Enhancing retention and permeation of rapamycin for osteoarthritis therapy using a two-stage drug delivery system

Osteoarthritis (OA) remains a challenging degenerative joint disease, largely associated with chondrocyte apoptosis during its development. Preserving chondrocytes stands as a promising strategy for OA treatment. Rapamycin (RP) exhibits chondrocyte protection by fostering autophagy. Nevertheless, the swift clearance of intra-articular injections and the dense cartilage extracellular matrix (ECM) hinder RP from effectively reaching chondrocytes. Herein, we developed a "two-stage" drug delivery system (RP@PEG-PA@P-Lipo). This system comprises primary nanoparticles (P-Lipo), liposomes modified with a collagen II targeting peptide (WYRGRLC), and secondary nanoparticles (RP@PEG-PA), PEG-modified PAMAM encapsulating rapamycin (RP). RP@PEG-PA@P-Lipo demonstrates adherence to the cartilage surface with WYRGRLC, substantially prolonging retention within the joint cavity. Subsequently, released RP@PEG-PA can effectively penetrate the cartilage and deliver RP to chondrocytes through small size and charge-driven forces. <i>In vitro</i> and <i>in vivo</i> experiments corroborate its notable therapeutic effects on OA. This study holds promise in offering a novel approach for clinical drug delivery and OA treatment.