Reduction-Responsive Polypeptide Nanogel for Intracellular Drug Delivery in Relieving Collagen-Induced Arthritis

Rheumatoid arthritis (RA) induces the destruction of cartilage and bone. Methotrexate (MTX) functions as an effective first-line drug to relieve RA in the clinic. However, patients treated with MTX often suffer from severe side effects mainly due to its off-target effects. Therefore, selective delivery of MTX to the affected joints may achieve upregulated efficacy and safety. The affected joints of RA feature hypoxic microenvironment and increased level of glutathione (GSH), resulting from synovial proliferation, lymphocyte infiltration, and neovascularization. In this study, a disulfide-cross-linked nanogel (NG) of methoxy poly(ethylene glycol)–poly(L-phenylalanine-co-L-cystine) (mPEG–P(LP-co-LC)) was synthesized as an intracellular delivery system of MTX. The loading nanogel NG/MTX exhibited apparent reduction-responsiveness and GSH-triggered release behavior of MTX. It also showed efficient internalization and high cytotoxicity toward activated macrophages. Moreover, NG/MTX possessed selective biodistribution in the inflammatory joints of collagen-induced arthritis mouse model. The clinical and histological scores of the mice after NG/MTX treatment were lower than those of the other groups, and the progress of collagen-induced arthritis was overall relieved. To conclude, the controlled delivery of MTX by smart polymer nanoparticles to the RA-affected joints may be a promising approach in the clinical therapy of RA.