Small interfering RNA delivery mediated by mPEG-PCL-g-PEI polymer nanoparticles

The aim of this paper is to report the synthesis of the mPEG-PCL-g-PEI copolymers as small interfering RNA (siRNA) delivery vector, and exploration of the siRNA delivery potential of mPEG-PCL-g-PEI in vitro.  The diblock copolymers mPEG-PCL-OH was prepared through the ring-opening polymerization.  Then, the hydroxyl terminal (-OH) of mPEG-PCL-OH was chemically converted into the carboxy (-COOH) and N-hydroxysuccinimide (NHS) in turn to prepare mPEG-PCL-NHS.  The branched PEI was reacted with mPEG-PCL-NHS to synthesize the ternary copolymers mPEG-PCL-g-PEI.  The structure of mPEG-PCL-g-PEI copolymers was characterized with Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC).  The mPEG-PCL-g-PEI/siRNA nanoparticles were prepared by complex coacervation, and the nanoparticles size and zeta potential were determined, separately.  The cytotoxicities of mPEG-PCL-g-PEI/siRNA nanoparticles and PEI/siRNA nanoparticles were compared through cells MTT assays in vitro.  The inhibition efficiencies of firefly luciferase gene expression by mPEG-PCL-g-PEI/ siRNA nanoparticle at various N/P ratios were investigated through cell transfection in vitro.  The experimental results suggested that the ternary (mPEG_5k-PCL_1.2k)_1.4-g-PEI_10k copolymers were successfully synthesized.  (mPEG_5k-PCL_1.2k)_1.4-g-PEI_10k could condense siRNA into nanoparticles (50−200 nm) with positive zeta potential.  MTT assay results showed that the cytotoxicity of (mPEG_5k-PCL_1.2k)_1.4-g-PEI_10k/siRNA nanoparticles was significantly lower than that of PEI_10k/siRNA nanoparticles (P < 0.05).  The expression of firefly luciferase gene could be significantly down-regulated at a range of N/P ratio from 50 to 150 (P < 0.01), and maximally inhibited at the N/P ratio of 125.  The mPEG-PCL-g-PEI polymers could delivery siRNA into cells to inhibit the expression of target gene with very low cytotoxicity, which suggested that mPEG-PCL-g-PEI could serve as a new type of siRNA delivery vector.