A potential approach for gene therapy targeting hepatoma using a liver-specific promoter on a retroviral vector

Applications of tissue-specific and cancer-selective gene promoters for cancer diagnosis and therapy

Current treatment of solid tumors with standard of care chemotherapies, radiation therapy and/or immunotherapies are often limited by severe adverse toxic effects, resulting in a narrow therapeutic index. Cancer gene therapy represents a targeted approach that in principle could significantly reduce undesirable side effects in normal tissues while significantly inhibiting tumor growth and progression. To be effective, this strategy requires a clear understanding of the molecular biology of cancer development and evolution and developing biological vectors that can serve as vehicles to target cancer cells. The advent and fine tuning of omics technologies that permit the collective and spatial recognition of genes (genomics), mRNAs (transcriptomics), proteins (proteomics), metabolites (metabolomics), epiomics (epigenomics, epitranscriptomics, and epiproteomics), and their interactomics in defined complex biological samples provide a roadmap for identifying crucial targets of relevance to the cancer paradigm. Combining these strategies with identified genetic elements that control target gene expression uncovers significant opportunities for developing guided gene-based therapeutics for cancer. The purpose of this review is to overview the current state and potential limitations in developing gene promoter-directed targeted expression of key genes and highlights their potential applications in cancer gene therapy.

Chemoenzymatic labeling to visualize intercellular contacts using lipidated sortase A

Methods to label intercellular contact have attracted attention because of their potential in cell biological and medical applications for the analysis of intercellular communications. In this study, a simple and versatile method for chemoenzymatic labeling of intercellularly contacting cells is demonstrated using a cell-surface anchoring reagent of a poly(ethylene glycol)(PEG)-lipid conjugate. The surfaces of each cell in the cell pairs of interest were decorated with sortase A (SrtA) and triglycine peptide that were lipidated with PEG-lipid. In the mixture of the two cell populations, the triglycine-modified cells were enzymatically labeled with a fluorescent labeling reagent when in contact with SrtA-modified cells on a substrate. The selective labeling of the contacting cells was confirmed by confocal microscopy. The method is a promising tool for selective visualization of intercellularly contacting cells in cell mixtures for cell-cell communication analysis.

Gene Therapy for Hemophilia: Progress to Date

Hemophilia is a congenital bleeding disorder that affects nearly half a million individuals worldwide. Joint bleeding and other co-morbidities are a significant source of debilitation for this population. Current therapies are effective but must be given lifelong at regular intervals, are costly, and are available to only about 25% of the hemophilia population living in resource-rich countries. Gene therapy for hemophilia has been in development for three decades and is now entering pivotal-stage clinical trials. While many different technology platforms exist for gene therapy, all current clinical trials for hemophilia employ adeno-associated vector (AAV)-based cell transduction. This small viral particle is capable of packaging modified F8 or F9 transgenes, can be generated robustly from cell lines, and transduces several relatively end-differentiated target tissues such as the liver with high efficiency. While pre-existing neutralizing antibodies to the AAV capsid are recognized to limit current therapy, other challenges have been identified in human studies that were not seen in preclinical studies. Both liver transaminase elevations and immune-mediated loss of transgene expression have been observed in clinical trials. Toll-like receptors, cytotoxic T cells, and other components of the immune response have been implicated in the loss of factor expression, but a full understanding of the immune response awaits clarification. Despite these challenges, many patients enrolled in gene therapy trials have attained long-term expression of factors VIII and IX. This emerging technology now represents a cure for the severe bleeding and joint damage associated with hemophilia.

Construction of a general albumin promoter reporter system for real-time monitoring of the differentiation status of functional hepatocytes from stem cells in mouse, rat and human

Genetic constructs with promoters fused to reporter genes for simultaneous monitoring of cellular events have been the focus of attention in recent years. Adenoviral vectors, which have distinctive characteristics, have been used to monitor the differentiation of stem cells in vitro. In the present study, a modified adenoviral vector was constructed, containing a mouse, rat, and human general albumin promoter sequence fused to a ZsGreen reporter gene, and evaluated its efficiency in different cell types. Two hepatocyte cell lines (Hepa1-6 and HepG2), rat primary hepatocytes, rat bone marrow mesenchymal stem cells (BM-MSCs) and rat BM-MSCs-derived hepatocyte-like cells were transduced with this vector, and the transfection efficiency and functional capabilities of the promoter were evaluated by fluorescent microscopy. The results demonstrated efficient expression of ZsGreen in Hepa1-6 cells, HepG2 cells, rat primary hepatocytes, and rat BM-MSCs-derived hepatocyte-like cells, but not in rat BM-MSCs. In conclusion, the current study demonstrates a simple, high-efficiency, general tool for real-time monitoring of the differentiation status of hepatocytes from stem cells in mice, rats, and humans. This tool may be useful for evaluating different protocols to generate functional hepatocytes from stem cells in multiple species.

Adeno-Associated Virus Gene Therapy for Liver Disease

The field of adeno-associated virus (AAV) gene therapy has progressed rapidly over the past decade, with the advent of novel capsid serotype and organ-specific promoters, and an increasing understanding of the immune response to AAV administration. In particular, liver-directed therapy has made remarkable strides, with a number of clinical trials currently planned and ongoing in hemophilia A and B, as well as other liver disorders. This review focuses on liver-directed AAV gene therapy, including historic context, current challenges, and future developments.

A review of therapeutic prospects of non-viral gene therapy in the retinal pigment epithelium

Ocular gene therapy has been extensively explored in recent years as a therapeutic avenue to target diseases of the cornea, retina and retinal pigment epithelium (RPE). Adeno-associated virus (AAV)-mediated gene therapy has shown promise in several RPE clinical trials but AAVs have limited payload capacity and potential immunogenicity. Traditionally however, non-viral alternatives have been plagued by low transfection efficiency, short-term expression and low expression levels. Recently, these drawbacks have begun to be overcome by the use of specialty carriers such as polylysine, liposomes, or polyethyleneimines, and by inclusion of suitable DNA elements to enhance gene expression and longevity. Recent advancements in the field have yielded non-viral vectors that have favorable safety profiles, lack immunogenicity, exhibit long-term elevated gene expression, and show efficient transfection in the retina and RPE, making them poised to transition to clinical applications. Here we discuss the advancements in nanotechnology and vector engineering that have improved the prospects for clinical application of non-viral gene therapy in the RPE.

Liver-directed gene expression employing synthetic transcriptional control units

AIM: To generate and characterize the synthetic transcriptional control units for transcriptional targeting of the liver, thereby compensating for the lack of specificity of currently available gene therapeutic vector systems.

METHODS: Synthetic transcriptional control unit constructs were generated and analyzed for transcriptional activities in different cell types by FACS quantification, semi-quantitative RT-PCR, and Western blotting.

RESULTS: A new bifunctionally-enhanced green fluorescent protein (EGFP)/neo^r fusion gene cassette was generated, and could flexibly be used both for transcript quantification and for selection of stable cell clones. Then, numerous synthetic transcriptional control units consisting of a minimal promoter linked to “naturally” derived composite enhancer elements from liver-specific expressed genes or binding sites of liver-specific transcription factors were inserted upstream of this reporter cassette. Following liposome-mediated transfection, EGFP reporter protein quantification by FACS analysis identified constructs encoding multimerized composite elements of the apolipoprotein B100 (ApoB) promoter or the ornithin transcarbamoylase (OTC) enhancer to exhibit maximum transcriptional activities in liver originating cell lines, but only background levels in non-liver originating cell lines. In contrast, constructs encoding only singular binding sites of liver-specific transcription factors, namely hepatocyte nuclear factor (HNF)1, HNF3, HNF4, HNF5, or CAAT/enhancer binding protein (C/EBP) only achieved background levels of EGFP expression. Finally, both semi-quantitative RT-PCR and Western blotting analysis of Hep3B cells demonstrated maximum transcriptional activities for a multimeric 4xApoB cassette construct, which fully complied with the data obtained by initial FACS analysis.

CONCLUSION: Synthetic transcriptional control unit constructs not only exhibit a superb degree of structural compactness, but also provide new means for liver-directed expression of therapeutic genes.

Identification of synthetic endothelial cell-specific promoters by use of a high-throughput screen

Transcriptional targeting is a desirable property for many gene transfer applications. Because endothelial cells line most blood vessels, they are attractive candidates for the introduction of therapeutic gene products. As a proof-of-concept study, we attempted to identify a synthetic, endothelial cell-specific promoter by use of a high-throughput screen involving self-inactivating (SIN) human immunodeficiency virus type 1 (HIV-1)-based vectors. Select duplex oligodeoxynucleotides recognized by transcription factors and located 5' of endothelial cell-specific mRNA transcripts were randomly ligated and cloned upstream of a minimal ICAM-2 promoter driving enhanced green fluorescent protein (eGFP) in a SIN HIV-1-based vector. Vesicular stomatitis virus G protein-pseudotyped particles were prepared from a library of >10(6) vector recombinants and used to transduce an endothelial cell line. The highest eGFP expressers were repeatedly sorted, and the synthetic promoters were recovered and retested by a luciferase reporter. Several promoters were active and specific to endothelial cells of varied species, with high selectivity indexes and inducibility under hypoxia-mimetic conditions. One in particular was then introduced back into a SIN HIV-1-based vector to confirm its endothelial cell activity and specificity. This study suggests that SIN vectors may be used in a high-throughput manner to identify tissue-specific promoters of high activity, with potential applications for both transcriptional targeting and gene transfer.

Transcriptional Targeting in Cancer Gene Therapy

Cancer gene therapy has been one of the most exciting areas of therapeutic research in the past decade. In this review, we discuss strategies to restrict transcription of transgenes to tumour cells. A range of promoters which are tissue-specific, tumour-specific, or inducible by exogenous agents are presented. Transcriptional targeting should prevent normal tissue toxicities associated with other cancer treatments, such as radiation and chemotherapy. In addition, the specificity of these strategies should provide improved targeting of metastatic tumours following systemic gene delivery. Rapid progress in the ability to specifically control transgenes will allow systemic gene delivery for cancer therapy to become a real possibility in the near future.

Hydroxyapatite ceramics as a carrier of gene-transduced bone marrow cells

The aim of this study was to develop an efficient exogenous gene delivery system using cultured marrow cells and porous hydroxyapatite ceramics. Bone marrow cells were obtained from the femoral shaft of a Fischer 344 rat and cultured in a medium containing 15% fetal bovine serum until confluent. After trypsinization, cells were subcultured at a cell density of 1 x 10(4) cells/cm2 in the presence of fetal bovine serum. The subcultured bone marrow cells were infected with recombinant retroviruses carrying the lacZ gene. The retrovirus infection was performed seven times from day 1 to day 7 during the culturing procedure. Cells expressing the lacZ gene were stained blue with the X-gal staining and represented approximately 80%. Composites of virus-infected bone marrow cells and hydroxyapatite ceramics were implanted at the subcutaneous site of recipient Fischer 344 rats. Four weeks after the implantation the ceramics were harvested. The histological sections of the ceramics showed abundant bone formation in the pores of the ceramics and obviously blue-stained osteoblasts and osteocytes. Other cell types that were stained blue were some fibroblastic cells and endothelial cells in the newly formed capillaries. These findings indicate that osteoblasts and osteocytes in the newly formed bone were derived from the cultured bone marrow cells, and therefore gene transfection by retroviruses did not disturb the bone formation process. Because of the durability of the newly formed bone tissue, creating composites of cultured bone marrow cells and hydroxyapatite ceramics might be an ideal method for exogenous gene transfection.

In vitro and in vivo comparative study of chimeric liver-specific promoters

Targeting therapeutic genes to the liver is essential to improve gene therapy protocols of hepatic diseases and of some hereditary disorders. Transcriptional targeting can be achieved using liver-specific promoters. In this study we have made chimeric constructs combining promoter and enhancer regions of the albumin, alpha 1-antitrypsin, hepatitis B virus core protein, and hemopexin genes. Tissue specificity, activity, and length of gene expression driven from these chimeric regulatory sequences have been analyzed in cultured cells from hepatic and nonhepatic origin as well as in mice livers and other organs. We have identified a collection of liver-specific promoters whose activities range from twofold to less than 1% of the CMV promoter in human hepatoma cells. We found that the best liver specificity was attained when both enhancer and promoter sequences of hepatic genes were combined. In vivo studies were performed to analyze promoter function during a period of 50 days after gene transfer to the mouse liver. We found that among the various chimeric constructs tested in this work, the alpha1-antitrypsin promoter alone or linked to the albumin or hepatitis B enhancers is the most potent in directing stable gene expression in liver cells.

Retrovirus-mediated in vivo gene therapy using the herpes simplex virus thymidine kinase gene against carcinomatous peritonitis

BACKGROUND

Carcinomatous peritonitis is characterized by massive malignant ascites, while peritoneally disseminated carcinomatosis is characterized by a large number of metastatic solid tumors in the peritoneal cavity. Although both are fatal end-stage manifestations of malignancies derived from the digestive system, the former is usually more serious than the latter due to massive malignant ascites. Although the effectiveness of gene therapy against peritoneally disseminated carcinomatosis has been shown in animal experiments, its effectiveness against carcinomatous peritonitis remains to be examined.

METHODS

A carcinomatous peritonitis model was made by inoculating murine hepatocellular carcinoma cells, MH134, into the peritoneal cavity of syngeneic C3H/He mice, resulting in production of massive malignant ascites without development of intraperitoneal solid tumors. Model animals were injected intraperitoneally with retroviruses carrying the herpes simplex virus thymidine kinase (HSV-tk) gene followed by ganciclovir (GCV) treatment.

RESULTS

Retrovirus-mediated in vivo gene therapy with the HSV-tk/GCV system was shown to have a significant impact on survival of animals with carcinomatous peritonitis not only at an early stage, but also at an advanced stage. Furthermore, repeated injections of HSV-tk-carrying retroviruses significantly prolonged the survival of animals with carcinomatous peritonitis compared with a single injection protocol. When intraperitoneal administration of recombinant interleukin-2 (IL-2) was added to the HSV-tk/GCV system, levels of IL-1beta and IL-2 in malignant ascites were significantly increased, resulting in significantly reduced ascite volume and prolonged survival.

CONCLUSIONS

Our results indicate the feasibility of retrovirus-mediated in vivo gene therapy with the HSV-tk/GCV system plus IL-2 treatment against carcinomatous peritonitis.

Particle-mediated gene transfer into murine livers using a newly developed gene gun

Although particle-mediated gene transfer using gene gun technology has been applied for gene transfer into epidermis, applications of this technology to visceral tissues have not been well investigated. Although all helium gas-driven gene gun instruments have used macrocarriers to discharge DNA-coated microprojectiles so far, we used a newly developed gene gun instrument, in which a hammering bullet is used to discharge microprojectiles. With the gene gun, gold particles coated with lacZ expression plasmid were discharged to murine livers. LacZ expression was induced much more profoundly in the liver by particle-mediated gene transfer than by simple plasmid injection and electroporation-mediated gene transfer. LacZ expression was broadly and randomly distributed throughout the bombarded livers, indicating that particle-mediated gene transfer can induce transgene expression even at relatively distant areas from the surface of the bombarded tissue. Furthermore, although transgene expression was at its peak on day 2 after the bombardment, it was still detectable even on day 28. These results indicate that particle-mediated gene transfer with a newly developed gene gun may provide a new approach to gene therapy for human diseases.

Gene therapy: designer promoters for tumour targeting

One of the biggest challenges facing cancer therapy is to generate tumour-specific treatment strategies. Gene therapy hopes to achieve this by directing the activity of therapeutic genes specifically to the sites of disease. Of paramount importance for the success of this approach is the availability of tumour-specific delivery systems: both the transductional targeting of the vector vehicle and the restriction of transgene expression to the tumour are promising strategies towards this goal. This review will focus on the recent achievements in the field of transcriptional targeting and the different strategies to improve or design promoters with the desired specificities.

Immunomodulation with FK506 around the time of intravenous re-administration of an adenoviral vector facilitates gene transfer into primed rat liver

Although adenoviruses are an attractive vehicle for gene transfer into tissues including various tumors, in vivo adenoviral administration elicits a neutralizing antibody response which eliminates or substantially reduces the efficacy of subsequent treatments. Transiently immunosuppressive strategies at the time of initial adenoviral exposure have shown to prevent the formation of neutralizing antibodies and permit the successful adenoviral readministration in animals. Initial treatment in humans may, however, correspond to adenoviral readministration into animals, because the exposure to wild-type adenoviruses is common in humans. In the present study, we infused Adex1CAlacZ adenoviruses carrying the lacZ gene into the tail vein of rats, and examined whether a transient treatment with the immunosuppressant FK506 around the time of i.v. readministration of adenoviruses could induce the re-expression of the lacZ gene in animals primed with adenoviruses. Although i.v. infusion of adenoviruses carrying the lacZ gene resulted in transiently high levels of transgene expression in rat liver, i.v. reinfusion of adenoviruses failed to induce detectable levels of transgene expression. Conversely, when animals were treated transiently with FK506 around the time of adenoviral reinfusion, development of neutralizing antibodies and antigen-specific T cell proliferation in response to adenoviral reinfusion were significantly suppressed, and re-expression of the transgene was achievable.

Transient cyclophosphamide treatment before intraportal readministration of an adenoviral vector can induce re-expression of the original gene construct in rat liver

Although adenovirus is an attractive vehicle for transferring therapeutic genes in vivo, animal studies have indicated that the clinical usefulness of adenoviruses may be limited by their immunogenicity. Although immunosuppressive strategies around the time of initial exposure of adenoviruses have been shown to prevent the formation of neutralizing antibodies and permit the successful readministration of adenoviruses in animals, the practicality of the approaches remains questionable. Because the majority of prospective gene therapy patients have already been infected with wild-type adenoviruses, initial treatment with adenoviruses in humans may correspond to readministration of adenoviruses into animals. It is shown here that although intraportal infusion of adenoviruses carrying a reporter lacZ gene resulted in transient high levels of transgene expression in the rat liver, intraportal readministration of adenoviruses failed to induce detectable levels of transgene expression. Conversely, when animals were treated transiently with cyclophosphamide before the intraportal readministration of adenoviruses, development of neutralizing antibodies and antigen-specific T cell proliferation in response to adenoviral readministration was significantly suppressed and successful re-expression of the transgene was achievable. These results may have important implications for efficacy considerations when adenoviral vectors are employed in clinical settings.

Complete cure of established murine hepatocellular carcinoma is achievable by repeated injections of retroviruses carrying the herpes simplex virus thymidine kinase gene

Although xenotransplantation of retrovirus-producing cells into a tumor has been shown to be effective for the treatment of cancer, injections of recombinant retroviruses are much more feasible for clinical applications. We established a clone producing retroviruses carrying the herpes simplex virus thymidine kinase (HSVtk) gene with titers of up to 4 x 10(7) colony-forming units/ml, and examined the effectiveness of in vivo gene therapy against cancer. Syngeneic mice were inoculated subcutaneously with murine hepatocellular carcinoma (HCC) cells, BNL1ME A.7R.1, and the treatment was initiated after tumors were established. When mice were given an intratumoral injection of HSVtk-carrying retroviruses or their producing cells followed by ganciclovir (GCV) treatment, significantly prolonged survival periods were observed. When mice were treated with repeated intratumoral injections of HSVtk-carrying retrovirus-producing cells, significant antitumor responses and some cures were induced by GCV treatment. Furthermore, repeated intratumoral injections of HSVtk-carrying retroviruses and GCV treatment resulted in complete regression of established HCC tumors in all animals used in the experiment. Mice that completely eradicated tumors exhibited protective immunity against wild-type HCC tumors. These results suggest that repeated injections of HSVtk-carrying retroviruses followed by GCV treatment is a potent modality for the treatment of solid tumors.

Hepatoma-specific antitumor activity of an albumin enhancer/promoter regulated herpes simplex virus in vivo

Targeting viral vectors to appropriate cell types so that normal cells are not adversely affected is an important goal for gene therapy. Previously, we described a novel approach to viral gene therapy using a conditional, replication-competent herpes simplex virus (HSV), where replication and associated cytotoxicity are limited to a specific cell-type by the regulated expression of an essential immediate-early viral gene product. In this report we analyze the hepatoma-specific replication, cytotoxicity and anti-tumor effect of recombinant HSV G92A, regulated by the albumin enhancer/promoter. G92A efficiently replicated in vitro in two human hepatoma cell lines expressing albumin, but not in four human non-hepatoma, albumin-non-expressing tumor cell lines, while all cell lines were equally susceptible to a tissue nonspecific HSV recombinant, hrR3. In vivo, G92A replicated well in subcutaneous xenografts of human hepatoma cells (Hep3B) in athymic mice, but not in non-hepatoma subcutaneous tumors (PC3 and HeLa), whereas, hrR3 replicated well in both tumor types. Intratumoral inoculation of G92A inhibited the growth of established subcutaneous hepatoma tumors in nude mice, but not prostate tumors. Replication-competent viral vectors controlled by cell-specific transcriptional regulatory sequences provide a new therapeutic strategy for tumor therapy.

Comparison of carcinoembryonic antigen promoter regions isolated from human colorectal carcinoma and normal adjacent mucosa to induce strong tumor-selective gene expression

To establish in vivo gene therapy against cancer, it is requisite to induce strong, cancer cell-selective expression of a therapeutic gene. Comparison of the promoter activity of 5' flanking regions of the carcinoembryonic antigen (CEA) gene isolated from various origins is therefore of considerable interest. The 5' flanking region of the CEA gene between -135 and +69 bp upstream from the transcriptional start site, which is recognized as the core promoter region, was isolated from CEA-producing human colorectal carcinoma (CRC), normal adjacent mucosa, CEA-producing cell lines and CEA-non-producing cell lines. No mutations were observed by single-strand conformation polymorphism in the CEA promoter regions. Subsequent sequence analysis revealed that there were no mutations in the CEA promoter regions isolated from CEA-producing CRC and normal adjacent mucosa. Furthermore, nuclear extracts prepared from CEA-producing human CRC cells could equally bind to both the CEA promoter fragments isolated from CEA-producing CRC and normal mucosa. Both CEA promoter regions could direct 5- to 20-fold higher expression of a luciferase reporter gene in CEA-producing cells than in CEA-non-producing cells. Therefore, we suggest that the use of either CEA promoter region isolated from CRC or normal mucosa is equally effective to induce strong, CEA-producing cancer-selective expression of a therapeutic gene.

The mouse equivalent of the human p53ser249 mutation p53ser246 enhances aflatoxin hepatocarcinogenesis in hepatitis B surface antigen transgenic and p53 heterozygous null mice

The relative contribution to development of hepatocellular carcinoma of the mouse equivalent to the human p53ser249 mutation, found in human hepatocellular carcinoma associated with aflatoxin (AFB1) exposure, is compared with other major risk factors in a transgenic mouse model. Transgenic p53ser246 mice, expressing the mutant protein gene under the control of a truncated albumin promoter, were bred to mice lacking p53 (p53-/-) and to transgenic mice expressing hepatitis B surface antigen (HBsAg). AFB1 hepatocarcinogenesis was then determined in offspring with single or multiple risk factors by determination of the numbers of high-grade hepatic tumors at 13 months of age. In AFB1-treated male mice, expression of the p53ser246 mutation increases the incidence of high-grade tumors from 0% to 14% in HBsAg-negative, p53+/+ (wild-type homozygous) control mice; from 14% to 71% in HBsAg-negative, p53+/- (wild-type heterozygous) mice; and from 62% to 100% in HBsAg-positive, p53+/+ mice. Thus, whereas HBsAg expression and AFB1 together are strongly cocarcinogenic, the presence of the p53ser246 mutant not only significantly enhances this cocarcinogenic effect, it also increases tumorigenesis in AFB1-treated p53 heterozygous and homozygous mice not expressing HBsAg. The possibility that the p53ser246 mutant protein may act as a promoting agent for AFB1 hepatocarcinogenesis is discussed.

Expression of alpha-fetoprotein and albumin genes in human hepatocellular carcinomas: limitations in the application of the genes for targeting human hepatocellular carcinoma in gene therapy

For an approach of gene therapy for hepatocellular carcinoma (HCC), transcriptional regulatory sequence (TRS) of either alpha-fetoprotein (AFP) or albumin has been used for targeting cancer cells. To examine the feasibility of using TRSs of these genes for possible gene therapy of HCCs, the cellular distribution of AFP and albumin gene transcripts was studied in 25 cases of surgically removed human HCCs. AFP gene expression was observed in HCC nodules of 13 cases. The expression in HCC was heterogeneous, and the distribution of the transcripts was mostly sparse and spotty. The higher the serum AFP levels, the larger population of the AFP-expressing HCC cells tended to reflect. In noncancerous liver, a slight AFP expression was found by Northern blot analysis, but the transcripts were not detected in the liver sections. In contrast, albumin expression was found in all HCCs as well as in noncancerous hepatocytes. In HCC, the transcripts for albumin were distributed in cancer cells, and the expression varied with nodules. There were more albumin-expressing cancer cells than the AFP-expressing cells. Albumin expression was retained even in poorly differentiated HCC, although the intensity of the signal was not as strong as in more-differentiated HCCs. Metastatic HCC nodules revealed transcripts for both AFP and albumin genes, and those were clearly recognized in the lung tissue. These results suggest that, for gene therapy for HCCs, neither AFP nor albumin are ideal options for targeting HCC cells. AFP-TRS may be used as a transcriptional regulator in selected cases in which AFP gene expression is observed in the cancer nodules. The serum AFP level appears to be an important indicator in selecting cases. Albumin-TRS in conjunction with retroviral vector might be used in limited cases such as HCCs with no AFP expression. However, careful consideration must be taken, because albumin is constitutively expressed in normal hepatocytes, and AFP-expressing nonmalignant progenitor cells possibly exist.

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.

Tissue-specific expression of HSV-tk gene can induce efficient antitumor effect and protective immunity to wild-type hepatocellular carcinoma

The efficacy of expression of the herpes simplex virus thymidine kinase (HSV-tk) gene under the transcriptional control of the liver-specific albumin gene promoter, followed by ganciclovir treatment, was investigated both in vitro and in vivo. Murine and rat hepatocellular carcinoma (HCC) cells infected with retroviruses carrying the HSV-tk gene under the control of the murine albumin gene promoter were selectively killed by ganciclovir treatment in vitro, whereas non-HCC cells, such as murine mammary tumor cells and fibroblast cells, which were infected with the same retroviruses, were not. Susceptibility of the retroviral-infected HCC cells to ganciclovir was more than 100-fold higher than that of the retroviral-infected non-HCC cells. When mice bearing a bulky HCC mass consisting of the retroviral-infected HCC cells were treated with systemic ganciclovir administration, complete regression of the tumors was observed without any signs of overt toxicity. Profound antitumor effects on preestablished murine HCCs were observed when wild-type HCC cells were implanted into animals with a small percentage of the retroviral-infected counterparts. When only 5% of the cells were infected with retroviruses carrying the HSV-tk gene, significant inhibition of tumor development was observed with systemic ganciclovir treatment. Importantly, animals that were treated with implantation of mixtures of the retroviral-infected and parental HCC cells, followed by ganciclovir administration, did not exhibit tumor formation and resisted subsequent rechallenge with wild-type HCC cells. Our results indicate the feasibility of combination therapy with the HSV-tk gene and ganciclovir for the treatment of HCC.

Targeted killing of migrating glioma cells by injection of HTK-modified glioma cells

The "bystander effect" describes the killing of nearby unmodified cells and herpes simplex thymidine kinase (HTK)-transduced cells by ganciclovir (GCV) treatment. This effect is thought to be produced by contact between these cells. In this study, we showed that injected glioma cells migrated rapidly to a place distant from the injection point whereas injected virus-producing fibroblast cells did not migrate in a murine brain model. Moreover, the initially injected glioma cells and glioma cells injected at a later time mix very well, even at a place distant from the injection point. This suggested that glioma cells migrating after injection could be targeted by HTK-modified glioma cells introduced in a second injection and be killed together by GCV treatment. Therefore, we injected HTK-modified glioma cells 3 days after injection of wild glioma cells to investigate whether wild-type glioma cells that migrated to a place distant from the injection point could also be killed by GCV treatment. Tumor growth was suppressed after the GCV treatment. Suppression of tumor growth of wild glioma cells is not solely mediated by the immune response, which may be triggered by the killing of HTK-modified glioma cells with GCV, because inoculation of HTK-modified glioma to the contralateral side followed by GCV treatment did not cure the initial wild glioma. Moreover, the migration of the second inoculum of glioma cells is necessary for effective killing, because early administration of GCV resulted in insufficient killing.

Construction of retroviral vectors to induce strong hepatoma cell-specific expression of cytokine genes

Continuing advances in molecular biology have provided tools for a promising approach to the treatment of cancer. Among the various strategies of gene therapy for cancer, many are aimed at killing tumour cells indirectly by the induction or reinforcement of a host immune response by gene transduction of various cytokines, major histocompatibility complex or immune accessory molecules. In the present study, we selected the tumour necrosis factor-alpha, interleukin-2 and interleukin-3 genes as potential cytokine genes to induce antitumour effects. We constructed retroviral vectors carrying these cytokine genes under the control of the murine albumin enhancer and promoter and retrovirally transduced these genes into hepatoma and non-hepatoma cell lines. Strong expression of the cytokine genes was induced in transduced hepatoma cells, while no evident expression was detected in transduced non-hepatoma cells. These results demonstrate the hepatoma-specific expression of cytokine genes and imply the feasibility of in vivo gene transfer into hepatomas without affecting any other tissues. Furthermore, these cytokine genes were expressed much more intensively when they were derived from the albumin enhancer and promoter than when derived from the simian virus 40 early region promoter. These results indicate that transcriptional regulatory sequences specific for the target tissues could be preferable to viral promoters for the gene therapy of cancer.

Direct cell killing by suicide genes

Cell death can be induced by genetic intervention in a variety of ways. We review genetic prodrug activation therapies using both mammalian and non-mammalian enzyme systems as well as the expression of toxin genes and apoptotic triggers. Targeting of the genetic intervention using both transductional restriction and transcriptional control elements is examined in both in vitro and in vivo systems, and the present state of clinical trials is reviewed.

Selective killing of AFP-positive hepatocellular carcinoma cells by adeno-associated virus transfer of the herpes simplex virus thymidine kinase gene

The use of viral thymidine kinase (TK) gene coupled with the administration of ganciclovir to render cancer cell death has been studied extensively. Many of these experiments utilized retrovirus to transfer the TK gene under the control of a nonspecific promoter. Because nonspecific expression of the viral TK gene may cause death of proliferating cells, other than cancer cells, we explored the use of a liver-specific promoter and a tumor-specific AFP enhancer to achieve regulated viral TK gene expression for treatment of hepatocellular carcinoma. We also used the adeno-associated virus (AAV) as vector for the delivery of the TK gene because this virus is not associated with any pathological consequences in humans. Because it can infect nondividing S-phase cells, AAV can transfer genes into noncycling tumor cells. A recombinant AAV virus was constructed to include the selectable marker neoR gene and the herpes simplex virus (HSV)-TK gene driven by the human AFP enhancer and the albumin promoter. The liver-predominant expression pattern of the TK gene was observed when this construct was tested in transgenic mice. When human hepatocellular carcinoma cell lines displaying different levels of AFP and albumin and nonhepatocyte tumor cell lines were infected with the recombinant AAV virus, ganciclovir treatment caused only AFP and albumin-positive hepatocellular carcinoma cells death, but not nonhepatocyte tumor cells or AFP and albumin-negative hepatic tumor cells. Moreover, the dose required to kill the cancer cells was inversely proportional to the level of AFP expression in the cells.

Development of drug targeting based on recombinant expression of the chicken avidin gene

The chemistry required for covalent biotinylation of drugs, radiopharmaceuticals and other ligands is highly developed, and a large number of biotinylated reagents can be readily synthesized. In order to investigate whether expression of avidin cDNA in mammalian cells might be useful as part of a drug targeting strategy, we transiently expressed the avidin gene in two human tumor cell lines (the cervical carcinoma cell line, HeLa, and the liver derived line, Hep G2). Avidin protein as detected by either immunohistochemistry or binding of streptavidin-biotin complexes was present and functional following transient expression. This result indicated that the mechanisms underlying avidin oligomerization which are necessary for proper protein folding are present within mammalian carcinoma cell lines. Next, we generated a producer cell line (derived from psi2) capable of releasing a recombinant retrovirus encoding chicken avidin, and a tumorigenic murine breast cancer cell line (16/C) with stable avidin expression. We show that these cell lines are suitable for conferring functional expression of avidin in vitro. These experiments establish a means by which avidin gene expression can be explored as a mechanism for targeted gene delivery of biotin-derivitized drugs in vitro, and have important implications for utilization of this strategy in vivo.

Activation of the radiosensitive EGR-1 promoter induces expression of the herpes simplex virus thymidine kinase gene and sensitivity of human glioma cells to ganciclovir

Herein we describe experiments showing that the early growth response gene 1 (EGR-1) promoter is sufficient to confer selective expression of the luciferase gene (Luc) in glioma cell lines exposed to ionizing radiation. Activity of the EGR-1 promoter was investigated in human glioblastoma cells using the plasmid vector, pEGR-Luc. The EGR-1 promoter gene directed radiosensitive expression of luciferase. This promoter showed high levels of activity (10-fold) in irradiated glioma cell lines as compared to basal levels of activity in nonirradiated cell lines. Maximum activation was detectable at 1-3 hr after stimulation with 20 Gy. The results also demonstrate that cells modified to contain the herpes simplex virus-thymidine kinase (HSV-tk) gene under control of the EGR-1 promoter become sensitive to treatment with the antiviral agent ganciclovir (GCV), whereas nonirradiated cells and nontransfected cells were unaffected by this agent. This results suggest that therapeutic genes can be expressed selectively in irradiated glioma cells. The results also indicate that the EGR-1 promoter can be used to induce exogenous genes selectively in radiation fields used for the treatment of malignant brain tumors.

Prostate tissue specificity of the prostate-specific antigen promoter isolated from a patient with prostate cancer

We have cloned and characterized a 620-bp fragment of DNA that flanks 5' of the prostate-specific antigen (PSA) gene from a prostate cancer patient. Using DNA transfection, the efficacy of this putative promoter in regulating gene expression was quantitated in several prostate and nonprostate tissue cell lines. Our results demonstrated that the 620-dp DNA fragment actively drives gene expression in LNCaP, a PSA-producing prostate tumor cell line. No promoter activity was detected in the non-PSA-producing prostate tumor lines, DU145 and PC-3, nor in a renal (R11) or breast (MCF-7) cancer cell line. Furthermore, the promoter activity could be regulated in vitro by androgen stimulation. Dihydrotestosterone (DHT) concentrations between 3 and 30 nM induced the highest promoter activity in the transfected LNCaP cells, which parallels the expression profile of the androgen receptor in LNCaP cells. In addition, our PSA promoter exhibited competitive inhibition of the endogenous genomic PSA promoter in transfected LNCaP cells, suggesting that prostate cell-specific DNA-binding proteins are required to activate the PSA promoter. increased its potency four- to five-fold while retaining tissue specificity. Our data suggest that a strong tissue-specific negative regulatory element capable of overriding the nonspecific CMV promoter is present in the PSA promoter and confers its tissue specificity. The use of a highly specific promoter-driven gene vector will allow selective expression of therapeutic genes within PSA-producing prostate cancer cells, providing a unique strategy for prostate cancer gene therapy.

Gene-modified cells for the treatment of cancer

Gene therapy involves the insertion of a gene into an organism to treat a disease. Since its early development in the 1970s, gene therapy has expanded rapidly both in terms of the methods available and the number of candidate diseases for treatment. This report reviews gene therapy for cancer, including methodology, pre-clinical studies and experimental clinical trials.

Gene therapy: applications to the treatment of gastrointestinal and liver diseases

There has been much progress in our understanding of molecular mechanisms in the pathogenesis of inherited metabolic disorders. In addition, powerful new molecular techniques have made possible phenotypic alterations by delivery of foreign genes to target cells. As a result, concepts and methods that would have been considered purely science fiction 10 years ago can now be found in human clinical trials engaged in the treatment of these disorders. In this review, we have attempted to provide an introduction and survey of the topic of gene therapy, with specific examples of laboratory and clinical achievements to date, and highlights on potentials for applications in digestive diseases.

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

Human surfactant protein A (SPA) expression is considered a marker of respiratory epithelial differentiation. Non-small cell lung cancers (NSCLC) are respiratory epithelial derivatives, and it was previously shown that a minority of these cancers expressed SPA, presumably a consequence of their respiratory epithelial origin. In the studies reported here, SPA-I gene transcriptional regulatory sequences were localized to a 2.75-kb genomic 5'-flanking region fragment obtained by screening a human genomic library. The 2.75-kb fragment was used to direct a luciferase coding sequence transcriptionally within a plasmid construct. In plasmid transduction experiments, the SPA-directed luciferase plasmid produced significant luciferase activity in the SPA-expressing NSCLC cell line, H441, but only background levels in the non-SPA-expressing A549 cells. Because Northern blot analysis of resected NSCLC showed that the majority expressed SPA, an SPA-transcriptional targeting strategy was investigated using chimeric toxin genes comprising the coding sequence for herpes simplex virus thymidine kinase (HSV-TK) under transcriptional control of SPA or SV40 regulatory sequences. As expected, transduction of the constitutive, SV40-directed plasmid followed by ganciclovir treatment reduced numbers of both the A549 and H441 cells. In contrast, the SPA-directed plasmid reduced only the SPA-expressing H441 cells and had no significant effect on the A549 cells. The results of these in vivo experiments suggest the concept of transcriptionally directing toxin genes with SPA can produce targeted toxicity in NSCLC.

Selective expression of foreign genes in glioma cells: use of the mouse myelin basic protein gene promoter to direct toxic gene expression

We have previously demonstrated that retrovirus-mediated genes were transferred to mouse glioma cells in a meningeal gliomatosis model (Yamada et al.: Japanese Journal of Cancer Research 83:1244-1247, 1992). This retrovirus vector contains the Escherichia coli. beta-galactosidase (beta-gal) gene as a marker for integration of the lacZ gene, which is controlled by the SV40 early promoter. We investigated whether lacZ genes could be specifically controlled in mouse glioma cells by glial-specific promoters, including the 2.5 kb 5' flanking region of the mouse glial fibrillary acidic protein (GFAP) gene, the 1.3 kb 5' flanking region of the myelin basic protein (MBP) gene, and the 1.5 kb 5' flanking region of the myelin proteolipid protein (PLP) gene. Psi-2 packaging cells were transfected with each retrovirus vector (GFAP promoter-, MBP promoter-, and PLP promoter-lacZ) and the infectious virus particles were recovered from the supernatants. Blue staining for beta-gal was detected in various fibroblast, myeloma, and glioma cell lines transduced with the retrovirus BAG vector. On the other hand, blue staining was only detected in glioma cells after transduction with the lacZ gene-bearing retrovirus controlled by glial-specific promoters. The strongest promoter activity was detected after transduction with the retrovirus in which the MBP promoter controlled the lacZ gene. Mouse glioma cells transduced with retrovirus containing the MBP promoter directing the herpes simplex virus type 1 thymidine kinase (HTK) gene were extremely sensitive to ganciclovir, while the parental cells and cells transduced with retrovirus containing the lacZ gene were not sensitive to ganciclovir.(ABSTRACT TRUNCATED AT 250 WORDS)

Cancer in the elderly

This article reviews geriatric oncology and assesses options for treatment and care of the elderly patient with cancer. The size of the population over 65 years old is defined, with particular reference to the continuing growth of this subsection of the community. The high incidence of many cancers and their associated mortality rates in the elderly are identified and the epidemiology of such diseases in the geriatric population is addressed. Given the discrepancies in incidence and survival rates between patients younger and older than 65 years, the association between tumorigenesis and the aging process is explored. Specific aspects of tumor growth in the elderly are considered. General considerations of therapy for elderly patients with cancer are discussed, including the pharmacokinetics and pharmacodynamics of chemotherapy in those over 65 years old, surgical options, the use of radiotherapy, and overall patient assessment. Next, treatment options for individual cancer states are reviewed, with particular emphasis on newer treatment options designed specifically for the elderly. Sections on cancer screening and supportive care are also included, the latter dealing with aspects of symptom control, quality of life assessment, and the physical and psychologic rehabilitation of the elderly patient with cancer who is undergoing treatment. Conclusions are then drawn as to the extent of the oncological process in those over 65 years old, with particular emphasis on the underdiagnosis and undertreatment of many malignancies in the past. The challenge created by the growing elderly population is underscored and necessary plans of action for oncologists in the future are defined. Such proposals are necessary if inroads are to be made into the unacceptable morbidity and mortality rates borne by our elderly patients with cancer.

Retrovirus-mediated gene transfer targeted to malignant glioma cells in murine brain

A murine model for meningeal metastasis of malignant glioma was developed to study selective gene transfer into tumor cells and to establish a reliable means of determining the rate of tumor cell infection. A murine ecotropic retroviral vector was created in which the Escherichia coli beta-galactosidase gene served as a marker for gene expression from the integrated retrovirus. This retrovirus exhibited a high rate of infectivity in RSV-M mouse glioma cells in vitro. The recombinant retrovirus was injected directly into the cisterna magna of the mice. Staining of beta-galactosidase showed that the rate of gene integration was high in the disseminated glioma cells. These results suggest the possibility of retrovirus-mediated gene therapy for meningeal dissemination of malignant glioma.