Extracellular Vesicles in Chemoresistance.

Chemotherapy represents the current mainstay therapeutic approach for most types of cancer. Despite the development of targeted chemotherapeutic strategies, the efficacy of anti-cancer drugs is severely limited by the development of drug resistance. Multidrug resistance (MDR) consists of the simultaneous resistance to various unrelated cytotoxic drugs and is one of the main causes of anticancer treatment failure. One of the principal mechanisms by which cancer cells become MDR involves the overexpression of ATP Binding Cassette (ABC) transporters, such as P-glycoprotein (P-gp), mediating the active efflux of cytotoxic molecules from the cytoplasm. Extracellular vesicles (EVs) are submicron lipid-enclosed vesicles that are released by all cells and which play a fundamental role in intercellular communication in physiological and pathological contexts. EVs have fundamental function at each step of cancer development and progression. They mediate the transmission of MDR through the transfer of vesicle cargo including functional ABC transporters as well as nucleic acids, proteins and lipids. Furthermore, EVs mediate MDR by sequestering anticancer drugs and stimulate cancer cell migration and invasion. EVs also mediate the communication with the tumour microenvironment and the immune system, resulting in increased angiogenesis, metastasis and immune evasion. All these actions contribute directly and indirectly to the development of chemoresistance and treatment failure. In this chapter, we describe the many roles EVs play in the acquisition and spread of chemoresistance in cancer. We also discuss possible uses of EVs as pharmacological targets to overcome EV-mediated drug resistance and the potential that the analysis of tumour-derived EVs offers as chemoresistance biomarkers.