Disulfide-Based Poly(amido amine)s for siRNA Delivery: Effects of Structure on siRNA Complexation, Cellular Uptake, Gene Silencing and Toxicity

Purpose

RNA interference (RNAi) is a process by which small interfering RNAs (siRNA) induce sequence-specific gene silencing. Therefore, siRNA is an emerging promise as a novel therapeutic. In order to realize the high expectations for therapeutic applications, efficient delivery systems for siRNA are necessary.

Methods

In this study, a new series of biodegradable poly(amido amine)s with disulfide linkages in the backbone was synthesized out of N,N??-cystaminebisacrylamide (CBA), 4-amino-1-butanol (ABOL) and ethylene diamine (EDA). Effects of different percentages of butanolic side chains and protonatable fragments in the main chain on siRNA complexation, cellular uptake, gene silencing and toxicity were investigated.

Results

Incorporation of EDA in the polymer resulted in increased siRNA condensation. Efficient siRNA condensation was shown to be necessary for cellular uptake; however, excess of polymer decreased siRNA uptake for polymers with high amounts of EDA. Silencing efficiency did not correlate with uptake, since silencing increased with increasing w/w ratio for all polymers. More than 80% knockdown was found for polyplexes formed with polymers containing 25% or 50% EDA, which was combined with low cytotoxicity.

Conclusions

Poly(amido amine)s with minor fractions of protonatable fragments in the main chain are promising carriers for delivery of siRNA.     

Endocytic Transport of Polyplex and Lipoplex siRNA Vectors in HeLa Cells

Purpose

siRNA may be delivered as electrostatic complexes with cationic lipids (lipoplexes) or polycations (polyplexes). The purpose of this project was to determine the effect of cellular internalization mechanism(s) on siRNA-mediated gene silencing efficiency.

Methods

Lipoplexes were formed comprising siRNA and N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl-sulfate (DOTAP), cholesterol and dioleoyl phosphatidylethanolamine (DOPE), and polyplexes comprised siRNA with polyethylenimine (PEI). During transfections, specific uptake mechanisms were inhibited by pharmacological agents and RNAi-mediated knockdown of proteins involved in various endocytosis pathways. Confocal fluorescence microscopy further elucidated the predominant endocytic pathways of siRNA delivery via colocalization of vectors with endocytic vesicle markers.

Results

Inhibition of macropinocytosis (MP), caveolin-mediated endocytosis (CvME), flotillin-mediated endocytosis (FME) and knockdown of ARF6 significantly decreased PEI/siRNA-mediated gene silencing. Inhibition of endocytosis pathways, however, had negligible effect on lipoplex uptake and gene silencing mediated by lipoplexes. Rather, internalization of lipoplexes and subsequent siRNA-mediated gene silencing occurred via an energy-independent process.

Conclusions

MP, CvME and FME, but not the acidified clathrin-mediated pathway, lead to effective gene silencing by PEI/siRNA polyplexes. Lipoplexes, in contrast, deliver siRNA primarily by direct fusion of the liposomal and cellular membranes. These results provide a new understanding of the mechanisms of siRNA delivery materials in HeLa cells and may aid in design of more effective RNAi strategies.

     

Recombinant High Density Lipoprotein Nanoparticles for Target-Specific Delivery of siRNA

Purpose

Regulation of gene expression using small interfering RNA (siRNA) is a promising strategy for treatments of numerous diseases. However, the progress towards broad application of siRNA requires the development of safe and effective vectors that target to specific cells. In this study, we developed a novel recombinant high density lipoprotein (rHDL) vector with high siRNA encapsulation efficiency.

Methods

They were prepared by condensing siRNA with various commercial cationic polymers and coating the polyplex with a layer of lipids and apolipoprotein AI (apo AI). The rHDL nanoparticles were used to transfect SMMC-7721 hepatoma cells with stable luciferase expression. The uptake and intracellular trafficing of siRNA were also investigated.

Results

Characterization studies revealed these rHDL nanoparticles had similar physical properties as natural HDLs. The various rHDL formulations had high silencing efficiency (more than 70% knockdown) in hepatocytes with minimum cytotoxicity. Moreover, the uptake of rHDL by SMMC-7721 was confirmed to be mediated through the natural HDL uptake pathway.

Conclusions

The work described here demonstrated the optimized rHDL nanoparticles may offer a promising tool for siRNA delivery to the liver.     

Insight into Polycation Chain Length Affecting Transfection Efficiency by O-Methyl-Free N,N,N-Trimethyl Chitosans as Gene Carriers

Purpose

The structure–function relationship and mechanism of polycations as gene carriers have attracted considerable research interest in recent years. The present study was to investigate the relationship between polycation chain length and transfection efficiency (R_CL-TE), and the corresponding mechanism by O-methyl-free N,N,N-trimethyl chitosans (TMCs) as gene carriers.

Methods

Four TMCs with various chain lengths were synthesized and used to evaluate the R_CL-TE. To investigate the details of R_CL-TE, a number of factors such as cytotoxicity, cellular uptake efficiency, cellular uptake pathway and intracellular trafficking, were evaluated.

Results

In comparison to short chain length TMCs (S-TMCs), long chain length ones (L-TMCs) mediated higher gene expression. The polyplexes formed by L-TMCs and pDNA showed higher stability. The cellular uptake pathway and intracellular trafficking of these TMC/pDNA polyplexes were different. These above factors are probably the key ones in R_CL-TE rather than polycation–DNA binding affinity, polyplex particle size in water, zeta potential, serum, cytotoxicity, and cellular uptake efficiency.

Conclusions

For rational design of chitosan-based polycations as gene carriers, polycations with relative long chain lengths are more favorable and more attention should be paid to polyplex stability, function of uncomplexed polycation chains, cellular uptake pathway, and intracellular trafficking.     

Pulmonary Gene Silencing in Transgenic EGFP Mice Using Aerosolised Chitosan/siRNA Nanoparticles

Purpose

This work describes the production and application of an aerosolised formulation of chitosan nanoparticles for improved pulmonary siRNA delivery and gene silencing in mice.

Methods

Aerosolised chitosan/siRNA nanoparticles were pneumatically formed using a nebulising catheter and sized by laser diffraction. In vitro silencing of aerosolised and non-aerosolised formulations was evaluated in an EGFP endogenous-expressing H1299 cell line by flow cytometry. Non-invasive intratracheal insertion of the catheter was used to study nanoparticle deposition by histological detection of Cy3-labeled siRNA and gene silencing in transgenic EGFP mouse lungs using a flow cytometric method.

Results

Flow cytometric analysis demonstrated minimal alteration in gene silencing efficiency before (68%) and after (62%) aerosolisation in EGFP-expressing H1299 cells. Intratracheal catheter administration in mice resulted in nanoparticle deposition throughout the entire lung in both alveoli and bronchiolar regions using low amounts of siRNA. Transgenic EGFP mice dosed with the aerosolised nanoparticle formulation showed significant EGFP gene silencing (68% reduction compared to mismatch group).

Conclusions

This work provides a technology platform for effective pulmonary delivery and gene silencing of RNAi therapeutics with potential use in preclinical studies of respiratory disease treatment.     

Amine-Modified Poly(Vinyl Alcohol)s as Non-viral Vectors for siRNA Delivery: Effects of the Degree of Amine Substitution on Physicochemical Properties and Knockdown Efficiency

Purpose

The objective of this study was to investigate how the degree of amine substitution of amine-modified poly(vinyl alcohol) (PVA) affects complexation of siRNA, protection of siRNA against degrading enzymes, intracellular uptake and gene silencing.

Methods

A series of DEAPA-PVA polymers with increasing amine density was synthesized by modifying the hydroxyl groups in the PVA backbone with diethylamino propylamine groups using CDI chemistry. These polymers were characterized with regard to their ability to complex and protect siRNA against RNase. Finally, their potential to mediate intracellular uptake and gene silencing in SKOV-luc cells was investigated.

Results

A good correlation between amine density and siRNA complexation as well as protection of siRNA against RNase was found. Consisting solely of tertiary amines, this class of polymer was able to mediate efficient gene silencing when approximately 30% of the hydroxyl groups in the PVA backbone were modified with diethylamino propylamine groups. Polymers with a lower amine density (up to 23%) were inefficient in gene silencing, while increasing the amine density to 48% led to non-specific knockdown effects.

Conclusion

DEAPA-PVA polymers were shown to mediate efficient gene silencing and offer a promising platform for further structural modifications.     

In Vitro Investigations of the Efficacy of Cyclodextrin-siRNA Complexes Modified with Lipid-PEG-Octaarginine: Towards a Formulation Strategy for Non-viral Neuronal siRNA Delivery

Purpose

Development of RNA interference based therapeutics for neurological and neurodegenerative diseases is hindered by a lack of non-viral vectors with suitable properties for systemic administration. Amphiphilic and cationic cyclodextrins (CD) offer potential for neuronal siRNA delivery. We aimed to improve our CD-based siRNA formulation through incorporation of a polyethyleneglycol (PEG) shielding layer and a cell penetrating peptide, octaarginine (R8).

Methods

CD.siRNA complexes were modified by addition of an R8-PEG-lipid conjugate. Physical properties including size, charge and stability were assessed. Flow cytometry was used to determine uptake levels in a neuronal cell model. Knockdown of an exogenous gene and an endogenous housekeeping gene were used to assess gene silencing abilities.

Results

CD.siRNA complexes modified with R8-PEG-lipid exhibited a lower surface charge and greater stability to a salt-containing environment. Neuronal uptake was increased and significant reductions in the levels of two target genes were achieved with the new formulation. However, the PEG layer was not sufficient to protect against serum-induced aggregation.

Conclusions

The R8-PEG-lipid-CD.siRNA formulation displayed enhanced salt-stability due to the PEG component, while the R8 component facilitated transfection of neuronal cells and efficient gene silencing. Further improvements will be investigated in the future in order to optimise stability in serum and enhance neuronal specificity.     

Efficient siRNA Delivery Using a Polyamidoamine Dendrimer with a Modified Pentaerythritol Core

Purpose

Delivery of siRNA into cells remains a critical challenge. Our lab has shown a novel polyamidoamine (PAMAM) dendrimer with modified pentaerythritol derivative core (PD dendrimer) to exhibit high plasmid DNA transfection efficiency and low cytotoxicity. Here, we evaluate PD dendrimer as a siRNA carrier.

Methods

Agarose gel electrophoresis and AFM were used to confirm formation of generation 5 (G5)-PD dendrimer/siRNA nanoparticles (NPs). G5 PD dendrimer/anti-luciferase siRNA NPs were used to transfect SK Hep-1 cells with stable luciferase expression. Effects of various endocytic pathway inhibitors on uptake of G5 PD dendrimer/siRNA NPs in SK Hep-1 cells were also investigated.

Results

Agarose gel electrophoresis indicated that G5 PD dendrimer and siRNA formed NPs at weight ratios >0.5:1. G5 PD dendrimer showed effective luciferase gene silencing when weight ratio was 3.0:1 and above. Treatment with endocytosis inhibitors showed that clathrin-mediated endocytosis was the main endocytic pathway by which G5-PD dendrimer/siRNA NPs enter the cell.

Conclusions

These results show that the novel G5 PD dendrimer has high siRNA delivery activity and is promising as a delivery agent for its therapeutic application.     

Ternary Polymeric Nanoparticles for Oral siRNA Delivery

Purpose

Poor stability and inefficient absorption in the intestinal tract are major barriers confronting oral delivery of siRNA. We aimed to uncover if ternary polymeric nanoparticles (cationic polymer/siRNA/anionic component) can overcome these obstacles through changing the formulation-related parameters.

Methods

Ternary polymeric nanoparticles were prepared by ionic gelation of chitosan, N-trimethyl chitosan (TMC), or thiolated trimethyl chitosan (TTMC) with tripolyphosphate (TPP) or hyaluronic acid (HA), and siRNA was simultaneously encapsulated. Structural stabilities and siRNA protection of these nanoparticles were assessed in simulated intestinal milieu. Their transport across ex vivo rat ileum, macrophage uptake, in vitro gene silencing, and in vivo biodistribution after oral administration were investigated.

Results

Ternary polymeric nanoparticles formed by TTMC, siRNA, and TPP (TTMC/siRNA/TPP nanoparticles) showed suitable structural stability and siRNA protection in the intestinal tract, good permeability across ex vivo rat ileum, superior cellular uptake and gene silencing efficiency in Raw 264.7 cells, and high systemic biodistribution after oral administration.

Conclusions

TTMC/siRNA/TPP nanoparticles demonstrated efficient gene silencing in vitro and systemic biodistribution in vivo, therefore, they were expected to be potential vehicles for oral siRNA delivery.     

Enhanced Transfection by Antioxidative Polymeric Gene Carrier that Reduces Polyplex-Mediated Cellular Oxidative Stress

Purpose

To test the hypothesis in which polyplex-induced oxidative stress may affect overall transfection efficiency, an antioxidative transfection system minimizing cellular oxidative stress was designed for enhanced transfection.

Methods

An amphiphilic copolymer (PEI-PLGA) was synthesized and used as a micelle-type gene carrier containing hydrophobic antioxidant, α-tocopherol. Cellular oxidative stress and the change of mitochondrial membrane potential after transfection was measured by using a fluorescent probe (H₂DCFDA) and lipophilic cationic probe (JC-1), respectively. Transfection efficiency was determined by measuring a reporter gene (luciferase) expression level.

Results

The initial transfection study with conventional PEI/plasmid DNA polyplex showed significant generation of reactive oxygen species (ROS). The PEI-PLGA copolymer successfully carried out the simultaneous delivery of α-tocopherol and plasmid DNA (PEI-PLGA/Toco/pDNA polyplex) into cells, resulting in a significant reduction in cellular ROS generation after transfection and helped to maintain the mitochondrial membrane potential (ΔΨ). In addition, the transfection efficiency was dramatically increased using the antioxidative transfection system.

Conclusions

This work showed that oxidative stress would be one of the important factors that should be considered in designing non-viral gene carriers and suggested a possible way to reduce the carrier-mediated oxidative stress, which consequently leads to enhanced transfection.     

Ultrasound Enhanced PEI-Mediated Gene Delivery Through Increasing the Intracellular Calcium Level and PKC-δ Protein Expression

Purpose

Polyethylenimine (PEI), a cationic polymer, has been shown to aggregate plasmid DNA and facilitate its internalization. It has also been shown that combining ultrasound (US) with PEI could enhance and prolong in vitro and in vivo transgene expression. However, the role US in the enhancement of PEI uptake is poorly understood. This study investigates the impact of US on PEI-mediated gene transfection.

Methods

Specific endocytosis pathway siRNA, including clathrin HC siRNA, caveolin-1 siRNA and protein kinase C-delta (PKC-δ) siRNA, are used to block the corresponding endocytosis pathways prior to the transfection of luciferase DNA/PEI polyplexes to cultured cells by 1-MHz pulsed US with ultrasound contrast agent SonoVue®.

Results

Transgene expression was found not to be enhanced by US treatment in the presence of the PKC-δ siRNA. We further demonstrated that PKC-δ protein could be enhanced at 6 h after US exposure. Moreover, intracellular calcium levels were found to be significantly increased at 3 h after US exposure, while transgene expressions were significantly reduced in the presence of calcium channel blockers both in vitro and in vivo.

Conclusions

Our results suggest that US enhanced PEI-mediated gene transfection specifically by increasing PKC-δ related fluid phase endocytosis, which was induced by increasing the intracellular calcium levels.     

Polymeric Plerixafor: Effect of PEGylation on CXCR4 Antagonism,Cancer Cell Invasion,and DNA Transfection

Purpose

To determine the effect of PEG modification on pharmacologic and gene delivery properties of polymeric CXCR4 antagonist based on Plerixafor.

Methods

Polymeric Plerixafor (PAMD) was synthesized from Plerixafor (AMD3100) and grafted with different amounts of PEG (2 kDa). CXCR4 antagonism of the synthesized polymers was determined using receptor redistribution assay. Inhibition of cancer cell invasion by the polyplexes of the synthesized polymers was assessed using Boyden-chamber method. Transfection activity of DNA polyplexes formed with the synthesized polymers was evaluated in U2OS osteosarcoma and B16F10 melanoma cells.

Results

Our results demonstrate that modification of PAMD with PEG decreased toxicity of the polymers, while preserving their CXCR4 antagonism. Polyplexes prepared with PEG-PAMD inhibited invasion of cancer cells to an extent similar to the commercial CXCR4 antagonist Plerixafor. Negative effect of PEG on transfection activity of PEG-PAMD polyplexes could be overcome by using polyplexes formulated with a mixture of PAMD and PEG-PAMD.

Conclusion

Modification of PAMD with PEG is a viable strategy to preserve the desirable CXCR4 antagonism and ability to inhibit cancer cell invasion of PAMD, while improving safety and colloidal stability of the PAMD polyplexes.     

Effect of PEGylation on Biodistribution and Gene Silencing of siRNA/Lipid Nanoparticle Complexes

Purpose

To determine the influence of physicochemical properties of lipid nanoparticles (LNPs) carrying siRNA on their gene silencing in vivo. Mechanistic understanding of how the architecture of the nanoparticle can alter gene expression has also been studied.

Methods

The effect of 3-N-[(ω-methoxypoly(ethylene glycol)2000)carbamoyl]-1,2-dimyristyloxy-propylamine (PEG-C-DMA) on hepatic distribution and FVII gene silencing was determined. FVII mRNA in hepatocytes and liver tissues was determined by Q-PCR. Hepatic distribution was quantified by FACS analysis using Cy5 labeled siRNA.

Results

Gene silencing was highly dependent on the amount of PEG-C-DMA present. FVII gene silencing inversely correlated to the amount of PEG-C-DMA in LNPs. High FVII gene silencing was obtained in vitro and in vivo when the molar ratio of PEG-C-DMA to lipid was 0.5 mol%. Surprisingly, PEGylation didn’t alter the hepatic distribution of the LNPs at 5 h post administration. Instead the amount of PEG present in the LNPs has an effect on red blood cell disruption at low pH.

Conclusion

Low but sufficient PEG-C-DMA amount in LNPs plays an important role for efficient FVII gene silencing in vivo. PEGylation did not alter the hepatic distribution of LNPs, but altered gene silencing efficacy by potentially reducing endosomal disruption.     

Chitosan-Based Hybrid Nanocomplex for siRNA Delivery and Its Application for Cancer Therapy

Purpose

Chitosan, a natural and biocompatible cationic polymer, is an attractive carrier for small interfering RNA (siRNA) delivery. The purpose of this study was to develop a chitosan-based hybrid nanocomplex that exhibits enhanced physical stability in the bloodstream compared with conventional chitosan complexes. Hybrid nanocomplexes composed of chitosan, protamine, lecithin, and thiamine pyrophosphate were prepared for systemic delivery of survivin (SVN) siRNA.

Methods

Physicochemical properties of the nanoparticles including mean diameters and zeta potentials were characterized, and target gene silencing and cellular uptake efficiencies of the siRNA nanocomplexes in prostate cancer cells (PC-3 cells) were measured. In vivo tumor targetability and anti-tumor efficacy by systemic administration were assessed in a PC-3 tumor xenograft mouse model by near-infrared fluorescence (NIRF) imaging and tumor growth monitoring, respectively.

Results

Mean diameters of the SVN siRNA-loaded hybrid nanocomplex (GP-L-CT) were less than 200 nm with a positive zeta potential value in water and were maintained without aggregation in culture media and 50% fetal bovine serum. SVN expression in PC-3 cells was reduced to 21.9% after treating with GP-L-CT. The tumor targetability and growth inhibitory efficacies of GP-L-CT supported the use of this novel hybrid nanocomplex as a cancer therapeutic and as a theranostic system for systemic administration.

Conclusions

A chitosan-based hybrid nanocomplex was successfully developed for the systemic delivery of SVN siRNA, which could serve as an alternative to cationic polymeric nanoparticles that are unstable in serum.     

Photo-Inducible Crosslinked Nanoassemblies for pH-Controlled Drug Release

Purpose

To control drug release from block copolymer nanoassemblies by variation in the degree of photo-crosslinking and inclusion of acid sensitive linkers.

Methods

Poly(ethylene glycol)-poly(aspartate-hydrazide-cinnamate) (PEG-CNM) block copolymers were prepared and conjugated with a model drug, doxorubicin (DOX), through acid sensitive hydrazone linkers. The block copolymers formed photo-inducible, self-assembled nanoassemblies (piSNAs), which were used to produce photo-inducible crosslinked nanoassemblies (piCNAs) through UV crosslinking. The nanoassemblies were characterized to determine particle size, surface charge, pH- and crosslinking-dependent DOX release, in vitro cytotoxicity, and intracellular uptake as a function of photo-crosslinking degree.

Results

Nanoassemblies with varying photo-crosslinking degrees were successfully prepared while retaining particle size and surface charge. Photo-crosslinking caused no noticeable change in DOX release from the nanoassemblies at pH 7.4, but the DOX-loaded nanoassemblies modulated drug release as a function of crosslinking at pH 6.0. The nanoassemblies showed similar cytotoxicity regardless of crosslinking degrees, presumably due to the low cellular uptake and cell nucleus drug accumulation.

Conclusions

Photo-crosslinking is useful to control drug release from pH-sensitive block copolymer nanoassemblies as a function of crosslinking without altering the particle properties, and thus providing unique tools to investigate the pharmaceutical effects of drug release on cellular response.     

Trimethyl Chitosan-Cysteine Nanoparticles for Systemic Delivery of TNF-α siRNA via Oral and Intraperitoneal Routes

Purpose

The lack of effective delivery vehicles impedes in vivo applications of siRNA. The trimethyl chitosan-cysteine (TC) nanoparticles (NPs) were developed for in vivo delivery of tumor necrosis factor α (TNF-α) siRNA via oral gavage and intraperitoneal injection.

Methods

The nanoparticles formulated from TC conjugate of 100, 200, and 500 kDa were prepared through ionic gelation with sodium tripolyphosphate, termed as TC100 NPs, TC200 NPs, and TC500 NPs, respectively. They were evaluated in terms of stability, siRNA protection, cellular uptake and TNF-α knockdown in peritoneal exudates macrophage cells (PECs), and in vivo TNF-α silencing in acute hepatic injury mice.

Results

TC100 NPs exhibited poor stability in simulated physiological environment compared to TC200 NPs and TC500 NPs. Compared to TC500 NPs, TC200 NPs could significantly enhance in vitro and in vivo cellular uptake by PECs and facilitate cytoplasmic siRNA release, resulting in high in vitro and in vivo TNF-α knockdown. Superior TNF-α suppressing level was obtained with TC200 NPs via oral gavage rather than intraperitoneal injection.

Conclusions

The efficacies of in vivo TNF-α silencing were related to the molecular weight of TC conjugate and the administration route, which would assist in the rational design of siRNA vehicles.     

Factors influencing polycation/siRNA colloidal stability toward aerosol lung delivery

Hexanediol diacrylate cross-linked oligoethylenimine (OEI-HD) is a non-viral polymeric vector designed to deliver siRNA. To achieve safe and effective in vivo siRNA delivery using this vector, the polyplex must have sufficient colloidal stability if administered intravenously or nebulized for delivery by the pulmonary route. In this study, polyplexes from OEI-HD and siRNA were formulated for aerosol-based lung delivery, regarding their colloidal stability, optimal particle size, and in vitro biological activity. Herein, we describe how these properties are dependent upon the polymer-to siRNA weight ratios, buffer composition they were complexed in, PEG-grafting, and the addition of commercial lung surfactants and/or non-ionic surfactants to the formulation. Lastly, the effects of nebulization of the formulation into aerosol droplets, on the polyplex particle size and transfection efficiency, were evaluated.Polyplex size was monitored for up to 2 h after polyplex formation to determine the extent of aggregation and final particle sizes when stability was achieved. Our results suggest that PEG-grafting and polyethylenimine-PEG mixing were effective in achieving colloidal stability in isotonic saline buffers. In addition, colloidal stability was achieved in isotonic glucose buffers using commercially available non-ionic surfactant Pluronic™ P68 or the lung-derived surfactant Alveofact™. The smallest particle size, 140 nm, was obtained with Pluronic™ F68. For transfection efficiency, both Alveofact™ and Pluronic™ F68 achieved equal or better transfection when added to the OEI-HD/siRNA polyplexes. For long term storage of OEI-HD/siRNA formulations, we propose a lyophilization method that created in situ polyplexes upon addition of water. Preparation of OEI-HD/siRNA polyplexes by this method allowed dry storage at room temperature for up to the 3 months. In conclusion, we have identified approaches to achieve formulation and colloidal stability of OEI-HD/siRNA complexes, a step toward successful application of polyplexes for in vivo siRNA delivery.     

Evaluation of Pharmacokinetics of Bioreducible Gene Delivery Vectors by Real-time PCR

Purpose

To investigate pharmacokinetics of reversibly stabilized DNA nanoparticles (rSDN) using a single-step lysis RT-PCR.

Methods

rSDN were prepared by coating bioreducible polycation/DNA polyplexes with multivalent N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers. Targeted polyplexes were formulated by linking cyclic RGD ligand (c(RGDyK)) to the HPMA surface layer of rSDN. The pharmacokinetic parameters in tumor-bearing mice were analyzed by PKAnalyst®.

Results

The pharmacokinetics of naked plasmid DNA, simple DNA polyplexes, rSDN, and RGD-targeted rSDN exhibited two-compartment model characteristics with area under the blood concentration–time curve (AUC) increasing from 1,102 ng?ml^?1?min^?1 for DNA to 3,501 ng?ml^?1?min^?1 for rSDN. Non-compartment model analysis revealed increase in mean retention time (MRT) from 4.5 min for naked DNA to 22.9 min for rSDN.

Conclusions

RT-PCR is a sensitive and convenient method suitable for analyzing pharmacokinetics and biodistribution of DNA polyplexes. Surface stabilization of DNA polyplexes can significantly extend their MRT and AUC compared to naked DNA. DNA degradation in rSDN in blood circulation, due to a combined effect of disulfide reduction and competitive reactions with charged molecules in the blood, contributes to DNA elimination.