Reactive Oxygen Species-Responsive Micellar Nanodrug for Alleviating Osteoarthritis Progression via Inhibiting Chondrocyte Ferroptosis

Retinoic acid-related orphan nuclear receptor (ROR) α, a transcription factor that regulates the expression of several key ferroptosis factors including P53, glutathione peroxidase 4 (GPX4), ferritin heavy chain 1 (FTH1), and osteoarthritis factors such as type II collagen (Col II), matrix metalloproteinase 3 (MMP3) in the joint, has been found to overexpress as a key cause for chondrocyte ferroptosis, degeneration of articular cartilage, and osteoarthritis progression. Notably, this RORα-driven ferroptotic program is accompanied by excessive reactive oxygen species (ROS) accumulation, creating a ROS-rich microenvironment in the affected joint, and the link between RORα and chondrocyte ferroptosis has not been reported previously. Thus, inhibiting chondrocyte ferroptosis via RORα suppression provides an avenue for osteoarthritis treatment. Here, aiming at the targeted nanomedicine treatment of osteoarthritis, we develop a ROS-responsive micellar nanodrug (S-PEPM) by encapsulating the hydrophobic RORα antagonist SR3335 into self-assembled mPEG-PMEMA micelles. The micelles are spherical in morphology, and the SR3335-loaded formulation exhibits an average particle size of 92.75 ± 4.86 nm with a narrow size distribution (polydispersity index, 0.12) and a zeta potential of 7 ± 0.62 mV; to exploit the pathologically elevated ROS resulting from RORα overexpression, the nanodrug is engineered with a ROS-responsive moiety that confers a chemotaxis-like homing ability toward ROS-enriched osteoarthritic cartilage, thereby achieving joint-specific accumulation and drug release while simultaneously improving the half-life of the drug. Using the interleukin-1 beta (IL-1β)-stimulated mouse chondrocyte model, we demonstrate that this formulation can lower the ROS level and suppress the RORα expression, resulting in down-regulation of pro-ferroptosis factors P53, FTH1, and MMP3 and meanwhile upregulation of anti-ferroptosis factor GPX4 to prevent chondrocyte ferroptosis. More importantly, the nanodrug shows obvious efficacy in alleviating the characteristic pathological changes of osteoarthritis in the cartilage and adjacent bone structure of the mouse joints on a destabilized medial meniscus (DMM) surgery mouse model, further evidencing its great potential as a targeted nanomedicine for osteoarthritis therapy.