Self-Assembly Regulation, Drug Release Behavior, Anti-Multidrug Resistance of Redox-Responsive Gemcitabine-Quinine Nanoassemblies in Glioblastoma Therapy.

To overcome multidrug resistance (MDR) in chemotherapy, a redox-responsive self-assembling nanoprodrug was developed for codelivering gemcitabine (Gem) and the P-glycoprotein (P-gp) inhibitor quinine (Qu). Initially, Gem and Qu were conjugated via a disulfide bond to form the Gem-Qu (GQ) prodrug, but its poor self-assembly capability (forming unstable nanoaggregates) limited its further use. To address this problem, GQ was modified using 3,3'-dithiodipropionic acid or adipic acid to improve the aqueous solubility, yielding GQ-S and GQ-C, respectively. It is noteworthy that both GQ-S and GQ-C could self-assemble into spherical nanoparticles (GQ-S NPs and GQ-C NPs) with uniform size and excellent stability. GQ-S NPs exhibited a hydrodynamic diameter of approximately 147.5 nm, while GQ-C NPs were around 180.5 nm, both with low polydispersity indices. Under tumor-mimicking redox conditions (elevated glutathione or H2O2), GQ-S NPs released approximately 30% of Gem and 48% of Qu simultaneously, whereas Gem release from GQ-C NPs remained below 10%, confirming the enhanced dual redox-responsiveness of GQ-S NPs. Cellular uptake in U251 and U87 glioma cells was efficient for both nanoparticles. GQ-S NPs demonstrated greater cytotoxicity, with an IC50 of 1.560 ± 0.123 μM in U251 cells─7-fold and 2.7-fold lower than that of free Gem and GQ-C NPs, respectively. Mechanistic studies revealed that GQ-S NPs induced apoptosis and markedly suppressed P-gp expression, and promoted intracellular Gem accumulation. In summary, GQ-S NPs integrate the advantages of carrier-free design, low toxicity, high stability, and redox-responsive release, offering a promising strategy for targeted combination therapy in drug-resistant glioblastoma.