Microtubular disruption prolongs the expression of human bilirubin-uridinediphosphoglucuronate-glucuronosyltransferase-1 gene transferred into Gunn rat livers

The alpha-adrenergic antagonist prazosin promotes cytosolic siRNA delivery from lysosomal compartments

The widespread use of small interfering RNA (siRNA) is limited by the multiple extra- and intracellular barriers upon in vivo administration. Hence, suitable delivery systems, based on siRNA encapsulation in nanoparticles or its conjugation to targeting ligands, have been developed. Nevertheless, at the intracellular level, these state-of-the-art delivery systems still suffer from a low endosomal escape efficiency. Consequently, the bulk of the endocytosed siRNA drug rapidly accumulates in the lysosomal compartment. We recently reported that a wide variety of cationic amphiphilic drugs (CADs) can promote small nucleic acid delivery from the endolysosomal compartment into the cytosol via transient induction of lysosomal membrane permeabilization. Here, we describe the identification of alternate siRNA delivery enhancers from the NIH Clinical Compound Collection that do not have the typical physicochemical properties of CADs. Additionally, we demonstrate improved endolysosomal escape of siRNA via a cholesterol conjugate and polymeric carriers with the α1-adrenergic antagonist prazosin, which was identified as the best performing delivery enhancer from the compound screen. A more detailed assessment of the mode-of-action of prazosin suggests that a different cellular phenotype compared to typical CAD adjuvants drives cytosolic siRNA delivery. As it has been described in the literature that prazosin also induces cancer cell apoptosis and promotes antigen cross-presentation in dendritic cells, the proof-of-concept data in this work provides opportunities for the repurposing of prazosin in an anti-cancer combination strategy with siRNA.

Modulating intracellular pathways to improve non-viral delivery of RNA therapeutics

RNA therapeutics (e.g. siRNA, oligonucleotides, mRNA, etc.) show great potential for the treatment of a myriad of diseases. However, to reach their site of action in the cytosol or nucleus of target cells, multiple intra- and extracellular barriers have to be surmounted. Several non-viral delivery systems, such as nanoparticles and conjugates, have been successfully developed to meet this requirement. Unfortunately, despite these clear advances, state-of-the-art delivery agents still suffer from relatively low intracellular delivery efficiencies. Notably, our current understanding of the intracellular delivery process is largely oversimplified. Gaining mechanistic insight into how RNA formulations are processed by cells will fuel rational design of the next generation of delivery carriers. In addition, identifying which intracellular pathways contribute to productive RNA delivery could provide opportunities to boost the delivery performance of existing nanoformulations. In this review, we discuss both established as well as emerging techniques that can be used to assess the impact of different intracellular barriers on RNA transfection performance. Next, we highlight how several modulators, including small molecules but also genetic perturbation technologies, can boost RNA delivery by intervening at differing stages of the intracellular delivery process, such as cellular uptake, intracellular trafficking, endosomal escape, autophagy and exocytosis.

A versatile and tunable coating strategy allows control of nanocrystal delivery to cell types in the liver

There are many liver diseases that could be treated with delivery of therapeutics such as DNA, proteins, or small molecules. Nanoparticles are often proposed as delivery vectors for such therapeutics; however, achieving nanoparticle accumulations in the therapeutically relevant hepatocytes is challenging. In order to address this issue, we have synthesized polymer coated, fluorescent iron oxide nanoparticles that bind and deliver DNA, as well as produce contrast for magnetic resonance imaging (MRI), fluorescence imaging, and transmission electron microscopy (TEM). The composition of the coating can be varied in a facile manner to increase the quantity of poly(ethylene glycol) (PEG) from 0% to 5%, 10%, or 25%, with the aim of reducing opsonization but maintaining DNA binding. We investigated the effect of the nanoparticle coating on DNA binding, cell uptake, cell transfection, and opsonization in vitro. Furthermore, we exploited MRI, fluorescence imaging, and TEM to investigate the distribution of the different formulations in the liver of mice. While MRI and fluorescence imaging showed that each formulation was heavily taken up in the liver at 24 h, the 10% PEG formulation was taken up by the therapeutically relevant hepatocytes more extensively than either the 0% PEG or the 5% PEG, indicating its potential for delivery of therapeutics to the liver.

Gene therapy for metabolic diseases of the liver

Significant advances have been made in the field of liver-directed gene therapy. Many diseases are potential targets for gene therapy, including diseases that have exclusive liver involvement and those with systemic manifestations as a result of defective protein synthesis from the liver. Examples are Crigler-Najjar syndrome type 1, alpha(1)-antitrypsin deficiency and haemophilia A and B. Strategies for gene delivery include the use of viral and nonviral vectors. In addition to previously developed viral vectors, such as retroviruses, adenoviruses and adeno-associated viruses, new viral vectors such as lentiviruses are being investigated extensively. Nonviral vectors for gene delivery include liposomes and receptor-mediated gene therapy. A strategy to correct gene defects has been developed using chimaeric RNA/DNA oligonucleotides, and methods to inhibit aberrant or deleterious gene expression using ribozymes, antisense oligonucleotides and dominant-negative gene products are being developed. However, more research focusing on more efficient gene expression and safety will be required before gene therapy can be routinely applicable.

Fluorescence methods for evaluating lipoplex-mediated gene delivery

The biological activity of cationic liposome/DNA complexes ("lipoplexes") is strongly dependent on their ability to protect DNA and to interact with cells, including binding to the cell surface, internalization via endocytosis and cytoplasmic delivery of the DNA. In this chapter, we describe a number of methods and procedures to study these processes, based on the use of fluorescent probes.

Synergistic antitumoral effect of vinblastine and HSV-Tk/GCV gene therapy mediated by albumin-associated cationic liposomes

Despite recent advances in conventional therapeutic approaches for cancer, the frequently observed acquired drug resistance and toxic side effects have limited their clinical application. The main goal of this work was to investigate the combined antitumoral effect of vinblastine with HSV-Tk/GCV "suicide" gene therapy mediated by human serum albumin (HSA)-associated lipoplexes, in mammary adenocarcinoma cells (TSA cells). Our results show that, among the different lipoplex formulations tested, HSA-associated complexes prepared from EPOPC:Chol liposomes, at the (4/1) (+/-) charge ratio, was the most efficient to mediate gene delivery, even in the presence of serum. The simultaneous addition of vinblastine and HSA-EPOPC:Chol/DNA (+/-) (4/1) lipoplexes to TSA cells improved transgene expression more than 10 times. When combined with the HSV-Tk/GCV "suicide" gene therapy mediated by HSA-EPOPC:Chol/DNA (+/-) (4/1) lipoplexes, vinblastine induced a great enhancement in the antitumoral activity in TSA cells. Most importantly, this combined strategy resulted in a significant synergistic effect, thus allowing the use of a much lower dose of the drug to achieve the same therapeutic effect. Overall, our results indicate that this approach has the potential to overcome some major limitations of conventional chemotherapy, and may therefore constitute a promising strategy for future applications in antitumoral therapy.

A novel G418 conjugate results in targeted selection of genetically protected hepatocytes without bystander toxicity

G418, an aminoglycoside neomycin analogue, is an antimicrobial agent that interferes with protein synthesis and has been used extensively for selection of mammalian cell lines that possess neomycin resistance (NR). It is potent and nonspecific in its effects that occur through tight binding to ribosomal elements. Because of the potent intracellular effect, we wondered whether G418 could be used to select a specific cell type based on receptor-mediated endocytosis. The objective of this study was to target G418 specifically to liver cells via asialoglycoprotein receptors (AsGR) which are known to be highly selective for these cells. A novel G418 conjugate was synthesized chemically by coupling G418 to a galactose-terminating carrier protein, asialoorosomucoid (AsOR), in a molar ratio of 5:1. AsOR-G418 conjugates inhibited viability of AsGR (+) cells by 84.3%, while inhibition in AsGR (-) cells was only by 19%. In AsGR (+) cells, stably transfected with a NR gene, the conjugate decreased viability by less than 9%. Furthermore, incubation of conjugate in cocultures of AsGR (+), and AsGR (-) cells did not result in the loss of viability of neighboring AsGR (-) cells. Our data demonstrate for the first time that G418 can be covalently bound to AsOR to form a conjugate for hepatocyte-specific targeting and toxicity. AsOR-G418 conjugates may be useful tools for genetic manipulation of human liver cells in the presence of nonhepatic cells.

Gene therapy for liver enzyme deficiencies: what have we learned from models for Crigler-Najjar and tyrosinemia?

The liver is the site of numerous metabolic inherited diseases. It has unique features that make it compliant to various gene therapy approaches. Many vector types and gene delivery strategies have been evaluated during the past 20 years in a number of animal models of metabolic liver diseases. However, the complete cure of inherited liver deficiencies by gene therapy in relevant animal models were only reported recently. These successes were achieved thanks to major advances in vector technology. In this review, we will focus on Crigler-Najjar disease and hereditary tyrosinemia, two paradigmatic examples of the two categories of enzymatic liver deficiencies: type I, in which the genetic defect does not affect liver histology; and type II, in which liver lesions are present.

Noncovalently linked nuclear localization peptides for enhanced calcium phosphate transfection

The generation of cell lines stably expressing recombinant material is a lengthy process and there has thus been much interest in the use of transient expression systems to rapidly produce recombinant material. To achieve this, the DNA of interest must be delivered into the nucleus of the target cell. The mechanisms by which this process occurs are poorly understood and the efficiency of various methods differs widely. Recently, nuclear localization signals (NLSs) have been investigated to target entry of DNA into the nucleus of mammalian cells. We have used NLSs from the SV40 and Tat antigens mixed with our model luciferase reporter gene plasmid for the transfection of Chinese hamster ovary (CHO) cells using calcium phosphate and FuGENE 6 transfection technology. The noncovalent complexation of NLSs with plasmid DNA before calcium phosphate-mediated transfection resulted in enhanced reporter gene expression with increasing ratios of NLS to plasmid until reaching a maximum. At higher ratios than maximum expression, the expression levels decreased. On the other hand, when using FuGENE 6 reagent NLSs did not enhance reporter gene expression. Cell cycle arrest in G(2)/M phase obliterated the effect of the NLS on reporter gene expression when using the calcium phosphate transfection method.

Ex vivo lentivirus transduction and immediate transplantation of uncultured hepatocytes for treating hyperbilirubinemic Gunn rat

BACKGROUND

Ex vivo liver gene therapy provides an attractive alternative to orthotopic liver transplantation for the treatment of liver diseases. We previously reported a protocol in which human primary hepatocytes are highly transduced in Suspension with Lentiviral vectors and Immediately Transplanted (SLIT). Here, we evaluated the SLIT approach in Gunn rats, the animal model for Crigler-Najjar syndrome type 1, a defect in bilirubin UDP-glucuronosyltransferase (BUGT).

METHODS

We constructed lentiviral vectors coding for BUGT under control of an ubiquitous promoter. Control vectors contained Green Fluorescent Protein (GFP) under control of the same promoter. Hepatocytes were isolated from jaundiced Gunn rats and transduced in suspension for four hr. After washing, 2x10 hepatocytes were immediately transplanted into syngeneic rats. Bilirubinemia and bile pigments were regularly assessed after cell transplantation. The percentage and presence of transduced hepatocytes was analyzed by immunohistochemistry in GFP-transplanted animals.

RESULTS

In rats receiving BUGT-transduced hepatocytes, bilirubinemia decreased by about 30%. The level of correction remained stable for up to 240 days. Bilirubin glucuronides were present in the bile of treated animals, indicating the metabolic activity of engrafted hepatocytes. In contrast, bilirubinemia in GFP-transplanted rats did not decline but rather increased. GFP-positive hepatocytes amounted to 0.5-1% of the liver, which is in agreement with the number of transplanted and genetically-modified hepatocytes (6x10).

CONCLUSIONS

This work reports the first demonstration of long-term metabolic benefit after rapid transplantation of ex vivo lentivirally tranduced hepatocytes. Therefore, this study demonstrates the therapeutic proof-of-principle and potential of the SLIT approach for treating inherited metabolic liver diseases.

The prospects of hepatic drug delivery and gene therapy

Liver targeted therapy is designed to deliver a substance preferentially to the organ in order to increase the accumulation, improve the therapeutic effect and reduce toxicity to other organs. The aim of selective targeting is to deliver a substance to a specific cell type in the liver. A variety of vehicles have been designed and further modified for selective targeting of therapeutics to the liver. The targeting properties and strategies of commonly used agents, such as liposomes, microspheres and recombinant chylomicrons, are discussed. Viral and non-viral vectors, such as cationic liposomes, reconstituted chylomicron remnants, adenoviruses, adeno-associated viruses, retroviruses, and SV-40, are currently being evaluated for the delivery of DNA to the liver. New developments in improving the targeting efficiency of the available vectors while avoiding their disadvantages have made their use in clinical trials of various genetic disorders possible. For viral hepatitis, antisense and ribozyme techniques are being employed with selective targeting approaches. A commonly employed current strategy for targeting hepatocellular carcinoma cells is to make the tumour cells convert non-toxic 'prodrugs' to toxic metabolites in situ, achieving a high concentration of the toxic product in the local milieu, while avoiding systemic toxicity. Although gene therapy itself is in its infancy, some encouraging results have been developed in studies of familial hypercholesterolaemia, haemophilia, alpha1-antitrypsin deficiency and Crigler-Najjar syndrome. The potential strengths as well as the problems with these studies are discussed.

Liver gene therapy: advances and hurdles

Liver gene therapy is being developed as an alternative to orthotopic liver transplantation, which is the only effective therapy for many liver diseases. The liver has unique features that make it attractive for in vivo and ex vivo gene transfer. In vivo approach is far less invasive than ex vivo approach, although in most cases, host immune response directed against the transgene product and/or vector particles severely impairs the efficiency of gene transfer, and precludes long-term transgene expression after in vivo gene delivery. Ex vivo approach allows for an elective targeting of the hepatocytes, avoiding that the transgene be expressed in professional antigen-presenting, but is faced with the low in vitro proliferative ability of hepatocytes, and to the low in vivo liver repopulating ability of transplanted cells. In some specific situations where immune response was controlled or transplanted cells had a strong growth advantage over host hepatocytes, gene transfer resulted in long-term and complete correction of a liver genetic defect. In this review, we will outline the liver diseases that may benefit from gene therapy, the vector technology under investigation, the advances and the problems to be overcome.

Engineering synthetic vectors for improved DNA delivery: insights from intracellular pathways

Significant progress has been made in the area of nonviral gene delivery to date. Yet, synthetic vectors remain less efficient by orders of magnitude than their viral counterparts. Research continues toward unraveling and overcoming various barriers to the efficient delivery of DNA, whether in plasmid form encoding a gene or as an oligonucleotide for the selective inhibition of target gene expression. Novel components for overcoming these hurdles are continually being incorporated into the design of synthetic vectors, leading to increasingly more virus-like particles. Despite these advances, general principles defining the design of synthetic vectors are yet to be developed fully. A more quantitative analysis of the cellular uptake and intracellular processing of these vectors is required for the rational manipulation of vector design. Mathematical frameworks with a more conceptual basis will help obtain an integrated perspective on these complex systems. In this review, we critically examine the progress made toward the improved design of synthetic vectors by the strategic exploitation of intracellular mechanisms and explore newer possibilities to overcome obstacles in the practical realization of this field.

Glucuronidation and the UDP-glucuronosyltransferases in health and disease

This article is an updated report of a symposium held at the June 2000 annual meeting of the American Society for Pharmacology and Experimental Therapeutics in Boston. The symposium was sponsored by the ASPET Divisions for Drug Metabolism and Molecular Pharmacology. The report covers research from the authors' laboratories on the structure and regulation of UDP-glucuronosyltransferase (UGT) genes, glucuronidation of xenobiotics and endobiotics, the toxicological relevance of UGTs, the role of UGT polymorphisms in cancer susceptibility, and gene therapy for UGT deficiencies.

Effects of Microtubule-Depolymerizing Agents on the Transfection of Cultured Vascular Smooth Muscle Cells: Enhanced Expression with Free Drug and Especially with Drug–Gene Lipoplexes

The microtubule-depolymerizing agents colchicine, vinblastine (VB), vincristine, nocodazole, and podophyllotoxin were found to increase dramatically the transfection of cationic phospholipid-DNA (CMV-beta-gal) complexes on cultured vascular smooth muscle cells (VSMCs). Pretreatment of cells with free colchicine before addition of lipoplexes increased transgene expression both in the presence and in the absence of serum. Free vinblastine had similar effects; however, vinblastine was more effective (approximately 30-fold maximal stimulation) when incorporated into the lipoplexes. Under optimal conditions, vincristine, nocodazole, and podophyllotoxin produced 25- and 39-, 31- and 14-, and 26- and 14-fold increases in the absence and presence of serum, respectively. Taxol, which stabilizes microtubules, had no effect on transfection, but it blocked the positive effect of colchicine. Cytochalasin B, which inhibits microfilament polymerization, had no effect on transgene expression. By fluorescence microscopy, normal lipoplexes colocalized with lysosomes. In contrast, there was little, if any, colocalization of VB lipoplexes with lysosomes. Because depolymerization of microtubules induces NF-kappaB-dependent gene expression, the effects of pyrrolidinedithiocarbamate and Nalpha-p-tosyl-L-lysine chloromethyl ketone, inhibitors of NF-kappaB activation, were tested; inhibition of vinblastine stimulation of transfection was 85 and 66%, respectively. Also, immunofluorescence microscopy showed that vinblastine induced the translocation of NF-kappaB from the cytoplasm to the nucleus. It is concluded that microtubule-depolymerizing agents, especially when incorporated into lipoplexes, dramatically increase transfection of VSMCs, probably by two mechanisms: (i) inhibition of transport of lipoplexes to lysosomes and (ii) activation of transcription (via NF-kappaB). There have been some reports on the use of pharmaceutical agents to enhance gene expression, but generally these have involved separate applications of drug and gene. The ability to deliver a drug and a gene in a single therapeutic formulation could have significant clinical implications.

Transient production of recombinant proteins by Chinese hamster ovary cells using polyethyleneimine/DNA complexes in combination with microtubule disrupting anti-mitotic agents

We have developed a simple and robust transient expression system utilizing the 25 kDa branched cationic polymer polyethylenimine (PEI) as a vehicle to deliver plasmid DNA into suspension-adapted Chinese hamster ovary cells synchronized in G2/M phase of the cell cycle by anti-mitotic microtubule disrupting agents. The PEI-mediated transfection process was optimized with respect to PEI nitrogen to DNA phosphate molar ratio and the plasmid DNA mass to cell ratio using a reporter construct encoding firefly luciferase. Optimal production of luciferase was observed at a PEI N to DNA P ratio of 10:1 and 5 mug DNA 10(6) cells(-1). To manipulate transgene expression at mitosis, we arrested cells in G2/M phase of the cell cycle using the microtubule depolymerizing agent nocodazole. Using secreted human alkaline phosphatase (SEAP) and enhanced green fluorescent protein (eGFP) as reporters we showed that continued inclusion of nocodazole in cell culture medium significantly increased both transfection efficiency and reporter protein production. In the presence of nocodazole, greater than 90% of cells were eGFP positive 24 h post-transfection and qSEAP was increased almost fivefold, doubling total SEAP production. Under optimal conditions for PEI-mediated transfection, transient production of a recombinant chimeric IgG4 encoded on a single vector was enhanced twofold by nocodazole, a final yield of approximately 5 microg mL(-1) achieved at an initial viable cell density of 1 x 10(6) cells mL(-1). The glycosylation of the recombinant antibody at Asn297 was not significantly affected by nocodazole during transient production by this method.

Roles of the cytoskeleton and motor proteins in endocytic sorting

After internalization, endocytic material is actively transported through the cytoplasm, predominantly by microtubule motor proteins. Microtubule-based endocytic transport facilitates sorting of endocytic contents, vesicle fusion and fission, delivery to lysosomes, cytosolic dispersal, as well as nuclear uptake and cytosolic egress of pathogens. Endosomes, like most organelles, move bidirectionally through the cytosol and regulate their cellular location by controlling the activity of motor proteins, and potentially by controlling microtubule and actin polymerization. Control of motor protein activity is manifest by increased microtubule "run lengths", and the binding of motor proteins to organelles can be regulated by motor protein receptors. A mechanistic understanding of how organelles control motor protein activity to allow for endocytic sorting presents an exciting avenue for future research.

Improvement of hepatocyte-specific gene expression by a targeted colchicine prodrug

Colchicine, an established tubulin inhibitor, interferes with the trafficking of endocytotic vesicles and thereby promotes the escape of lysosome-entrapped compounds. To improve its potency and cell specificity, a targeted prodrug of colchicine was synthesized by conjugation to a high-affinity ligand (di-N(alpha),N(epsilon)-(5-(2-acetamido-2-deoxy-beta-D-galactopyranosyloxy)pentanomido)lysine, K(GalNAc)(2)) for the asialoglycoprotein receptor on parenchymal liver cells. The resulting colchicine-K(GalNAc)(2) conjugate bound to this receptor with an affinity of 4.5 nM. Confocal microscopy studies confirmed rapid uptake and receptor dependency of a prodrug conjugated with fluorescein isothiocyanate. Colchicine-K(GalNAc)(2) substantially increased the transfection efficiency of polyplexed DNA in parenchymal liver cells in a concentration- and receptor-dependent fashion. Colchicine-K(GalNAc)(2) was found to enhance the transfection efficiency by 50-fold at 1 nM, whereas the parental colchicine was ineffective. In conclusion, this nontoxic colchicine-K(GalNAc)(2) conjugate can be a useful tool to improve the transfection efficiency of hepatic nonviral gene transfer vehicles.

Targeted lysosome disruptive elements for improvement of parenchymal liver cell-specific gene delivery

The transfection ability of nonviral gene therapy vehicles is generally hampered by untimely lysosomal degradation of internalized DNA. In this study we describe the development of a targeted lysosome disruptive element to facilitate the escape of DNA from the lysosomal compartment, thus enhancing the transfection efficacy, in a cell-specific fashion. Two peptides (INF7 and JTS-1) were tested for their capacity to disrupt liposomes. In contrast to JTS-1, INF7 induced rapid cholesterol-independent leakage (EC(50), 1.3 microm). INF7 was therefore selected for coupling to a high affinity ligand for the asialoglycoprotein receptor (ASGPr), K(GalNAc)(2), to im- prove its uptake by parenchymal liver cells. Although the parent peptide disrupted both cholesterol-rich and -poor liposomes, the conjugate, INF7-K(GalNAc)(2), only induced leakage of cholesterol-poor liposomes. Given that endosomal membranes of eukaryotic cells contain <5% cholesterol, this implies that the conjugate will display a higher selectivity toward endosomal membranes. Although both INF7 and INF7-K(GalNAc)(2) were found to increase the transfection efficiency on polyplex-mediated gene transfer to parenchymal liver cells by 30-fold, only INF7-K(GalNAc)(2) appeared to do so in an ASGPr-specific manner. In mice, INF7-K(GalNAc)(2) was specifically targeted to the liver, whereas INF7 was distributed evenly over various organs. In summary, we have prepared a nontoxic cell-specific lysosome disruptive element that improves gene delivery to parenchymal liver cells via the ASGPr. Its high cell specificity and preference to lyse intracellular membranes make this conjugate a promising lead in hepatocyte-specific drug/gene delivery protocols.

Enhancement of transgene expression by combining glucocorticoids and anti-mitotic agents during transient transfection using DNA-cationic liposomes

The anti-mitotic drugs colchicine and paclitaxel increase transfection efficiency of cationic liposomes. Using combined lipid-mediated transfection with anti-mitotic agents for gene therapy of cancer has been limited due to the likely development of multi-drug resistance (MDR). We treated human cancer cell lines and normal liver cells with glucocorticoids in combination with the antimitotics paclitaxel or colchicine before transient, cationic lipid-mediated transfection. Colchicine and paclitaxel each enhanced transgene expression in several cell lines. Moreover, glucocorticoid, combined with paclitaxel or colchicine, significantly increased reporter gene expression above that seen in cells treated with each drug alone. P-glycoprotein (PGP), a drug exporter encoded by ABCB1, exports both paclitaxel and colchicine. To determine the influence of PGP in colchicine- or paclitaxel-mediated enhancement of transgene expression, cells were treated with a histone deacetylase inhibitor, trichostatin A (TSA), known to induce ABCB1 expression, before treatment with colchicine or paclitaxel. TSA significantly reduced colchicine-mediated increases in reporter gene expression. Addition of glucocorticoid to colchicine pretreatment significantly attenuated TSA-mediated inhibition of colchicine-induced increases in transgene expression. TSA accelerated and glucocorticoid blocked export of rhodamine 123, a molecule known to be exported by PGP. The glucocorticoid/paclitaxel combination also increased reporter gene expression in BE(2)C cells, which constitutively express high levels of PGP. Thus, the degree of enhancement of transgene expression mediated by these anti-mitotics seems to be dependent on PGP activity. Glucocorticoids augment colchicine- or paclitaxel-mediated enhancement of transgene expression most likely by reducing drug egress through PGP.

Time course of gene expression after plasmid DNA gene transfer to the liver

BACKGROUND

High levels of expression in hepatocytes can be achieved after intraportal delivery of plasmid DNA vectors with up to 10% of all liver cells transfected. CMV promoter-driven expression is very high on Day 1 after injection, but is diminished strongly by Day 2. Expression slowly declines after 1 week. We describe experiments aimed at elucidating the reasons for this rapid decline in transgene expression.

METHODS

Histological methods were used to determine the presence and extent of liver damage and hepatocyte proliferation. Viral and liver-specific promoters were tested to study promoter shut-off, Southern blotting was performed to determine the loss of the pDNA vector over time, and several mouse models were used to study the host immunological response.

RESULTS

pDNA is lost rapidly early after injection, but remains at a relatively stable copy number after Day 4. Southern blotting experiments showed that plasmid DNA could be detected for at least 12 weeks after injection (0.2 copies per genome). The early rapid decline of expression is promoter dependent. A liver-specific albumin promoter resulted in similar levels of expression on Days 1 and 7, suggesting that promoter inactivation may be responsible for the instability of CMV promoter-driven expression. The slow decline in expression levels after 1 week appears to be the result of an immune response directed against the expressed transgene. Expression was much prolonged in immunosuppressed, immunodeficient, or antigen-tolerized mice.

CONCLUSION

The present data suggest that if promoter inactivation can be overcome, intravascular delivery of plasmid DNA could be a highly efficient, simple and non-toxic liver gene therapy approach. Intravascular delivery of pDNA allows for the rapid screening of novel expression vectors in vivo.

In vivo liver-directed gene transfer in rats and pigs with large anionic multilamellar liposomes: routes of administration and effects of surgical manipulations on transfection efficiency

Conventional large (500-800 nm) multilamellar liposomes encapsulating DNA have been used in vivo as gene vectors into rat and pig liver. By using the intraportal vein route, high dose DNA (10 mg/kg) provided low efficiency and transient luciferase gene expression in the liver. This gene expression was, however, increased by liver resection (> 50%), ischemia (20 min) or orthotopic transplantation. As evidenced by histochemical analysis of beta-galactosidase expression, the gene transfection mainly ensued in Kupffer cells, but spleen and lung were contaminated. In comparison, injection into the bile duct of even 25-fold lower dose of liposome-encapsulated DNA (0.4 mg/kg) produced higher (100-fold) and long-lasting (during 6 days, at least) luciferase expression in rat liver. The gene expression was restricted to the liver and enhanced by liver resection. By this route, transgene-expressing cells were mainly hepatocytes. A treatment with colchicine prior to the administration of the vector allowed the persistence of relative high gene expression for at least 7 days. In pigs, qualitatively similar, but quantitatively less efficient gene expression was obtained by either the portal vein or the bile duct route. These results indicate that intrabile duct route might render large non-viral vectors applicable to gene transfer into the hepatocytes. The efficiency of liposome-mediated gene transfer into the liver can be increased by liver resection, ischemia or transplantation performed before DNA injection.

Receptor-mediated targeting of gene delivery vectors: insights from molecular mechanisms for improved vehicle design

One way to deliver transgenes to cells in a selective manner is to target the delivery vehicles, or vectors, to specific cell-surface receptors as a first step toward ultimate transport of the gene to the nucleus for expression. While selective delivery, although often to undesired cell types, occurs naturally for some viral vectors and can be achieved for nonviral vehicles, current understanding and control of the delivery mechanism is inadequate for many therapeutic applications. The complicated nature of receptor-mediated transgene uptake and transport requires improved analysis to more effectively evaluate delivery vehicles. As receptor-mediated pathways for gene delivery typically involve vector binding, internalization, subcellular trafficking, vesicular escape, nuclear translocation, and unpackaging for transcription, each of these processes offer mechanisms that can be exploited to enhance targeted gene delivery via properly designed vehicles. For the purpose of this review, current targeted gene delivery vehicles are divided into three approaches: viral, synthetic, and hybrid vectors. Each approach possesses advantages as well as disadvantages at the present time for in vitro and in vivo application, and provides particular challenges to overcome in order to gain significantly improved targeted delivery properties. Quantitative experiments and mathematical modeling of the gene delivery pathway will serve to provide insight into molecular mechanisms and rate-limiting steps for effective gene expression. Information on molecular mechanisms obtained by such methodologies can then be applied to specific vectors, whether viral, synthetic, or hybrid, allowing for the creation of targeted, effective, and safe gene therapeutics.

Liver-directed gene therapy: promises, problems and prospects at the turn of the century

Although liver-directed gene therapy arrived later than gene therapy directed at bone marrow cells, intrinsic advantages of the liver as a target organ make it likely that gene therapy for liver diseases will be among the first therapeutically relevant applications of this treatment modality at the onset of the 21st century. Vectorology for gene transfer to the liver is advancing rapidly, and it is safe to predict that gene therapy vehicles that will be in clinical use a decade from now, have not yet been developed. None of the currently available modes of gene transfer to the liver is optimal for all types of applications. Nonetheless, the concerted effort of many investigators has provided a wide choice of non-viral and viral vectors for gene transfer to the liver for use in specific situations. Original strategies for liver-directed gene therapy included substitution of missing gene products, overexpression of intrinsic or extrinsic genes and inhibition of expression of specific genes. To the list is now added the possibility of site-specific correction or generation of mutations within specific genes in somatic cells of living adult animals. Thus, despite some initial faux pas, liver-directed gene therapy is poised to make an important impact on health care in the year 2000 and beyond.

A DNA delivery system containing listeriolysin O results in enhanced hepatocyte-directed gene expression

AIM: To determine whether incorporation of the pH-dependent ba cterial toxin listeriolysin O (LLO) into the DNA carrier system could increase the endosomal escape of internalized DNA and result gene expression.

METHODS: A multi-component delivery system was prepared consist ing of asialoglycoprotein (ASG), poly L-lysine (PL), and LLO. Two marker genes, luciferase and β-galactosidase in plasmids were complexed and administered in vitro to Huh7[ASG receptor (+)] and SK Hep1 [ASG rece ptor(-)] cells. Purity, hemolytic activity, gene expression, specificity, and toxicity were evaluated.

RESULTS: An LLO-containing conjugate retained cell-targeting specificity and membranolytic activity. In ASG receptor (+) cells, luciferas e gene expression was enhanced by more than 7-fold over that of conjugates with out the incorporation of listeriolysin O. No significant expression occurred in ASG receptor (-) cells. Enhancement of β-galactosidase gene expression was less, but still significantly increased over controls. There was no detectable toxicity at concentrations shown to be effective in transfection studies.

CONCLUSIONS: ASOR-PL can be coupled to LLO using disulfide bonds, and successfully target and increase the gene expression of foreign DNA.

Taking polycation gene delivery systems from in vitro to in vivo

It is widely believed that non-viral gene delivery systems may improve safety and overcome tissue-tropism limitations associated with viral-based gene therapies. Cationic liposome-based gene delivery currently accounts for 9-12% of ongoing gene therapy clinical trials in the United States and Europe. Polycation-based gene delivery is at an earlier development stage. However, both in vitro and in vivo studies have demonstrated that this is an area of much promise. Complexes of polycations with DNA result in major improvements in the control of size, charge, and the hydrophilic-lipophilic characteristics of the transfecting species, when compared with other non-viral systems. This review serves as an introduction to the current status of this field.

Application of membrane-active peptides for nonviral gene delivery

A variety of membrane-modifying agents including pH-specific fusogenic or lytic peptides, bacterial proteins, lipids, glycerol, or inactivated virus particles have been evaluated for the enhancement of DNA-polycation complex-based gene transfer. The enhancement depends on the characteristics of both the cationic carrier for DNA and the membrane-modifying agent. Peptides derived from viral sequences such as the N-terminus of influenza virus haemagglutinin HA-2, the N-terminus of rhinovirus HRV2 VP-1 protein, and other synthetic or natural sequences such as the amphipathic peptides GALA, KALA, EGLA, JTS1, or gramicidin S have been tested. Ligand-polylysine-mediated gene transfer can be improved up to more than 1000-fold by membrane-active compounds. Other polycations like dendrimers or polyethylenimines as well as several cationic lipids provide a high transfection efficiency per se. Systems based on these polymers or lipids are only slightly enhanced by endosomolytic peptides or adenoviruses. Electroneutral cationic lipid-DNA complexes however can be strongly improved by the addition of membrane-active peptides.

Targeting endocytosis and motor proteins to enhance DNA persistence

Gene therapy provides a major new therapeutic strategy for the treatment of disease. Despite its potential for the inhibition of disease progression at the molecular level, gene therapy has faced numerous challenges. Foremost amongst these is the introduction of a sufficient amount of DNA-based drug to the target cell under conditions that encourage persistence of the introduced DNA. Because many DNA-based drugs enter cells via receptor-mediated endocytosis, clearly modulation of this process is a key issue in maximizing DNA persistence. In this review, a particular protein that participates in receptor-mediated endocytosis, the microtubule-based motor protein, cytoplasmic dynein, is introduced. In addition, recent advances in the study of cytoplasmic dynein in receptor-mediated endocytosis are discussed, and there is consideration of the potential of cytoplasmic dynein as a critical target for the regulation of DNA-uptake and persistence.

Metabolic instability of plasmid DNA in the cytosol: a potential barrier to gene transfer

Inefficient nuclear delivery of plasmid DNA is thought to be one of the daunting hurdles to gene transfer, utilizing a nonviral delivery system such as polycation-DNA complex. Following its internalization by endocytosis, plasmid DNA has to be released into the cytosol before its nuclear entry can occur. However, the stability of plasmid DNA in the cytoplasm, that may play a determinant role in the transfection efficiency, is not known. The turnover of plasmid DNA, delivered by microinjection into the cytosol, was determined by fluorescence in situ hybridization (FISH) and quantitative single-cell fluorescence video-image analysis. Both single- and double-stranded circular plasmid DNA disappeared with an apparent half-life of 50-90 min from the cytoplasm of HeLa and COS cells, while the amount of co-injected dextran (MW 70,000) remained unaltered. We propose that cytosolic nuclease(s) are responsible for the rapid-degradation of plasmid DNA, since (1) elimination of plasmid DNA cannot be attributed to cell division or to the activity of apoptotic and lysosomal nucleases; (2) disposal of microinjected plasmid DNA was inhibited in cytosol-depleted cells or following the encapsulation of DNA in phospholipid vesicles; (3) generation and subsequent elimination of free 3'-OH ends could be detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay (TUNEL), reflecting the fragmentation of the injected DNA; and finally (4) isolated cytosol, obtained by selective permeabilization of the plasma membrane, exhibits divalent cation-dependent, thermolabile nuclease activity, determined by Southern blotting and 32P-release from end-labeled DNA. Collectively, these findings suggest that the metabolic instability of plasmid DNA, caused by cytosolic nuclease, may constitute a previously unrecognized impediment for DNA translocation into the nucleus and a possible target to enhance the efficiency of gene delivery.

Lysosome-disrupting peptide increases the efficiency of in-vivo gene transfer by liposome-encapsulated DNA

The main limitation of liposome-mediated gene transfer is its low efficiency, a result of degradation of the transferred DNA in the lysosome compartment. In an effort to overcome this problem, lysosome-disrupting peptide was co-encapsulated with a luciferase expression vector in liposomes. The encapsulation level of the peptide was high (> 80%) and did not affect DNA encapsulation efficiency. Liposomes encapsulating DNA were injected into mice and the efficiency of gene transfer and expression were measured. Polymerase chain reaction (PCR) analysis of DNA purified from mouse livers and spleens indicated that co-encapsulation of lysosome-disrupting peptide with DNA significantly increased the amount of transferred DNA found 5 days post-injection in the organ cells. Luciferase activity at 5 days post-injection in spleens of mice that were injected with liposomes containing luciferase expression vector and lysosome-disrupting peptide was significantly higher than that in mice injected with liposomes containing only luciferase expression vector or liposomes containing luciferase expression vector and control peptide. These results indicate that the efficiency of in-vivo liposome-mediated gene transfer can be significantly increased by co-encapsulation of lysosome-disrupting peptide with the transferred DNA.

Gene therapy: Recent advances and applications in gastroenterology and hepatology

The advantages and disadvantages of viral and non-viral vectors for gene delivery are reviewed. Advances in systems for introduction of new gene expression are described, including self-deleting retroviral transfer vectors, chimeric viruses and chimeric oligonucleotides. Systems for inhibition of gene expression are also discussed including antisense oligonucleotides, ribozymes and dominant-negative genes. Examples of the use of these systems in animal models and clinical trials for gastrointestinal disorders are discussed.

Biochemical and molecular aspects of genetic disorders of bilirubin metabolism

Bilirubin, the oxidative product of heme in mammals, is excreted into the bile after its esterification with glucuronic acid to polar mono- and diconjugated derivatives. The accumulation of unconjugated and conjugated bilirubin in the serum is caused by several types of hereditary disorder. The Crigler-Najjar syndrome is caused by a defect in the gene which encodes bilirubin UDP-glucuronosyltransferase (UGT), whereas the Dubin-Johnson syndrome is characterized by a defect in the gene which encodes the canalicular bilirubin conjugate export pump of hepatocytes. Animal models such as the unconjugated hyperbilirubinemic Gunn rat, the conjugated hyperbilirubinemic GY/TR-, and the Eisai hyperbilirubinemic rat, have contributed to the understanding of the molecular basis of hyperbilirubinemia in humans. Elucidation of both the structure of the UGT1 gene complex, and the Mrp2 (cMoat) gene which encodes the canalicular conjugate export pump, has led to a greater understanding of the genetic basis of hyperbilirubinemia.

Liver-directed gene transfer vectors

The ultimate goal of liver-directed gene therapy for genetic diseases is the stable expression of a therapeutic transgene in a significant proportion of hepatocytes. This article considers the various liver-directed gene transfer procedures studied so far. Performances and limitations of currently available vector systems are discussed with respect to their clinical relevance. Although some improvements have been reported, naked DNA and nonviral gene transfer vectors induce transient expression in only a limited number of cells. Clinical applications of retrovirus-mediated gene transfer are hampered by the need to induce hepatocyte division. First-generation adenovirus vectors are highly efficient; however, they induce an immune response leading to the rapid rejection of transduced cells. Promising new vector systems have emerged, including gutless adenovirus vectors, adeno-associated vectors, and lentivirus vectors. However, these systems are still poorly documented and their relevance to liver-directed gene therapy must be confirmed.

Transfer of the human Alpha1-antitrypsin gene into pulmonary macrophages in vivo

Several viral and nonviral methods have introduced functional genes into the lungs. An alternative strategy, receptor-mediated gene transfer, exploits the ability of receptors on the surface of cells to bind and internalize DNA complexes and could potentially be used to deliver genes to specific cells in the lung. The gene encoding human alpha1-antitrypsin (A1AT) was delivered to macrophages in vitro and in vivo by targeting the mannose receptor with mannose-terminal molecular conjugates. The human A1AT transcript was detected 2 d after transfection of macrophages in culture, but transgene expression was transient. Human A1AT protein was secreted into the culture medium, and Western blot hybridization revealed the mature human antiprotease. In addition, Sprague-Dawley rats underwent intravenous injections of increasing doses of plasmid DNA (0.2 mg, 1.0 mg, and 2.0 mg) complexed to the molecular conjugate. Four days after transfection, human A1AT mRNA was found in lungs from six of the 13 rats (46%) that received the higher doses of plasmid. Transgene expression was limited to cells in perivascular and alveolar regions, which conformed to the distribution of pulmonary macrophages. Human A1AT was measured in the epithelial lining fluid of rats treated with transfection complexes. Animals that received 1.0 mg of plasmid had human A1AT levels of 7.4 +/- 3.4 pM, which was significantly different from nontransfected and mock-transfected controls. Thus the mannose receptor permitted direct delivery of genes to pulmonary macrophages, though transgene expression was detected in the lung only at low levels.

Pre-clinical trials using hepatic gene delivery

The development of gene therapy as a potential technique for treating serious metabolic or infectious disorders has generated much interest. The general applicability of gene therapy depends on the efficient transfer of the desired gene to specific tissues and cells. One of the most attractive sites for gene transfer is the liver because it plays a major role in many metabolic processes and is involved in a large variety of diseases. Nonviral strategies have been conceived for delivering genes to the liver but this approach is still at the preclinical stage. This review outlines the more commonly used approaches and discusses the progress that has been made toward developing a widely applicable, clinically relevant gene transfer procedure for the liver.

Synthetic peptide-based DNA complexes for nonviral gene delivery

A major advantage of synthetic peptide-based DNA delivery systems is its flexibility. By design, the composition of the final complex can be easily modified in response to experimental results in vitro and in vivo to take advantage of specific peptide sequences to overcome extra- and intracellular barriers to gene delivery. The extreme heterogeneity which greatly complicates both the kinetics of DNA-poly(L-lysine) interaction and the thermodynamic stability of the final DNA complexes is avoided. Other unique features include the absence of biohazards related to the viral genome as well as the production of the viral vector and the absence of limitations on the size of the therapeutic genes that can be inserted in the recombinant viral vector. In principle, if the gene can be cloned into an expression plasmid, it can be delivered as a synthetic DNA complex. Since these synthetic delivery systems are composed of small peptides which may be poorly antigenic, they hold the promise of repeated gene administration, a highly desirable feature which will be important for gene targeting in vivo to endothelial cells, monocytes, hepatocytes and tumor cells.

Polylysine-based transfection systems utilizing receptor-mediated delivery

Receptor-mediated gene transfer is a promising gene delivery technique. It employs a DNA-binding polycation, such as polylysine, to compact plasmid DNA to a size that can be taken up by cells (<100-200 nm). To allow internalization by receptor-mediated endocytosis, cell binding ligands, such as asialoglycoproteins or galactose for hepatocytes, anti-CD3 and anti-CD5 for T-cells, and transferrin, have been covalently attached to polylysine. Intracellular barriers for successful gene transfer include release of DNA complexes from endosomes or lysosomes, nuclear import of DNA complexes, and disassembly of the DNA-polylysine particles. Release of particles from internal vesicles has been achieved by the addition of lysosomotropic agents or glycerol to the transfection medium, or by the incorporation of endosomolytic compounds, such as viruses or membrane active peptides. This technique has already been used to transfect certain organs in vivo, including liver and lung.

Gene therapy with bilirubin-UDP-glucuronosyltransferase in the Gunn rat model of Crigler-Najjar syndrome type 1

Crigler-Najjar syndrome type 1 (CN type 1) is an autosomal recessive disorder characterized by nonhemolytic jaundice resulting from mutations to the gene encoding bilirubin-UDP-glucuronosyltransferase (UDPGT). The Gunn rat is an accurate animal model of this disease because the bilirubin-UDPGT gene in this strain carries a premature stop codon. The primary objective of this study was to complement this deficiency in vivo using liver-directed gene therapy. The efficiency of adenovirus type 5 (Ad5)-mediated gene transfer to the neonatal rat liver was first assessed by intravenous (i.v.) injection of an Ad5 vector carrying a nuclear-localized LacZ gene. An Ad5 vector expressing the cDNA encoding human bilirubin-UDPGT (Ad5/CMV/hUG-Br1) was then generated and injected i.v. into neonatal Gunn rats. Plasma samples were collected and bilirubin levels were determined at regular intervals. Although the mean level of bilirubin in homozygous Gunn rats 1-2 days after birth was already 14.5-fold higher than that of heterozygous siblings, treatment with Ad5/CMV/hUG-Br1 reduced plasma bilirubin to normal levels within 1 week. Plasma bilirubin in the treated homozygous rats remained normal for 4 weeks before gradually climbing to intermediate levels that were approximately half that of untreated homozygotes by 12 weeks. Administration of Ad5-mediated gene therapy to neonatal Gunn rats effectively complemented the deficiency in bilirubin-UDPGT, resulting in substantial reductions in plasma bilirubin over a 3-month period. The efficacy of Ad5-mediated gene therapy in neonates suggests that this approach might be effective against other hepatic disorders, including autosomal recessive deficiencies in lipid metabolism and vascular homeostasis.

Receptor-mediated delivery of foreign genes to hepatocytes

Naturally existing cell surface receptors provide convenient systems for transporting substances from the extracellular environment to the interior of cells. When such receptors are highly selective for certain cell types, the possibility exists for targeting biological agents of interest to specific tissues. In this review, the concepts, progress and problems in targeting genes and their subsequent expression in hepatocytes based on the asialoglycoprotein receptor in vitro and in vivo will be discussed. The use of protein carriers for hepatocyte specific delivery of double stranded DNA to introduce novel gene expression novel, as well as, delivery of single stranded DNA for inhibition of endogenous genes with examples of each are reviewed.

Molecular motors and their role in membrane traffic

Recent investigations support a role for the vesicle motor proteins (kinesin, cytoplasmic dynein, and myosin) in numerous membrane trafficking events including endocytosis and transcytosis. Kinesin and cytoplasmic dynein are responsible for movement of membrane vesicles along cellular microtubules to and from cellular membrane compartments, while certain members of the myosin family also appear to drive membrane vesicles along actin filaments to and from membrane compartments. In this review, our current understanding of the role of these vesicle motors in membrane trafficking is highlighted. Future areas of interest which may be able to make use of these vesicle motors as potential targets for drug delivery are also discussed.

Pharmaceutical approach to somatic gene therapy

The pharmaceutical approach to somatic gene therapy is based on consideration of a gene as a chemical entity with specific physical, chemical and colloidal properties. The genes that are required for gene therapy are large molecules (> 1 x 10(6) Daltons, > 100 nm diameter) with a net negative charge that prevents diffusion through biological barriers such as an intact endothelium, the plasma membrane or the nuclear membrane. New methods for gene therapy are based on increasing knowledge of the pathways by which DNA may be internalized into cells and traffic to the nucleus, pharmaceutical experience with particulate drug delivery systems, and the ability to control gene expression with recombined genetic elements. This article reviews two themes in the development of gene therapies: first, the current approaches involving the administration of cells, viruses and plasmid DNA; second, the emerging pharmaceutical approach to gene therapy based on the pharmaceutical characteristics of DNA itself and methods for advanced drug delivery.