A complex adenovirus vector that delivers FASL-GFP with combined prostate-specific and tetracycline-regulated expression

Multivalent and Multipathogen Viral Vector Vaccines

The presentation and delivery of antigens are crucial for inducing immunity and, desirably, lifelong protection. Recombinant viral vectors-proven safe and successful in veterinary vaccine applications-are ideal shuttles to deliver foreign proteins to induce an immune response with protective antibody levels by mimicking natural infection. Some examples of viral vectors are adenoviruses, measles virus, or poxviruses. The required attributes to qualify as a vaccine vector are as follows: stable insertion of coding sequences into the genome, induction of a protective immune response, a proven safety record, and the potential for large-scale production. The need to develop new vaccines for infectious diseases, increase vaccine accessibility, reduce health costs, and simplify overloaded immunization schedules has driven the idea to combine antigens from the same or various pathogens. To protect effectively, some vaccines require multiple antigens of one pathogen or different pathogen serotypes/serogroups in combination (multivalent or polyvalent vaccines). Future multivalent vaccine candidates are likely to be required for complex diseases like malaria and HIV. Other novel strategies propose an antigen combination of different pathogens to protect against several diseases at once (multidisease or multipathogen vaccines).

Targeting the Fas/FasL signaling pathway in cancer therapy

INTRODUCTION

The Fas/FasL system plays a significant role in tumorigenesis. Research has shown that its impairment in cancer cells may lead to apoptosis resistance and contribute to tumor progression. Thus, the development of effective therapies targeting the Fas/FasL system may play an important role in the fight against cancer.

AREAS COVERED

In this review the recent literature on targeting the Fas/FasL system for therapeutic exploitation at different levels is reviewed. Promising pre-clinical approaches and various exceptions are highlighted. The potential of combined therapies is also explored, whereby tumor sensitivity to Fas-mediated apoptosis is restored, before an effective targeted therapy is employed.

EXPERT OPINION

The success of the Fas/FasL system targeting for therapeutics will require a better understanding of the alterations conferring resistance, in order to use the most appropriate sensitizing chemotherapeutic or radiotherapeutic agents in combination with effective targeted therapies.

Harnessing tumor necrosis factor receptors to enhance antitumor activities of drugs

Cancer is the second-leading cause of death in the U.S. behind heart disease and over stroke. The hallmarks of cancer comprise six biological capabilities acquired during the multistep development of human tumors. The inhibition of cell death pathways is one of these tumor characteristics which also include sustained proliferative signaling, evading growth suppressor signaling, replicative immortality, angiogenesis, and promotion of invasion and metastasis. Cell death is mediated through death receptor (DR) stimulation initiated by specific ligands that transmit signaling to the cell death machinery or through the participation of mitochondria. Cell death involving DR is mediated by the superfamily of tumor necrosis factor receptor (TNF-R) which includes TNF-R type I, CD95, DR3, TNF-related apoptosis-inducing ligand (TRAIL) receptor-1 (TRAIL-R1) and -2 (TRAIL-R2), DR6, ectodysplasin A (EDA) receptor (EDAR), and the nerve growth factor (NGF) receptor (NGFR). The expression of these receptors in healthy and tumor cells induces treatment side effects that limit the systemic administration of cell death-inducing therapies. The present review is focused on the different therapeutic strategies such as targeted antibodies or small molecules addressed to selective stimulated DR-mediated apoptosis or reduce cell proliferation in cancer cells.

Engineering death receptor ligands for cancer therapy

CD95, TNFR1, TRAILR1 and TRAILR2 belong to a subgroup of TNF receptors which is characterized by a conserved cell death-inducing protein domain that connects these receptors to the apoptotic machinery of the cell. Activation of death receptors in malignant cells attracts increasing attention as a principle to fight cancer. Besides agonistic antibodies the major way to stimulate death receptors is the use of their naturally occurring "death ligands" CD95L, TNF and TRAIL. However, dependent from the concept followed to develop a death ligand-based therapy various limiting aspects have to be taken into consideration on the way to a "bedside" usable drug. Problems arise in particular from the cell associated transmembrane nature of the death ligands, the poor serum half life of the soluble fragments derived from the transmembrane ligands, the ubiquitous expression of the death receptors and the existence of additional non-death receptors of the death ligands. Here, we summarize strategies how these limitations can be overcome by genetic engineering.

The role of FasL and Fas in health and disease

The FS7-associated cell surface antigen (Fas, also named CD95, APO-1 or TNFRSF6) attracted considerable interest in the field of apoptosis research since its discovery in 1989. The groups of Shin Yonehara and Peter Krammer were the first reporting extensive apoptotic cell death induction upon treating cells with Fas-specific monoclonal antibodies.1,2 Cloning of Fas3 and its ligand,4,5 FasL (also known as CD178, CD95L or TNFSF6), laid the cornerstone in establishing this receptor-ligand system as a central regulator of apoptosis in mammals. Therapeutic exploitation of FasL-Fas-mediated cytotoxicity was soon an ambitous goal and during the last decade numerous strategies have been developed for its realization. In this chapter, we will briefly introduce essential general aspects of the FasL-Fas system before reviewing its physiological and pathophysiological relevance. Finally, FasL-Fas-related therapeutic tools and concepts will be addressed.

Protection of nonhuman primates against two species of Ebola virus infection with a single complex adenovirus vector

Ebola viruses are highly pathogenic viruses that cause outbreaks of hemorrhagic fever in humans and other primates. To meet the need for a vaccine against the several types of Ebola viruses that cause human diseases, we developed a multivalent vaccine candidate (EBO7) that expresses the glycoproteins of Zaire ebolavirus (ZEBOV) and Sudan ebolavirus (SEBOV) in a single complex adenovirus-based vector (CAdVax). We evaluated our vaccine in nonhuman primates against the parenteral and aerosol routes of lethal challenge. EBO7 vaccine provided protection against both Ebola viruses by either route of infection. Significantly, protection against SEBOV given as an aerosol challenge, which has not previously been shown, could be achieved with a boosting vaccination. These results demonstrate the feasibility of creating a robust, multivalent Ebola virus vaccine that would be effective in the event of a natural virus outbreak or biological threat.

Molecular imaging of biological gene delivery vehicles for targeted cancer therapy: beyond viral vectors

Cancer persists as one of the most devastating diseases in the world. Problems including metastasis and tumor resistance to chemotherapy and radiotherapy have seriously limited the therapeutic effects of present clinical treatments. To overcome these limitations, cancer gene therapy has been developed over the last two decades for a broad spectrum of applications, from gene replacement and knockdown to vaccination, each with different requirements for gene delivery. So far, a number of genes and delivery vectors have been investigated, and significant progress has been made with several gene therapy modalities in clinical trials. Viral vectors and synthetic liposomes have emerged as the vehicles of choice for many applications. However, both have limitations and risks that restrict gene therapy applications, including the complexity of production, limited packaging capacity, and unfavorable immunological features. While continuing to improve these vectors, it is important to investigate other options, particularly nonviral biological agents such as bacteria, bacteriophages, and bacteria-like particles. Recently, many molecular imaging techniques for safe, repeated, and high-resolution in vivo imaging of gene expression have been employed to assess vector-mediated gene expression in living subjects. In this review, molecular imaging techniques for monitoring biological gene delivery vehicles are described, and the specific use of these methods at different steps is illustrated. Linking molecular imaging to gene therapy will eventually help to develop novel gene delivery vehicles for preclinical study and support the development of future human applications.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

Death receptors as targets for anti-cancer therapy

Human tumour cells are characterized by their ability to avoid the normal regulatory mechanisms of cell growth, division and death. The classical chemotherapy aims to kill tumour cells by causing DNA damage-induced apoptosis. However, as many tumour cells possess mutations in intracellular apoptosis-sensing molecules like p53, they are not capable of inducing apoptosis on their own and are therefore resistant to chemotherapy. With the discovery of the death receptors the opportunity arose to directly trigger apoptosis from the outside of tumour cells, thereby circumventing chemotherapeutic resistance. Death receptors belong to the tumour necrosis factor receptor superfamily, with tumour necrosis factor (TNF) receptor-1, CD95 and TNF-related apoptosis-inducing ligand-R1 and -R2 being the most prominent members. This review covers the current knowledge about these four death receptors, summarizes pre-clinical approaches engaging these death receptors in anti-cancer therapy and also gives an overview about their application in clinical trials conducted to date.

Fas-mediated killing of primary prostate cancer cells is increased by mitoxantrone and docetaxel

Therapies for prostate cancer based on Fas (CD95) modulation have been under active development at the preclinical stage using immortalized cell lines. To address clinical applicability, the potential of 11 cultures of primary prostate cancer cells to be killed by Fas-mediated apoptosis was investigated. In addition, the effect of the chemotherapeutic agents mitoxantrone and docetaxel on this killing was determined. Apoptosis was induced in patient-derived, primary prostate cancer cells using effector cells engineered by recombinant lentivirus infection to express Fas ligand (FasL) and measured by 51Cr release assays. All cultured prostate cells were found to undergo Fas-mediated killing; cytotoxicity ranged from 12% to 87% after 6 h. These cells were significantly more sensitive to FasL-mediated killing than PC-3 cells. The basal expression of Fas or the expression of five inhibitors of apoptosis (c-FLIP, survivin, cellular inhibitors of apoptosis protein 1 and 2, and bcl-2) was not found to correlate with susceptibility to Fas-mediated killing. Both mitoxantrone and docetaxel were able to induce Fas receptor expression on primary prostate cancer cells, which translated into a 1.5- to 3-fold enhancement of apoptosis mediated by FasL. Whereas mitoxantrone increased the Fas-induced apoptotic response of all cultured prostate cells tested, docetaxel pretreatment was found to preferentially enhance the killing of bcl-2-expressing cells. These findings show that cultured primary prostate cancer cells are sensitive to Fas-mediated apoptosis. Furthermore, the incidence of apoptosis was found to be improved by combining Fas-mediated therapy with standard chemotherapeutic agents. These findings may have significant implications for prostate cancer therapy.

Vaccine to confer to nonhuman primates complete protection against multistrain Ebola and Marburg virus infections

Filoviruses (Ebola and Marburg viruses) are among the deadliest viruses known to mankind, with mortality rates nearing 90%. These pathogens are highly infectious through contact with infected body fluids and can be easily aerosolized. Additionally, there are currently no licensed vaccines available to prevent filovirus outbreaks. Their high mortality rates and infectious capabilities when aerosolized and the lack of licensed vaccines available to prevent such infectious make Ebola and Marburg viruses serious bioterrorism threats, placing them both on the category A list of bioterrorism agents. Here we describe a panfilovirus vaccine based on a complex adenovirus (CAdVax) technology that expresses multiple antigens from five different filoviruses de novo. Vaccination of nonhuman primates demonstrated 100% protection against infection by two species of Ebola virus and three Marburg virus subtypes, each administered at 1,000 times the lethal dose. This study indicates the feasibility of vaccination against all current filovirus threats in the event of natural hemorrhagic fever outbreak or biological attack.

Rescue and production of vaccine and therapeutic adenovirus vectors expressing inhibitory transgenes

Expression of certain transgenes from an adenovirus vector can be deleterious to its own replication. This can result in the inhibition of virus rescue, reduced viral yields, or, in the worst case, make it impossible to construct a vector expressing the inhibiting transgene product. A gene regulation system based on the tet operon was used to allow the rescue and efficient growth of adenovectors that express transgenes to high levels. A key advantage to this system is that repression of transgene expression is mediated by the packaging cell line, thus, expression of regulatory products from the adenovector are not required. This provides a simple, broadly applicable system wherein transgene repression is constitutive during vector rescue and growth and there is no effect on adenovector-mediated expression of gene products in transduced cells. Several high-level expression vectors based on first- and second-generation adenovectors were rescued and produced to high titer that otherwise could not be grown. Yields of adenovectors expressing inhibitory transgene products were increased, and the overgrowth of cultures by adenovectors with nonfunctional expression cassettes was prevented. The gene regulation system is a significant advancement for the development of adenovirus vectors for vaccine and other gene transfer applications.

Fas Ligand Delivery by a Prostate-Restricted Replicative Adenovirus Enhances Safety and Antitumor Efficacy

PURPOSE

Recent studies showed that Fas ligand (FasL) induced apoptosis in tumor cells and suppressed the immune response in several types of tumors. However, the toxicity of FasL limited further administration. This study delivered FasL in prostate cancer cells using an improved prostate-restricted replicative adenovirus (PRRA), thereby improving the antitumor effect while decreasing systemic toxicity.

EXPERIMENTAL DESIGN

We designed a FasL-armed PRRA, called AdIU3, by placing adenoviral E1a and E4 genes, FasL cDNA, and E1b gene under the control of two individual PSES enhancers. Tissue-specific viral replication and FasL expression were analyzed, and the tumor killing effect of AdIU3 was investigated both in vitro and in vivo using androgen-independent CWR22rv s.c. models via local administration and bone models via systemic administration. The safety of systemic administration of AdIU3 was evaluated. AdCMVFasL, in which FasL was controlled by a universal cytomegalovirus (CMV) promoter, was used as a control.

RESULTS

AdIU3 enhanced FasL expression in prostate-specific antigen (PSA)/prostate-specific membrane antigen (PSMA)-positive cells but not in PSA/PMSA-negative cells. It induced apoptosis and killed PSA/PMSA-positive prostate cancer cells but spared normal human fibroblasts, hepatocytes, and negative cells. The increase in killing activity was confirmed to result in part from a bystander killing effect. Furthermore, AdIU3 was more effective than a plain PRRA in inhibiting the growth of androgen-independent prostate cancer xenografts and bone tumor formation. Importantly, systemic administration of AdIU3 resulted in undetectable toxicity, whereas the same doses of AdCMVFasL killed all mice due to multiviscera failure in 16 h.

CONCLUSIONS

AdIU3 decreased the toxicity of FasL by controlling its expression with PSES, with greatly enhanced prostate cancer antitumor efficacy. The results suggested that toxic antitumor factors can be delivered safely by a PRRA.

Characterization of the RSL1-dependent conditional expression system in LNCaP prostate cancer cells and development of a single vector format

BACKGROUND

Conditional expression systems are useful tools for the study of gene function but the use of these systems in prostate cancer cells is limited by the undesired biological effects of the inducing ligands. The RheoSwitch system employs RheoSwitch Ligand 1 (RSL1), a non-steroidal analog of the insect hormone ecdysone, to activate a modified nuclear receptor heterodimer that controls target gene expression via GAL4 response elements. This system has not been tested in prostate cancer cells.

METHODS

We established LNCaP human prostate cancer cell lines that constitutively express RheoSwitch transcription factors to quantify RSL1-dependent expression and assess the effects of RSL1 on cell proliferation and endogenous gene expression. Potential RSL1-responsive genes were identified using Affymetrix microarrays and validated by Northern blot hybridization. A single-vector format was developed to establish cell lines that conditionally produce a recombinant protein.

RESULTS

Stable cell lines displayed tight and potent (over several orders of magnitude) RSL1-dependent regulation of a transiently transfected luciferase reporter gene. RSL1 did not affect basal or androgen-stimulated cell proliferation and exerted minimal effects on the expression of endogenous genes. Cell lines established using the single-vector system also displayed strictly RSL1-dependent production of the recombinant protein encoded by the stably integrated RSL1-responsive expression cassette.

CONCLUSIONS

The RheoSwitch system is well suited for conditional gene expression in prostate cancer cells. The single-vector format should facilitate the production of stable cell lines. This system should be useful for the study of proteins involved in prostate cancer in both cell and animal models of the disease.

Advances in preclinical investigation of prostate cancer gene therapy

Treating recurrent prostate cancer poses a great challenge to clinicians. Research efforts in the last decade have shown that adenoviral vector-based gene therapy is a promising approach that could expand the arsenal against prostate cancer. This maturing field is at the stage of being able to translate many preclinical discoveries into clinical practices. At this juncture, it is important to highlight the promising strategies including prostate-targeted gene expression, the use of oncolytic vectors, therapy coupled to reporter gene imaging, and combined treatment modalities. In fact, the early stages of clinical investigation employing combined, multimodal gene therapy focused on loco-regional tumor eradication and showed promising results. Clinicians and scientists should seize the momentum of progress to push forward to improve the therapeutic outcome for the patients.

Novel system uses probasin-based promoter, transcriptional silencers and amplification loop to induce high-level prostate expression

Background

Despite several effective treatment options available for prostate cancer, it remains the second leading cause of cancer death in American men. Thus, there is a great need for new treatments to improve outcomes. One such strategy is to eliminate cancer through the expression of cytotoxic genes specifically in prostate cells by gene therapy vectored delivery. To prevent systemic toxicity, tissue- and/or cancer-specific gene expression is required. However, the use of tissue- or cancer-specific promoters to target transgene expression has been hampered by their weak activity.

Results

To address this issue, we have developed a regulation strategy that includes feedback amplification of gene expression along with a differentially suppressible tetracycline regulated expression system (DiSTRES). By differentially suppressing expression of the tetracycline-regulated transcriptional activator (tTA) and silencer (tTS) genes based on the cell origin, this leads to the activation and silencing of the TRE promoter, respectively. In vitro transduction of LNCaP cells with Ad/GFP_DiSTRES lead to GFP expression levels that were over 30-fold higher than Ad/CMV-GFP. Furthermore, Ad/FasL-GFP_DiSTRES demonstrated cytotoxic effects in prostate cancer cells known to be resistant to Fas-mediated apoptosis.

Conclusion

Prostate-specific regulation from the DiSTRES system, therefore, serves as a promising new regulation strategy for future applications in the field of cancer gene therapy and gene therapy as a whole.

Complex adenovirus-vectored vaccine protects guinea pigs from three strains of Marburg virus challenges

The Marburg virus (MARV), an African filovirus closely related to the Ebola virus, causes a deadly hemorrhagic fever in humans, with up to 90% mortality. Currently, treatment of disease is only supportive, and no vaccines are available to prevent spread of MARV infections. In order to address this need, we have developed and characterized a novel recombinant vaccine that utilizes a single complex adenovirus-vectored vaccine (cAdVax) to overexpress a MARV glycoprotein (GP) fusion protein derived from the Musoke and Ci67 strains of MARV. Vaccination with the cAdVaxM(fus) vaccine led to efficient production of MARV-specific antibodies in both mice and guinea pigs. Significantly, guinea pigs vaccinated with at least 5 x 10(7) pfu of cAdVaxM(fus) vaccine were 100% protected against lethal challenges by the Musoke, Ci67 and Ravn strains of MARV, making it a vaccine with trivalent protective efficacy. Therefore, the cAdVaxM(fus) vaccine serves as a promising vaccine candidate to prevent and contain multi-strain infections by MARV.

Combined therapeutic use of AdGFPFasL and small molecule inhibitors of ceramide metabolism in prostate and head and neck cancers: a status report

As of January 2005, there were 1020 gene therapy clinical trials ongoing worldwide with 675 or 66.2% devoted to cancer gene therapy. The majority are occurring in the US and Europe (http://www.wiley.co.uk/genetherapy/clinical/). At the present time, to our knowledge there are no trials that employ gene delivery of Fas Ligand (FasL). As an important note, and in contrast to somatic cell therapy trials, there are no reported deaths due to therapeutic vector administration in any cancer gene therapy trial. That said, from our studies and from the published literature, the issue of gene delivery remains the major obstacle to successfully employing gene therapy for cancer treatment. Numerous laboratories are studying this with many different approaches. My co-workers and I have focused on the delivery issue by using various approaches that address tumor targeting and transgene expression. In addition, we are focusing on enhancing tumor cell killing via the bystander effect and through use of small molecules to enhance bystander activity.

Eukaryotic expression vectors and immunoconjugates for cancer therapy

This review considers ways to address specificity to therapeutic targeted anticancer agents. These include transcriptional activation of tissue- and tumor-specific promoters in eukaryotic expression vectors and use of antitumor-directed immunoconjugates. The review deals with analysis of strategies used for selection of targeted promoters and examples of antibody fusion proteins exhibiting antitumor activity. A new direction in antitumor treatment pooling together methods of gene therapy and antibody therapy has appeared. This direction is based on the development of vectors encoding secreted forms of immunoconjugates. After vector introduction into a cell, the latter is capable of synthesizing and secreting antibody fusion protein composed of a therapeutic anticancer agent and antibody specifically targeted to cancer cells.

Development of a cAdVax-based bivalent ebola virus vaccine that induces immune responses against both the Sudan and Zaire species of Ebola virus

Ebola virus (EBOV) causes a severe hemorrhagic fever for which there are currently no vaccines or effective treatments. While lethal human outbreaks have so far been restricted to sub-Saharan Africa, the potential exploitation of EBOV as a biological weapon cannot be ignored. Two species of EBOV, Sudan ebolavirus (SEBOV) and Zaire ebolavirus (ZEBOV), have been responsible for all of the deadly human outbreaks resulting from this virus. Therefore, it is important to develop a vaccine that can prevent infection by both lethal species. Here, we describe the bivalent cAdVaxE(GPs/z) vaccine, which includes the SEBOV glycoprotein (GP) and ZEBOV GP genes together in a single complex adenovirus-based vaccine (cAdVax) vector. Vaccination of mice with the bivalent cAdVaxE(GPs/z) vaccine led to efficient induction of EBOV-specific antibody and cell-mediated immune responses to both species of EBOV. In addition, the cAdVax technology demonstrated induction of a 100% protective immune response in mice, as all vaccinated C57BL/6 and BALB/c mice survived challenge with a lethal dose of ZEBOV (30,000 times the 50% lethal dose). This study demonstrates the potential efficacy of a bivalent EBOV vaccine based on a cAdVax vaccine vector design.

CD95L/FasL and TRAIL in tumour surveillance and cancer therapy

The membrane-bound death ligands CD95L/FasL and TRAIL, which activate the corresponding death receptors CD95/Fas, TRAILR1 and TRAILR2, induce apoptosis in many tumour cells, but can also elicit an inflammatory response. This chapter focuses on the relevance of CD95L/FasL and TRAIL for the tumour surveillance function of natural killer cells and cytotoxic T-cells and discuss current concepts of utilizing these ligands in tumour therapy.

Development of a murine prostatespecific 2-in-1 inducible bicistronic expression vector

Transgenic research often suffers from the lack of strong tissue specific promoters and the lack of suitable antibodies for transgene detection. We have now constructed a novel prostate specific 2-in-1 Tetracycline-off (Tet-off), bicistronic expression vector, designated PbTetOIE, for transgenic research. The vector allows potent induction as well as inducible suppression of transgene expression in the prostate epithelial cells, and also allows the detection of transgene expression at the cellular level through the detection of the internal enhanced green fluorescent protein (EGFP) downstream of the transgene.

Targeting proliferating tumor cells via the transcriptional control of therapeutic genes

We have previously reported the construction of a cell cycle-regulated HSV-1 amplicon vector (denoted as pC8-36) that confers luciferase reporter gene activities dependent on cellular divisions. However, luciferase reporter gene is well known for its relatively high sensitivity, thus, it is crucial to evaluate the therapeutic efficacy of a transcriptional targeted vector. In this report, we have engineered the FasL and FADD genes into pC8-36 and demonstrated their efficacy for the treatment of human gliomas in vitro and in vivo. Using trypan blue dye exclusion and TUNEL assay, FasL expression mediated by pC8-36 was shown to induce a significantly higher percentage of cell death in proliferating cells than those observed in the G(1)-arrested cells. The observed cell killing effect correlated well with the level of FasL protein expression when analyzed by ELISA assay. Furthermore, the incorporation of both FasL and FADD into pC8-36 resulted in the enhancement of apoptosis in the target glioma cells both in vitro and in vivo. Targeting proliferating tumor cells via the transcriptional control of therapeutic genes could potentially improve the safety and efficacy of cancer gene therapy, and thus would allow the development of strategies for more effective anticancer therapies.

Adenovirus-mediated FasL gene transfer into human gastric carcinoma

AIM: To evaluate the possible value of FasL in gastric cancer gene therapy by investigating the effects of FasL expression on human gastric cancer cell line.

METHODS: An adenoviral vector encoding the full-length human FasL cDNA was constructed and used to infect a human gastric cancer (SGC-7901) cell line. FasL expression was confirmed by X-gal staining, flow cytometric analysis and RT-PCR. The effect of FasL on cell proliferation was determined by clonogenic assay, cytotoxicity was detected by MTT assay, and cell viability was measured by trypan blue exclusion. The therapeutic efficiency of Ad-FasL in vivo was investigated with a xenograft tumor model in nude mice.

RESULTS: SGC-7901 cells infected with Ad-FasL showed increased expression of FasL, resulting in significantly decreased cell growth and colony-forming activity when compared with control adenovirus-infected cells. The cytotoxicity of anti-Fas antibody (CH-11) in gastric cancer cells was stronger than that of ActD (91±8 vs 60±5, P<0.01), and the cytotoxicity of Ad-FasL was stronger than that of CH-11 (60±5 vs 50±2, P<0.05). In addition, G₁-phase arrest (67.75±0.39 vs 58.03±2.16, P<0.05) and apoptosis were observed in Ad-FasL-infected SGC-7901 cells, and the growth of SGC-7901 xenografts in nude mice was retarded after intra-tumoral injection with Ad-FasL (54% vs 0%, P<0.0001).

CONCLUSION: Infection of human gastric carcinoma cells with Ad-FasL induces apoptosis, indicating that this target gene might be of potential value in gene therapy for gastric cancer.

Direct comparison of the insulating properties of two genetic elements in an adenoviral vector containing two different expression cassettes

Targeted gene expression can be achieved through the use of cell-selective promoters. However, when the expression cassette is delivered by an adenovirus, "promoter interference," resulting in the loss of specificity, has been reported. To overcome this problem, insulator elements (the bovine growth hormone transcription stop signal or HS4 chromatin insulators of the chicken beta-globin locus) have been used. The present study examines the efficacy of these insulators elements, when two independent expression cassettes (one in which a strong, ubiquitous promoter drives the expression of the green fluorescent protein and another in which the "cancer-selective" ERBB2 promoter drives the expression of the herpes simplex virus thymidine kinase [HSVtk] gene) are incorporated into the same recombinant adenovirus. As expected, the presence of either insulator does not alter the expression of HSVtk in ERBB2-positive cells, measured through sensitization of the cells to ganciclovir. When ERBB2-negative cells were infected at a multiplicity of infection (MOI) of 10, the uninsulated virus sensitized ERBB2-negative cells to the same extent as it did for ERBB2-positive cells; partial sensitization was observed when transcriptional terminators were used, indicating a partial insulating effect; and complete insulation (no sensitization to ganciclovir) was observed when HS4 chromatin insulators were used. However, this complete insulation was lost when the MOI of virus was increased to 100. Our study demonstrates the possibility of insulating a conditionally expressed transgene in the vicinity of another expression cassette, but this insulating effect is lost when the multiplicity of infection is increased.

The present and future for gene and viral therapy of directly accessible prostate and squamous cell cancers of the head and neck

Gene therapy has been in a continuous evolutionary process since the first approved trial occurred in 1990 at the National Institute of Health. In the USA, as of March 2004, there were 619 approved gene therapy/transfer protocols and 405 of these were for cancer treatment. Another 294 trials are in progress worldwide, with most concentrated in Europe. However, cancer gene therapy is in its relative infancy when compared with the well-established use of chemo-radiotherapy for treating cancer. As the field develops it is becoming clear that using gene therapy in conjunction with established chemo-radiotherapy approaches is yielding the best results. This concept shall be reviewed in the context of the status of the field, and a future direction based on a combination of gene therapy with small molecule modification of sphingolipid metabolism shall be discussed.

Highly specific transgene expression mediated by a complex adenovirus vector incorporating a prostate-specific amplification feedback loop

Development of novel therapeutic agents is needed to address the problems of locally recurrent, metastatic, and advanced hormone-refractory prostate cancer. We have constructed a novel complex adenovirus (Ad) vector regulation system that incorporates both the prostate-specific ARR2PB promoter and a positive feedback loop using the TRE promoter to enhance gene expression. This regulation strategy involves the incorporation of the TRE upstream of the prostate-specific ARR2PB promoter to enhance its activity with Tet regulation. The expressions of both GFP and tTA were placed under the control of these TRE-ARR2PB promoters, so that in the cells of prostate origin a positive feedback loop would be generated. This design greatly enhanced GFP reporter expression in prostate cancer cells, while retaining tight control of expression in nonprostate cancer cells, even at an MOI as high as 1000. This novel positive feedback loop with prostate specificity (PFLPS) regulation system we have developed may have broad applications for expressing not only high levels of toxic proteins in cancer cells, but alternatively could also be manipulated to regulate essential genes in a highly efficient conditionally replicative adenovirus vector specifically directed to prostate cancer cells. The PFLPS regulation system, therefore, serves as a promising new approach in the development of both a specific and effective vector for cancer gene therapy.

Enhanced apoptosis of glioma cell lines is achieved by co-delivering FasL-GFP and TRAIL with a complex Ad5 vector

Brain tumors (BTs) are among the most malignant forms of human cancer. Unfortunately, current treatments are often ineffective and produce severe side effects. Cytotoxic gene therapy is an alternative treatment strategy, with the potential advantages of reduced toxicity to normal brain tissue. Apoptosis-inducing "death ligands" Fas ligand and TNF-related apoptosis-inducing ligand (TRAIL) are genes with substantial cytotoxic activity in susceptible tumor cells. Here, we compared the effectiveness of Ad vector-mediated delivery of Fas ligand-green fluorescent protein (FasL-GFP) fusion protein, human TRAIL, and both genes simultaneously. We examined a panel of 13 cell lines (eight derived from primary isolates) for susceptibility to Ad5-based vector infection and for sensitivity to FasL- and TRAIL-mediated apoptosis. All cell lines were efficiently transduced, but, as expected, varied in their sensitivity to ligand-induced apoptosis. Generally, sensitivity to FasL-GFP correlated with cell surface FasR levels, but no such correlation was seen for TRAIL and its functional receptors, DR4 and DR5. The vector expressing both FasL-GFP and TRAIL was more effective than either of the single-gene vectors at comparable transduction levels, and it was effective against a broader range of cell lines. In five cell lines, coexpression resulted in apoptosis levels greater than those predicted for strictly additive activity of the two death ligands. We believe that Ad vector-mediated delivery of multiple death ligands may be developed as a potential BT therapy, either alone or in conjunction with surgical resection of the primary tumor.

Optimization of the Tet-on system to regulate interleukin 12 expression in the liver for the treatment of hepatic tumors

Interleukin 12 (IL-12) is a potent antitumoral cytokine, but it can be toxic at high doses. Therapy of liver tumors might benefit from the use of vectors enabling tight control of IL-12 expression in hepatic tissue for long periods of time. To this aim, we have improved the Tet-on system by modifying the minimal region of the inducible promoter and adjusting the level of the trans-activator using liver-specific promoters with graded activities. The resulting vectors allowed hepato-specific gene regulation with lower basal activity and higher inducibility compared with the original system in the absence of repressor molecules. The basal and final protein levels depend on the strength of the promoter that directs the transcripcional activator as well as the relative orientation of the two genes in the same plasmid. We have selected the construct combining minimal leakage with higher level of induced gene expression to regulate IL-12 after DNA transfer to mouse liver. Administration of doxycycline (Dox) enhanced IL-12 expression in a dose-dependent manner, whereas it was undetectable in serum in the noninduced state. Gene activation could be repeated several times, and sustained levels of IL-12 were achieved by daily administration of Dox. The antitumor effect of IL-12 was evaluated in a mouse model of metastatic colon cancer to the liver. Complete eradication of liver metastasis and prolonged survival was observed in all mice receiving Dox for 10 days. These data demonstrate the potential of a naked DNA gene therapy strategy to achieve tight control of IL-12 within the liver for the treatment of cancer.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.

Optical imaging: bacteria, viruses, and mammalian cells encoding light-emitting proteins reveal the locations of primary tumors and metastases in animals

Early detection of tumors and their metastases is crucial for the prognosis of cancer treatment. Traditionally, tumor detection is achieved by various methods, including magnetic resonance imaging and computerized tomography. With the recent cloning, cellular expression, and real-time imaging of light-emitting proteins, such as Renilla luciferase (Ruc), bacterial luciferase (Lux), firefly luciferase (Luc), green fluorescent protein (GFP), or Ruc-GFP fusion protein, significant efforts have been focused on using these marker proteins for tumor detection. It has also been demonstrated that certain bacteria, viruses, and mammalian cells (BVMC), when administered systemically, are able to gain entry and replicate selectively in tumors. In addition, many tissue/tumor specific promoters have been cloned which allow transgene expression specifically in tumor tissues. Therefore, when light-emitting protein encoded BVMC are injected systemically into rodents, tumor-specific marker gene expression is achieved and is detected in real time based on light emission. Consequently, the locations of primary tumors and previously unknown metastases in animals are revealed in vivo. In the future it will likely be feasible to use engineered light-emitting BVMC as probes for tumor detection and as gene-delivery vehicles in vivo for cancer therapy.

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.

Quantification and characterization of the bystander effect in prostate cancer cells following adenovirus-mediated FasL expression

Inducing Fas-mediated apoptosis in prostate cancer (PCa) is a promising new therapeutic approach with the potential to overcome delivery issues currently problematic in cancer gene therapy. We have previously demonstrated that a Fas Ligand (FasL) expressing adenovirus (AdGFPFasL(TET)) was able to induce Fas-mediated apoptosis in a panel of PCa cell lines regardless of their Fas-sensitivity as determined by the agonistic Fas antibody CH-11. We now report that AdGFPFasL(TET)-infected cells produce apoptotic bodies and cellular debris that continues to elicit FasL-mediated bystander killing in uninfected neighboring cells. Using light microscopy, we demonstrate that AdGFPFasL(TET)-infected cells release apoptotic bodies and cellular debris into the local environment and that this material will induce bystander killing in Jurkat, PPC-1, and PC-3 target cells, but not in DU145 and K-562 cells. The bystander killing mechanism is mediated through Fas/FasL interaction because it is significantly inhibited if target cells are pretreated with the pan spectrum caspase inhibitor Z-VAD-FMK or the Fas neutralizing antibody ZB-4. Coincubation of PPC-1 target cells with apoptotic bodies and cellular debris (effector material) induce nearly complete target cell killing at a ratio of 1:1 target to effector. Collectively, these data indicate that AdGFPFasL(TET)-infected PCa cells release apoptotic and cellular debris capable of inducing bystander killing in PCa and supports the development of FasL as a gene therapy agent.

Nonviral genetic transfer of Fas ligand induced significant growth suppression and apoptotic tumor cell death in prostate cancer in vivo

To accomplish efficient nonviral gene therapy against prostate cancer (PC), Epstein-Barr virus (EBV)-based plasmid vectors containing EBNA1 gene and oriP were employed and combined with a cationic polymer or cationic lipid. When EBV-plasmid/poly-amidoamine dendrimer complex was injected into PC-3-derived tumors established in severe combined immunodeficiency mice, a considerable expression of marker gene was obtained in the tumors, and the expression level was more than eight-fold higher than that achieved by conventional plasmid vector/dendrimer. Since most PC cells express the apoptotic signal molecule Fas (Apo-1/CD95) on their surface, Fas ligand (FasL) gene was transferred into PC cells to kill the tumor cells. In vitro transfection with pGEG.FasL (an EBV-plasmid with the FasL gene) significantly reduced the viability of PC cells, which subsequently underwent apoptosis. Intratumoral injections of pGEG.FasL into PC induced significant growth suppression of the xenograft tumors, in which typical characteristics of apoptosis were demonstrated by TUNEL staining and electron microscopic observations. When pGEG.FasL transfer was accompanied by systemic administrations of cisplatin, the tumors were inhibited even more remarkably, leading to prolonged survival of the animals. FasL gene transfection by means of EBV-based plasmid/cationic macromolecule complexes may provide a practical therapeutic strategy against PC.

Transcription initiation activity of adenovirus left-end sequence in adenovirus vectors with e1 deleted

We analyzed the transcription initiation activity of the left-end sequence (first 342 bp) of the adenovirus genome in the context of an adenovirus vector with E1 deleted in in vitro and in vivo gene transfer models. While nucleotide sequences 1 to 190 and 1 to 342 showed strong activity in three out of three lung cancer cell lines, nucleotide sequence 1 to 103 showed limited activity in H358, cells which show characteristics of type 2 alveolar cells. In vivo, the transcription initiation activities of nucleotide sequence 1 to 103 in the liver and the lung were minimal, while nucleotide sequences 1 to 190 and 1 to 342 showed strong activity comparable to that of the cytomegalovirus promoter. Further understanding of the transcription initiation activity of the left-end sequence of the adenovirus genome should lead to optimization of adenovirus vectors.

Tumor growth inhibition by interferon-alpha using PEGylated protein or adenovirus gene transfer with constitutive or regulated expression

Inducible synthesis and secretion of therapeutic proteins following gene transfer could be a viable strategy to deliver biopharmaceuticals that currently require parenteral administration. Evaluating the protein pharmacokinetics and biological responses generated by different delivery modalities will provide a better understanding of the advantages and disadvantages of each strategy. The interferon-alpha (IFN-alpha) family of proteins, used clinically for infectious and malignant diseases, has a short half-life, and IFN-alpha therapy requires frequent administration of the drug by injection. Subcutaneous xenograft tumors were inhibited by weekly administration of polyethylene glycol modified (PEGylated) IFN-alpha protein or by a single administration of an adenovirus constitutively expressing IFN-alpha (IACB). Both treatment modalities inhibited tumor growth in a dose-dependent manner, suggesting that increasing exposure to IFN-alpha could result in effective tumor control. A single adenovirus that encodes the components necessary for tetracycline induction (IADR) expressed IFN-alpha in a ligand-dependent manner. Adding doxycycline to the drinking water of mice treated intravenously with the inducible adenovirus IADR inhibited tumor growth by 85% compared with mice that were not given doxycycline. The correlation between serum IFN-alpha concentration and the degree of tumor growth inhibition did not depend on the delivery technology used. It is likely that it will be feasible to control expression of IFN-alpha by oral administration of small molecule drugs after gene delivery to induce therapeutic concentrations of proteins.