In vitro study of a siRNA delivery liposome constructed with an ionizable cationic lipid

Small interfering RNA (siRNA) can silence disease-related genes through sequence-specific RNA interference (RNAi). Cationic lipid-based liposomes effectively deliver nucleic acids into the cytoplasm but often exhibit significant toxicity. This study aims to synthesize a novel ionizable lipid, Nε-laruoyl-lysine amide (LKA), from natural amino acids, constructed LKA-based liposomes, and perform physicochemical characterization and cell-based experiments to systematically evaluate the potential of these ionizable lipid-based liposomes for nucleic acid delivery.

LKA was chemically synthesized and characterized by hydrogen nuclear magnetic resonance (NMR) and mass spectrometry (MS). Paper electrophoresis was used to evaluate the pH-responsive changes in the lipid's net charge. Liposomes without payload (LKA-LP), with signal transducer and activator of transcription 3-siRNA (STAT3-siRNA) (LKA-LP@STAT3-siRNA), or with Nile Red (LKA-LP@Nile Red) were prepared by the ethanol injection method. The particle size and morphology of LKA-LP@STAT3-siRNA were measured by laser particle size analyzer and scanning electron microscope, while agarose gel electrophoresis determined the encapsulation efficiency of siRNA. Uptake of the liposomes by human cervical cancer HeLa cells and mouse embryonic fibroblast 3T3 cells was assessed using LKA-LP@Nile Red. Lysosome escape capabilities in human lung adenocarcinoma A549 cells were evaluated by labeling STAT3-siRNA with Cyanine 5 (Cy5) and using a green lysosomal probe. STAT3 gene silencing was assessed by real-time fluorescence quantitative PCR, and cell viability was determined using cell counting kit-8 (CCK-8).

Hydrogen NMR and MS confirmed the successful synthesis of LKA. Paper electrophoresis demonstrated an increase in LKA's positive charge as pH shifted from 7.4 to 5.5. The LKA-LP@STAT3-siRNA liposomes had a near-spherical morphology with a uniform size of (164.1±3.27) nm, polydispersity index (PDI) of 0.174±0.029, remaining stable for up to 7 days, and a siRNA encapsulation efficiency of (64.6±2.8)%. Cell uptake studies revealed increased uptake of LKA-LP at pH 5.0 compared with pH 7.4, with HeLa cells showing a more pronounced uptake than 3T3 cells. Lysosomal escape experiments showed 42.34% colocalization with lysosomes, indicating successful escape. Gene silencing assays demonstrated a significant decrease (P<0.01) in STAT3 mRNA expression in HeLa cells treated with 50 or 100 nmol/L LKA-LP@STAT3-siRNA. Cytotoxicity assays showed these concentrations induced a markedly greater reduction in HeLa cell viability than in 3T3 cells (P<0.01).

LKA, an ionizable cationic lipid, can form LKA-LP liposomes for siRNA delivery. The system successfully achieved gene silencing at the cellular level, showing specific cytotoxicity to HeLa cells, providing a solid foundation for developing nucleic acid therapeutics using LKA-LP as a nucleic acid delivery vehicle.