Cancer gene therapy: scientific basis

The impact of oncolytic adenoviral therapy on the therapeutic efficacy of PD-1/PD-L1 blockade

Immunotherapy has revolutionized treatment of cancer during the last decades. Oncolytic virotherapy has also emerged as a strategy to fight against cancer cells both via lysis of malignant cells and activating immune responses. Accepted as a logical strategy, combination of monoclonal antibodies particularly against the programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) is introduced to improve clinical responses to immune checkpoint inhibitors (ICIs). Accordingly, Talimogene laherparepvec (T-VEC) has received approval for clinical use, while a number of oncolytic Adenoviruses (Ads) are being investigated in clinical trials of malignancies. Combination of oncolytic Ads with PD-1/PD-L1 inhibitors have shown potentials in promoting responses to ICIs, changing the tumor microenvironment, inducing long-term protection against tumor, and promoting survival among mice models of malignancies. Regarding the increasing importance of oncolytic Ads in combination therapy of cancers, in this review we decide to outline recent studies in this field.

Novel Synthesized N-Ethyl-Piperazinyl-Amides of C2-Substituted Oleanonic and Ursonic Acids Exhibit Cytotoxic Effects through Apoptotic Cell Death Regulation

A series of novel hybrid chalcone N-ethyl-piperazinyl amide derivatives of oleanonic and ursonic acids were synthesized, and their cytotoxic potential was evaluated in vitro against the NCI-60 cancer cell line panel. Compounds 4 and 6 exhibited the highest overall anticancer activity, with GI₅₀ values in some cases reaching nanomolar values. Thus, the two compounds were further assessed in detail in order to identify a possible apoptosis- and antiangiogenic-based mechanism of action induced by the assessed compounds. DAPI staining revealed that both compounds induced nuclei condensation and overall cell morphological changes consistent with apoptotic cell death. rtPCR analysis showed that up-regulation of pro-apoptotic Bak gene combined with the down-regulation of the pro-survival Bcl-XL and Bcl-2 genes caused altered ratios between the pro-apoptotic and anti-apoptotic proteins’ levels, leading to overall induced apoptosis. Molecular docking analysis revealed that both compounds exhibited high scores for Bcl-XL inhibition, suggesting that compounds may induce apoptotic cell death through targeted anti-apoptotic protein inhibition, as well. Ex vivo determinations showed that both compounds did not significantly alter the angiogenesis process on the tested cell lines.

shRNA-armed conditionally replicative adenoviruses: a promising approach for cancer therapy

The small-interfering RNAs (siRNAs) have been employed to knockdown the expression of cancer-associated genes and shown some promise in cancer therapy. However, synthetic siRNA duplexes or plasmid mediated delivery of siRNAs have several problems, such as short half-life, low transfection efficiency and cytotoxicity associated with transfection. Conditionally replicating adenovirus (CRAds) as the delivery vector for short hairpin RNAs (shRNAs) could overcome these limitations and have shown augmented anti-tumor effects in experimental studies and preclinical trials. In this review, we summarize recent progress in the development of CRAds-shRNA for cancer treatment. Combination of CRAds-shRNA with chemotherapeutics, radiation, dendritic cells, monoclonal antibodies and small-molecule inhibitors will be necessary to eradicate cancer cells and cancer stem cells and achieve superior outcomes. The use of CRAd platform for efficient delivery of shRNAs and foreign genes will open a new avenue for cancer therapy.

Impact of O6-methylguanine-DNA methyltransferase expression on the drug resistance of clear cell renal cell carcinoma

OBJECTIVE

The deoxyribonucleic acid-repair protein O(6)-methylguanine-deoxyribonucleic acid methyltransferase is a major determinant of resistance of cells to various alkylating drugs. Its expression profile is different in different cancer types. Here, we studied the expression and function of O(6)-methylguanine-deoxyribonucleic acid methyltransferase in clear cell renal cell carcinoma.

METHODS

The expression of O(6)-methylguanine-deoxyribonucleic acid methyltransferase was evaluated in clear cell renal cell carcinoma tissues and cell lines by quantitative real-time polymerase chain reaction and immunohistochemistry. The relationship between O(6)-methylguanine-deoxyribonucleic acid methyltransferase expression and clinicopathological characteristics was analyzed. To further investigate the function of O(6)-methylguanine-deoxyribonucleic acid methyltransferase in clear cell renal cell carcinoma resistance to alkylating agents, siRNA targeting O(6)-methylguanine-deoxyribonucleic acid methyltransferase were used to silence the O(6)-methylguanine-deoxyribonucleic acid methyltransferase expression.

RESULTS

We found that O(6)-methylguanine-deoxyribonucleic acid methyltransferase is over-expressed in clear cell renal cell carcinoma tissues and cell lines. O(6)-methylguanine-deoxyribonucleic acid methyltransferase expression is related with tumor progression in clear cell renal cell carcinoma patients. Up-regulation of O(6)-methylguanine-deoxyribonucleic acid methyltransferase plays a critical role in primary resistance to alkylating agents.

CONCLUSIONS

The overexpression of O(6)-methylguanine-deoxyribonucleic acid methyltransferase contributes to resistance of clear cell renal cell carcinoma to standard chemotherapy. Our results have significance for understanding a new pathway of the development of drug resistance of clear cell renal cell carcinoma.

Single-walled carbon nanotubes as candidate recombinant subunit vaccine carrier for immunization of grass carp against grass carp reovirus

Grass carp reovirus (GCRV), the most pathogenic aquareovirus, can cause fatal hemorrhagic disease in fingerling and yearling grass carp. Vaccination by injection is by far the most effective method of combating disease. However it is labor intensive, costly and not feasible to vaccinate large numbers of the fish. Thus, an efficient and economic strategy for the prevention of GCRV infection becomes urgent. Here, functionalized single-walled carbon nanotubes (SWCNTs) as carrier were used to manufacture SWCNTs-VP7 subunit vaccine with chemical modification. Different developmental stages of grass carps were immunized by VP7/SWCNTs-VP7 subunit vaccine against GCRV by intramuscular injection and bath immunization. The results indicate that better immune responses of grass carp immunized with the SWCNTs-VP7 subunit vaccine were induced in comparison with VP7 subunit vaccine alone. Immunization doses/concentrations are significantly reduced (about 5-8 times) to prevent GCRV infection in different developmental stages of grass carp with injection or bath treatment when SWCNTs carrier was used. A good immune protective effect (relative percentage survival greater than 95%) is observed in smaller size fish (0.2 g) with SWCNTs-VP7 bath immunization. In addition, serum respiratory burst activity, complement activity, lysozyme activity, superoxide dismutase activity, alkaline phosphatase activity, immune-related genes and antibody levels were significantly enhanced in fish immunized with vaccine. This study suggested that functionalized SWCNTs was the promising carrier for recombinant subunit vaccine and might be used to vaccinate fish by bath approach.

Bio-Encapsulation for the Immune-Protection of Therapeutic Cells

The design of new technologies for treatment of human disorders is a complex and difficult task. The aim of this article is to explore state of art discussion of various techniques and materials involve in cell encapsulations. Encapsulation of cells within semi-permeable polymer shells or beads is a potentially powerful tool, and has long been explored as a promising approach for the treatment of several human diseases such as lysosomal storage disease (LSD), neurological disorders, Parkinsons disease, dwarfism, hemophilia, cancer and diabetes using immune-isolation gene therapy.

Nanomaterials in the application of tumor vaccines: advantages and disadvantages

Tumor vaccines are a novel approach to the treatment of malignancy, and are attracting the attention of the medical profession. Nanomaterials have significant advantages in the preparation of a tumor vaccine, including their ability to penetrate and target cancer tissue and their antigenic properties. In this review, we focus on several nanomaterials, ie, carbon nanotubes, nanoemulsions, nanosized aluminum, and nanochitosan. Applications for these nanomaterials in nanovaccines and their biological characteristics, as well as their potential toxicity, are discussed.

Exploring N-imidazolyl-O-carboxymethyl chitosan for high performance gene delivery

Chitosan shows good biocompatibility and biodegradability, but the poor water solubility and low transfection efficiency hinder its applications as a gene delivery vector. We here report the detailed synthesis and characterization of a novel ampholytical chitosan derivative, N-imidazolyl-O-carboxymethyl chitosan (IOCMCS), used for high performance gene delivery. After chemical modification, the solubility of the resulting polymer is enhanced, and the polymer is soluble in a wide pH range (4-10). Gel electrophoresis study reveals the strong binding ability between plasmid DNA and the IOCMCS. Moreover, the IOCMCS does not induce remarkable cytotoxicity against human embryonic kidney (HEK293T) cells. The cell transfection results with HEK293T cells using the IOCMCS as gene delivery vector demonstrate the high transfection efficiency, which is dependent on the degree of imidazolyl substitution. Therefore, the IOCMCS is a promising candidate as the DNA delivery vector in gene therapy due to its high solubility, high gene binding capability, low cytotoxicity, and high gene transfection efficiency.

Advancement and prospects of tumor gene therapy

Gene therapy is one of the most attractive fields in tumor therapy. In past decades, significant progress has been achieved. Various approaches, such as viral and non-viral vectors and physical methods, have been developed to make gene delivery safer and more efficient. Several therapeutic strategies have evolved, including gene-based (tumor suppressor genes, suicide genes, antiangiogenic genes, cytokine and oxidative stress-based genes) and RNA-based (antisense oligonucleotides and RNA interference) approaches. In addition, immune response-based strategies (dendritic cell- and T cell-based therapy) are also under investigation in tumor gene therapy. This review highlights the progress and recent developments in gene delivery systems, therapeutic strategies, and possible clinical directions for gene therapy.

Enhancement of radiosensitivity in human glioblastoma cells by the DNA N-mustard alkylating agent BO-1051 through augmented and sustained DNA damage response

Background

1-{4-[Bis(2-chloroethyl)amino]phenyl}-3-[2-methyl-5-(4-methylacridin-9-ylamino)phenyl]urea (BO-1051) is an N-mustard DNA alkylating agent reported to exhibit antitumor activity. Here we further investigate the effects of this compound on radiation responses of human gliomas, which are notorious for the high resistance to radiotherapy.

Methods

The clonogenic assay was used to determine the IC₅₀ and radiosensitivity of human glioma cell lines (U87MG, U251MG and GBM-3) following BO-1051. DNA histogram and propidium iodide-Annexin V staining were used to determine the cell cycle distribution and the apoptosis, respectively. DNA damage and repair state were determined by γ-H2AX foci, and mitotic catastrophe was measure using nuclear fragmentation. Xenograft tumors were measured with a caliper, and the survival rate was determined using Kaplan-Meier method.

Results

BO-1051 inhibited growth of human gliomas in a dose- and time-dependent manner. Using the dosage at IC₅₀, BO-1051 significantly enhanced radiosensitivity to different extents [The sensitizer enhancement ratio was between 1.24 and 1.50 at 10% of survival fraction]. The radiosensitive G₂/M population was raised by BO-1051, whereas apoptosis and mitotic catastrophe were not affected. γ-H2AX foci was greatly increased and sustained by combined BO-1051 and γ-rays, suggested that DNA damage or repair capacity was impaired during treatment. In vivo studies further demonstrated that BO-1051 enhanced the radiotherapeutic effects on GBM-3-beared xenograft tumors, by which the sensitizer enhancement ratio was 1.97. The survival rate of treated mice was also increased accordingly.

Conclusions

These results indicate that BO-1051 can effectively enhance glioma cell radiosensitivity in vitro and in vivo. It suggests that BO-1051 is a potent radiosensitizer for treating human glioma cells.

Toxin-based therapeutic approaches

Protein toxins confer a defense against predation/grazing or a superior pathogenic competence upon the producing organism. Such toxins have been perfected through evolution in poisonous animals/plants and pathogenic bacteria. Over the past five decades, a lot of effort has been invested in studying their mechanism of action, the way they contribute to pathogenicity and in the development of antidotes that neutralize their action. In parallel, many research groups turned to explore the pharmaceutical potential of such toxins when they are used to efficiently impair essential cellular processes and/or damage the integrity of their target cells. The following review summarizes major advances in the field of toxin based therapeutics and offers a comprehensive description of the mode of action of each applied toxin.

Combination of bifunctional alkylating agent and arsenic trioxide synergistically suppresses the growth of drug-resistant tumor cells

Drug resistance is a crucial factor in the failure of cancer chemotherapy. In this study, we explored the effect of combining alkylating agents and arsenic trioxide (ATO) on the suppression of tumor cells with inherited or acquired resistance to therapeutic agents. Our results showed that combining ATO and a synthetic derivative of 3a-aza-cyclopenta[a]indenes (BO-1012), a bifunctional alkylating agent causing DNA interstrand cross-links, was more effective in killing human cancer cell lines (H460, H1299, and PC3) than combining ATO and melphalan or thiotepa. We further demonstrated that the combination treatment of H460 cells with BO-1012 and ATO resulted in severe G(2)/M arrest and apoptosis. In a xenograft mouse model, the combination treatment with BO-1012 and ATO synergistically reduced tumor volumes in nude mice inoculated with H460 cells. Similarly, the combination of BO-1012 and ATO effectively reduced the growth of cisplatin-resistant NTUB1/P human bladder carcinoma cells. Furthermore, the repair of BO-1012-induced DNA interstrand cross-links was significantly inhibited by ATO, and consequently, gammaH2AX was remarkably increased and formed nuclear foci in H460 cells treated with this drug combination. In addition, Rad51 was activated by translocating and forming foci in nuclei on treatment with BO-1012, whereas its activation was significantly suppressed by ATO. We further revealed that ATO might mediate through the suppression of AKT activity to inactivate Rad51. Taken together, the present study reveals that a combination of bifunctional alkylating agents and ATO may be a rational strategy for treating cancers with inherited or acquired drug resistance.

Is Ozone Really a “Wonder Drug”?

Even if the reader has only browsed through the previous chapters, he ought to have received my feeling that ozone has an enormous therapeutic potential that, so far, has been either disregarded, if not obstructed by world medical authorities. Reasons for delaying the use of ozone are multiple: while quacks and inexpert ozonetherapists are at fault for poor work, other aspects such as commercial and pharmaceutical interests, prejudice, lack of knowledge and a myopic medical vision have done their best to block a substantial and rapid progress.

Derivation of a triple mosaic adenovirus for cancer gene therapy

A safe and efficacious cancer medicine is necessary due to the increasing population of cancer patients whose particular diseases cannot be cured by the currently available treatment. Adenoviral (Ad) vectors represent a promising therapeutic medicine for human cancer therapy. However, several improvements are needed in order for Ad vectors to be effective cancer therapeutics, which include, but are not limited to, improvement of cellular uptake, enhanced cancer cell killing activity, and the capability of vector visualization and tracking once injected into the patients. To this end, we attempted to develop an Ad as a multifunctional platform incorporating targeting, imaging, and therapeutic motifs. In this study, we explored the utility of this proposed platform by generating an Ad vector containing the poly-lysine (pK), the herpes simplex virus type 1 (HSV-1) thymidine kinase (TK), and the monomeric red fluorescent protein (mRFP1) as targeting, tumor cell killing, and imaging motifs, respectively. Our study herein demonstrates the generation of the triple mosaic Ad vector with pK, HSV-1 TK, and mRFP1 at the carboxyl termini of Ad minor capsid protein IX (pIX). In addition, the functionalities of pK, HSV-1 TK, and mRFP1 proteins on the Ad vector were retained as confirmed by corresponding functional assays, indicating the potential multifunctional application of this new Ad vector for cancer gene therapy. The validation of the triple mosaic Ad vectors also argues for the ability of pIX modification as a base for the development of multifunctional Ad vectors.

Therapeutic and tumor-specific immunity induced by combination of dendritic cells and oncolytic adenovirus expressing IL-12 and 4-1BBL

Recently, gene-based cytokine treatment has been actively pursued as a new promising approach in treating cancer. In an effort to augment the efficiency of antitumor effect by cytokine-mediated immunotherapy, we selected both interleukin (IL)-12 and 4-1BB ligand (4-1BBL) as suitable cytokines to fully activate the type-1 immune response. Coexpression of IL-12 and 4-1BBL mediated by oncolytic adenovirus (Ad) greatly enhanced the antitumor effect. Further, synergistic enhancement in interferon (IFN)-gamma levels were seen in mice treated with oncolytic Ad expressing both IL-12 and 4-1BBL. Next, to improve the overall antitumor immune response, we coadministered IL-12- and 4-1BBL-coexpressing oncolytic Ad with dendritic cells (DCs). Combination treatment of IL-12- and 4-1BBL-coexpressing oncolytic Ad and DCs elicited greater antitumor and antimetastatic effects than either treatment alone. Moreover, enhanced type-1 antitumor immune response and higher migratory abilities of DCs in tumors were also observed in the combination arms. The nature of the enhanced antitumor immune response seems to be mediated through the enhanced cytolytic activity of cytotoxic T lymphocytes (CTLs) and IFN-gamma-releasing immune cells. Taken together, these data highlight the potential therapeutic benefit of combining IL-12- and 4-1BBL-coexpressing oncolytic Ad with DCs and warrants further evaluation in the clinic.

AAV-mediated local delivery of interferon-beta for the treatment of retinoblastoma in preclinical models

Interferon-beta (IFN-beta) has been found to have anti-tumor properties against a variety of malignancies through different mechanisms. However, clinical trials involving systemic administration of IFN-beta have been hampered by secondary toxicity and the short half-life of IFN-beta in the circulation. In order to circumvent these limitations, we have developed an adeno-associated viral (AAV) vector gene-therapy approach to deliver IFN-beta to tumors. In this study, we tested the efficacy of AAV-mediated local delivery of IFN-beta for the treatment of retinoblastoma in preclinical models. Retinoblastoma is an ideal candidate for gene-therapy-based anti-cancer treatment because target cell transduction and, therefore, IFN-beta delivery can be contained within the ocular environment, thereby minimizing systemic toxicity. We report here that retinoblastoma cell lines exhibit pleiotropic responses to IFN-beta consistent with previous studies on a variety of tumor cell lines. Intravitreal injection of AAV-IFN-beta resulted in efficient retinal infection and sustained IFN-beta production in the eye with minimal systemic exposure. Vector spread outside of the eye was not detected. Using our orthotopic xenograft model of retinoblastoma, we found that intravitreal injection of AAV-IFN-beta had a potent anti-tumor effect in vivo. These data suggest that AAV-mediated delivery of IFN-beta may provide a complementary approach to systemic chemotherapy which is the standard of care for retinoblastoma around the world.

Epidermal growth factor receptor-targeted gelatin-based engineered nanocarriers for DNA delivery and transfection in human pancreatic cancer cells

Type B gelatin-based engineered nanocarrier systems (GENS) have been used over the last several years as a non-condensing systemic and oral DNA delivery system. In this study, we have modified the surface of GENS with epidermal growth factor receptor (EGFR)-targeting peptide for gene delivery and transfection in pancreatic cancer cell lines. GENS were prepared by the solvent displacement method and the EGFR-targeting peptide was grafted on the surface using a hetero-bifunctional poly(ethylene glycol) (PEG) spacer. Plasmid DNA, encoding for enhanced green fluorescent protein (GFP), was efficiently encapsulated and protected from degrading enzymes in the control and surface-modified GENS. Upon incubation with EGFR over-expressing Panc-1 human pancreatic adenocarcinoma cells, the peptide-modified nanoparticles were found to be internalized efficiently by receptor-mediated endocytosis. Both quantitative and qualitative transgene expression efficiencies were significantly enhanced when plasmid DNA was administered with EGFR-targeted GENS relative to the control-unmodified gelatin or PEG-modified gelatin nanoparticle systems. Based on these preliminary results, EGFR-targeted GENS show tremendous promise as a safe and effective gene delivery vector with the potential to treat pancreatic cancer.

DNA repair proteins as molecular targets for cancer therapeutics

Cancer therapeutics include an ever-increasing array of tools at the disposal of clinicians in their treatment of this disease. However, cancer is a tough opponent in this battle and current treatments which typically include radiotherapy, chemotherapy and surgery are not often enough to rid the patient of his or her cancer. Cancer cells can become resistant to the treatments directed at them and overcoming this drug resistance is an important research focus. Additionally, increasing discussion and research is centering on targeted and individualized therapy. While a number of approaches have undergone intensive and close scrutiny as potential approaches to treat and kill cancer (signaling pathways, multidrug resistance, cell cycle checkpoints, anti-angiogenesis, etc.), much less work has focused on blocking the ability of a cancer cell to recognize and repair the damaged DNA which primarily results from the front line cancer treatments; chemotherapy and radiation. More recent studies on a number of DNA repair targets have produced proof-of-concept results showing that selective targeting of these DNA repair enzymes has the potential to enhance and augment the currently used chemotherapeutic agents and radiation as well as overcoming drug resistance. Some of the targets identified result in the development of effective single-agent anti-tumor molecules. While it is inherently convoluted to think that inhibiting DNA repair processes would be a likely approach to kill cancer cells, careful identification of specific DNA repair proteins is increasingly appearing to be a viable approach in the cancer therapeutic cache.

Fusion of the Human Immunodeficiency Virus Type 1 Tat Protein Transduction Domain to Thymidine Kinase Increases Bystander Effect and Induces Enhanced Tumor KillingIn Vivo

The clinical success of suicide gene therapy using herpes simplex virus type 1 thymidine kinase (TK) is largely dependent on the capacity of this enzyme to effectively induce the death of bystander cells. We have shown that fusion of TK to an 11-amino acid peptide from the basic domain of the human immunodeficiency virus type 1 Tat protein (Tat11) imparts cell membrane-translocating ability to the enzyme and significantly increases its cytotoxic activity. Here we report on the efficacy of this strategy in two different mouse models of adoptive tumorigenesis, based on the implantation of human Kaposi sarcoma (KS-IMM) cells in nude mice or of B16F10 melanoma cells in syngeneic C57BL/6J mice. Experiments were performed by the subcutaneous injection of mixtures of unmodified tumor cells containing different fractions of TK or Tat11-TK producing cells followed by animal treatment with ganciclovir (GCV). In both systems we consistently found that mice bearing tumors containing Tat11-TK cells displayed significantly retarded tumor growth and prolonged survival as compared with mice inoculated with cells expressing unmodified TK. Collectively, these results demonstrate that fusion of Tat11 to TK imparts remarkable intercellular trafficking capability to the enzyme. This modification of TK might constitute an important step in the optimization of TK suicide gene strategy for gene therapy of cellular proliferation.

Mitochondrial targeting of human O6-methylguanine DNA methyltransferase protects against cell killing by chemotherapeutic alkylating agents

DNA repair capacity of eukaryotic cells has been studied extensively in recent years. Mammalian cells have been engineered to overexpress recombinant nuclear DNA repair proteins from ectopic genes to assess the impact of increased DNA repair capacity on genome stability. This approach has been used in this study to specifically target O(6)-methylguanine DNA methyltransferase (MGMT) to the mitochondria and examine its impact on cell survival after exposure to DNA alkylating agents. Survival of human hematopoietic cell lines and primary hematopoietic CD34(+) committed progenitor cells was monitored because the baseline repair capacity for alkylation-induced DNA damage is typically low due to insufficient expression of MGMT. Increased DNA repair capacity was observed when K562 cells were transfected with nuclear-targeted MGMT (nucl-MGMT) or mitochondrial-targeted MGMT (mito-MGMT). Furthermore, overexpression of mito-MGMT provided greater resistance to cell killing by 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) than overexpression of nucl-MGMT. Simultaneous overexpression of mito-MGMT and nucl-MGMT did not enhance the resistance provided by mito-MGMT alone. Overexpression of either mito-MGMT or nucl-MGMT also conferred a similar level of resistance to methyl methanesulfonate (MMS) and temozolomide (TMZ) but simultaneous overexpression in both cellular compartments was neither additive nor synergistic. When human CD34(+) cells were infected with oncoretroviral vectors that targeted O(6)-benzylguanine (6BG)-resistant MGMT (MGMT(P140K)) to the nucleus or the mitochondria, committed progenitors derived from infected cells were resistant to 6BG/BCNU or 6BG/TMZ. These studies indicate that mitochondrial or nuclear targeting of MGMT protects hematopoietic cells against cell killing by BCNU, TMZ, and MMS, which is consistent with the possibility that mitochondrial DNA damage and nuclear DNA damage contribute equally to alkylating agent-induced cell killing during chemotherapy.

Gene therapy for esophageal carcinoma: the use of an explant model to test adenoviral vectors ex vivo

Adenoviral gene therapy might be a promising therapeutic strategy for esophageal carcinoma. However, adenoviral transduction efficacy in vivo is still limited. This efficacy can be improved by the insertion of an Arg-Gly-Asp (RGD) peptide in the HI-loop of the viral fiber knob. Indeed in established esophageal cell lines, we observed an up to six-fold improved transduction using the RGD-targeted adenovirus. Established cell lines, however, are easily transformed and do not represent the more complex in vivo histology and anatomy. Therefore, we set up an esophageal explant model using esophageal biopsies from patients. Viability is a limiting factor for this system. Cultured squamous epithelium, intestinal metaplasia and squamous cell carcinoma had a sufficient viability to study adenoviral transduction. Viability of the cultured adenocarcinoma biopsies was poor. Adenoviral transduction in the explant model was poor and was localized in particular cells. The transduction of the nontargeted and RGD-targeted adenovirus was similar in localization and efficacy. In conclusion, we established an esophageal explant system to test the transduction of adenoviral vectors ex vivo. The transduction was limited and localized in specific cells. RGD-targeted adenovirus did not show an improved transduction in this system.

Combined suicide gene therapy for pancreatic peritoneal carcinomatosis using BGTC liposomes

Peritoneal dissemination is a common end-stage complication of pancreatic cancer for which novel therapeutic modalities are actively investigated, as there is no current effective therapy. Thus, we evaluated, in a mouse model of pancreatic peritoneal carcinomatosis, the therapeutic potential of a novel nonviral gene therapy approach consisting of bis-guanidinium-tren-cholesterol (BGTC)-mediated lipofection of a combined suicide gene system. Human BxPC-3 pancreatic cells secreting the carcinoembryonic antigen (CEA) tumor marker were injected into the peritoneal cavity of nude mice. After 8 days, intraperitoneal (i.p.) lipofection was performed using BGTC/DOPE cationic liposomes complexed with plasmids encoding the two prodrug-activating enzymes Herpes Simplex Virus thymidine kinase and Escherichia coli cytosine deaminase, the latter being expressed from a bicistronic cassette also encoding E. coli uracil phosphoribosyltransferase. Administration of the lipoplexes was followed by treatment with the corresponding prodrugs ganciclovir and 5-fluorocytosine. The results presented herein demonstrate that BGTC/DOPE liposomes can efficiently mediate gene transfection into peritoneal tumor nodules. Indeed, HSV-TK mRNA was detected in tumor nodule tissues by semiquantitative reverse transcription-polymerase chain reaction analysis. In addition, green fluorescent protein (GFP) fluorescence and X-gal staining were observed in the peritoneal tumor foci following lipofection of the corresponding EGFP and LacZ reporter genes. These expression analyses also showed that transgene expression lasted for about 2 weeks and was preferential for the tumor nodules, this tumor preference being in good agreement with the absence of obvious treatment-related toxicity. Most importantly, mice receiving the full treatment scheme (BGTC liposomes, suicide genes and prodrugs) had significantly lower serum CEA levels than those of the various control groups, a finding indicating that peritoneal carcinomatosis progression was strongly reduced in these mice. In conclusion, our results demonstrate the therapeutic efficiency of BGTC-mediated i.p. lipofection of a combined suicide gene system in a mouse peritoneal carcinomatosis model and suggest that BGTC-based prodrug-activating gene therapy approaches may constitute a potential treatment modality for patients with peritoneal carcinomatosis and minimal residual disease.

Parvovirus vectors for cancer gene therapy

Parvoviruses comprise a group of single-stranded DNA viruses with greater potential for gene therapy applications. Unique characteristics of paroviruses, such as non-pathogenicity, antioncogenicity and methods of efficient recombinant vector production, have drawn more attention towards utilising parvovirus-based vectors in cancer gene therapy. Although > 30 different parvoviruses have been identified so far, recombinant vectors derived from adeno-associated virus (AAV), minute virus of mice (MVM), LuIII and parvovirus H1 have been successfully tested in many preclinical models of human diseases, including cancer. The present article will focus on the potential of non-replicating and autonomously replicating parvoviral vectors in cancer gene therapy, including strategies that target tumour cells directly or indirectly.

Low-dose interferon-gamma-producing human neuroblastoma cells show reduced proliferation and delayed tumorigenicity

Interferon-γ (IFN-γ) directs T helper-1 cell differentiation and mediates antitumour effects in preclinical models. However, high-dose IFN-γ is toxic in vivo, and IFN-γ-transfected neuroblastoma (NB) cells secreting high amounts of the cytokine may be lost due to cell apoptosis or differentiation. Two human NB cell lines (ACN and SK-N-BE2(c)) differing as to genetic and phenotypic features were transfected with the human IFN-γ gene and selected on the grounds of the low concentrations of IFN-γ produced. In both IFN-γ-transfected cell lines, autocrine and paracrine activation of IFN-γ-mediated pathways occurred, leading to markedly reduced proliferation rate, to increased expression of surface HLA and CD40 molecules and of functional TNF binding sites. ACN/IFN-γ cells showed a significantly delayed tumorigenicity in nude mice as compared to parental cells. ACN/IFN-γ tumours were smaller, with extensive necrotic area as a result of a damaged and defective microvascular network. In addition, a significant reduction in the proliferation index was observed. This is the first demonstration that IFN-γ inhibits in vivo proliferation of NB cell by acting on the tumour cell itself. This effect adds to the immunoregulatory and antiangiogenic activities operated by IFN-γ in syngeneic tumour-bearing hosts.

Gene therapy for gastric cancer: A review

Gastric cancer is common in China, and its early diagnosis and treatment are difficult. In recent years great progress has been achieved in gene therapy, and a wide array of gene therapy systems for gastric cancer has been investigated. The present article deals with the general principles of gene therapy and then focuses on how these principles may be applied to gastric cancer.

Human-yeast chimeric repair protein protects mammalian cells against alkylating agents: enhancement of MGMT protection

Chemotherapeutic DNA alkylating agents are common weapons employed to fight both pediatric and adult cancers. In addition to cancerous cells, nontarget tissues are subjected to the cytotoxicity of these agents, and dose-limiting toxicity in the form of myelosuppression is a frequent result of treatment. One approach to prevent myelosuppression that results from the use of chemotherapeutic agents is to increase the levels of DNA repair proteins in bone marrow cells. Here we report our second successful attempt to create a fusion protein that possesses both direct reversal and base excision repair pathway DNA repair activities. The chimeric protein is composed of the human O(6)-Methylguanine-DNA Methyltransferase (MGMT) and the yeast Apn1 proteins and retains both MGMT and AP endonuclease activities as determined by biochemical analysis. We have also demonstrated that the chimeric protein is able to protect mammalian cells from the DNA alkylating agents 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) and methyl methanesulfonate (MMS). The protection by the chimeric protein against BCNU is even greater than MGMT alone, which has potential translational significance given that MGMT is currently in clinical trials. Additionally, we show that the chimeric MGMT-Apn1 protein can protect mammalian cells from dual treatments of BCNU and MMS and that this effect is greater than that provided by MGMT alone. The data support our previous finding that a protein with multiple DNA repair activities can be constructed and that this and other constructs may play an important clinical role in guarding against dose-limiting effects of chemotherapy, particularly in situations of multiple drug use.

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Genetically targeted radiotherapy for multiple myeloma

Multiple myeloma is a disseminated neoplasm of terminally differentiated plasma cells that is incurable with currently available therapies. Although the disease is radiosensitive, external beam radiation leads to significant toxicity due to sensitive end-organ damage. Thus, genetic approaches for therapy are required. We hypothesized that the incorporation of immunoglobulin promoter and enhancer elements in a self-inactivating (SIN) lentiviral vector should lead to specific and high-level transgene expression in myeloma cells. A SIN lentivector with enhanced green fluorescent protein (EGFP) expression under the control of a minimal immunoglobulin promoter as well as the Kappa light chain intronic and 3' enhancers transduced myeloma cell lines with high efficiency (30%-90%). EGFP was expressed at a high level in myeloma cells but silent in all nonmyeloma cell lines tested compared with the cytomegalovirus (CMV) promoter/enhancer. Transduction of myeloma cells with the targeted vector coding for the human sodiumiodide symporter (hNIS) led to hNIS expression by these cells allowing them to concentrate radioiodine up to 18-fold compared with controls. Tumor xenografts in severe combined immunodeficiency mice expressing hNIS could be imaged using iodine-123 (123I) and shown to retain iodide for up to 48 hours. These tumor xenografts were completely eradicated by a single dose of the therapeutic isotope iodine-131 (131I) without evidence of recurrence up to 5 months after therapy. We conclude that lentivectors can be transcriptionally targeted for myeloma cells and the use of hNIS as a therapeutic gene for myeloma in combination with 131I needs further exploration.

Gene therapy: theoretical and bioethical concepts

Gene therapy holds great promise. Somatic gene therapy has the potential to treat a wide range of disorders, including inherited conditions, cancers, and infectious diseases. Early progress has already been made in the treatment of a range of disorders. Ethical issues surrounding somatic gene therapy are primarily those concerned with safety. Germline gene therapy is theoretically possible but raises serious ethical concerns concerning future generations.

Identification of novel enzyme-prodrug combinations for use in cytochrome P450-based gene therapy for cancer

Gene-directed enzyme prodrug therapy can be used to increase the therapeutic activity of anti-cancer prodrugs that undergo liver cytochrome P450 (CYP)-catalyzed prodrug to active drug conversion. The present report describes a cell-culture-based assay to identify CYP gene-CYP prodrug combinations that generate bystander cytotoxic metabolites and that may potentially be useful for CYP-based gene therapy for cancer. A panel of rat liver microsomes, comprising distinct subsets of drug-inducible hepatic CYPs, was evaluated for prodrug activation in a four-day 9L gliosarcoma cell growth inhibition assay. A strong NADPH- and liver microsome-dependent increase in 9L cytotoxicity was observed for the CYP prodrugs cyclophosphamide, ifosfamide, and methoxymorpholinyl doxorubicin (MMDX) but not with three other CYP prodrugs, procarbazine, dacarbazine, and tamoxifen. MMDX activation was potentiated approximately 250-fold by liver microsomes from dexamethasone-induced rats (IC(50) (MMDX) approximately 0.1nM), suggesting that dexamethasone-inducible CYP3A enzymes contribute to activation of this novel anthracycline anti-tumor agent. This CYP3A dependence was verified in studies using liver microsomes from uninduced male and female rats and by using the CYP3A-selective inhibitors troleandomycin and ketoconazole. These findings highlight the advantages of using cell culture assays to identify novel CYP prodrug-CYP gene combinations that are characterized by production of cell-permeable, cytotoxic metabolites and that may potentially be incorporated into CYP-based gene therapies for cancer treatment.

Exploiting the differential production of angiogenic factors within the tumor microenvironment in the design of a novel vascular-targeted gene therapy-based approach to the treatment of cancer

PURPOSE

The aim of this study is to explore a novel strategy through which the differential production of pro-angiogenic cytokines within the tumor microenvironment can be exploited as a means of selectively killing the vascular endothelial cells upon which the survival and growth of a tumor depend.

METHODS AND MATERIALS

Adenoviral vectors encoding a chimeric cell surface receptor composed of the extracellular domain of the vascular endothelial growth factor (VEGF) receptor Flk-1/KDR fused in frame to the membrane spanning and cytoplasmic domain of Fas were constructed and used to transduce primary human endothelial cells in vitro. The apoptotic response of these cells induced upon ligation of the chimeric receptor with VEGF was determined by measuring caspase-3 activation, AnnexinV-FITC binding, and the release of glucose-6-phosphate dehydrogenase.

RESULTS

The chimeric Flk-1/Fas protein is stable and expressed at high levels on the surface of adenovirally transduced cells. Upon the addition of exogenous VEGF, these cells undergo rapid apoptosis.

CONCLUSIONS

Receptor/Fas chimeras that recognize and bind pro-angiogenic cytokines represent a novel means by which the signal transduction events normally triggered in vascular endothelial cells upon the binding of angiogenic cytokines may be redirected toward the induction of apoptotic cell death. It is proposed that these constructs will prove of value in the further development of safe and effective vascular-targeted gene therapy-based approaches to the treatment of cancer.

Novel gene therapy approach for nasopharyngeal carcinoma

This article will provide an overview on the status of cancer gene therapy, focussed specifically on its potential application in nasopharyngeal carcinoma (NPC). The concepts and strategies behind the design of therapeutic targets such as p53, p16, and death genes will be described. One of the major challenges in cancer gene therapy is tumor-specific expression of therapeutic genes, and a transcriptional targeting approach will be reviewed, in reference to NPC. Specifically, the ability to exploit the presence of Epstein-Barr virus (EBV) will be emphasized. The currently available preclinical data on genetic therapeutic approaches for NPC will be reviewed, and an outline for its future role in management of NPC, in conjunction with existing cytotoxic modalities of ionizing radiation and chemotherapy will be provided.

In vivo plasmid DNA electrotransfer

In vivo electrotransfer is a physical technique for gene delivery in various mammalian tissues, which involves the injection of plasmid DNA into a target tissue and administration of an electric field. Its ease of performance, as well as recent understanding of its mechanism and applications to different mammalian tissues such as skeletal muscle, liver, brain and tumors, makes it a powerful technique. It could be used in gene therapy and as a laboratory tool to study gene functions.

Applications of plasmid electrotransfer

The use of electric pulses to transfect cells has recently been extended to show the utility of this procedure in vivo. Electrotransfer has been performed in vivo on several tissue types including skin, blood vessels, liver, tumor, muscle, cornea, brain and spleen. The most widely targeted tissue has been skeletal muscle. In addition to its potential use in gene therapy, in vivo DNA electrotransfer is also, because of its simplicity, a powerful laboratory tool to study in vivo gene expression and function in a given tissue. Many published studies have now shown that plasmid electrotransfer can lead to a long-lasting therapeutic effect in various pathologies, such as cancer, blood disease, or muscle ischemia. The future potential for this gene therapy approach will include delivery for both local action or distal effect by secretion of the transgenic proteins in the circulation.