Reversible Disorder-to-Order Transition of Coacervates for Tumor Microenvironment-Responsive Intracellular Drug Delivery

Biological condensates formed via liquid–liquid phase separation (LLPS) have inspired the development of droplet-based vehicles for intracellular drug delivery. However, the inherent metastability impedes precise phase control for responsive drug release under pathological conditions. To address this challenge, we engineered peptide coacervates with thermoreversible disorder-to-order transition by incorporating the low-complexity aromatic-rich kinked segments (LARKS) as a phase modulator. Interestingly, loading small molecules (Nile Red, FITC, Rhodamine B) into the coacervates at body temperature (37 °C) triggers the formation of liquid-crystalline shells, thereby enhancing the thermostability of coacervates without sacrificing their liquid nature. In contrast, elevated acidity and glutathione (GSH) levels, characteristics of the tumor microenvironment (TME), trigger a reverse order-to-disorder transition and dissolution of coacervates for on-demand drug release. Using erastin as a model drug, we demonstrate that erastin-loaded coacervates are efficiently internalized into malignant melanoma cells via caveolin-mediated endocytosis. Upon GSH-triggered dissolution of coacervates, erastin is released into the cytosol, inducing ferroptosis more effectively than free erastin. This work establishes a gel-free, droplet-based delivery system that leverages reversible disorder-to-order transitions for TME-responsive intracellular drug delivery.