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--glycero-3-phosphoethanolamine (DSPE) to facilitate their uptake into tumor cells folate receptor (FR), and with PEG-cholesterol (PEG-Chol) or PEG-chondroitin sulfate conjugate (PEG-CS), to enhance their systemic stability. Among the FA-PEG-modified siRNA lipoplexes, 0.5 mol% FA-PEG-DSPE-modified lipoplexes with 2.5 mol% PEG-CS or PEG-Chol (LP-0.5F/2.5P-CS and LP-0.5F/2.5P-CL, respectively) exhibited selective growth inhibition of human nasopharyngeal carcinoma KB cells through transduction with polo-like kinase 1 (PLK1) siRNA. Furthermore, the LP-0.5F/2.5P-CS and LP-0.5F/2.5P-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-0.5F/2.5P-CS and LP-0.5F/2.5P-CL lipoplexes resulted in accumulation of siRNA in KB tumor xenografts. These findings suggest that PEGylation of FA-PEG-DSPE-modified siRNA lipoplexes with PEG-CS or PEG-Chol might improve their systemic stability without the loss of selective transfection activity in tumor cells.