Engineered Histidine-Enriched Facial Lipopeptides for Enhanced Intracellular Delivery of Functional siRNA to Triple Negative Breast Cancer Cells.

Cytosolic delivery of functional siRNA remains the major challenge to develop siRNA-based therapeutics. Designing clinically safe and effective siRNA transporter to deliver functional siRNA across the plasma and endosomal membrane remains a key hurdle. With the aim of improving endosomal release, we have designed cyclic and linear peptide-based transporters having an Arg-^DHis-Arg template. Computational studies show that the Arg-^DHis-Arg template is also stabilized by the Arg-His side-chain hydrogen bonding interaction at physiological pH, which dissociates at lower pH. The overall atomistic interactions were examined by molecular dynamics simulations, which indicate that the extent of peptide_siRNA assembly formation depends greatly on physicochemical properties of the peptides. Our designed peptides having the Arg-^DHis-Arg template and two lipidic moieties facilitate high yield of intracellular delivery of siRNA. Additionally, unsaturated lipid, linoleic acid moieties were introduced to promote fusogenicity and facilitate endosomal release and cytosolic delivery. Interestingly, such protease-resistant peptides provide serum stability to siRNA and exhibit high efficacy of erk1 and erk2 gene silencing in the triple negative breast cancer (TNBC) cell line. The peptide having two linoleyl moieties demonstrated comparable efficacy with commercial transfection reagent HiPerFect, as evidenced by the erk1 and erk2 gene knockdown experiment. Additionally, our study shows that ERK1/2 silencing siRNA and doxorubicin-loaded gramicidin-mediated combination therapy is more effective than siRNA-mediated gene silencing-based monotherapy for TNBC treatment.