Treatment of relapsed malignant glioma with an adenoviral vector containing the herpes simplex thymidine kinase gene followed by ganciclovir

Immunotherapeutic Strategies for the Treatment of Glioblastoma: Current Challenges and Future Perspectives

Despite decades of research and the best up-to-date treatments, grade 4 Glioblastoma (GBM) remains uniformly fatal with a patient median overall survival of less than 2 years. Recent advances in immunotherapy have reignited interest in utilizing immunological approaches to fight cancer. However, current immunotherapies have so far not met the anticipated expectations, achieving modest results in their journey from bench to bedside for the treatment of GBM. Understanding the intrinsic features of GBM is of crucial importance for the development of effective antitumoral strategies to improve patient life expectancy and conditions. In this review, we provide a comprehensive overview of the distinctive characteristics of GBM that significantly influence current conventional therapies and immune-based approaches. Moreover, we present an overview of the immunotherapeutic strategies currently undergoing clinical evaluation for GBM treatment, with a specific emphasis on those advancing to phase 3 clinical studies. These encompass immune checkpoint inhibitors, adoptive T cell therapies, vaccination strategies (i.e., RNA-, DNA-, and peptide-based vaccines), and virus-based approaches. Finally, we explore novel innovative strategies and future prospects in the field of immunotherapy for GBM.

Ganciclovir as a potential treatment for glioma: a systematic review and meta-analysis

BACKGROUND

Glioma is a challenging malignant tumor with a low survival rate and no effective treatment. Recently, ganciclovir, an antiviral drug, combined with gene therapy and its own antiviral ability, has been proposed as a potential treatment for glioma. However, there are differences in the results of various clinical trials. In this study, we conducted a systematic review and meta-analysis to evaluate the efficacy of ganciclovir in treating glioma.

METHODS

We searched databases such as PubMed, EMBASE, and Cochrane Library before March 30, 2023. The search terms included glioma, ganciclovir, valganciclovir and treatment. Calculated 1, 2 and 4-year survival rate by risk difference (RD), and overall survival (OS) by odds ratio (OR).

RESULTS

Five randomized controlled trials (RCTs) with a total of 606 high-grade glioma patients were included. The results showed that ganciclovir can improve 2-yeaer (RD = 0.179, 95% CI 0.012-0.346, P = 0.036) and 4-year survival rate (RD = 0.185, 95% CI 0.069-0.3, P = 0.002) and OS (OR 2.393, 95% CI 1.212-4.728, P = 0.012) compared with the control group.

CONCLUSIONS

This meta-analysis showed that ganciclovir significantly improved the prognosis of glioma patients. Therefore, we suggest that more cases of ganciclovir as a glioma treatment can be conducted, or a large clinical trial can be designed.

The Development of Immunotherapy for the Treatment of Recurrent Glioblastoma

Recurrent glioblastoma (rGBM) is a highly aggressive form of brain cancer that poses a significant challenge for treatment in neuro-oncology, and the survival status of patients after relapse usually means rapid deterioration, thus becoming the leading cause of death among patients. In recent years, immunotherapy has emerged as a promising strategy for the treatment of recurrent glioblastoma by stimulating the body's immune system to recognize and attack cancer cells, which could be used in combination with other treatments such as surgery, radiation, and chemotherapy to improve outcomes for patients with recurrent glioblastoma. This therapy combines several key methods such as the use of monoclonal antibodies, chimeric antigen receptor T cell (CAR-T) therapy, checkpoint inhibitors, oncolytic viral therapy cancer vaccines, and combination strategies. In this review, we mainly document the latest immunotherapies for the treatment of glioblastoma and especially focus on rGBM.

Case report: Stem cell-based suicide gene therapy mediated by the herpes simplex virus thymidine kinase gene reduces tumor progression in multifocal glioblastoma

Introduction

The prognosis for glioblastoma multiforme (GBM), a malignant brain tumor, is poor despite recent advancements in treatments. Suicide gene therapy is a therapeutic strategy for cancer that requires a gene to encode a prodrug-activating enzyme which is then transduced into a vector, such as mesenchymal stem cells (MSCs). The vector is then injected into the tumor tissue and exerts its antitumor effects.

Case presentation

A 37-year-old man presented to our department with two evident foci of glioblastoma multiforme at the left frontal and left parietal lobes. The patient received an injection of bone marrow-derived MSCs delivering the herpes simplex virus thymidine kinase (HSV-tk) gene to the frontal focus of the tumor, followed by ganciclovir administration as a prodrug for 14 days. For follow-up, the patient was periodically assessed using magnetic resonance imaging (MRI). The growth and recurrence patterns of the foci were assessed. After the injection on 09 February 2019, the patient's follow-up appointment on 19 December 2019 MRI revealed a recurrence of parietal focus. However, the frontal focus had a slight and unremarkable enhancement. On the last follow-up (18 March 2020), the left frontal focus had no prominent recurrence; however, the size of the left parietal focus increased and extended to the contralateral hemisphere through the corpus callosum. Eventually, the patient passed away on 16 July 2020 (progression-free survival (PFS) = 293 days, overall survival (OS) = 513 days).

Conclusion

The gliomatous focus (frontal) treated with bone marrow-derived MSCs carrying the HSV-TK gene had a different pattern of growth and recurrence compared with the non-treated one (parietal).

Trial registration

IRCT20200502047277N2. Registered 10 May 2020-Retrospectively registered, https://eng.irct.ir/trial/48110.

Viral therapies for glioblastoma and high-grade gliomas in adults: a systematic review

OBJECTIVE

High-grade gliomas (HGGs) inevitably recur and progress despite resection and standard chemotherapies and radiation. Viral therapies have emerged as a theoretically favorable adjuvant modality that might overcome intrinsic factors of HGGs that confer treatment resistance.

METHODS

The authors present the results of systematic searches of the MEDLINE and ClinicalTrials.gov databases that were performed for clinical trials published or registered up to July 15, 2020.

RESULTS

Fifty-one completed clinical trials were identified that made use of a virus-based therapeutic strategy to treat HGG. The two main types of viral therapies were oncolytic viruses and viral vectors for gene therapy. Among clinical trials that met inclusion criteria, 20 related to oncolytic viruses and 31 to gene therapy trials. No oncolytic viruses have progressed to phase III clinical trial testing, although there have been many promising early-phase results and no reported cases of encephalitis or death due to viral therapy. Three phase III trials in which viral gene therapy was used have been completed but have not resulted in any FDA-approved therapy. Recent efforts in this area have been focused on the delivery of suicide genes such as herpes simplex virus thymidine kinase and cytosine deaminase.

CONCLUSIONS

Decades of research efforts and an improving understanding of the immunomodulatory effects of viral therapies for gliomas are informing ongoing clinical efforts aimed at improving outcomes in patients with HGG. The available clinical data reveal varied efficacy among different virus-based treatment strategies.

Teschemacher A, Kasparov S. Viral Vectors as Gene Therapy Agents for Treatment of Glioblastoma

In this review, we scrutinize the idea of using viral vectors either as cytotoxic agents or gene delivery tools for treatment of glioblastoma multiforme (GBM) in light of the experience that our laboratory has accumulated over ~20 years when using similar vectors in experimental neuroscience. We review molecular strategies and current clinical trials and argue that approaches which are based on targeting a specific biochemical pathway or a characteristic mutation are inherently prone to failure because of the high genomic instability and clonal selection characteristics of GBM. For the same reasons, attempts to develop a viral system which selectively transduces only GBM cells are also unlikely to be universally successful. One of the common gene therapy approaches is to use cytotoxic viruses which replicate and cause preferential lysis of the GBM cells. This strategy, in addition to its reliance on the specific biochemical makeup of the GBM cells, bears a risk of necrotic cell death accompanied by release of large quantities of pro-inflammatory molecules. On the other hand, engaging the immune system in the anti-GBM response seems to be a potential avenue to explore further. We suggest that a plausible strategy is to focus on viral vectors which efficiently transduce brain cells via a non-selective, ubiquitous mechanism and which target (ideally irreversibly) processes that are critical only for dividing tumor cells and are dispensable for quiescent brain cells.

Great expectations: virus-mediated gene therapy in neurological disorders

Gene therapy (GT) has tremendous potential for the treatment of neurological disorders to transform patient care. The successful application of virus-mediated GT to treat spinal muscular atrophy is a significant milestone, serving to accelerate similar progress in a spectrum of neurological conditions, with more than 50 clinical trials currently underway, across neurodevelopmental, neurodegenerative, muscular dystrophy, epilepsy, chronic pain and neoplastic diseases. This review provides an overview of the key features of virus-mediated GT, paradigms of delivery and dosing, potential risks and highlights ongoing research to optimise safe and effective delivery of vectors into the nervous system. Examples of the application of GT in various neurological diseases alongside clinical development challenges will be presented. As the development and translation of GTs gain pace, success can only ultimately be realised for patients following implementation in the health system. The challenges and controversies of daunting costs, ethics, early diagnosis and health system readiness will require innovative pricing schemes, regulatory policies, education and organisation of a skilled workforce to deliver of high-quality care in clinical practice as we prepare for advanced therapeutics in neurology.

The cell-based approach in neurosurgery: ongoing trends and future perspectives

OBJECTIVE

Examination of the current trends and future perspectives of the cell-based therapies in neurosurgery.

METHODS

A PubMed/MEDLINE-based systematic review has been performed combining the main Medical Subject Headings (MeSH) regarding the cell- and tissue-based therapies with the "Brain", "Spinal Cord", "Spine" and "Skull" MeSH terms. Only articles in English published in the last 10 years and pertinent to neurosurgery have been selected.

RESULTS

A total of 1,173 relevant articles have been chosen. Somatic cells and gene-modification technologies have undergone the greatest development. Immunotherapies and gene therapies have been tested for the cure of glioblastoma, stem cells mainly for brain and spinal cord traumatic injuries. Stem cells have also found a rationale in the treatment of the cranial and spinal bony defects, and of the intervertebral disc degeneration, as well.Most of the completed or ongoing trials concerning the cell-based therapies in neurosurgery are on phase 2. Future perspectives involve the need to overcome issues related to immunogenicity, oncogenicity and routes for administration. Refinement and improvement of vector design and delivery are required within the gene therapies.

CONCLUSION

The last decade has been characterised by a progressive evolution of neurosurgery from a purely mechanical phase to a new biological one. This trend has followed the rapid and parallel development of translational medicine and nanotechnologies.The introduction of new technologies, the optimisation of the already existing ones, and the reduction of costs are among the main challenges of the foreseeable future.

Dual-vector prodrug activator gene therapy using retroviral replicating vectors

Retroviral replicating vectors (RRVs) have been shown to achieve efficient tumor transduction and enhanced therapeutic benefits in a variety of cancer models. In the present study, we evaluated a possible combinatorial effect of prodrug activator genes delivered by two different RRVs derived from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV) on human hepatocellular carcinoma Hep3B cells. Both RRVs showed efficient replicative spread in culture and can overcame superinfection resistance each other. Notably, the replication and spread of each RRV in culture remained unaffected by pretransduction with the counterpart RRV. We further transduced cells with RRVs which individually possessed the prodrug activator genes yeast cytosine deaminase (CD) and herpes simplex virus thymidine kinase (TK) alone or in combination, and evaluated the cytotoxic effects of RRV-mediated gene therapy with CD and TK in the presence of the respective prodrugs, 5-fluorocytosine and ganciclovir. All combinations of the two prodrug activator genes produced synergistic cytocidal effects, but the combined effects of the different genes were significantly greater than those of the same genes when delivered by two different vectors. The present findings indicate the potential utility of dual-vector gene therapy using two different RRVs carrying different prodrug activator genes.

Pathogens and glioma: a history of unexpected discoveries ushering in novel therapy

In the late 19th century, Dr. William B. Coley introduced the theory that infections may aid in the treatment of malignancy. With the creation of Coley’s toxin, reports of remission during viral illnesses for systemic malignancies soon emerged. A few decades after this initial discovery, Austrian physicians performed intravascular injections of Clostridium to induce oncolysis in patients with glioblastoma. Since then, suggestions between improved survival and infectious processes have been reported in several patients with glioma, which ultimately marshaled the infamous use of intracerebral Enterobacter. These early observations of tumor regression and concomitant infection piloted a burgeoning field focusing on the use of pathogens in molecular oncology.

Biodegradable brain-penetrating DNA nanocomplexes and their use to treat malignant brain tumors

The discovery of powerful genetic targets has spurred clinical development of gene therapy approaches to treat patients with malignant brain tumors. However, lack of success in the clinic has been attributed to the inability of conventional gene vectors to achieve gene transfer throughout highly disseminated primary brain tumors. Here, we demonstrate ex vivo that small nanocomplexes composed of DNA condensed by a blend of biodegradable polymer, poly(β-amino ester) (PBAE), with PBAE conjugated with 5kDa polyethylene glycol (PEG) molecules (PBAE-PEG) rapidly penetrate healthy brain parenchyma and orthotopic brain tumor tissues in rats. Rapid diffusion of these DNA-loaded nanocomplexes observed in fresh tissues ex vivo demonstrated that they avoided adhesive trapping in the brain owing to their dense PEG coating, which was critical to achieving widespread transgene expression throughout orthotopic rat brain tumors in vivo following administration by convection enhanced delivery. Transgene expression with the PBAE/PBAE-PEG blended nanocomplexes (DNA-loaded brain-penetrating nanocomplexes, or DNA-BPN) was uniform throughout the tumor core compared to nanocomplexes composed of DNA with PBAE only (DNA-loaded conventional nanocomplexes, or DNA-CN), and transgene expression reached beyond the tumor edge, where infiltrative cancer cells are found, only for the DNA-BPN formulation. Finally, DNA-BPN loaded with anti-cancer plasmid DNA provided significantly enhanced survival compared to the same plasmid DNA loaded in DNA-CN in two aggressive orthotopic brain tumor models in rats. These findings underscore the importance of achieving widespread delivery of therapeutic nucleic acids within brain tumors and provide a promising new delivery platform for localized gene therapy in the brain.

Adenovirus-mediated delivery of herpes simplex virus thymidine kinase administration improves outcome of recurrent high-grade glioma

BACKGROUND

This randomized, open-label, multicenter, phase II clinical trial was conducted to assess the anti-tumor efficacy and safety of replication-deficient adenovirus mutant thymidine kinase (ADV-TK) in combination with ganciclovir administration in patients with recurrent high-grade glioma (HGG).

PATIENTS AND METHODS

53 patients with recurrent HGG were randomly allocated to receive intra-arterial cerebral infusion of ADV-TK or conventional treatments. The primary end point was 6-month progression-free survival (PFS-6). Secondary end points included progression-free survival (PFS), overall survival (OS), safety, and clinical benefit. This trial is registered with Clinicaltrials.gov, NCT00870181.

RESULTS

In ADV-TK group, PFS-6 was 54.5%, the median PFS was 29.6 weeks, the median OS was 45.4 weeks, and better survivals were achieved when compared with control group. The one-year PFS and OS were 22.7% and 44.6% in ADV-TK group respectively, and clinical benefit was 68.2%. There are 2 patients alive for more than 4 years without progression in ADV-TK group. In the subgroup of glioblastoma received ADV-TK, PFS-6 was 71.4%, median PFS was 34.9 weeks, median OS was 45.7 weeks respectively, much better than those in control group. The one-year PFS and OS were 35.7% and 50.0% in ADV-TK group respectively. ADV-TK/ganciclovir gene therapy was well tolerated, and no treatment-related severe adverse events were noted.

CONCLUSION

Our study demonstrated a notable improvement of PFS-6, PFS and OS in ADV-TK treated group, and the efficacy and safety appear to be comparable to other reported treatments used for recurrent HGG. ADV-TK gene therapy is therefore a valuable therapeutic option for recurrent HGG.

Chimeric adeno-associated virus and bacteriophage: a potential targeted gene therapy vector for malignant glioma

The incipient development of gene therapy for cancer has fuelled its progression from bench to bedside in mere decades. Of all malignancies that exist, gliomas are the largest class of brain tumors, and are renowned for their aggressiveness and resistance to therapy. In order for gene therapy to achieve clinical success, a multitude of barriers ranging from glioma tumor physiology to vector biology must be overcome. Many viral gene delivery systems have been subjected to clinical investigation; however, with highly limited success. In this review, the current progress and challenges of gene therapy for malignant glioma are discussed. Moreover, we highlight the hybrid adeno-associated virus and bacteriophage vector as a potential candidate for targeted gene delivery to brain tumors.

Biodegradable DNA Nanoparticles that Provide Widespread Gene Delivery in the Brain

Successful gene therapy of neurological disorders is predicated on achieving widespread and uniform transgene expression throughout the affected disease area in the brain. However, conventional gene vectors preferentially travel through low-resistance perivascular spaces and/or are confined to the administration site even with the aid of a pressure-driven flow provided by convection-enhanced delivery. Biodegradable DNA nanoparticles offer a safe gene delivery platform devoid of adverse effects associated with virus-based or synthetic nonbiodegradable systems. Using a state-of-the-art biodegradable polymer, poly(β-amino ester), colloidally stable sub-100 nm DNA nanoparticles are engineered with a nonadhesive polyethylene glycol corona that are able to avoid the adhesive and steric hindrances imposed by the extracellular matrix. Following convection enhanced delivery, these brain-penetrating nanoparticles are able to homogeneously distribute throughout the rodent striatum and mediate widespread and high-level transgene expression. These nanoparticles provide a biodegradable DNA nanoparticle platform enabling uniform transgene expression patterns in vivo and hold promise for the treatment of neurological diseases.

Experimental therapies: gene therapies and oncolytic viruses

Glioblastoma is the most common and aggressive primary brain tumor in adults. Over the past three decades, the overall survival time has only improved by a few months, therefore novel alternative treatment modalities are needed to improve clinical management strategies. Such strategies should ultimately extend patient survival. At present, the extensive insight into the molecular biology of gliomas, as well as into genetic engineering techniques, has led to better decision processes when it comes to modifying the genome to accommodate suicide genes, cytokine genes, and tumor suppressor genes that may kill cancer cells, and boost the host defensive immune system against neoantigenic cytoplasmic and nuclear targets. Both nonreplicative viral vectors and replicating oncolytic viruses have been developed for brain cancer treatment. Stem cells, microRNAs, nanoparticles, and viruses have also been designed. These have been armed with transgenes or peptides, and have been used both in laboratory-based experiments as well as in clinical trials, with the aim of improving selective killing of malignant glioma cells while sparing normal brain tissue. This chapter reviews the current status of gene therapies for malignant gliomas and highlights the most promising viral and cell-based strategies under development.

A systematic review and meta-analysis of gene therapy in animal models of cerebral glioma: why did promise not translate to human therapy?

BACKGROUND

The development of therapeutics is often characterized by promising animal research that fails to translate into clinical efficacy; this holds for the development of gene therapy in glioma. We tested the hypothesis that this is because of limitations in the internal and external validity of studies reporting the use of gene therapy in experimental glioma.

METHOD

We systematically identified studies testing gene therapy in rodent glioma models by searching three online databases. The number of animals treated and median survival were extracted and studies graded using a quality checklist. We calculated median survival ratios and used random effects meta-analysis to estimate efficacy. We explored effects of study design and quality and searched for evidence of publication bias.

RESULTS

We identified 193 publications using gene therapy in experimental glioma, including 6,366 animals. Overall, gene therapy improved median survival by a factor of 1.60 (95% CI 1.53-1.67). Study quality was low and the type of gene therapy did not account for differences in outcome. Study design characteristics accounted for a significant proportion of between-study heterogeneity. We observed similar findings in a data subset limited to the most common gene therapy.

CONCLUSION

As the dysregulation of key molecular pathways is characteristic of gliomas, gene therapy remains a promising treatment for glioma. Nevertheless, we have identified areas for improvement in conduct and reporting of studies, and we provide a basis for sample size calculations. Further work should focus on genes of interest in paradigms recapitulating human disease. This might improve the translation of such therapies into the clinic.

Glioblastoma multiforme: State of the art and future therapeutics

BACKGROUND

Glioblastoma multiforme (GBM) is the most common and lethal primary malignancy of the central nervous system (CNS). Despite the proven benefit of surgical resection and aggressive treatment with chemo- and radiotherapy, the prognosis remains very poor. Recent advances of our understanding of the biology and pathophysiology of GBM have allowed the development of a wide array of novel therapeutic approaches, which have been developed. These novel approaches include molecularly targeted therapies, immunotherapies, and gene therapy.

METHODS

We offer a brief review of the current standard of care, and a survey of novel therapeutic approaches for treatment of GBM.

RESULTS

Despite promising results in preclinical trials, many of these therapies have demonstrated limited therapeutic efficacy in human clinical trials. Thus, although survival of patients with GBM continues to slowly improve, treatment of GBM remains extremely challenging.

CONCLUSION

Continued research and development of targeted therapies, based on a detailed understanding of molecular pathogenesis can reasonably be expected to yield improved outcomes for patients with GBM.

Adenoviral vector-mediated gene therapy for gliomas: coming of age

INTRODUCTION

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and it carries a dismal prognosis. Adenoviral vector (Ad)-mediated gene transfer is being developed as a promising therapeutic strategy for GBM. Preclinical studies have demonstrated safety and efficacy of adenovirus administration into the brain and tumor mass in rodents and into the non-human primates' brain. Importantly, Ads have been safely administered within the tumor resection cavity in humans.

AREAS COVERED

This review gives background on GBM and Ads; we describe gene therapy strategies for GBM and discuss the value of combination approaches. Finally, we discuss the results of the human clinical trials for GBM that have used Ads.

EXPERT OPINION

The transduction characteristics of Ads, and their safety profile, added to their capacity to achieve high levels of transgene expression have made them powerful vectors for the treatment of GBM. Recent gene therapy successes in the treatment of retinal diseases and systemic brain metabolic diseases encourage the development of gene therapy for malignant glioma. Exciting clinical trials are currently recruiting patients; although, it is the large randomized Phase III controlled clinical trials that will provide the final decision on the success of gene therapy for the treatment of GBM.

Adenoviral vector-mediated gene therapy for gliomas: coming of age

INTRODUCTION

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and it carries a dismal prognosis. Adenoviral vector (Ad)-mediated gene transfer is being developed as a promising therapeutic strategy for GBM. Preclinical studies have demonstrated safety and efficacy of adenovirus administration into the brain and tumor mass in rodents and into the non-human primates' brain. Importantly, Ads have been safely administered within the tumor resection cavity in humans.

AREAS COVERED

This review gives background on GBM and Ads; we describe gene therapy strategies for GBM and discuss the value of combination approaches. Finally, we discuss the results of the human clinical trials for GBM that have used Ads.

EXPERT OPINION

The transduction characteristics of Ads, and their safety profile, added to their capacity to achieve high levels of transgene expression have made them powerful vectors for the treatment of GBM. Recent gene therapy successes in the treatment of retinal diseases and systemic brain metabolic diseases encourage the development of gene therapy for malignant glioma. Exciting clinical trials are currently recruiting patients; although, it is the large randomized Phase III controlled clinical trials that will provide the final decision on the success of gene therapy for the treatment of GBM.

Prognostic utility of gene therapy with herpes simplex virus thymidine kinase for patients with high-grade malignant gliomas: a systematic review and meta analysis

The aim of this study was to assess the effectiveness of adding viral vector-mediated gene therapy with herpes simplex virus thymidine kinase (HSV-tk) to standard treatment, in comparison with standard treatment alone to treat patients with high-grade gliomas (HGGs). A literature search of the databases PubMed, Embase, the Cochrane Library, Web of Science, and Chinese biomedicine was performed to identify eligible studies. Three randomized controlled trials (involving a total of 532 patients) were included in this systematic review. A meta-analysis of included studies demonstrated a significant increase in median survival time (MST) in patients who were treated with HSV-tk gene therapy (mean deviation 0.59, 95% CI: 0.41-0.76, p < 0.0001). The results of pooled analysis for different patient groups show that overall survival (OS) for all HGG patients was improved by adding gene therapy [hazard ratio (HR) = 0.91, 95% CI: 0.74-1.13, p = 0.42], while a different result was seen for glioblastoma multiforme (GBM) patients (HR = 1.06, 95% CI: 0.80-1.41, p = 0.70). Furthermore, the combined results for tumor progression implied that standard therapy was superior to gene therapy [odds ratio (OR) = 1.31, p = 0.09]; yet differences in HR and OR between experimental groups and control groups had no statistical significance (p > 0.05). Based on the best available evidence, it appears that adding gene therapy with HSV-tk has some effect in treating HGG patients, especially with respect to MST. However, neither the pooled analysis of OS, nor the combined analysis of tumor progress indicates any significant advantage to adding gene therapy compared with standard treatment alone. More prospective studies are needed to draw solid conclusions about whether gene therapy has significant prognostic advantage.

Glioma virus therapies between bench and bedside

Despite extensive research, current glioma therapies are still unsatisfactory, and novel approaches are pressingly needed. In recent years, both nonreplicative viral vectors and replicating oncolytic viruses have been developed for brain cancer treatment, and the mechanistic background of their cytotoxicity has been unveiled. A growing number of clinical trials have convincingly established viral therapies to be safe in glioma patients, and maximum tolerated doses have generally not been reached. However, evidence for therapeutic benefit has been limited: new generations of therapeutic vectors need to be developed in order to target not only tumor cells but also the complex surrounding microenvironment. Such therapies could also direct long-lasting immune responses toward the tumor while reducing early antiviral reactions. Furthermore, viral delivery methods are to be improved and viral spread within the tumor will have to be enhanced. Here, we will review the outcome of completed glioma virus therapy trials as well as highlight the ongoing clinical activities. On this basis, we will give an overview of the numerous strategies to enhance therapeutic efficacy of new-generation viruses and novel treatment regimens. Finally, we will conclude with approaches that may be crucial to the development of successful glioma therapies in the future.

Clinical trials of viral therapy for malignant gliomas

Despite recent scientific advances in the understanding of the biology of malignant gliomas, there has been little change in the overall survival for this devastating disease. New and innovative treatments are under constant investigation. Starting in the 1990s, there was an interest in using viral therapeutics for the treatment of malignant gliomas. Multiple strategies were pursued, including oncolytic viral therapy, enzyme/pro-drug combinations and gene transfer with viral vectors. Multiple Phase I and II trials demonstrated the safety of these techniques, but clinically showed limited efficacy. However, this led to a better understanding of the pitfalls of viral therapy and encouraged the development of new approaches and improved delivery methods. Here we review the prior and ongoing clinical trials of viral therapy for gliomas, and discuss how novel strategies are currently being utilized in clinical trials.

Current status of local therapy in malignant gliomas--a clinical review of three selected approaches

Malignant gliomas are the most frequently occurring, devastating primary brain tumors, and are coupled with a poor survival rate. Despite the fact that complete neurosurgical resection of these tumors is impossible in consideration of their infiltrating nature, surgical resection followed by adjuvant therapeutics, including radiation therapy and chemotherapy, is still the current standard therapy. Systemic chemotherapy is restricted by the blood-brain barrier, while methods of local delivery, such as with drug-impregnated wafers, convection-enhanced drug delivery, or direct perilesional injections, present attractive ways to circumvent these barriers. These methods are promising ways for direct delivery of either standard chemotherapeutic or new anti-cancer agents. Several clinical trials showed controversial results relating to the influence of a local delivery of chemotherapy on the survival of patients with both recurrent and newly diagnosed malignant gliomas. Our article will review the development of the drug-impregnated release, as well as convection-enhanced delivery and the direct injection into brain tissue, which has been used predominantly in gene-therapy trials. Further, it will focus on the use of convection-enhanced delivery in the treatment of patients with malignant gliomas, placing special emphasis on potential shortcomings in past clinical trials. Although there is a strong need for new or additional therapeutic strategies in the treatment of malignant gliomas, and although local delivery of chemotherapy in those tumors might be a powerful tool, local therapy is used only sporadically nowadays. Thus, we have to learn from our mistakes in the past and we strongly encourage future developments in this field.

Progress in gene therapy for neurological disorders

Diseases of the nervous system have devastating effects and are widely distributed among the population, being especially prevalent in the elderly. These diseases are often caused by inherited genetic mutations that result in abnormal nervous system development, neurodegeneration, or impaired neuronal function. Other causes of neurological diseases include genetic and epigenetic changes induced by environmental insults, injury, disease-related events or inflammatory processes. Standard medical and surgical practice has not proved effective in curing or treating these diseases, and appropriate pharmaceuticals do not exist or are insufficient to slow disease progression. Gene therapy is emerging as a powerful approach with potential to treat and even cure some of the most common diseases of the nervous system. Gene therapy for neurological diseases has been made possible through progress in understanding the underlying disease mechanisms, particularly those involving sensory neurons, and also by improvement of gene vector design, therapeutic gene selection, and methods of delivery. Progress in the field has renewed our optimism for gene therapy as a treatment modality that can be used by neurologists, ophthalmologists and neurosurgeons. In this Review, we describe the promising gene therapy strategies that have the potential to treat patients with neurological diseases and discuss prospects for future development of gene therapy.

The art of gene therapy for glioma: a review of the challenging road to the bedside

Glioblastoma multiforme (GBM) is a highly invasive brain tumour that is unvaryingly fatal in humans despite even aggressive therapeutic approaches such as surgical resection followed by chemotherapy and radiotherapy. Unconventional treatment options such as gene therapy provide an intriguing option for curbing glioma related deaths. To date, gene therapy has yielded encouraging results in preclinical animal models as well as promising safety profiles in phase I clinical trials, but has failed to demonstrate significant therapeutic efficacy in phase III clinical trials. The most widely studied antiglioma gene therapy strategies are suicide gene therapy, genetic immunotherapy and oncolytic virotherapy, and we have attributed the challenging transition of these modalities into the clinic to four major roadblocks: (1) anatomical features of the central nervous system, (2) the host immune system, (3) heterogeneity and invasiveness of GBM and (4) limitations in current GBM animal models. In this review, we discuss possible ways to jump these hurdles and develop new gene therapies that may be used alone or in synergy with other modalities to provide a powerful treatment option for patients with GBM.

Gene therapy for brain tumors: basic developments and clinical implementation

Glioblastoma multiforme (GBM) is the most common and deadliest of adult primary brain tumors. Due to its invasive nature and sensitive location, complete resection remains virtually impossible. The resistance of GBM against chemotherapy and radiotherapy necessitate the development of novel therapies. Gene therapy is proposed for the treatment of brain tumors and has demonstrated pre-clinical efficacy in animal models. Here we review the various experimental therapies that have been developed for GBM including both cytotoxic and immune stimulatory approaches. We also review the combined conditional cytotoxic immune stimulatory therapy that our lab has developed which is dependent on the adenovirus mediated expression of the conditional cytotoxic gene, Herpes Simplex Type 1 Thymidine Kinase (TK) and the powerful DC growth factor Fms-like tyrosine kinase 3 ligand (Flt3L). Combined delivery of these vectors elicits tumor cell death and an anti-tumor adaptive immune response that requires TLR2 activation. The implications of our studies indicate that the combined cytotoxic and immunotherapeutic strategies are effective strategies to combat deadly brain tumors and warrant their implementation in human Phase I clinical trials for GBM.

Cytotoxic immunotherapy strategies for cancer: mechanisms and clinical development

Traditional therapies for cancer include surgery, chemotherapy, and radiation. Chemotherapy has widespread systemic cytotoxic effects against tumor cells but also affects normal cells. Radiation has more targeted local cytotoxicity but is limited to killing cells in the radiation field. Immunotherapy has the potential for systemic, specific killing of tumor cells. However, if the immune response is specific to a single antigen, tumor evasion can occur by down-regulation of that antigen. An immunotherapy approach that induces polyvalent immunity to autologous tumor antigens can provide a personalized vaccine with less potential for immunologic escape. A cytotoxic immunotherapy strategy creates such a tumor vaccine in situ. Immunogenic tumor cell death provides tumor antigen targets for the adaptive immune response and stimulates innate immunity. Attraction and activation of antigen presenting cells such as dendritic cells is important to process and present tumor antigens to T cells. These include cytotoxic T cells that kill tumor cells and T cells which positively and negatively regulate immunity. Tipping the balance in favor of anti-tumor immunity is an important aspect of an effective strategy. Clinically, immunotherapies may be most effective when combined with standard therapies in a complimentary way. An example is gene-mediated cytotoxic immunotherapy (GMCI) which uses an adenoviral vector, AdV-tk, to deliver a cytotoxic and immunostimulatory gene to tumor cells in vivo in combination with standard therapies creating an immunostimulatory milieu. This approach, studied extensively in animal models and early stage clinical trials, is now entering a definitive Phase 3 trial for prostate cancer.

Gene therapy and targeted toxins for glioma

The most common primary brain tumor in adults is glioblastoma. These tumors are highly invasive and aggressive with a mean survival time of 15-18 months from diagnosis to death. Current treatment modalities are unable to significantly prolong survival in patients diagnosed with glioblastoma. As such, glioma is an attractive target for developing novel therapeutic approaches utilizing gene therapy. This review will examine the available preclinical models for glioma including xenographs, syngeneic and genetic models. Several promising therapeutic targets are currently being pursued in pre-clinical investigations. These targets will be reviewed by mechanism of action, i.e., conditional cytotoxic, targeted toxins, oncolytic viruses, tumor suppressors/oncogenes, and immune stimulatory approaches. Preclinical gene therapy paradigms aim to determine which strategies will provide rapid tumor regression and long-term protection from recurrence. While a wide range of potential targets are being investigated preclinically, only the most efficacious are further transitioned into clinical trial paradigms. Clinical trials reported to date are summarized including results from conditionally cytotoxic, targeted toxins, oncolytic viruses and oncogene targeting approaches. Clinical trial results have not been as robust as preclinical models predicted; this could be due to the limitations of the GBM models employed. Once this is addressed, and we develop effective gene therapies in models that better replicate the clinical scenario, gene therapy will provide a powerful approach to treat and manage brain tumors.

Phase IB study of gene-mediated cytotoxic immunotherapy adjuvant to up-front surgery and intensive timing radiation for malignant glioma

PURPOSE

Despite aggressive therapies, median survival for malignant gliomas is less than 15 months. Patients with unmethylated O(6)-methylguanine-DNA methyltransferase (MGMT) fare worse, presumably because of temozolomide resistance. AdV-tk, an adenoviral vector containing the herpes simplex virus thymidine kinase gene, plus prodrug synergizes with surgery and chemoradiotherapy, kills tumor cells, has not shown MGMT dependency, and elicits an antitumor vaccine effect.

PATIENTS AND METHODS

Patients with newly diagnosed malignant glioma received AdV-tk at 3 × 10(10), 1 × 10(11), or 3 × 10(11) vector particles (vp) via tumor bed injection at time of surgery followed by 14 days of valacyclovir. Radiation was initiated within 9 days after AdV-tk injection to overlap with AdV-tk activity. Temozolomide was administered after completing valacyclovir treatment.

RESULTS

Accrual began December 2005 and was completed in 13 months. Thirteen patients were enrolled and 12 completed therapy, three at dose levels 1 and 2 and six at dose level 3. There were no dose-limiting or significant added toxicities. One patient withdrew before completing prodrug because of an unrelated surgical complication. Survival at 2 years was 33% and at 3 years was 25%. Patient-reported quality of life assessed with the Functional Assessment of Cancer Therapy-Brain (FACT-Br) was stable or improved after treatment. A significant CD3(+) T-cell infiltrate was found in four of four tumors analyzed after treatment. Three patients with MGMT unmethylated glioblastoma multiforme survived 6.5, 8.7, and 46.4 months.

CONCLUSION

AdV-tk plus valacyclovir can be safely delivered with surgery and accelerated radiation in newly diagnosed malignant gliomas. Temozolomide did not prevent immune responses. Although not powered for efficacy, the survival and MGMT independence trends are encouraging. A phase II trial is ongoing.

Truncating the i-leader open reading frame enhances release of human adenovirus type 5 in glioma cells

Background

The survival of glioma patients with the current treatments is poor. Early clinical trails with replicating adenoviruses demonstrated the feasibility and safety of the use of adenoviruses as oncolytic agents. Antitumor efficacy has been moderate due to inefficient virus replication and spread. Previous studies have shown that truncation of the adenovirus i-leader open reading frame enhanced cytopathic activity of HAdV-5 in several tumor cell lines. Here we report the effect of an i-leader mutation on the cytopathic activity in glioma cell lines and in primary high-grade glioma cell cultures.

Results

A mutation truncating the i-leader open reading frame was created in a molecular clone of replication-competent wild-type HAdV-5 by site-directed mutagenesis. We analyzed the cytopathic activity of this RL-07 mutant virus. A cell-viability assay showed increased cytopathic activity of the RL-07 mutant virus on U251 and SNB19 glioma cell lines. The plaque sizes of RL-07 on U251 monolayers were seven times larger than those of isogenic control viruses. Similarly, the cytopathic activity of the RL-07 viruses was strongly increased in six primary high-grade glioma cell cultures. In glioma cell lines the RL-07 virus was found to be released earlier into the culture medium. This was not due to enhanced viral protein synthesis, as was evident from equivalent E1A, Fiber and Adenovirus Death Protein amounts, nor to higher virus yields.

Conclusion

The cytopathic activity of replicating adenovirus in glioblastoma cells is increased by truncating the i-leader open reading frame. Such mutations may help enhancing the antitumor cytopathic efficacy of oncolytic adenoviruses in the treatment of glioblastoma.

Sitimagene ceradenovec: a gene-based drug for the treatment of operable high-grade glioma

The field of gene therapy for malignant glioma has made important advances since the first gene transfer studies were performed 20 years ago. Multiple Phase I/II trials and two Phase III trials have been performed and have demonstrated the feasibility and safety of intratumoral vector delivery in the brain. Sitimagene ceradenovec is an adenoviral vector encoding the herpes simplex thymidine kinase gene, developed by Ark Therapeutics Group plc (UK and Finland) for the treatment of patients with operable high-grade glioma. In preclinical and Phase I/II clinical studies, sitimagene ceradenovec exhibited a significant increase in survival. Although the preliminary results of a Phase III clinical study demonstrated a significant positive effect of sitimagene ceradenovec treatment on time to reintervention or death when compared with standard care treatment (hazard ratio: 1.43; 95% CI: 1.06-1.93; p < 0.05), the European Committee for Medicinal Products for Human Use did not consider the data to provide sufficient evidence of clinical benefit. Further clinical evaluation, powered to demonstrate a benefit on a robust end point, is required. This article focuses on sitimagene ceradenovec and provides an overview of the developments in the field of gene therapy for malignant glioma.

Inhibition of ATP-sensitive potassium channels increases HSV-tk/GCV bystander effect in U373 human glioma cells by enhancing gap junctional intercellular communication

It is well known that the efficiency of Herpes simplex virus thymidine kinase gene/ganciclovir (HSV-tk/GCV) therapy is improved by the bystander effect, which mainly relies on gap junctional intercellular communication (GJIC). Malignant gliomas communicate poorly through gap junctions, consequently, agents with the ability to increase GJIC are good candidates to improve the efficiency of this therapy. Since we previously showed that the inhibition of ATP-sensitive potassium (KATP) channels promoted by tolbutamide increased GJIC in rat C6 glioma cells, we have investigated whether tolbutamide could increase the bystander effect in HSV-tk/GCV therapy against human glioma cells. We found that tolbutamide increased GJIC in U373 human glioma cells, an effect that was due to the up-regulation of connexin43, a protein that forms gap junctions channels. More interestingly, our results show that tolbutamide increased the efficiency of HSV-tk/GCV in co-cultures containing U373 cells and U373 cells transfected with HSV-tk. This effect was impaired in the presence of carbenoxolone, an inhibitor of GJIC. Furthermore, tolbutamide did not enhance the bystander effect in connexin43-silenced co-cultures. Together our results reveal that the inhibition of KATP channels promoted by tolbutamide enhances the bystander effect in HSV-tk/GCV therapy by increasing connexin43-mediated gap junctional intercellular communication in U373 human glioma cells.

Comparative evaluation of preclinical in vivo models for the assessment of replicating retroviral vectors for the treatment of glioblastoma

Despite impressive improvements in neurosurgical techniques, radiation and chemotherapy during the past few years, little progress has been made in the treatment of malignant gliomas. Recently, the efficacy of suicide gene therapy based on replication-competent retroviral (RCR) vectors as delivery vehicles for the therapeutic gene has been described in the treatment of experimental cancer, including gliomas. In this study, we have thus critically evaluated a panel of human and rodent glioma/glioblastoma cell lines (U-87MG, U-118MG, LN-18, LN-229, 8-MG-BA, 42-MG-BA, A-172, T-98G, UVW, C6, 9L, G-26, GL-261, Tu-2449, Tu-9648) with respect to RCR virus vector spread, sensitivity towards the cytosine deaminase (CD)/5-flurocytosine (5-FC)/5-flurouracil (5-FU) suicide system, and orthotopic growth characteristics in mice to identify suitable preclinical animal models for the development of a glioblastoma gene therapy. Rapid virus spread was observed in eight out of nine human cell lines tested in vitro. As expected, only CD-expressing cells became sensitive to 5-FC, due to their ability to convert the prodrug in its toxic form, 5-FU. All LD(50) values were within the range of concentrations obtained in human body fluids after conventional antifungal 5-FC administration. In addition, a significant bystander effect was observed in all human glioma cell lines tested. Injection of the RCR vector into pre-established orthotopic mouse tumor xenografts revealed substantial infection and virus spread of tumor tissue from most cell types.

A preclinical assessment of the safety and biodistribution of an adenoviral vector containing the herpes simplex virus thymidine kinase gene (Cerepro) after intracerebral administration

BACKGROUND

Cerepro (sitimagene ceradenovec) is an adenoviral vector containing herpes simplex virus thymidine kinase gene (HSV-tk), which is being developed for the treatment of high-grade glioma with oral ganciclovir (GCV). The nonclinical safety and biodistribution of Cerepro were assessed following intravenous (i.v.) or intracerebral (i.c.) injection.

METHODS

Crl : WI(GLX/BRL/Han) rats (n = 198) were injected i.c. or i.v. with Cerepro or vehicle control, with GCV by intraperitoneal (i.p.) injection to selected groups. Safety was assessed by observation of animal behaviour and post mortem histology. Antibody response was assessed, and biodistribution measured using the quantitative polymerase chain reaction (PCR) and reverse transcriptase-PCR in blood and tissues.

RESULTS

Following i.v. or i.c. injection, there was no antibody response and no effect on behaviour, body weight, food consumption or haematological and clinical chemistry parameters. Minor needle track changes were observed in control and Cerepro-i.c. injection groups. Transient myeloid hyperplasia was observed in five of the 24 animals in the i.v. injection group and spleen weight increased in both the i.c. and i.v. groups. Cerepro was detected in the brain and at low levels in blood and spleen following i.c. injection, decreasing with time. Following i.v. injection, Cerepro was detected in viscera and blood, decreasing with time. Transcription of Cerepro was detected in the brain following i.c. injection, with lower levels in spleen; following i.v. injection, transcription was seen in viscera. Germline integration was not seen.

CONCLUSIONS

Intracerebral injection of Cerepro is safe and produces a high level of transgene expression in the brain, with limited biodistribution.

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.

Gene therapy as an adjuvant treatment for malignant gliomas: from bench to bedside

Malignant brain tumors, including high-grade gliomas, are among the most lethal of all cancers. Despite considerable advances, including multi-modality treatments with surgery, radiotherapy, and chemotherapy, the overall prognosis for patients with this disease remains dismal. Currently available treatments necessitate the development of more effective tumor-selective therapies. The use of gene therapy for brain tumor therapy is promising as it can be delivered in situ and selectively targets brain tumor cells while sparing the adjacent normal brain tissue. In this article, we summarize the laboratory and clinical work using viral, cell-based, and synthetic vectors, as well as other strategies focused on potentiate gene delivery. Although tangible results on patients' survival remains to be further documented, significant advances in therapeutic gene transfer strategies have been made. The enthusiasm of this progress needs to be tempered by the realistic assessment of the challenges needed to be overcome. Finally, as the field of gene delivery progresses, advances must be made in identifying genes and proteins key to the treatment of malignant gliomas. Due to the great heterogeneity of malignant glioma cells, only approaches combining different strategies may be ultimately successful in defeating this disease.

MLH1 deficiency enhances tumor cell sensitivity to ganciclovir

Suicide gene therapy with herpes simplex virus thymidine kinase and ganciclovir is notable for producing multi-log cytotoxicity in a unique pattern of delayed cytotoxicity in S-phase. Because hydroxyurea, a ribonucleotide reductase inhibitor that activates mismatch repair, can increase sensitivity to ganciclovir, we evaluated the role of MLH1, an essential mismatch repair protein, in ganciclovir cytotoxicity. Using HCT116TK (HSV-TK-expressing) colon carcinoma cells that express or lack MLH1, cell survival studies demonstrated greater ganciclovir sensitivity in the MLH1 deficient cells, primarily at high concentrations. This could not be explained by differences in ganciclovir metabolism, as the less sensitive MLH1-expresssing cells accumulated more ganciclovir triphosphate and incorporated more of the analog into DNA. SiRNA suppression of MLH1 in U251 glioblastoma or SW480 colon carcinoma cells also enhanced sensitivity to high concentrations of ganciclovir. Studies in a panel of yeast deletion mutants confirmed the results with MLH1, and further suggested a role for homologous recombination repair and several cell cycle checkpoint proteins in ganciclovir cytotoxicity. These data suggest that MLH1 can prevent cytotoxicity with ganciclovir. Targeting mismatch repair-deficient tumors may increase efficacy of this suicide gene therapy approach to cancer treatment.

Molecular strategies for the treatment of malignant glioma--genes, viruses, and vaccines

The standard treatment paradigm of surgery, radiation, and chemotherapy for malignant gliomas has only a modest effect on survival. It is well emphasized in the literature that despite aggressive multimodal therapy, most patients survive approximately 1 year after diagnosis, and less than 10% survive beyond 2 years. This dismal prognosis provides the impetus for ongoing investigations in search of improved therapeutics. Standard multimodal therapy has largely reached a plateau in terms of effectiveness, and there is now a growing body of literature on novel molecular approaches for the treatment of malignant gliomas. Gene therapy, oncolytic virotherapy, and immunotherapy are the major investigational approaches that have demonstrated promise in preclinical and early clinical studies. These new molecular technologies each have distinct advantages and limitations, and none has yet demonstrated a significant survival benefit in a phase II or III clinical trial. Molecular approaches may not lead to the discovery of a "magic bullet" for these aggressive tumors, but they may ultimately prove synergistic with more conventional approaches and lead to a broadening of the multimodal approach that is the current standard of care. This review will discuss the scientific background, therapeutic potential, and clinical limitations of these novel strategies with a focus on those that have made it to clinical trials.

Targeting malignant gliomas with a glial fibrillary acidic protein (GFAP)-selective oncolytic adenovirus

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein abundantly expressed in malignant gliomas. We have constructed a novel oncolytic adenovirus, Ad5-gfa2(B)3-E1, for treatment of these tumors. In this construct, the E1 region is under control of the tissue-specific GFAP promoter (gfa2) with three additional copies of the glial specific 'B' enhancer. Infection of a GFAP-positive cell line with Ad5-gfa2(B)3-E1 resulted in E1A and E1B expression at 75% and 30% of the levels obtained after wtAd5 infection. Q-PCR showed that Ad5-gfa2(B)3-E1 replicated 4.5 times more efficiently in the GFAP-positive than in the GFAP-negative cell lines. Cell viability assays showed efficient elimination of GFAP-positive cells by Ad5-gfa2(B)3-E1, in some cell lines as efficiently as wtAd5, while the elimination was attenuated in GFAP-negative cell lines. When tested in human tumor xenografts in nude mice, Ad5-gfa2(B)3-E1 effectively suppressed the growth of GFAP-positive SNB-19 glial tumors but not of GFAP-negative A549 lung tumors. In Ad5-gfa2(B)3-E1, the E3 region was deleted to create space for future insertion of heterologous therapeutic genes. Experiments with dl7001, an E3-deleted variant of wtAd5, confirmed that the specificity of Ad5-gfa2(B)3-E1 replication was based on the promoter driving E1 and not on the E3 deletion. Strategies to further improve the efficacy of Ad5-gfa2(B)3-E1 for the treatment of malignant gliomas include the insertion of therapeutic genes in E3 or retargeting to receptors that are more abundantly expressed on primary glioma cells than CAR.

A phase I trial of intratumoral administration of reovirus in patients with histologically confirmed recurrent malignant gliomas

Reovirus is an oncolytic virus with activity in in vivo models of malignant gliomas (MGs). The primary aims were to determine the dose-limiting toxicity (DLT) and maximum tolerated dose (MTD) of intratumoral administration of reovirus in patients with recurrent MGs. Response, survival, and time to progression (TTP) were secondary aims. Patients were adults, had Karnofsky Performance score > or = 60, received prior radiotherapy with or without chemotherapy, and had up to the third recurrence of MG. Reovirus was administered intratumorally stereotactically at 1 x 10(7), 1 x 10(8), or 1 x 10(9) tissue culture infectious dose 50 (TCID50) in a volume of 0.9 ml. Twelve patients were treated at three dose levels (3, 6, and 3 patients, respectively). Seven were men, median Karnofsky Performance score was 80, and median age was 53.5 years. There were no grade III or IV adverse events (AEs) definitely or probably related to treatment. Ten patients had tumor progression, one had stabilization, and one was not evaluable for response. Median survival was 21 weeks (range, 6-234), and one is alive 54 months after treatment. Median TTP was 4.3 weeks (range, 2.6-39). An MTD was not reached. The intratumoral administration of the genetically unmodified reovirus was well tolerated using these doses and schedule, in patients with recurrent MG.

An inventory of shedding data from clinical gene therapy trials

Viruses are the most commonly used vectors for clinical gene therapy. The risk of dissemination of a viral vector into the environment via excreta from the treated patient, a phenomenon called shedding, is a major safety concern for the environment. Despite the significant number of clinical gene therapy trials that have been conducted worldwide, there is currently no overview of actual shedding data available. In this article, an inventory of shedding data obtained from a total of 100 publications on clinical gene therapy trials using retroviral, adenoviral, adeno-associated viral and pox viral vectors is presented. In addition, the experimental set-up for shedding analysis including the assays used and biological materials tested is summarized. The collected data based on the analysis of 1619 patients in total demonstrate that shedding of these vectors occurs in practice, mainly determined by the type of vector and the route of vector administration. Due to the use of non-quantitative assays, the lack of information on assay sensitivity in most publications, and the fact that assay sensitivity is expressed in various ways, general conclusions cannot be made as to the level of vector shedding. The evaluation of the potential impact and consequences of the observations is complicated by the high degree of variety in the experimental design of shedding analysis between trials. This inventory can be supportive to clinical gene therapy investigators for the establishment of an evidence-based risk assessment to be included in a clinical protocol application, as well as to national regulatory authorities for the ongoing development of regulatory guidelines regarding gene therapy.

Gene therapy in The Netherlands: highlights from the Low Countries

Gene therapy is an active research area in The Netherlands and Dutch scientists involved in fundamental and clinical gene therapy research significantly contribute to the progresses made in this field. This ranges from the establishment of the 293, 911 and PER.C6 cell lines, which are used worldwide for the production of replication‐defective adenoviral vectors, to the development of targeted viral vectors and T lymphocytes as well as of non‐viral vectors. Several milestones have been achieved in Dutch clinical gene therapy trials, including the first treatment worldwide of patients with adenosine deaminase deficiency with genetically corrected hematopoietic stem cells in collaboration with French and British scientists. Until now, about 230 patients with various diseases have been treated with viral and non‐viral gene therapy in this country. Ongoing and upcoming Dutch clinical trials focus on the translation of new developments in gene therapy research, including the restoration of genetic defects other than SCID, and the use of oncolytic adenoviruses and targeted T cells for the treatment of cancer. The growing commercial interest in Dutch clinical gene therapy is reflected by the involvement of two Dutch companies in ongoing trials as well as the participation of Dutch clinical centres in large phase III international multicenter immuno‐gene therapy trials on prostate cancer sponsored by an American company. Translational gene therapy research in The Netherlands is boosted at a governmental level by the Dutch Ministry of Health via a dedicated funding programme. This paper presents an overview on milestones in Dutch basic gene therapy research as well as on past, present and future clinical gene therapy trials in The Netherlands. Copyright © 2007 John Wiley & Sons, Ltd.

Targeting adenovirus to CD80 and CD86 receptors increases gene transfer efficiency to malignant glioma cells

OBJECT

Gene therapy protocols for malignant gliomas utilize adenoviral vectors that rely almost exclusively on the adenovirus serotype 5 (Ad5) backbone. The authors have previously shown that chimeric vectors that bind to the Ad3 receptor, or CD46, increase the transduction efficiency of malignant brain tumors. In light of the debate regarding the efficacy of CD46 compared with CD80/CD86 in binding Ad3 virions, the authors now examine the expression and transduction efficiency of Ad5/3 chimeras that bind via CD80/CD86.

METHODS

The authors first analyzed CD80/CD86 expression in glioma cell lines. They then used three replication-defective vectors containing a luciferase reporter gene: Ad5/3 (containing the tail and shaft domain of Ad5 and the knob domain of Ad3); Ad3/5 (containing the tail of Ad5, shaft of Ad3, and knob of Ad5); and Ad3/3 (containing the tail of Ad5, shaft of Ad3, and knob of Ad3). These vectors were analyzed both in vitro and in vivo against malignant glioma cells. To examine further the effect of Ad5/3 fiber modification, the authors created an oncolytic vector, conditionally replicative Ad5/3 (CRAd5/3).

RESULTS

The Ad5/3 vector showed a 10- to 100-fold enhanced transduction efficiency of malignant glioma compared with replication-defective wild-type adenovirus (reAd5) (p < 0.05). Moreover the use of Ad5/3 reduced transgene expression by more than 90% in normal human brain cells compared with reAd5. Finally, the use of CRAd5/3 inhibited tumor cell proliferation by 43% more than replication-competent wild-type virus in vitro (p < 0.05).

CONCLUSIONS

The results of this study demonstrate that the Ad5/3 vector offers superior transduction efficiency and low toxicity in the setting of brain tumors, and therefore represents a potential new approach to gene therapy for malignant gliomas.

Adenoviruses 16 and CV23 efficiently transduce human low-passage brain tumor and cancer stem cells

Most clinical protocols involving adenovirus (Ad) vectors for gene therapy use a vector based on serotype 5 (Ad5). We believe that this serotype is not suitable for all gene therapy applications and that alternative vectors based on other serotypes should be developed. We have compared the ability of Ad5, Ad11p, Ad16p, and a chimpanzee Ad (CV23) to infect human low-passage brain tumor cells as well as primary glioma cells sorted into a CD133(+) and CD133(-) population. Cancer stem cells have been shown to reside in the CD133(+) population of cells in human glioma tumors and they are of considerable interest in glioma therapy. Ad16p and CV23 infected the low-passage brain tumor cell lines and also the CD133(+) and CD133(-) primary tumor cells most efficiently. Interestingly, as the passage number of the cells increased, the infection capacity of Ad5 increased significantly, whereas this was not seen for CV23. To ensure the therapeutic effect of Ad vectors on brain tumors, the vector must be capable of addressing both the CD133(+) cancer stem cells and the CD133(-) cells of the tumor. In particular, Ad16 and CV23 are meeting this challenge.

GCV modulates the antitumoural efficacy of a replicative adenovirus expressing the Tat8-TK as a late gene in a pancreatic tumour model

Replication-competent adenoviruses carrying the herpes simplex thymidine kinase (TK) gene have shown contradictory evidence with regard to their antitumoural efficacy in combination with ganciclovir (GCV) treatment. We generated a replication-competent adenovirus carrying Tat8-TK, a modified form of the TK gene, under the control of the adenoviral major late promoter (AdRGDTat8-TK-L). Pancreatic cancer cell lines with different sensitivity to the TK/GCV system were infected with AdRGDTat8-TK-L, both in the presence and absence of GCV, and tested for treatment efficacy. We observed that, although the presence of GCV reduced viral replication in all infected cell lines, in three out of four GCV significantly enhanced the efficacy of the virotherapy. Interestingly, the cytotoxicity of the AdRGD-Tat8-TK-L/GCV was found more potent than that of a first generation AdTK/GCV system. In tumour xenografts from BxPC-3 and NP-18 pancreatic cells, both AdRGDTat8-TK-L and AdRGDTat8-TK-L/GCV treatment showed antitumoural activity. In BxPC-3 tumours scheduling of virus and prodrug was a key factor to determine the outcome of the therapy. Importantly, the addition of GCV enhanced the antitumoural effect of AdRGDTat8-TK-L only when applied in two rounds of virus+GCV. Interestingly, in spite of interfering with viral replication in vitro, GCV treatment of NP-18 tumours did not compromise the antitumoural efficacy of the AdRGDTat8-TK-L adenovirus. Thus, our results show that the combination therapy of a replicative adenovirus and the Tat8-TK/GCV suicide system can prove beneficial, when the appropriate regimen of virus and GCV is applied.

Suicide genes for cancer therapy

The principle of using suicide genes for gene directed enzyme prodrug therapy (GDEPT) of cancer has gained increasing significance during the 20 years since its inception. The astute application of suitable GDEPT systems should permit tumour ablation in the absence of off-target toxicity commonly associated with classical chemotherapy, a hypothesis which is supported by encouraging results in a multitude of pre-clinical animal models. This review provides a clear explanation of the rationale behind the GDEPT principle, outlining the advantages and limitations of different GDEPT strategies with respect to the roles of the bystander effect, the immune system and the selectivity of the activated prodrug in contributing to their therapeutic efficacy. An in-depth analysis of the most widely used suicide gene/prodrug combinations is presented, including details of the latest advances in enzyme and prodrug optimisation and results from the most recent clinical trials.