Liver gene therapy: advances and hurdles

Various AAV Serotypes and Their Applications in Gene Therapy: An Overview

Despite scientific discoveries in the field of gene and cell therapy, some diseases still have no effective treatment. Advances in genetic engineering methods have enabled the development of effective gene therapy methods for various diseases based on adeno-associated viruses (AAVs). Today, many AAV-based gene therapy medications are being investigated in preclinical and clinical trials, and new ones are appearing on the market. In this article, we present a review of AAV discovery, properties, different serotypes, and tropism, and a following detailed explanation of their uses in gene therapy for disease of different organs and systems.

Novel AAV-mediated genome editing therapy improves health and survival in a mouse model of methylmalonic acidemia

Methylmalonic acidemia (MMA) is an inborn error of metabolism mostly caused by mutations in the mitochondrial methylmalonyl-CoA mutase gene (MMUT). MMA patients suffer from frequent episodes of metabolic decompensation, which can be life threatening. To mimic both the dietary restrictions and metabolic decompensation seen in MMA patients, we developed a novel protein-controlled diet regimen in a Mmut deficient mouse model of MMA and demonstrated the therapeutic benefit of mLB-001, a nuclease-free, promoterless recombinant AAV GeneRide^TM vector designed to insert the mouse Mmut into the endogenous albumin locus via homologous recombination. A single intravenous administration of mLB-001 to neonatal or adult MMA mice prevented body weight loss and mortality when challenged with a high protein diet. The edited hepatocytes expressed functional MMUT protein and expanded over time in the Mmut deficient mice, suggesting a selective growth advantage over the diseased cells. In mice with a humanized liver, treatment with a human homolog of mLB-001 resulted in site-specific genome editing and transgene expression in the transplanted human hepatocytes. Taken together, these findings support the development of hLB-001 that is currently in clinical trials in pediatric patients with severe forms of MMA.

Cytokines in Liver Transplantation

Cytokines, soluble mediators of the immune system, play a critical role in the pathogenesis of autoimmune, allergic and infectious diseases. They are also implicated in the initiation and development of allograft rejection. During recent years, there have been considerable advances in generating novel anti-cytokine agents with promoted efficacy and safety, which could be administrated for managing dysregulated cytokine secretion; besides, gene therapy for overexpression of immunomodulatory cytokines has shown substantial improvements. Liver transplantation has been established as a life-saving treatment for end-stage hepatic diseases but the growing number of recipients urge for improved post-transplant care including tolerance induction, infection control and resolving immunosuppressant drugs adverse effects. Cytokines with a wide range of proinflammatory and regulatory properties might be considered as potential therapeutic targets for selective suppression or enhancement of the immune responses in recipients. In the present review, we aimed to summarize the positive and negative effects of cytokines on liver allograft in addition to their prognostic and therapeutic values.

Genome editing in the human liver: Progress and translational considerations

Liver-targeted genome editing offers the prospect of life-long therapeutic benefit following a single treatment and is set to rapidly supplant conventional gene addition approaches. Combining progress in liver-targeted gene delivery with genome editing technology, makes this not only feasible but realistically achievable in the near term. However, important challenges remain to be addressed. These include achieving therapeutic levels of editing, particularly in vivo, avoidance of off-target effects on the genome and the potential impact of pre-existing immunity to bacteria-derived nucleases, when used to improve editing rates. In this chapter, we outline the unique features of the liver that make it an attractive target for genome editing, the impact of liver biology on therapeutic efficacy, and disease specific challenges, including whether the approach targets a cell autonomous or non-cell autonomous disease. We also discuss strategies that have been used successfully to achieve genome editing outcomes in the liver and address translational considerations as genome editing technology moves into the clinic.

Facile synthesis of GalNAc monomers and block polycations for hepatocyte gene delivery

Here, we present a facile synthetic route for a monomer displaying N-acetyl-d-galactosamine and subsequent copolymerization in a block format with cationic subunits readily accessing liver-targeted polymeric pDNA delivery vehicles with low toxicity.

A peptide-functionalised dendronised polymer for selective transfection in human liver cancer cells

A dendronised polymer functionalised with SP94 targeting peptide achieves highly selective transient transfection of liver cancer cells over normal non-transformed hepatocytes.

AAV serotype 8-mediated liver specific GNMT expression delays progression of hepatocellular carcinoma and prevents carbon tetrachloride-induced liver damage

Glycine N-methyltransferase (GNMT) is abundantly expressed in normal livers and plays a protective role against tumor formation. GNMT depletion leads to progression of hepatocellular carcinoma (HCC). In this study, we investigated the activity of ectopic GNMT delivered using recombinant adeno-associated virus (AAV) gene therapy in mouse models of liver cirrhosis and HCC. Injection of AAV serotype 8 (AAV8) vector carrying the GNMT gene (AAV8-GNMT) in Gnmt^−/− mice increased GNMT expression and downregulated pro-inflammatory responses, resulting in reduced liver damage and incidence of liver tumors. Moreover, AAV8-GNMT resulted in the amelioration of carbon tetrachloride (CCl₄)-induced liver fibrosis in BALB/c mice. We showed that AAV8-GNMT protected hepatocytes from CCl₄-induced liver damage.  AAV8-GNMT significantly attenuated the levels of pro-fibrotic markers and increased efficiency of hepatocyte proliferation. These results suggest that correction of hepatic GNMT by gene therapy of AAV8-mediated gene enhancement may provide a potential strategy for preventing and delaying development of liver diseases.

Induction of apoptosis in imatinib sensitive and resistant chronic myeloid leukemia cells by efficient disruption of bcr-abl oncogene with zinc finger nucleases

Background

The bcr-abl fusion gene is the pathological origin of chronic myeloid leukemia (CML) and plays a critical role in the resistance of imatinib. Thus, bcr-abl disruption-based novel therapeutic strategy may warrant exploration. In our study, we were surprised to find that the characteristics of bcr-abl sequences met the design requirements of zinc finger nucleases (ZFNs).

Methods

We constructed the ZFNs targeting bcr-abl with high specificity through simple modular assembly approach. Western blotting was conducted to detect the expression of BCR-ABL and phosphorylation of its downstream STAT5, ERK and CRKL in CML cells. CCK8 assay, colony-forming assay and flow cytometry (FCM) were used to evaluate the effect of the ZFNs on the viablity and apoptosis of CML cells and CML CD34⁺ cells. Moreover, mice model was used to determine the ability of ZFNs in disrupting the leukemogenesis of bcr-abl in vivo.

Results

The ZFNs skillfully mediated 8-base NotI enzyme cutting site addition in bcr-abl gene of imatinib sensitive and resistant CML cells by homology-directed repair (HDR), which led to a stop codon and terminated the translation of BCR-ABL protein. As expected, the disruption of bcr-abl gene induced cell apoptosis and inhibited cell proliferation. Notably, we obtained similar result in CD34⁺ cells from CML patients. Moreover, the ZFNs significantly reduced the oncogenicity of CML cells in mice.

Conclusion

These results reveal that the bcr-abl gene disruption based on ZFNs may provide a treatment choice for imatinib resistant or intolerant CML patients.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0732-4) contains supplementary material, which is available to authorized users.

Induction of apoptosis in imatinib sensitive and resistant chronic myeloid leukemia cells by efficient disruption of bcr-abl oncogene with zinc finger nucleases

BACKGROUND

The bcr-abl fusion gene is the pathological origin of chronic myeloid leukemia (CML) and plays a critical role in the resistance of imatinib. Thus, bcr-abl disruption-based novel therapeutic strategy may warrant exploration. In our study, we were surprised to find that the characteristics of bcr-abl sequences met the design requirements of zinc finger nucleases (ZFNs).

METHODS

We constructed the ZFNs targeting bcr-abl with high specificity through simple modular assembly approach. Western blotting was conducted to detect the expression of BCR-ABL and phosphorylation of its downstream STAT5, ERK and CRKL in CML cells. CCK8 assay, colony-forming assay and flow cytometry (FCM) were used to evaluate the effect of the ZFNs on the viablity and apoptosis of CML cells and CML CD34⁺ cells. Moreover, mice model was used to determine the ability of ZFNs in disrupting the leukemogenesis of bcr-abl in vivo.

RESULTS

The ZFNs skillfully mediated 8-base NotI enzyme cutting site addition in bcr-abl gene of imatinib sensitive and resistant CML cells by homology-directed repair (HDR), which led to a stop codon and terminated the translation of BCR-ABL protein. As expected, the disruption of bcr-abl gene induced cell apoptosis and inhibited cell proliferation. Notably, we obtained similar result in CD34⁺ cells from CML patients. Moreover, the ZFNs significantly reduced the oncogenicity of CML cells in mice.

CONCLUSION

These results reveal that the bcr-abl gene disruption based on ZFNs may provide a treatment choice for imatinib resistant or intolerant CML patients.

Long-Term Correction of Diabetes in Mice by In Vivo Reprogramming of Pancreatic Ducts

Direct lineage reprogramming can convert readily available cells in the body into desired cell types for cell replacement therapy. This is usually achieved through forced activation or repression of lineage-defining factors or pathways. In particular, reprogramming toward the pancreatic β cell fate has been of great interest in the search for new diabetes therapies. It has been suggested that cells from various endodermal lineages can be converted to β-like cells. However, it is unclear how closely induced cells resemble endogenous pancreatic β cells and whether different cell types have the same reprogramming potential. Here, we report in vivo reprogramming of pancreatic ductal cells through intra-ductal delivery of an adenoviral vector expressing the transcription factors Pdx1, Neurog3, and Mafa. Induced β-like cells are mono-hormonal, express genes essential for β cell function, and correct hyperglycemia in both chemically and genetically induced diabetes models. Compared with intrahepatic ducts and hepatocytes treated with the same vector, pancreatic ducts demonstrated more rapid activation of β cell transcripts and repression of donor cell markers. This approach could be readily adapted to humans through a commonly performed procedure, endoscopic retrograde cholangiopancreatography (ERCP), and provides potential for cell replacement therapy in type 1 diabetes patients.

Alternative Start Sites Downstream of Non-Sense Mutations Drive Antigen Presentation and Tolerance Induction to C-Terminal Epitopes

CTL responses to the transgene product remain an active area of concern for the gene therapy field. A patient's underlying genetic mutation may influence the qualitative nature of these potentially destructive T cell responses. Individuals with a mutation that introduces a premature termination codon (PTC) that prevents synthesis of the full-length peptide are considered more likely to mount a transgene-specific T cell response because of a lack of immune tolerance to C-terminal epitopes as a consequence of absent endogenous Ag presentation. In this article, we demonstrate that a human ornithine transcarbamylase gene containing various PTC-inducing non-sense mutations is able to generate and present epitopes downstream of the termination codon. Generation of these epitopes occurs primarily from alternative translation start sites downstream of the stop codon. Furthermore, we show that expression of these genes from adeno-associated virus vectors in C57BL/6 mice is able to induce peripheral tolerance to epitopes downstream of the PTC. These results suggest that, despite the lack of full-length endogenous protein, patients with PTC-inducing non-sense mutations may still present T cell epitopes downstream of the premature termination site that may render the subject tolerant to wild-type transgene products.

Charge-altering releasable transporters (CARTs) for the delivery and release of mRNA in living animals

Functional delivery of mRNA to tissues in the body is key to implementing fundamentally new and potentially transformative strategies for vaccination, protein replacement therapy, and genome editing, collectively affecting approaches for the prevention, detection, and treatment of disease. Broadly applicable tools for the efficient delivery of mRNA into cultured cells would advance many areas of research, and effective and safe in vivo mRNA delivery could fundamentally transform clinical practice. Here we report the step-economical synthesis and evaluation of a tunable and effective class of synthetic biodegradable materials: charge-altering releasable transporters (CARTs) for mRNA delivery into cells. CARTs are structurally unique and operate through an unprecedented mechanism, serving initially as oligo(α-amino ester) cations that complex, protect, and deliver mRNA and then change physical properties through a degradative, charge-neutralizing intramolecular rearrangement, leading to intracellular release of functional mRNA and highly efficient protein translation. With demonstrated utility in both cultured cells and animals, this mRNA delivery technology should be broadly applicable to numerous research and therapeutic applications.

Hereditary Angioedema as a Metabolic Liver Disorder: Novel Therapeutic Options and Prospects for Cure

Hereditary angioedema (HAE) is a rare autosomal dominant disorder caused by mutations of the SERPING1 or the Factor 12 genes. It is potentially fatal, particularly if not identified at an early stage. Apart from androgens, which are contraindicated in children and in pregnant women, a range of effective, albeit very expensive treatments have recently become available for HAE patients. The cost of these new treatments is beyond the reach of most developing countries. At this time, there is no cure for the disorder. In spite of mutations of the SERPING1 gene, autoimmunity and infections are not prominent features of the condition. Here, we present the argument that HAE should be viewed primarily as a metabolic liver disorder. This conceptual paradigm shift will stimulate basic research and may facilitate new therapeutic approaches to HAE outlined in this paper. We suggest several novel potential treatment options for HAE from the perspectives of clinical immunology, molecular biology, and liver transplantation. Many of these offer the prospect of curing the disorder. The effectiveness of these options is rapidly improving in many cases, and their risks are decreasing. Given the very high costs of treating HAE, some of these curative options may become feasible in the next decade.

Hepatocyte cell therapy in liver disease

Liver disease is a leading cause of morbidity and mortality. Liver transplantation remains the only proven treatment for end-stage liver failure but is limited by the availability of donor organs. Hepatocyte cell therapy, either with bioartificial liver devices or hepatocyte transplantation, may help address this by delaying or preventing liver transplantation. Early clinical studies have shown promising results, however in most cases, the benefit has been short lived and so further research into these therapies is required. Alternative sources of hepatocytes, including stem cell-derived hepatocytes, are being investigated as the isolation of primary human hepatocytes is limited by the same shortage of donor organs. This review summarises the current clinical experience of hepatocyte cell therapy together with an overview of possible alternative sources of hepatocytes. Current and future areas for research that might lead towards the realisation of the full potential of hepatocyte cell therapy are discussed.

Efficient gene transfection to liver cells via the cellular regulation of a multifunctional polylactitol-based gene transporter

A new polylactitol-based multifunctional gene carrier has shown low cytotoxicity, a high transfection efficiency, and liver cell targeting bothin vitroandin vivo.

Phosphorylation of the nuclear receptor corepressor 1 by protein kinase B switches its corepressor targets in the liver in mice

Nuclear receptor corepressor 1 (NCoR1) is a transcriptional coregulator that has wide-ranging effects on gene expression patterns. In the liver, NCoR1 represses lipid synthesis in the fasting state, whereas it inhibits activation of peroxisome proliferator-activated receptor alpha (PPARα) upon feeding, thereby blunting ketogenesis. Here, we show that insulin by activation of protein kinase B induces phosphorylation of NCoR1 on serine 1460, which selectively favors its interaction with PPARα and estrogen-related receptor alpha (ERRα) over liver X receptor alpha (LXRα). Phosphorylation of NCoR1 on S1460 selectively derepresses LXRα target genes, resulting in increased lipogenesis, whereas, at the same time, it inhibits PPARα and ERRα targets, thereby attenuating oxidative metabolism in the liver. Phosphorylation-gated differential recruitment of NCoR1 to different nuclear receptors explains the apparent paradox that liver-specific deletion of NCoR1 concurrently induces both lipogenesis and oxidative metabolism owing to a global derepression of LXRα, PPARα, and ERRα activity.

CONCLUSION

Phosphorylation-mediated recruitment switch of NCoR1 between nuclear receptor subsets provides a mechanism by which corepressors can selectively modulate liver energy metabolism during the fasting-feeding transition.

Therapeutic genome editing: prospects and challenges

Recent advances in the development of genome editing technologies based on programmable nucleases have substantially improved our ability to make precise changes in the genomes of eukaryotic cells. Genome editing is already broadening our ability to elucidate the contribution of genetics to disease by facilitating the creation of more accurate cellular and animal models of pathological processes. A particularly tantalizing application of programmable nucleases is the potential to directly correct genetic mutations in affected tissues and cells to treat diseases that are refractory to traditional therapies. Here we discuss current progress toward developing programmable nuclease-based therapies as well as future prospects and challenges.

Sugar-appended polyamidoamine dendrimer conjugates with cyclodextrins as cell-specific non-viral vectors

The widespread use of various cyclodextrin (CyD)-appended polymers and polyrotaxanes as gene carriers has been reported. Among the various polyamidoamine dendrimer (dendrimer) conjugates with CyDs (CDE), the dendrimer (G3) conjugate with α-CyD having an average degree of substitution (DS) of 2.4 (α-CDE (G3, DS 2)) displayed remarkable properties as DNA carriers. In an attempt to develop cell-specific gene transfer carriers, we prepared some sugar-appended α-CDEs, e.g. mannosylated, galactosylated, and lactosylated α-CDEs. In addition, PEGylated Lac-α-CDEs (G3) were prepared and evaluated as a hepatocyte-selective and serum-resistant gene transfer carrier. Moreover, PEGylated-α-CDE/CyD polypseudorotaxane systems for novel sustained DNA release system have been developed. Interestingly, glucronylglucosyl-β-cyclodextrin (GUG-β-CyD) conjugates with dendrimer (G2) (GUG-β-CDE (G2)) had superior gene transfer activity to α-CDE (G2), expecting a development of new series of sugar-appended CDEs over α-CDEs (G2). Collectively, sugar-appended α-CDEs have the potential as novel cell-specific and safe carriers for DNA.

Therapeutic efficiency of folated poly(ethylene glycol)-chitosan-graft-polyethylenimine-Pdcd4 complexes in H-ras12V mice with liver cancer

Background

Chitosan and chitosan derivatives have been proposed as alternative and biocompatible cationic polymers for nonviral gene delivery. However, the low transfection efficiency and low specificity of chitosan is an aspect of this approach that must be addressed prior to any clinical application. In the present study, folated poly(ethylene glycol)-chitosan-graft-polyethylenimine (FPCP) was investigated as a potential folate receptor-overexpressed cancer cell targeting gene carrier.

Methods

The FPCP copolymer was synthesized in two steps. In the first step, folate-PEG was synthesized by an amide formation reaction between the activated carboxyl groups of folic acid and the amine groups of bifunctional poly(ethylene glycol) (PEG). In the second step, FPCP was synthesized by an amide formation reaction between the activated carboxyl groups of folate-PEG and amine groups of CHI-g-polyethyleneimine (PEI). The composition of FPCP was characterized by 1H nuclear magnetic resonance.

Results:

FPCP showed low cytotoxicity in various cell lines, and FPCP-DNA complexes showed good cancer cell specificity as well as good transfection efficiency in the presence of serum. Further, FPCP-Pdcd4 complexes reduced tumor numbers and progression more effectively than PEI 25 kDa in H-ras12V liver cancer mice after intravenous administration.

Conclusion

Our data suggest that FPCP, which has improved transfection efficiency and cancer cell specificity, may be useful in gene therapy for liver cancer.

Liver-targeted gene delivery through retrograde intrabiliary infusion

Retrograde intrabiliary infusion (RII) has recently been characterized as a safe and effective administration route for liver-targeted gene delivery. Efficient transgene expression in the liver has been achieved by infusing a variety of gene vectors including adenovirus, retrovirus, lipoplexes, polyplexes, and naked DNA through the common bile duct. Here, we describe the RII technique and key infusion parameters for delivering plasmid DNA and DNA nanoparticles to the rat liver. After RII of plasmid DNA, the level of transgene expression in rat liver is comparable to that achieved by hydrodynamic injection of plasmid DNA, which is considered to be "gold standard" for liver-targeted gene delivery. RII has also been shown to significantly enhance the gene delivery efficiency by polymer/DNA nanoparticles in comparison with intravenous and intraportal infusions. This method induces minimal level of cytotoxicity and damage to the liver and bile duct. Due to these advantages, RII has the potential to be used for delivering various gene vectors in clinical setting through the endoscopic retrograde cholangiopancreatography procedure.

The liver as a target organ for gene therapy: state of the art, challenges, and future perspectives

The liver is a target for gene therapy of inborn errors of metabolism, of hemophilia, and of acquired diseases such as liver cancer and hepatitis. The ideal gene transfer strategy should deliver the transgene DNA to parenchymal liver cells with accuracy and precision in the absence of side effects. Liver sinusoids are highly specialized capillaries with a particular endothelial lining: the endothelium contains open fenestrae, whereas a basal lamina is lacking. Fenestrae provide a direct access of gene transfer vectors to the space of Disse, in which numerous microvilli from parenchymal liver cells protrude. The small diameter of fenestrae in humans constitutes an anatomical barrier for most gene transfer vectors with the exception of adeno-associated viral (AAV) vectors. Recent studies have demonstrated the superiority of novel AAV serotypes for hepatocyte-directed gene transfer applications based on enhanced transduction, reduced prevalence of neutralizing antibodies, and diminished capsid immune responses. In a landmark clinical trial, hemophilia B was successfully treated with an AAV8 human factor IX expressing vector. Notwithstanding significant progress, clinical experience with these technologies remains very limited and many unanswered questions warrant further study. Therefore, the field should continue to progress as it has over the past decade, cautiously and diligently.

Gene transfer of c-met confers protection against D-galactosamine/lipopolysaccharide-induced acute liver failure

BACKGROUND

Acute liver failure (ALF) is characterized by impaired regeneration of hepatocytes, partially resulting from the defective signaling between elevated levels of hepatocyte growth factor (HGF) and the downregulation of its receptor, c-met.

AIMS

In this study, we assess the therapeutic efficacy of in vivo c-met gene transfer in ALF.

METHODS

We established a D: -galactosamine/lipopolysaccharide (D: -GalN/LPS)-induced ALF model in rats. The levels of HGF and c-met in D: -GalN/LPS rats were compared with vehicle-injected rats and those undergoing liver regeneration following partial hepatectomy (PH). To deliver c-met in vivo, pcDNA-c-met was constructed and transfected into the rat liver via hydrodynamic injection. Control rats were transfected with the pcDNA3.1 plasmid. The expressions of c-met in different tissues were examined by immunohistochemistry. Hepatocyte proliferation and apoptosis were determined by PCNA staining and TUNEL assay, respectively. The survival of rats in the control and c-met-expressing rats was compared by Kaplan-Meier analysis.

RESULTS

Compared with control rats, D: -GalN/LPS or PH -treated rats had significantly higher levels of HGF (P < 0.01). D: -GalN/LPS also led to significantly lower c-met expression in the liver (P < 0.01) than PH. The in vivo c-met gene transfer led to its specific expression on hepatocytes, which was accompanied by the enhancement of hepatocyte proliferation, a reduction in apoptosis, as well as significant improvement in overall survival (P < 0.01).

CONCLUSIONS

This study provides the initial evidence that c-met may serve as a novel target for gene therapy, and may be of clinical benefit in the treatment of patients with ALF.

Multiple components in serum contribute to hepatic transgene expression by lipoplex in mice

BACKGROUND

Interaction of cationic liposome/plasmid DNA complex (lipoplex) with serum was not a limiting factor for in vivo transfection. After intraportal injection of lipoplex, hepatic transgene expression was enhanced by interaction with serum in mice. In the present study, we analyzed the mechanism of enhanced hepatic transgene expression of lipoplex by interaction with serum components.

METHODS

Lipoplexes were incubated with several serum components for 5  min at 37  ° C before administration. Transfection efficiency of lipoplexes was measured 6  h after intraportal injection of lipoplex in mice.

RESULTS

Depletion of divalent cation from serum decreased hepatic transgene expression. The addition of calcium ion to divalent cation-depleted serum restored transgene expression. Heat-inactivated serum and bovine serum albumin diminished the enhancing effect of serum on hepatic transgene expression. On the other hand, removal of anionic proteins from serum using an anion-exchanging column was critical for the enhancing effect of serum on transgene expression. Among the serum components tested, fibronectin and complement component C3 enhanced hepatic transgene expression.

CONCLUSIONS

Hepatic transgene expression by lipoplex was enhanced by interaction with multiple components in serum. Interaction of lipoplex with serum could be an important factor for successful in vivo gene transfer. Hence, the information obtained in the present study is valuable for the future development of effective gene carriers.

Design and synthesis of dual-ligand modified chitosan as a liver targeting vector

Vector plays an important role in hepatic targeted drug delivery system. In this study, a novel material as a liver targeting vector, dual-ligand modified chitosan (GCGA) composed of chitosan (CTS), glycyrrhetinic acid (GA) and lactobionic acid (LA), was designed and synthesized by an orthogonal experiment with two-step synthesis under mild conditions. The synthesized final product was characterized and confirmed by FTIR and (1)H-NMR spectroscopy, and DS of GA and LA in CTS were measured to be 13.77 and 16.74 mol% using (1)H-NMR, respectively. The cytotoxicity of CTS and GCGA was concentration dependent which was inverse proportion to the cell viability by MTT assay using L929 cell line, and inhibitory concentration 50% (IC50) was 0.2 mg/ml for GCGA. The in vitro targeting efficiency and the in vitro cellular uptake were investigated. Compared with CTS NPs and GA-CTS NPs, GCGA NPs showed good cell specificity to BEL-7402 cells via the dual-ligand-receptor-mediated recognition, leading to a higher affinity to BEL-7402 cells. The results suggested that GCGA described here has the potential to be used as an effective vector for hepatic targeted drug therapy.

Hepatocyte-targeted expression by integrase-defective lentiviral vectors induces antigen-specific tolerance in mice with low genotoxic risk

Lentiviral vectors are attractive tools for liver-directed gene therapy because of their capacity for stable gene expression and the lack of preexisting immunity in most human subjects. However, the use of integrating vectors may raise some concerns about the potential risk of insertional mutagenesis. Here we investigated liver gene transfer by integrase-defective lentiviral vectors (IDLVs) containing an inactivating mutation in the integrase (D64V). Hepatocyte-targeted expression using IDLVs resulted in the sustained and robust induction of immune tolerance to both intracellular and secreted proteins, despite the reduced transgene expression levels in comparison with their integrase-competent vector counterparts. IDLV-mediated and hepatocyte-targeted coagulation factor IX (FIX) expression prevented the induction of neutralizing antibodies to FIX even after antigen rechallenge in hemophilia B mice and accounted for relatively prolonged therapeutic FIX expression levels. Upon the delivery of intracellular model antigens, hepatocyte-targeted IDLVs induced transgene-specific regulatory T cells that contributed to the observed immune tolerance. Deep sequencing of IDLV-transduced livers showed only rare genomic integrations that had no preference for gene coding regions and occurred mostly by a mechanism inconsistent with residual integrase activity.

CONCLUSION

IDLVs provide an attractive platform for the tolerogenic expression of intracellular or secreted proteins in the liver with a substantially reduced risk of insertional mutagenesis.

Spermine grafted galactosylated chitosan for improved nanoparticle mediated gene delivery

Despite multitude of beneficial features, chitosan has poor water solubility and transfection ability which affect its gene delivery efficacy. The two features are improved when certain chemical modifications are incorporated into the chitosan parent backbone. This strategy is adopted here, by coupling galactose and spermine into the chitosan backbone. The conjugation was determined with FTIR and (1)H NMR and nanoparticle morphology was assessed by TEM and AFM techniques. Particle size, zeta potential, buffering capacity and DNA binding ability gave encouraging result of enhanced solubility and stability. In vitro studies of GCSM in HepG2 cell lines displayed low cytotoxicity and improved transfection. We also identified the preference of receptor mediated internalization for nanoparticles cellular uptake by treating with cellular uptake inhibitors. The results evidently led us to comprehend that galactosylated chitosan-g-spermine could be considered as a promising chitosan derivative for conducting nanoparticle mediated gene delivery.

Transplantation of encapsulated hepatocytes during acute liver failure improves survival without stimulating native liver regeneration

The aim of this study was to evaluate the effects of intraperitoneal transplantation of encapsulated human hepatocytes on liver metabolism and regeneration of mice with acute liver failure. Primary human hepatocytes were immortalized using lentiviral vectors coding for antiapoptotic genes and microencapsulated using alginate-polylysine polymers. In vitro, immortalized human hepatocytes showed low, but stable, synthetic and catabolitic functions over time, when compared to primary hepatocytes. In vivo, mice with acute liver failure and transplanted with encapsulated immortalized human hepatocytes had a significantly improved survival and biochemical profile, compared to mice transplanted with empty capsules. Serum levels of cytokines implicated in liver regeneration were lower in mice transplanted with hepatocytes compared to mice receiving empty capsules. This decrease was significant for IL-6 and HGF at 3 h. Measurement of liver regeneration showed no significant difference between mice transplanted with hepatocytes compared to control groups. Intraperitoneal transplantation of encapsulated immortalized hepatocytes significantly improved survival of mice with acute liver failure by providing metabolic support and without modifying liver regeneration. The lower levels of cytokines implicated in liver regeneration suggest that the metabolic support provided by the encapsulated hepatocytes reduced the inflammatory stress on the liver and herein decreased the regenerative trigger on residual hepatocytes. These data emphasize that metabolic function and regeneration of hepatocytes are two distinct aspects that need to be studied and approached separately during acute liver failure.

Intra-arterial targeted islet-specific expression of Sirt1 protects β cells from streptozotocin-induced apoptosis in mice

Gene therapy provides a promising approach to curing diabetes. However, an effective route for islet-specific targeting has yet to be established. Toward this end, the pancreatic blood circulation system in Balb/c mice was determined by the injection of rhodamine-containing beads. The efficiency of islet targeting was then measured by the injection of adenoviral vectors carrying a green fluorescence gene via the celiac trunk (C.T.). The results showed that >95% of islets and about 60% of β cells within the pancreatic body and tail could be labeled 3 days after surgery. α-Cell labeling was not as efficient, whereas labeling of nonendocrine tissues was barely detectable. For proof of principle, adenoviral vectors carrying a Sirtuin transgene were injected similarly to test the islet protection effect in the streptozotocin (STZ)-induced type 1 diabetic model. The results demonstrated that overexpression of Sirtuin in STZ-treated mice reduced the level of β-cell death and extent of glucose intolerance. This study reports on efficient islet-specific targeting by using adenoviral injection. This procedure could be invaluable to the treatment of diabetes and the study of islet biology.

Gene therapy for liver regeneration: experimental studies and prospects for clinical trials

The liver is an exceptional organ, not only because of its unique anatomical and physiological characteristics, but also because of its unlimited regenerative capacity. Unfolding of the molecular mechanisms that govern liver regeneration has allowed researchers to exploit them to augment liver regeneration. Dramatic progress in the field, however, was made by the introduction of the powerful tool of gene therapy. Transfer of genetic materials, such as hepatocyte growth factor, using both viral and non-viral vectors has proved to be successful in augmenting liver regeneration in various animal models. For future clinical studies, ongoing research aims at eliminating toxicity of viral vectors and increasing transduction efficiency of non-viral vectors, which are the main drawbacks of these systems. Another goal of current research is to develop gene therapy that targets specific liver cells using receptors that are unique to and highly expressed by different liver cell types. The outcome of such investigations will, undoubtedly, pave the way for future successful clinical trials.

Gene therapy for dyslipidemia: a review of gene replacement and gene inhibition strategies

Despite numerous technological and pharmacological advances and more detailed knowledge of molecular etiologies, cardiovascular diseases remain the leading cause of morbidity and mortality worldwide claiming over 17 million lives a year. Abnormalities in the synthesis, processing and catabolism of lipoprotein particles can result in severe hypercholesterolemia, hypertriglyceridemia or low HDL-C. Although a plethora of antidyslipidemic pharmacological agents are available, these drugs are relatively ineffective in many patients with Mendelian lipid disorders, indicating the need for new and more effective interventions. In vivo somatic gene therapy is one such intervention. This article summarizes current strategies being pursued for the development of clinical gene therapy for dyslipidemias that cannot effectively be treated with existing drugs.

Targeted gene delivery to selected liver segments via isolated hepatic perfusion

BACKGROUND

Development of targeted gene transfer technologies is essential for in vivo gene therapy. In this study, we examined the feasibility of physically targeting an adenoviral vector to selected liver segments in rats by isolating the hepatic perfusion (IHSP) and clamping the portal vein between the upper and lower segments.

MATERIALS AND METHODS

The rats were divided into two groups: IHSP group and the inferior vena cava (IVC) group. The adenoviral vector, which harbored the beta-galactosidase (beta-gal) gene, was administered via the portal vein, after which unbound vector particles were washed out with phosphate-buffered saline (PBS) and removed via the cannulated inferior vena cava (IVC) in IHSP group, while the IVC group received the transgene directly via the IVC without isolation of the hepatic perfusion.

RESULTS

With this configuration (IHSP group), >99% of the beta-gal activity was limited to the targeted hepatic lobes, findings which were confirmed by histochemical staining with X-gal. We also found there to be significant differences in transgene expression among the hepatic lobes in the IVC group.

CONCLUSIONS

Taken together, these results indicate that the IHSP technique is useful for local gene delivery to selected liver segments, and that when evaluating the efficacy of IHSP in the treatment of liver disease (e.g., nonresectable tumors), interlobar differences must be given careful consideration to ensure that sufficient drug or vector is delivered to all targeted hepatic lobes.

AAV8-mediated gene therapy prevents induced biochemical attacks of acute intermittent porphyria and improves neuromotor function

Acute intermittent porphyria (AIP), an autosomal dominant hepatic porphyria due to half-normal hydroxymethylbilane synthase (HMB-synthase) activity, is manifested by life-threatening acute neurological attacks that are precipitated by factors that induce heme biosynthesis. The acute attacks are currently treated with intravenous hemin, but a more continuous therapy is needed, particularly for patients experiencing frequent attacks. Thus, a recombinant AAV8-based serotype vector expressing murine HMB-synthase driven by liver-specific regulatory elements was generated and its effectiveness to prevent the biochemical induction of an acute attack was evaluated in an AIP mouse model. Intraperitoneal administration of the adeno-associated viral (AAV) vector resulted in a rapid and dose-dependent increase of HMB-synthase activity that was restricted to the liver. Stable expression of hepatic HMB-synthase was achieved and wild-type or greater levels were sustained for 36 weeks. When heme synthesis was periodically induced by a series of phenobarbital injections, the treated mice did not accumulate urinary delta-aminolevulinic acid (ALA) or porphobilinogen (PBG), indicating that the expressed enzyme was functional in vivo and prevented induction of the acute attack. Further, rotarod performance and footprint analyses improved significantly. Thus, liver-directed gene therapy provided successful long-term correction of the hepatic metabolic abnormalities and improved neuromotor function in the murine model of human AIP.

Liver- and lobe-specific gene transfer following the continuous microinstillation of Plasmid DNA onto the liver surface in mice: effect of instillation speed

Development of technology to deliver foreign gene(s) to a specific organ/tissue is one of the major challenges in gene therapy. Here, we show liver- and lobe-specific gene transfer following the continuous microinstillation of plasmid DNA (pDNA) onto the liver surface in mice. Naked pDNA was continuously instilled onto the right medial liver lobe using syringe pump in male ddY mice. Our previous studies showed liver- and lobe-selective gene expression after instillation of 30 mul of pDNA solution onto the liver surface, but gene expression was also found in the other liver lobe, kidney and spleen. To improve target site selectivity of gene expression, the instillation volume was decreased; however, non-specific gene expression in the other liver lobe and diaphragm was still detected. To prevent immediate diffusion of the pDNA solution, we performed continuous microinstillation of pDNA using a syringe pump; as a result, target site selectivity was greatly improved. As for instillation speed, 5 min infusion was enough to prevent diffusion of pDNA solution. Furthermore, transfection efficiency in the target site was maintained when instillation speed was slowed. Wiping off residual pDNA solution from the applied liver lobe resulted in a further improvement in selectivity, suggesting not only immediate diffusion, but also gradual diffusion, are important factors for successful target site-specific gene transfer. Information in this study will be useful for further development of an effective gene delivery system targeted to a specific organ/tissue by use of other non-viral or viral vectors.

Improved survival of fulminant liver failure by transplantation of microencapsulated cryopreserved porcine hepatocytes in mice

The aim of this study was to establish hepatocyte isolation in pigs, and to evaluate function of isolated hepatocytes after encapsulation, cryopreservation, and transplantation (Tx) in a mouse model of fulminant liver failure (FLF). After isolation, porcine hepatocytes were microencapsulated with alginate-poly-L-Lysine-alginate membranes and cryopreserved. In vitro, albumin production of free and encapsulated hepatocytes were measured by enzyme linked-immunoadsorbent assay. In vivo, encapsulated hepatocytes were transplanted into different groups of mice with FLF and the following experimental groups were performed: group 1, Tx of empty capsules; group 2, Tx of free primary porcine hepatocytes; group 3, Tx of fresh encapsulated porcine hepatocytes; group 4, Tx of cryopreserved encapsulated porcine hepatocytes. In vitro, fresh or cryopreserved encapsulated porcine hepatocytes showed a continuous decreasing metabolic function over 1 week (albumin and urea synthesis, drug catabolism). In vivo, groups 1 and 2 showed similar survival (18% and 25%, respectively, p > 0.05). In groups 3 and 4, Tx of fresh or cryopreserved encapsulated porcine hepatocytes significantly increased survival rate to 75% and 68%, respectively (p < 0.05). Primary porcine hepatocytes maintained metabolic functions after encapsulation and cryopreservation. In mice with FLF, Tx of encapsulated xenogeneic hepatocytes significantly improved survival. These results indicate that porcine hepatocytes can successfully be isolated, encapsulated, stored using cryopreservation, and transplanted into xenogeneic recipients with liver failure and sustain liver metabolic functions.

High Efficiency and Long-Term Foreign Gene Expression in Cultured Liver Sinusoidal Endothelial Cells by Retroviral Transduction

The liver sinusoidal endothelial cells (LSECs) constitute a very specialized endothelium. Due to their multiple functions and privileged location in the liver, these cells constitute an excellent target for gene therapy. In this work, the authors investigate the efficiency of retroviral gene transduction as a method for in vitro gene delivery into murine LSECs. Gene transduction into murine LSECs was performed using the PCMMP-eGFP/pIK-MLVgp retrovirus pseudotyped with the vesicular stomatitis virus G glycoprotein (VSV-g), containing eGFP as a reporter gene. Retroviral transduction resulted in a high efficiency of gene transfer (99%) and stable expression of eGFP in LSECs. The retroviral transduction protocol did not affect the morphology or expression of endothelial cell markers or the biological functions of LSECs. The authors have developed conditions for high-efficiency and stable retroviral gene transduction of LSECs. These results raise the possibility of liver gene therapy using LSECs as vehicle for the delivery of therapeutic proteins by means of retroviral vectors.

Matriptase-2 (TMPRSS6): a proteolytic regulator of iron homeostasis

Maintaining the body's levels of iron within precise boundaries is essential for normal physiological function. Alterations of these levels below or above the healthy limit lead to a systemic deficiency or overload in iron. The type-two transmembrane serine protease (TTSP), matriptase-2 (also known as TMPRSS6), is attracting significant amounts of interest due to its recently described role in iron homeostasis. The finding of this regulatory role for matriptase-2 was originally derived from the observation that mice deficient in this protease present with anemia due to elevated levels of hepcidin and impaired intestinal iron absorption. Further in vitro analysis has demonstrated that matriptase-2 functions to suppress bone morphogenetic protein stimulation of hepcidin transcription through cell surface proteolytic processing of the bone morphogenetic protein co-receptor hemojuvelin. Consistently, the anemic phenotype of matriptase-2 knockout mice is mirrored in humans with matripase-2 mutations. Currently, 14 patients with iron-refractory iron deficiency anemia (IRIDA) have been reported to harbor various genetic mutations that abrogate matriptase-2 proteolytic activity. In this review, after overviewing the membrane anchored serine proteases, in particular the TTSP family, we summarize the identification and characterization of matriptase-2 and describe its functional relevance in iron metabolism.

Progress toward liver-based gene therapy

The liver is involved in the synthesis of serum proteins, regulation of metabolism and maintenance of homeostasis and provides a variety of opportunities for gene therapy. The enriched vasculature and blood circulation, fenestrated endothelium, abundant receptors on the plasma membranes of the liver cells, and effective transcription and translation machineries in the hepatocytes are some unique features that have been explored for delivery, and functional analysis, of genetic sequences in the liver. Both viral and non-viral methods have been developed for effective gene delivery and liver-based gene therapy. This review describes the fundamentals of gene delivery, and the preclinical and clinical progress that has been made toward gene therapy using the liver as a target.

Engineered glucagon-like peptide-1-producing hepatocytes lower plasma glucose levels in mice

Glucagon-like peptide (GLP)-1 is an incretin hormone with well-characterized antidiabetic properties, including glucose-dependent stimulation of insulin secretion and enhancement of beta-cell mass. GLP-1 agonists have recently been developed and are now in clinical use for the treatment of type 2 diabetes. Rapid degradation of GLP-1 by enzymes including dipeptidyl-peptidase (DPP)-IV and neutral endopeptidase (NEP) 24.11, along with renal clearance, contribute to a short biological half-life, necessitating frequent injections to maintain therapeutic efficacy. Gene therapy may represent a promising alternative approach for achieving long-term increases in endogenous release of GLP-1. We have developed a novel strategy for glucose-regulated production of GLP-1 in hepatocytes by expressing a DPP-IV-resistant GLP-1 peptide in hepatocytes under control of the liver-type pyruvate kinase promoter. Adenoviral delivery of this construct to hepatocytes in vitro resulted in production and secretion of bioactive GLP-1 as measured by a luciferase-based bioassay developed to detect the NH2-terminally modified GLP-1 peptide engineered for this study. Transplantation of encapsulated hepatocytes into CD-1 mice resulted in an increase in plasma GLP-1 levels that was accompanied by a significant reduction in fasting plasma glucose levels. The results from this study demonstrate that a gene therapy approach designed to induce GLP-1 production in hepatocytes may represent a novel strategy for long-term secretion of bioactive GLP-1 for the treatment of type 2 diabetes.

Ectopic expression of neural autoantigen in mouse liver suppresses experimental autoimmune neuroinflammation by inducing antigen-specific Tregs

Tregs are important mediators of immune tolerance to self antigens, and it has been suggested that Treg inactivation may cause autoimmune disease. Therefore, immunotherapy approaches that aim to restore or expand autoantigen-specific Treg activity might be beneficial for the treatment of autoimmune disease. Here we report that Treg-mediated suppression of autoimmune disease can be achieved in vivo by taking advantage of the ability of the liver to promote immune tolerance. Expression of the neural autoantigen myelin basic protein (MBP) in the liver was accomplished stably in liver-specific MBP transgenic mice and transiently using gene transfer to liver cells in vivo. Such ectopic MBP expression induced protection from autoimmune neuroinflammation in a mouse model of multiple sclerosis. Protection from autoimmunity was mediated by MBP-specific CD4+CD25+Foxp3+ Tregs, as demonstrated by the ability of these cells to prevent disease when adoptively transferred into nontransgenic mice and to suppress conventional CD4+CD25- T cell proliferation after antigen-specific stimulation with MBP in vitro. The generation of MBP-specific CD4+CD25+Foxp3+ Tregs in vivo depended on expression of MBP in the liver, but not in skin, and occurred by TGF-beta-dependent peripheral conversion from conventional non-Tregs. Our findings indicate that autoantigen expression in the liver may generate autoantigen-specific Tregs. Thus, targeting of autoantigens to hepatocytes may be a novel approach to prevention or treatment of autoimmune diseases.

Acute intermittent porphyria: vector optimization for gene therapy

BACKGROUND

Acute intermittent porphyria (AIP) is an autosomal dominant disorder caused by the half-normal activity of hydroxymethylbilane synthase (HMB-synthase). Affected individuals can experience episodic, life-threatening, acute neurological attacks that are precipitated by various drugs, dieting, and hormonal changes. Intravenous hematin is used to treat the attacks, but a more effective, preventive therapy is needed, especially for patients with frequent attacks. Since the disease is a hepatic encephalopathy, efforts were focused towards evaluating four different combinations of liver-specific enhancers and promoters for maximal hepatic HMB-synthase expression.

METHODS

Four different mammalian expression vectors, each carrying a unique combination of liver-specific enhancers and promoters driving murine HMB-synthase cDNA expression, were transiently transfected into HepG2 cells. The vectors included: HMBS-1; human alpha1-microglobulin enhancer/alpha1-antityrpsin promoter (alpha1Me/alpha1ATp), HMBS-2; alpha1Me/human serum albumin promoter (alpha1Me/SAp), HMBS-3; human prothrombin enhancer/SAp (PTe/SAp), and HMBS-4; (PTe/alpha1ATp). Each HMB-synthase construct and a luciferase reporter construct were hydrodynamically coinjected into mice with HMB-synthase deficiency and evaluated for hepatic expression 24 h post-injection, the time-point of peak hepatic HMB-synthase expression.

RESULTS

Following transient transfection into HepG2 cells, HMBS-1 (alpha1Me/alpha1ATp) had the highest HMB-synthase expression level, with an approximately 8-fold increase over endogenous cellular activities. Construct HMBS-1 also had the highest hepatic HMB-synthase activity following hydrodynamic delivery into HMB-synthase deficient mice, with a approximately 6-fold increase over saline-treated mice.

CONCLUSIONS

These studies support the use of a gene therapy vector containing the alpha1Me/alpha1ATp combination for preclinical studies of the efficacy and safety of liver-targeted gene therapy for AIP.