Adenovirus-mediated p53 gene therapy for human gliomas

Against the Resilience of High-Grade Gliomas: Gene Therapies (Part II)

Introduction: High-grade gliomas (HGGs) still have a high rate of recurrence and lethality. Gene therapies were projected to overcome the therapeutic resilience of HGGs, due to the intrinsic genetic heterogenicity and immune evasion pathways. The present literature review strives to provide an updated overview of the novel gene therapies for HGGs treatment, highlighting evidence from clinical trials, molecular mechanisms, and future perspectives. Methods: An extensive literature review was conducted through PubMed/Medline and ClinicalTrials.gov databases, using the keywords “high-grade glioma,” “glioblastoma,” and “malignant brain tumor”, combined with “gene therapy,” “oncolytic viruses,” “suicide gene therapies,” “tumor suppressor genes,” “immunomodulatory genes,” and “gene target therapies”. Only articles in English and published in the last 15 years were chosen, further screened based on best relevance. Data were analyzed and described according to the PRISMA guidelines. Results: Viruses were the most vehicles employed for their feasibility and transduction efficiency. Apart from liposomes, other viral vehicles remain largely still experimental. Oncolytic viruses and suicide gene therapies proved great results in phase I, II preclinical, and clinical trials. Tumor suppressor, immunomodulatory, and target genes were widely tested, showing encouraging results especially for recurrent HGGs. Conclusions: Oncolytic virotherapy and suicide genes strategies are valuable second-line treatment options for relapsing HGGs. Immunomodulatory approaches, tumor suppressor, and target genes therapies may implement and upgrade standard chemoradiotherapy. Future research aims to improve safety profile and prolonging therapeutic effectiveness. Further clinical trials are needed to assess the efficacy of gene-based therapies.

Current Approaches for Glioma Gene Therapy and Virotherapy

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in the adult population and it carries a dismal prognosis. Inefficient drug delivery across the blood brain barrier (BBB), an immunosuppressive tumor microenvironment (TME) and development of drug resistance are key barriers to successful glioma treatment. Since gliomas occur through sequential acquisition of genetic alterations, gene therapy, which enables to modification of the genetic make-up of target cells, appears to be a promising approach to overcome the obstacles encountered by current therapeutic strategies. Gene therapy is a rapidly evolving field with the ultimate goal of achieving specific delivery of therapeutic molecules using either viral or non-viral delivery vehicles. Gene therapy can also be used to enhance immune responses to tumor antigens, reprogram the TME aiming at blocking glioma-mediated immunosuppression and normalize angiogenesis. Nano-particles-mediated gene therapy is currently being developed to overcome the BBB for glioma treatment. Another approach to enhance the anti-glioma efficacy is the implementation of viro-immunotherapy using oncolytic viruses, which are immunogenic. Oncolytic viruses kill tumor cells due to cancer cell-specific viral replication, and can also initiate an anti-tumor immunity. However, concerns still remain related to off target effects, and therapeutic and transduction efficiency. In this review, we describe the rationale and strategies as well as advantages and disadvantages of current gene therapy approaches against gliomas in clinical and preclinical studies. This includes different delivery systems comprising of viral, and non-viral delivery platforms along with suicide/prodrug, oncolytic, cytokine, and tumor suppressor-mediated gene therapy approaches. In addition, advances in glioma treatment through BBB-disruptive gene therapy and anti-EGFRvIII/VEGFR gene therapy are also discussed. Finally, we discuss the results of gene therapy-mediated human clinical trials for gliomas. In summary, we highlight the progress, prospects and remaining challenges of gene therapies aiming at broadening our understanding and highlighting the therapeutic arsenal for GBM.

Gene therapies for high-grade gliomas: from the bench to the bedside

Background:

Gene therapy is the most attractive therapeutic approach against high-grade gliomas (HGGs). This is because of its theoretical capability to rework gene makeup in order to yield oncolytic effects. However, some factors still limit the upgrade of these therapies at a clinical level of evidence. We report an overview of glioblastoma gene therapies, mainly focused on the rationale, classification, advances and translational challenges.

Methods:

An extensive review of the online literature on gene therapy for HGGs was carried out. The PubMed/MEDLINE and ClinicalTrials.gov websites were the main sources. Articles in English published in the last five years were sorted according to the best match with the multiple relevant keywords chosen. A descriptive analysis of the clinical trials was also reported.

Results:

A total of 85 articles and 45 clinical trials were selected. The main types of gene therapies are the suicide gene, tumor suppressor gene, immunomodulatory gene and oncolytic therapies (virotherapies). The transfer of genetic material entails replication-deficient and replication-competent oncolytic viruses and nanoparticles, such as liposomes and cationic polymers, each of them having advantages and drawbacks. Forty-eight clinical trials were collected, mostly phase I/II.

Conclusion:

Gene therapies constitute a promising approach against HGGs. The selection of new and more effective target genes, the implementation of gene-delivery vectors capable of greater and safer spreading capacity, and the optimization of the administration routes constitute the main translational challenges of this approach. (www.actabiomedica.it)

Glioblastoma Treatment Modalities besides Surgery

Glioblastoma multiforme (GBM) is commonly known as the most aggressive primary CNS tumor in adults. The mean survival of it is 14 to 15 months, following the standard therapy from surgery, chemotherapy, to radiotherapy. Efforts in recent decades have brought many novel therapies to light, however, with limitations. In this paper, authors reviewed current treatments for GBM besides surgery. In the past decades, only radiotherapy, temozolomide (TMZ), and tumor treating field (TTF) were approved by FDA. Though promising in preclinical experiments, therapeutic effects of other novel treatments including BNCT, anti-angiogenic therapy, immunotherapy, epigenetic therapy, oncolytic virus therapy, and gene therapy are still either uncertain or discouraging in clinical results. In this review, we went through current clinical trials, underlying causes, and future therapy designs to present neurosurgeons and researchers a sketch of this field.

p53 Plays a Key Role in the Apoptosis of Human Ovarian Cancer Cells Induced by Adenovirus-Mediated CRM197

Cross-reacting material 197 (CRM197) is a mutant form of the diphtheria toxin. Recent studies have found that CRM197 exerts an experimental antitumor effect on several types of tumors. This study applied a novel treatment of adenovirus-mediated CRM197 (AdCRM197) to human ovarian cancer cells. Interestingly, it was found that A2780 cells were sensitive to AdCRM197, but SKOV3 cells were resistant to it. Since SKOV3 cells are p53 deletion cells, while A2780 cells are p53 wild-type cells, it was postulated that p53 might play a key role in AdCRM197-induced apoptosis. This presumption was demonstrated by means of knockdown of p53 of the A2780 cells through lentivirus-mediated RNA interference. This knockdown resulted in the A2780 cells becoming resistant to AdCRM197. To verify this presumption further, the wild-type p53 gene in the SKOV3 cells was replaced with adenovirus-mediated p53 (Adp53). As expected, AdCRM197 plus Adp53 resulted in apoptosis of the SKOV3 cells. The combined treatment of AdCRM197 plus Adp53 also showed a good antitumor effect in the in vivo experiment on nude mice with xenograft tumors. Taking these results together, it is concluded that AdCRM197 induces apoptosis of human ovarian cancer cells via the p53 pathway. Moreover, it was found that Adp53 can reverse the resistance of p53-deletion human ovarian cancer cells to AdCRM197. The combination of AdCRM197 and Adp53 may be a potentially effective method for overcoming the resistance of p53-deficient human ovarian cancer to AdCRM197.

New perspective on targeting the tumor suppressor p53 pathway in the tumor microenvironment to enhance the efficacy of immunotherapy

About 50% of human cancers harbor somatic mutations of the tumor suppressor p53 (p53 or Trp53) gene. Many of those mutations result in the inactivation of the p53 pathway and are often associated with the stabilization and accumulation of mutant p53 proteins. Therefore, increased p53 expression in tumors is frequently used as a surrogate marker for p53 mutation and inactivation. Moreover, this elevated p53 expression also makes it an ideal tumor associated antigen (TAA) for cancer vaccines. Recent advances in our understanding of p53 as a crucial transcription factor reveal that p53 is an important sensor of cellular stress under genotoxic, chemotoxic, pathological, and even normal physiological conditions. Experimental and clinical observations by our laboratory and others have demonstrated that p53 also participates in immune regulation as p53 dysfunction skews host immune responses towards pro-inflammation, which further promotes tumor progression. Furthermore, recent studies using a genetic approach revealed that p53-restoration or re-activation led to tumor regression and clearance, which were at least partially caused by the activation of innate antitumor immunity. Since many of the currently used cancer therapeutics, including radiotherapy and chemotherapy, disrupt tumor growth by inducing DNA damage via genotoxic or chemotoxic stress, which activates the p53 pathway in the tumor microenvironment, we postulate that some of those observed therapeutic benefits might also be partially mediated through their immune stimulatory effects. Here, we briefly review our current understanding of the potential cellular and molecular mechanisms by which p53 participates in immune regulation and, subsequently, extend our discussion to the immunostimulatory potential of existing and new approaches of targeting the p53-pathway to alter the immunological landscape of tumors for maximizing immunotherapy outcome.

Gene therapy for malignant glioma

Glioblastoma multiforme (GBM) is the most frequent and devastating primary brain tumor in adults. Despite current treatment modalities, such as surgical resection followed by chemotherapy and radiotherapy, only modest improvements in median survival have been achieved. Frequent recurrence and invasiveness of GBM are likely due to the resistance of glioma stem cells to conventional treatments; therefore, novel alternative treatment strategies are desperately needed. Recent advancements in molecular biology and gene technology have provided attractive novel treatment possibilities for patients with GBM. Gene therapy is defined as a technology that aims to modify the genetic complement of cells to obtain therapeutic benefit. To date, gene therapy for the treatment of GBM has demonstrated anti-tumor efficacy in pre-clinical studies and promising safety profiles in clinical studies. However, while this approach is obviously promising, concerns still exist regarding issues associated with transduction efficiency, viral delivery, the pathologic response of the brain, and treatment efficacy. Tumor development and progression involve alterations in a wide spectrum of genes, therefore a variety of gene therapy approaches for GBM have been proposed. Improved viral vectors are being evaluated, and the potential use of gene therapy alone or in synergy with other treatments against GBM are being studied. In this review, we will discuss the most commonly studied gene therapy approaches for the treatment of GBM in preclinical and clinical studies including: prodrug/suicide gene therapy; oncolytic gene therapy; cytokine mediated gene therapy; and tumor suppressor gene therapy. In addition, we review the principles and mechanisms of current gene therapy strategies as well as advantages and disadvantages of each.

Advances in adenovirus-mediated p53 cancer gene therapy

INTRODUCTION

The tumor suppressor p53 gene regulates diverse cellular processes, such as cell-cycle arrest, senescence, apoptosis and autophagy, and it is frequently inactivated by genetic alterations in ∼ 50% of all types of human cancers. To restore wild-type p53 function in p53-inactivated tumors, adenovirus-mediated p53 gene therapy has been developed as a promising antitumor strategy in preclinical experiments and clinical studies.

AREAS COVERED

This review focuses on the clinical relevance of replication-deficient adenovirus vectors that carry the wild-type p53 gene (Ad-p53; Advexin, Gendicine and SCH-58500) in clinical studies of patients with various cancers and the future perspectives regarding conditionally replicating adenovirus vectors expressing the wild-type p53 gene (CRAd-p53; AdDelta24-p53, SG600-p53, OBP-702) in preclinical experiments. Moreover, the recent advances in our understanding of the molecular basis for the p53-mediated tumor suppression network induced by Ad-p53 and CRAd-p53 vectors and the combination therapies for promoting the therapeutic potential of adenovirus-mediated p53 gene therapy are discussed.

EXPERT OPINION

Exploration of the molecular mechanism underlying the p53-mediated tumor suppression network and the effective strategy for enhancing the p53-mediated cell death signaling pathway would provide novel insights into the improvement of clinical outcome in p53-based cancer gene therapy.

Strategies in gene therapy for glioblastoma

Glioblastoma (GBM) is the most aggressive form of brain cancer, with a dismal prognosis and extremely low percentage of survivors. Novel therapies are in dire need to improve the clinical management of these tumors and extend patient survival. Genetic therapies for GBM have been postulated and attempted for the past twenty years, with variable degrees of success in pre-clinical models and clinical trials. Here we review the most common approaches to treat GBM by gene therapy, including strategies to deliver tumor-suppressor genes, suicide genes, immunomodulatory cytokines to improve immune response, and conditionally-replicating oncolytic viruses. The review focuses on the strategies used for gene delivery, including the most common and widely used vehicles (i.e., replicating and non-replicating viruses) as well as novel therapeutic approaches such as stem cell-mediated therapy and nanotechnologies used for gene delivery. We present an overview of these strategies, their targets, different advantages, and challenges for success. Finally, we discuss the potential of gene therapy-based strategies to effectively attack such a complex genetic target as GBM, alone or in combination with conventional therapy.

Targeting the p53 signaling pathway in cancer therapy - the promises, challenges and perils

INTRODUCTION

Research over the past three decades has identified p53 as a multi-functional transcription factor. p53 influences myriad, highly diverse cellular processes, and represents one of the most important and extensively studied tumor suppressors. Activated by various stresses, p53 blocks cancer progression by provoking transient or permanent growth arrest, by enabling DNA repair, or by advancing cellular death programs. This anti-cancer activity profile, together with genomic and mutational analyses documenting inactivation of p53 in more than 50% of human cancers, motivated drug development efforts to (re-) activate p53 in established tumors.

AREAS COVERED

The complexities of p53 signaling in cancer are summarized, including current strategies and challenges to restore p53's tumor suppressive function in established tumors, to inactivate p53 inhibitors, and to restore wild type function of p53 mutant proteins.

EXPERT OPINION

p53 represents an attractive target for the development of anti-cancer therapies. Whether p53 is 'druggable', however, remains an area of active research and discussion, as p53 has pro-survival functions and chronic p53 activation accelerates aging, which may compromise the long-term homeostasis of an organism. The complex biology and dual functions of p53 in cancer prevention and age-related cellular responses pose significant challenges to the development of p53-targeting cancer therapies.

Experimental approaches for the treatment of malignant gliomas

Malignant gliomas, which include glioblastomas and anaplastic astrocytomas, are the most common primary tumors of the brain. Over the past 30 years, the standard treatment for these tumors has evolved to include maximal safe surgical resection, radiation therapy and temozolomide chemotherapy. While the median survival of patients with glioblastomas has improved from 6 months to 14.6 months, these tumors continue to be lethal for the vast majority of patients. There has, however, been recent substantial progress in our mechanistic understanding of tumor development and growth. The translation of these genetic, epigenetic and biochemical findings into therapies that have been tested in clinical trials is the subject of this review.

Adenoviral virotherapy for malignant brain tumors

Glioblastoma multiforme is the most common form of primary brain cancer. In the past decade, virotherapy of tumors has gained credence, particularly in glioma management, as these tumors are not completely resectable and tend to micro-metastasize. Adenoviral vectors have an advantage over other viral vectors in that they are relatively non-toxic and do not integrate in the genome. However, the lack of coxsackie and adenovirus receptors on surface of gliomas provides for inefficient transduction of wild-type adenoviral vectors in these tumors. By targeting receptors that are overexpressed in gliomas, modified adenoviral constructs have been shown to efficiently infect glioma cells. In addition, by taking advantage of tumor-specific promoter elements, oncolytic adenoviral vectors offer the promise of selective tumor-specific replication. This dual targeting strategy has enabled specificity in both laboratory and pre-clinical settings. This review examines current trends in adenoviral virotherapy of gliomas, with an emphasis on targeting modalities and future clinical applications.

Antitumor effect of humanized anti–interleukin-6 receptor antibody (tocilizumab) on glioma cell proliferation

Object

Interleukin-6 (IL-6) is a pleiotropic cytokine that regulates diverse physiological functions, including cell proliferation and survival. Recent studies have shown that IL-6 expression is often elevated in response to several types of glioma. Although IL-6 is said to play an important role in glioma, the involvement of IL-6 signaling has been quite controversial. The aim of this study was to evaluate the involvement of IL-6 signaling in glioma and the inhibitory effect of IL-6 signaling on glioma tumor proliferation.

Methods

The expression of IL-6 receptors (IL-6Rs) was evaluated in glioma tissues by means of immunohistochemical analysis, and the involvement of IL-6 signaling in glioblastoma multiforme (GBM) U87MG cell proliferation was also determined. In addition, to examine the inhibitory effect of IL-6 signaling on glioma cell proliferation, the authors investigated the effects of tocilizumab, the humanized anti–human IL-6R antibody in U87MG cells.

Results

Increased immunoreactivity for IL-6R was predominantly found in the cytoplasm of endothelial cells in all GBM samples. Inhibition of IL-6 signaling by both IL-6– and IL-6R–specific small interfering RNA and AG490, a specific inhibitor of JAK2 phosphorylation, suppressed glioma cell proliferation. Furthermore, tocilizumab, a clinically developed humanized anti–human IL-6R antibody, exerted an antiproliferative effect on cells from the GBM cell line U87MG via the IL-6R–dependent JAK-STAT3 pathway.

Conclusions

The IL-6 signaling pathway plays an important role in glioma cell proliferation, and tocilizumab exerts an antitumor effect in U87MG glioma cells. These results may bring new insight into the molecular pathogenesis of glioma and may lead to a new therapeutic intervention.

Adenovirus mediated transfer of p53, GM-CSF and B7-1 suppresses growth and enhances immunogenicity of glioma cells

OBJECTIVES

Malignant gliomas are good targets for gene therapy because they have been proven incurable with conventional treatments. However, malignant gliomas are genetically and physiologically highly heterogeneous, and current gene therapy interventions have been designed to target only a few variations of this kind of disease. Hence, we developed a combined gene therapy approach using a recombinant adenovirus carrying human wild-type p53 (WT-p53), granulocyte-macrophage colony-stimulating factor (GM-CSF) and B7-1 genes (designated BB-102) to combat the disease.

METHODS

Human malignant glioma cells U251 and U87 were transduced with BB-102. Expression of WT-p53, GM-CSF and B7-1 genes were determined by Western blot, enzyme linked immunosorbent assay and flow cytometric analysis, respectively. Growth rates were determined by serial cell counts. Apoptosis was detected by flow cytometric analysis. Proliferation of autologous peripheral blood lymphocytes (PBLs) and cytotoxicity against primary glioma cells were assessed by cell proliferation and cytotoxicity assay kits, respectively.

RESULTS

By the transduction of BB-102, high expression levels of the three exogenesis genes were detected in glioma cells. Cell growth was inhibited and apoptosis was induced. Significant proliferation of autologous PBLs and specific cytotoxicity against primary glioma cells were also induced by the infection of BB-102 in vitro, with the effect being more evident than that of Ad-p53.

CONCLUSION

These results suggest that glioma cell vaccination co-transferred with p53, GM-CSF and B7-1 genes may be a feasible and effective immunotherapeutic approach in glioma treatments.

Simultaneous phosphorylation of p53 at serine 15 and 20 induces apoptosis in human glioma cells by increasing expression of pro-apoptotic genes

Understanding the mechanism underlying p53's ability to induce cell cycle arrest versus apoptosis is critical to treating human gliomas, 70% of which contain wild-type p53. Although N-terminal phosphorylation results in activation of p53, the role of N-terminal phosphorylation, particularly at serines 15 and 20, in p53's ability to induce cell cycle arrest versus apoptosis remains controversial. Here we test the hypothesis that phosphorylation of serine 15 and/or 20 is causally related to p53-mediated apoptosis in human gliomas. Introduction of p53 plasmids containing alanine mutations at serine 15 or/and serine 20 (which block phosphorylation) or aspartate mutations (which mimic phosphorylation) at the same sites, implicated simultaneous phosphorylation of both sites in the induction of apoptosis. When a double phosphorylation-mimicking adenoviral p53 vector (Ad-p53-15D20D) was compared with an unphosphorylated p53 vector (Ad-p53), treatment with Ad-p53 resulted in G1-arrest, whereas Ad-p53-15D20D induced apoptosis. These effects occurred independent of phosphorylation of other N-terminal serine (i.e., serines 6, 9, 33, 37, 46) indicating that phosphorylation of S15 and S20 is sufficient for inducing apoptosis. Mechanistically, Ad-p53 was capable only of increasing the expression of p21/CIP, whereas Ad-p53-15D20D increased the binding to and expression of the pro-apoptotic genes Fas, Puma and PIG3. However, Ad-p53-15D20D did not alter the expression of Noxa, Bid, IGFBP3, PERP and Killer/DR5, suggesting that phosphorylation of S15 and S20 resulted in the expression of specific pro-apoptotic gene. In conclusion, simultaneous phosphorylation of S15 and S20 is causally associated with apoptosis, resulting in increased expression of specific p53-responsive pro-apoptotic genes.

Phosphorylation of Thr18 and Ser20 of p53 in Ad-p53-induced apoptosis

The p53 protein plays a critical role in inducing cell cycle arrest or apoptosis. Because p53 is inactivated in human gliomas, restoring p53 function is a major focus of glioma therapy. The most clinically tested strategy for replacing p53 has been adenoviral-mediated p53 gene therapy (Ad-p53). In addition to their therapeutic implications, investigations into Ad-p53 provide model systems for understanding p53's ability to induce cell cycle arrest versus apoptosis, particularly because wild-type p53 cells are resistant to Ad-p53-induced apoptosis. Here we use Ad-p53 constructs to test the hypothesis that simultaneous phosphorylation of p53 at threonine 18 (Thr18) and serine 20 (Ser20) is causally associated with p53-mediated apoptosis. Studies using phosphorylation-specific antibodies demonstrated that p53-induced apoptosis correlates with phosphorylation of p53 at Thr18 and Ser20 but not with carboxy-terminal phosphorylation (Ser392). To prove a causal relationship between apoptosis and Thr18 and Ser20 phosphorylation of p53, the effects of an adenoviral p53 construct that was not phosphorylated (Ad-p53) was compared with a Thr18/Ser20 phosphomimetic construct (Ad-p53-18D20D) in wild-type p53 gliomas. Whereas treatment with Ad-p53 resulted only in cell cycle arrest, treatment with Ad-p53-18D20D induced dramatic apoptosis. Microarray and Western blot analyses showed that only Ad-p53-18D20D was capable of inducing expression of apoptosis-inducing proteins. Chromatin immunoprecipitation assays indicated that the protein product of Ad-p53-18D20D, but not Ad-p53, was capable of binding to apoptosis-related genes. We thus conclude that phosphorylation of Thr18 and Ser20 is sufficient for inducing p53-mediated apoptosis in glioma cells. These results have implications for p53 gene therapy and inform other strategies that aim to restore p53 function.

Fatty acid synthase: a novel target for antiglioma therapy

High levels of fatty acid synthase (FAS) expression have been observed in several cancers, including breast, prostate, colon and lung carcinoma, compared with their respective normal tissue. We present data that show high levels of FAS protein in human and rat glioma cell lines and human glioma tissue samples, as compared to normal rat astrocytes and normal human brain. Incubating glioma cells with the FAS inhibitor cerulenin decreased endogenous fatty acid synthesis by approximately 50%. Cell cycle analysis demonstrated a time- and dose-dependent increase in S-phase cell arrest following cerulenin treatment for 24 h. Further, treatment with cerulenin resulted in time- and dose-dependent decreases in glioma cell viability, as well as reduced clonogenic survival. Increased apoptotic cell death and PARP cleavage were observed in U251 and SNB-19 cells treated with cerulenin, which was independent of the death receptor pathway. Overexpressing Bcl-2 inhibited cerulenin-mediated cell death. In contrast, primary rat astrocytes appeared unaffected. Finally, RNAi-mediated knockdown of FAS leading to reduced FAS enzymatic activity was associated with decreased glioma cell viability. These findings suggest that FAS might be a novel target for antiglioma therapy.

INGN 201 (Advexin): adenoviral p53 gene therapy for cancer

Mutations in the p53 gene are the most frequent genetic alterations in human tumours, occurring in approximately 50% of all cancers. The p53 protein is pivotal in maintaining genetic integrity after DNA damage, and alterations in the p53 pathway, including mutations in the p53 gene, greatly increase the probability of tumour formation. Gene therapy using adenoviral p53 has emerged as a novel treatment option, with the potential to be safe and effective in a wide range of cancer types. INGN 201 (Ad5CMV-p53, Advexin), a replication-impaired adenoviral vector that carries the p53 gene, has been evaluated in both preclinical and clinical trials. Results show that Advexin is a well-tolerated and efficacious treatment for numerous cancers, both as monotherapy and in combination with radiation and/or chemotherapy agents. In addition, there is now data to support the use of Advexin in cancer immunotherapy.

Gene therapy for malignant glioma: current clinical status

Glioblastoma is an aggressive brain tumor with a dismal prognosis. Gene therapy may offer a new option for the treatment of these patients. Several gene therapy approaches have shown anti-tumor efficiency in experimental studies, and the first clinical trials for the treatment of malignant glioma were conducted in the 1990s. HSV-tk gene therapy has been the pioneering and most commonly used approach, but oncolytic conditionally replicating adenoviruses and herpes simplex virus mutant vectors, p53, interleukins, interferons, and antisense oligonucleotides have also been used. During the past few years, adenoviruses have become the most popular gene transfer vectors, and some recent randomized, controlled trials have shown significant anti-tumor efficacy in clinical use. However, efficient gene delivery into the brain still presents a major problem, and there is a lack of definitive phase III trials, which would avoid potential problems associated with a small number of patients, inadvertent patient selection, and overinterpretation of results based on a few long-time survivors. For clinical efficacy, median survival is one of the most rigorous endpoints. It is used here to evaluate the usefulness of various treatment approaches and current clinical status of gene therapy for malignant glioma.

Neurosurgical oncology at the university of Texas M. D. Anderson Cancer Center: its genesis and evolution

The practice of neurosurgery at The University of Texas M. D. Anderson Cancer Center began in 1944 with one neurosurgeon among the 11 physicians present in a makeshift 16-room outpatient clinic at a temporary location. Neurosurgical oncology evolved as the hospital did, first as a neurosurgery service in 1951, then as the Section of Neurosurgery within the Department of Head and Neck Surgery in 1979, and finally, as the Department of Neurosurgery in 1990. Although M. D. Anderson is now one of the largest institutions in the world devoted exclusively to cancer patient care, research, education, and prevention, it has an unusual history, which is reviewed in terms of the institution's origin in 1941, its development under three presidents, and its fostering of neurosurgical oncology. We chronicle the growth and development of the department from 1990 to 2003 and describe the unique opportunities it presents for surgical innovation, for clinical and basic research, for training residents and fellows, and for multidisciplinary collaboration in neurosurgical oncology.

Tp53-gene transfer induces hypersensitivity to low doses of X-rays in glioblastoma cells: a strategy to convert a radio-resistant phenotype into a radiosensitive one

Tp53 is frequently mutated or inactivated in glioblastomas. Due to the impairment of p53 activity, glioblastomas show a high degree of radioresistance. In an attempt to convert the radioresistant phenotype to a more radiosensitive one, we evaluated the efficacy of the combination of Adp53 gene transfer and X-ray irradiation. The combination of Adp53, at low multiplicity in order to mimic the low in vivo efficiency of virus-mediated gene delivery, with X-ray irradiation resulted in a marked decrease of glioblastoms cell survival. Interestingly, Adp53 was able to induce low dose (<2Gy) hypersensitivity. The data suggest the possibility for the development of new therapeutic strategies.

Mild hyperthermia plus adenoviral p53 over-expression additively inhibits the viability of human malignant glioma cells

Adenoviral replacement of the p53 gene has already been proved effective for the treatment of various tumours, including malignant gliomas. However, it is difficult to treat malignant glioma with p53 gene therapy alone because of problems with resistance or a less-than-satisfactory response to the treatment. This study investigated whether heat shock at 43 degrees C (mild hyperthermia) augments the cytotoxic effect of p53 gene transfer on malignant glioma cells expressing wild-type p53 (D54) or mutant p53 (U373-MG and U251-MG). The combination of mild hyperthermia and adenoviral p53 over-expression had an additive inhibitory effect on cellular proliferation in all three cell lines studied. Further, both cell cycle analysis and a DNA fragmentation assay showed that apoptosis was induced by p53 over-expression alone but not by heat shock at 43 degrees C alone. However, p53 over-expression followed by mild hyperthermia additively increased the proportion of cells in which apoptosis was induced, regardless of the endogenous p53 status of the tumour cells. Interestingly, a caspase-independent mechanism was observed to be involved in the p53-induced apoptosis in U251-MG and D54 cells. Taken together, the findings showed that combining adenoviral p53 transfer with mild hyperthermia inhibits the proliferation of malignant glioma cells in an additive manner, irrespective of their endogenous p53 status, suggesting a novel treatment strategy for this malignancy.

Therapeutic efficacy of PUMA for malignant glioma cells regardless of p53 status

Replacement of the p53 tumor suppressor gene is a rational approach to the management of malignant gliomas because p53 is frequently mutated or inactivated in these cancers. Major weaknesses of this approach are that malignant gliomas are mixtures of cells with wild-type and mutant p53, and that tumor cells exhibiting wildtype p53 are resistant to p53 gene transfer. An effective alternative is needed to overcome these difficulties. p53-upregulated modulator of apoptosis (PUMA) was identified as a p53-inducible proapoptotic molecule. Our purpose was to elucidate a role for PUMA in p53 gene therapy and to investigate whether PUMA is an efficient substitute for p53 in cancer therapy. We demonstrated that PUMA was upregulated in mutant p53 malignant glioma cells (U373-MG and T98G) undergoing apoptosis but was not upregulated in apoptosis-resistant wild-type p53 malignant glioma cells (U87-MG and D54) after adenoviral transfer of p53. Overexpression of PUMA resulted in massive apoptosis associated with mitochondrial damage and caspase-3 activation in all tumor cells tested. Use of the human telomerase reverse transcriptase (hTERT) promoter system induced apoptosis only in malignant glioma cells with telomerase activity, while sparing normal cells lacking telomerase. The ability of PUMA to induce apoptosis was greater than that of caspase-6 or caspase-8 transfer, using the same system. Moreover, exogenous expression of PUMA under the hTERT promoter system significantly suppressed the growth of subcutaneous U87-MG tumors in nude mice and did not induce apoptosis in surrounding nontumor tissues. These results indicate that PUMA, which is regulated under a tumor-specific expression system such as the hTERT promoter, may be better than p53 as a therapeutic tool for malignant gliomas.

X-irradiation to human malignant glioma cells enhances the cytotoxicity of autologous killer lymphocytes under specific conditions

PURPOSE

To clarify the effect of combining x-irradiation and human killer lymphocytes against autologous malignant glioma cells, we analyzed not only the alteration of surface antigen expression in irradiated tumor cells, but also the cytotoxic effects of human killer lymphocytes on the autologous tumor cells with and without x-irradiation.

METHODS AND MATERIALS

Six malignant glioma cell-lines (MG 1-6) established from each patient with a malignant glioma in our institute, and U87MG, were used as materials. They were irradiated by 0-50 Gy of X-rays, and the alternations of their human histocompatability leukocyte antigen (HLA), HLA-ABC, HLA-DR, -DP, -DQ, and FAS expressions were examined. Then, three sets of autologous natural killer (NK) cells, and autologous tumor-specific T lymphocytes (ATTL) were induced from the peripheral blood mononuclear cells (PBMCs) of three patients, and in vitro cytotoxic effects of these killer cells on the irradiated autologous tumor cells were analyzed.

RESULTS

Irradiation-enhanced HLA-DR, -DP, -DQ, and FAS expression in glioma cell lines with low p53 expression. However, there was no correlation between HLA-ABC expression and X-ray dose. After irradiation of the tumor cells, cytotoxicity was enhanced in four of six effectors; in particular, it was significantly elevated in two killer lymphocytes. It was speculated that the enhancing effect was influenced not only by the p53 status of the tumor, but also by the types of killer lymphocytes; the alteration of cytotoxicity in NK cells on irradiated tumor cells may be compensatory for alteration in ATTLs.

CONCLUSION

It was indicated that irradiation of malignant tumor cells enhanced killer cell-mediated cytotoxicity in autologous models under specific conditions. These basic data should contribute to clinical trials using local radiotherapy and systemic adoptive immunotherapy with killer lymphocytes.

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.

Evolution of a gene therapy clinical trial. From bench to bedside and back

Developing and conducting gene therapy clinical trials poses unique challenges which must be addressed to satisfy regulatory requirements and, most importantly, to protect human subjects. Experimental products used for gene transfer studies, such as viral vectors, are often complex and cannot be sterilized or completely characterized to the extent of a typical pharmaceutical. Thus, quality and characterization must be built into the production process. Extensive preclinical studies must be performed to determine the feasibility of the approach, the safety of the product, and the appropriate dose range to evaluate in humans. Once a clinical trial is initiated, subjects must be followed carefully for short- and long-term toxicity especially since preclinical studies may not adequately predict the toxicity profile of these novel, complicated products. Results of early phase studies in gene therapy have often sent the investigators back to the laboratory to improve the delivery vector or identify a more potent or less toxic gene. This circular developmental process is expected for the early stages of a new technology such as gene therapy. Although these hurdles appear extensive, they can be overcome, as evidenced by the initiation of more than 500 clinical gene therapy trials in the United States to date, and are imperative for the maintenance of high-quality studies and public trust. This article describes the step-by-step process for developing a gene therapy trial incorporating specific examples relevant to neuro-oncology.

Clinical trials of adenoviruses in brain tumors: a review of Ad-p53 and oncolytic adenoviruses

Adenoviruses have been critical in the development of the molecular approaches to brain tumors. They have been engineered to function as vectors for delivering therapeutic genes in gene therapy strategies, and as direct cytotoxic agents in oncolytic viral therapies. This review outlines the uses of adenoviruses in brain tumor therapy by examining clinical trials of adenovirus-mediated p53 gene therapy and by reviewing the application of two conditionally replicative adenoviruses (CRAds) ONYX-015 and Delta 24 in brain tumors. The potential clinical use of CRAds that deliver trangenes, particularly p53, is also discussed.

Gene therapy: a primer for neurosurgeons

Gene therapy involves the transfer of genes into cells with therapeutic intent. Although several methods can accomplish this, vectors based on viruses still provide the most efficient approach. For neurosurgical purposes, preclinical and clinical applications in the areas of glioma therapy, spinal neurosurgery, and neuroprotection for treatment of Parkinson's disease and cerebral ischemia are reviewed. In general, therapies applied in the neurosurgical realm have proven relatively safe, despite occasional, well-publicized cases of morbidity and death in non-neurosurgical trials. However, continued clinical and preclinical research in this area is critical, to fully elucidate potential toxicities and to generate truly effective treatments that can be applied in neurological diseases.

Phase I trial of adenovirus-mediated p53 gene therapy for recurrent glioma: biological and clinical results

PURPOSE

Advances in brain tumor biology indicate that transfer of p53 is an alternative therapy for human gliomas. Consequently, we undertook a phase I clinical trial of p53 gene therapy using an adenovirus vector (Ad-p53, INGN 201).

MATERIALS AND METHODS

To obtain molecular information regarding the transfer and distribution of exogenous p53 into gliomas after intratumoral injection and to determine the toxicity of intracerebrally injected Ad-p53, patients underwent a two-stage approach. In stage 1, Ad-p53 was stereotactically injected intratumorally via an implanted catheter. In stage 2, the tumor-catheter was resected en bloc, and the postresection cavity was treated with Ad-p53. This protocol provided intact Ad-p53-treated biologic specimens that could be analyzed for molecular end points, and because the resection cavity itself was injected with Ad-p53, patients could be observed for clinical toxicity.

RESULTS

Of fifteen patients enrolled, twelve underwent both treatment stages. In all patients, exogenous p53 protein was detected within the nuclei of astrocytic tumor cells. Exogenous p53 transactivated p21CIP/WAF and induced apoptosis. However, transfected cells resided on average within 5 mm of the injection site. Clinical toxicity was minimal and a maximum-tolerated dose was not reached. Although anti-adenovirus type 5 (Ad5) titers increased in most patients, there was no evidence of systemic viral dissemination.

CONCLUSION

Intratumoral injection of Ad-p53 allowed for exogenous transfer of the p53 gene and expression of functional p53 protein. However, at the dose and schedule evaluated, transduced cells were only found within a short distance of the injection site. Although toxicity was minimal, widespread distribution of this agent remains a significant goal.

Apoptotic effect in the glioma cells induced by specific protein extracted from Okinawa Habu (Trimeresurus flavoviridis) venom in relation to oxidative stress

Okinawa Habu (Trimeresurus flavoviridis) venom is well known for its toxic efficacy, from which one kind of specific protein, Okinawa Habu apoxin protein-1 (OHAP-1) has been extracted. The purpose of this study was to investigate whether OHAP-1 could induce apoptosis in some glioma cells, and if so, to elucidate the possible mechanism involved. Three malignant glioma cell lines were tested. The malignant glioma cell lines were rat C6 and human RBR 17T, U251. OHAP-1 inhibited growth of all cell lines. Whether or not the apoptosis had been induced was determined by using DNA gel electrophoresis, DNA flow cytometry and TUNEL assay. After OHAP-1 treatment, DNA fragmentation, an increase in the percentage of subdiploid DNA content, and TUNEL positive cells were found in the C6, RBR17T, and U251 cells. Furthermore, OHAP-1 showed L-amino acid oxidase (LAAO) activity. In order to study the mechanism of apoptosis induced by OHAP-1, the changes of intracellular reactive oxygen species (ROS) were measured using flow cytometry, and the expression of p53 protein was examined using immunohistochemistry. OHAP-1 was found to generate ROS and increase the expression of p53 protein in glioma cells. The inhibiting effect of OHAP-1 on three tested cells was reversed when an antioxidant of either catalase or reduced glutathione (GSH) was added; its apoptotic effect correspondingly became weaker. In this study, the apoptotic effect of OHAP-1 on some malignant glioma cells was confirmed, and it could be that this effect might be mediated through promoting the generation of intracellular ROS and p53 protein expression in glioma cells. It was suggested that OHAP-1 is promising as a potential candidate for clinical tumor therapy.

Current and Future Gene Therapy for Malignant Gliomas

Malignant gliomas are the most common neoplasm in the central nervous system. When treated with conventional treatments including surgery, irradiation, and chemotherapy, the average life expectancy of the most malignant type, glioblastoma multiforme is usually less than 1 year. Therefore, gene therapy is expected to be an effective and possibly curative treatment. Many gene therapeutic approaches have demonstrated efficacy in experimental animal models. However, the current clinical trials are disappointing. This review focuses on current therapeutic genes/vectors/delivery systems/targeting strategies in order to introduce updated trends and hopefully indicate prospective gene therapy for malignant gliomas.

An adenovirus encoding proapoptotic Bax synergistically radiosensitizes malignant glioma

PURPOSE

We explore the utility of the adenovirus-mediated delivery of proapoptotic Bax for enhancing the cytotoxicity of radiotherapy (RT) in RT-refractory glioma cells.

MATERIALS AND METHODS

Cell lines D54 MG and U87 MG (p53 wild-type), and U251 MG and U373 MG (p53 mutant), and patient-derived astrocytes were evaluated. Cells were irradiated and infected with an inducible adenovirus encoding Bax. Cell proliferation, colony formation assay, quantification of early apoptotic alteration in the plasma membrane by fluorescence-activated cell sorter using annexin V, and nuclear staining with H33258 were used to evaluate apoptosis. The capacity of the combined treatment to induce regression of subcutaneous D54 MG tumors was tested in nude mice. A dose of 5 Gy was administered every other day, four times, for a total dose of 20 Gy. One day after each irradiation, tumors were injected with 1 x 10(9) plaque-forming units (PFU).

RESULTS

Apoptotic death was enhanced by the combination of Ad/Bax and RT. In D54 MG, levels of apoptosis after RT alone, Ad/Bax alone, or the combination were, respectively, 12.3%, 32.1%, and 78.5%. In contrast, treatment of astrocytes did not significantly induce apoptosis. A colony-formation assay showed a 2-log inhibition with respect to controls after combined treatment, irrespective of the endogenous levels of p53. The other apoptosis assays also showed the defining characteristics of apoptosis in the combination group. Remarkably, combined treatment induced regression of tumors in mice.

CONCLUSIONS

Ad/Bax synergistically radiosensitizes glioma, with a seemingly favorable therapeutic index.

Melanoma differentiation associated gene-7, mda-7/IL-24, selectively induces growth suppression, apoptosis and radiosensitization in malignant gliomas in a p53-independent manner

Malignant gliomas are extremely aggressive cancers currently lacking effective treatment modalities. Gene therapy represents a promising approach for this disease. A requisite component for improving gene-based therapies of brain cancer includes tumor suppressor genes that exhibit cancer constrained inhibitory activity. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7) as a gene associated with melanoma cell growth, differentiation and progression. Ectopic expression of mda-7 by means of a replication-incompetent adenovirus (Ad), Ad.mda-7, induces growth suppression and apoptosis selectively in diverse human cancers, without producing any apparent harmful effect in normal cells. We presently demonstrate that Ad.mda-7 induces growth inhibition and apoptosis in malignant human gliomas expressing both mutant and wild-type p53, and these effects correlate with an elevation in expression of members of the growth arrest and DNA damage (GADD) gene family. In contrast, infection with a recombinant Ad expressing wild-type p53, Ad.wtp53, specifically affects mutant p53 expressing gliomas. When tested in early passage normal and immortal human fetal astrocytes, growth inhibition resulting from infection with Ad.mda-7 or Ad.wtp53 is significantly less than in malignant gliomas and no toxicity is evident in these normal cells. Moreover, infection of gliomas with Ad.mda-7 or treatment with purified GST-MDA-7 protein sensitizes both wild-type and mutant p53 expressing tumor cells to the growth inhibitory and antisurvival effects of ionizing radiation, and this response correlates with increased expression of specific members of the GADD gene family. Since heterogeneity in p53 expression is common in evolving gliomas, the present findings suggest that Ad.mda-7 may, in many instances, prove more beneficial for the gene-based therapy of malignant gliomas than administration of wild-type p53.

Gene therapy of gliomas

Malignant glioma formation is associated with characteristic genetic alterations, although epigenetic mechanisms may contribute in tumorigenesis. Until recently, our knowledge has mainly been based on chromosomal and molecular studies performed in the last two decades. This has increased tremendously with the advent of new technologies, in particular expression arrays for simultaneous analysis of thousands of genes. Consequently, gene therapy of gliomas may aim at molecular interference with 'gain of function' genes (oncogenes) or replacement of 'loss of function' genes (tumor suppressor genes). Such approaches require transgene expression in whole tumor cell populations (if not other mechanisms come into play) which cannot be achieved with current vector systems. Hence other strategies have been pursued which may be independent of genes actually involved in tumorigenesis. Microbial genes (e.g. herpes simplex virus thymidine kinase) may be transferred into the tumors allowing for prodrug activation (e.g. ganciclovir). Furthermore, cytokines or other immunomodulatory genes may be used for vaccination purposes which frequently involves ex vivo transfection of autologous tumor cells with such genes. These approaches proved promising in preclinical studies performed in cell culture and different inbred rodent models. A considerable number of clinical trials have been initiated based on these approaches. Although most therapeutic strategies proved safe, clinical responses fell short of expectations raised by preclinical results. This, to a large extent, has to be attributed to a lag in the development of efficient vector systems. Although much effort has been put into this area of research, neuro-oncologists are still in await of a vector system allowing for selective and efficient tumor cell transduction. This has led to increased interest in distinct but related strategies, e.g. oncolytic viruses or direct intra-tumoral delivery of anti-sense oligonucleotides.

In vitro enhancement of tumor cell radiosensitivity by a selective inhibitor of cyclooxygenase-2 enzyme: mechanistic considerations

PURPOSE

Selective cyclooxygenase-2 inhibitors have been reported to enhance the tumor response to radiation in vivo, but the cellular mechanisms underlying the radiosensitizing effect are not understood. In the present study, we investigated several possible mechanisms using a murine sarcoma cell culture system.

METHODS AND MATERIALS

Cells derived from a murine sarcoma, designated NFSA, were cultured in vitro and exposed to different (either single or split) doses of radiation with and without a pretreatment of SC-236 (4-[5-(4-chlorophenyl)-3-(trifluoromethyl)-1H-pyrazol-l-yl] benzene sulfonamide), a selective cyclooxygenase-2 (COX-2) inhibitor. The cells were assayed for clonogenic survival to determine the radiosensitizing effect of SC-236. In addition, MTT assay and TUNEL assay were performed to determine the effects of SC-236 and radiation on the cell survival and cell cycle distribution. RNase protection assay was performed on the total RNA extract using probes that encoded for selected cell cycle regulatory proteins, such as cyclins and cyclin-dependent kinases. To monitor the extent of COX-2 activity and its role in radiosensitization, the cellular content of prostaglandin E2, a major metabolite of COX-2 activity on arachidonic acid, was also determined.

RESULTS

The cell clonogenic survival assay showed that SC-236 significantly enhanced tumor cell radiosensitivity: 50 microM SC-236 increased it by a factor of 1.51 at the 0.1 cell survival level. Treatment with SC-236 (50 microM, 3 days) removed the "shoulder" region on the radiation survival curve, suggesting that the drug inhibited repair of sublethal radiation damage. The inhibition was confirmed by split-dose experiments where two doses (3 Gy each) of radiation were given 4 h apart. The cells exposed to radiation only repaired the damage by a factor of 1.44, whereas those treated with SC-236 plus radiation repaired it by a factor of 1.1 only. Whereas SC-236 induced apoptosis in these NFSA cells, radiation did not. No further increase in apoptosis was observed when the cells were exposed to both SC-236 and radiation, suggesting that SC-236 did not render tumor cells more susceptible to radiation-induced apoptosis. The RNase protection assay showed that SC-236 (50 microM, 3 days) inhibited the expression of cyclins A and B, as well as cyclin-dependent kinase-1. Inhibition of these cell cycle regulatory elements by SC-236 was associated with the arrest of cells in the radiosensitive G2-M phase (67%), determined by flow cytometry.

CONCLUSIONS

SC-236 significantly enhanced radiosensitivity of tumor cells; the magnitude of sensitivity was dependent on the drug's concentration. The likely mechanisms involve accumulation of cells in the radiosensitive G2-M phase of the cell cycle and inhibition of repair from sublethal radiation damage.

The diversity of p53 mutations among human brain tumors and their functional consequences

The p53 tumor suppressor is implicated in cell cycle control, DNA repair, replicative senescence and programmed cell death. Inactivation of the p53 contributes to the wide range of human tumors, including glial neoplasms. In this review, we describe the regulation and biochemical properties of p53 protein that may explain its ability to activate various genetic programs underlying cellular responses to stress conditions. The overall spectrum of p53 mutations is rather shared between tumor types indicating that these mutations are not tumor type-specific. However, there is one example of germ-line mutation of p53 gene (the deletion of the codon 236) that is associated with a familiar brain tumor syndrome. We compare the frequency and type of most common mutations among various brain tumours (focusing on glioblastomas) and their consequences on protein functions. Furthermore, we discuss the most promising approaches of potential brain tumor therapy, including an adenovirus-mediated p53 gene transfer. Human glioblastomas are highly sensitive to the effects of p53 activity when the wild-type p53 is introduced ectopically. It suggests that the genetic or pharmacological modulation of the p53 pathway is potentially important strategy in the treatment of human cancers.

Human adenovirus serotypes 4p and 11p are efficiently expressed in cell lines of neural tumour origin

Most currently used adenovirus vectors are based upon adenovirus serotypes 2 and 5 (Ad2 and Ad5), which have limited efficiencies for gene transfer to human neural cells. Both serotypes bind to the known adenovirus receptor, CAR (coxsackievirus and adenovirus receptor), and have restricted cell tropism. The purpose of this study was to find vector candidates that are superior to Ad5 in infecting human neural tumours. Using flow cytometry, the vector candidates Ad4p, Ad11p and Ad17p were compared to the commonly used adenovirus vector Ad5v for their binding capacity to neural cell lines derived from glioblastoma, medulloblastoma and neuroblastoma cell lines. The production of viral structural proteins and the CAR-binding properties of the different serotypes were also assessed in these cells. Computer-based models of the fibre knobs of Ad4p and Ad17 were created based upon the crystallized fibre knob structure of adenoviruses and analysed for putative receptor-interacting regions that differed from the fibre knob of Ad5. The non CAR-binding vector candidate Ad11p showed clearly the best binding capacity to all of the neural cell lines, binding more than 90% of cells of all of the neural cell lines tested, in contrast to 20% or less for the commonly used vector Ad5v. Ad4p and Ad11p were also internalized and produced viral proteins more successfully than Ad5. Ad4p showed a low binding ability but a very efficient capacity for infection in cell culture. Ad17p virions neither bound or efficiently infected any of the neural cell lines studied.

Apoptosis induced by box jellyfish (Chiropsalmus quadrigatus) toxin in glioma and vascular endothelial cell lines

This study was made to investigate whether Chiropsalmus Quadrigatus toxins (CqTX), which isolated from box jellyfish C. Quadrigatus venom, could induce apoptosis in human U251 and rat C6 malignant glioma cells and transformed vascular endothelial ECV 304 cell lines. Cell viability was estimated by MTT assay. Apoptosis was evaluated using TdT (terminal deoxynucleotidyl transferase)-mediated dUTP nick-end labeling (TUNEL) method and DNA gel electrophoresis. Furthermore, the expression of p53 protein was examined immunohistochemically in the U251 cells. After the CqTX treatment, the growth of all cell lines was inhibited, the fragmented DNA was observed and some cells became TUNEL positive. The expression of p53 protein was increased in the tested U251 cells. The results suggested that CqTX induced apoptosis in these cell lines. The promotion of the p53 expression might be one mechanism of apoptosis induced by CqTX in the glioma cells.

Intra-arterial delivery of p53-containing adenoviral vector into experimental brain tumors

Human tumor xenografts established in athymic rat brains were used to determine the feasibility of intravascular delivery of tumor suppressor genes to brain tumors. Both tumor size and number were compared to characterize the effect of tumor burden on tumor transduction efficacy by a control LacZ-containing adenoviral vector. Experiments with tumors grown in vivo for either 3, 5, or 7 days demonstrated that 5-day-old tumors provided the best target for vector infection and transgene expression by this mode of administration. Intra-arterial mannitol facilitated transduction efficiency. Tumor burden did not seem to affect transduction, while tumor location appeared to be an important factor. Based on these results, intra-arterial infusion of a p53-containing adenoviral vector was carried out and resulted in significant retardation of brain tumor growth 3 days after administration. Effects at longer time points were not as significant. These findings indicate that intra-arterial administration of adenoviral vectors containing p53 is efficient and can result in changes in tumor size, but that long-term control of tumor growth may require multiple adenoviral treatments.

Intratumoral gene therapy of malignant brain tumor in a rat model with angiostatin delivered by adeno-associated viral (AAV) vector

We have utilized a recombinant adeno-associated viral (AAV) vector carrying the angiostatin gene as an anti-angiogenesis strategy to treat the malignant brain tumor in a C6 glioma/Wistar rat model. Angiostatin, as a potent angiogenesis inhibitor, shows high promises as an anti-cancer drug through the inhibition of tumor neovessel formation. However, sustained in vivo protein delivery is required to achieve the therapeutic effects. The AAV vector has been proven to be able to deliver sustained and high-level gene expression in vivo, and therefore, is well suited to such a purpose. In this study, we implanted 5 x 10(5) C6 glioma cells into the rat brain 7 days before gene therapy. Intratumoral injection of a high-titer AAV-angiostatin vector has rendered efficacious tumor suppression and resulted in long-term survival in 40% of the treated rats, whereas the control AAV-GFP vector did not have any therapeutic benefits. In addition, we have investigated the combined gene therapy of an adenoviral vector carrying the suicidal thymidine kinase gene along with the AAV-angiostatin vector. The combined therapy offered the best tumor-suppressive effects and increased long-term survival to 55% in the treated rats. Our study has demonstrated the potential of using AAV as a safe and effective vector for anti-angiogenic gene therapy of brain tumors.

Molecular biology of nervous system tumors

Many genetic alterations that contribute to CNS tumorigenesis and progression have been identified. One goal of such studies is to identify loci that would serve as diagnostic prognostic markers or both. A significant advance is the observation that chromosome 1p loss identified anaplastic oligodendroglioma and a subset of high-grade glioma patients who responded to chemotherapy and had longer survival times. Combined 1p and 19q loss was a predictor of prolonged survival of patients having pure oligodendrogliomas. Such markers eventually may be used to identify patients upfront who would benefit from treatment, while sparing patients who would not benefit. Although many molecular participants involved in the biologic pathways that promote proliferation, angiogenesis, and invasion have been elucidated, there are still many gaps in clinicians' knowledge. It is expected that the use of the human genome project information and databases such as SAGEmap, in combination with techniques such as cDNA arrays and proteomics, will facilitate greatly the identification of novel genes that contribute to CNS tumors. cDNA arrays and tissue arrays will permit the construction of CNS-specific screening tools that will permit the identification of tumor-specific mutations and alterations so that patient-specific therapies can be designed.

Adenovirus-p53 gene therapy in human nasopharyngeal carcinoma xenografts

BACKGROUND

One major challenge to human cancer gene therapy, is efficient delivery of the gene-vector complex.

METHODS AND RESULTS

Using two distinct human nasopharyngeal carcinoma (NPC) models, we demonstrate that intra-tumoural (IT) administration of adenoviral-mediated wild-type p53 gene therapy (Ad-p53) caused no greater inhibition of tumour growth as compared to ionizing radiation (XRT) alone. Detailed histologic examination of tumour sections demonstrated that <15% of tumour cells were transduced by IT adv-beta-gal.

CONCLUSIONS

This report underscores the importance of developing gene transfer vectors, which can provide therapeutic levels of transgene expression efficiently in solid tumours.

The developmental biology of brain tumors

Tumors of the central nervous system (CNS) can be devastating because they often affect children, are difficult to treat, and frequently cause mental impairment or death. New insights into the causes and potential treatment of CNS tumors have come from discovering connections with genes that control cell growth, differentiation, and death during normal development. Links between tumorigenesis and normal development are illustrated by three common CNS tumors: retinoblastoma, glioblastoma, and medulloblastoma. For example, the retinoblastoma (Rb) tumor suppressor protein is crucial for control of normal neuronal differentiation and apoptosis. Excessive activity of the epidermal growth factor receptor and loss of the phosphatase PTEN are associated with glioblastoma, and both genes are required for normal growth and development. The membrane protein Patched1 (Ptc1), which controls cell fate in many tissues, regulates cell growth in the cerebellum, and reduced Ptc1 function contributes to medulloblastoma. Just as elucidating the mechanisms that control normal development can lead to the identification of new cancer-related genes and signaling pathways, studies of tumor biology can increase our understanding of normal development. Learning that Ptc1 is a medulloblastoma tumor suppressor led directly to the identification of the Ptc1 ligand, Sonic hedgehog, as a powerful mitogen for cerebellar granule cell precursors. Much remains to be learned about the genetic events that lead to brain tumors and how each event regulates cell cycle progression, apoptosis, and differentiation. The prospects for beneficial work at the boundary between oncology and developmental biology are great.

Comparisons of tumor suppressor p53, p21, and p16 gene therapy effects on glioblastoma tumorigenicity in situ

The mutation and/or deletion of tumor suppressor genes have been postulated to play a major role in the genesis and the progression of gliomas. In this study, the functional expression and efficacy in tumor suppression of 3 tumor suppressor genes (p53, p21, and p16) were tested and compared in a rat GBM cell line (RT-2) after retrovirus mediated gene delivery in vitro and in vivo. Significant reductions in tumor cell growth rate were found in p16 and p21 infected cells (60 +/- 12% vs 66 +/- 15%) compared to p53 (35 +/- 9%). In vitro colony formation assay also showed significant reductions after p16 and p21 gene delivery (98 +/- 5% vs 91 +/- 10%) compared to p53 (50 +/- 18%). In addition, the tumor suppression efficacy were investigated and compared in vivo. Retroviral mediated p16 and p21 gene deliveries in glioblastomas resulted in more than 90% reductions in tumor growth (92 +/- 26% vs 90 +/- 22%) compared to p53 (62 +/- 18%). Tumor suppressor gene insertions in situ further prolonged animal survival. Overall p16 and p21 genes showed more powerful tumor suppressor effects than p53. The results were not surprising, as p16 and p21 are more downstream in the cell cycle regulatory pathway compared to p53. Moreover, the mechanism involved in each of their suppressor effects is different. This study demonstrates the feasibility of using tumor suppressor genes in regulating the growth of glioma in vitro and in situ.

Adenovirus-mediated transfer of p53 augments hyperthermia-induced apoptosis in U251 glioma cells

PURPOSE

Hyperthermia kills glioma cells by inducing apoptosis and is thereby an effective therapeutic modality for the treatment of malignant gliomas. However, cells harboring mutated p53 are refractory to hyperthermia-induced apoptosis. In this study, we assessed whether or not adenovirus (Adv)-mediated transduction of p53 overrides this resistant mechanism.

METHODS AND MATERIALS

We transduced the p53 wild-type tumor suppressor gene into U251 glioma cells harboring mutated p53 using Adv vectors in combination with hyperthermia (43, 44.5 degrees C), and evaluated the degree of cell death and apoptosis.

RESULTS

The percentage of cells that had died, as measured by trypan blue staining, among U251 cells infected with the Adv for p53 (Adv-p53) and treated with hyperthermia, was significantly higher than the percentage of cells that had died among U251 cells infected with Adv-p53 and not treated with hyperthermia, or those infected with the control Adv for dE (Adv-dE) and treated with hyperthermia. The degree of apoptosis, measured at 24 h after treatment, in hyperthermia-treated U251 cells infected with Adv-p53 (43 degrees C, 73%; 44.5 degrees C, 92%) was much higher than that infected with Adv-p53 (41%), or that infected with control Adv-dE and treated with hyperthermia (43 degrees C, 1.3%; 44.5 degrees C, 19%). Treatment with combined hyperthermia and Adv-p53 infection induced cleavage of caspase-3 in U251 cells.

CONCLUSION

These results indicate that Adv-mediated transduction of p53 would render glioma cells highly sensitive to hyperthermia.

Multi-modal combination gene therapy for malignant glioma using replication-defective HSV vectors

Herpes simplex virus (HSV) may be modified to produce a non-pathogenic vector that is capable of delivering multiple transgenes simultaneously to cells, both safely and efficiently. We have exploited this property to develop viruses that target glioblastoma, a malignancy that is currently associated with a poor prognosis. Using rationally selected combinations of therapeutic transgenes coupled with gamma-knife radiotherapy, the ablation of experimental tumours in animal models has been demonstrated. Combination gene therapy using replication-defective HSV vectors represents a promising and exciting approach to tackling malignancy in the CNS.

DNA binding chelates for nonviral gene delivery imaging

Noninvasive in vivo monitoring of gene delivery would provide a critically important information regarding the spatial distribution, local concentration, kinetics of removal and/or biodegradation of the expression vector. We developed a novel approach to noninvasive gene delivery imaging using heterobifunctional peptide-based chelates (PBC) bearing double-stranded DNA-binding groups and a technetium-binding amino acid motif. One of such chelates: Gly-Cys(Acm)-Gly-Cys(Acm)-Gly-Lys(4)-Lys-(N-epsilon-[4-(psoralen-8-yloxy)]butyrate)-NH(2) has been characterized and labeled with reduced (99m)Tc pertechnetate (oxotechnetate). The psoralen moiety (a DNA binding group of PBC) allowed linking to double-stranded DNA upon short-term irradiation with the near UV range light (>320 nm). Approximately 30-40% of added (99m)Tc-labeled PBC was nonextractable and co-eluted with a model pCMV-GFP vector during the gel-permeation chromatography. Nuclear imaging of "naked" DNA and DNA complexes with lipid-based transfection reagents ("lipoplexes") has been performed after systemic or local administration of (99m)Tc-PBC-labeled DNA in mice. Imaging results were corroborated with the biodistribution using (99m)Tc-PBC and (32)P-labeled DNA and lipoplexes. A markedly different biodistribution of (99m)Tc PBC-labeled DNA and lipoplexes was observed with the latter being rapidly trapped in the liver, spleen and lung. (99m)Tc PBC-DNA was used as an imaging tracer during in vivo transfection of B16 melanoma by local injection of "naked" (99m)Tc PBC-DNA and corresponding lipoplexes. As demonstrated by nuclear imaging, (99m)Tc PBC-DNA lipoplexes showed a slower elimination from the site of injection than (99m)Tc PBC-DNA alone. This result correlated with a higher expression of marker mRNA and green fluorescent protein as determined using RT-PCR and immunohistochemistry, respectively.

Gene therapy for high grade gliomas

High grade gliomas in adults are devastating diseases, with very poor survival despite their lack of distant metastases. Local treatments, such as surgical resection and stereotactic radiosurgery, have been most successful, whereas systemic therapy (for example, chemotherapy and immunotherapy) have been rather disappointing. Several gene therapy systems have been successful in controlling or eradicating these tumours in animal models and are now being tested as a logical addition to current clinical management. This review describes the gene therapy clinical protocols that have been completed or that are ongoing for human gliomas. These include the prodrug activating system, herpes simplex thymidine kinase (HSVtk)/ganciclovir (GCV), utilising either retrovirus vector producer cells or adenovirus vectors; adenovirus mediated p53 gene transfer; adenovirus mediated IFN-beta gene transfer and oncolytic herpes virus and adenovirus vectors. To date, all of the clinical studies have used direct injection of the vector into the glioma. The Phase I clinical studies have demonstrated low to moderate toxicity and variable levels of gene transfer and in some cases anti-tumour effect. Future directions will rely upon improvements in gene delivery as well as gene therapies and combinations of gene therapy with other treatment modalities.