Serum Nucleases Research Articles

Polyvalent Immunostimulatory Nanoagents with Self‐Assembled CpG Oligonucleotide‐Conjugated Gold Nanoparticles

During the past decade, nucleic acid based therapeutics has developed from experimental techniques to preclinically practical strategies. Compared to conventional plasmid-containing transgenic methods, synthetic oligodeoxynucleotides (ODNs), including antisense DNA, aptamers, and small interfering RNAs (siRNAs), have emerged as highly attractive candidates for the treatment of various human diseases. [1] These ODNs are generally water soluble and stable with extremely low in vivo toxicity, and often interact with their targets with high specificity and sensitivity. Despite these advances, drug applications of ODNs are largely limited by delivery approaches. Naked ODNs cannot penetrate through the cell membrane and are prone to be cleared by nucleases in serum or cytoplasm. [1] The emergence of nanobiotechnology has provided unprecedented opportunities for biocompatible, low-toxicity, and highly efficient approaches for exogenous ODN administration in target cells. [2] Several promising nanomaterials, including gold nanoparticles (AuNPs), mesoporous silica nanoparticles, quantum dots, and carbon nanomaterials, have shown great promise as intracellular delivery nanoagents for imaging and gene regulation purposes. [3] In this work, we develop an AuNP-based polyvalent immunostimulatory nanoagent by using self-assembled cytosine–phosphate–guanosine (CpG) oligonucleotide-conjugated AuNPs (see Scheme 1). Unmethylated CpG motifs are widely present in the genomic DNA of invading bacteria and viruses, while most of the CpG sequences are methylated in the vertebrate

Nuclease-resistant immunostimulatory phosphodiester CpG oligodeoxynucleotides as human Toll-like receptor 9 agonists

BackgroundUnmethylated cytosine-guanine (CpG) motif-containing oligodeoxynucleotides (ODNs) have been well characterized as agonists of Toll-like receptor 9 (TLR9). ODNs with a phosphorothioate (PTO) backbone have been studied as TLR9 agonists since natural ODNs with a phosphodiester (PD) backbone are easily degraded by a serum nuclease, which makes them problematic for therapeutic applications. However, ODNs with a PTO backbone have been shown to have undesirable side effects. Thus, our goal was to develop nuclease-resistant, PD ODNs that are effective as human TLR9 (hTLR9) agonists.ResultsThe sequence of ODN2006, a CpG ODN that acts as an hTLR9 agonist, was used as the basic CpG ODN material. The 3'-end modification of ODN2006 with a PD backbone (PD-ODN2006) improved its potential as an hTLR9 agonist because of increased resistance to nucleolytic degradation. Moreover, 3'-end modification with oligonucleotides showed higher induction than modification with biotin, FITC, and amino groups. Further, enhancement of hTLR9 activity was found to be dependent on the number of CpG core motifs (GTCGTT) in the PD ODN containing the 3'-end oligonucleotides. In particular, ODN sequences consisting of two to three linked ODN2006 sequences with a PD backbone (e.g., PD-ODN2006-2006 and PD-ODN2006-2006-2006) acted as effective agonists of hTLR9 even at lower concentrations.ConclusionsThis study showed that PD-ODN2006-2006 and PD-ODN-2006-2006-2006 can be used as potentially safe agonists for hTLR9 activation instead of CpG ODNs with a PTO backbone. We propose these CpG ODNs consisting of only a PD backbone as a novel class of CpG ODN.

Polycation-Based Gene Therapy: Current Knowledge and New Perspectives

At present, gene transfection insufficient efficiency is a major drawback of non-viral gene therapy. The 2 main types of delivery systems deployed in gene therapy are based on viral or non-viral gene carriers. Several non-viral modalities can transfer foreign genetic material into the human body. To do so, polycation-based gene delivery methods must achieve sufficient efficiency in the transportation of therapeutic genes across various extracellular and intracellular barriers. These barriers include interactions with blood components, vascular endothelial cells and uptake by the reticuloendothelial system. Furthermore, the degradation of therapeutic DNA by serum nucleases is a potential obstacle for functional delivery to target cells. Cationic polymers constitute one of the most promising approaches to the use of viral vectors for gene therapy. A better understanding of the mechanisms by which DNA can escape from endosomes and traffic to enter the nucleus has triggered new strategies of synthesis and has revitalized research into new polycation-based systems. The objective of this review is to address the state of the art in gene therapy with synthetic and natural polycations and the latest advances to improve gene transfer efficiency in cells.

Duplex End Breathing Determines Serum Stability and Intracellular Potency of siRNA–Au NPs

Structural requirements of siRNA-functionalized gold nanoparticles (siRNA-Au NPs) for Dicer recognition and serum stability were studied. We show that the 3' overhang on the nucleic acids of these particles is preferentially recognized by Dicer but also makes the siRNA duplexes more susceptible to nonspecific serum degradation. Dicer and serum nucleases show lower preference for blunt duplexes as opposed to those with 3' overhangs. Importantly, gold nanoparticles functionalized with blunt duplexes with relatively less thermal breathing are up to 15 times more stable against serum degradation without compromising Dicer recognition. This increased stability leads to a 300% increase in cellular uptake of siRNA-Au NPs and improved gene knockdown.

Differentially charged hollow core/shell lipid-polymer-lipid hybrid nanoparticles for small interfering RNA delivery.

Since the discovery of RNA interference (RNAi), by which the activity of specific genes can be efficiently suppressed, synthetic small interfering RNA (siRNA)-mediated RNAi has been of substantial interest for various disease treatments.[1] However, the safe and effective delivery of siRNA to target cells remains a major hurdle for its widespread clinical applications.[2] Due to its polyanionic and macromolecular characteristics, naked siRNA cannot readily cross the cell membrane, and thus requires specific delivery vehicles to facilitate its intracellular uptake and cytosolic delivery for bioactivity. These delivery vehicles are also expected to improve the pharmacological properties of siRNA by reducing its susceptibility to serum nucleases, renal filtration, and uptake by the mononuclear phagocyte system.

Abstract 5408: PEG surface modification of Poly(D/L Asp-DET)/DNA polyplexes greatly increases tumor accumulation and improves biodistribution

Abstract Cationic polymers have received much attention as promising non-viral vectors for gene transfer. However, generating polymers that are stable and can systemically deliver large amounts of nucleic acids to specific disease sites continues to be a significant hurdle to non-viral vector success. Therefore, the purpose of this study was to develop a new biocompatible and biodegradable cationic polymer system for non-viral gene delivery of plasmid DNA. Poly-d/l Aspartate-Diethylenetriamine [Poly(d/l Asp-DET)] polymers were synthesized and used to complex plasmid DNA. Polymer/DNA polyplexes were further modified by covalent coupling with various polyethylene glycol (PEG) polymers. Polyplexes were characterized and evaluated for particle size, zeta potential and morphology by TEM. Plasmid DNA stability was assessed by challenging polyplexes with serum nucleases, and the efficacy of DNA delivery and gene expression was examined by performing transfection experiments on cancer cells. In vivo DNA tumor delivery and biodistribution was also investigated using tumor bearing nude mice. Poly(d/l Asp-DET) polymers were able to bind to plasmid DNA and formed polyplex particles the were amenable to surface coating with PEG. PEG-Polyplexes were approximately ∼70nm in diameter with neutral zeta potentials. TEM confirmed that the polyplexes were uniform in size. PEG-Polyplexes were also extremely stable and maintained the structural integrity of DNA following incubation in nucleases, and were also capable of transfecting HCT-116 and PC-3 culture cells with no cell toxicity. Tail vein administration of PEG-Polyplexes to tumor bearing nude mice did not reveal any observable toxicities. Moreover, improvements in PEG polymer chemistry increased nucleic acid accumulation in tumors while reducing DNA accumulation in other tissues including liver, kidney and spleen. Poly(d/l Asp-DET) cationic polymers show enormous potential as non-viral drug delivery agents. Further, the surface modification of polyplexes with PEG allowed for sustained systemic delivery of nucleic acids to tumors. The characterization of PEG-Poly(Asp-DET)/DNA polyplexes provides useful insights that can be used to the design vectors for targeted nucleic acid delivery. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5408. doi:10.1158/1538-7445.AM2011-5408

Conjugation of siRNA with Comb‐Type PEG Enhances Serum Stability and Gene Silencing Efficiency

A thiol-modified siRNA targeting the enhanced green fluorescence protein (eGFP) gene was conjugated with RAFT-synthesized, pyridyl disulfide-functional poly(PEG methyl ether acrylate)s (p(PEGA)s). siRNA-p(PEGA) conjugates demonstrated significantly enhanced in vitro serum stability and nuclease resistance compared to the unmodified and thiol-modified siRNA. The complexes of siRNA-p(PEGA) conjugates with a fusogenic peptide, KALA ((+)/(-) = 2) inhibited the protein expression approximately 28-fold more than the KALA complex of the unmodified siRNA. The protein inhibition caused by siRNA-p(PEGA)-KALA complexes (56 ± 5%-58 ± 3% of the fluorescence expressed in non-treated cells) was comparable to the effect of the unmodified siRNA-lipofectamine complex (77 ± 7%).

The effect of pegylation on the transfection activity of two homologous cationic cholesteryl cytofectins

Polyethylene glycol is being used increasingly to improve circulation times and enhance bioavailability of therapeutic molecules and nano sized macromolecular assemblies. Here, two homologous cationic cholesteryl cytofectins 3β[N-(N’,N’-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol) and 3β[N- (N’,N’-dimethylaminopropane)-carbamoyl] cholesterol (Chol-T) with 2 and 3 carbon spacer elements, respectively, have been formulated into liposomes with near equimolar amounts of dioleoylphosphatidyl ethanolamine (DOPE) and 2 and 5% polyethylene glycol 2000 (PEG 2000 ). Pegylated liposomes (80 - 150 nm diameter) formed electrostatic complexes with plasmid DNA in the 1.5:1 – 2.5:1 range of liposome (positive): DNA (negative) charge ratio, which afforded protection to the DNA cargo against serum nuclease digestion. Plasmid pGL3-containing pegylated lipoplexes were only weakly cytotoxic in the human embryonic kidney cell line HEK 293. Gene transfer experiments in this cell line confirmed that the homologue with the 3 carbon spacer Chol-T, is associated with higher transgene activity, a trend which has been previously observed in unpegylated lipoplexes. Furthermore, only a 15% drop in transfection activity was recorded in increase of pegylation level from 2 to 5 mole percent. Key words : Cationic cytofectin, gene transfer, polyethylene glycol, HEK 293.

Poly(oligo-D-arginine) With Internal Disulfide Linkages as a Cytoplasm-sensitive Carrier for siRNA Delivery

Small interfering RNA (siRNA) has emerged as a therapeutic strategy for various diseases due to its target-specific gene silencing; however, its relatively high molecular weight, negative charge, and low stability hamper in vitro and in vivo applications. Approaches to overcome those drawbacks have relied on nonviral siRNA carriers based on cationic polymers or peptides. Nevertheless, cationic polymer-based siRNA carriers have yet to resolve intrinsic problems such as cytotoxicity and immunogenicity. An environment-sensitive carrier was recently proposed to enhance siRNA bioactivity and to reduce the carrier safety issues. Only a few studies, however, have shown cytoplasm-sensitive dissociation of the polyplex. In the present study, we clearly demonstrated decondensation of siRNA/poly(oligo-D-arginine) polyplex in the cytoplasm in response to intracellular glutathione (GSH) and the enhanced bioactivity of siRNA against VEGF (siVEGF) used as a model both in vitro and in an animal model. Reducible poly(oligo-D-arginine) (rPOA) rapidly dissociated in the cytoplasm, resulting in fast siRNA release to its target location while maintaining siRNA bioactivity both in vitro and in vivo.

2′-Substituted 2-amino-3-methylpyridine ribonucleosides in triplex-forming oligonucleotides: triplex stability is determined by chemical environment

A new synthetic route to the phosphoramidite monomer of 2-amino-3-methyl-5-(2′-O-methyl-β-D-ribofuranosyl)pyridine (Me-MAP) and its 2′-O-methoxyethyl analogue (MOE-MAP) has been established using D-ribose and 2-amino-3-methyl-5-bromopyridine as precursors. Ultraviolet melting and DNase I footprinting studies indicate that the triplex stabilizing properties of 2′-modified MAPs are determined by the conformation of the entire oligonucleotide backbone. Me-MAP confers a higher triplex stability than 2′-deoxycytidine whereas triplex stabilization by MOE-MAP is similar to that of dC. Incorporation of Me-MAP or MOE-MAP into oligonucleotides renders them dramatically more resistant to degradation by serum nucleases than incorporation of 2-amino-3-methyl-5-(2′-deoxy-β-D-ribofuranosyl)pyridine (dMAP) or dC.

Synthesis and properties of triplex-forming oligonucleotides containing 2′- O-(2-methoxyethyl)-5-(3-aminoprop-1-ynyl)-uridine

2′- O-(2-Methoxyethyl)-5-(3-aminoprop-1-ynyl)-uridine phosphoramidite (MEPU) has been synthesized from d-ribose and 5-iodouracil and incorporated into triplex-forming oligonucleotides (TFOs) by automated solid-phase oligonucleotide synthesis. The TFOs gave very high triplex stability with their target duplexes as measured by ultraviolet/fluorescence melting and DNase I footprinting. The incorporation of MEPU into TFOs renders them resistant to degradation by serum nucleases.

SiRNA Delivery to CNS Cells using a Membrane Translocation Peptide

RNA interference (RNAi) is a sequence-specific gene silencing technique that has been applied to multiple pathological conditions. In this report, we describe the generation and in vitro characterization of an RNAi-based fluorescent probe for use as a therapeutic in the setting of ischemic stroke. Probe delivery to bEnd.3 brain endothelial cells and primary cortical neurons and astrocytes was promoted by incorporating small interfering RNA (siRNA) into complexes with fluorescently labeled myristoylated polyarginine peptides. The resulting probe was partially protected from serum nuclease degradation and was efficiently internalized by cells as confirmed by flow cytometry and confocal microscopy. In addition, application of the siRNA probe directed against c-Src, a protein implicated in stroke pathology, led to statistically significant reduction of endogenous c-src mRNA levels in all cell types tested. Results demonstrate the proof-of-principle that functionalized peptide--siRNA probes can be used as potential tools for dual imaging and therapeutic applications.

Synergistic effects between analogs of DNA and RNA improve the potency of siRNA-mediated gene silencing.

We report that combining a DNA analog (2′F-ANA) with rigid RNA analogs [2′F-RNA and/or locked nucleic acid (LNA)] in siRNA duplexes can produce gene silencing agents with enhanced potency. The favored conformations of these two analogs are different, and combining them in a 1–1 pattern led to reduced affinity, whereas alternating short continuous regions of individual modifications increased affinity relative to an RNA:RNA duplex. Thus, the binding affinity at key regions of the siRNA duplex could be tuned by changing the pattern of incorporation of DNA-like and RNA-like nucleotides. These heavily or fully modified duplexes are active against a range of mRNA targets. Effective patterns of modification were chosen based on screens using two sequences targeting firefly luciferase. We then applied the most effective duplex designs to the knockdown of the eIF4E binding proteins 4E-BP1 and 4E-BP2. We identified modified duplexes with potency comparable to native siRNA. Modified duplexes showed dramatically enhanced stability to serum nucleases, and were characterized by circular dichroism and thermal denaturation studies. Chemical modification significantly reduced the immunostimulatory properties of these siRNAs in human peripheral blood mononuclear cells.

Abstract 4073: The PNA oligonucleotide is effective miRNA inhibitor that transfection reagents are not required

Abstract The miRNAs are approximately ∼23 nucleotides non-coding RNAs. They regulate major processes such as development, apoptosis, cell proliferation, hematopoiesis, and patterning of the nervous system. MiRNA inhibition using antisense oligonucleotide is an effective tool for understanding miRNA function. The peptide nucleic acid (PNA) is an artificial oligonucleotide with a peptide backbone. PNAs have a stronger affinity and greater specificity than DNA or RNA and are resistant to nuclease, which is essential characteristic for a miRNA inhibitor that will be exposed to abundant serum and cellular nucleases. In here, we evaluated PNAs™ miRNA inhibitors in cultured cells including stem cell using luciferase assay and qPCR. FACS analysis was showed that PNAs™ miRNA inhibitors can penetrate to intra cells without transfection reagent. Also, miRNA inhibition effects are sustained until 15 days after treatment. PNAs™ miRNA inhibitor has a lower cytotoxicity than other nucleic acid-based miRNA inhibitors. PNAs™ miRNA inhibitors can be stored at room temperature for 20 weeks without losing the activity. These results demonstrate that PNAs are a powerful and effective tool to studies of miRNA mechanism. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4073.

Abstract 4139: Development of a transcription factor decoy for efficient systemic administration in head and neck cancer

Abstract This study was aimed to develop a transcription factor decoy for efficient systemic administration in head and neck cancer. Signal Transducer and Activator of Transcription-3 (STAT3) is upregulated in numerous human cancers including head and neck squamous cell carcinoma (HNSCC). Small molecules that target STAT3 are limited by lack of specificity. We developed a transcription factor decoy targeting STAT3 consisting of a 15-mer double-stranded oligonucleotide with three phosphorothioate modifications (PTO) at the 3′ and 5′ end of the double-stranded structure. This decoy exhibits antitumor efficacy in preclinical cancer models and is now being tested in a phase 0 human trial with intratumoral inoculation. To enable systemic administration, the STAT3 decoy formulation has been modified to enhance stability and uptake into tumors. A series of chemically modified STAT3 decoys have been designed to increase resistance to nucleases and enhance stability when administered in vivo. These include tetra-nucleotide single stranded DNA sequences (DN4), 18-atom hexa-ethyleneglycol spacers (DS18), and locked nucleic acid (LNA-1) modifications to enhance stability in serum. The modified STAT3 decoys were tested for serum nuclease degradation, melting temperature, binding to pSTAT3 protein, uptake and biologic activity. LNA-1 showed increased half-life of up to 8 h in serum, whereas DN4 is stable up to 4 h, DS18 up to 3 h compared with the parent STAT3 decoy, which is resistant only up to 2 h. The melting temperature demonstrated increased thermal stability for all the modified decoys compared to the parent STAT3 decoy. The DN4, DS18 and LNA-1 modified decoy bound to recombinant STAT3 protein as well as the parent decoy and inhibited head and neck cancer cell proliferation in vitro at nanomolar concentrations. The modified STAT3 decoys (DN4, DS18 and LNA-1) showed increased uptake into head and neck cancer cells similar compared with the parent STAT3 decoy. These modified decoys will be tested for their effect on STAT3 target gene expression and in vivo antitumor efficacy when administered systemically with anticipation of implementing a phase I clinical trial if tumor growth inhibition is observed upon intravenous injection. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4139.

Structural Diversity of Triplet Repeat RNAs

Tandem repeats of various trinucleotide motifs are present in the human transcriptome, but the functions of these regular sequences, which likely depend on the structures they form, are still poorly understood. To gain new insight into the structural and functional properties of triplet repeats in RNA, we have performed a biochemical structural analysis of the complete set of triplet repeat transcripts, each composed of a single sequence repeated 17 times. We show that these transcripts fall into four structural classes. The repeated CAA, UUG, AAG, CUU, CCU, CCA, and UAA motifs did not form any higher order structure under any analyzed conditions. The CAU, CUA, UUA, AUG, and UAG repeats are ordered according to their increasing tendency to form semistable hairpins. The repeated CGA, CGU, and all CNG motifs form fairly stable hairpins, whereas AGG and UGG repeats fold into stable G-quadruplexes. The triplet repeats that formed the most stable structures were characterized further by biophysical methods. UV-monitored structure melting revealed that CGG and CCG repeats form, respectively, the most and least stable hairpins of all CNG repeats. Circular dichroism spectra showed that the AGG and UGG repeat quadruplexes are formed by parallel RNA strands. Furthermore, we demonstrated that the different susceptibility of various triplet repeat transcripts to serum nucleases can be explained by the sequence and structural features of the tested RNAs. The results of this study provide a comprehensive structural foundation for the functional analysis of triplet repeats in transcripts.

Functionalization of poly(amidoamine) dendrimers with hydrophobic chains for improved gene delivery in mesenchymal stem cells

A new family of gene delivery vectors is synthesized consisting of a medium-size generation PAMAM dendrimer (generation 5, with amine termini) core randomly linked at the periphery to hydrophobic chains that vary in length (12 to 16 carbon alkyl chains) and number (from 4.2 to 9.7 in average). The idea subjacent to the present work is to join the advantages of the cationic nature of the dendrimer with the capacity of lipids to interact with biological membranes. Unlike other amphiphilic systems designed for the same purpose, where the hydrophobic and hydrophilic moieties coexist in opposite sides, the present vectors have a hydrophilic interior and a hydrophobic corona. The vectors are characterized in respect to their ability to neutralize, bind and compact plasmid DNA (pDNA). The complexes formed between the vectors and pDNA are analyzed concerning their size, ζ-potential, resistance to serum nucleases, capacity of being internalized by cells and transfection efficiency. These new vectors show a remarkable capacity for mediating the internalization of pDNA with minimum cytotoxicity, being this effect positively correlated with the –CH 2– content present in the hydrophobic corona. Gene expression in MSCs, a cell type with relevancy in the regenerative medicine clinical context, is also enhanced using the new vectors but, in this case, the higher efficiency is shown by the vectors containing the smallest hydrophobic chains.

Nanomedicine based approaches for the delivery of siRNA in cancer.

Small interfering RNA (siRNA) technology holds great promise as a therapeutic intervention for targeted gene silencing in cancer and other diseases. However, in vivo systemic delivery of siRNA-based therapeutics to tumour tissues/cells remains a challenge. The major limitations against the use of siRNA as a therapeutic tool are its degradation by serum nucleases, poor cellular uptake and rapid renal clearance following systemic administration. Several siRNA-based loco-regional therapeutics are already in clinical trials. Further development of siRNAs for anti-cancer therapy depends on the development of safe and effective nanocarriers for systemic administration. To overcome these hurdles, nuclease-resistant chemically modified siRNAs and variety of synthetic and natural biodegradable lipids and polymers have been developed to systemically deliver siRNA with different efficacy and safety profiles. Cationic liposomes have emerged as one of the most attractive carriers because of their ability to form complexes with negatively charged siRNA and high in vitro transfection efficiency. However, their effectiveness as potential therapeutic carriers is limited by potential for pulmonary toxicity. Recently, our laboratories described the use of neutral 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine based nanoliposomes in murine tumour models. We found this approach to be safe and 10- and 30-fold more effective than cationic liposomes and naked siRNA, respectively, for systemic delivery of siRNA into tumour tissues. Here, we review potential approaches for systemic delivery of siRNA for cancer therapy.

Solid polymeric microparticles enhance the delivery of siRNA to macrophages in vivo

Therapeutics based on small interfering RNA (siRNA) have a great clinical potential; however, delivery problems have limited their clinical efficacy, and new siRNA delivery vehicles are greatly needed. In this report, we demonstrate that submicron particles (800–900 nm) composed of the polyketal PK3 and chloroquine, termed as the PKCNs, can deliver tumor necrosis factor-α (TNF-α) siRNA in vivo to Kupffer cells efficiently and inhibit gene expression in the liver at concentrations as low as 3.5 μg/kg. The high delivery efficiency of the PKCNs arises from the unique properties of PK3, which can protect siRNA from serum nucleases, stimulate cell uptake and trigger a colloid osmotic disruption of the phagosome and release encapsulated siRNA into the cell cytoplasm. We anticipate numerous applications of the PKCNs for siRNA delivery to macrophages, given their high delivery efficiency, and the central role of macrophages in causing diseases such as hepatitis, liver cirrhosis and chronic renal disease.

Novel graft copolymers enhance in vitro delivery of antisense oligonucleotides in the presence of serum

Antisense technology holds tremendous potential in the research and clinical settings. However, successful delivery of antisense oligodeoxynucleotides (ODNs) to the intracellular site of action requires the passage of many barriers, including survival against extracellular serum nucleases and escape from endolysosomal degradation. Previous work has shown that the effectiveness of antisense delivery by the cationic liposome, dioleoyl-3-trimethylammonium-propane (DOTAP), is enhanced substantially by the incorporation of a pH-sensitive polymer, poly (propylacrylic acid) (PPAA), in serum-free media. To improve this system for application in serum-containing media conditions, PPAA was modified in this work by grafting onto it either poly(ethylene oxide) (PEO) or a more hydrophobic analog, poly (oxyalkylene amine), known as Jeffamine. The ternary formulation of DOTAP/ODN/PPAA-g-Jeffamine resulted in 8-fold increased uptake of fluorescently-labeled ODNs compared to DOTAP/ODN/PPAA and ~80% silencing of green fluorescent protein (GFP) expression in CHO-d1EGFP cells treated in the presence of 10% FBS-containing media. In contrast, the carrier systems that contained PPAA or PPAA-g-PEO failed to display any significant antisense activity in the presence of serum, even though all of the delivery systems displayed moderate to high levels of antisense activity in serum-free conditions. The results reveal that the carrier system with the Jeffamine graft copolymer effectively mediates specific gene silencing in the presence of serum, while the system with the PEO graft copolymer fails to do so. While the pH-dependent lytic functionality of PPAA was found to be lost upon grafting with PEO or Jeffamine, the hydrophobicity of the latter was sufficient to mediate cellular internalization and endosomal escape. Thus, the PPAA-g-Jeffamine copolymers hold substantial promise as agents for controlled therapeutic delivery of antisense oligonucleotides.