Curcumin coacervates for supramolecular-interaction-responsive cytosolic siRNA delivery to enhance pyroptosis

Rationale: Synthetic molecules, meticulously designed according to the "sticker-and-spacer model", tend to form coacervates via liquid-liquid phase separation (LLPS), thereby acquiring properties beyond their discrete and soluble states. However, natural compounds, such as those from traditional Chinese medicines (TCMs), are not known to undergo phase separation. In this study, we demonstrate that curcumin, the active ingredient in the spice turmeric, forms phase-separated fluorescent coacervates when diluted from a concentrated organic-solvent solution into an aqueous solution. Methods: Curcumin coacervates were formed by diluting a concentrated stock solution in organic solvents into the aqueous solution. We utilized the coacervate droplets to encapsulate and transport various biomacromolecules, such as proteins and nucleic acids, across the plasma membrane into the cell. Supramolecular interaction between β-cyclodextrin (β-CD) and curcumin disassembles curcumin coacervates, leading to cargo release in the cytosol. Results: Intravenously injected curcumin coacervates spontaneously enrich in the tumor tissue in tumor-bearing BALB/c mice. Subsequent intratumoral injection of β-CD significantly enhances anticancer effects in mice, demonstrating the efficacy of coacervate-mediated siRNA drug delivery and supramolecular-interaction-responsive intracellular release in vivo. Conclusions: Taken together, we report here the coacervate-forming properties of the natural TCM compound curcumin, presenting a unique strategy for controlling coacervate states through supramolecular interactions with β-cyclodextrin in vitro and in vivo, along with the unexplored potential of curcumin coacervate-mediated siRNA delivery to enhance pyroptosis.