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

Construction of nanostructured DNA harbouring phosphorodiamidate morpholino oligonucleotide for controlled tissue distribution in mice

Phosphorodiamidate morpholino oligonucleotides (PMOs) are a class of antisense oligonucleotides used in the treatment of neuromuscular diseases. Their major drawbacks are high blood clearance and poor cellular delivery. Previously, we demonstrated that tripod-like nanostructured DNA, or tripodna, was efficiently taken up by macrophages and dendritic cells. In this study, we used iodine-125(¹²⁵I)-labelled PMOs, designed a tripodna harbouring an ¹²⁵I-PMO (¹²⁵I-PMO/tripodna), and evaluated whether this tripodna could control the pharmacokinetic properties of PMO. Gel electrophoresis showed that ¹²⁵I-PMO was almost completely incorporated into the tripodna. Compared to ¹²⁵I-PMO, ¹²⁵I-PMO/tripodna was more efficiently taken up by macrophage-like RAW264.7 cells. Moreover, after intravenous injection into mice, the area under the plasma concentration-time curve of ¹²⁵I-PMO/tripodna was significantly larger than that of ¹²⁵I-PMO. The distribution of ¹²⁵I-PMO/tripodna in the liver and spleen at 24 h was 32- and 51-fold higher than that of ¹²⁵I-PMO, respectively. The fractionation of liver cells revealed that non-parenchymal cells were the major cells contributing to the hepatic uptake of ¹²⁵I-PMO/tripodna. These results indicate that tripodna has the potential to deliver PMO, particularly to the liver and spleen.

Fetal and Placental DNA Stimulation of TLR9: A Mechanism Possibly Contributing to the Pro-inflammatory Events During Parturition

INTRODUCTION

While there is evidence for a relationship between cell-free fetal DNA (cffDNA) and parturition, questions remain regarding whether cffDNA could trigger a pro-inflammatory response on the pathway to parturition. We hypothesized that placental and/or fetal DNA stimulates toll-like receptor 9 (TLR9) leading to secretion of pro-inflammatory cytokines by macrophage cells.

METHODS

Four in vitro DNA stimulation studies were performed using RAW 264.7 mouse peritoneal macrophage cells incubated in media containing the following DNA particles: an oligodeoxynucleotide (ODN2395), intact genomic DNA (from mouse placentas, fetuses and adult liver), mouse DNA complexed with DOTAP (a cationic liposome forming compound), and telomere-depleted mouse DNA. Interleukin 6 (IL6) secretion was measured in the media by enzyme-linked immunosorbent assay; and the cell pellet was homogenized for protein content (picograms IL6/mg protein).

RESULTS

Robust IL6 secretion was observed in response to ODN2395 (a CpG-rich TLR9 agonist), mouse DNA-DOTAP complexes, and telomere-depleted mouse DNA in concentrations of 5 to 15 μg/mL. In contrast, ODN A151 (containing telomere sequence motifs), intact genomic mouse DNA, and restriction enzyme-digested DNA had no effect on IL6 secretion. The IL6 response was significantly inhibited by chloroquine (10 μg/mL), thereby confirming the important role for TLR9 in the response by macrophage cells.

CONCLUSIONS

DNA derived from mouse placentas and fetuses, and depleted of telomeric sequences, stimulates a robust pro-inflammatory response by macrophage cells, thereby supporting the hypothesis that cffDNA is able to stimulate an innate immune response that could trigger the onset of parturition. These findings are of clinical importance, as we search for effective treatment/prevention of preterm parturition.

Structure-Activity Relationship of PEGylated Polylysine Peptides as Scavenger Receptor Inhibitors for Non-Viral Gene Delivery

PEGylated polylysine peptides of the general structure PEG30 kDa-Cys-Trp-LysN (N = 10 to 30) were used to form fully condensed plasmid DNA (pGL3) polyplexes at a ratio of 1 nmol of peptide per μg of DNA (ranging from N:P 3:1 to 10:1 depending on Lys repeat). Co-administration of 5 to 80 nmols of excess PEG-peptide with fully formed polyplexes inhibited the liver uptake of (125)I-pGL3-polyplexes. The percent inhibition was dependent on the PEG-peptide dose and was saturable, consistent with inhibition of scavenger receptors. The scavenger receptor inhibition potency of PEG-peptides was dependent on the length of the Lys repeat, which increased 10-fold when comparing PEG30 kDa-Cys-Trp-Lys10 (IC50 of 20.2 μM) with PEG30 kDa-Cys-Trp-Lys25 (IC50 of 2.1 μM). We hypothesize that PEG-peptides inhibit scavenger receptors by spontaneously forming small 40 to 60 nm albumin nanoparticles that bind to and saturate the receptor. Scavenger receptor inhibition delayed the metabolism of pGL3-polyplexes, resulting in efficient gene expression in liver hepatocytes following delayed hydrodynamic dosing. PEG-peptides represent a new class of scavenger inhibitors that will likely have broad utility in blocking unwanted liver uptake and metabolism of a variety of nanoparticles.

"Evolving nanoparticle gene delivery vectors for the liver: What has been learned in 30 years"

Nonviral gene delivery to the liver has been under evolution for nearly 30years. Early demonstrations established relatively simple nonviral vectors could mediate gene expression in HepG2 cells which understandably led to speculation that these same vectors would be immediately successful at transfecting primary hepatocytes in vivo. However, it was soon recognized that the properties of a nonviral vector resulting in efficient transfection in vitro were uncorrelated with those needed to achieve efficient nonviral transfection in vivo. The discovery of major barriers to liver gene transfer has set the field on a course to design biocompatible vectors that demonstrate increased DNA stability in the circulation with correlating expression in liver. The improved understanding of what limits nonviral vector gene transfer efficiency in vivo has resulted in more sophisticated, low molecular weight vectors that allow systematic optimization of nanoparticle size, charge and ligand presentation. While the field has evolved DNA nanoparticles that are stable in the circulation, target hepatocytes, and deliver DNA to the cytosol, breaching the nucleus remains the last major barrier to a fully successful nonviral gene transfer system for the liver. The lessons learned along the way are fundamentally important to the design of all systemically delivered nanoparticle nonviral gene delivery systems.

Cell-Free Fetal DNA, Telomeres, and the Spontaneous Onset of Parturition

Multiple previous reports have provided compelling support for the premise that spontaneous parturition is mediated by activation of inflammation-related signaling pathways leading to increased secretion of cytokines and chemokines, the influx of neutrophils and macrophages into the pregnant uterus, increased production of uterine activation proteins (eg, connexin-43, cyclo-oxygenase-2, oxytocin receptors, etc), activation of matrix metalloproteinases, and the release of uterotonins leading to cervical ripening, membrane rupture, and myometrial contractions. The missing link has been the fetal/placental signal that triggers these proinflammatory events in the absence of microbial invasion and intrauterine infection. This article reviews the biomedical literature regarding the increase in cell-free fetal DNA (cffDNA), which is released during apoptosis in the placenta and fetal membranes at term, the ability of apoptosis modified vertebrate DNA to stimulate toll-like receptor-9 (TLR9) leading to increased release of cytokines and chemokines, and the potential "fail-safe" role for the anti-inflammatory cytokine IL-10. This article also reviews the literature supporting the key role that telomere loss plays in regard to increasing the ability of vertebrate (including placental) DNA to stimulate TLR9, and in regard to signaling the onset of apoptosis in the placenta and fetal membranes, thereby providing a biologic clock that determines the length of gestation and the timing for the onset of parturition. In summary, this literature review provides a strong rationale for future research to test the hypothesis that telomere loss and increased cffDNA levels trigger the proinflammatory events leading to the spontaneous onset of parturition in mammals: the "cffDNA/telomere hypothesis."

Interaction of nucleic acids with the glycocalyx

Mammalian cells resist the uptake of nucleic acids. The lipid bilayer of the plasma membrane presents one barrier. Here, we report on a second physicochemical barrier for uptake. To create a sensitive probe for nucleic acid-cell interactions, we synthesized fluorescent conjugates in which lipids are linked to DNA oligonucleotides. We found that these conjugates incorporate readily into the plasma membrane but are not retained there. Expulsion of lipid-oligonucleotide conjugates from the plasma membrane increases with oligonucleotide length. Conversely, the incorporation of conjugates increases markedly in cells that lack the major anionic components of the glycocalyx, sialic acid and glycosaminoglycans, and in cells that had incorporated highly cationic lipids into their plasma membrane. We conclude that anionic oligosaccharides provide a formidable barrier to the uptake of nucleic acids by mammalian cells. This conclusion has implications for genomic stability, as well as the delivery of genes and siRNAs into mammalian cells.

Glycyrrhizin and isoliquiritigenin suppress the LPS sensor toll-like receptor 4/MD-2 complex signaling in a different manner

Recent evidences suggest that the extracts of plant products are able to modulate innate immune responses. A saponin GL and a chalcone ILG are representative components of Glycyrrhiza uralensis, which attenuate inflammatory responses mediated by TLRs. Here, we show that GL and ILG suppress different steps of the LPS sensor TLR4/MD-2 complex signaling at the receptor level. Extract of G. uralensis suppressed IL-6 and TNF-α production induced by lipid A moiety of LPS in RAW264.7 cells. Among various G. uralensis-related components of saponins and flavanones/chalcones, GL and ILG could suppress IL-6 production induced by lipid A in dose-dependent manners in RAW264.7 cells. Furthermore, elevation of plasma TNF-α in LPS-injected mice was attenuated by passive administration of GL or ILG. GL and ILG inhibited lipid A-induced NF-κB activation in Ba/F3 cells expressing TLR4/MD-2 and CD14 and BMMs. These components also inhibited activation of MAPKs, including JNK, p38, and ERK in BMMs. In addition, GL and ILG inhibited NF-κB activation and IL-6 production induced by paclitaxel, a nonbacterial TLR4 ligand. Interestingly, GL attenuated the formation of the LPS-TLR4/MD-2 complexes, resulting in inhibition of homodimerization of TLR4. Although ILG did not affect LPS binding to TLR4/MD-2, it could inhibit LPS-induced TLR4 homodimerization. These results imply that GL and ILG modulate the TLR4/MD-2 complex at the receptor level, leading to suppress LPS-induced activation of signaling cascades and cytokine production, but their effects are exerted at different steps of TLR4/MD-2 signaling.

Involvement of activated transcriptional process in efficient gene transfection using unmodified and mannose-modified bubble lipoplexes with ultrasound exposure

Recently, our group developed ultrasound (US)-responsive and mannose-modified gene carriers (Man-PEG(2000) bubble lipoplexes), and successfully obtained a high level of gene expression in mannose receptor-expressing cells following gene transfection using Man-PEG(2000) bubble lipoplexes and US exposure. We also reported that large amounts of plasmid DNA (pDNA) were transferred into the cytoplasm of the targeted cells in the gene transfection using this method. In the present study, we investigated the involvement of transcriptional processes on enhanced gene expression obtained by unmodified and Man-PEG(2000) bubble lipoplexes with US exposure. The transcriptional process related to activator protein-1 (AP-1) and nuclear factor-κB (NFκB) was activated by US exposure, and was founded to be involved in enhanced gene expression obtained by gene transfection using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure. On the other hand, activation of AP-1 and NFκB pathways followed by US exposure was hardly involved in the inflammatory responses in the gene transfection using this method. These findings suggest that activation of AP-1 and NFκB followed by US exposure is involved in the enhanced gene expression using unmodified and Man-PEG(2000) bubble lipoplexes with US exposure, and the selection of pDNAs activated by US exposure is important in this gene transfection method.

Human serum amyloid P functions as a negative regulator of the innate and adaptive immune responses to DNA vaccines

The utility of DNA vaccines has been limited by their failure to elicit sufficiently potent immune responses in many human applications, whereas DNA vaccinations in mice have been very successful. However, the underlying mechanisms remain unknown. We hypothesize that serum amyloid P component (SAP), which has a species-specific, DNA-binding ability, contributes to the differences between human and mice and then limits DNA vaccine's efficacy in vivo. In our study, DNA vaccine-induced adaptive immune responses were also significantly decreased in the human SAP (hSAP) transgenic mice. Using human promonocytic cell line THP-1-derived macrophages as a cell model, we found that cells incubated with a hSAP-DNA complex showed significant defects in innate immune activations, whereas mouse SAP had similar, albeit very weak, activities. hSAP also significantly inhibited the functions of two identified DNA sentinels, high-mobility group B protein 1 and antimicrobial peptide LL37, and redirected DNA update to FcRs leading to endocytosis and endosomal degradation. We also found that a chemical SAP inhibitor strongly recovered the suppressed innate immune responses to DNA in the presence of human serum and enhanced the immunogenicity of DNA vaccines in vivo. Our data indicated that SAP is a key negative regulator for innate immune responses to DNA and may be partly responsible for the insufficient immune responses after DNA vaccinations in humans. SAP suppression may be a novel strategy for improving efficacy of human DNA vaccines and requires further clinical investigations.

Gene delivery by surface immobilization of plasmid to tissue-engineering scaffolds

Biomaterial scaffolds that serve as vehicles for gene delivery to promote expression of inductive factors have numerous regenerative medicine applications. In this report, we investigate plasmid delivery from biomaterial scaffolds using a surface immobilization strategy. Porous scaffolds were fabricated from poly(D,L-lactide-co-glycolide) (PLG), and plasmids were immobilized by drying. In vitro plasmid release indicated that the majority (>70%) of adsorbed plasmids were released within 24 h and >98% within 3 days; however, in vivo implantation of the scaffolds at the subcutaneous site yielded transgene expression that persisted for at least 28 weeks and was localized to the site of implantation. Histological analysis of DNA-adsorbed scaffolds indicated that macrophages at the scaffold were transfected in the first 2 weeks after implantation, whereas muscle cells adjacent to the implant primarily expressed the transgene at 4 weeks. In addition to localized gene expression, a secreted protein (human factor IX) was retained at the implant site and not available systemically after 3 days, indicating minimal off-target effects. These findings show that surface immobilization of plasmid onto microporous PLG scaffolds can produce localized and long-term gene expression in vivo, which may be used to enhance the bioactivity of scaffolds used for regenerative medicine.

DNA-based nano-sized systems for pharmaceutical and biomedical applications

DNA is one of the most important components for all living organisms and many species, including humans, use DNA to store and transmit genetic information to new generations. Recent advances in the handling of DNA have made it possible to use DNA as a building block of nano-sized materials with precisely designed architectures. Although various approaches have been proposed to obtain DNA assemblies with designed architecture in the nano- to micrometer range, there is little information about their interaction with biological components, including target molecules. Understanding the interaction between DNA assemblies and the body is highly important for successful pharmaceutical and biomedical applications. Here, we first review the basic aspects of externally administered DNA molecules, including the stability, permeability and delivery issues. Then, we discuss the unique responses observed in the interaction of structured DNA assemblies and cells expressing Toll-like receptor-9, the receptor responsible for the recognition of unmethylated CpG dinucleotides that are abundant in the DNA of invading pathogens, such as bacteria and viruses.

Glycyrrhizin, the main active compound in liquorice, attenuates pro-inflammatory responses by interfering with membrane-dependent receptor signalling

The triterpene glycoside glycyrrhizin is the main active compound in liquorice. It is used as a herbal medicine owing to its anticancer, antiviral and anti-inflammatory properties. Its mode of action, however, remains widely unknown. In the present study, we aimed to elucidate the molecular mechanism of glycyrrhizin in attenuating inflammatory responses in macrophages. Using microarray analysis, we found that glycyrrhizin caused a broad block in the induction of pro-inflammatory mediators induced by the TLR (Toll-like receptor) 9 agonist CpG-DNA in RAW 264.7 cells. Furthermore, we found that glycyrrhizin also strongly attenuated inflammatory responses induced by TLR3 and TLR4 ligands. The inhibition was accompanied by decreased activation not only of the NF-kappaB (nuclear factor kappaB) pathway but also of the parallel MAPK (mitogen-activated protein kinase) signalling cascade upon stimulation with TLR9 and TLR4 agonists. Further analysis of upstream events revealed that glycyrrhizin treatment decreased cellular attachment and/or uptake of CpG-DNA and strongly impaired TLR4 internalization. Moreover, we found that the anti-inflammatory effects were specific for membrane-dependent receptor-mediated stimuli, as glycyrrhizin was ineffective in blocking Tnfa (tumour necrosis factor alpha gene) induction upon stimulation with PMA, a receptor- and membrane-independent stimulus. These observations suggest that the broad anti-inflammatory activity of glycyrrhizin is mediated by the interaction with the lipid bilayer, thereby attenuating receptor-mediated signalling.

Cellular activation by plasmid DNA in various macrophages in primary culture

Macrophages are an important group of cells responsible for the inflammatory response to unmethylated CpG dinucleotide (CpG motif) in plasmid DNA (pDNA) via Toll-like receptor 9 (TLR9). This finding is primarily based on in vitro studies. Previous in vivo studies also have suggested that tissue macrophages are involved in inflammatory cytokine release in the circulation following intravenous administration of pDNA to mice. However, the relationship between the in vitro and in vivo studies has not been sufficiently clarified. To gain insight into which types of cells are responsible for the production of cytokines upon interaction with pDNA, peritoneal macrophages, splenic macrophages, hepatic nonparenchymal cells (NPCs) including Kupffer cells and mesangial cells were isolated from mice. All types of primary cultured cells, except for mesangial cells, express TLR9 at varying levels. Splenic macrophages and hepatic NPCs were activated to produce tumor necrosis factor-alpha (TNF-alpha) by naked pDNA, whereas peritoneal macrophages and mesangial cells were not. pDNA complexed with N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethyl-ammonium chloride/cholesterol liposome induced TNF-alpha in the splenic macrophages but not in the other cell types. These results indicate that splenic macrophages and hepatic NPCs are closely involved in TNF-alpha production in response to pDNA.

Layered PLG scaffolds for in vivo plasmid delivery

Gene delivery from tissue engineering scaffolds can induce localized expression of tissue inductive factors to direct the function of progenitor cells, either endogenous or transplanted. In this report, we developed a layering approach for fabricating scaffolds with encapsulated plasmid, and investigated in vivo gene transfer following implantation into intraperitoneal fat, a widely used site for cell transplantation. Porous poly(lactide-co-glycolide) (PLG) scaffolds were fabricated using a gas foaming method, in which a non-porous layer containing plasmid was inserted between two porous polymer layers. The layered scaffold design decouples the scaffold structural requirements from its function as a drug delivery vehicle, and significantly increased the plasmid incorporation efficiency relative to scaffolds formed without layers. For multiple plasmid doses (200, 400, and 800mug), transgene expression levels peaked during the first few days and then declined over a period of 1-2 weeks. Transfected cells were observed both in the surrounding adipose tissue and within the scaffold interior. Macrophages were identified as an abundantly transfected cell type. Scaffolds delivering plasmid encoding fibroblast growth factor-2 (FGF-2) stimulated a 40% increase in the total vascular volume fraction relative to controls at 2 weeks. Scaffold-based gene delivery systems capable of localized transgene expression provide a platform for inductive and cell transplantation approaches in regenerative medicine.

What happens to the DNA vaccine in fish? A review of current knowledge

The primary function of DNA vaccines, a bacterial plasmid DNA containing a construct for a given protective antigen, is to establish specific and long-lasting protective immunity against diseases where conventional vaccines fail to induce protection. It is acknowledged that less effort has been made to study the fate, in terms of cellular uptake, persistence and degradation, of DNA vaccines after in vivo administration. However, during the last year some papers have given new insights into the fate of DNA vaccines in fish. By comparing the newly acquired information in fish with similar knowledge from studies in mammals, similarities with regard to transport, blood clearance, cellular uptake and degradation of DNA vaccines have been found. But the amount of DNA vaccine redistributed from the administration site after intramuscular administration seems to differ between fish and mammals. This review presents up-to-date and in-depth knowledge concerning the fate of DNA vaccines with emphasis on tissue distribution, cellular uptake and uptake mechanism(s) before finally describing the intracellular hurdles that DNA vaccines need to overcome in order to produce their gene product.

Unique cytokine production profile following stimulation with DNA in macrophages from NZB/W F1 mice

Nucleosome is the major autoantigen in systemic lupus erythematosus (SLE). Professional antigen-presenting cells (APCs), such as macrophages (M Phis) and dendritic cells (DCs), play the central roles in the acquisition of Ag-specific immune responses and activation of such APCs is required for the efficient Ag-presentation. Therefore, adjuvant activity of DNA in nucleosomes would cause the prominent effects on the production of anti-nucleosome antibodies. In this study, we report that elicited peritoneal M Phis from New Zealand Black/White F1 (NZB/W) mice showed a unique cytokine production profile following stimulation with DNA. M Phis from 5-week old NZB/W mice produced a higher amount of IL-6 and about a half amount of TNF-alpha after stimulation with DNA complexed with cationic liposomes compared with those from control ICR mice. These results suggest that M Phis of NZB/W mice have altered responsiveness to DNA and this might elevate the antigenicity of nucleosomes to induce the production of anti-nucleosome antibodies.

Efficient peritoneal dissemination treatment obtained by an immunostimulatory phosphorothioate-type CpG DNA/cationic liposome complex in mice

Peritoneal dissemination remains the most difficult type of metastasis to treat, and current systemic chemotherapy or radiotherapy tends to have little effect; therefore, immunotherapy using immunostimulatory CpG DNA could be a promising new therapeutic approach. Recently, we have reported that intraperitoneal administration of phosphodiester (PO) CpG DNA-lipoplex could efficiently inhibit peritoneal dissemination in mice. In this study, chemically modified phosphorothioate (PS)-CpG DNA and natural PO-CpG DNA were complexed with DOTMA/cholesterol cationic liposomes (PS-CpG DNA-lipoplex and PO-CpG DNA-lipoplex) and their antitumor activity was evaluated in a mouse model of peritoneal dissemination. Intraperitoneal administration of the PS-CpG DNA-lipoplex inhibited the proliferation of tumor cells in the greater omentum and the mesentery more efficiently than PO-CpG DNA-lipoplex. PS-CpG DNA-lipoplex induced higher cytokine production from primary cultured mouse peritoneal macrophages, suggesting that the high antitumor activity of the PS-CpG DNA-lipoplex is mediated by a high rate of cytokine production from immunocompetent cells such as macrophages. The serum transaminase levels of mice receiving intraperitoneal PS-CpG DNA-lipoplex treatment were measured to evaluate systemic toxicity, and these were found to be the same as those of untreated mice. These results suggest that intraperitoneal administration of PS-CpG DNA-lipoplex could be efficient immunotherapy for peritoneal dissemination.

The uptake and degradation of DNA is impaired in macrophages and dendritic cells from NZB/W F(1) mice

DNA/anti-DNA Ab immune complexes seem to play the critical roles in the development of systemic lupus erythematosus (SLE). However, little is known about the removal of DNA by MPhi and DC. We found that elicited peritoneal MPhis and BM-derived DCs from a lupus-prone strain of New Zealand Black/White F(1) (NZB/W) mice showed impaired DNA uptake and degradation compared with those from control ICR mice. The impairment was mainly observed as the reduced degradation of DNA probably in endosomal compartment and this impaired DNA degradation might, at least in part, result from the reduced DNA uptake in these phagocytic cells. In addition, these impairments was not related to the disease progression since the cells from diseased, 6-month-old NZB/W mice as well as the cells from prediseased, 5-week-old NZB/W mice also exhibited the similar impairment. We also found that the MPhis and DCs of diseased NZB/W mice showed reduced DNA binding at 4 degrees C. However, this reduced DNA binding could be restored to the control level by pretreatment with DNase. Interestingly, this pretreatment had little effect on the DNA uptake in MPhis and DCs of diseased NZB/W mice at 37 degrees C. Hence, the present results imply an impaired function of lupus MPhis and DCs of NZB/W mice to cause retained DNA clearance.

Specific uptake of plasmid DNA without reporter gene expression in Atlantic salmon (Salmo salar L.) kidney after intramuscular administration

In this study we investigated tissue distribution of pDNA after intramuscular and intravenous administration, cellular localisation, receptor-specific uptake, integrity of pDNA and transgene expression in Atlantic salmon (Salmo salar L). Anatomical distribution of plasmid DNA was determined using both radiotracing and fluorescence microscopy. Cellular uptake was studied in cultures of adherent anterior kidney leucocytes. The integrity of the pDNA in vivo was investigated by Southern blot analysis. Transcription of plasmid DNA encoded luciferase gene and protein synthesis were investigated in salmon tissues by means of real-time reverse transcription-polymerase chain reaction and enzyme activity measurements, respectively. Approximately 50% of the total recovered radioactivity was redistributed from the carcass 168h after intramuscular administration and accumulated mainly in the kidneys (37% of total). The majority of radiolabelled plasmid DNA administered intravenously was taken up within the first 15min mainly by the kidney. Intravenous co-administration of trace amounts of radiolabelled plasmid DNA with excess amounts of unlabelled plasmid DNA or formaldehyde treated albumin (a ligand for the scavenger receptors) significantly inhibited accumulation of the radiotracer in the kidney. Fluorescence microscopy demonstrated that fluorescence was localised intracellularly in cells lining the sinusoids of the kidney after intravenous administration of rhodamine-labelled plasmid DNA. Southern blot analysis demonstrated presence of supercoiled plasmid DNA in all organs and tissue samples 168h after intramuscular administration, but degradation products were only revealed at the administration site. Luciferase transcript and activity were only detectable at the administration site 24-168h after intramuscular administration of plasmid DNA. After incubation with trace amounts of radiolabelled plasmid DNA, only minor amounts of radiolabelled plasmid DNA were cell associated in cultures of adherent anterior kidney leucocytes. These results suggested that a substantial portion of radiolabelled plasmid DNA was redistributed from the carcass and was mainly cleared by a receptor-specific uptake in the kidney. Although intact plasmid DNA was detected in the kidney and other tissues, no luciferase transcripts or activity were detected in these samples at any time points investigated (24-168h), except for the administration site following intramuscular administration.

Identification of proteins released by mammalian cells that mediate DNA internalization through proteoglycan-dependent macropinocytosis

Naked DNA plasmid represents the simplest vehicle for gene therapy and DNA-based vaccination purposes; however, the molecular mechanisms of DNA uptake in mammalian cells are poorly understood. Here, we show that naked DNA uptake occurs via proteoglycan-dependent macropinocytosis, thus challenging the concept of a specific DNA-internalizing receptor. Cells genetically deficient in proteoglycans, which constitute a major source of cell-surface polyanions, exhibited substantially decreased uptake of likewise polyanionic DNA. The apparent paradox was explained by the action of DNA-transporting proteins present in conditioned medium. Complexes between these proteins and DNA require proteoglycans for cellular entry. Mass spectrometry analysis of cell medium components identified several proteins previously shown to associate with DNA and to participate in membrane transport of macromolecular cargo. The major pathway for proteoglycan-dependent DNA uptake was macropinocytosis, whereas caveolae-dependent and clathrin-dependent pathways were not involved, as determined by using caveolin-1 knock-out cells, dominant-negative constructs for dynamin and Eps15, and macropinocytosis-disruptive drugs, as well as confocal fluorescence co-localization studies. Importantly, a significant fraction of internalized DNA was translocated to the nucleus for expression. Our results provide novel insights into the mechanism of DNA uptake by mammalian cells and extend the emerging role of proteoglycans in macromolecular transport.

Plasmid DNA Uptake and Subsequent Cellular Activation Characteristics in Human Monocyte-Derived Cells in Primary Culture

Plasmid DNA (pDNA) uptake and subsequent cellular activation characteristics were studied in three types of human monocyte-derived cells, that is, human monocytes, macrophages, and dendritic cells (DCs) in primary culture. Naked pDNA was bound to and taken up by the macrophages and DCs while only significant binding occurred in the monocytes. pDNA binding to these monocyte-derived cells was significantly inhibited by polyinosinic acid (poly[I]), dextran sulfate, maleylated bovine serum albumin (Mal-BSA) and to a lesser extent by polycytidylic acid (poly[C]), but not by dextran or galactosylated BSA (Gal-BSA), mannosylated BSA (Man-BSA), suggesting that a specific mechanism for polyanions is involved in the pDNA binding. In cellular activation studies, naked pDNA could not induce TNF-alpha production from any monocyte-derived cells, regardless of the abundant presence of CpG motifs in the pDNA. However, when complexed with cationic liposomes, pDNA produced a significant amount of TNF-alpha from the human macrophages. TNF-alpha induction was not observed in the monocytes or DCs. Moreover, calf thymus DNA (CT DNA) complexed with cationic liposomes also induced TNF-alpha production to a similar extent in the human macrophages. These results indicate that, among human monocyte-derived cells, macrophages are activated by DNA when complexed with cationic liposomes in a CpG motif-independent manner.

DNA and its cationic lipid complexes induce CpG motif-dependent activation of murine dendritic cells

Unmethylated CpG motifs in bacterial DNA, but not in vertebrate DNA, are known to trigger an inflammatory response of antigen-presenting cells (APC). In this study, we investigated the cytokine release from murine dendritic cells (DC) by the addition of various types of DNA in the free or complexed form with cationic lipids. Naked plasmid DNA and Escherichia coli DNA with immunostimulatory unmethylated CpG motifs induced pro-inflammatory cytokine secretion from granulocyte-macrophage colony-stimulating factor (GM-CSF)-cultured bone marrow-derived DC and the DC cell-line, DC2.4 cells, though vertebrate calf thymus DNA (CT DNA) with less CpG motifs did not. These characteristics differed from mouse peritoneal resident macrophages that do not respond to any naked DNA. The amount of cytokines released from the DC was significantly increased by complex formation with cationic lipids when CpG-motif positive DNAs were used. Unlike murine macrophages or Flt-3 L cultured DC, GM-CSF DC did not release inflammatory cytokines in response to the addition of CT DNA/cationic lipid complex, suggesting that the activation is completely dependent on CpG motifs. Taken together, the results of the present study demonstrate that murine DC produce pro-inflammatory cytokines upon stimulation with CpG-containing DNAs and the responses are enhanced by cationic lipids. These results also suggest that DC are the major cells that respond to naked CpG DNA in vivo, although both DC and macrophages will release inflammatory cytokines after the administration of a DNA/cationic lipid complex.

Role of scavenger receptor MARCO in macrophage responses to CpG oligodeoxynucleotides

The macrophage Class A scavenger receptor MARCO (macrophage receptor with a collagenous structure) functions as a pattern-recognition receptor for bacterial components, but its role in responses to CpG oligonucleotide sequences (CpG-ODN) in microbial DNA has not been characterized. Phosphorothioate (PS)-linked CpG-ODN stimulated IL-12 and NO production in wild-type but not in MARCO-deficient, thioglycollate-elicited peritoneal macrophages. MARCO and the related class A receptor SR-A belong to a redundant system of receptors for PS ODNs. The ability of MARCO to bind CpG-ODNs and conversely, to costimulate IL-12 and NO production upon specific ligation with immobilized mAb is consistent with MARCO being a signaling receptor for CpG-ODNs, costimulating TLR9-mediated NO and IL-12 production in macrophages. In contrast to MARCO, SR-A is likely to mediate negative regulation of macrophage responses to CpG-ODNs. In particular, increased affinity toward SR-A may contribute to decreased potency of oligo G-modified CpG-ODNs in stimulating IL-12 production. The results suggest that differential involvement of activating and inhibitory membrane receptors, such as SR-A and MARCO, may underlie profound differences observed in biological activities of different ODN sequences.

Novel PEG-matrix metalloproteinase-2 cleavable peptide-lipid containing galactosylated liposomes for hepatocellular carcinoma-selective targeting

In order to obtain an HCC-selective drug delivery system, a novel functional lipid, which is cleaved by the protease activity of matrix metalloproteinase-2 (MMP-2), was developed. The amino group of dioleoylphosphatidylethanolamine (DOPE) was conjugated with PEGylated MMP-2 substrate peptide (Gly-Pro-Leu-Gly-Ile-Ala-Gly-Gln), and MMP-2-cleavable PEG-Peptide-DOPE (PEG-PD) was synthesized. When PEG-PD was incorporated in galactosylated liposomes (Gal-PEG-PD-liposomes), we expected that Gal-PEG-PD-liposomes would not be taken up by normal hepatocytes due to the steric hindrance effect, but would be activated around HCC cells by secreted MMPs. In the pretreatment by hMMP2 (1, 5, and 10mug/ml), an hMMP2 concentration-dependent higher uptake of Gal-PEG-PD-liposomes was observed in HepG2 cells, suggesting PEG-PD cleavage. In the presence of an excess of galactose, the uptake of Gal-PEG-PD-liposomes with hMMP2 was significantly inhibited, suggesting asialoglycoprotein receptor-mediated uptake of Gal-PEG-PD-liposomes following the PEG-PD cleavage. Pretreatment of Gal-PEG-PD-liposomes with the conditioned medium of B16BL6, which contained secreted MMPs, enhanced the binding to HepG2 cells, as in the case of hMMP-2 treatment. Moreover, the cytotoxicity of N(4)-octadecyl-1-beta-d-arabinofuranosylcytosine (NOAC) incorporated Gal-PEG-PD-liposomes was enhanced by hMMPs (5mug/ml) and its cytotoxicity was significantly reduced by the presence of an excess of galactose in HepG2 cells. In conclusion, Gal-PEG-PD-liposomes were successfully developed for novel HCC-selective targeting.

Differences in macrophage activation by bacterial DNA and CpG-containing oligonucleotides

Bacterial DNA activates mouse macrophages, B cells, and dendritic cells in a TLR9-dependent manner. Although short ssCpG-containing phosphodiester oligonucleotides (PO-ODN) can mimic the action of bacterial DNA on macrophages, they are much less immunostimulatory than Escherichia coli DNA. In this study we have assessed the structural differences between E. coli DNA and PO-ODN, which may explain the high activity of bacterial DNA on macrophages. DNA length was found to be the most important variable. Double-strandedness was not responsible for the increased activity of long DNA. DNA adenine methyltransferase (Dam) and DNA cytosine methyltransferase (Dcm) methylation of E. coli DNA did not enhance macrophage NO production. The presence of two CpG motifs on one molecule only marginally improved activity at low concentration, suggesting that ligand-mediated TLR9 cross-linking was not involved. The major contribution was from DNA length. Synthetic ODN >44 nt attained the same levels of activity as bacterial DNA. The response of macrophages to CpG DNA requires endocytic uptake. The length dependence of the CpG ODN response was found to correlate with the presence in macrophages of a length-dependent uptake process for DNA. This transport system was absent from B cells and fibroblasts.

Cellular uptake and activation characteristics of naked plasmid DNA and its cationic liposome complex in human macrophages

Plasmid DNA (pDNA) is an important macromolecular therapeutic agent suitable for DNA-based therapies, such as non-viral gene therapy and DNA vaccination. Unmethylated CpG motifs abundant in bacterial DNA, but not in vertebrate DNA, are known to trigger an inflammatory response, which inhibits transgene expression, while modulating immunological consequences following vaccination. We studied cellular uptake and activation characteristics of naked pDNA and its cationic liposome complex in human macrophage-like cells. The present study has demonstrated that naked pDNA was recognized by human macrophage-like cells via specific mechanisms for polyanions. Moreover, it has shown that pDNA complexed with cationic liposomes activates human macrophage-like cells to induce the production of tumor necrosis factor-alpha (TNF-alpha) in a CpG motif-independent manner, while any types of naked DNA could not induce TNF-alpha production from these cells, regardless of the presence of CpG motifs in pDNA or oligonucleotide (ODN). These findings form an important basis for DNA-based therapies including gene therapy and DNA vaccination.

Intracellular distribution of NFκB decoy and its inhibitory effect on TNFα production by LPS stimulated RAW 264.7 cells

Nuclear factor kappa B (NFkappaB) is a transcriptional factor for the expression of many cytokines that are involved in the pathogenesis of inflammatory diseases. Unstimulated NFkappaB sequestered in the cytoplasm bound to inhibitory proteins is called IkappaBs. Many activators of NFkappaB cause degradation of IkappaB proteins and free NFkappaB can enter the nucleus and induce gene expression. In this study, we analyzed the relationship between the intracellular distribution and pharmacological effect of NFkappaB decoy in RAW 264.7 cells. Most of the fluorescent labeled NFkappaB decoy was observed in the cytoplasm both with or without cationic transfection without LPS stimulation. Furthermore, under LPS stimulation, most of NFkappaB decoy was also observed in the cytoplasm. However, NFkappaB decoy effectively inhibited the production of TNFalpha in RAW 264.7 cells. The inhibitory effect of TNFalpha production by NFkappaB decoy transfected by cationic liposomes was much stronger than that by naked NFkappaB decoy, because the amount of cellular association of NFkappaB transfected by cationic liposome decoy was 7 times higher than that of naked NFkappaB decoy. This information is of great value for the design of NFkappaB decoy carrier systems.

Immunostimulatory capacity of DNA vaccine vectors in porcine PBMC: a specific role for CpG-motifs?

With the development of DNA vaccines in pigs, the possibility was investigated that the nature and the amount of certain CpG-motifs present on plasmid DNA might have an effect on their immunostimulatory capacity. A panel of three CpG-oligodeoxynucleotides (ODN) and three eukaryotic expression vectors currently used in experimental DNA vaccines in pigs (pcDNA1, pcDNA3.1 and pCI) were screened for their immunostimulatory activity on porcine PBMC by evaluating in vitro the lymphocyte proliferative responses and cytokine profiles (IL-1alpha, IL-2, IL-4, IL-6, IL-10, IFN-gamma, TGF-beta, TNF-alpha). The vectors were chosen so that they differed in number and nature of certain CpG-motifs present on their backbone. CpG-ODN A (5'ATCGAT3') and to a lesser extend CpG-ODN C (5'AACGTT3') significantly enhanced the proliferation of porcine PBMC in contrast to CpG-ODN B (5'GACGTT3') where no effect was observed. Furthermore, CpG-ODN A significantly induced IL-6 and TNF-alpha together with elevated levels of IFN-gamma and IL-2 mRNA expression even though considerable heterogeneity was observed in the response of individual pigs. Comparison of the three vectors showed significantly increased proliferative responses for both pcDNA3.1 and pCI combined with a significant increase in IL-6 mRNA levels for pCI. For pcDNA1, proliferation was absent together with significantly decreased levels of IL-6 and IFN-gamma. CpG-ODN and plasmids both suppressed the TGF-beta and IL-1alpha mRNA expression. Taken together, these data confirm the identity of an optimal immunostimulating CpG-motif in pigs (5'-ggTGCATCGATGCAG-3') and demonstrates that the choice of the vector or the insertion of immunostimulatory motifs can be important in the future design of DNA vaccines in pigs, although further research is necessary to explore the possible link between certain CpG-motifs and the immunogenicity of DNA vaccines.

Oil-in-water lipid emulsions: implications for parenteral and ocular delivering systems

Lipid emulsions (LEs) are heterogenous dispersions of two immiscible liquids (oil-in-water or water-in-oil) and they are subjected to various instability processes like aggregation, flocculation, coalescence and hence eventual phase separation according to the second law of thermodynamics. However, the physical stability of the LE can substantially be improved with help of suitable emulsifiers that are capable of forming a mono- or multi-layer coating film around the dispersed liquid droplets in such a way to reduce interfacial tension or to increase droplet-droplet repulsion. Depending on the concentrations of these three components (oil-water-emulsifier) and the efficiency of the emulsification equipments used to reduce droplet size, the final LE may be in the form of oil-in-water (o/w), water-in-oil (w/o), micron, submicron and double or multiple emulsions (o/w/o and w/o/w). The o/w type LEs (LE) are colloidal drug carriers, which have various therapeutic applications. As an intravenous delivery system it incorporates lipophilic water non-soluble drugs, stabilize drugs that tend to undergo hydrolysis and reduce side effects of various potent drugs. When the LE is used as an ocular delivery systems they increase local bioavailability, sustain the pharmacological effect of drugs and decrease systemic side effects of the drugs. Thus, the rationale of using LE as an integral part of effective treatment is clear. Following administration of LE through these routes, the biofate of LE associated bioactive molecules are somehow related to the vehicles disposition kinetics inside blood or eyeball. However, the LE is not devoid from undergoing various bio-process while exerting their efficacious actions. The purpose of this review is therefore to give an implication of LE for parenteral and ocular delivering systems.

Pharmacokinetics of Plasmid DNA-Based Non-viral Gene Medicine

Non-viral gene therapy can be realized by optimization of the pharmacokinetic properties of both the vector and the encoded therapeutic protein. A major obstacle to its successful clinical application is the limited ability of plasmid DNA, the most convenient gene-coding compound, to distribute within the body after in vivo administration. Under normal conditions, plasmid DNA and its non-viral vector complexes have difficulty in passing through various anatomical and biological barriers. These characteristics greatly limit the number and distribution of cells transduced with the vector, because transgene expression only occurs in cells that are reached by the vector. New approaches to the design of vectors as well as the methods of administration, such as electroporation and a hydrodynamic delivery, have increased the transgene expression in vivo, suggesting that improved distribution of plasmid DNA is possible by these approaches. In this chapter, the basic pharmacokinetic properties of naked plasmid DNA under normal conditions are first reviewed, then the properties of both naked and complexed plasmid DNA are discussed under conditions where significant transgene expression takes place.

Lipid Carrier Systems for Targeted Drug and Gene Delivery

For effective chemotherapy, it is necessary to deliver therapeutic agents selectively to their target sites, since most drugs are associated with both beneficial effects and side effects. The use of lipid dispersion carrier systems, such as lipid emulsions and liposomes, as carriers of lipophilic drugs has attracted particular interest. A drug delivery system can be defined as a methodology for manipulating drug distribution in the body. Since drug distribution depends on the carrier, administration route, particle size of the carrier, lipid composition of the carrier, electric charge of the carrier and ligand density of the targeting carrier, these factors must be optimized. Recently, the lipid carrier system has also been applied to gene delivery systems for gene therapy. However, in both drug and gene medicine cases, a lack of cell-selectivity limits the wide application of this kind of drug and/or gene therapy. Therefore, lipid carrier systems for targeted drug and gene delivery must be developed for the rational therapy. In this review, we shall focus on the progress of research into lipid carrier systems for drug and gene delivery following systemic or local injection.

Macrophage activation by a DNA/cationic liposome complex requires endosomal acidification and TLR9-dependent and -independent pathways

Previously, we showed that bacterial DNA and vertebrate DNA/cationic liposome complexes stimulate potent inflammatory responses in cultured mouse macrophages. In the present study, we examined whether endocytosis and subsequent acidification are associated with these responses. The endocytosis inhibitor, cytochalasin B, reduced tumor necrosis factor alpha (TNF-alpha) production by a plasmid DNA (pDNA)/cationic liposome complex. The endosomal acidification inhibitor, monensin, inhibited cytokine production by pDNA or a calf thymus DNA/liposome complex. These results suggest, similarly to CpG motif-dependent responses, that endocytosis and subsequent endosomal acidification are also required for these inflammatory responses. It is intriguing that another inhibitor of endosomal acidification, bafilomycin A, stimulated the production of TNF-alpha mRNA and its protein after removal of the pDNA/liposome complex and inhibitors, although it inhibited the release of interleukin-6. Similar phenomena were observed in the activation of macrophages by CpG oligodeoxynucleotide, calf thymus DNA, and Escherichia coli DNA complexed with liposomes. Moreover, bafilomycin A also induced a high degree of TNF-alpha release after stimulation with naked pDNA. These results suggest that bafilomycin A increases TNF-alpha production induced by DNA at the transcriptional level via an as-yet unknown mechanism. Furthermore, we investigated the contribution of Toll-like receptor 9 (TLR9), the receptor of CpG motifs, to the cell activation by the DNA/cationic liposome complex using the macrophages from TLR9-/- mice. We observed a reduced inflammatory cytokine release from macrophages of TLR9-/- mice compared with wild-type mice. However, the cytokine production was not completely abolished, suggesting that the DNA/cationic liposome complex can induce macrophage activation via TLR9-dependent and -independent pathways.

Analysis of hepatic disposition of galactosylated cationic liposome/plasmid DNA complexes in perfused rat liver

PURPOSE

To determine the intrahepatic disposition characteristics of galactosylated liposome/plasmid DNA (pDNA) complexes in perfused rat liver.

METHODS

Galactosylated liposomes containing N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA), cholesterol (Chol), and cholesten-5-yloxy-N-14-[(1-imino-2-D-thiogalactosylethyl)amino]butyl] formamide (Gal-C4-Chol) were prepared. The liposome/[32P]-labeled pDNA complexes were administered to perfused liver, and the venous outflow patterns were analyzed based on a two-compartment dispersion model.

RESULTS

The single-pass hepatic extraction of pDNA complexed with DOTMA/Chol/Gal-C4-Chol liposomes was greater than that with control DOTMA/Chol liposomes. A two-compartment dispersion model revealed that both the tissue binding and cellular internalization rate were higher for the DOTMA/Chol/Gal-C4-Chol liposome complexes compared with the control liposome complexes. The tissue binding was significantly reduced by the presence of 20 mM galactose. When their cellular localization in the perfused liver at 30 min postinjection was investigated, it was found that the parenchymal uptake of the DOTMA/Chol/Gal-C4-Chol liposome complexes was greater than that of the control liposome complexes. The parenchymal cell/ nonparenchymal cell uptake ratio was as high as unity.

CONCLUSION

Galactosylation of the liposome/pDNA complexes increases the tissue binding and internalization rate via an asialoglycoprotein receptor-mediated process. Because of the large particle size of the complexes (approximately 150 nm), however, penetration across the fenestrated sinusoidal endothelium appears to be limited.

Enhancement of immune responses by DNA vaccination through targeted gene delivery using mannosylated cationic liposome formulations following intravenous administration in mice

The present study investigated the potency of the mannosylated cationic liposomes (Man liposomes) that we have developed in novel DNA vaccine carrier. Ovalbumin (OVA) was selected as a model antigen for vaccination; accordingly, OVA-encoding pDNA (pCMV-OVA) was constructed to evaluate DNA vaccination. The potency of the Man liposome/pCMV-OVA complex was compared with naked pCMV-OVA and that complexed with DC-Chol liposomes. In cultured mouse peritoneal macrophages, MHC class I-restricted antigen presentation of the Man liposome/pCMV-OVA complex was significantly higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. After intravenous administration, OVA mRNA expression and MHC class I-restricted antigen presentation on CD11c+ cells and inflammatory cytokines, such as TNF-alpha, IL-12, and IFN-gamma, that can enhance the Th1 response of the Man liposome/pCMV-OVA complex were higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. Also, the spleen cells from mice immunized by intravenous administration of the Man liposome/pCMV-OVA complex showed the highest proliferation response and IFN-gamma secretion. These findings suggest that the targeted delivery of DNA vaccine by Man liposomes is a potent vaccination method for DNA vaccine therapy.

Restricted cytokine production from mouse peritoneal macrophages in culture in spite of extensive uptake of plasmid DNA

The production of inflammatory cytokines from macrophages (Mphi), upon stimulation with plasmid DNA (pDNA) containing CpG motifs, is a critical process for DNA-based therapies such as DNA vaccination and gene therapy. We compared Mphi activation, following stimulation with naked pDNA, based on the production of cytokines from cell lines (RAW264.7 and J774A1) and peritoneal Mphis in primary culture. The Mphi cell lines RAW264.7 and J774A1 produced a significant amount of tumour necrosis factor-alpha (TNF-alpha) upon stimulation with naked pDNA and this response required endosomal acidification. On the other hand, peritoneal Mphis (both resident and elicited) in primary culture did not secrete TNF-alpha or interleukin-6, although they contain the mRNA of toll-like receptor-9 (TLR-9) and are able to respond to CpG oligodeoxynucleotides. This unresponsiveness was not a result of impaired cellular uptake of pDNA because the primary cultured Mphis showed a higher uptake of pDNA than the RAW264.7 and J774A1 cell lines. These findings have important implications for Mphi activation by naked pDNA as it has been generally assumed that pDNA that contains CpG motifs is a potent agent for inducing inflammatory cytokines in vivo, based on evidence from in vitro studies using Mphi cell lines.

Disposition and gene expression characteristics in solid tumors and skeletal muscle after direct injection of naked plasmid DNA in mice

Previous studies have suggested that direct injection of naked plasmid DNA (pDNA) into solid tumors can be a useful method for in vivo gene transfer into tumor cells. To gain more insight into this approach, we studied the disposition and gene expression characteristics of naked pDNA after intratumoral injection by direct comparison with those after intramuscular injection in mice. pDNA encoding reporter genes were directly injected into subcutaneous solid tumor models and skeletal muscles. Biodistribution studies using radiolabeled pDNA showed that the elimination of pDNA from the injection site was relatively fast and a part of the pDNA was absorbed from the lymphatic system after both local injections. Confocal microscopic studies using fluorescein-labeled pDNA demonstrated that pDNA distributed efficiently throughout the muscle tissue whereas pDNA localization in the tumor tissue was restricted. Characterization of gene expression clarified the variation in expression level between tumor preparations and some factors affecting the expression level in the tumor. Reporter gene expression was significantly inhibited by simultaneous administration of some polyanions in both cases, suggesting that a specific mechanism may be involved in the naked pDNA uptake by muscle and tumor cells. These findings provide useful information for direct naked pDNA delivery into solid tumors.

Analysis of Hepatic Disposition of Native and Galactosylated Polyethylenimine Complexed with Plasmid DNA in Perfused Rat Liver

We studied the intrahepatic disposition characteristics of galactosylated polyethylenimine (Gal-PEI)/plasmid DNA (pDNA) complexes using rat liver perfusion experiment. After intraportal administration, transfection activity in liver of Gal-PEI complexes was approximately 26-fold higher than that of native PEI complexes. To evaluate the relationship between hepatic gene expression and disposition profiles, hepatic disposition of Gal-PEI complexes were pharmacokinetically analyzed by use of perfused rat liver, which enables uptake characteristics intrinsic to the liver to be elucidated. Moment analysis revealed that both complexes exhibited very high single-pass extraction. To characterize each kinetic process in hepatic uptake of Gal-PEI complexes, their outflow profiles were analyzed based on a two-compartment dispersion model. Consequently, the tissue binding affinity of Gal-PEI complexes was 3.0-fold larger than that of native PEI complexes, suggesting the increasing of hepatic binding affinity much enhanced the hepatic gene transfection efficiency. In contrast, galactosylation of PEI did not affected internalization (and/or sequestration) rate.

Efficient uptake and rapid degradation of plasmid DNA by murine dendritic cells via a specific mechanism

In spite of the important roles of dendritic cells in DNA-based therapies, the cellular uptake mechanism of plasmid DNA (pDNA) in dendritic cells is poorly understood. The present study was undertaken to investigate the binding and uptake of pDNA in vitro using a murine dendritic cell line, DC2.4 cells. A significant and time-dependent cellular association of [32P]pDNA with DC2.4 cells was observed at 37 degrees C and this fell markedly at 4 degrees C. The binding and uptake of [32P]pDNA were significantly inhibited by cold pDNA, polyinosinic acid (poly[I]), dextran sulfate, or heparin, but not by polycytidylic acid (poly[C]), dextran, or EDTA, suggesting that a specific mechanism mediated by a receptor like the macrophage scavenger receptor may be involved. The TCA precipitation experiments showed that DC2.4 cells rapidly endocytosed and degraded a significant amount of [32P]pDNA at 37 degrees C and released the degradation products into the medium. The pDNA degradation was also significantly inhibited by poly[I], but not poly[C]. The rate of pDNA degradation by DC2.4 cells was significantly higher than that by macrophages. A confocal microscopic study using fluorescein-labeled pDNA confirmed the rapid internalization and degradation of pDNA by the dendritic cells. Taken together, these results indicate that pDNA is efficiently taken up and rapidly digested by the dendritic cells via a specific mechanism. These findings may suggest the important role of the dendritic cells in the innate immune system for host defense.

Plasmid DNA activates murine macrophages to induce inflammatory cytokines in a CpG motif-independent manner by complex formation with cationic liposomes

Plasmid DNA (pDNA) is very important in non-viral gene therapy and DNA vaccination. Unmethylated CpG motifs in bacterial DNA, but not in vertebrate DNA, are known to trigger an inflammatory response, which inhibits gene expression while improving immunological consequences. In this report, we investigated the cytokine secretion induced by pDNA/cationic liposome complexes using murine macrophages. Naked CpG DNA induced tumor necrosis factor-alpha (TNF-alpha) secretion from the macrophages, but DNA without CpG motif did not, demonstrating that the cytokine induction was mediated by CpG motifs. pDNA complexed with cationic liposomes, but not the cationic liposomes alone, produced a significant amount of TNF-alpha from the macrophages. Surprisingly, methylated pDNA and calf thymus DNA complexed with the cationic liposomes were also able to induce TNF-alpha production, indicating that these responses were not dependent on CpG motifs. Taken together, the present study demonstrated that for the first time DNA can stimulate murine macrophages in a CpG motif-independent manner when it is complexed with the cationic liposomes.

The role of the macrophage scavenger receptor in immune stimulation by bacterial DNA and synthetic oligonucleotides

To assess the role of the macrophage scavenger receptor type A (SRA) in immune activation by CpG DNA, cytokine induction and DNA uptake were tested in vitro and in vivo using SRA knockout (SRA-/-) and wild type (WT) mice. As a source of CpG DNA, Escherichia coli DNA (EC DNA) and a 20-mer phosphorothioate oligodeoxynucleotide with two CpG motifs (CpG ODN) were used. In vitro, both EC DNA and the CpG ODN induced dose-dependent increases of interleukin (IL)-12 production by spleen cells and bone-marrow-derived macrophages (BMMPhi) from both SRA-/- and WT mice. The levels of cytokines produced by SRA-/- spleen cells and BMMPhi were similar to those of WT spleen cells and BMMPhi. When injected intravenously with CpG ODN and EC DNA, both SRA-/- and WT mice showed elevated serum levels of IL-12. To investigate further the role of the SRA, flow cytometry and confocal microscopy were performed to examine the uptake of fluorescently labelled oligonucleotides. SRA-/- and WT BMMPhi showed similarity in the extent of uptake and distribution of oligonucleotides as assessed by these two techniques. Together, these findings indicate that, while the SRA may bind DNA, this receptor is not essential for the uptake of CpG DNA or its immunostimulatory activity.

The immune response to ocular herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) is a prevalent microbial pathogen infecting 60% to 90% of the adult world population. The co-evolution of the virus with humans is due, in part, to adaptations that the virus has evolved to aid it in escaping immune surveillance, including the establishment of a latent infection in its human host. A latent infection allows the virus to remain in the host without inducing tissue pathology or eliciting an immune response. During the acute infection or reactivation of latent virus, the immune response is significant, which can ultimately result in corneal blindness or fatal sporadic encephalitis. In fact, HSV-1 is one of the leading causes of infectious corneal blindness in the world as a result of chronic episodes of viral reactivation leading to stromal keratitis and scarring. Significant inroads have been made in identifying key immune mediators that control ocular HSV-1 infection and potentially viral reactivation. Likewise, viral mechanisms associated with immune evasion have also been identified and will be discussed. Lastly, novel therapeutic strategies that are currently under development show promise and will be included in this review. Most investigators have taken full advantage of the murine host as a viable working in vivo model of HSV-1 due to the sensitivity and susceptibility to viral infection, ease of manipulation, and a multitude of developed probes to study changes at the cellular and molecular levels. Therefore, comments in this review will primarily be restricted to those observations pertaining to the mouse model and the assumption (however great) that similar events occur in the human condition.

Recombinant lipoproteins: lipoprotein-like lipid particles for drug targeting

Lipoproteins are endogenous particles that transport lipids through the blood to various cell types, where they are recognised and taken up via specific receptors. These particles are, therefore, excellent candidates for the targeted delivery of drugs to various tissues. For example, the remnant receptor and the asialoglycoprotein receptor (ASGPr), which are uniquely localised on hepatocytes, recognise chylomicrons and lactosylated high density lipopoteins (HDL), respectively. In addition, tumour cells of various origins overexpress the low density lipoprotein (LDL) receptor that recognises apolipoprotein E (apoE) on small triglyceride-rich particles and apoB-100 on LDL. Being endogenous, lipoproteins are biodegradable, do not trigger immune reactions, and are not recognised by the reticuloendothelial system (RES). However, their endogenous nature also hampers large-scale pharmaceutical application. In the past two decades, various research groups have successfully synthesised recombinant lipoproteins from commercially available natural and synthetic lipids and serum-derived or recombinant apolipoproteins, which closely mimic the metabolic behaviour of their native counterparts in animal models as well as humans. In this paper, we will summarise the studies that led to the development of these recombinant lipoproteins, and we will address the possibility of using these lipidic particles to selectively deliver a wide range of lipophilic, amphiphilic, and polyanionic compounds to hepatocytes and tumour cells. In addition, the intrinsic therapeutic activities of recombinant chylomicrons and HDL in sepsis and atherosclerosis will be discussed.

Development of gene drug delivery systems based on pharmacokinetic studies

A series of pharmacokinetic studies following systemic or local administration for the development of delivery systems for gene drugs, such as plasmid DNA and oligonucleotides, are reviewed. The pharmacokinetics of gene drugs after intravenous injection into mice was evaluated based on clearance concepts. Pharmacokinetic analysis revealed that the overall disposition characteristics of the gene drug itself were determined by the physicochemical properties of its polyanionic DNA. Based on these findings, liver cell-specific carrier systems via receptor-mediated endocytosis were successfully developed by optimizing physicochemical characteristics. On the other hand, the pharmacokinetics of gene drugs after intratumoral injection were assessed in a tissue-isolated tumor perfusion system. The relationship between the physicochemical properties of gene drug delivery systems and intratumoral pharmacokinetics was determined and the therapeutic effect was also discussed in relation to pharmacokinetics. Collectively, it was demonstrated that a rational design of gene drug delivery systems that can control their in vivo disposition is possible by means of pharmacokinetic studies at whole body, organ and cellular levels.

A human gene coding for a membrane-associated nucleic acid-binding protein

Studies to clone a cell-surface DNA-binding protein involved in the binding and internalization of extracellular DNA have led to the isolation of a gene for a membrane-associated nucleic acid-binding protein (MNAB). The full-length cDNA is 4.3 kilobases with an open reading frame of 3576 base pairs encoding a protein of approximately 130 kDa (GenBank accession numbers and ). The MNAB gene is on human chromosome 9 with wide expression in normal tissues and tumor cells. A C3HC4 RING finger and a CCCH zinc finger have been identified in the amino-terminal half of the protein. MNAB bound DNA (K(D) approximately 4 nm) and mutagenesis of a single conserved amino acid in the zinc finger reduced DNA binding by 50%. A potential transmembrane domain exists near the carboxyl terminus. Antibodies against the amino-terminal half of the protein immunoprecipitated a protein of molecular mass approximately 150 kDa and reacted with cell surfaces. The MNAB protein is membrane-associated and primarily localized to the perinuclear space, probably to the endoplasmic reticulum or trans-Golgi network. Characterization of the MNAB protein as a cell-surface DNA-binding protein, critical in binding and internalization of extracellular DNA, awaits confirmation of its localization to cell surfaces.

Strength of conjugate binding to plasmid DNA affects degradation rate and expression level in vivo

In vitro assays have demonstrated the capability of poly-L-lysine to protect plasmid DNA from serum nucleases and cellular lysates. Our purpose was to evaluate the stability and potency of poly-L-lysine-DNA polyplexes after intravenous injection into mice. Polyplexes consisted of 32P-radiolabeled plasmid DNA complexed with poly-L-lysine at specified charge ratios. Variations in conjugate hydrophobicity and levels of modification with polyethylene glycol were investigated. Our results show that, in contrast to in vitro studies, the systemically administered polyplexes exhibited marked DNA degradation in the vascular compartment within 5 min. Substitution of poly-L-lysine epsilon-amino sites with polyethylene glycol or hydrocarbon chains resulted in faster degradation even when complexed at higher charge (+/-) ratios. Use of excess cationic charge in the polyplexes (+/- 2.5) diminished degradation rates only slightly. An analysis was made of the strength of the poly-L-lysine:DNA interaction by competition with poly-aspartic acid. Polyplexes with the strongest binding between conjugate and DNA in the competition assay were also the most stable in blood. However, tighter binding was not enough to fully protect the polyplex in vivo and polyplex DNA was substantially degraded within 10 min. Increased polyplex stability did not correlate with improved in vivo transfection efficiency.

Quantification of DNA binding to cell-surfaces by flow cytometry

DNA binding to cell-surfaces has been documented in several studies. The interaction of DNA with cells has been shown to have therapeutic potential as a non-viral form of gene delivery and DNA vaccination. Recently, bacterial DNA binding and internalization has been demonstrated in some cells to trigger secretion of cytokines and cell activation. Previous studies to quantify DNA binding to cells have used radiolabeled DNA. Here we report a non-radioactive assay for quantification of cell-surface DNA binding based on the isoparametric analysis of flow cytometric data as described by Chatelier et al., Embo J., 5 (1986) 1181. This assay has the advantage over previously used procedures in not employing radioactive material and being able to discriminate viable from non-viable cells that bind DNA. With the importance of understanding the interaction of DNA with cells, this assay may have application for the identification and characterization of reagents designed to either enhance or inhibit DNA binding to cells.