A proline-rich peptide improves cell transfection of solid lipid nanoparticle-based non-viral vectors

The aim of this work was to improve the transfection efficacy of solid lipid nanoparticle (SLN)-based non-viral vectors into ARPE-19 cells through the addition of Sweet Arrow Peptide (SAP). First, we prepared SAP–DNA complexes at ratios of at least 50:1, and then incorporated them into the SLNs. All formulations were able to protect DNA, and the peptide favoured the most bioactive form (supercoiled) of open circular DNA turns. In vitro transfection studies of the vectors containing the pCMS-EGFP plasmid in HEK293 and ARPE-19 cell lines revealed that incorporation of SAP led to greater transfection in both cell lines, although via different mechanisms. The presence of SAP in the formulations did not affect the viability of HEK293 or ARPE-19 cells. In HEK293 cells, SAP enabled greater uptake of the vectors, and an SAP to DNA ratio of 50:1 was sufficient for enhancing transfection. In contrast, in ARPE-19 cells, SAP induced a change in the dominant entrance mechanism, from clathrin endocytosis to caveolae/raft-dependent endocytosis, thereby decreasing use of the lysosomal pathway and consequently, reducing vector degradation. The extent to which SAP uses one mechanism or the other largely depends on its concentration in the formulation.