Mediation of radiation-induced bystander effect and epigenetic modification: The role of exosomes in cancer radioresistance.

Exosomes are nano-sized extracellular vesicles produced by almost all mammalian cells. They play an important role in cell-to-cell communication by transferring biologically active molecules from the cell of origin to the recipient cells. Ionizing radiation influences exosome production and molecular cargo loading. In cancer management, ionizing radiation is a form of treatment that exerts its cancer cytotoxicity by induction of DNA damage and other alterations to the targeted tissue cells. However, normal bystander non-targeted cells may exhibit the effects of ionizing radiation, a phenomenon called radiation-induced bystander effect (RIBE). The mutual communication between the two groups of cells (targeted and non-targeted) via radiation-influenced exosomes enables the exchange of radiosensitive molecules. This facilitates indirect radiation exposure, leading, among other effects, to epigenetic remodeling and subsequent adaptation to radiation. This review discusses the role exosomes play in epigenetically induced radiotherapy resistance through the mediation of RIBE.