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PH-responsive polymeric micelle carriers for siRNA drugs.

ABSTRACT: The ability of small interfering RNA (siRNA) to efficiently silence the expression of specific genes provides the basis for exciting new therapies based on RNA interference (RNAi). The efficient intracellular delivery of siRNA from cell uptake through the endosomal trafficking pathways into the cytoplasm remains a significant challenge. Previously we described the synthesis of a new family of diblock copolymer siRNA carriers using controlled reversible addition-fragmentation chain transfer (RAFT) polymerization. The carriers were composed of a positively charged block of dimethylaminoethyl methacrylate (DMAEMA) to mediate siRNA binding and a second pH-responsive endosome releasing block composed of DMAEMA and propylacrylic acid (PAA) in roughly equimolar ratios and butyl methacylate (BMA). Here we describe the development of a new generation of siRNA delivery polymers based on this design that exhibit enhanced transfection efficiency and low cytotoxicity. This design incorporates a longer endosomolytic block with increased hydrophobic content to induce micelle formation. These polymers spontaneously form spherical micelles in the size range of 40 nm with CMC (critical micelle concentration) values of approximately 2 ?g/mL based on dynamic light scattering (DLS), (1)H NMR, electron microscopy, and selective partitioning of the small molecule pyrene into the hydrophobic micelle core. The siRNA binding to the cationic shell block did not perturb micelle stability or significantly increase particle size. The self-assembly of the diblock copolymers into particles was shown to provide a significant enhancement in mRNA knockdown at siRNA concentrations as low as 12.5 nM. Under these conditions, the micelle-based systems showed an 89% reduction in GAPDH mRNA levels as compared to only 23% (10 nM siRNA) for the nonmicelle system. The reduction in mRNA levels becomes nearly quantitative as the siRNA concentration is increased to 25 nM and higher. Flow cytometry analysis of fluorescent-labeled siRNA showed uptake in 90% of cells and a 3-fold increase in siRNA per cell compared to a standard lipid transfection agent. These results demonstrate the potential utility of this carrier design for siRNA drug delivery.

SUBMITTER: Convertine AJ

PROVIDER: S-EPMC3026907 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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pH-responsive polymeric micelle carriers for siRNA drugs.

Convertine A J AJ Diab C C Prieve M M Paschal A A Hoffman A S AS Johnson P H PH Stayton P S PS

Biomacromolecules 20101001 11

The ability of small interfering RNA (siRNA) to efficiently silence the expression of specific genes provides the basis for exciting new therapies based on RNA interference (RNAi). The efficient intracellular delivery of siRNA from cell uptake through the endosomal trafficking pathways into the cytoplasm remains a significant challenge. Previously we described the synthesis of a new family of diblock copolymer siRNA carriers using controlled reversible addition-fragmentation chain transfer (RAFT ...[more]

PMID: 20886830

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Project description:Small interfering RNA (siRNA)-based therapies have great potential for the treatment of debilitating diseases such as cancer, but an effective delivery strategy for siRNA is elusive. Here, pH-responsive complexes were developed for the delivery of siRNA in order to sensitize drug-resistant ovarian cancer cells (NCI/ADR-RES) to doxorubicin. The electrostatic complexes consisted of a cationic micelle used as a nucleating core, siRNA, and a pH-responsive endosomolytic polymer. Cationic micelles were formed from diblock copolymers of dimethylaminoethyl methacrylate (pDMAEMA) and butyl methacrylate (pDbB). The hydrophobic butyl core mediated micelle formation while the positively charged pDMAEMA corona enabled siRNA condensation. To enhance cytosolic delivery through endosomal release, a pH-responsive copolymer of poly(styrene-alt-maleic anhydride) (pSMA) was electrostatically complexed with the positively charged siRNA/micelle to form a ternary complex. Complexes exhibited size (30-105 nm) and charge (slightly positive) properties important for endocytosis and were found to be noncytotoxic and mediate uptake in >70% of ovarian cancer cells after 1 h of incubation. The pH-responsive ternary complexes were used to deliver siRNA against polo-like kinase 1 (plk1), a gene upregulated in many cancers and responsible for cell cycle progression, to ovarian cancer cell lines. Treatment resulted in approximately 50% reduction of plk1 gene expression in the drug-resistant NCI/ADR-RES ovarian cancer cell model and in the drug-sensitive parental cell line, OVCAR8. This knockdown functionally sensitized NCI/ADR-RES cells to doxorubicin at levels similar to OVCAR8. Sensitization occurred through a p53 signaling pathway, as indicated by caspase 3/7 upregulation following plk1 knockdown and doxorubicin treatment, and this effect could be abrogated using a p53 inhibitor. To demonstrate the potential for dual delivery from this polymer system, micelle cores were subsequently loaded with doxorubicin and utilized in ternary complexes to achieve cell sensitization through simultaneous siRNA and drug delivery from a single carrier. These results show knockdown of plk1 results in sensitization of multidrug resistant cells to doxorubicin, and this combination of gene silencing and small molecule drug delivery may prove useful to achieve potent therapeutic effects.

Project description:Synthetic subunit vaccines need to induce CD8(+) cytotoxic T cell (CTL) responses for effective vaccination against intracellular pathogens. Most subunit vaccines primarily generate humoral immune responses, with a weaker than desired CD8(+) cytotoxic T cell response. Here, a neutral, pH-responsive polymer micelle carrier that alters intracellular antigen trafficking was shown to enhance CD8(+) T cell responses with a correlated increase in cytosolic delivery and a decrease in exocytosis. Polymer diblock carriers consisted of a N-(2-hydroxypropyl) methacrylamide corona block with pendent pyridyl disulfide groups for reversible conjugation of thiolated ovalbumin, and a tercopolymer ampholytic core-forming block composed of propylacrylic acid (PAA), dimethylaminoethyl methacrylate (DMAEMA), and butyl methacrylate (BMA). The diblock copolymers self-assembled into 25-30nm diameter micellar nanoparticles. Conjugation of ovalbumin to the micelles significantly enhanced antigen cross-presentation in vitro relative to free ovalbumin, an unconjugated physical mixture of ovalbumin and polymer, and a non-pH-responsive micelle-ovalbumin control. Mechanistic studies in a murine dendritic cell line (DC 2.4) demonstrated micelle-mediated enhancements in intracellular antigen retention and cytosolic antigen accumulation. Approximately 90% of initially internalized ovalbumin-conjugated micelles were retained in cells after 1.5h, compared to only ~40% for controls. Furthermore, cells dosed with conjugates displayed 67-fold higher cytosolic antigen levels relative to soluble ovalbumin 4h post uptake. Subcutaneous immunization of mice with ovalbumin-polymer conjugates significantly enhanced antigen-specific CD8(+) T cell responses (0.4% IFN-?(+) of CD8(+)) compared to immunization with soluble protein, ovalbumin and polymer mixture, and the control micelle without endosome-releasing activity. Additionally, pH-responsive carrier facilitated antigen delivery to antigen presenting cells in the draining lymph nodes. As early as 90min post injection, ova-micelle conjugates were associated with 28% and 55% of dendritic cells and macrophages, respectively. After 24h, conjugates preferentially associated with dendritic cells, affording 30-, 3-, and 3-fold enhancements in uptake relative to free protein, physical mixture, and the non-pH-responsive conjugate controls, respectively. These results demonstrate the potential of pH-responsive polymeric micelles for use in vaccine applications that rely on CD8(+) T cell activation.

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PH-responsive polymeric micelle carriers for siRNA drugs.

Publications

pH-responsive polymeric micelle carriers for siRNA drugs.

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