Polyethylenimine-mediated gene transfer into pancreatic tumor dissemination in the murine peritoneal cavity

Nanoemulsion-Assisted siRNA Delivery to Modulate the Nervous Tumor Microenvironment in the Treatment of Pancreatic Cancer

Pancreatic cancer (PC) is a fatal human cancer, whose progression is highly dependent on the nervous tumor microenvironment. In the present study, cationic perfluorocarbon nanoemulsions were employed as an intraperitoneal delivery platform to facilitate the delivery and penetration of a therapeutic small interfering RNA (siRNA) to orthotopic pancreatic tumors. The nanoemulsion was used to silence the expression of the nerve growth factor (NGF) as a way of favorably modulating the tumor-neuronal interactions in pancreatic tumors. The nanoemulsions exhibited deep tumor penetration that was dependent on exocytosis and enhanced NGF gene silencing in vitro and in vivo when compared with control polycation/siRNA polyplexes, leading to the effective and safe suppression of tumor growth in orthotopic PC. Overall, emulsion-assisted delivery of NGF siRNA is a promising treatment approach for PC by targeting the interactions between the tumor cells and the nervous microenvironment.

Stromal Modulation and Treatment of Metastatic Pancreatic Cancer with Local Intraperitoneal Triple miRNA/siRNA Nanotherapy

Nanomedicines achieve tumor-targeted delivery mainly through enhanced permeability and retention (EPR) effect following intravenous (IV) administration. Unfortunately, the EPR effect is severely compromised in pancreatic cancer due to hypovascularity and dense desmoplastic stroma. Intraperitoneal (IP) administration may be an effective EPR-independent local delivery approach to target peritoneal tumors. Besides improved delivery, effective combination delivery strategies are needed to improve pancreatic cancer therapy by targeting both cancer cells and cellular interactions within the tumor stroma. Here, we described simple cholesterol-modified polymeric CXCR4 antagonist (PCX) nanoparticles (to block cancer-stroma interactions) for codelivery of anti-miR-210 (to inactivate stroma-producing pancreatic stellate cells (PSCs)) and siKRASG12D (to kill pancreatic cancer cells). IP administration delivered the nanoparticles to an orthotopic syngeneic pancreatic tumors as a result of preferential localization to the tumors and metastases with disrupted mesothelium and effective tumor penetration. The local IP delivery resulted in nearly 15-fold higher tumor accumulation than delivery by IV injection. Through antagonism of CXCR4 and downregulation of miR-210/KRASG12D, the triple-action nanoparticles favorably modulated desmoplastic tumor microenvironment via inactivating PSCs and promoting the infiltration of cytotoxic T cells. The combined therapy displayed improved therapeutic effect when compared with individual therapies as documented by the delayed tumor growth, depletion of stroma, reduction of immunosuppression, inhibition of metastasis, and prolonged survival. Overall, we present data that a local IP delivery of a miRNA/siRNA combination holds the potential to improve pancreatic cancer therapy.

Systemic tumor-targeted sodium iodide symporter (NIS) gene therapy of hepatocellular carcinoma mediated by B6 peptide polyplexes

BACKGROUND

Nonviral polymer-based gene transfer represents an adaptable system for tumor-targeted gene therapy because various design strategies of shuttle systems, together with the mechanistic concept of active tumor targeting, lead to improved gene delivery vectors resulting in higher tumor specificity, efficacy and safety.

METHODS

Using the sodium iodide symporter (NIS) as a theranostic gene, nonviral gene delivery vehicles based on linear polyethylenimine (LPEI), polyethylene glycol (PEG) and coupled to the synthetic peptide B6 (LPEI-PEG-B6), which specifically binds to tumor cells, were investigated in a hepatocellular carcinoma xenograft model for tumor selectivity and transduction efficiency.

RESULTS

In vitro incubation of three different tumor cell lines with LPEI-PEG-B6/NIS resulted in significant increase in iodide uptake activity compared to untargeted and empty vectors. After establishment of subcutaneous HuH7 tumors, NIS-conjugated nanoparticles were injected intravenously followed by analysis of radioiodide biodistribution using ¹²³ I-scintigraphy showing significant perchlorate-sensitive iodide accumulation in tumors of LPEI-PEG-B6/NIS-treated mice (8.0 ± 1.5% ID/g ¹²³ I; biological half-life of 4 h). After four cycles of repetitive polyplex/¹³¹ I applications, a significant delay of tumor growth was observed, which was associated with markedly improved survival in the therapy group.

CONCLUSIONS

These results clearly demonstrate that systemic in vivo NIS gene transfer using nanoparticle vectors coupled to B6 tumor targeting ligand is capable of inducing tumor-specific radioiodide uptake. This promising gene therapy approach opens the exciting prospect of NIS-mediated radionuclide therapy in metastatic cancer, together with the possibility of combining several targeting ligands to enhance selective therapeutic efficacy in a broad field of cancer types with various receptor expression profiles.

Targeting Promoter-Associated Noncoding RNA In Vivo

There are many classes of noncoding RNAs (ncRNAs), with wide-ranging functionalities (e.g., RNA editing, mediation of mRNA splicing, ribosomal function). MicroRNAs (miRNAs) and long ncRNAs (lncRNAs) are implicated in a wide variety of cellular processes, including the regulation of gene expression. Incorrect expression or mutation of lncRNAs has been reported to be associated with several disease conditions, such a malignant transformation in humans. Importantly, pivotal players in tumorigenesis and cancer progression, such as c-Myc, may be regulated by lncRNA at promoter level. The function of lncRNA can be reduced with antisense oligonucleotides that sequester or degrade mature lncRNAs. In alternative, lncRNA transcription can be blocked by small interference RNA (RNAi), which had acquired, recently, broad interested in clinical applications. In vivo-jetPEI™ is a linear polyethylenimine mediating nucleic acid (DNA, shRNA, siRNA, oligonucelotides) delivery with high efficiency. Different in vivo delivery routes have been validated: intravenous (IV), intraperitoneal (IP), intratumoral, subcutaneous, topical, and intrathecal. High levels of nucleic acid delivery are achieved into a broad range of tissues, such as lung, salivary glands, heart, spleen, liver, and prostate upon systemic administration. In addition, in vivo-jetPEI™ is also an efficient carrier for local gene and siRNA delivery such as intratumoral or topical application on the skin. After systemic injection, siRNA can be detected and the levels can be validated in target tissues by qRT-PCR. Targeting promoter-associated lncRNAs with siRNAs (small interfering RNAs) in vivo is becoming an exciting breakthrough for the treatment of human disease.

Linear polyethylenimine as (multi) functional initiator for organocatalytic l-lactide polymerization

The preparation of polyethylenimine (PEI)–polylactide (PLA) copolymer structures is promising as these materials may find use in gene and/or drug delivery applications.

Non-viral DNA delivery from porous hyaluronic acid hydrogels in mice

The lack of vascularization within tissue-engineered constructs remains the primary cause of construct failure following implantation. Porous constructs have been successful in allowing for vessel infiltration without requiring extensive matrix degradation. We hypothesized that the rate and maturity of infiltrating vessels could be enhanced by complementing the open pore structure with the added delivery of DNA encoding for angiogenic growth factors. Both 100 and 60 μm porous and non-porous hyaluronic acid hydrogels loaded with pro-angiogenic (pVEGF) or reporter (pGFPluc) plasmid nanoparticles were used to study the effects of pore size and DNA delivery on angiogenesis in a mouse subcutaneous implant model. GFP-expressing transfected cells were found inside all control hydrogels over the course of the study, although transfection levels peaked by week 3 for 100 and 60 μm porous hydrogels. Transfection in non-porous hydrogels continued to increase over time corresponding with continued surface degradation. pVEGF transfection levels were not high enough to enhance angiogenesis by increasing vessel density, maturity, or size, although by 6 weeks for all pore size hydrogels more hydrogel implants were positive for vascularization when pVEGF polyplexes were incorporated compared to control hydrogels. Pore size was found to be the dominant factor in determining the angiogenic response with 60 μm porous hydrogels having more vessels/area present than 100 μm porous hydrogels at the initial onset of angiogenesis at 3 weeks. The results of this study show promise for the use of polyplex loaded porous hydrogels to transfect infiltrating cells in vivo and guide tissue regeneration and repair.

Enhanced Performance of Plasmid DNA Polyplexes Stabilized by a Combination of Core Hydrophobicity and Surface PEGylation

Nonviral gene therapy has high potential for safely promoting tissue restoration and for treating various genetic diseases. One current limitation is that conventional transfection reagents such as polyethylenimine (PEI) form electrostatically stabilized plasmid DNA (pDNA) polyplexes with poor colloidal stability. In this study, a library of poly(ethylene glycol-b-(dimethylaminoethyl methacrylate-co-butyl methacrylate)) [poly(EG-b-(DMAEMA-co-BMA))] polymers were synthesized and screened for improved colloidal stability and nucleic acid transfection following lyophilization. When added to pDNA in the appropriate pH buffer, the DMAEMA moieties initiate formation of electrostatic polyplexes that are internally stabilized by hydrophobic interactions of the core BMA blocks and sterically stabilized against aggregation by a PEG corona. The BMA content was varied from 0% to 60% in the second polymer block in order to optimally tune the balance of electrostatic and hydrophobic interactions in the polyplex core, and polymers with 40 and 50 mol% BMA achieved the highest transfection efficiency. Diblock copolymers were more stable than PEI in physiologic buffers. Consequently, diblock copolymer polyplexes aggregated more slowly and followed a reaction-limited colloidal aggregation model, while fast aggregation of PEI polyplexes was governed by a diffusion-limited model. Polymers with 40% BMA did not aggregate significantly after lyophilization and produced up to 20-fold higher transfection efficiency than PEI polyplexes both before and after lyophilization. Furthermore, poly(EG-b-(DMAEMA-co-BMA)) polyplexes exhibited pH-dependent membrane disruption in a red blood cell hemolysis assay and endosomal escape as observed by confocal microscopy.Lyophilized polyplexes made with the lead candidate diblock copolymer (40% BMA) also successfully transfected cells in vitro following incorporation into gas-foamed polymeric scaffolds. In summary, the enhanced colloidal stability, endosomal escape, and resultant high transfection efficiency of poly(EG-b-(DMAEMA-co-BMA))-pDNA polyplexes underscores their potential utility both for local delivery from scaffolds as well as systemic, intravenous delivery.

Anticancer effects of chitin and chitosan derivatives

Despite considerable progress in medical research, cancer is still one of the high-ranking causes of death in the world. It is the second most common cause of death due to disease after heart disease, and according to World Health Organization it will be the cause of death for more than 10 million people in 2020; therefore, one of the main research goals for researchers investigating new anticancer agents. But the major complication for the cancer cure without surgeries is side effects. Especially, cytotoxic anticancer chemotherapeutic agents generally produce severe side effects, while reducing host resistance to cancer and infections. Therefore, it is important to find new, powerful anticancer agents that are highly effective, biodegradable, and biocompatible. Chitin and chitosan are biopolymers which have unique structural possibilities for chemical and mechanical modifications to generate novel properties, functions. These biopolymers are biocompatible, biodegradable, and nontoxic, and their chemical properties allow them to be easily processed into gels, sponges, membranes, beads, and scaffolds forms also. Due to their unique properties, they are excellent candidates for cancer cure or cancer diagnosis.

On the efficacy of malaria DNA vaccination with magnetic gene vectors

We investigated the efficacy and types of immune responses from plasmid malaria DNA vaccine encoding VR1020-PyMSP119 condensed on the surface of polyethyleneimine (PEI)-coated SPIONs. In vivo mouse studies were done firstly to determine the optimum magnetic vector composition, and then to observe immune responses elicited when magnetic vectors were introduced via different administration routes. Higher serum antibody titers against PyMSP119 were observed with intraperitoneal and intramuscular injections than subcutaneous and intradermal injections. Robust IgG2a and IgG1 responses were observed for intraperitoneal administration, which could be due to the physiology of peritoneum as a major reservoir of macrophages and dendritic cells. Heterologous DNA prime followed by single protein boost vaccination regime also enhanced IgG2a, IgG1, and IgG2b responses, indicating the induction of appropriate memory immunity that can be elicited by protein on recall. These outcomes support the possibility to design superparamagnetic nanoparticle-based DNA vaccines to optimally evoke desired antibody responses, useful for a variety of diseases including malaria.

Design and characterization of microporous hyaluronic acid hydrogels for in vitro gene transfer to mMSCs

The effective and sustained delivery of DNA locally could increase the applicability of gene therapy in tissue regeneration and therapeutic angiogenesis. One promising approach is to use porous hydrogel scaffolds to encapsulate and deliver nucleotides in the form of nanoparticles to the affected sites. We have designed and characterized microporous (μ-pore) hyaluronic acid hydrogels which allow for effective cell seeding in vitro post-scaffold fabrication and allow for cell spreading and proliferation without requiring high levels of degradation. These factors, coupled with high loading efficiency of DNA polyplexes using a previously developed caged nanoparticle encapsulation (CnE) technique, then allowed for long-term sustained transfection and transgene expression of incorporated mMSCs. In this study, we examined the effect of pore size on gene transfer efficiency and the kinetics of transgene expression. For all investigated pore sizes (30, 60, and 100 μm), encapsulated DNA polyplexes were released steadily, starting by day 4 for up to 10 days. Likewise, transgene expression was sustained over this period, although significant differences between different pore sizes were not observed. Cell viability was also shown to remain high over time, even in the presence of high concentrations of DNA polyplexes. The knowledge acquired through this in vitro model can be utilized to design and better predict scaffold-mediated gene delivery for local gene therapy in an in vivo model where host cells infiltrate the scaffold over time.

Development of peritoneal tumor-targeting vector by in vivo screening with a random peptide-displaying adenovirus library

The targeting of gene transfer at the cell-entry level is one of the most attractive challenges in vector development. However, attempts to redirect adenovirus vectors to alternative receptors by engineering the capsid-coding region have shown limited success, because the proper targeting ligands on the cells of interest are generally unknown. To overcome this limitation, we have constructed a random peptide library displayed on the adenoviral fiber knob, and have successfully selected targeted vectors by screening the library on cancer cell lines in vitro. The infection of targeted vectors was considered to be mediated by specific receptors on target cells. However, the expression levels and kinds of cell surface receptors may be substantially different between in vitro culture and in vivo tumor tissue. Here, we screened the peptide display-adenovirus library in the peritoneal dissemination model of AsPC-1 pancreatic cancer cells. The vector displaying a selected peptide (PFWSGAV) showed higher infectivity in the AsPC-1 peritoneal tumors but not in organs and other peritoneal tumors as compared with a non-targeted vector. Furthermore, the infectivity of the PFWSGAV-displaying vector for AsPC-1 peritoneal tumors was significantly higher than that of a vector displaying a peptide selected by in vitro screening, indicating the usefulness of in vivo screening in exploring the targeting vectors. This vector-screening system can facilitate the development of targeted adenovirus vectors for a variety of applications in medicine.

Transgene therapy for rat anti-Thy1.1 glomerulonephritis via mesangial cell vector with a polyethylenimine/decorin nanocomplex

Polyethylenimine (PEI), a cationic polymer, is one of the most efficient non-viral vectors for transgene therapy. Decorin (DCN), a leucine-rich proteoglycan secreted by glomerular mesangial cells (MC), is a promising anti-fibrotic agent for the treatment of glomerulonephritis. In this study, we used PEI-DCN nanocomplexes with different N/P ratios to transfect MC in vitro and deliver the MC vector with PEI-DCN expressing into rat anti-Thy1.1 nephritis kidney tissue via injection into the left renal artery in vivo. The PEI-plasmid DNA complex at N/P 20 had the highest level of transfection efficiency and the lowest level of cytotoxicity in cultured MC. Following injection, the ex vivo gene was transferred successfully into the glomeruli of the rat anti-Thy1.1 nephritis model by the MC vector with the PEI-DCN complex. The exogenous MC with DCN expression was located mainly in the mesangium and the glomerular capillary. Over-expression of DCN in diseased glomeruli could result in the inhibition of collagen IV deposition and MC proliferation. The pathological changes of rat nephritis were alleviated following injection of the vector. These findings demonstrate that the DCN gene delivered by the PEI-DNA nanocomplex with the MC vector is a promising therapeutic method for the treatment of glomerulonephritis.

Efficient in vivo gene transfer by intraperitoneal injection of plasmid DNA and calcium carbonate microflowers in mice

Gene transfer to intraperitoneal organs is thought to be a promising approach to treat such conditions as peritoneal fibrosis and peritoneal dissemination of cancers. We previously discovered that simple instillation of naked plasmid DNA (pDNA) onto intraperitoneal organs such as the liver and stomach could effectively transfer foreign genes in mice. In this study, we developed a novel nonviral method to enhance transfection efficiency of naked pDNA to intraperitoneal organs using a calcium carbonate suspension containing pDNA. Using commercially available calcium carbonate, we successfully transfected pDNA to the stomach. Handling of commercially available calcium carbonate, however, was troublesome owing to rapid precipitation and caking. To obtain slowly settling particles of calcium carbonate, we tried to synthesize novel versions of such particles and succeeded in creating flower-shaped particles, named calcium carbonate microflowers. Sedimentation of calcium carbonate microflowers was sufficiently slow for in vivo experiments. Moreover, the transfection efficiency of the suspension of calcium carbonate microflowers to the stomach was more effective than that of commercially available calcium carbonate, especially at low concentrations. Intraperitoneal injection of the suspension of calcium carbonate microflowers containing pDNA greatly enhanced naked pDNA transfer to whole intraperitoneal organs in mice. Furthermore, lactate dehydrogenase activities in intraperitoneal fluid and plasma were not raised by the suspension of calcium carbonate microflowers.

Effective transgene expression without toxicity by intraperitoneal administration of PEG-detachable polyplex micelles in mice with peritoneal dissemination

Block copolymer of poly(ethylene glycol)-block-poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (PEG-P[Asp(DET)]) has been originally introduced as a promising gene carrier by forming a nanomicelle with plasmid DNA. In this study, the polyplex micelle of PEG-SS-P[Asp(DET)], which disulfide linkage (SS) between PEG and cationic polymer can detach the surrounding PEG chains upon intracellular reduction, was firstly evaluated with respect to in vivo transduction efficiency and toxicity in comparison to that of PEG-P[Asp(DET)] in peritoneally disseminated cancer model. Intraperitoneal (i.p.) administration of PEG-SS-P[Asp(DET)] polyplex micelles showed a higher (P<0.05) transgene expression compared with PEG-P[Asp(DET)] in tumors. In contrast, the delivered distribution of the micelles was not different between the two polyplex micelles. PEG-SS-P[Asp(DET)] micelle encapsulating human tumor necrosis factor α (hTNF-α) gene exhibits a higher antitumor efficacy against disseminated cancer compared with PEG-P[Asp(DET)] or saline control. No hepatic and renal toxicities were observed by the administration of polyplex micelles. In conclusion, PEG-detachable polyplex micelles may represent an advantage in gene transduction in vivo over PEG-undetachable polyplex micelles after i.p. administration for peritoneal dissemination of cancer.

Utilizing cell-matrix interactions to modulate gene transfer to stem cells inside hyaluronic acid hydrogels

The effective delivery of DNA locally would increase the applicability of gene therapy in tissue regeneration, where diseased tissue is to be repaired in situ. One promising approach is to use hydrogel scaffolds to encapsulate and deliver plasmid DNA in the form of nanoparticles to the diseased tissue, so that cells infiltrating the scaffold are transfected to induce regeneration. This study focuses on the design of a DNA nanoparticle-loaded hydrogel scaffold. In particular, this study focuses on understanding how cell-matrix interactions affect gene transfer to adult stem cells cultured inside matrix metalloproteinase (MMP) degradable hyaluronic acid (HA) hydrogel scaffolds. HA was cross-linked to form a hydrogel material using a MMP degradable peptide and Michael addition chemistry. Gene transfer inside these hydrogel materials was assessed as a function of polyplex nitrogen to phosphate ratio (N/P = 5 to 12), matrix stiffness (100-1700 Pa), RGD (Arg-Gly-Asp) concentration (10-400 μM), and RGD presentation (0.2-4.7 RGDs per HA molecule). All variables were found to affect gene transfer to mouse mensenchymal stem cells culture inside the DNA loaded hydrogels. As expected, higher N/P ratios lead to higher gene transfer efficiency but also higher toxicity; softer hydrogels resulted in higher transgene expression than stiffer hydrogels, and an intermediate RGD concentration and RGD clustering resulted in higher transgene expression. We believe that the knowledge gained through this in vitro model can be utilized to design better scaffold-mediated gene delivery for local gene therapy.

Biodistribution and blood clearance of plasmid DNA administered in arginine peptide complexes

Background

Peptide/DNA complexes have great potential as non-viral methods for gene delivery. Despite promising results for peptide-mediated gene delivery technology, an effective systemic peptide-based gene delivery system has not yet been developed.

Methods

This study used pCMV-Luc as a model gene to investigate the biodistribution and the in vivo efficacy of arginine peptide-mediated gene delivery by polymerase chain reaction (PCR).

Results

Plasmid DNA was detected in all organs tested 1 h after intraperitoneal administration of arginine/DNA complexes, indicating that the arginine/DNA complexes disseminated widely through the body. The plasmid was primarily detected in the spleen, kidney, and diaphragm 24 h post administration. The mRNA expression of plasmid DNA was noted in the spleen, kidney, and diaphragm for up to 2 weeks, and in the other major organs, for at least 1 week. Blood clearance studies showed that injected DNA was found in the blood as long as 6 h after injection.

Conclusions

Taken together, our results demonstrated that arginine/DNA complexes are stable in blood and are effective for in vivo gene delivery. These findings suggest that intraperitoneal administration of arginine/DNA complexes is a promising tool in gene therapy.

Comparisons of three polyethyleneimine-derived nanoparticles as a gene therapy delivery system for renal cell carcinoma

Background

Polyethyleneimine (PEI), which can interact with negatively charged DNA through electrostatic interaction to form nanocomplexes, has been widely attempted to use as a gene delivery system. However, PEI has some defects that are not fit for keeping on gene expression. Therefore, some modifications against PEI properties have been done to improve their application value in gene delivery. In this study, three modified PEI derivatives, including poly(ε-caprolactone)-pluronic-poly(ε-caprolactone) grafted PEI (PCFC-g-PEI), folic acid-PCFC-isophorone diidocyanate-PEI (FA-PEAs) and heparin-PEI (HPEI), were evaluated in terms of their cytotoxicity and transfection efficiency in vitro and in vivo in order to ascertain their potential application in gene therapy.

Methods

MTT assay and a marker GFP gene, encoding green fluorescent protein, were used to evaluate cell toxicity and transfection activity of the three modified PEI in vitro. Renal cell carcinoma (RCC) models were established in BALB/c nude mice inoculated with OS-RC-2 cells to detect the gene therapy effects using the three PEI-derived nanoparticles as gene delivery vehicles. The expression status of a target gene Von Hippel-Lindau (VHL) in treated tumor tissues was analyzed by semiquantitative RT-PCR and immunohistochemistry.

Results

Each of three modified PEI-derived biomaterials had an increased transfection efficiency and a lower cytotoxicity compared with its precursor PEI with 25-kD or 2-kD molecule weight in vitro. And the mean tumor volume was obviously decreased 30% by using FA-PEAs to transfer VHL plasmids to treat mice RCC models. The VHL gene expression was greatly improved in the VHL-treated group. While there was no obvious tumor inhibition treated by PCFC-g-PEI:VHL and HPEI:VHL complexes.

Conclusions

The three modified PEI-derived biomaterials, including PCFC-g-PEI, FA-PEAs and HPEI, had an increased transfection efficiency in vitro and obviously lower toxicities compared with their precursor PEI molecules. The FA-PEAs probably provide a potential gene delivery system to treat RCC even other cancers in future.

Liposome based delivery systems in pancreatic cancer treatment: from bench to bedside

Despite rapid advances in cancer diagnosis and treatment, pancreatic cancer remains one of the most difficult human malignancies to be treated, with a mortality rate nearly equal to its incidence. Although gemcitabine has been established as the standard first-line treatment for advanced pancreatic cancer, gemcitabine-based combination chemotherapy showed either marginal or no improvement in survival. Developments in liposomal delivery systems have facilitated the targeting of specific agents for cancer treatment. Such systems could be developed as platforms for future multi-functional theranostic nanodevices tailor-made for the combined detection of early cancer and functional drug delivery. We systemically review liposome based drug-delivery systems, which can provide improved pharmacokinetics, reduced side effects and potentially increased tumor uptake, for pancreatic cancer therapy. Novel liposomal formulations allowing for higher tumor targeting efficiencies and used in current clinical trials to treat this challenging disease are emphasized.

Pancreatic cancer gene therapy: from molecular targets to delivery systems

The continuous identification of molecular changes deregulating critical pathways in pancreatic tumor cells provides us with a large number of novel candidates to engineer gene-targeted approaches for pancreatic cancer treatment. Targets—both protein coding and non-coding—are being exploited in gene therapy to influence the deregulated pathways to facilitate cytotoxicity, enhance the immune response or sensitize to current treatments. Delivery vehicles based on viral or non-viral systems as well as cellular vectors with tumor homing characteristics are a critical part of the design of gene therapy strategies. The different behavior of tumoral versus non-tumoral cells inspires vector engineering with the generation of tumor selective products that can prevent potential toxic-associated effects. In the current review, a detailed analysis of the different targets, the delivery vectors, the preclinical approaches and a descriptive update on the conducted clinical trials are presented. Moreover, future possibilities in pancreatic cancer treatment by gene therapy strategies are discussed.

Two and three-dimensional gene transfer from enzymatically degradable hydrogel scaffolds

The ability to genetically modify mesenchymal stem cells (MSCs) seeded inside synthetic hydrogel scaffolds would offer an alternative approach to guide MSC differentiation. In this report, we explored gene transfer to MSCs seeded on top or inside matrix metalloproteinase (MMP) degradable hydrogels that were loaded with DNA/poly(ethylene imine) (PEI) polyplexes. DNA/PEI polyplexes were encapsulated inside poly(ethylene glycol) (PEG) hydrogels crosslinked with MMP degradable peptides via Michael Addition chemistry. Gene transfer was visualized and quantified through using a vector encoding for green fluorescent protein and luciferase. We found that gene transfer to MSCs was possible for cells seeded both in two and three dimensions. The amount of luciferase expression was similar for cells seeded in two and three dimensions even though the number of cells in three dimensions is significantly higher, indicating that gene transfer to cells seeded in two dimensions is more efficient than for cells seeded in three dimensions. The use of hydrogel scaffolds that allow cellular infiltration to deliver DNA may result in long-lasting signals in vivo, which are essential for the regeneration of functional tissues.

Incorporation of active DNA/cationic polymer polyplexes into hydrogel scaffolds

The effective and sustained delivery of DNA and siRNAs locally would increase the applicability of gene therapy in tissue regeneration and cancer therapy. One promising approach is to use hydrogel scaffolds to encapsulate and deliver nucleotides in the form of nanoparticles to the disease sites. However, this approach is currently limited by the inability to load concentrated and active gene delivery nanoparticles into the hydrogels due to the severe nanoparticle aggregation during the loading process. Here, we present a process to load concentrated and un-aggregated non-viral gene delivery nanoparticles, using DNA/polyethylene imine (PEI) polyplexes as an example, into neutral polyethylene glycol (PEG), negatively charged hyaluronic acid (HA) and protein fibrin hydrogels crosslinked through various chemistries. The encapsulated polyplexes are highly active both in vitro and in vivo. We believe this process will significantly advance the applications of hydrogel scaffold mediated non-viral gene delivery in tissue regeneration and cancer therapy.

Pancreatic cancer: gene therapy approaches and gene delivery systems

IMPORTANCE OF THE FIELD

Due to the absence of early diagnosis, the highly invasive and metastatic features and the lack of effective therapeutic modalities, the prognosis of patients with pancreatic cancer is poor. Gene therapy is currently regarded as a potential and promising therapeutic modality for pancreatic cancer.

AREAS COVERED IN THIS REVIEW

This article summarizes an update of gene therapy approaches and reviews the latest progress in gene delivery systems that have been tested on pancreatic cancer.

WHAT THE READER WILL GAIN

The treatment effectiveness of gene combination therapy is better than that of the regulation of single-gene or single gene therapy approaches. Naked DNA is limited because of degradation by intracellular and extracellular nucleases. Virus vectors show high transfection efficiency but are limited due to immunogenicity, inflammatory response and potential carcinogenicity. Non-viral vectors, such as cationic polymers or inorganic nanoparticles, show an important feature that they can be easily modified, and the progress of materials science will provide more and better non-viral vectors, accordingly improving the efficiency and safety of gene therapy, which will make them the most promising vectors for pancreatic cancer.

Design and synthesis of N4,N9-disubstituted spermines for non-viral siRNA delivery--structure-activity relationship studies of siFection efficiency versus toxicity

PURPOSE

To study the effect of sequentially changing the chain length, oxidation level, and charge distribution in N4,N9-diacyl and N4,N9-dialkyl spermines on siRNA formulation, and then to compare their lipoplex transfection efficiency in cell lines.

METHODS

Eight N4,N9-diacyl polyamines: N4,N9-[didecanoyl, dilauroyl, dimyristoyl, dimyristoleoyl, dipalmitoyl, distearoyl, dioleoyl and diretinoyl]-1,12-diamino-4,9-diazadodecane were synthesized. Their abilities to bind to siRNA and form nanoparticles were studied using a RiboGreen intercalation assay and particle sizing. Two diamides were also reduced to afford tetraamines N4,N9-distearyl- and N4,N9-dioleyl-1,12-diamino-4,9-diazadodecane. Delivery of fluorescein-labelled Label IT RNAi Delivery Control was studied in FEK4 primary skin cells and in an immortalized cancer cell line (HtTA), and compared with TransIT-TKO.

RESULTS

The design, synthesis, and structure-activity relationship studies of a series of N4,N9-disubstituted spermines as efficient vectors for non-viral siRNA delivery to primary skin and cancer cell lines is reported. These non-liposomal cationic lipids are promising siRNA carriers based on the naturally occurring polyamine spermine showing that C-18 is a better chain length as shorter chains are more toxic.

CONCLUSIONS

N4,N9-Distearoyl spermine and N4,N9-dioleoyl spermine are efficient siRNA formulation and delivery vectors, even in the presence of serum, comparable to TransIT-TKO. However, four positive charges distributed as in spermine was significantly more toxic.

DNA delivery from matrix metalloproteinase degradable poly(ethylene glycol) hydrogels to mouse cloned mesenchymal stem cells

The ability to genetically modify mesenchymal stem cells (MSCs) seeded inside synthetic hydrogel scaffolds would offer an alternative approach to guide MSC differentiation and to study molecular pathways in three dimensions than protein delivery. In this report, we explored gene transfer to infiltrating MSCs into matrix metalloproteinase (MMP) degradable hydrogels that were loaded with DNA/poly(ethylene imine) (PEI) polyplexes. DNA/PEI polyplexes were encapsulated inside poly(ethylene glycol) (PEG) hydrogels crosslinked with MMP-degradable peptides via Michael addition chemistry. A large fraction of encapsulated polyplexes remained active after encapsulation (65%) and the mechanical properties of the hydrogels were unchanged by the encapsulation of the polyplexes. Cells were seeded inside the hydrogel scaffolds using two different approaches: clustered and homogeneous. The viability of MSCs was similar in hydrogels with and without polyplexes. Transgene expression was characterized with time using a secreted reporter gene and showed different profiles for clustered and homogeneously seeded cells. Clustered cells resulted in cumulative transgene expression that increased through the 21-day incubation, while homogeneously seeded cells resulted in cumulative transgene expression that plateaued after 7 days of culture. The use of hydrogel scaffolds that allow cellular infiltration to deliver DNA may result in long lasting signals in vivo, which are essential for the regeneration of functional tissues.

Genuine DNA/polyethylenimine (PEI) Complexes Improve Transfection Properties and Cell Survival

Polyethylenimine (PEI) has been described as one of the most efficient cationic polymers for in vitro gene delivery. Systemic delivery of PEI/DNA polyplexes leads to a lung-expression tropism. Selective in vivo gene transfer would require targeting and stealth particles. Here, we describe two strategies for chemically coupling polyethylene glycol (PEG) to PEI, to form protected ligand-bearing particles. Pre-grafted PEG-PEI polymers lost their DNA condensing property, hence their poor performances. Coupling PEG to pre-formed PEI/DNA particles led to the expected physical properties. However, low transfection efficacies raised the question of the fate of excess free polymer in solution. We have developed a straightforward a purification assay, which uses centrifugation-based ultrafiltration. Crude polyplexes were purified, with up to 60% of the initial PEI dose being removed. The resulting purified and unshielded PEI/DNA polyplexes are more efficient for transfection and less toxic to cells in culture than the crude ones. Moreover, the in vivo toxicity of the polyplexes was greatly reduced, without affecting their efficacy.

Characterization of the transgene expression generated by branched and linear polyethylenimine-plasmid DNA nanoparticles in vitro and after intraperitoneal injection in vivo

Polyethylenimine (PEI) is a cationic polymer that has shown significant potential for delivering genes in vitro and in vivo. Mixing cationic PEI with negatively charged plasmid DNA (pDNA) results in the spontaneous electrostatic formation of stable nanoparticle complexes. The structure of PEI can be branched or linear. In this study, we show that branched PEI has a stronger electrostatic interaction with pDNA than linear PEI, which accounts for greater compaction, higher zeta potentials and smaller nanoparticle sizes at equivalent pDNA concentrations. For both linear and branched PEI, increasing the concentration of pDNA mixed in the same volume and at the same nitrogen to phosphate (N:P) ratio results in larger average particle sizes. Increasing the N:P ratio increases luciferase activity generated by branched PEI-pDNA nanoparticles and linear PEI-pDNA nanoparticles in HEK293, COS7 and HeLa cell lines. Increasing the N:P ratio at which branched PEI-pDNA nanoparticles are prepared also increases luciferase expression in HepG2 cells but does not increase luciferase expression generated by linear PEI-pDNA nanoparticles. In all of the cell lines, branched PEI-pDNA nanoparticles prepared at N:P ratios of 10 and above generated significantly higher luciferase activity than linear PEI-pDNA nanoparticles. Luciferase activity was highest in the HEK293 cells and luciferase expression in each of the cell lines followed the order of HEK293>COS7>HepG2>HeLa. Intraperitoneal (IP) injection of PEI-pDNA nanoparticles is attractive because it is simple, reproducible and often leads to a depot effect of nanoparticle complexes residing in the peritoneum. The IP route of administration avoids PEI-pDNA nanoparticle accumulation in the lung and the nanoparticles do not pass through the blood-brain barrier. In this study, using bioluminescent imaging (BLI), we show that changing the PEI structure and dose of the PEI-pDNA nanoparticles has a significant impact on the strength and duration of transgene expression after IP injection in vivo but increasing the N:P ratio does not. Increasing the dose and N:P ratio for all the PEI-pDNA nanoparticle formulations injected IP did not reduce mice survival and all mice remained in good health as determined by the Body Condition Scoring (BCS) technique.

Smad7 transgene attenuates peritoneal fibrosis in uremic rats treated with peritoneal dialysis

Transforming growth factor beta (TGF-beta) plays a critical role in the pathogenesis of the peritoneal fibrosis that complicates long-term peritoneal dialysis (PD). We studied the TGF-beta/Smad signaling pathway in peritoneal fibrosis induced in uremic rats treated with PD and explored the therapeutic potential of Smad7 to prevent fibrogenesis. After subtotal nephrectomy, uremic rats were treated with peritoneal dialysis using 4.25% dextrose-containing fluid. The peritoneum of uremic rats treated with PD demonstrated fibrosis, increased TGF-beta expression, increased Smad2/3 activation, decreased Smad7 expression, and increased expression of fibrogenic and angiogenic factors. In addition, peritoneal function was impaired and its structure was altered, including a thickened submesothelial layer. In rats transfected with a Smad7 transgene using an ultrasound-microbubble-mediated system, peritoneal fibrosis was attenuated, peritoneal function was improved, and Smad2/3 activation was inhibited. We suggest that administration of Smad7 inhibits peritoneal fibrogenesis in uremic rats treated with PD by correcting the imbalance between downregulated Smad7 and activated Smad2/3. Blockade of the TGF-beta/Smad signaling pathway may represent a novel therapeutic approach to prevent peritoneal fibrosis in patients treated with PD.

Direct selection of targeted adenovirus vectors by random peptide display on the fiber knob

Targeting of gene transfer at the level of cell entry is one of the most attractive challenges in vector development. However, attempts to redirect adenovirus vectors to alternative receptors by engineering the capsid-coding region have shown limited success because proper targeting ligand-receptor systems on the cells of interest are generally unknown. Systematic approaches to generate adenovirus vectors targeting any given cell type need to be developed to achieve this goal. Here, we constructed an adenovirus library that was generated by a Cre-lox-mediated in vitro recombination between an adenoviral fiber-modified plasmid library and genomic DNA to display random peptides on a fiber knob. As proof of concept, we screened the adenovirus display library on a glioma cell line and observed selection of several particular peptide sequences. The targeted vector carrying the most frequently isolated peptide significantly enhanced gene transduction in the glioma cell line but not in many other cell lines. Because the insertion of a pre-selected peptide into a fiber knob often fails to generate an adenovirus vector, the selection of targeting peptides is highly useful in the context of the adenoviral capsid. This vector-screening system can facilitate the development of a targeted adenovirus vector for a variety of applications in medicine.

Intraperitoneal linear polyethylenimine (L-PEI)-mediated gene delivery to ovarian carcinoma nodes in mice

Linear polyethylenimine (L-PEI) is an efficient transfection agent for ovarian carcinoma cells in vitro and ex vivo. In the present work, we go a step further and evaluate the efficacy of L-PEI in human ovarian tumor nodes developed in mice. PEI/DNA complexes were administered intraperitoneally instead of intravenously to avoid sequestering of complexes in the lung and liver and to allow transfection of nonvascularized tumor nodes. Plasmid biodistribution was studied by PCR and gene expression was characterized using complementary luciferase and beta-galactosidase assays. Intraperitoneal (i.p.) injection of L-PEI/DNA complexes allowed the straightforward distribution of plasmid in the whole peritoneal cavity. Gene expression occurred in many organs, but tumor nodes appeared as preferential sites for transgene expression. The i.p. delivery route allowed repeated injections and administration of large amounts of DNA (up to 400 mug) without signs of toxicity, even for doses well beyond the intravenous lethal dose. Transgene expression was dose-dependent and transient. However, multiple injections allowed its persistence to increase. These results provide encouraging elements towards the development of PEI-based gene therapy protocols for the treatment of advanced stage ovarian carcinoma.

Recent advances in rational gene transfer vector design based on poly(ethylene imine) and its derivatives

The continually increasing wealth of knowledge about the role of genes involved in acquired or hereditary diseases renders the delivery of regulatory genes or nucleic acids into affected cells a potentially promising strategy. Apart from viral vectors, non-viral gene delivery systems have recently received increasing interest, due to safety concerns associated with insertional mutagenesis of retro-viral vectors. Especially cationic polymers may be particularly attractive for the delivery of nucleic acids, since they allow a vast synthetic modification of their structure enabling the investigation of structure-function relationships. Successful clinical application of synthetic polycations for gene delivery will depend primarily on three factors, namely (1) an enhancement of the transfection efficiency, (2) a reduction in toxicity and (3) an ability of the vectors to overcome numerous biological barriers after systemic or local administration. Among the polycations presently used for gene delivery, poly(ethylene imine), PEI, takes a prominent position, due to its potential for endosomal escape. PEI as well as derivatives of PEI currently under investigation for DNA and RNA delivery will be discussed. This review focuses on structure-function relationships and the physicochemical aspects of polyplexes which influence basic characteristics, such as complex formation, stability or in vitro cytotoxicity, to provide a basis for their application under in vivo conditions. Rational design of optimized polycations is an objective for further research and may provide the basis for a successful cationic polymer-based gene delivery system in the future.

Rapid optimization of gene delivery by parallel end-modification of poly(beta-amino ester)s

Poly(beta-amino ester)s are cationic degradable polymers that have significant potential as gene delivery vectors. Here we present a generalized method to modify poly(beta-amino ester)s at the chain ends to improve their delivery performance. End-chain coupling reactions were developed so that polymers could be synthesized and tested in a high-throughput manner, without the need for purification. In this way, many structural variations at the polymer terminus could be rapidly evaluated. End-modification of the terminal amine structure of a previously optimized poly(beta-amino ester), C32, significantly enhanced its in vitro transfection efficiency. In vivo, intraperitoneal (IP) gene delivery using end-modified C32 polymers resulted in expression levels over one order of magnitude higher than unmodified C32 and jet-polyethylenimine (jet-PEI) levels in several abdominal organs. The rapid end-modification strategy presented here has led to the discovery of many effective polymers for gene delivery and may be a useful method to develop and optimize cationic polymers for gene therapy.

Gene therapy based on gemcitabine chemosensitization suppresses pancreatic tumor growth

Excepting surgical resection, there is no efficient treatment against pancreatic cancer. The chemotherapeutic agent gemcitabine improves the patient's clinical status but survival is not prolonged. The aim of this study was to design a new strategy to render gemcitabine more efficient in the treatment of pancreatic cancer using gene therapy. We have generated a fusion gene (DCK::UMK) combining deoxycytidine kinase (DCK) and uridine monophosphate kinase (UMK), which converts gemcitabine into its toxic phosphorylated metabolite. Antitumor effects of DCK::UMK gene expression were tested in vitro and in vivo in an orthotopic transplantable model of pancreatic cancer established in hamsters. DCK::UMK sensitizes pancreatic cancer cells to gemcitabine by reducing dramatically both in vitro cell viability and in vivo tumor volume. We found that in vivo expression of DCK::UMK resulted in an antitumor bystander effect due to apoptosis of untransduced cells. In vivo intratumoral gene transfer of DCK::UMK using the synthetic carrier PEI induced a potent tumor regression. Taken together, the results show that the fusion gene DCK::UMK sensitizes pancreatic cancer cells to gemcitabine treatment to induce cell death by apoptosis and tumor regression. Intratumoral delivery of the DCK::UMK gene in combination with gemcitabine might be of high interest for pancreatic cancer management.

Eradication of p53-mutated head and neck squamous cell carcinoma xenografts using nonviral p53 gene therapy and photochemical internalization

Photochemical internalization (PCI) technology has been used for PEI-mediated p53 gene transfer in mice bearing head and neck squamous cell carcinoma (HNSCC) xenografts. Using luciferase as a reporter gene, PCI led to a 20-fold increase in transgene expression 48 h after transfection and sustained transgene expression for 7 days. Therefore, iterative p53 gene transfer was performed by means of a weekly single injection of PEIGlu4/p53 complexes alone or with PCI for 5 (group A) or 7 (group B) weeks. The efficiency of p53 gene therapy was evaluated by following tumor growth and expression of P53-related downstream proteins (P21, MDM2, Bcl2, Bax). Apoptosis induction was evidenced through caspase-3 activation and PARP cleavage. Using PCI, tumor growth inhibition was observed in all transfected animals. Further, successful tumor cure was achieved in 17% (group A) and 83% (group B) of animals. PCI-mediated p53 gene transfer led to higher P53 protein expression that was correlated with induction of Bax and P21 proapoptotic proteins, repression of Bcl2 as well as activation of caspase-3, and cleavage of PARP. The present study demonstrates that PCI enhances the in vivo efficiency of PEI-mediated p53 gene transfer and can be proposed for p53 gene therapy in HNSCC.

Optimising non-viral gene delivery in a tumour spheroid model

BACKGROUND

Our current understanding of how the unique tumour microenvironment influences the efficacy of gene delivery is limited. The current investigation systematically examines the efficiency of several non-viral gene transfer agents to transfect multicellular tumour spheroids (MCTS), an in vitro model that displays a faithful three-dimensional (3D) representation of solid tumour tissue.

METHODS

Using a luciferase reporter assay, gene transfer to MCTS was optimised for 22 kDa linear and 25 kDa branched polyethyleneimine (PEI), the cationic lipids Lipofectamine(trade mark) and DCChol : DOPE, and the physical approach of tissue electroporation. Confocal microscopy was used to take optical tissue slices to identify the tissue localisation of green fluorescent protein (GFP) reporter gene expression and the distribution of fluorescently labelled complexes. A MCTS model of quiescent tumour regions was used to establish the influence of cellular proliferation status on gene transfer efficiency.

RESULTS

Of the polyplexes tested, 22 kDa linear PEI provided optimal gene delivery, with gene expression peaking at 46 h. Despite being the optimal vector tested, PEI-mediated transfection was limited to cells at the MCTS periphery. Using fluorescent PEI, it was found that complexes could only penetrate the outer 3-5 proliferating cell layers of the MCTS, sparing the deeper quiescent cells. Gene delivery in an MCTS model comprised entirely of quiescent cells demonstrated that in addition to being inaccessible to the vector, quiescent tumour regions are inherently less susceptible to PEI-mediated transfection than proliferating regions. This 'resistance' to transfection observed in quiescent cells was overcome through the use of electroporation. Despite the improved efficacy of electroporation in quiescent tissue, the gene expression was still confined to the outer regions of MCTS. The results suggest that limited access to central regions of an MCTS remain a significant barrier to gene delivery.

CONCLUSIONS

This data provides new insights into tumour-specific factors affecting non-viral gene transfer and highlights the difficulties in delivering genes to avascular tumour regions. The MCTS model is a useful system for the initial screening of future gene therapy strategies for solid tumours.

Glucosylated polyethylenimine as a tumor-targeting gene carrier

Glucosylated polyethylenimine (GPEI) was synthesized as a tumor-targeting gene carrier through facilitative glucose metabolism by tumor glucose transporter. Particle sizes of GPEI/DNA complex increased in proportion to glucose content of GPEI, whereas surface charge of the complex was not dependent on glucosylation, partially due to inefficient shielding of the short hydrophilic group introduced. GPEI with higher glucosylation (36 mol-%) had no cytotoxic effect on cells even at polymer concentrations higher than 200 microg/mL. Compared to unglucosylated PEI, glucosylation induced less than one-order decrease of transfection efficiency. Transfection of GPEI/DNA complex into tumor cells possibly occurred through specific interaction between glucose-related cell receptors and glucose moiety of GPEI. Gamma imaging technique revealed GPEI/DNA complex was distributed in liver, spleen, and tumors.

Application of poly(2-(dimethylamino)ethyl methacrylate)-based polyplexes for gene transfer into human ovarian carcinoma cells

Previously, attempts were made in our laboratory to transfect human ovarian cancer (OVCAR-3) cells, growing in the peritoneal cavity of nude mice, by intraperitoneal administration of poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA)-based polyplexes. However, hardly any transfection of the OVCAR-3 cells was observed. The aim of the present study was to examine whether pDMAEMA-polyplexes can transfect OVCAR-3 cells in vivo at DNA doses much higher than used previously [J. Gene Med. 1 (1999) 156-158]. We also explored a specific targeting strategy based on the use of folic acid (FA) as a targeting ligand directed against the folate receptor overexpressed on OVCAR-3 cells. Luciferase expression by OVCAR-3 cells mediated by pDMAEMA-based polyplexes was evaluated in the mouse i.p. OVCAR-3 xenograft model of ovarian cancer. By virtue of new formulation options, we were able to administer polyplex dispersions into OVCAR-3 bearing mice at much larger doses (75-120 microg DNA) than used previously (15 microg). The feasibility of folate-mediated targeting of the polyplexes was studied after coupling of FA to preformed polyplexes with poly(ethylene glycol) (PEG) as a spacer. Intraperitoneal administration of naked pLuc plasmid did not result in significant gene expression by the tumor cells. Administration of uncoated, positively charged pDMAEMA-based polyplexes at a DNA dose of 75-120 microg yielded significant transfection activity. However, also considerable gene expression was observed in non-target cells. To avoid transfection of non-target cells, an active targeting strategy based on the use of FA was studied. At a dose of 75 microg DNA (N/P 5), the folate-targeting approach yielded about 10-fold lower luciferase transfection levels in organs lined by the mesenthelial layer. This beneficial site-avoidance effect was achieved without compromising the degree of tumor cell transfection. Successful transfection of OVCAR-3 cells growing in the peritoneal cavity of nude mice can be achieved by i.p. administration of polyplexes at doses between 75 and 120 microg DNA. It was further demonstrated that active targeting of polyplexes to OVCAR-3 cells growing in the peritoneal cavity of mice is a realistic possibility to avoid transfection of non-target cells.

Cancer gene therapy

The prognosis of patients with some kinds of cancers whose patients are often found unresectable upon diagnosis is still dismal. In these fields, development of a new therapeutic modality is needed and gene therapy represents one promising strategy. So far, numerous cancer gene therapy clinical trials based on these principles have been carried out and have shown the safety of such modalities, but have fallen short of the initial expectations to cure cancers. In this review, we would like to make a problem-oriented discussion of current status of cancer gene therapy research by using mainly gastrointestinal cancers as an example. In order to overcome obstacles for full realization of cancer gene therapy, numerous researches have been conducted by many researchers. Various cancer-selective and non-selective genes, as well as lytic viruses themselves have been employed for gene therapy. In the context of gene delivery method, different kinds of viral and non-viral strategies have been utilized. In addition, surrogate assays, such as soluble markers and imaging, have been developed for safer and more informative clinical trials. Many experiments and clinical trials to date have figured out current obstacles for the realization of an effective cancer gene therapy modality. Tireless efforts to overcome such hurdles and continuous infusion of novel concepts into this field should lead to break through technologies and the cure of the patients.

Polyethylenimine-based non-viral gene delivery systems

Gene therapy has become a promising strategy for the treatment of many inheritable or acquired diseases that are currently considered incurable. Non-viral vectors have attracted great interest, as they are simple to prepare, rather stable, easy to modify and relatively safe, compared to viral vectors. Unfortunately, they also suffer from a lower transfection efficiency, requiring additional effort for their optimization. The cationic polymer polyethylenimine (PEI) has been widely used for non-viral transfection in vitro and in vivo and has an advantage over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. Here, we give some insight into strategies developed for PEI-based non-viral vectors to overcome intracellular obstacles, including the improvement of methods for polyplex preparation and the incorporation of endosomolytic agents or nuclear localization signals. In recent years, PEI-based non-viral vectors have been locally or systemically delivered, mostly to target gene delivery to tumor tissue, the lung or liver. This requires strategies to efficiently shield transfection polyplexes against non-specific interaction with blood components, extracellular matrix and untargeted cells and the attachment of targeting moieties, which allow for the directed gene delivery to the desired cell or tissue. In this context, materials, facilitating the design of novel PEI-based non-viral vectors are described.

Intraperitoneal injection of adenovirus expressing antisense K-ras RNA suppresses peritoneal dissemination of hamster syngeneic pancreatic cancer without systemic toxicity

We examined the antitumor effect and safety of the adenovirus-mediated expression of antisense K-ras RNA in two peritoneal dissemination models of pancreatic cancer. First, we found that the infection of an adenovirus vector expressing antisense human K-ras RNA (AxCA-AS) induced significant apoptosis in vitro in human pancreatic cancer cells with K-ras mutation. Second, the intraperitoneal (ip) injection of AxCA-AS effectively suppressed the growth of human pancreatic cancer cells in the peritoneal cavity of nude mice. Third, in the hamster syngeneic peritoneal dissemination model, the ip injection of an adenovirus expressing antisense hamster K-ras RNA significantly suppressed the peritoneal growth of hamster pancreatic cancer cells, and no significant systemic toxicity was observed in the treated hamsters. This study suggests a feasibility of the development of a therapeutic strategy against pancreatic cancer based on the adenovirus-mediated transduction of an antisense K-ras construct.