Vehicles For Cancer Gene Therapy Research Articles

Viruses, the vehicle for cancer gene therapy: A Review

Viruses, the vehicle for cancer gene therapy: A Review

The growth inhibitory effect of human gingiva-derived mesenchymal stromal cells expressing interferon-\u03b2 on tongue squamous cell carcinoma cells and xenograft model

BackgroundInterferon-β (IFN-β) is a cytokine with pleiotropic cellular functions, including antiviral, antiproliferative, and immunomodulatory activities. IFN-β inhibits multiple tumor cell growth in vitro. However, the contradiction between the therapeutic dose of IFN-β and its maximally tolerated dose is still inextricable in vivo. Human gingiva-derived mesenchymal stromal cells (GMSCs) represent promising vehicles for cancer gene therapy. This study evaluated the potential of GMSCs genetically engineered to produce IFN-β as a targeted gene delivery system to treat tongue squamous cell carcinoma (TSCC) in vitro and in vivo.MethodsA lentiviral vector encoding IFN-β was constructed and transfected into GMSCs to obtain IFN-β gene-modified GMSCs (GMSCs/IFN-β). Enzyme-linked immunosorbent assay (ELISA) was used to measure the IFN-β concentration in conditioned medium (CM) from GMSCs/IFN-β. The Cell Counting Kit-8 (CCK8), colony formation assay, and flow cytometry were used to detect the effects of GMSCs/IFN-β on TSCC cell line CAL27 cell growth and apoptosis in vitro. TSCC xenograft model was developed by subcutaneous injection of CAL27 cells into BALB/c nude mouse, and the role of intravenously injected GMSCs/IFN-β in engrafting in TSCC and controlling tumor progression was measured in vivo.ResultsGMSCs/IFN-β expressed a high level of IFN-β. Both CCK8 and colony forming assay showed that GMSCs/IFN-β significantly inhibited the proliferation of CAL27 cells compared with the GMSCs, GMSCs/vector, or DMEM group. Flow cytometry analysis demonstrated that the CAL27 cell apoptosis rate was higher in the GMSCs/IFN-β group than in the other three groups. The in vivo experiment revealed that GMSCs/IFN-β engrafted selectively in TSCC xenograft and expressed a high level of IFN-β. There were smaller tumor volume and lower number of Ki67-positive cells in the GMSCs/IFN-β group than in the GMSCs, GMSCs/vector, or phosphate-buffered saline (PBS) group. Interestingly, GMSCs and GMSCs/vector also presented the potential of CAL27 cell growth inhibition in vitro and in vivo, although such an effect was weaker than GMSCs/IFN-β.ConclusionsGMSCs/IFN-β inhibits the proliferation of TSCC cells in vitro and in vivo. These results provide evidence that delivery of IFN-β by GMSCs may be a promising approach to develop an effective treatment option for TSCC therapy.

In vitro exploration of a myeloid-derived suppressor cell line as vehicle for cancer gene therapy

Recent research indicates that cell-mediated gene therapy can be an interesting method to obtain intratumoral expression of therapeutic proteins. This paper explores the possibility of using transfected myeloid-derived suppressor cells (MDSCs), derived from a murine cell line, as cellular vehicles for transporting plasmid DNA (pDNA) encoding interleukin-12 (IL-12) to tumors. Transfecting these cells via electroporation caused massive cell death. This was not due to electroporation-induced cell damage, but was mainly the result of the intracellular presence of plasmids. In contrast, pDNA transfection using Lipofectamine 2000 (LF2000) did not result in a significant loss of viability. Differences in delivery mechanism may explain the distinctive effects on cell viability. Indeed, electroporation is expected to cause a rapid and massive influx of pDNA resulting in cytosolic pDNA levels that most likely surpass the activation threshold of the intracellular DNA sensors leading to cell death. In contrast, a more sustained intracellular release of the pDNA is expected with LF2000. After lipofection with LF2000, 56% of the MDSCs were transfected and transgene expression lasted for at least 24 h. Moreover, biologically relevant amounts of IL-12 were produced by the MDSCs after lipofection with an IL-12 encoding pDNA. In addition, IL-12 transfection caused a significant upregulation of CD80 and considerably reduced the immunosuppressive capacity of the MDSCs. IL-12-transfected MDSCs were still able to migrate to tumor cells, albeit that lipofection of the MDSCs seemed to slightly decrease their migration capacity.

Synthesis and application of poly(ethylene glycol)-co-poly(β-amino ester) copolymers for small cell lung cancer gene therapy

The design of polymeric nanoparticles for gene therapy requires engineering of polymer structure to overcome multiple barriers, including prolonged colloidal stability during formulation and application. Poly(β-amino ester)s (PBAEs) have been shown effective as polymeric vectors for intracellular DNA delivery, but limited studies have focused on polymer modifications to enhance the stability of PBAE/DNA polyplexes. We developed block copolymers consisting of PBAE oligomer center units and poly(ethylene glycol) (PEG) end units. We fabricated a library of PEG-PBAE polyplexes by blending PEGylated PBAEs of different PEG molecular weights and non-PEGylated PBAEs of different structures at various mass ratios of cationic polymer to anionic DNA. Non-PEGylated PBAE polyplexes aggregated following a 24h incubation in acidic and physiological buffers, presenting a challenge for therapeutic use. In contrast, among 36 PEG-PBAE polyplex formulations evaluated, certain polyplexes maintained a small size under these conditions. These selected polyplexes were further evaluated for transfection in human small cell lung cancer cells (H446) in the presence of serum, and the best formulation transfected ∼40% of these hard-to-transfect cells while preventing polymer-mediated cytotoxicity. When PEG-PBAE polyplex delivered Herpes simplex virus thymidine kinase plasmid in combination with the prodrug ganciclovir, the polyplexes killed significantly more H446 cancer cells (35%) compared to healthy human lung fibroblasts (IMR-90) (15%). These findings indicate that PEG-PBAE polyplexes can maintain particle stability without compromising their therapeutic function for intracellular delivery to human small cell lung cancer cells, demonstrate potential cancer specificity, and have potential as safe materials for small cell lung cancer gene therapy. Statement of SignificanceMany natural and synthetic biomaterials have been investigated as non-viral vectors to deliver nucleic acids for cancer therapy. However, there are multiple hurdles to successful transfection including achieving particle stability, efficient delivery to cancer cells, and low cytotoxicity. In particular, engineering the physicochemical surface properties of a nanoparticle to improve stability is often offset by a decrease in the cellular entry and transfection efficiency. We developed stable polymeric nanoparticles that demonstrate high transfection efficiency by modifying synthetic biodegradable cationic polymers and engineering nanoparticle formulations using a combinatorial approach. The results of this study show the potential of biodegradable surface-modified polymeric nanoparticles as clinically translatable, biomaterial-based vehicles for cancer gene therapy.

IL-21-Expressing Mesenchymal Stem Cells Prevent Lethal B-Cell Lymphoma Through Efficient Delivery of IL-21, Which Redirects the Immune System to Target the Tumor

Interleukin (IL)-21, a proinflammatory cytokine, has been developed as an immunotherapeutic approach due to its effects on various lymphocytes, including natural killer (NK) cells and T cells; however, the clinical success in cancer patients has been limited. Recently, mesenchymal stem cells (MSCs) have emerged as vehicles for cancer gene therapy due to their inherent migratory abilities toward tumors. In the present study, we hypothesized that MSCs, genetically modified to express high levels of IL-21 (IL-21/MSCs), can enhance antitumor responses through localized delivery of IL-21. For tumor induction, BALB/c mice were injected intravenously with syngeneic A20 B-cell lymphoma cells to develop a disseminated B-cell lymphoma model. Then, 6 days following tumor induction, the tumor-bearing mice were treated with IL-21/MSCs weekly, four times. Systemic infusion of A20 cells led to hind-leg paralysis as well as severe liver metastasis in the control group. The IL-21/MSC-treated group showed delayed tumor incidence as well as improved survival, whereas the MSC- and recombinant adenovirus-expressing IL-21 (rAD/IL-21)-treated groups did not show significant differences from the untreated mice. These therapeutic effects were associated with high levels of IL-21 delivered to the liver, which prevented the formation of tumor nodules. Furthermore, the infusion of IL-21/MSCs led to induction of effector T and NK cells, while potently inhibiting immune suppressor cells. Our findings demonstrate that IL-21-expressing MSCs have the therapeutic potential to induce potent antitumor effects against disseminated B-cell lymphoma through localized IL-21 delivery and induction of systemic antitumor immunity.

Bone marrow-derived mesenchymal stem cells co-expressing interleukin-18 and interferon-β exhibit potent antitumor effect against intracranial glioma in rats.

Bone marrow-derived mesenchymal stem cells (BMSCs) are promising gene vehicles for cancer gene therapy. In our previous study, we reported that BMSCs expressing interleukin (IL)-18 effectively inhibit the growth of glioma in rats. In the present study, we further detected the effect of BMSCs co-expressing IL-18 and interferon (IFN)-β, both of which are immunostimulatory cytokines. BMSCs were genetically engineered to express IL-18 and IFN-β by transfection of recombinant lentivirus-mediated gene transfer. Results showed that BMSCs co-expressing the two cytokines displayed more significant inhibition effect on glioma cell growth invitro when compared with BMSCs solely expressing IL-18 or IFN-β. Treatment of BMSCs co-expressing IL-18 and IFN-β significantly prolonged the survival and inhibited tumor growth in a rat intracranial glioma model. Furthermore, these genetically engineered BMSCs remarkably promoted cell apoptosis, antitumor cytokine production and CD4+ and CD8+ T-cell infiltration in intracranial glioma tissues than BMSCs solely expressing IL-18 or IFN-β. Results of the present study suggested that IL-18 and IFN-β had a synergistic effect on glioma inhibition. Moreover, results provided evidence that delivery of IL-18 and IFN-β by BMSCs may be an excellent and promising approach to develop an effective treatment protocol for glioma therapy.

Enhanced therapeutic efficacy of an adenovirus-PEI-bile-acid complex in tumors with low coxsackie and adenovirus receptor expression

Adenovirus (Ad) is a potential vehicle for cancer gene therapy. However, cells that express low levels of the coxsackie and adenovirus receptor (CAR) demonstrate poor Ad infection efficiency. We developed a bile acid-conjugated poly(ethyleneimine) (DA3)-coated Ad complex (Ad/DA3) to enhance Ad transduction efficiency. The size distribution and zeta potential of Ad/DA3 increased to 324 ± 3.08 nm and 10.13 ± 0.21 mV, respectively, compared with those of naked Ad (108 ± 2.26 nm and −17.7 ± 1.5 mV). The transduction efficiency of Ad/DA3 increased in a DA3 polymer concentration-dependent manner. Enhanced gene transfer by Ad/DA3 was more evident in CAR-moderate and CAR-negative cancer cells. Competition assays with a CAR-specific antibody revealed that internalization of Ad/DA3 was not mediated primarily by CAR but involved clathrin-, caveolae-, and macropinocytosis-mediated endocytosis. Cancer cell death was significantly increased when oncolytic Ad and DA3 were complexed (RdB-KOX/DA3) compared to that of naked oncolytic Ad and was inversely proportional to CAR levels. Importantly, RdB-KOX/DA3 significantly enhanced apoptosis, reduced angiogenesis, reduced proliferation, and increased active viral replication in human tumor xenografts compared to that of naked Ad. These results demonstrate that a hybrid vector system can increase the efficacy of oncolytic Ad virotherapy, particularly in CAR-limited tumors.

Mesenchymal stromal cells retrovirally transduced with prodrug-converting genes are suitable vehicles for cancer gene therapy

Mesenchymal stem/stromal cells (MSC) possess a set of several fairly unique properties which make them ideally suitable both for cellular therapies and regenerative medicine. These include: relative ease of isolation, the ability to differentiate along mesenchymal and non-mesenchymal lineages in vitro and the ability to be extensively expanded in culture without a loss of differentiative capacity. MSC are not only hypoimmunogenic, but they mediate immunosuppression upon transplantation, and possess pronounced anti-inflammatory properties. They are able to home to damaged tissues, tumors, and metastases following systemic administration. The ability of homing holds big promise for tumor-targeted delivery of therapeutic agents. Viruses are naturally evolved vehicles efficiently transferring their genes into host cells. This ability made them suitable for engineering vector systems for the delivery of genes of interest. MSC can be retrovirally transduced with genes encoding prodrug-converting genes (suicide genes), which are not toxic per se, but catalyze the formation of highly toxic metabolites following the application of a nontoxic prodrug. The homing ability of MSC holds advantages compared to virus vehicles which display many shortcomings in effective delivery of the therapeutic agents. Gene therapies mediated by viruses are limited by their restricted ability to track cancer cells infiltrating into the surrounding tissue, and by their low migratory capacity towards tumor. Thus combination of cellular therapy and gene delivery is an attractive option - it protects the vector from immune surveillance, and supports targeted delivery of a therapeutic gene/protein to the tumor site.

Preparation and drug release mechanism of CTS-TAX-NP-MSCs drug delivery system

Targeting delivery of anticancer agents is a promising field in anticancer therapy. Inherent tumor-tropic and migratory properties of mesenchymal stem cells (MSCs) make them potential vehicles for targeting drug delivery systems for tumors. Although, MSCs have been successfully studied and discussed as a vehicle for cancer gene therapy, they have not yet been studied adequately as a potential vehicle for traditional chemical anticancer drugs. In this study, we have engineered MSCs as a potential targeting delivery vehicle for paclitaxel (TAX)-loaded nanoparticles (NPs). The size, surface charge, starving time of MSCs, incubating time and concentration of NPs could influence the efficiency of NPs uptake. In vitro release of TAX from CTS (chitosan)-TAX-NP-MSCs and the expression of P-glycoprotein demonstrated that release of TAX from MSCs might involve both passive diffusion and active transport. In vitro migration assays indicated that MSCs at passage number 3 have the highest migrating ability. Although, the migration ability of CTS-TAX-NP-MSCs could be inhibited by uptake of CTS-TAX-NPs, this ability could recover 6 days after the internalization.

An Adenovirus Vector Incorporating Carbohydrate Binding Domains Utilizes Glycans for Gene Transfer

BackgroundVectors based on human adenovirus serotype 5 (HAdV-5) continue to show promise as delivery vehicles for cancer gene therapy. Nevertheless, it has become clear that therapeutic benefit is directly linked to tumor-specific vector localization, highlighting the need for tumor-targeted gene delivery. Aberrant glycosylation of cell surface glycoproteins and glycolipids is a central feature of malignant transformation, and tumor-associated glycoforms are recognized as cancer biomarkers. On this basis, we hypothesized that cancer-specific cell-surface glycans could be the basis of a novel paradigm in HAdV-5-based vector targeting.Methodology/Principal FindingsAs a first step toward this goal, we constructed a novel HAdV-5 vector encoding a unique chimeric fiber protein that contains the tandem carbohydrate binding domains of the fiber protein of the NADC-1 strain of porcine adenovirus type 4 (PAdV-4). This glycan-targeted vector displays augmented CAR-independent gene transfer in cells with low CAR expression. Further, we show that gene transfer is markedly decreased in cells with genetic glycosylation defects and by inhibitors of glycosylation in normal cells.Conclusions/SignificanceThese data provide the initial proof-of-concept for HAdV-5 vector-mediated gene delivery based on the presence of cell-surface carbohydrates. Further development of this new targeting paradigm could provide targeted gene delivery based on vector recognition of disease-specific glycan biomarkers.

Antitumor activity of placenta-derived mesenchymal stem cells producing pigment epithelium-derived factor in a mouse melanoma model

Mesenchymal stem cells (MSCs) are a new tool that can be used for the delivery of therapeutic agents to tumor cells. Among the various types of MSCs, placenta-derived MSCs (PDMSCs) have emerged as one of the most attractive vehicles for gene therapy due to their high throughput, lack of ethical concerns, non-invasive procedure for their harvesting and ease of isolation. In this study, we evaluated the antitumor activity of human PDMSCs loaded with recombinant adenoviruses expressing pigment epithelium-derived factor (PEDF). PDMSCs were transduced with adenovirus PEDF and the expression of PEDF was confirmed by western blotting and ELISA. The inhibition of angiogenesis mediated by PEDF-expressing PDMSCs (PDMSC-PEDF) was determined using human umbilical vein endothelial cell (HUVEC) proliferation inhibition assay and migration inhibition assay in vitro. In in vivo experiments, C57BL/6 mice bearing B16-F10 melanoma were treated with intratumoral injection of PDMSC-PEDF twice at a 4-day interval. The tumor volume and weight were recorded. The results demonstrated that the administration of PDMSC-PEDF resulted in marked suppression of tumor growth in an established melanoma model, which was associated with a decreased number of microvessels and increased apoptosis of tumor cells compared with the controls. The results suggest that human PDMSCs have potential use as effective delivery vehicles for cancer gene therapy.

Retracted: Tumor Tropism of Intravenously Injected Human‐Induced Pluripotent Stem Cell‐Derived Neural Stem Cells and Their Gene Therapy Application in a Metastatic Breast Cancer Model

Human pluripotent stem cells can serve as an accessible and reliable source for the generation of functional human cells for medical therapies. In this study, we used a conventional lentiviral transduction method to derive human-induced pluripotent stem (iPS) cells from primary human fibroblasts and then generated neural stem cells (NSCs) from the iPS cells. Using a dual-color whole-body imaging technology, we demonstrated that after tail vein injection, these human NSCs displayed a robust migratory capacity outside the central nervous system in both immunodeficient and immunocompetent mice and homed in on established orthotopic 4T1 mouse mammary tumors. To investigate whether the iPS cell-derived NSCs can be used as a cellular delivery vehicle for cancer gene therapy, the cells were transduced with a baculoviral vector containing the herpes simplex virus thymidine kinase suicide gene and injected through tail vein into 4T1 tumor-bearing mice. The transduced NSCs were effective in inhibiting the growth of the orthotopic 4T1 breast tumor and the metastatic spread of the cancer cells in the presence of ganciclovir, leading to prolonged survival of the tumor-bearing mice. The use of iPS cell-derived NSCs for cancer gene therapy bypasses the sensitive ethical issue surrounding the use of cells derived from human fetal tissues or human embryonic stem cells. This approach may also help to overcome problems associated with allogeneic transplantation of other types of human NSCs.

Viral Vectors in Cancer Immunotherapy: Which Vector for Which Strategy?

Gene therapy involves the transfer of genetic information to a target cell to facilitate the production of therapeutic proteins and is now a realistic prospect as a cancer treatment. Gene transfer may be achieved through the use of both viral and non-viral delivery methods and the role of this method in the gene therapy of cancer has been demonstrated. Viruses represent an attractive vehicle for cancer gene therapy due to their high efficiency of gene delivery. Many viruses can mediate long term gene expression, while some are also capable of infecting both dividing and non-dividing cells. Given the broadly differing capabilities of various viral vectors, it is imperative that the functionality of the virus meets the requirements of the specific treatment. A number of immunogene therapy strategies have been undertaken, utilising a range of viral vectors, and studies carried out in animal models and patients have demonstrated the therapeutic potential of viral vectors to carry genes to cancer cells and induce anti-tumour immune responses. This review critically discusses the advances in the viral vector mediated delivery of immunostimulatory molecules directly to tumour cells, the use of viral vectors to modify tumour cells, the creation of whole cell vaccines and the direct delivery of tumour antigens in animal models and clinical trials, specifically in the context of the suitability of vector types for specific strategies.

Carrier Cell-based Delivery of an Oncolytic Virus Circumvents Antiviral Immunity

Oncolytic viruses capable of tumor-selective replication and cytolysis have shown early promise as cancer therapeutics. However, the host immune system remains a significant obstacle to effective systemic administration of virus in a clinical setting. Here, we demonstrate the severe negative impact of the adaptive immune response on the systemic delivery of oncolytic vesicular stomatitis virus (VSV) in an immune-competent murine tumor model, an effect mediated primarily by the neutralization of injected virions by circulating antibodies. We show that this obstacle can be overcome by administering virus within carrier cells that conceal viral antigen during delivery. Infected cells were delivered to tumor beds and released virus to infect malignant cells while sparing normal tissues. Repeated administration of VSV in carrier cells to animals bearing metastatic tumors greatly improved therapeutic efficacy when compared with naked virion injection. Whole-body molecular imaging revealed that carrier cells derived from solid tumors accumulate primarily in the lungs following intravenous injection, whereas leukemic carriers disseminate extensively throughout the body. Furthermore, xenogeneic cells were equally effective at delivering virus as syngeneic cells. These findings emphasize the importance of establishing cell-based delivery platforms in order to maximize the efficacy of oncolytic therapeutics.

Analysis of the production efficiency and titration of various recombinant adeno-associated viruses

Recombinant adeno-associated virus type 2 (rAAV2) viral vector, a non-pathogenic human parvovirus, has recently emerged as a gene transfer vehicle for cancer gene therapy. To utilize rAAV2 properly and safely while carrying out preclinical and clinical studies, it is crucial to exactly titer the virus. We therefore compared biological infectious rAAV2 titers with physical titers of rAAV2 vectors encoding various transgenes with different sized viral genomes. Biological rAAV2 infectivity was assayed by measuring the number of virus particles able to transduce Hela cells using several detection methods, including X-gal staining and immunocytostaining. Physical titers of rAAV2 were determined using a commercially available rAAV2 particle-specific enzyme-linked immunosorbent assay. We found that total rAAV2 particle production was consistent within the limited size variations of the rAAV2 genome, regardless of the difference in transgenes. In contrast, the infectious titer of rAAV2 differed greatly, even for the same viruses, due to variation in the sensitivity of the relevant assays. Thus, the results suggest that both infectious virus titer and total virus particle should be precisely measured for rAAV2 vector utilized in each study.

118. Efficient Infection of Head and Neck Cancer Cells by Ad5/35 Hybrid Virus

Top of pageAbstract Most adenoviral vectors that are currently being employed as gene delivery vehicles for cancer gene therapy are derivatives of adenovirus serotype 5 (Ad5). These vectors enter target cells via two specific interactions: between the viral fiber knob and the coxsackievirus and adenovirus receptor (CAR) and the penton base and integrins αVβ3 and αVβ5. However, adenovirus-mediated gene transfer to many important gene therapy targets is limited due to the low expression levels of CAR. Redirecting Ad5-based vectors to other, preferentially target specific cellular receptors and simultaneously abrogating the interaction between the viral capsid proteins and their cellular counterparts, has thus become a major goal in gene therapy. Group B adenovirus-based vectors have recently gained interest as attractive gene delivery vehicles. Subgroup B2 adenoviruses, including Ad35, infect cells in a CAR-independent manner and may thus transduce cells that are resistant to Ad5 infection. Notably, human CD46 was recently identified as the cellular attachment receptor for these viruses. Squamous cell carcinoma of the head and neck (HNSCC) has several characteristics that make it a suitable target for gene therapy. Most HNSCC are localized and thus easily accessible by direct intratumoral injection. In addition, metastases of the tumor are a late-stage occurrence and therefore early loco-regional control of the disease is paramount. On the basis of these favorable characteristics, gene delivery strategies that utilize adenoviruses have been developed for HNSCC. However, effective in vivo transduction has been a limiting factor in the initial clinical trials using standard Ad5-based vectors for this disease. In order to determine the feasibility of adenoviral retargeting to head and neck cancer, primary HNSCC cells collected from cancer patients were used. Full clinical as well as histological data is available on these cells. Our retargeting scheme was based on the Ad5/35 hybrid system, where the serotype 5 fiber has been replaced with the fiber of serotype 35. Flow cytometric analyses demonstrated that the level of CD46 expression was uniformly high in all primary cells studied (85–99%, average positive ratio 96%). In contrast, CAR expression was clearly lower and also highly variable (1.6–62%, average positive ratio 30%). αV integrin expression was between 39–98% with an average expression of 82%. In situ stainings for b-galactosidase gene expression demonstrated that Ad5/35.lacZ was clearly more effective than Ad5.lacZ in transducing primary HNSCC cells, and quantification of b-galactosidase expression revealed 3 to 58-fold differences in transduction efficacy between the two viruses. As expected, the infection efficacies of the viruses correlated with the receptor expression levels. When the viral transduction and receptor expression data was compared against the clinical data, the difference between the efficacies of the two viruses was found to be clearest in tumors with a high degree of malignancy, although the trend was not statistically significant. These data suggest that the group B2 adenovirus cell entry pathway is highly efficient in transducing HNSCC cells. These results warrant further development of the Ad5/35 hybrid system for head and neck cancer.

739. Lentiviruses as Gene Transfer Vehicles for Cancer Gene Therapy

Lentiviral vectors are very efficient gene transfer vehicles for most cell types, regardless of the species or tissue of origin. Several reports suggest that these vectors are efficient for most human tumor cells, but their utility in cancer gene therapy has not been examined systematically. To study this, VSV-G pseudotyped HIV-1 vector and E1/E3 deleted adenoviral vector (serotype 5) were compared for their capability to transduce 42 different human cancer cell lines. In most cases MOI 3 yielded 50-90 % transduction efficiency with both vectors. In vivo studies with nude mouse s.c. tumor model (A549 lung cancer cells) revealed that lentiviruses were more efficient vehicles than adenoviruses when same amount of virus was used.

Cellular Vehicles for Cancer Gene Therapy

Cancer is a difficult target for any therapeutic strategy; therefore, there is a continuous search for new therapeutic modalities, for application either alone or in combination. In this regard, gene-based therapy is a new approach that offers hope of improved control of tumors. Intensive research to apply gene therapy for cancer treatment has led to identification of the most important technical and theoretical barriers that need to be overcome for clinical success. One of the central unresolved challenges remains the issue of specific and efficient delivery of genes to target cells or tissues, emphasizing the importance of the gene carrier. Along with different viral and non-viral vector systems, mammalian cells have also been considered as vehicles for delivery of anti-cancer therapeutics. The cell-based delivery approach was introduced as the first attempt to apply gene therapy to cancer treatment, and in general, has followed most of the ups and downs of gene therapy applications, progressing alongside new knowledge gained in this field. As a result, significant progress has been made in some aspects of the cell-based approach, while the development of other essential issues is only just gaining speed. It appears that the initial phase of development of cell-based protocols - the achievement of efficient ex vivo cell loading with therapeutics - has largely been fulfilled. However, the desired efficacy of cell-based strategies in general has not yet been reached, and specificity of tumor homing needs to be improved considerably. There is hope that advances in related scientific fields will promote the utilization of cells as powerful and versatile vehicles for cancer gene therapy.

The therapeutic efficacy of adenoviral vectors for cancer gene therapy is limited by a low level of primary adenovirus receptors on tumour cells

Replication-defective adenoviral vectors are currently being employed as gene delivery vehicles for cancer gene therapy. To address the hypothesis that the therapeutic efficacy of adenoviral vectors is restricted by their inability to infect tumour cells expressing low levels of the primary cellular receptor for adenoviruses, the coxsackievirus and adenovirus receptor (CAR), we have employed a pair of ovarian cancer cell lines differing only in the expression of a primary receptor for Ad5. This novel system thus allowed the direct evaluation of the relationship between the efficacy of an adenoviral vector and the primary receptor levels of the host cancer cell, without the confounding influence of other variable cellular factors. We demonstrate that a deficiency of the primary cellular receptor on the tumour cells restricts the efficacy of adenoviral vectors in two distinct cancer gene therapy approaches, TP53 gene replacement therapy and herpes simplex virus thymidine kinase/ganciclovir suicide gene therapy. Moreover, we show that a deficiency of the primary receptor on the tumour cells limits the efficiency of adenovirus-mediated gene transfer in vivo. Since a number of studies have reported that primary cancer cells express only low levels of CAR, our results suggest that strategies to redirect adenoviruses to achieve CAR-independent infection will be necessary to realize the full potential of adenoviral vectors in the clinical setting.

Cells as vehicles for cancer gene therapy: the missing link between targeted vectors and systemic delivery?

Systemic administration of currently manufactured viral stocks has not so far achieved sufficient circulating titers to allow therapeutic targeting of metastatic disease. This is due to low initial viral titers, immune inactivation, nonspecific adhesion, and loss of particles. One way to exploit the elegant molecular manipulations that have been made to increase vector targeting is to protect these vectors until they reach the local sites of tumor growth. Various cell types home preferentially to tumors and can be loaded with the constructs required to produce targeted vectors. Here we discuss the potential of using such cell carriers to chaperone precious vectors directly to the tumors. The vectors can incorporate mechanisms to achieve tumor site-inducible expression, along with tumor cell-specific expression of the therapeutic gene and/or replicating viral genomes that would be released at the tumor. In this way, the great advances that have so far been made with the engineering of vector tropisms might be genuinely exploited and converted into clinical benefit.