Exosomes, via heat shock protein 70 (HSP70) expressed in their membrane, are able to interact with the toll-like receptor 2 (TLR2) on myeloid-derived suppressive cells (MDSCs), thereby activating them.
Researchers at INSERM, UMR 866 analyzed exosomes from mouse (C57Bl/6) and breast, lung, and ovarian cancer patient samples and cultured cancer cells with different approaches, including nanoparticle tracking analysis, biolayer interferometry, FACS, and electron microscopy. Data were analyzed with the Student’s t and Mann-Whitney tests. All statistical tests were two-sided.
The researchers showed that the A8 peptide aptamer binds to the extracellular domain of membrane HSP70 and used the aptamer to capture HSP70 exosomes from cancer patient samples. The number of HSP70 exosomes was higher in cancer patients than in healthy donors. Accordingly, all cancer cell lines examined abundantly released HSP70 exosomes, whereas “normal” cells did not. Chemotherapeutic agents such as cisplatin or 5FU increase the amount of HSP70 exosomes, favoring the activation of MDSCs and hampering the development of an antitumor immune response. In contrast, this MDSC activation was not observed if cisplatin or 5FU was combined with A8. As a result, the antitumor effect of the drugs was strongly potentiated.
A8 peptide aptamer: a tool to detect exosomes expressing HSP70 in their membranes in cancer samples. A) The binding of exosomes (nm), derived from B16F10 or HCT116 cell lines to immobilized biotinylated A8 was determined by biolayer interferometry. Where indicated, cmHSP70 was also added. B) Association curves (nm) of HSP70 exosomes in urine samples of patients with breast (n = 3) or pulmonary (n = 3) cancer or healthy individuals (controls, n = 2) with biotinylated A8 immobilized on streptavidin sensor tips. Binding curves represent mean signal of triplicate measurements for each sample. Mann-Whitney: ***P < .001. C) Exosomes expressing HSP70 were determined by a customized enzyme-linked immunosorbent assay in urine samples from healthy individuals (n = 5) and cancer patients (breast, pulmonary and ovary, n = 8). Data are means and standard deviations of the nanovesicle concentrations (P = .004). D) Nanoparticle tracking analysis (NTA) to quantify total number of exosomes in the urine samples described above. Samples were diluted in PBS and analyzed using a NanoSight LM10 instrument. Data points are total numbers of exosomes (109/mL). Error bars represent standard deviations, Mann-Whitney: **P = .0016. All statistical tests were two-sided.