Effect of PEG anchor in PEGylation of folate-modified cationic liposomes with PEG-derivatives on systemic siRNA delivery into the Tumor

In this study, we prepared small interfering RNA (siRNA)/cationic liposome complexes (lipoplexes) modified with folate (FA)-polyethylene glycol (PEG, MW 2000, 3400 or 5000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) to facilitate their uptake into tumor cells via folate receptor (FR), and with PEG1600-cholesterol (PEG1600-Chol) or PEG2000-chondroitin sulfate conjugate (PEG2000-CS), to enhance their systemic stability. Among the FA-PEG-modified siRNA lipoplexes, 0.5 mol% FA-PEG5000-DSPE-modified lipoplexes with 2.5 mol% PEG2000-CS or PEG1600-Chol (LP-0.5F5/2.5P2-CS and LP-0.5F5/2.5P1.6-CL, respectively) exhibited selective growth inhibition of human nasopharyngeal carcinoma KB cells through transduction with polo-like kinase 1 (PLK1) siRNA. Furthermore, the LP-0.5F5/2.5P2-CS and LP-0.5F5/2.5P1.6-CL lipoplexes exhibited decreased agglutination with erythrocytes through PEGylation, and markedly decreased the accumulation of siRNA in murine lungs after systemic injection. Finally, systemic injection of LP-0.5F5/2.5P2-CS and LP-0.5F5/2.5P1.6-CL lipoplexes resulted in accumulation of siRNA in KB tumor xenografts. These findings suggest that PEGylation of FA-PEG5000-DSPE-modified siRNA lipoplexes with PEG2000-CS or PEG1600-Chol might improve their systemic stability without the loss of selective transfection activity in tumor cells.