Gelatin and lipidoid integrate to create gelasomes to enhance siRNA delivery with low toxicity.

RNAi therapeutics possess the potential to cure many uncurable human diseases. For instance, RNAi therapeutics using liposomes showed remarkable survival benefits in patients with liver diseases. However, the extension of liposomes to deliver RNA to cure other ailments has largely been unsuccessful. Therefore, researchers are focusing on designing and testing different combinations of materials for versatile RNA delivery applications. Yet, an efficient and safe RNA delivery platform has not been identified. In this work, we have developed a new class of RNA-delivery vehicle called "Gelasomes," using an incongruous combination of gelatin and lipidoid to exploit each material's unique properties while overcoming their inherent limitations. The low in vivo toxicity of Gelasomes is attributed to the exterior gelatin layers that shield the exposure of cationic lipidoid-siRNA clusters and yet present a biocompatible surface. Indeed, toxicity studies in mice indicate that repeated administration of Gelasomes (up to 48 mg/kg BW) is well-tolerated with no notable changes in body weight, hematology, or serum chemistry. Interestingly, the gelatin outer layer efficiently protects siRNA from serum degradation (48 h), preserving its functionality beyond two months of storage. Notably, Gelasomes possess dual siRNA conjugation modes, i.e., electrostatic binding with lipidoid core and covalent attachment to gelatin surface. The bivalency coupled with lipidoids' high transfection efficiency rendered Gelasomes with remarkably high gene silencing efficiency (>90 %) at very low treatment doses in vitro (40 μg/mL). In vivo studies further confirmed the high gene silencing ability of Gelasomes in non-small cell lung tumor mouse models. This new platform is tunable on all fronts: size, degree of surface coating, and biomolecule functionalization. Truncating the lipidoid C14-tail to a C8-tail yielded Gelasomes of reduced size. As lipidoids with different carbon lengths are synthesizable, we can develop a library of Gelasomes with different sizes. The surface coating with less gelatin resulted in high transfection efficiency at low doses of Gelasomes. The structure of Gelasomes offers chemical handles to couple target-specific molecules like antibodies to tune their properties for efficient biological application.