Harnessing small extracellular vesicles for pro-oxidant delivery: novel approach for drug-sensitive and resistant cancer therapy.

Multidrug resistance (MDR) is an inevitable clinical problem in chemotherapy due to the activation of abundant P-glycoprotein (P-gp) that can efflux drugs. Limitations of current cancer therapy highlight the need for the development of a comprehensive cancer treatment strategy, including drug-resistant cancers. Small extracellular vesicles (sEVs) possess significant potential in surmounting drug resistance as they can effectively evade the efflux mechanism and transport small molecules directly to MDR cancer cells. One mechanism mediating MDR in cancer cells is sustaining increased levels of reactive oxygen species (ROS) and maintenance of the redox balance with antioxidants, including glutathione (GSH). Herein, we developed GSH-depleting benzoyloxy dibenzyl carbonate (B2C)-encapsulated sEVs (BsEVs), which overcome the efflux system to exert highly potent anticancer activity against human MDR ovarian cancer cells (OVCAR-8/MDR) by depleting GSH to induce oxidative stress and, in turn, apoptotic cell death in both OVCAR-8/MDR and OVCAR-8 cancer cells. BsEVs restore drug responsiveness by inhibiting ATP production through the oxidation of nicotinamide adenine dinucleotide with hydrogen (NADH) and inducing mitochondrial dysfunction, leading to the dysfunction of efflux pumps responsible for drug resistance. In vivo studies showed that BsEV treatment significantly inhibited the growth of OVCAR-8/MDR and OVCAR-8 tumors. Additionally, OVCAR-8/MDR tumors showed a trend towards a greater sensitivity to BsEVs compared to OVCAR tumors. In summary, this study demonstrates that BsEVs hold tremendous potential for cancer treatment, especially against MDR cancer cells.