified that analysing cancer-secreted exosomes are helpful in cancer screenings, this will contribute to increasing the number of screenings. It can also be applied to cancer tests, treatment effectiveness, predictions of cancer transferal, and post-treatment prognoses."

Source: Kobe University

Photo credit: Kobe University