Enhanced Reactive Oxygen Species Generation by Mitochondria Targeting of Anticancer Drug To Overcome Tumor Multidrug Resistance

As a major clinical tumor chemotherapeutic burden, multidrug resistance (MDR) is often a result of up-regulation of P-glycoprotein (P-gp), which strongly enhances anticancer drug efflux. The excess mitochondrial reactive oxygen species (ROS) could not only inhibit the function of P-gp through insufficient adenosine triphosphate supply but also cause apoptosis in MDR cells. Here, we designed a mitochondria targeting nanoparticulate system (GNPs-P-Dox-GA) for overcoming MDR through enhanced ROS generation, where increased cellular uptake as well as mitochondria accumulation were both realized by glycyrrhetinic acid (GA). First, doxorubicin was conjugated with GA (GA-Dox) and then grafted onto a N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer backbone via hydrazone bond (P-Dox-GA). The obtained P-Dox-GA was subsequently attached to the surface of gelatin nanoparticles (GNPs). As gelatin is a substrate of tumor extracellular metal matrix protease-2 (MMP2), GNPs-P-Dox-GA nanoparticles could be degraded and release small size P-Dox-GA to facilitate tumor tissue penetration. After P-Dox-GA internalized by tumor cells under GA mediation, Dox-GA detached from HPMA copolymer through hydrolysis of hydrazone bond and then efficiently delivered to mitochondria. Compared to non-GA modified carriers, GNPs-P-Dox-GA exhibited increased cellular uptake nearly 4-fold and mitochondria distribution 8.8-fold, and increased ROS production level nearly 3-fold, significantly decreased efflux rate (55% compared with Dox group) in drug resistant HepG2/ADR cells, and then led to improved in vitro antitumor efficiency in HepG2/ADR cells (IC₅₀ only 19.5% of unmodified ones) as well as exciting in vivo antitumor efficiency on HepG2/ADR heterotopic tumor nude mice (1.75-fold higher tumor growth inhibition rate than free drug).