Targeted alleviation of local inflammation by a hydroxypropyl-cyclodextrin-encapsulated prodrug of methyl salicylate and menthol though Nrf2/NF-κB pathway

Antibiotics remain the conventional mainstay for acute local inflammation, such as pharyngitis, but concerns over bacterial resistance, superinfections, and hepatorenal toxicity have driven research toward natural alternatives. Methyl salicylate (SAM) and L-menthol (MENT), derived from medicinal plants, exhibit anti-inflammatory, analgesic, and antimicrobial properties. However, their clinical translation is hampered by inadequate synergy, rapid metabolism, and low bioavailability in existing formulations. To overcome these issues, we synthesized an ROS-responsive prodrug, SSM, by conjugating SAM and MENT via a sulfide bond, and further encapsulated it within hydroxypropyl-β-cyclodextrin (HP-β-CD) to form HP-β-CD@SSM. This complex enabled targeted drug release in high-ROS inflammatory microenvironments, enhancing local bioavailability and reducing systemic exposure. The use of HP-β-CD not only enhanced the water solubility and stability of SSM but also masked the unpleasant odor of the drugs, thereby improving patient compliance. In vitro and in vivo studies demonstrated that HP-β-CD@SSM effectively disrupts the vicious cycle of inflammation and oxidative stress through synergistic inhibition of the NF-κB pathway and activation of the Nrf2 pathway, resulting in significantly enhanced anti-inflammatory and analgesic effects in both pharyngitis and paw edema models, with no observable systemic toxicity. This work presents not only a promising therapeutic candidate for pharyngitis but also a robust localized drug delivery strategy for natural products with considerable translational value.