Surfactant protein A-directed toxin gene kills lung cancer cells in vitro

Lessons learned from lung and liver in-vivo gene therapy: implications for the future

INTRODUCTION

Ex-vivo gene therapy has had significant clinical impact over the last couple of years and in-vivo gene therapy products are being approved for clinical use. Gene therapy and gene editing approaches have huge potential to treat genetic disease and chronic illness.

AREAS COVERED

This article provides a review of in-vivo approaches for gene therapy in the lung and liver, exploiting non-viral and viral vectors with varying serotypes and pseudotypes to target-specific cells. Antibody responses inhibiting viral vectors continue to constrain effective repeat administration. Lessons learned from ex-vivo gene therapy and genome editing are also discussed.

EXPERT OPINION

The fields of lung and liver in-vivo gene therapy are thriving and a comparison highlights obstacles and opportunities for both. Overcoming immunological issues associated with repeated administration of viral vectors remains a key challenge. The addition of targeted small molecules in combination with viral vectors may offer one solution. A substantial bottleneck to the widespread adoption of in-vivo gene therapy is how to ensure sufficient capacity for clinical-grade vector production. In the future, the exploitation of gene editing approaches for in-vivo disease treatment may facilitate the resurgence of non-viral gene transfer approaches, which tend to be eclipsed by more efficient viral vectors.

Adenoviral vectors: development and application

One of the prerequisites for the successful application of gene vaccination and therapy is the development of efficient gene delivery vectors. The rate-limiting nature of vectors was clearly manifested during the first wave of gene therapy testing, resulting in the demand for more effective and suitable vector systems. Adenoviral (Ad) vectors have recently played a central role in the development of gene-vector technology due to their practical advantages and potential applications. A large number of preclinical and clinical studies both have generated an overwhelming amount of data and literature on this vector system. It is the intention of this article to provide a systematic and broad spectrum review of this system, outlining the principle, potential, and limitations, and evaluating the rational development of this delivery approach. Recombinant adenoviruses (Ad), helper cell lines, and related technologies have been developed and applied to many indications owing to progress in virological research, molecular and cellular biology, eukaryotic protein expression, recombinant vaccines, and gene therapy. The technical depth this article covers should be useful to both the experienced researcher and to beginners in this field.

Replacement and Suicide Gene Therapy for Targeted Treatment of Lung Cancer

Lung cancer is the leading cause of cancer-related death in the developed world; consequently, novel therapeutic strategies are in high demand. A major problem with the present treatment modalities is the lack of tumor specificity giving rise to dose-limiting toxicity and side effects. Gene therapy constitutes an experimental approach gaining increased attention as a putative future cancer therapeutic strategy. Using this strategy, cancer cytotoxicity can be obtained by replacing mutated genes with functional analogues or introducing a suicide gene into the malignant cells. Insight into the molecular biology of cancer cells has identified a number of regulatory gene sequences, which can be used to selectively activate the therapeutic gene specifically in cancer cells, thereby reducing nonspecific toxicity. Although further improvements are necessary, recent encouraging results have shown promise for future clinical application of gene therapy. This article presents an update on the experimental and clinical results obtained within the field of lung cancer gene therapy, concentrating on strategies to specifically activate expression of the therapeutic gene in cancer cells. Furthermore, status of the development of delivery vector constructs for lung cancer gene therapy will be presented.

MIA (melanoma inhibitory activity) promoter mediated tissue-specific suicide gene therapy of malignant melanoma

Suicide gene therapy of malignant melanoma essentially requires efficient gene transfer and highly selective therapeutic gene expression. To achieve this, recombinant adeno-associated virus (rAAV) particles were constructed containing the tissue-specific promoter of the human melanoma inhibitory activity (hMIA) gene combined with four copies of the enhancer element of the murine tyrosinase gene. Three melanoma and one cervix carcinoma cell line were infected with rAAV particles carrying a reporter gene under control of the enhancer/hMIA promoter in order to determine transcriptional activity and specificity of this system. Viral particles containing the enhancer/hMIA promoter mediated reporter gene activity only in melanoma cells, whereas infection with a cytomegalovirus (CMV)-based promoter construct induced unspecific gene expression. Correspondingly, transient transduction with viral particles bearing the HSVtk gene under the control of the enhancer/MIA promoter elements followed by treatment with ganciclovir (GCV) resulted in growth inhibition only in melanoma cells, whereas the CMV promoter-based construct induced unspecific cytotoxicity. In vivo experiments in nude mice demonstrated that tumors originating from human melanoma cells disappeared after stable, but not transient transduction with vectors bearing the HSVtk gene under the control of the enhancer/hMIA promoter in response to GCV application. In face of higher transduction efficiency, these rAAV particles might therefore be a useful tool for suicide gene therapy of malignant melanoma.

Development of a cancer-targeted tissue-specific promoter system

Present cancer gene therapy using proapoptotic genes has had limited success because the therapy is prone to cause side effects as a result of the lack of tissue and cancer specificity. To target cancer cells without damaging normal cells, we have designed a novel dual promoter system in which a tissue-specific transcription system under the control of a cancer-specific promoter drives expression of a therapeutic gene. The applicability of this system was demonstrated by adapting it to target lung cancer. We termed this lung cancer system TTS (TTF1 gene under the control of human telomerase reverse transcriptase promoter and human surfactant protein A1 promoter). The TTS system showed much higher promoter activity in lung cancer cells compared with other kinds of cancer and normal lung cells, including stem cells. Moreover, insertion of negative glucocorticoid responsive elements in the system allows it to be drug controllable. The approaches that we have used could be adapted to target other types of cancer. We report a novel cancer-targeted tissue-specific dual promoter system designed for gene therapy.

Conditional gene targeting for cancer gene therapy

Current treatment of solid tumors is limited by severe adverse effects, resulting in a narrow therapeutic index. Therefore, cancer gene therapy has emerged as a targeted approach that would significantly reduce undesired side effects in normal tissues. This approach requires a clear understanding of the molecular biology of both the malignant clone and the biological vectors that serve as vehicles to target cancer cells. In this review we discuss novel approaches for conditional gene expression in cancer cells. Targeting transgene expression to malignant tissues requires the use of specific regulatory elements including promoters based on tumor biology, tissue-specific promoters and inducible regulatory elements. We also discuss the regulation of both replication and transgene expression by conditionally-replicative viruses. These approaches have the potential to restrict the expression of transgenes exclusively to tissues of interest and thereby to increase the therapeutic index of future vectors for cancer gene therapy.

Direct correlation between positron emission tomographic images of two reporter genes delivered by two distinct adenoviral vectors

Biodistribution, magnitude and duration of a therapeutic transgene's expression may be assessed by linking it to the expression of a positron emission tomography (PET) reporter gene (PRG) and then imaging the PRG's expression by a PET reporter probe (PRP) in living animals. We validate the simple approach of co-administering two distinct but otherwise identical adenoviruses, one expressing a therapeutic transgene and the other expressing the PRG, to track the therapeutic gene's expression. Two PET reporter genes, a mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) and dopamine-2 receptor (D(2)R), each regulated by the same cytomegalovirus (CMV) promoter, have been inserted into separate adenoviral vectors (Ad). We demonstrate that cells co-infected with equivalent titers of Ad-CMV-HSV1-sr39tk and Ad-CMV-D(2)R express both reporter genes with good correlation (r(2) = 0.93). Similarly, a high correlation (r(2) = 0.97) was observed between the expression of both PRGs in the livers of mice co-infected via tail-vein injection with equivalent titers of these two adenoviruses. Finally, microPET imaging of HSV1-sr39tk and D(2)R expression with 9-(4-[(18)F]fluoro-3-hydroxymethylbutyl) guanine ([(18)F]FHBG) and 3-(2-[(18)F]fluoroethyl)spiperone ([(18)F]FESP), utilizing several adenovirus-mediated delivery routes, illustrates the feasibility of evaluating relative levels of transgene expression in living animals, using this approach.

Isolated limb perfusion for local gene delivery: efficient and targeted adenovirus-mediated gene transfer into soft tissue sarcomas

OBJECTIVE

To evaluate the potential of isolated limb perfusion (ILP) for efficient and tumor-specific adenovirus-mediated gene transfer in sarcoma-bearing rats.

SUMMARY BACKGROUND DATA

A major concern in adenovirus-mediated gene therapy in cancer is the transfer of genes to organs other than the tumor, especially organs with a rapid cell turnover. Adjustment of the vector delivery route might be an option creating tumor specificity in therapeutic gene expression.

METHODS

Rat hind limb sarcomas (5-10 mm) were transfected with recombinant adenoviruses. Intratumoral luciferase expression after ILP was compared with systemic administration, regional infusion, or intratumoral injection using a similar dose of adenoviruses carrying the luciferase marker gene. Localization studies using lacZ as a marker gene were performed to evaluate the intratumoral distribution of transfected cells after both ILP and intratumoral injection.

RESULTS

Intratumoral luciferase activity after ILP or intratumoral administration was significantly higher compared with regional infusion or systemic administration. After ILP, luciferase gene expression was minimal in extratumoral organs, whether outside or inside the isolated circuit. Localization studies demonstrated that transfection was confined to tumor cells lying along the needle track after intratumoral injection, whereas after ILP, lacZ expression was found in viable tumor cells and in the tumor-associated vasculature.

CONCLUSIONS

Using ILP, efficient and tumor-specific gene transfection can be achieved. The ILP technique might be useful for the delivery of recombinant adenoviruses carrying therapeutic gene constructs to enhance tumor control.

Cutaneous gene therapy. Principles and prospects

As investigators continue to close the gap between basic research and clinical science, gene therapy is becoming of increasing interest to the dermatologist. Most notably, recent advances in gene-based cancer therapy, DNA vaccination, and molecular pharmacology have opened new avenues for investigation beyond those of the traditional gene replacement applications. Different gene delivery systems are currently being tested, each with specific advantages and disadvantages. This article summarizes some of the principles of gene therapy and its applications to cutaneous diseases.

Lipoplexes and tumours. A review

The need for genotherapy to refocus its attention on to laboratory evaluation of better methods rather than proceeding to the clinic with semi-apt tools for genetic transfer has been highlighted in clinical study reports documented to date. Quintessential for tumour genotherapy is the ability to target abnormal cells, hence reducing exposure of normal cells to genetic material whilst maximizing gene dosage to tumour cells. This becomes increasingly important as genotherapy establishes itself in the clinic alongside the older modes of treatment. This review has discussed the applicability of lipoplexes for genotherapy of solid tumours. Lipoplexes have been used extensively for gene transfer into cells, such as cancerous cells, deficient for a certain gene product. While cationic liposomes have many advantages over other forms of delivery mechanisms, several problems hinder their use in-vivo. A closer examination of the physical limitations of current lipoplex preparations, the development and testing of novel formulations, combined with more attention to the cellular processes of cell membrane breaching and nuclear entry, may enhance gene delivery. Essential for tumour genotherapy is the ability to target these lipoplexes into tumour sites whilst reducing gene dosage to other normal tissues. Development of a better lipofection agent may indeed require a collaboration of the fields of physiology, cell biology, molecular biology, biochemistry, chemistry and membrane physics.

Augmentation of melanoma-specific gene expression using a tandem melanocyte-specific enhancer results in increased cytotoxicity of the purine nucleoside phosphorylase gene in melanoma

The lineage-specific human tyrosinase promoter has been used to successfully target gene expression at the transcriptional level to melanoma cells. The tyrosinase promoter, alone and in combination with a single, or a dual, tandem melanocyte-specific enhancer, was used to regulate expression of the firefly luciferase reporter gene. Transient transfections of these tissue-specific luciferase constructs in human and murine melanoma (Pmel, B16mel) and colon carcinoma (WiDr, MC38) cell lines resulted in melanoma-specific luciferase expression that was amplified 5- and 500-fold with the addition of a single or double enhancer, respectively, to the tyrosinase promoter. When the double enhancer-promoter construct expressed the highly toxic Escherichia coli purine nucleoside phosphorylase (PNP) gene, transfection of the same cell lines followed by administration of the prodrug 6-methyl purine deoxyriboside (6-MPDR) at a concentration of 50 microM caused melanoma-specific in vitro cell killing. Within 5 days after prodrug administration methylthiazol-tetrazolium (MTT) cytotoxicity assays showed that only 15 and 9% of Pmel and B16mel cells, respectively, remained viable compared with controls. This effect was highly specific, as 90 and 96% of WiDr and MC38 colon carcinoma cells remained viable 5 days after identical treatment. This effect was a direct result of increased tissue-specific conversion of 6-MPDR to the toxic metabolite 6-methylpurine (6-MP), as documented by HPLC analysis of culture supernatants. These results show that the dual tandem melanocyte-specific enhancer provides powerful amplification of the transcriptional targeting of gene expression afforded by use of the tyrosinase promoter. This amplification translates into increased, highly specific cytotoxicity to melanoma by the PNP/6-MPDR enzyme/prodrug system and, therefore, has potential efficacy in the use of gene therapy for the treatment of metastatic melanoma.

Adenovirus-mediated granulocyte-macrophage colony-stimulating factor improves lung pathology of pulmonary alveolar proteinosis in granulocyte-macrophage colony-stimulating factor-deficient mice

Mutation of the granulocyte-macrophage colony-stimulating factor (GM-CSF) gene by homologous recombination causes progressive pulmonary alveolar proteinosis (PAP) in GM-CSF-deficient mice (GM-/-). The present study tested whether adenovirus-mediated expression of GM-CSF alters the progression of PAP in GM-/- mice. Adult mice were pretreated with an anti-T cell receptor (TCR) antibody to block T cell-mediated immune response, followed by intratracheal instillation of deltaE1-E3 replication-deficient adenovirus expressing mouse GM-CSF (Av1mGM). Mice were killed 1, 3, and 5 weeks after treatment to assess lungs for GM-CSF, surfactant protein B (SP-B), alveolar macrophage maturation, and type II cell proliferation. GM-CSF was detected in BAL fluid from GM-/- mice 1 week after Av1mGM treatment, and GM-CSF mRNA was detected by RT-PCR through 5 weeks. Five weeks after Av1mGM treatment, PAP was improved and SP-B decreased as assessed by ELISA and immunostaining. Increased numbers of alveolar macrophages stained with alpha-naphthyl acetate esterase (alpha-NAE) following treatment with Av1mGM. Local expression of GM-CSF with a recombinant adenovirus ameliorated PAP in the GM-/- mice in association with enhanced maturation of alveolar macrophages.

Gene therapy for lung cancer

Gene therapy has received considerable attention and some speculation as to its value. Although few patients have been treated, the preliminary results of the phase I lung cancer gene therapy clinical trials are very promising. Clinically relevant basic research in the molecular pathogenesis and immunology of lung cancer is progressing. As improved vector technologies are developed, new opportunities will be available to initiate lung cancer gene therapy trials that are based on a more detailed understanding of lung cancer biology. In conclusion, although important biologic and technical questions remain unanswered, recent research suggests that gene therapy will have a profound impact on lung cancer treatment.

Recombinant adenoviral vector disrupts surfactant homeostasis in mouse lung

Although replication-deficient adenoviruses efficiently transfer genes into epithelial cells of the lung, host immune responses limit the extent and duration of gene expression. To define further the role of inflammatory responses to first-generation, recombinant, deltaE1, deltaE3 adenovirus in lung pathology and surfactant protein homeostasis, expression of the surfactant proteins SP-A, SP-B, and proSP-C was determined by immunohistochemistry 2, 7, and 14 days following intratracheal administration of 2 x 10(9) pfu of a recombinant adenovirus, Av1Luc1, to BALB/c nu/nu and BALB/c wild-type mice. Two to 7 days after virus administration, an acute inflammatory response was observed in both mouse strains. Respiratory epithelial cells were sloughed, and extracellular accumulation of SP-A and SP-B was detected in the airways. Diminished immunostaining for SP-A and SP-B was noted in type II cells, and SP-A and SP-B mRNA expression was decreased in focal regions of the lungs from both mouse strains. One week after virus administration, immunostaining for proSP-C was markedly increased in cells lining the regenerating alveolar epithelial surfaces. Two weeks after Av1Luc1 treatment of nu/nu mice, immunostaining for SP-A, SP-B, and proSP-C was similar to those patterns observed prior to adenoviral administration. In immunocompetent wild-type mice, however, immunostaining for surfactant proteins was absent in areas associated with chronic lymphocytic infiltration. The recombinant adenoviral vector, Av1Luc1, caused acute inflammatory responses in the respiratory epithelium with disruption of surfactant protein homeostasis in both wild-type and nu/nu mice. Alterations in surfactant homeostasis persisted in wild-type mice. Thus, both acute and thymic-dependent immune responses limit transgene expression and disrupt surfactant protein gene expression and homeostasis. Because surfactant proteins are critical to host defense and to the maintenance of alveolar stability following injury, these findings raise concerns regarding both acute and chronic toxicity of first-generation recombinant adenoviral vectors for gene transfer.

Transcriptional targeting of herpes simplex virus for cell-specific replication

Tissue- or cell-specific targeting of vectors is critical to the success of gene therapy. We describe a novel approach to virus-mediated gene therapy, where viral replication and associated cytotoxicity are limited to a specific cell type by the regulated expression of an essential immediate-early viral gene product. This is illustrated with a herpes simplex virus type 1 (HSV-1) vector (G92A) whose growth is restricted to albumin-expressing cells. G92A was constructed by inserting an albumin enhancer/promoter-ICP4 transgene into the thymidine kinase gene of mutant HSV-1 d120, deleted for both copies of the ICP4 gene. This vector also contains the Escherichia coli lacZ gene under control of the thymidine kinase promoter, a viral early promoter, to permit easy detection of infected cells containing replicating vector. In the adult, albumin is expressed uniquely in the liver and in hepatocellular carcinoma and is transcriptionally regulated. The plaquing efficiency of G92A is > 10(3) times higher on human hepatoma cells than on non-albumin-expressing human cells. The growth kinetics of G92A in albumin-expressing cells is delayed compared with that of wild-type HSV-1, likely due to aberrant expression of ICP4 protein. Cells undergoing a productive infection expressed detectable levels of ICP4 protein, as well as the reporter gene product beta-galactosidase. Confining a productive, cytotoxic viral infection to a specific cell type should be useful for tumor therapy and the ablation of specific cell types for the generation of animal models of disease.

Gene therapy for colon cancer with the herpes simplex thymidine kinase gene

BACKGROUND

The suicide gene and prodrug, herpes simplex thymidine kinase (HStk) and ganciclovir (GCV), are now in clinical trials for recurrent malignancies.

METHODS

We evaluated in vitro and in vivo efficacy of HStk gene transfer and GCV treatment of colonic adenocarcinoma in a syngeneic murine model.

RESULTS

In vitro analysis demonstrated that CT-26 adenocarcinoma cells transduced with LTKOSN.2 retroviral vector inhibited the proliferation of wild-type CT-26 (nontransduced) cells after GCV exposure. Cooperative killing with HStk gene therapy was shown in vivo, mixtures of HStk CT-26 transduced cells (CT-26 TK), and nontransduced (CT-26 NV) cells and tumors containing only 9% CT-26 TK cells demonstrated complete regression after GCV (100 mg/kg).

CONCLUSIONS

This in vitro and in vivo demonstration suggests that metabolic cooperation permits destruction of tumors even when gene transfer is effective only to a relatively small portion of the tumor. These important results suggest new avenues can be developed for the treatment of this lethal malignancy.

Interleukin-2 gene transduction into freshly isolated lung adenocarcinoma cells with adenoviral vectors

We evaluated the efficiency of gene transduction and of gene expression by adenoviral vectors in human lung adenocarcinoma cells. Freshly isolated cancer cells were collected from pleural effusions in adenocarcinoma patients by centrifugation with a Percoll gradient. Adenoviral vectors resulted in effective gene transduction into human lung cancer cell lines and into freshly isolated lung adenocarcinoma cells. In an experiment using the beta-galactosidase (LacZ) gene, the Adex1CA vector with a regulatory sequence of chicken beta-actin as promoter and an enhancer derived from cytomegalovirus produced a higher transduction ratio and greater expression levels than adenoviral vectors with other promoter systems. Transduction with Adex1CA vectors containing the human interleukin-2 (IL-2) gene (Adex1CAhIL-2) resulted in enhanced secretion of IL-2 from gene-modified lung cancer cells. Treatment with normal human serum inhibited gene transduction by Adex1CAhIL-2 but did not inhibit gene expression after transduction by Adex1CAhIL-2. The secretion of IL-2 from the gene-modified cells, which were irradiated at 100 Gy before transduction, continued for 8 days. In a mouse model, the intrapleural injection of IL-2 gene-modified 3LL cells transduced by Adex1CAhIL-2 could cure the pre-existing lung tumours with malignant pleural effusions to induce tumor-specific immunity. But these therapies did not show any therapeutic benefit on the pre-existing tumor in subcutaneous region. These data suggest a potentially useful but limited clinical role of Adex1CAhIL-2 in gene therapy for lung cancer patients.

Gene therapy for cancer: what have we done and where are we going?

Gene-based therapies for cancer in clinical trials include strategies that involve augmentation of immunotherapeutic and chemotherapeutic approaches. These strategies include ex vivo and in vivo cytokine gene transfer, drug sensitization with genes for prodrug delivery, and the use of drug-resistance genes for bone marrow protection from high-dose chemotherapy. Inactivation of oncogene expression and gene replacement for tumor suppressor genes are among the strategies for targeting the underlying genetic lesions in the cancer cell. A review of clinical trial results to date, primarily in patients with very advanced cancers refractory to conventional treatments, indicates that these treatments can mediate tumor regression with acceptably low toxicity. Vector development remains a critical area for future research. Important areas for future research include modifying viral vectors to reduce toxicity and immunogenicity, increasing the transduction efficiency of nonviral vectors, enhancing vector targeting and specificity, regulating gene expression, and identifying synergies between gene-based agents and other cancer therapeutics.

Characterization of factors involved in modulating persistence of transgene expression from recombinant adenovirus in the mouse lung

One potential limitation of adenovirus (Ad)-based vectors for the gene therapy of cystic fibrosis (CF) and other genetic diseases is the transience of expression observed in most in vivo systems. In this study, the influence of various factors on persistence of transgene expression in the lung was investigated. In the absence of immune pressure, such as in the nude mouse, the genomic structure of the vector was found to be predominant in determining the persistence of expression; Ad vector constructs with an E1-E3+E4ORF6+ backbone encoding beta-galactosidase (beta-Gal) or the cystic fibrosis transmembrane conductance regulator (CFTR) produced declining levels of expression while an Ad/CMV beta Gal vector with an E1-E3+E4+ backbone gave rise to sustained, long-term reporter gene expression. The ability of the latter vector to persist was in turn limited in part by the presence of cytotoxic T lymphocytes (CTLs). Adoptive transfer experiments indicated that CTLs directed against either viral proteins or the beta-Gal reporter gene product were able to reduce expression in nude C57BL/6 mice stably expressing beta-Gal from the E4+ vector. Finally, the specificity and strength of the CTL response elicited by Ad vector was found to vary considerably depending on mouse strain haplotype. These results indicate that persistence of transgene expression in a given system is determined by the interplay between several factors including genomic structure of the vector, host background, and immune response.

Systematic analysis of repeated gene delivery into animal lungs with a recombinant adenovirus vector

Adenovirus-based vectors are promising candidates for genetic therapy of cystic fibrosis (CF). Because adenoviruses naturally infect airway cells, they grow to very high titers, and the transgenes carried by the adenoviruses are expressed at high levels. In addition, adenoviruses are relatively safe because the disease caused by the wild-type virus is self-limiting. One disadvantage of adenovirual vectors is that the transgene expression would be transient because adenoviruses do not integrate their DNA into the genome of the host cells. Adenoviral gene delivery into the lungs is also complicated by the anatomy of the airways and the defense mechanisms of the recipient. To assess the feasibility of adenovirus-mediated gene therapy for CF, a recombinant adenovirus carrying a lacZ gene was delivered into animal lungs to study the efficiency and cellular distribution of gene transfer, the duration of gene expression, the possible histopathology of the lungs after gene transfer, and the efficacy of repeated administrations of the viral agent. The results of these studies demonstrate that (i) efficient gene transfer into animal lungs can be achieved; (ii) a near-homogenous delivery of the vectors can be achieved by airway instillation, although the pattern of transduction varies among individual animals; (iii) pathological effects are generally mild in CD1 mice; (iv) gene expression is transient; (v) repetitive gene transfer is achievable, but becomes progressively less efficient, and (vi) immune responses are induced against both the viral and transgene products.

Regulated expression of artificial chimeric genes contained in retroviral vectors: implications for virus-directed enzyme prodrug therapy (VDEPT) and other gene therapy applications

Replication-defective retroviral vectors were created that contained chimeric genes composed of either the albumin (ALB) or the alpha-fetoprotein (AFP) transcriptional regulatory sequences linked to the coding domain of the thymidine kinase gene from Varicella zoster virus (VZV TK). These viruses were used to infect the human hepatoblastoma cell line, HepG2. Subsequent to infection, the infected cells were single-cell cloned. The level of expression of VZV TK from the chimeric genes correlated with the level of endogenous expression of ALB or AFP in most clones, indicating that the transcription of the chimeric VZV TK gene is controlled in a similar manner to the endogenous ALB or AFP genes, and that sites of viral integration are less important to overall gene expression. Most importantly, as the expression of the endogenous ALB gene was modified, so was expression of VZV TK from the ALB/VZV TK chimeric gene. This demonstrates that retroviruses can deliver a chimeric gene containing tissue-specific transcriptional regulatory sequences that can respond to endogenous cell regulatory signals resulting in regulated gene expression.

"Sero-switch" adenovirus-mediated in vivo gene transfer: circumvention of anti-adenovirus humoral immune defenses against repeat adenovirus vector administration by changing the adenovirus serotype

Recombinant, replication-deficient adenovirus (Ad) vectors have been successfully used to transfer and express the normal human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA in vivo in the respiratory epithelium of experimental animals and humans with cystic fibrosis (CF). Since Ad-directed gene expression wanes over time, repeat administration is necessary to achieve an effective treatment for CF. A major hurdle to such a strategy is the possibility that anti-Ad humoral immunity may prevent gene expression in individuals with pre-existing anti-Ad immunity or following repeat administration. One strategy to circumvent such a problem would be alternating the use of Ad vectors belonging to different subgroups. Neutralizing antibodies developed with the administration of one Ad serotype do not cross-react with an Ad belonging to a second serotype in a manner that blocks infection and gene expression. To test this hypothesis, an immunizing dose of wild-type Ad5 (subgroup C), Ad4 (subgroup E), or Ad30 (subgroup D) was administered intratracheally to experimental animals, followed by an intratracheal administration of a replication-deficient subgroup C-derived vector coding for marker genes (chloramphenicol acetyl transferase or beta-galactosidase) or for the normal human CFTR cDNA. As expected, studies with vectors coding for marker genes or for CFTR cDNA demonstrated that airway administration of a vector does not yield efficient gene transfer, if there has been prior recent airway administration of the same Ad subgroup. In contrast, effective expression from the second administration can be achieved with an adenovirus vector belonging to a subgroup different from the first adenovirus administered. These data support the paradigm of alternating Ad vectors derived from different subgroups as strategy to circumvent anti-Ad humoral immunity, thus permitting the use of Ad vectors as a means to treat the respiratory manifestations of CF.

Modification of nasal epithelial potential differences of individuals with cystic fibrosis consequent to local administration of a normal CFTR cDNA adenovirus gene transfer vector

Mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR) manifest on the nasal epithelial surface of individuals with cystic fibrosis (CF) by Na+ hyperabsorption and diminished beta-agonist-induced Cl- conductance, resulting in an abnormal bioelectric phenotype across the nasal epithelium. A clinical trial was conducted to determine if a replication-deficient, recombinant adenovirus vector containing a normal copy of the CFTR cDNA (AdCFTR) could, when administered to the nasal epithelium, correct the abnormal bioelectric phenotype. Nine individuals with CF received 2 x 10(5) to 2 x 10(8.5) plaque forming units of AdCFTR to the epithelium of one nostril. Measurements made included: baseline electrical potential difference (PD) between the surface of the nasal epithelium and the interstitial fluid, change in PD in response to amiloride, which inhibits apical Na+ channels, and change in PD in response to isoproterenol in a low Cl- solution, a measure of cAMP-regulated Cl- conductance. The functional integrity of the epithelium was evaluated by the PD response to ATP. Each individual served as their own control with measurements made in the nostril to be treated before AdCFTR administration, and in the contralateral untreated nostril. On the average, in the treated nostril over 2 weeks after the local administration of the adenovirus vector compared to measurements made in the same nostril before treatment, baseline PD decreased toward normal (-53.3 +/- 4.0 to -34.6 +/- 3.4, p = 0.01), response to amiloride decreased toward normal (36.9 +/- 4.7 to 19.7 +/- 3.0, p = 0.02), and response to low Cl- and isoproterenol increased toward normal (-4.5 +/- 1.5 to -9.1 +/- 2.1, p = 0.05). There were no changes in response to ATP (-15.3 +/- 2.7 to -15.8 +/- 1.9, p = 0.39), suggesting that the epithelium remained functionally intact. Importantly, there were no significant changes in measurements made in the untreated nostril. While limited to the nasal epithelium, these data suggest an adenovirus vector can safely deliver sufficient CFTR cDNA function to improve the abnormal CF bioelectric phenotype.

Effect of adenoviral vector infection on cell proliferation in cultured primary human airway epithelial cells

Although recombinant adenoviruses are used as vectors for delivering therapeutic genes to the airways of cystic fibrosis (CF) patients, the effects of these vectors on the kinetics of airway epithelial cell growth have not been investigated. We tested whether E1, E3-deleted Ad vectors (Ad5-CMV-lacZ) affect the kinetics of cell proliferation of human airway epithelial cells in primary culture. There was a dose-dependent relationship between the vector multiplicity of infection (moi) and the efficiency of Ad-mediated lacZ gene transfer. Growth curves of cells exposed to vector were shifted to the right as compared to vehicle in a dose-dependent manner. The vector-induced slowing of cell proliferation resulted from both (i) increased apoptotic cell death and (ii) lower recruitment into S phase. UV inactivation of the vector genes abolished the effects on cell proliferation. These data demonstrate that as the moi of vectors is increased to achieve effective gene transfer, apoptosis and slowing of the cell cycle of infected cells increases concomitantly. The identification and inactivation of these vector effects on human airway cells may be important for reducing the toxicity of adenovirus vectors for gene therapy of CF airways.

Retroviral transfer of HSV1-TK gene into human lung cancer cell line

We used a recombinant retrovirus as one of the potential vectors for human gene therapy to transfer a drug sensitivity gene into human lung cancer cells. The gene encoding the thymidine kinase (TK) of herpes simplex virus type 1 (HSV1) was used as the drug sensitivity gene. The antiherpes drugs acyclovir (ACV) and ganciclovir (GCV) were chosen to test the HSV1-TK activity transferred into the human lung cancer cell lines. The rationale for this approach was that ACV and GCV are nucleoside analogs specifically converted by HSV1-TK to a toxic form capable of inhibiting DNA synthesis or disrupting cellular DNA replication. The results obtained from our experiments demonstrate that the retroviral vector-mediated HSV1-TK gene transfer leads to ACV- and GCV-dependent cytotoxicity in human lung cancer cell lines, including both small-cell carcinoma and non-small-cell carcinoma. Although the gene transfer of HSV1-TK gene into tumor cells would be one model for gene therapy to control lung cancer, further investigations are necessary for the proper choice of the therapeutic gene and vector targeting such as tumor cell specific delivery of the gene or tumor cell specific expression of the transduced gene.

Gene therapy for lung cancer

BACKGROUND

The techniques of molecular genetics are being applied in many areas of oncology and have been spectacularly successful in elucidating the pathogenesis of cancer. Attempts are now being made to harness this knowledge for therapeutic use. Lung cancers are common solid tumours of complex aetiology and represent a major challenge for gene therapy.

CURRENT INVESTIGATIONS

The approaches presently under investigation include the correction of acquired genetic abnormalities, such as mutation of p53 and activation of the ras oncogene, immunotherapy, enhancement of host resistance to cytotoxic insult, and genetic activation of prodrugs by tissue-specific promoters. A variety of vector systems arc available, including liposomes, replication-defective retroviruses and adenoviruses. Local, regional and systemic routes of administration are being studied, and it seems likely that a combination of these approaches will be needed if such treatments are to become generally available.