Effects of inflammatory response on in vivo transgene expression by plasmid DNA in mice

Interaction of Lipoplex with Albumin Enhances Gene Expression in Hepatitis Mice

Understanding the in vivo fate of lipoplex, which is composed of cationic liposomes and DNA, is an important issue toward gene therapy. In disease conditions, the fate of lipoplex might change compared with the normal condition. Here, we examined the contribution of interaction with serum components to in vivo transfection using lipoplex in hepatitis mice. Prior to administration, lipoplex was incubated with serum or albumin. In the liver, the interaction with albumin enhanced gene expression in hepatitis mice, while in the lung, the interaction with serum or albumin enhanced it. In normal mice, the interaction with albumin did not enhance hepatic and pulmonary gene expression. Furthermore, hepatic and pulmonary gene expression levels of albumin-interacted lipoplex were correlated with serum transaminases in hepatitis mice. The albumin interaction increased the hepatic accumulation of lipoplex and serum tumor necrosis factor-α level. We suggest that the interaction with albumin enhanced the inflammation level after the administration of lipoplex in hepatitis mice. Consequently, the enhancement of the inflammation level might enhance the gene expression level. Information obtained in the current study will be valuable toward future clinical application of the lipoplex.

PEG-Peptide Inhibition of Scavenger Receptor Uptake of Nanoparticles by the Liver

PEGylated polylysine peptides represent a new class of scavenger receptor inhibitors that may find utility at inhibiting DNA nanoparticle uptake by Kupffer cells in the liver. PEG-peptides inhibit scavenger receptors in the liver by a novel mechanism involving in situ formation of albumin nanoparticles. The present study developed a new in vivo assay used to explore the structure-activity-relationships of PEG-peptides to find potent scavenger receptor inhibitors. Radio-iodinated PEG-peptides were dosed i.v. in mice and shown to saturate liver uptake in a dose-dependent fashion. The inhibition potency (IC₅₀) was dependent on both the length of a polylysine repeat and PEG molecular weight. PEG_30kda-Cys-Tyr-Lys₂₅ was confirmed to be a high molecular weight (33.5 kDa) scavenger receptor inhibitor with an IC₅₀ of 18 μM. Incorporation of multiple Leu residues improved potency, allowing a decrease in PEG MW and Lys repeat, resulting in PEG_5kda-Cys-Tyr-Lys-(Leu-Lys₄)₃-Leu-Lys that inhibited scavenger receptors with an IC₅₀ = 20 μM. A further decrease in PEG MW to 2 kDa increased potency further, resulting in a low molecular weight (4403 g/mol) PEG-peptide with an IC₅₀ of 3 μM. Optimized low molecular weight PEG-peptides also demonstrated potency when inhibiting the uptake of radio-iodinated DNA nanoparticles by the liver. This study demonstrates an approach to discover low molecular weight PEG-peptides that serve as potent scavenger receptor inhibitors to block nanoparticle uptake by the liver.

Activation of TNF-α-AID axis and co-inhibitory signals in coordination with Th1-type immunity in a mouse model recapitulating hepatitis B

Hepatitis B virus (HBV) infection evokes host immune responses that primarily determine the outcome of HBV infection and the clinical features of HBV-associated liver disease. The precise mechanisms by which host factors restrict HBV replication, however, are poorly understood due to the lack of useful animal models that recapitulate immune responses to HBV. Here, we performed comprehensive immunologic gene expression profiling of the liver of a mouse model recapitulating anti-HBV immune response using a high sensitivity direct digital counting system. Anti-HBV cellular immunity with liver inflammation was elicited in mice hydrodynamically injected with a CpG-depleted plasmid encoding hepatitis B surface antigen (HBsAg) gene after preimmunization with HBsAg vaccine. Comprehensive expression analyses revealed the upregulation of Th1-associated genes including tumor necrosis factor (Tnf) and negative regulators of T cell function in the inflamed liver. Interestingly, activation-induced cytidine deaminase (Aicda, termed AID in humans), which reportedly suppresses HBV infection in vitro, was upregulated in hepatocytes in the course of anti-HBV immunity. Hepatocytic expression of Aicda in a Tnf-dependent manner was confirmed by the administration of Tnf antagonist into Aicda-tdTomato mice with anti-HBV immunity. Our findings suggest that activation of Tnf-Aicda axis and co-inhibitory signals to T cells in coordination with Th1-type immunity has critical roles in the immune response against HBV infection.

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

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

Evaluation of New Fluorescent Lipophosphoramidates for Gene Transfer and Biodistribution Studies after Systemic Administration

The objective of lung gene therapy is to reach the respiratory epithelial cells in order to deliver a functional nucleic acid sequence. To improve the synthetic carrier's efficacy, knowledge of their biodistribution and elimination pathways, as well as cellular barriers faced, depending on the administration route, is necessary. Indeed, the in vivo fate guides the adaptation of their chemical structure and formulation to increase their transfection capacity while maintaining their tolerance. With this goal, lipidic fluorescent probes were synthesized and formulated with cationic lipophosphoramidate KLN47 (KLN: Karine Le Ny). We found that such formulations present constant compaction properties and similar transfection results without inducing additional cytotoxicity. Next, biodistribution profiles of pegylated and unpegylated lipoplexes were compared after systemic injection in mice. Pegylation of complexes led to a prolonged circulation in the bloodstream, whereas their in vivo bioluminescent expression profiles were similar. Moreover, systemic administration of pegylated lipoplexes resulted in a transient liver toxicity. These results indicate that these new fluorescent compounds could be added into lipoplexes in small amounts without perturbing the transfection capacities of the formulations. Such additional properties allow exploration of the in vivo biodistribution profiles of synthetic carriers as well as the expression intensity of the reporter gene.

Horizontal gene transfer from macrophages to ischemic muscles upon delivery of naked DNA with Pluronic block copolymers

Intramuscular administration of plasmid DNA (pDNA) with non-ionic Pluronic block copolymers increases gene expression in injected muscles and lymphoid organs. We studied the role of immune cells in muscle transfection upon inflammation. Local inflammation in murine hind limb ischemia model (MHLIM) drastically increased DNA, RNA and expressed protein levels in ischemic muscles injected with pDNA/Pluronic. The systemic inflammation (MHLIM or peritonitis) also increased expression of pDNA/Pluronic in the muscles. When pDNA/Pluronic was injected in ischemic muscles the reporter gene, Green Fluorescent Protein (GFP) co-localized with desmin(+) muscle fibers and CD11b(+) macrophages (MØs), suggesting transfection of MØs along with the muscle cells. P85 enhanced (∼ 4 orders) transfection of MØs with pDNA in vitro. Moreover, adoptively transferred MØs were shown to pass the transgene to inflamed muscle cells in MHLIM. Using a co-culture of myotubes (MTs) and transfected MØs expressing a reporter gene under constitutive (cmv-luciferase) or muscle specific (desmin-luciferase) promoter we demonstrated that P85 enhances horizontal gene transfer from MØ to MTs. Therefore, MØs can play an important role in muscle transfection with pDNA/Pluronic during inflammation, with both inflammation and Pluronic contributing to the increased gene expression. pDNA/Pluronic has potential for therapeutic gene delivery in muscle pathologies that involve inflammation.

Efficient in vivo transfection and safety profile of a CpG-free and codon optimized luciferase plasmid using a cationic lipophosphoramidate in a multiple intravenous administration procedure

As any drug, the success of gene therapy is largely dependent on the vehicle that has to selectively and efficiently deliver therapeutic nucleic acids into targeted cells with minimal side-effects. In the case of chronic diseases that require a life-long treatment, non-viral gene delivery vehicles are less likely to induce an immune response, thereby allowing for repeated administration. Beyond the gene delivery efficiency of a given vector, the nature of nucleic acid constructs also has a central importance in gene therapy protocols. Herein, we investigated the impact of two firefly luciferase encoding plasmids on the transgene expression profile following systemic delivery of lipoplexes in mice, as well as their potential to be safely and efficiently readministered. Whereas pTG11033 plasmid is driven by a strong ubiquitous cytomegalovirus promoter, pGM144 plasmid, which has been designed to avoid inflammation and provide sustained transgene expression in lungs, is CpG-free and is under control of the human elongation factor-1 alpha promoter. Combined to the efficient cationic lipophosphoramidate BSV4, bioluminescence data showed that both plasmids were mostly expressed in the lungs of mice following a primary injection of lipoplexes. However, mice transfected with pGM144 exhibited a higher and more sustained transgene expression than those treated with pTG11033. Repeated administration studies revealed that several injections of lipoplexes could lead to similar transgene expression profiles if an interval of several weeks between subsequent injections was respected. A transient hepatotoxicity and a partial inflammatory response were caused by lipoplex injection, irrespective of the plasmid used. Altogether, these results indicate that repeated systemic administration of lipophosphoramidate-based lipoplexes in mice conducts to an effective lung transfection without serious side effects, and highlight the need to use long-lasting expressing and well tolerated plasmids in order to efficiently renew transgene expression by the successive doses.

A novel micro-linear vector for in vitro and in vivo gene delivery and its application for EBV positive tumors

BACKGROUND

The gene delivery vector for DNA-based therapy should ensure its transfection efficiency and safety for clinical application. The Micro-Linear vector (MiLV) was developed to improve the limitations of traditional vectors such as viral vectors and plasmids.

METHODS

The MiLV which contained only the gene expression cassette was amplified by polymerase chain reaction (PCR). Its cytotoxicity, transfection efficiency in vitro and in vivo, duration of expression, pro-inflammatory responses and potential application for Epstein-Barr virus (EBV) positive tumors were evaluated.

RESULTS

Transfection efficiency for exogenous genes transferred by MiLV was at least comparable with or even greater than their corresponding plasmids in eukaryotic cell lines. MiLV elevated the expression and prolonged the duration of genes in vitro and in vivo when compared with that of the plasmid. The in vivo pro-inflammatory response of MiLV group was lower than that of the plasmid group. The MEKK1 gene transferred by MiLV significantly elevated the sensitivity of B95-8 cells and transplanted tumor to the treatment of Ganciclovir (GCV) and sodium butyrate (NaB).

CONCLUSIONS

The present study provides a safer, more efficient and stable MiLV gene delivery vector than plasmid. These advantages encourage further development and the preferential use of this novel vector type for clinical gene therapy studies.

Nanostructured self assembled lipid materials for drug delivery and tissue engineering

Every living organism comprises of lipids as basic building blocks in addition to other components. Utilizing these lipids for pharmaceutical and biomedical applications can overcome biocompatibility and biodegradability issues. A well known example is liposomes (lipids arranged in lamellar structures), but other than that there are additional unique mesophasic structures of lipids formed as a result of lipid polymorphisms, which include cubic-, hexagonal- or sponge-phase structures. These structures provide the advantages of stability and production feasibility compared with liposomes. Cubosomes, which exist in a cubic structure, have improved stability, bioadhesivity and biocompatibility. Hexagonal phases or hexosomes exhibit hexagonal arrangements and can encapsulate different drugs with high stability. Lipids also forms tube-like structures known as tubules and ribbons that are also utilized in different biomedical applications, especially in tissue engineering. Immune stimulating complexes are nanocage-like structures formed as a result of interactions of lipid, antigen and Quillaja saponin. These lipidic mesophasic structures have been utilized for gene, vaccine and drug delivery. This article addresses lipid self-assembled supramolecular nanostructures, including cubosomes, hexosomes, tubules, ribbons, cochleates, lipoplexes and immune stimulating complexes and their biomedical applications.

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.

Tissue engineering tools for modulation of the immune response

Tissue engineering scaffolds have emerged as a powerful tool within regenerative medicine. These materials are being designed to create environments that promote regeneration through a combination of: (i) scaffold architecture, (ii) the use of scaffolds as vehicles for transplanting progenitor cells, and/or (iii) localized delivery of inductive factors or genes encoding for these inductive factors. This review describes the techniques associated with each of these components. Additionally, the immune response is increasingly recognized as a factor influencing regeneration. The immune reaction to an implant begins with an acute response to the injury and innate recognition of foreign materials, with the subsequent chronic immune response involving specific recognition of antigens (e.g., transplanted cells) by the adaptive immune response, which can eventually lead to rejection of the implant. Thus, we also describe the impact of each component on the immune response, and strategies (e.g., material design, anti-inflammatory cytokine delivery, and immune cell recruitment/transplantation) to modulate, yet not eliminate, the local immune response in order to promote regeneration, which represents another important tool for regenerative medicine.

Sustained, high transgene expression in liver with plasmid vectors using optimized promoter-enhancer combinations

BACKGROUND

Plasmid-based gene therapy approaches often lack long-term transgene expression in vivo as a result of silencing or loss of the vector. One way to overcome these limitations is to combine nonsilenced promoters with strong enhancers.

METHODS

In the present study, we combine murine or human cytomegalovirus (CMV)-derived enhancer elements with the human elongation factor 1α (EF1α) promoter in a plasmid backbone devoid of potentially immunostimulating cytosine-guanine repeat sequences. Luciferase transgene activity was monitored in mouse liver after hydrodynamic plasmid delivery.

RESULTS

Luciferase activity of a CMV-promoter driven plasmid rapidly declined within days, whereas the activity of the EF1α driven plasmid remained high for 2 weeks (murine enhancer) and detectable for > 80 days (human enhancer). Expression levels clearly correlated with higher plasmid copy number found in the liver at 2 months after gene delivery. Furthermore, we developed a novel synthetic CMV-EF1α hybrid promoter (SCEP) combining the high activity of CMV and sustained activity of EF1α promoter. The SCEP led to a constitutive three-fold increase in expression levels compared to the EF1α promoter in vivo.

CONCLUSIONS

This novel combination of enhancer and promoter element with optimized plasmid backbones will pave the way for more efficient nonviral approaches in gene therapy.

Transient depletion of kupffer cells leads to enhanced transgene expression in rat liver following retrograde intrabiliary infusion of plasmid DNA and DNA nanoparticles

In this report, we have demonstrated that by temporarily removing Kupffer cells (KCs), the transgene expression levels mediated by retrograde intrabiliary infusion (RII) of plasmid DNA, polyethylenimine-DNA, and chitosan nanoparticles were enhanced by 1,927-, 131-, and 23,450-fold, respectively, in comparison with the respective groups without KC removal. KC removal also led to significantly prolonged transgene expression in the liver that received all three carriers. This increased transgene expression was correlated with significantly reduced serum tumor necrosis factor-α level as an indicator for KC activation. These results suggest that KC activation is a significant contributing factor to the lowered transgene expression by polycation-DNA nanoparticles delivered by RII. More importantly, the combination of RII and transient removal of KCs may be adopted as an effective approach to achieving high and persistent transgene expression in the liver mediated by nonviral nanoparticles.

Plasmid injection and application of electric pulses alter endogenous mRNA and protein expression in B16.F10 mouse melanomas

The application of electric pulses to tissues causes cell membrane destabilization, allowing exogenous molecules to enter the cells. This delivery technique can be used for plasmid gene therapy. Reporter gene expression after plasmid delivery with eight representative published protocols was compared in B16.F10 mouse melanoma tumors. This expression varied significantly based on the pulse parameters utilized for delivery. To observe the possible influence of plasmid injection and/or pulse application on endogenous gene expression, levels of stress related mRNAs four and 24 hours after delivery were determined by PCR array. Increases in mRNA levels for several inflammatory chemokines and cytokines were observed in response to plasmid injection, electric pulses alone, or the combination. This upregulation was confirmed by individual real-time reverse transcription TaqMan PCR assays. Proteins were extracted at the same time points from identically treated tumors and inflammatory protein levels were assayed by ELISA and by a custom multiplex bead array. Increases in inflammatory protein levels generally paralleled mRNA levels. Some differences were observed, which may have been due to differing expression kinetics. The observed upregulated expression of these cytokines and chemokines may aid or inhibit the therapeutic effectiveness of immune-based cancer gene therapies.

Comparison of the type of liposome involving cytokine production induced by non-CpG Lipoplex in macrophages

To improve the transfection efficiency of plasmid DNA (pDNA) into cells, various types of cationic liposome have been used to prepare pDNA/cationic liposome complexes (lipoplexes). It is well-known that lipoplexes induce a large amount of proinflammatory cytokines because unmethylated CpG dinucleotides (CpG motifs) abundantly present in pDNA are recognized by Toll-like receptor-9 (TLR9) expressed in immune cells such as macrophages and dendritic cells. This nonspecific cytokine production is problematic in nonviral gene therapy. Moreover, recent studies have demonstrated that lipoplexes induce not only proinflammatory cytokines but also another type of cytokine, type I interferons (IFNs), irrespective of the frequency of CpG motifs in DNA and the expression of TLR9. To gain more insight into the CpG motif- and TLR9-independent induction of type I IFNs and proinflammatory cytokines by lipoplex, macrophage activation was evaluated in vitro using various cationic liposomes complexed with pDNA containing no CpG motifs. The production of IFN-beta, TNF-alpha and IL-6 by lipoplex was confirmed to be induced independently of the interaction between CpG DNA and TLR9 in macrophages from TLR9-knockout mice. Then, the release of the cytokines, the mRNA expression of Z-DNA binding protein-1 (Zbp1), a cytosolic double-stranded DNA sensor, and the cellular uptake of pDNA were examined in a macrophage-like cell line, RAW264.7. The level of cytokine production and the increase in the Zbp1 mRNA varied depending on the type of cationic liposome used. A good correlation was observed between the cytokine level and the Zbp1 mRNA. A confocal microscopic study using fluorescently labeled pDNA complexes showed that the complexes that released a lot of cytokines showed an enhanced distribution of pDNA-derived fluorescence into the cytosol. These results suggest that different intracellular trafficking derived from the type of liposomes determines the recognition of pDNA by ZBP1 after uptake of lipoplexes by the macrophages, followed by the release of type I IFNs and inflammatory cytokines. The present study demonstrates that cationic liposomes should be selected based on these findings for optimization of DNA-based therapies using lipoplexes.

Immunogenicity of intrathecal plasmid gene delivery: cytokine release and effects on transgene expression

BACKGROUND

One method for the delivery of therapeutic proteins to the spinal cord is to inject nonviral gene vectors including plasmid DNA into the cerebrospinal fluid (CSF) that surrounds the spinal cord (intrathecal space). This approach has produced therapeutic benefits in animal models of disease and several months of protein expression; however, there is little information available on the immune response to these treatments in the intrathecal space, the relevance of plasmid CpG sequences to any plasmid-induced immune response, or the effect of this immune response on transgene expression.

METHODS

In the present study, coding or noncoding plasmids were delivered to the intrathecal space of the lumbar spinal region in rats. Lumbosacral CSF was then collected at various time points afterwards for monitoring of cytokines and transgene expression.

RESULTS

This work demonstrates, for the first time, increased tumor necrosis factor-alpha and interleukin-1 in response to intrathecal plasmid vector injection and provides evidence indicating that this response is largely absent in a CpG-depleted vector. Transgene expression in the CSF is not significantly affected by this immune response. Expression after intrathecal plasmid injection is variable across rats but correlates with the amount of tissue associated plasmid and is increased by disrupting normal CSF flow.

CONCLUSIONS

The data obtained in the present study indicate that plasmid immunogenicity may affect intrathecal plasmid gene therapy safety but not transgene expression in the CSF. Furthermore, the development of methods to prevent loss of plasmid via CSF flow out of the central nervous system through the injection hole and/or natural outflow routes may increase intrathecal plasmid gene delivery efficacy.

Induction of tumor-specific immune response by gene transfer of Hsp70-cell-penetrating peptide fusion protein to tumors in mice

To induce a tumor-specific immune response by delivering tumor-associated antigens in tumor cells to antigen-presenting cells (APCs), we designed a fusion protein which consists of heat-shock protein 70 (Hsp70) and the C-terminal 34 amino acids of herpes simplex virus VP22 protein (VP22(268-301)), the former having a peptide binding domain and an ability to be recognized by APCs, and the latter able to achieve cell penetration. Hsp70-VP22(268-301), the fusion protein, was efficiently taken up by mouse dendritic cell (DC) line DC2.4. Major histocompatibility complex (MHC) class I-restricted presentation of an epitope peptide of ovalbumin (OVA) was examined in DC2.4, and Hsp70-VP22(268-301) significantly increased the presentation of the peptide compared with Hsp70. Electroporation-assisted injection of naked plasmid vector expressing Hsp70-VP22(268-301) (pHsp70-VP22(268-301)) into subcutaneous tumors of EG7-OVA, a mouse lymphoma-expressing OVA, significantly increased the survival of mice compared with the same treatment with pHSp70, a plasmid expressing Hsp70. Splenocytes from the pHsp70-VP22(268-301)-treated mice exhibited cytolytic activity against both EG7-OVA and the parent EL4, but not against mouse melanoma B16-F10, suggesting that not only OVA-derived antigens but those common to EG7-OVA and EL4 are delivered to APCs. These results provide a new therapeutic method to induce tumor-specific antitumor immunity without identifying nor isolating tumor-associated antigens.

Effect of the content of unmethylated CpG dinucleotides in plasmid DNA on the sustainability of transgene expression

BACKGROUND

Nonviral gene transfer generally suffers from short-term expression of transgenes. We have previously demonstrated that plasmids with reduced CpG content exhibited a more prolonged expression of murine interferon (IFN)-beta or IFN-gamma, which was effective in inhibiting metastatic tumor growth. A further extension of the duration of transgene expression could be achieved by controlling the number and location of CpG motifs in plasmid DNA.

METHODS

Luciferase-expressing plasmids with differing CpG content were injected into the tail vein of mice by the hydrodynamic injection method. The effects of CpG content on the duration of transgene expression were examined, focusing on cytosine methylation and pro-inflammatory cytokines. Based on the findings, IFN-gamma-expressing plasmids were constructed and their transgene expression and inhibitory effect on pulmonary metastasis were evaluated.

RESULTS

Plasmids with a few CpG motifs showed a prolonged luciferase activity in the liver. Methylation of CpG motifs in plasmids reduced the expression and the extent of this reduction was greater for plasmids with a high CpG content. Pro-inflammatory cytokines hardly affected the expression. pCpG-Mu gamma, the IFN-gamma-expressing plasmid, which contains 20 CpG motifs only in the cDNA region, exhibited a sustained IFN-gamma concentration at therapeutic levels, and had a great inhibitory effect on the pulmonary metastasis of tumor cells.

CONCLUSIONS

The duration of transgene expression of IFN-gamma was successfully increased by reducing the CpG content of IFN-expressing plasmid vector, which resulted in an increased anticancer activity of IFN gene transfer.

Pharmacokinetic considerations regarding non-viral cancer gene therapy

Cancer gene therapy, in which pharmacologically active compounds are administered to cancer patients in a genetic form, has been examined not only in animals but also in cancer patients. Viral vector-induced severe side effects in patients have greatly underscored the importance of non-viral gene transfer methods. Even though the importance of pharmacokinetics is undoubtedly understood in the development of anticancer therapies, its importance has been less well recognized in non-viral cancer gene therapy. When transgene products express their activity within transduced cells, such as herpes simplex virus type 1 thymidine kinase and short hairpin RNA, the pharmacokinetics of the vectors and the expression profiles of the transgenes will determine the efficacy of gene transfer. The percentage of cells transduced is highly important if few by-stander effects are expected. If transgene products are secreted from cells into the blood circulation, such as interferons and interleukins, the pharmacokinetics of transgenes becomes a matter of significant importance. Then, any approach to increasing the level and duration of transgene expression will increase the therapeutic effects of cancer gene therapy. Here we review the pharmacokinetics of both non-viral vectors and transgene products, and discuss what should be done to achieve safer and more effective non-viral cancer gene therapy.