Intracellular Delivery of siRNA by Polycationic Superparamagnetic Nanoparticles

Abstract

The siRNA transfection efficiency of nanoparticles (NPs), composed of a superparamagnetic iron oxide core modified with polycationic polymers (poly(hexamethylene biguanide) or branched polyethyleneimine), were studied in CHO-K1 and HeLa cell lines. Both NPs demonstrated to be good siRNA transfection vehicles, but unmodified branched polyethyleneimine (25 kD) was superior on both cell lines. However, application of an external magnetic field during transfection (magnetofection) increased the efficiency of the superparamagnetic NPs. Furthermore, our results reveal that these NPs are less toxic towards CHO-K1 cell lines than the unmodified polycationic-branched polyethyleneimine (PEI). In general, the external magnetic field did not alter the cell's viability nor it disrupted the cell membranes, except for the poly(hexamethylene biguanide)-modified NP, where it was observed that in CHO-K1 cells application of the external magnetic field promoted membrane damage. This paper presents new polycationic superparamagnetic NPs as promising transfection vehicles for siRNA and demonstrates the advantages of magnetofection.

Figure 1

Effect of nanoparticle/siRNA (N/P) ratio on the transfection efficiency of all materials in CHO-K1 (a) and HeLa (b) cell lines. Values represent mean ± standard error of the mean (SEM) from three independent transfections. Triplicates were normalized using Renilla luciferase as an internal transfection control.

Figure 2

Effect of nanoparticle/siRNA (N/P) ratio on metabolic activity in CHO-K1 ((a) and (b)) and HeLa ((c) and (d)) cell lines, as a function of polymer/siRNA (N/P) ratios. The cell viability was determined by MTS assay and was shown as the mean. Error bars are the standard deviation of eight determinations. Relative cell viability was calculated using untreated cells as a control.

Scheme 1

Structure of the core-shell superparamagnetic nanoparticles utilized in the present study.

Figure 3

Effect of nanoparticle/siRNA (N/P) ratio on membrane permeability of CHO-K1 ((a) and (b)) and HeLa ((c) and (d)) cell lines.

Figure 4

Panel (a) CHO-K1; (b) HeLa. N/P ratios: 39 for PEI, 34 for PEI-M/SiO₂, 43 for PHMBG, and 42 for PHMBG-M/SiO₂.

Figure 5

Effect of polymer: siRNA N/P ratios on the (a) relative binding affinity, and (b) the transfection efficiency. A decrease in fluorescence intensity (on a) correlates to increased binding between polymer/siRNA complexes. Note: the relative binding affinity was measured at the 3 lowest N/P ratios for all transfectin vehicles.