Low-dose inhalable amino acid-modified multilamellar nanoparticles activate STING for safe and effective regression of lung metastases.

Lung metastases present a significant therapeutic challenge, as disseminated tumor cells evade surgical resection and often resist systemic treatments. Pulmonary delivery of immunostimulatory agents, such as the STING agonist cyclic GMP-AMP (cGAMP), offers a promising strategy to activate mucosal immunity and suppress metastatic progression. However, current pulmonary delivery systems are hindered by aerosolization-induced instability, mucus entrapment, and inefficient cytosolic drug release. To overcome these barriers, we developed an inhalable formulation consisting of a hyaluronic acid (HA)-lipid hybrid multilamellar nanoparticle encapsulating cGAMP (HLHC). The HA-lipid stacking architecture confers an 8.5-fold increase in mechanical rigidity compared to conventional liposomes, preserving structural integrity during nebulization and enhancing pulmonary retention. Moreover, the multilamellar structure and HA surface coating enable a 35-fold improvement in mucus penetration relative to standard liposomal controls. Importantly, systematic screening of amino acid-modified ionizable lipids identified arginine-modified variants (Arg-HLHC) as the most effective for cytosolic cGAMP delivery. Low-dose pulmonary administration of Arg-HLHC (1.5 μg cGAMP per dose) induced complete regression (100 %) of established lung metastases in the MC38-luc model, significantly outperforming state-of-the-art lipid nanoparticles (analogous to Onpattro®) delivering the same cGAMP dose. Notably, Arg-HLHC triggered robust local STING activation without eliciting systemic inflammation. This modular nanoplatform-combining hierarchical structural reinforcement with rational lipid design-addresses key translational challenges in pulmonary STING agonist delivery, establishing a safe, curative, and low-dose therapeutic strategy for lung metastases with broad potential for next-generation respiratory immunotherapies.