Meta-analysis: IL28B polymorphisms predict sustained viral response in HCV patients treated with pegylated interferon-α and ribavirin

BACKGROUND

Interleukin (IL) 28B single nucleotide polymorphisms can predict sustained virological response (SVR) in hepatitis C virus (HCV) patients following pegylated interferon-alpha (PEG IFN-α) and ribavirin treatment.

AIM

To design a meta-analysis to determine IL28B genotypes', rs12979860 CC and rs8099917 TT, correlation with SVR in PEG IFN-α/ribavirin-treated HCV patients.

METHODS

Meta-analysis was performed in 17 studies of rs12979860 CC vs. CT/TT and 17 of rs8099917 TT vs. TG/GG. Odds ratios (OR) and confidence intervals (95% CI) were calculated by fixed- or random-effects models. Heterogeneity, sensitivity analysis and publication bias were also assessed.

RESULTS

Of 4252 Asian, Caucasian and African HCV patients analysed for rs12979860, SVR was more frequent in CC (vs. CT/TT; OR = 4.76, 95% CI: 3.15-7.20). Moreover, CC was associated with SVR for HCV genotype-1 or -4 infections (OR(genotype 1) = 5.52, 95% CI: 3.74-8.15; OR(genotype 4) = 8.11, 95% CI: 4.13-15.93), regardless of ethnicity. Of 4549 Caucasian and Asian HCV patients analysed for rs8099917, SVR was more frequent in TT (vs. TG/GG; OR = 3.31, 95% CI: 2.39-4.59). Moreover, TT was associated with SVR for HCV-1 (OR(genotype 1) = 4.28, 95% CI: 2.87-6.38). Rs8099917 TT predictive value was stronger in Asians (OR(Asians) = 8.09, 95% CI: 5.63-11.61; OR(Caucasians) = 3.00, 95% CI: 2.03-4.45). Ethnicity stratification revealed that rs8099917 TT had slight predictive value in Asian HCV-2/3 patients (OR = 1.99, 95% CI: 1.09-3.62).

CONCLUSIONS

IL28B rs12979860 CC and rs8099917 TT are strong SVR predictors for PEG IFN-α/ribavirin-treated HCV-1 patients, regardless of ethnicity. In HCV-2/3, rs12979860 CC has no SVR predictive value, but rs8099917 TT was slightly associated with SVR in Asians.

Adenovirus-based vascular endothelial growth factor gene delivery to human pancreatic islets

Islet transplantation is limited by islet graft failure due to poor revascularization, host immune rejection and nonspecific inflammatory response. Delivery of human vascular endothelial growth factor (hVEGF) gene to the islets is likely to promote islet revascularization and survival. We used a bicistronic adenoviral vector encoding hVEGF and CpG-free allele of green fluorescent protein (Adv-GFP-hVEGF) and introduced into human pancreatic islets by transfection. We found that transfection efficiency and apoptosis were dependent on the multiplicity of infection (MOI). Compared to Adv-GFP transfected and nontransfected islets, the levels of hVEGF secreted from Adv-GFP-hVEGF transfected islets were higher and exhibit a linear relationship between hVEGF expression and MOI (10-5000). Persistent, but low level expression of hVEGF from nontransfected islets was also observed. This may be due to expression of the endogenous hVEGF gene under hypoxic conditions. The levels of DNA fragmentation determined by ELISA of islet lysates were dependent on the MOI of Adv-GFP-hVEGF. On glucose challenge, insulin release from transfected islets was comparable to nontransfected islets. Immunohistochemical staining for hVEGF was very high in Adv-GFP-hVEGF transfected islets. Weak staining was also observed for hCD31 in both transfected and nontransfected islets. These findings suggest that Adv-GFP-hVEGF is a potential candidate for promoting islet revascularization.

Biodegradable polymer-based interleukin-12 gene delivery: role of induced cytokines, tumor infiltrating cells and nitric oxide in anti-tumor activity

The objective of this study was to investigate the role of induced cytokines, tumor infiltrating cells and nitric oxide (NO) in anti-tumor activity upon intratumoral injection of free and condensed plasmid DNA encoding murine interleukin-12 (pmIL-12) into BALB/c mice bearing subcutaneous tumors. Poly[alpha-(4-aminobutyl)-L-glycolic acid] (PAGA) was used for complex formation with pmIL-12 in presence of 5% (w/v) glucose. Upon characterization, PAGA/pmIL-12 (3/1, +/-) complexes were found to be most effective in gene transfer and were used consistently throughout this study. The levels of mIL-12 p70 and induced cytokines were determined by ELISA in the supernatant of the cultured tumors of the CT-26 subcutaneous tumor bearing BALB/c female mice 48 h after intratumoral injection of PAGA/pmIL-12 complexes and naked pmIL-12. The levels of IL-12, IFN-gamma, TNF-alpha and NO were higher for the PAGA/pmIL-12 complexes than those for the naked pmIL-12, PAGA alone and 5% glucose injected groups. The relative presence of natural killer (NK) cells, CD4(+) T cells, and antigen presenting cells, such as macrophages and dendritic cells determined using immunohistochemistry was higher for PAGA/pmIL-12 complexes compared with naked pmIL-12. The presence of CMV promoter in plasmid encoding IL-12 cDNAs did not induce any type I interferon response. There was a significant improvement in the survival rate and the inhibition of tumor growth after repeated injections of PAGA/pmIL-12 complexes.

Water-soluble lipopolymer for gene delivery

The use of biocompatible polymeric gene carriers may overcome the current problems associated with viral vectors in safety, immunogenicity, and mutagenesis. Nontoxic water-soluble lipopolymer (WSLP), poly(ethylenimine)-co-[N-(2-aminoethyl) ethyleneimin]-co-N-(N-cholesteryloxycarbonyl-(2-aminoethyl)ethylenimine) was synthesized using branched poly(ethylenimine) (PEI, mw 1800) and cholesteryl chloroformate. Following synthesis and purification, the structure and molecular weight of WSLP were confirmed by (1)H NMR and MADI-TOF mass spectrometry, respectively. The percentage of cholesterol conjugated to PEI was about 47%, and the average molecular weight of WSLP was approximately 2000 Da. WSLP/pDNA complexes were prepared at different N/P (nitrogen atoms of WSLP/phosphate of plasmid DNA) ratios and characterized in terms of particle size, zeta potential, osmolarity, surface morphology, and cytotoxicity. WSLP condensed plasmid DNA when N/P ratio reached 2.5/1 and no free DNA was detected at N/P ratio of 5/1 and above, as determined by agarose gel electrophoresis. The mean particle size was in the range of 25.9 to 148.5 nm and was dependent on N/P ratios. Atomic force microscopy (AFM) showed complete condensation of plasmid DNA with spherical particles of approximately 50 nm in diameter. WSLP/pDNA complexes or WSLP itself were nontoxic to CT-26 colon adenocarcinoma and 293 T human embryonic kidney transformed cells when formulated at the N/P ratio of 10/1 and below as determined by MTT assay. In contrast, PEI25000/pDNA complexes were toxic to these cells. Erythrocytes aggregated when incubated with PEI25000/pCMV-Luc complexes at high DNA concentrations, but there was little aggregation with WSLP/pCMV-Luc complexes. WSLP/pCMV-Luc complexes demonstrated higher transfection efficiency in both CT-26 and 293 T cells compared to PEI25000- or PEI1800-based formulations. WSLP/pCMV-Luc complexes are nontoxic and showed enhanced in vitro transfection. Thus, WSLP will be a suitable carrier for in vivo gene delivery.

Intratumoral delivery of p2CMVmIL-12 using water-soluble lipopolymers

Our objective was to design a water-soluble lipopolymer (WSLP) and an interleukin-12 (IL-12) expression plasmid for enhanced delivery of the IL-12 gene. We synthesized WSLP using branched polyethylenimine (PEI) of 1800 Da and cholesteryl chloroformate, and constructed p2CMVmIL-12, encoding the IL-12 subunits p35 and p40, each under the transcriptional control of a separate cytomegalovirus (CMV) promoter. The percentage of cholesterol conjugated to PEI was about 47% and the average molecular weight of WSLP was approximately 2000 Da. The mean particle size of WSLP/p2CMVmIL-12 complexes formulated in 5% glucose was 26 to 62 nm and xi potential was 8 to 60 mV. The WSLP/p2CMVmIL-12 complexes were nontoxic to CT-26 colon carcinoma cells at the N/P ratio (nitrogen atoms of WSLP/phosphate of plasmid DNA) of 20 and below; PEI25000/pDNA complexes were highly toxic. WSLP/p2CMVmIL-12 complexes demonstrated higher transfection in CT-26 cells compared with the DNA formulations prepared using PEI of molecular weights 1800, 10,000 and 25,000 Da. Transfection efficiency increased with an increase in N/P ratios from 5 to 15, then there was no significant increase in transfection up to the N/P ratio of 30/1. There was an increase in the level of IL-12 when free or complexed p2CMVmIL-12 was compared with free or complexed pIRESmIL-12 in which the p35 and p40 subunits were linked to the internal ribosome entry sites (IRES). At 48 hours post-injection of WSLP/p2CMVmIL-12 complexes into BALB/c mice bearing CT-26 subcutaneous tumors, the levels of IL-12, IFN-gamma, and nitric oxide (NO) in the supernatant of the cultured tumors were higher for the WSLP/p2CMVmIL-12 complexes than for the naked p2CMVmIL-12, WSLP, and 5% glucose injected groups. There was a significant improvement in the survival rate and the inhibition of tumor growth after a single injection of WSLP/p2CMVmIL-12 complexes. We have designed an effective, nontoxic WSLP and an IL-12 expression plasmid with two CMV promoters.

Folate-PEG-folate-graft-polyethylenimine-based gene delivery

Folate-polyethylene glycol-folate-grafted-polyethylenimine (FPF-g-PEI) was synthesized by linking folic acid to both ends of a mono-functional PEG and then grafting to PEI. The graft ratio was determined using Beer's law by measuring the UV absorbance at 363 nm. The pH profile, diameter and shape of the carriers were determined. Transfection efficiencies were optimized in normal smooth muscle cells (SMC) and CT-26 colon adenocarcinoma cells using plasmid DNA encoding luciferase reporter gene. Free folic acid was shown to inhibit transfection with FPF-2.3 g-PEI at neutral charge ratio. Relative toxicity between PEI and the modified carrier was measured using MTT colorimetric assay. Therapeutic potential of pmIFN-gamma complexed with these polymeric carriers in terms of gene expression was determined at protein and mRNA levels using ELISA and RT-PCR. FPF-g-PEI was determined to have 2.3 folate-PEG-folate (FPF) linear polymers grafted to each PEI molecule. The average molecular weight was measured to be approximately 33,500 Mw and the pH profile was characteristic of endosomal disruption capacity. Atomic Force Microscopy (AFM) and Dynamic Laser Light Scattering (DLLS) indicated FPF-2.3 g-PEI and PEI (at 2 w/w ratio) efficiently condensed plasmid DNA resulting in oblique spheroid polyplexes with a mean diameter of approximately 150 nm. FPF-2.3 g-PEI was superior to PEI in terms of cytotoxicity and transfection efficiency in cancer cells. Smooth muscle cells showed no specificity for folate tethered complexes, where PEI/pLuc complexes yielded higher efficiencies.

Development of biomaterials for gene therapy

Novel biocompatible polymeric gene carriers have been examined for their potential in treating various genetic and acquired diseases. The use of polymeric gene carriers may overcome the current problems associated with viral vectors in safety, immunogenicity, and mutagenesis. However, effective polymer-based gene therapy requires the control of cellular access and uptake, intracellular trafficking, and nuclear retention of plasmid DNA. Inefficient endosomal release, cytoplasmic transport, and nuclear entry of plasmids are currently limiting factors in the use of polymers for effective plasmid-based gene therapy. Therefore, several different polymeric gene carriers have been designed recently in an attempt to overcome these problems. This review explores the conceptual and experimental aspects of polymer-based gene delivery and presents an overview on the recent use of polymers to enhance the effectiveness of plasmid-based systems. Despite their current limitations, polymeric carriers have significant potential as commercially viable gene medicines.

pH-sensitive cationic polymer gene delivery vehicle: N-Ac-poly(L-histidine)-graft-poly(L-lysine) comb shaped polymer

Advancing biotechnology spurs the development of new pharmaceutically engineered gene delivery vehicles. Poly(L-histidine) ¿PLH¿ has been shown to induce membrane fusion at endosomal pH values, whereas PLL has a well documented efficacy in polyplex formation. Therefore, N-Ac-poly(L-histidine)-graft-poly(L-lysine) ¿PLH-g-PLL¿ was synthesized by grafting poly(L-histidine) to poly(L-lysine) ¿PLL¿. PLH-g-PLL formed polyplex particles by electrostatic interactions with plasmid DNA ¿pDNA¿. The mean particle size of the polyplexes was in the range of 117 +/- 6 nm to 306 +/- 77 nm. PLH-g-PLL gene carrier demonstrated higher transfection efficacy in 293T cells than PLL at all equivalent weight ratios with pDNA. The inclusion of chloroquine as an endosomolytic agent enhanced transfection for both PLL and PLH-g-PLL gene carriers. PLH-g-PLL enhanced beta-galactosidase expression compared to PLL, but still increased in efficacy when chloroquine was included.

Soluble biodegradable polymer-based cytokine gene delivery for cancer treatment

Transgene expression and tumor regression after direct injection of plasmid DNA encoding cytokine genes, such as mIL-12 and mIFN-gamma, remain very low. The objective of this study is to develop nontoxic biodegradable polymer-based cytokine gene delivery systems, which should enhance mIL-12 expression, increasing the likelihood of complete tumor elimination. We synthesized poly[alpha-(4-aminobutyl)-l-glycolic acid] (PAGA), a biodegradable nontoxic polymer, by melting condensation. Plasmids used in this study encoded luciferase (pLuc) and murine interleukin-12 (pmIL-12) genes. PAGA/plasmid complexes were prepared at different (+/-) charge ratios and characterized in terms of particle size, zeta potential, osmolality, surface morphology, and cytotoxicity. Polyplexes prepared by complexing PAGA with pmIL-12 as well as pLuc were used for transfection into cultured CT-26 colon adenocarcinoma cells as well as into CT-26 tumor-bearing BALB/c mice. The in vitro and in vivo transfection efficiency was determined by luciferase assay (for pLuc), enzyme-linked immunosorbent assay (for mIL-12, p70, and p40), and reverse transcriptase-polymerase chain reaction (RT-PCR) (for Luc and mIL-12 p35). PAGA condensed and protected plasmids from nuclease degradation. The mean particle size and zeta potential of the polyplexes prepared in 5% (w/v) glucose at 3:1 (+/-) charge ratio were approximately 100 nm and 20 mV, respectively. The surface characterization of polyplexes as determined by atomic force microscopy showed complete condensation of DNA with an ellipsoidal structure in Z direction. The levels of mIL-12 p40, mIL-12 p70, and mIFN-gamma were significantly higher for PAGA/pmIL-12 complexes compared to that of naked pmIL-12. This is in good agreement with RT-PCR data, which showed significant levels of mIL-12 p35 expression. The PAGA/pmIL-12 complexes did not induce any cytotoxicity in CT-26 cells as evidenced by 3-¿4, 5-dimethylthiazol-2-yl¿-2,5-diphenyltetrazolium bromide assay and showed enhanced antitumor activity in vivo compared to naked pmIL-12. PAGA/pmIL-12 complexes are nontoxic and significantly enhance mIL-12 expression at mRNA and protein levels both in vitro and in vivo.

Non-viral peptide-based approaches to gene delivery

To achieve effective non-viral gene therapy, the control of in vitro and in vivo stability, cellular access, intracellular trafficking and nuclear retention of plasmids must be achieved. Inefficient endosomal release, stability against cytosolic nucleases, cytoplasmic transport and nuclear entry of plasmids are amongst some of the key limiting factors in the use of plasmids for effective gene therapy. Synthetic peptide-based gene delivery systems can be designed for DNA compaction, serum stability, cell-specific targeting, endosomolysis, cytoplasmic stability and nuclear transport. The stability of compacted DNA under physiological conditions can be enhanced by the use of hydrophilic polymers, such as polyethylene glycol. The aims of this review are to (i) explore theoretical and experimental aspects of DNA compaction, (ii) describe approaches for stabilizing compacted DNA, (iii) assess techniques used for characterization of compacted DNA, and (iv) review possible use of peptides for efficient gene transfer.

Pharmaceutical perspectives of nonviral gene therapy

The use of nonviral plasmid-based gene medicines represents an attractive in vivo gene transfer strategy that is simple and lacks many risks that are inherent to viral systems. Commercialization of gene medicines requires a thorough analysis of business opportunities, unmet clinical needs, competitive products under development, and issues related to intellectual property. Synthetic gene delivery systems are designed to control the location of a gene within the body by affecting distribution and access of a gene expression system to the target cell, and/or recognition by a cell surface receptor and uptake followed by intracellular and nuclear translocation. Plasmid-based gene expression systems are designed to control the level, fidelity, and duration of in vivo production of a therapeutic gene product. This review will provide insights into the potentials of plasmid-based gene therapy and critical evaluation of gene delivery sciences and clinical applications of gene medicines.

Gene expression and antitumor effects following direct interferon (IFN)-gamma gene transfer with naked plasmid DNA and DC-chol liposome complexes in mice

Gene expression was assessed in three types of mouse solid tumors after direct injection of naked plasmid DNA encoding the luciferase gene (pCMV-Luc) and its DC-chol liposome complexes. Intratumoral injection of 5 or 100 micrograms naked pCMV-Luc into subcutaneously inoculated mouse colon tumor (CT-26), fibrosarcoma (MCA-15) and bladder carcinoma (MBT-2) resulted in significant gene expression. A DC-chol liposome formulation (5 micrograms pCMV-Luc complexed with 25 micrograms DC-chol liposome) showed lower level of gene expression in the tumor models. Based on the results using the reporter gene, we examined the antitumor effect after direct interferon-gamma (IFN-gamma) gene transfer into CT-26 tumors. A significant IFN-gamma production and growth inhibition were obtained following direct intratumoral injection of IFN-gamma gene with naked plasmid DNA (pCMV-Mu gamma). Interestingly, pCMV-Mu gamma/DC-chol liposome complexes exhibited more pronounced growth inhibitory effect despite lower IFN-gamma production. Induction of CT-26 specific antitumor immunity by IFN-gamma gene transfer was confirmed by rejection of a CT-26 tumor challenge in the mice showing complete regression of CT-26 tumors after both treatments. Further analysis demonstrated that a significant cDNA-independent induction of IFN-beta and TNF-alpha occurred following injection with the liposome complexes, suggesting a nonspecific suppressive effect on CT-26 tumor growth by these cytokines. Thus, the present study has demonstrated that tumor tissue might be a promising target for direct IFN-gamma gene transfer with plasmid-based nonviral vectors. It is also suggested that immunomodulatory effects by various cytokines could be involved in antitumor effects after direct intratumoral injection of plasmid DNA formulations.

Biodistribution and gene expression of lipid/plasmid complexes after systemic administration

The objectives of this study were to investigate the influence of physicochemical properties of lipid/plasmid complexes on in vivo gene transfer and biodistribution characteristics. Formulations based on 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA) and novel biodegradable cationic lipids, such as ethyl dioleoyl phosphatidylcholine (EDOPC), ethyl palmitoyl myristyl phosphatidylcholine (EPMPC), myristyl myristoyl carnitine ester (MMCE), and oleyl oleoyl L-carnitine ester (DOLCE), were assessed for gene expression after tail vein injection of lipid/plasmid complexes in mice. Gene expression was influenced by cationic lipid structure, cationic lipid-to-colipid molar ratios, plasmid-to-lipid charge ratios, and precondensation liposome size. Detectable levels of human growth hormone (hGH) in serum, human factor IX (hFIX) in plasma, and chloramphenicol acetyltransferase (CAT) in the lung and liver were observed with positively charged lipid/plasmid complexes prepared from 400-nm extruded liposomes with a cationic lipid-to-colipid ratio of 4:1 (mol/mol). Intravenous administration of lipid/CAT plasmid complexes resulted in distribution of plasmid DNA mainly to the lung at 15 min after injection. Plasmid DNA accumulation in the liver increased with time up to 24 hr postinjection. There was a 10-fold decrease in the amount of plasmid DNA in the lung at 15 min after injection, when the lipid/plasmid complex charge ratio was decreased from 3:1 to 0.5:1 (+/-). Bright fluorescent aggregates were evident in in vivo-transfected lung with the positively charged pCMV-CAT/DOLCE:dioleyl phosphatidylethanolamine (DOPE) (1:1, mol/mol) complexes, while more discrete punctate fluorescence was observed with a 4:1 molar ratio of cationic lipid:colipid formulations. Preinjection of polyanions such as plasmid, dextran sulfate, polycytidic acid, and polyinosinic acid decreased hGH expression, whereas the preinjection of both positively charged and neutral liposomes had no effect on hGH serum levels. Of the cationic lipids tested, DOLCE was found to be the most effective potentially biodegradable cationic lipid. A correlation between gene expression and cationic lipid:colipid ratios and lipid-to-plasmid charge ratio was also observed for DOTMA- and DOLCE-based formulations.

Involvement of specific mechanism in plasmid DNA uptake by mouse peritoneal macrophages

The binding and uptake of plasmid DNA encoding luciferase reporter gene (pCMV-Luc) were studied in vitro using cultured mouse peritoneal macrophages. A significant and time-dependent cellular association of [32P]pCMV-Luc with resident macrophages was observed at 37 degrees C and this decreased at 4 degrees C. The binding at 4 degrees C was saturable and a Scatchard plot gave a maximum binding capacity of 0.81 microgram/mg-protein and a dissociation constant of 0.30 microgram/ml. The binding of [32P]-pCMV-Luc was inhibited by polyinosinic acid, dextran sulfate and salmon sperm DNA, but not by polycytidylic acid, dextran and EDTA. A confocal microscopic study demonstrated that fluorescein-labeled pCMV-Luc was internalized at 37 degrees C while only cell surface binding occurred at 4 degrees C. No significant luciferase gene expression was obtained after incubation with a high concentration (100 micrograms/ml) of pCMV-Luc. These data suggest that plasmid DNA is taken up by macrophages via a mechanism mediated by a receptor like the macrophage scavenger receptor.

Cationic lipid-based gene delivery systems: pharmaceutical perspectives

Gene delivery systems are designed to control the location of administered therapeutic genes within a patient's body. Successful in vivo gene transfer may require (i) the condensation of plasmid and its protection from nuclease degradation, (ii) cellular interaction and internalization of condensed plasmid, (iii) escape of plasmid from endosomes (if endocytosis is involved), and (iv) plasmid entry into cell nuclei. Expression plasmids encoding a therapeutic protein can be, for instance, complexed with cationic liposomes or micelles in order to achieve effective in vivo gene transfer. A thorough knowledge of pharmaceutics and drug delivery, bio-engineering, as well as cell and molecular biology is required to design optimal systems for gene therapy. This mini-review provides a critical discussion on cationic lipid-based gene delivery systems and their possible uses as pharmaceuticals.

Physicochemical and disposition characteristics of antisense oligonucleotides complexed with glycosylated poly(L-lysine)

The disposition characteristics of a 20 mer antisense phosphodiester oligonucleotide (PO) and its fully phosphorothioated derivative (PS) alone or complexed with glycosylated poly(L-lysine) (galactosylated polylysine, Gal-PLL; mannosylated polylysine, Man-PLL) were studied in mice in relation to their physicochemical characteristics. Good complex formation was obtained at a ratio of 1:0.6, w/w [oligonucleotides (ODNs)/carrier]. The 1:0.6 weight ratio of ODNs/Gal-PLL and ODNs/Man-PLL complexes had zeta potentials of -27 to -31 mV and mean particle size of 100 to 160 nm. After intravenous injection, 35S-labeled ODNs were eliminated rapidly from the circulation; however, their organ disposition characteristics depended on their type. Complex formation with glycosylated PLL increased the hepatic uptake and decreased the urinary clearance of these ODNs to a great extent. These complexes were taken up by both liver parenchymal cells (PC) and nonparenchymal cells (NPC). However, ODNs/Gal-PLL complexes showed a fairly high PC concentration, whereas ODNs/Man-PLL complexes distributed equally to both PC and NPC. The hepatic uptakes of PS/Gal-PLL and PS/Man-PLL complexes were partially inhibited by prior administration of Gal-BSA and Man-BSA, respectively, suggesting their hepatic uptake via the respective receptor-mediated endocytosis. However, uptake by galactose receptors of Kupffer cells, zeta potential, particle size, and Kupffer cell phagocytosis also seem to influence their uptake process. In conclusion, this study illustrates that ODNs can be delivered to hepatocytes and macrophages via galactose and mannose receptors, respectively.

Development of targeted delivery systems for nucleic acid drugs

Our increased understanding of disease pathogenesis is the basis for developing novel nucleic acid drugs. The main challenge encountered in this development is how to maintain therapeutically meaningful concentrations of the drugs in the vicinity of their targets for the desired periods. The intrinsic difficulty arises from the fact that nucleic acid drugs are not readily transported across membranes. Hence, their delivery and transport characteristics at the whole body, organ and cellular levels need to be thoroughly examined. Liposomes and receptor-mediated polycation systems are promising carriers for their delivery in vivo. There are many barriers to be overcome for successful antisense and gene therapies. Along with other factors, disposition, stability against nucleases, binding to cell surface receptor and internalization, and intracellular trafficking affect the in vivo delivery and efficacy of nucleic acid drugs. This review article discusses the delivery and transport of these compounds.

Nonviral vectors for in vivo gene delivery: physicochemical and pharmacokinetic considerations

The use of nonviral vectors is an attractive in vivo gene delivery strategy that is simpler than, and lacks some risks inherent in, viral systems. Liposomes and receptor-mediated polycation systems are promising carriers for delivery and expression of plasmid DNA encoding genes into the target cells. Many barriers need to be overcome for successful in vivo DNA delivery using these carrier systems. Such factors as extent of DNA condensation, particle size of the DNA complex, route of administration, stability against nucleases, target sites, in vivo disposition, binding to cell surface receptor and internalization, and intracellular trafficking affect in vivo gene delivery and expression. This review will provide a critical discussion of the merits and limitations of liposomal and polycationic carrier systems for gene transfer from the viewpoints of their physicochemical and pharmacokinetic properties.

Disposition of oligonucleotides in isolated perfused rat kidney: involvement of scavenger receptors in their renal uptake

The objective of this study was to clarify the renal disposition characteristics of a 20-mer model phosphodiester oligonucleotide and its partially (PS3) and fully (PS) phosphorothioated derivatives, in isolated rat perfused kidney. Venous outflow and urinary excretion pattern, as well as tissue accumulation of radioactivity after bolus injection of 32P-labeled oligonucleotides, were evaluated under both filtering and nonfiltering conditions. The binding affinity of oligonucleotides to bovine serum albumin in the perfusate increased as the number of sulfur atoms present in the oligonucleotide molecules increased, resulting in 21, 60 and 86% binding to bovine serum albumin for phosphodiester oligonucleotide, PS3 and PS, respectively. The apparent steady-state distribution volumes of the oligonucleotides, as calculated from the venous outflow patterns, were larger than that of inulin, which corresponds to the extracellular volume of the kidney, suggesting their interaction with tissue from the vascular space. PS showed the largest distribution volume. Urinary excretion of oligonucleotides was greatly restricted, compared with that of inulin, which was used as a marker of glomerular filtration rate. The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. The uptake of oligonucleotides from the capillary side increased as the number of sulfur atoms present in the molecules increased, suggesting sulfur atom-dependent interactions between oligonucleotides and renal tissue. In addition, the uptake of PS3 was a saturable process. Furthermore, coadministration of dextran sulfate and polyinosinic acid inhibited the renal uptake of PS3, whereas polycytidic acid and 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid did not, suggesting that oligonucleotides were taken up via the scavenger receptor-mediated process for polyanions. These findings provide valuable information for the development of delivery systems for antisense oligonucleotides.

Disposition characteristics of plasmid DNA in the single-pass rat liver perfusion system

PURPOSE

To define the hepatic uptake mechanism of a plasmid DNA, we quantitated the uptake of pCAT (plasmid DNA encoding chloramphenicol acetyltransferase reporter gene fused to simian virus 40 promoter), a model plasmid, after a single pass through the perfused rat liver using albumin- and erythrocyte-free Krebs-Ringer bicarbonate buffer (pH 7.4).

METHODS

[32P]pCAT was introduced momentarily into this system from the portal vein as a bolus input or constant infusion mode, and the outflow patterns and hepatic uptake were evaluated using statistical moment analysis.

RESULTS

The venous outflow samples had electrophoretic bands similar to that of the standard pCAT, suggesting that the plasmid is fairly stable in the perfusate during liver perfusion. In bolus experiments, pCAT was largely taken up by the liver and the uptake was decreased with increase in injected dose. Statistical moment analysis against outflow patterns demonstrated that the apparent volume of distribution of pCAT was greater than that of human serum albumin, indicating a significant reversible interaction with the tissues. The results of collagenase perfusion experiments suggest that the hepatic accumulation of pCAT occurred preferentially in the nonparenchymal cells (NPC). The amount of total recovery in the liver decreased substantially by preceding administration of polyinosinic acid, dextran sulfate, succinylated bovine serum albumin, but not by polycytidylic acid. This suggests that pCAT is taken up by the liver via scavenger receptors for polyanions on the NPC. In constant infusion experiments, the presence of 2,4-dinitrophenol and NH4Cl caused a significant increase in the outflow concentration of [32P]pCAT and decrease by half in the total hepatic recovery than that of plasmid DNA administered alone, suggesting that plasmid DNA may undergo internalization by the NPC.

CONCLUSIONS

The liver plays an important role in the elimination of plasmid DNA and a successful delivery system will be required to avoid its recognition by the scavenger receptors on the liver NPC.

Uptake characteristics of oligonucleotides in the isolated rat liver perfusion system

The objective of this study was to examine the hepatic disposition characteristics of 20-mer model phosphodiester oligonucleotide (PO) and its partially phosphorothioated (PS3) and fully phosphorothioated (PS) derivatives in the single-pass isolated rat liver perfusion system. [32P]-labeled oligonucleotides were momentarily introduced into this system through the portal vein as a bolus input mode, and the venous outflow patterns were evaluated using statistical moment analysis. The apparent volumes of distribution of these oligonucleotides were greater than those of reference substances for vascular space (erythrocytes) and extracellular space (human serum albumin), indicating a significant interaction between oligonucleotides and the liver. Significant hepatic uptake of oligonucleotides was also observed. About 20%, 36%, and 52% of the injected dose (3 micrograms/rat) was taken up by the liver during a single passage after bolus injection of PO, PS3, and PS, respectively. In the case of PS injection, slow efflux from the liver was observed in the latter phase of perfusion. This suggests that the hepatic uptake process of these oligonucleotides greatly depended on their types. The results of collagenase perfusion experiments suggest that PS3 oligonucleotides were taken up by both liver parenchymal and nonparenchymal cells. The amount of total recovery in the liver decreased substantially by coadministration of polyinosinic acid, dextran sulfate, polycytidic acid and 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid. This suggests that PS3 was taken up by the liver as an anionic molecule in a nonspecific manner.

Physicochemical and pharmacokinetic characteristics of plasmid DNA/cationic liposome complexes

The objectives of this study were (i) to characterize the plasmid DNA encoding the chloramphenicol acetyltransferase reporter gene (pCAT) complexed with cationic liposomes (Lipofectin and LipofectACE) in terms of particle size and zeta potential, (ii) to compare pharmacokinetic characteristics, and (iii) to study the hepatic uptake mechanisms. DNA/LipofectACE complexes showed a negative zeta potential of -36 mV at 1:5 w/w ratio, but a positive zeta potential of (19 mV at 1:10 w/w ratio. Lipofectin samples showed a positive zeta potential) of 21-28 mV at these ratios. These preparations showed a wide particle size distribution ranging from 600 to 1200 nm. Following intravenous injection of 1:10 w/w ratio [32P]pCAT/liposome complexes at a dose of 0.1 mg DNA/kg into the tail vein of mice, radioactivity was rapidly eliminated from the plasma and almost 50-60% of the dose was taken up by the liver within 5 min after administration. Plasmid DNA/liposome complexes were predominantly taken up by the liver nonparenchymal cells. The hepatic uptake was inhibited by preceding administration of dextran sulfate (DS), but not by polycytidic acid (poly[C]) and polyinosinic acid (poly[I]), suggesting the involvement of a phagocytic process. We suggest that these complexes are preferentially taken up by the liver nonparenchymal cells mainly via Kupffer cell phagocytosis.

In vivo disposition characteristics of plasmid DNA complexed with cationic liposomes

To control disposition and hence gene expression, we investigated the disposition characteristics of plasmid DNA complexed with the cationic liposomes Lipofectin and LipofectACE after intravenous injection in mice via the tail vein. The optimum ratios of DNA and liposome complexes were selected through in vitro cytotoxicity and transfection studies. The highest transfection was found at the DNA:liposome ratio of 1:5 w/w. Hence, this ratio was used for in vivo disposition studies, and the distribution patterns were compared with that of naked pCAT. Following intravenous injection of [32P] pCAT, radioactivity was rapidly eliminated from plasma and approximately 60% of the dose was taken up by the liver within 1.5 min. In the case of LipofectACE samples, radioactivity elimination from plasma was equally rapid, but its accumulation was observed in both the liver (35%) and the lung (45%). For Lipofectin samples, radioactivity was initially accumulated in both the liver (55%) and the lung (25%), but lung accumulation was not sustained beyond 5 min after administration. Both liposomal samples showed in vivo gene expression in the lung, heart, kidney and spleen, but not in the liver. Thus, the present study demonstrated that disposition and gene expression of pCAT can be controlled by complex formation with liposomes.