Extracellular vesicles and anti-cancer drug resistance.

Extracellular vesicles (EVs) including exosomes, microvesicles, oncosomes, and microparticles have been associated with communicating anti-cancer drug-resistance. The in vitro, pre-clinical in vivo and patients' data linking EVs to drug-resistance (and the specific drugs involved) in breast cancer, prostate cancer, lung cancer, ovarian cancer, haematological malignancies, colorectal cancer, gastric cancer, pancreatic cancer, glioblastoma, neuroblastoma, melanoma, kidney cancer and osteosarcoma. Details of the mechanisms by which the resistance seems to be occurring (e.g. EVs transferring drug-efflux pumps from drug-resistant cancer cells, EVs binding monoclonal antibodies in the peripheral circulation and so reducing their bioavailability, EVs from tumour microenvironment cells, etc.) are outlined, as are efforts to try to block such resistance. Research to date strongly supports EVs as playing a key role in drug-resistance. Further studies including tailored clinical studies are now warranted to determine how best to prevent this occurring, in the interest of patients and also for economic benefit. Furthermore, efforts to exploit safe (non-cancer origin) EVs as anti-cancer drug delivery vehicles that may achieve efficacy with more limited side-effects than free drug, deserve further investigation.