Large oncosomes contain distinct protein cargo and represent a separate functional class of tumor-derived extracellular vesicles

Cancer‐derived extracellular vesicles (EVs) are membrane‐enclosed structures of highly variable size. EVs contain a myriad of substances (proteins, lipid, RNA, DNA) that provide a reservoir of circulating molecules, thus offering a good source of biomarkers. We demonstrate here that large EVs (L‐EV) (large oncosomes) isolated from prostate cancer (PCa) cells and patient plasma are an EV population that is enriched in chromosomal DNA, including large fragments up to 2 million base pair long. While L‐EVs and small EVs (S‐EV) (exosomes) isolated from the same cells contained similar amounts of protein, the DNA was more abundant in L‐EVs, despite S‐EVs being more numerous. Consistent with in vitro observations, the abundance of DNA in L‐EV obtained from PCa patient plasma was variable but frequently high. Conversely, negligible amounts of DNA were present in the S‐EVs from the same patients. Controlled experimental conditions, with spike‐ins of L‐EVs and S‐EVs from cancer cells in human plasma from healthy subjects, showed that circulating DNA is almost exclusively enclosed in L‐EVs. Whole genome sequencing revealed that the DNA in L‐EVs reflects genetic aberrations of the cell of origin, including copy number variations of genes frequently altered in metastatic PCa (i.e. MYC, AKT1, PTK2, KLF10 and PTEN). These results demonstrate that L‐EV‐derived DNA reflects the genomic make‐up of the tumour of origin. They also support the conclusion that L‐EVs are the fraction of plasma EVs with DNA content that should be interrogated for tumour‐derived genomic alterations.

Extracellular Vesicles (EVs) have received considerable attention in recent years, both as mediators of intercellular communication pathways that lead to tumor progression, and as potential sources for discovery of novel cancer biomarkers. For many years, research on EVs has mainly investigated either the mechanism of biogenesis and cargo selection and incorporation, or the methods of EV isolation from available body fluids for biomarker discovery. Recent studies have highlighted the existence of different populations of cancer-derived EVs, with distinct molecular cargo, thus pointing to the possibility that the various EV populations might play diverse roles in cancer and that this does not happen randomly. However, data attributing cancer specific intercellular functions to given populations of EVs are still limited. A deeper functional, biochemical and molecular characterization of the various EV classes might identify more selective clinical markers, and significantly advance our knowledge of the pathogenesis and disease progression of many cancer types.

Prostate cancer cells release atypically large extracellular vesicles (EVs), termed large oncosomes, which may play a role in the tumor microenvironment by transporting bioactive molecules across t...