Tumor-targeted suicide gene-directed enzyme prodrug therapy mediated by extracellular vesicles

In this article, we describe the gene-directed enzyme prodrug therapy, also known as the "Trojan Horse" therapy mediated by exosomes - small extracellular vesicles (sEVs) secreted from mesenchymal stem/stromal cells (MSCs) and cancer cells. MSC-EVs possess strong migrating tropism toward tumor sites. EVs derived from tumor cells mimic the parental cells in an invasive metastatic growth trait and the capability to reprogram the recipient cells. The behavior of these EVs when modified with the suicide gene predestinates them to be a drug with guided intracellular action. EVs with therapeutic suicide gene are prepared from cells with integrated retrovirus vector containing its genetic message. These EVs are internalized by tumor cells and the product of the gene converts the non-toxic prodrug into a cytotoxic drug inside the cell causing its suicide. The action of two suicide gene systems are described: the yCD::UPRT-MSC/5-FC system and the HSVTK-MSC-GCV system. Suicide gene EVs either MSCs or tumor cell origin due to their intrinsic targeting capabilities, high modification flexibility, as well as biological barrier permeability represent potential drugs for tumors untreatable with present standard cancer therapies.