Phase I study of adenoviral delivery of the HSV-tk gene and ganciclovir administration in patients with current malignant brain tumors

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.

Combined cytotoxic and immune-stimulatory gene therapy for primary adult high-grade glioma: a phase 1, first-in-human trial

BACKGROUND

High-grade gliomas have a poor prognosis and do not respond well to treatment. Effective cancer immune responses depend on functional immune cells, which are typically absent from the brain. This study aimed to evaluate the safety and activity of two adenoviral vectors expressing HSV1-TK (Ad-hCMV-TK) and Flt3L (Ad-hCMV-Flt3L) in patients with high-grade glioma.

METHODS

In this dose-finding, first-in-human trial, treatment-naive adults aged 18-75 years with newly identified high-grade glioma that was evaluated per immunotherapy response assessment in neuro-oncology criteria, and a Karnofsky Performance Status score of 70 or more, underwent maximal safe resection followed by injections of adenoviral vectors expressing HSV1-TK and Flt3L into the tumour bed. The study was conducted at the University of Michigan Medical School, Michigan Medicine (Ann Arbor, MI, USA). The study included six escalating doses of viral particles with starting doses of 1×1010 Ad-hCMV-TK viral particles and 1×109 Ad-hCMV-Flt3L viral particles (cohort A), and then 1×1011 Ad-hCMV-TK viral particles and 1×109 Ad-hCMV-Flt3L viral particles (cohort B), 1×1010 Ad-hCMV-TK viral particles and 1×1010 Ad-hCMV-Flt3L viral particles (cohort C), 1×1011 Ad-hCMV-TK viral particles and 1×1010 Ad-hCMV-Flt3L viral particles (cohort D), 1×1010 Ad-hCMV-TK viral particles and 1×1011 Ad-hCMV-Flt3L viral particles (cohort E), and 1×1011 Ad-hCMV-TK viral particles and 1×1011 Ad-hCMV-Flt3L viral particles (cohort F) following a 3+3 design. Two 1 mL tuberculin syringes were used to deliver freehand a mix of Ad-hCMV-TK and Ad-hCMV-Flt3L vectors into the walls of the resection cavity with a total injection of 2 mL distributed as 0·1 mL per site across 20 locations. Subsequently, patients received two 14-day courses of valacyclovir (2 g orally, three times per day) at 1-3 days and 10-12 weeks after vector administration and standad upfront chemoradiotherapy. The primary endpoint was the maximum tolerated dose of Ad-hCMV-Flt3L and Ad-hCMV-TK. Overall survival was a secondary endpoint. Recruitment is complete and the trial is finished. The trial is registered with ClinicalTrials.gov, NCT01811992.

FINDINGS

Between April 8, 2014, and March 13, 2019, 21 patients were assessed for eligibility and 18 patients with high-grade glioma were enrolled and included in the analysis (three patients in each of the six dose cohorts); eight patients were female and ten were male. Neuropathological examination identified 14 (78%) patients with glioblastoma, three (17%) with gliosarcoma, and one (6%) with anaplastic ependymoma. The treatment was well-tolerated, and no dose-limiting toxicity was observed. The maximum tolerated dose was not reached. The most common serious grade 3-4 adverse events across all treatment groups were wound infection (four events in two patients) and thromboembolic events (five events in four patients). One death due to an adverse event (respiratory failure) occurred but was not related to study treatment. No treatment-related deaths occurred during the study. Median overall survival was 21·3 months (95% CI 11·1-26·1).

INTERPRETATION

The combination of two adenoviral vectors demonstrated safety and feasibility in patients with high-grade glioma and warrants further investigation in a phase 1b/2 clinical trial.

FUNDING

Funded in part by Phase One Foundation, Los Angeles, CA, The Board of Governors at Cedars-Sinai Medical Center, Los Angeles, CA, and The Rogel Cancer Center at The University of Michigan.

Immunotherapy for Recurrent Glioma-From Bench to Bedside

Glioma is the most aggressive malignant tumor of the central nervous system, and most patients suffer from a recurrence. Unfortunately, recurrent glioma often becomes resistant to established chemotherapy and radiotherapy treatments. Immunotherapy, a rapidly developing anti-tumor therapy, has shown a potential value in treating recurrent glioma. Multiple immune strategies have been explored. The most-used ones are immune checkpoint blockade (ICB) antibodies, which are barely effective in monotherapy. However, when combined with other immunotherapy, especially with anti-angiogenesis antibodies, ICB has shown encouraging efficacy and enhanced anti-tumor immune response. Oncolytic viruses and CAR-T therapies have shown promising results in recurrent glioma through multiple mechanisms. Vaccination strategies and immune-cell-based immunotherapies are promising in some subgroups of patients, and multiple new tumor antigenic targets have been discovered. In this review, we discuss current applicable immunotherapies and related mechanisms for recurrent glioma, focusing on multiple preclinical models and clinical trials in the last 5 years. Through reviewing the current combination of immune strategies, we would like to provide substantive thoughts for further novel therapeutic regimes treating recurrent glioma.

Current Status and Challenges of Oncolytic Virotherapy for the Treatment of Glioblastoma

Despite decades of research and numerous clinical trials, the prognosis of patients diagnosed with glioblastoma (GBM) remains dire with median observed survival at 8 months. There is a critical need for novel treatments for GBM, which is the most common malignant primary brain tumor. Major advances in cancer therapeutics such as immune checkpoint inhibitors and chimeric antigen receptor (CAR) T-cell therapy have not yet led to improved outcomes for GBM. Conventional therapy of surgery followed by chemoradiation with or without tumor treating fields remains the standard of care. One of the many approaches to GBM therapy currently being explored is viral therapies. These typically work by selectively lysing target neoplastic cells, called oncolysis, or by the targeted delivery of a therapeutic transgene via a viral vector. In this review, we discuss the underlying mechanisms of action and describe both recent and current human clinical trials using these viruses with an emphasis on promising viral therapeutics that may ultimately break the field's current stagnant paradigm.

Oncolytic Viral Therapy for Malignant Glioma and Their Application in Clinical Practice

Glioblastoma is the most common primary malignant brain tumor in adults and outcomes remain poor despite the current standard of care multimodal therapy. Oncolytic virotherapy utilizes engineered viruses to exert an anti-tumor effect via both direct oncolysis and stimulation of an immune response within the tumor microenvironment, turning tumors from "cold" to "hot." This has shown promise as a novel therapeutic modality and attempts to circumvent the challenges associated with traditional treatments. Many oncolytic viruses have been investigated in completed and ongoing clinical trials and while safety has been demonstrated, clinical outcomes have been variable, often with only a subgroup of patients showing a significant response. This review summarizes these studies, addresses relevant technical aspects of oncolytic virus administration, and highlights practical considerations to assist providers in appropriately caring for patients treated with oncolytic virotherapy. Additionally, future directions within the field that may help to maximize efficacy of this modality are discussed.

Synthetic mammalian signaling circuits for robust cell population control

In multicellular organisms, cells actively sense and control their own population density. Synthetic mammalian quorum-sensing circuits could provide insight into principles of population control and extend cell therapies. However, a key challenge is reducing their inherent sensitivity to "cheater" mutations that evade control. Here, we repurposed the plant hormone auxin to enable orthogonal mammalian cell-cell communication and quorum sensing. We designed a paradoxical population control circuit, termed "Paradaux," in which auxin stimulates and inhibits net cell growth at different concentrations. This circuit limited population size over extended timescales of up to 42 days of continuous culture. By contrast, when operating in a non-paradoxical regime, population control became more susceptible to mutational escape. These results establish auxin as a versatile "private" communication system and demonstrate that paradoxical circuit architectures can provide robust population control.

A Brief Introduction to Current Cancer Gene Therapy

Gene therapy has started in the late 1980s as novel, clinically applicable therapeutic option. It revolutionized the treatment of genetic diseases with the initial intent to repair or replace defective genes. Gene therapy has been adapted for treatment of malignant diseases to improve the outcome of cancer patients. In fact, cancer gene therapy has rapidly gained great interest and evolved into a research field with highest proportion of research activities in gene therapy. In this context, cancer gene therapy has long entered translation into clinical trials and therefore more than two-thirds of all gene therapy trials worldwide are aiming at the treatment of cancer disease using different therapeutic strategies. During the decades in cancer gene therapy, tremendous knowledge has accumulated. This led to significant improvements in vector design, transgene repertoire, more targeted interventions, use of novel gene therapeutic technologies such as CRISPR/Cas, sleeping beauty vectors, and development of effective cancer immunogene therapies. In this chapter, a brief overview of current key developments in cancer gene therapy is provided to gain insights into the recent directions in research as well as in clinical application of cancer gene therapy.

Evolution of the Neurosurgeon's Role in Clinical Trials for Glioblastoma: A Systematic Overview of the Clinicaltrials.Gov Database

BACKGROUND

The therapeutic challenge of glioblastoma (GBM) has catalyzed the development of clinical trials to evaluate novel interventions. With increased understanding of GBM biology and technological advances, the neurosurgeon's role in neuro-oncology has evolved.

OBJECTIVE

To evaluate the current landscape of procedure-based clinical trials for GBM to characterize this evolution, gain insight into past failures, and accordingly outline implications for future research and practice that may inform future studies.

METHODS

The ClinicalTrials.gov database was searched for surgical/procedural trials in individuals with GBM. Demographics, specific intervention, trial phase, and main outcome measures were abstracted.

RESULTS

A total of 224 of 2311 GBM trials (9.7%) were identified as procedural, with the majority being based in the United States (155/224, 69.2%), single-center (155/224, 69.2%), and not randomized (176/224, 78.6%). Primary and recurrent GBMs were evenly addressed. The leading interventions were local delivery of therapeutics (50.0%), surgical techniques (33.9%), such as image-guided surgery, and novel device applications (14.3%). Phase I designs predominated (82/224, 36.6%). The top primary outcome was safety/tolerability/feasibility (88/224, 39.3%), followed by survival (46/224, 20.5%). Approximately 17% of studies were terminated, withdrawn, or suspended. Fifty-two linked publications were identified, among which 42 were classified as having a positive result.

CONCLUSION

Procedural interventions comprised ∼10% of all registered GBM trials. Local delivery of therapeutics, use of surgical imaging techniques and novel device applications, predominantly through phase I designs, represent the evolved role of the neurosurgeon in neuro-oncology. Improved reporting of trial designs, outcomes, and results are needed to better inform the field and increase efficiency.

Targeting stanniocalcin-1-expressing tumor cells elicits efficient antitumor effects in a mouse model of human lung cancer

Lung cancer is the most common cause of cancer‐related death in developed countries; therefore, the generation of effective targeted therapeutic regimens is essential. Recently, gene therapy approaches toward malignant cells have emerged as attractive molecular therapeutics. Previous studies have indicated that stanniocalcin‐1 (STC‐1), a hormone involved in calcium and phosphate homeostasis, positively regulates proliferation, apoptosis resistance, and glucose metabolism in lung cancer cell lines. In this study, we investigated if targeting STC‐1 in tumor cells could be a promising strategy for lung cancer gene therapy. We confirmed that STC‐1 levels in peripheral blood were higher in lung cancer patients than in healthy donors and that STC‐1 expression was observed in five out of eight lung cancer cell lines. A vector expressing a suicide gene, uracil phosphoribosyltransferase (UPRT), under the control of the STC‐1 promoter, was constructed (pP_STC‐1‐UPRT) and transfected into three STC‐1‐positive cell lines, PC‐9, A549, and H1299. When stably transfected, we observed significant cell growth inhibition using 5‐fluorouracil (5‐FU) treatment. Furthermore, growth of the STC‐1‐negative lung cancer cell line, LK‐2 was significantly arrested when combined with STC‐1‐positive cells transfected with pP_STC‐1‐UPRT.

We believe that conferring cytotoxicity in STC‐1‐positive lung cancer cells using a suicide gene may be a useful therapeutic strategy for lung cancer.

Immunovirotherapy for the Treatment of Glioblastoma and Other Malignant Gliomas

Glioblastoma multiforme (GBM) represents one of the most challenging malignancies due to many factors including invasiveness, heterogeneity, and an immunosuppressive microenvironment. Current treatment modalities have resulted in only modest effect on outcomes. The development of viral vectors for oncolytic immunovirotherapy and targeted drug delivery represents a promising therapeutic prospect for GBM and other brain tumors. A host of genetically engineered viruses, herpes simplex virus, poliovirus, measles, and others, have been described and are at various stages of clinical development. Herein we provide a review of the advances and current state of oncolytic virotherapy for the targeted treatment of GBM and malignant gliomas.

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.

Effects of oncolytic viruses and viral vectors on immunity in glioblastoma

Glioblastoma (GBM) is regarded as an incurable disease due to its poor prognosis and limited treatment options. Virotherapies were once utilized on cancers for their oncolytic effects. And they are being revived on GBM treatment, as accumulating evidence presents the immunogenic effects of virotherapies in remodeling immunosuppressive GBM microenvironment. In this review, we focus on the immune responses induced by oncolytic virotherapies and viral vectors in GBM. The current developments of GBM virotherapies are briefly summarized, followed by a detailed depiction of their immune response. Limitations and lessons inferred from earlier experiments and trials are discussed. Moreover, we highlight the importance of engaging the immune responses induced by virotherapies into the multidisciplinary management of GBM.

Human intratumoral therapy: Linking drug properties and tumor transport of drugs in clinical trials

Cancer therapies aim to kill tumor cells directly or engage the immune system to fight malignancy. Checkpoint inhibitors, oncolytic viruses, cell-based immunotherapies, cytokines, and adjuvants have been applied to prompt the immune system to recognize and attack cancer cells. However, systemic exposure of cancer therapies can induce unwanted adverse events. Intratumoral administration of potent therapies utilizes small amounts of drugs, in an effort to minimize systemic exposure and off-target toxicities. Here, we discuss the properties of the tumor microenvironment and transport considerations for intratumoral drug delivery. Specifically, we consider various tumor tissue factors and physicochemical factors that can affect tumor retention after intratumoral injection. We also review approved and clinical-stage intratumoral therapies and consider how the molecular and biophysical properties (e.g. size and charge) of these therapies influences intratumoral transport (e.g. tumor retention and cellular uptake). Finally, we offer a critical review and highlight several emerging approaches to promote tumor retention and limit systemic exposure of potent intratumoral therapies.

The History of Neurosurgery at Houston Methodist Hospital

The history of neurosurgery in Texas is linked with the development over the past century of the Houston Methodist Hospital (HMH) from a 30-bed hospital in downtown Houston to an academic medical center with 900 beds in the Texas Medical Center. Neurosurgery at HMH has developed to meet the needs of the Houston Metropolitan Area, which has grown from 130,000 people in 1919 to 7 million people today. Neurosurgery at HMH has had steady growth and stable leadership with Dr. James Greenwood Jr. 1936-1980, Dr. Robert Grossman 1980-2013, and Dr. Gavin Britz 2013-present, as Chiefs of the Neurosurgical Service. HMH has been affiliated with 2 medical schools: Baylor College of Medicine 1950-2003 and Weill College of Medicine Cornell University 2004-present. Neurosurgical training began at HMH with the establishment of the Baylor College of Medicine Neurosurgery Residency Program with Dr. George Ehni as Program Director 1959-1979 and Dr. Robert Grossman as Program Director 1980-2006. Training has continued in the HMH residency program from 2006 to present with Dr. David Baskin as Program Director. As of 2019, 138 neurosurgical residents have been trained at HMH. The goals of delivering responsible patient care, advancing neurosurgical knowledge, and training the next generation of practitioners and teachers of neurosurgery have remained constant and have been met and remain the mission of the department.

Innovative therapies for malignant brain tumors: the road to a tailored cure

Background:

Immune tolerance, immune escape, neoangiogenesis, phenotypic changes, and glioma stem cells are all responsible for the resistance of malignant brain tumors to current therapies and persistent recurrence. The present study provides a panoramic view of innovative therapies for malignant brain tumors, especially glioblastoma, aimed at achieving a tailored approach.

Methods:

PubMed/Medline and ClinicalTrials.gov were the main sources of an extensive literature review in which “Regenerative Medicine,” “Cell-Based Therapy,” “Chemotherapy,” “Vaccine,” “Cell Engineering,” “Immunotherapy, Active,” “Immunotherapy, Adoptive,” “Stem Cells,” “Gene Therapy,” “Target Therapy,” “Brain Cancer,” “Glioblastoma,” and “Malignant Brain Tumor” were the search terms. Only articles in English published in the last 5 years were included. A further selection was made according to the quality of the studies and level of evidence.

Results:

Cell-based and targeted therapies represent the newest frontiers of brain cancer treatment. Active and adoptive immunotherapies, stem cell therapies, and gene therapies represent a tremendous evolution in recent years due to many preclinical and clinical studies. Clinical trials have validated the effectiveness of antibody-based immunotherapies, including an in-depth study of bevacizumab, in combination with standard of care. Preclinical data highlights the role of vaccines, stem cells, and gene therapies to prevent recurrence.

Conclusion:

Monoclonal antibodies strengthen the first-line therapy for high grade gliomas. Vaccines, engineered cells, stem cells, and gene and targeted therapies are good candidates for second-line treatment of both newly diagnosed and recurrent gliomas. Further data are necessary to validate this tailored approach at the bedside. (www.actabiomedica.it)

Phase I study of gene-mediated cytotoxic immunotherapy with AdV-tk as adjuvant to surgery and radiation for pediatric malignant glioma and recurrent ependymoma

BACKGROUND

Gene-mediated cytotoxic immunotherapy (GMCI) is a tumor-specific immune stimulatory strategy implemented through local delivery of aglatimagene besadenovec (AdV-tk) followed by anti-herpetic prodrug. GMCI induces T-cell dependent tumor immunity and synergizes with radiotherapy. Clinical trials in adult malignant gliomas demonstrated safety and potential efficacy. This is the first trial of GMCI in pediatric brain tumors.

METHODS

This phase I dose escalation study was conducted to evaluate GMCI in patients 3 years of age or older with malignant glioma or recurrent ependymoma. AdV-tk at doses of 1 × 1011 and 3 × 1011 vector particles (vp) was injected into the tumor bed at the time of surgery followed by 14 days of valacyclovir. Radiation started within 8 days of surgery, and if indicated, chemotherapy began after completion of valacyclovir.

RESULTS

Eight patients (6 glioblastoma, 1 anaplastic astrocytoma, 1 recurrent ependymoma) were enrolled and completed therapy: 3 on dose level 1 and 5 on dose level 2. Median age was 12.5 years (range 7-17) and Lansky/Karnofsky performance scores were 60-100. Five patients had multifocal/extensive tumors that could not be resected completely and 3 had gross total resection. There were no dose-limiting toxicities. The most common possibly GMCI-related adverse events included Common Terminology Criteria for Adverse Events grade 1-2 fever, fatigue, and nausea/vomiting. Three patients, in dose level 2, lived more than 24 months, with 2 alive without progression 37.3 and 47.7 months after AdV-tk injection.

CONCLUSIONS

GMCI can be safely combined with radiation therapy with or without temozolomide in pediatric patients with brain tumors and the present results strongly support further investigation.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov NCT00634231.

Viral Vector-Mediated Gene Transfer of Glutamic Acid Decarboxylase for Chronic Pain Treatment: A Literature Review

Chronic pain is long-lasting nociceptive state, impairing the patient's quality of life. Existing analgesics are generally not effective in the treatment of chronic pain, some of which such as opioids have the risk of tolerance/dependence and overdose death with higher daily opioid doses for increasing analgesic effect. Opioid use disorders have already reached an epidemic level in the United States; therefore, nonopioid analgesic approach and/or use of nonpharmacologic interventions will be employed with increasing frequency. Viral vector-mediated gene therapy is promising in clinical trials in the nervous system diseases. Glutamic acid decarboxylase (GAD) enzyme, a key enzyme in biosynthesis of γ-aminobutyric acid (GABA), plays an important role in analgesic mechanism. In the literature review, we used PubMed and bioRxiv to search the studies, and the eligible criteria include (1) article written in English, (2) use of viral vectors expressing GAD67 or GAD65, and (3) preclinical pain models. We identified 13 eligible original research articles, in which the pain models include nerve injury, HIV-related pain, painful diabetic neuropathy, and formalin test. GAD expressed by the viral vectors from all the reports produced antinociceptive effects. Restoring GABA systems is a promising therapeutic strategy for chronic pain, which provides evidence for the clinical trial of gene therapy for pain in the near future.

Suicide gene therapy for the treatment of high-grade glioma: past lessons, present trends, and future prospects

Suicide gene therapy has represented an experimental cancer treatment modality for nearly 40 years. Among the various cancers experimentally treated by suicide gene therapy, high-grade gliomas have been the most prominent both in preclinical and clinical settings. Failure of a number of promising suicide gene therapy strategies in the clinic pointed toward a bleak future of this approach for the treatment of high-grade gliomas. Nevertheless, the development of new vectors and suicide genes, better prodrugs, more efficient delivery systems, and new combinatorial strategies represent active research areas that may eventually lead to better efficacy of suicide gene therapy. These trends are evident by the current increasing focus on suicide gene therapy for high-grade glioma treatment both in the laboratory and in the clinic. In this review, we give an overview of different suicide gene therapy approaches for glioma treatment and discuss clinical trials, delivery issues, and immune responses.

Recent progress in the research of suicide gene therapy for malignant glioma

Malignant glioma, which is characterized by diffuse infiltration into the normal brain parenchyma, is the most aggressive primary brain tumor with dismal prognosis. Over the past 40 years, the median survival has only slightly improved. Therefore, new therapeutic modalities must be developed. In the 1990s, suicide gene therapy began attracting attention for the treatment of malignant glioma. Some clinical trials used a viral vector for suicide gene transduction; however, it was found that viral vectors cannot cover the large invaded area of glioma cells. Interest in this therapy was recently revived because some types of stem cells possess a tumor-tropic migratory capacity, which can be used as cellular delivery vehicles. Immortalized, clonal neural stem cell (NSC) line has been used for patients with recurrent high-grade glioma, which showed safety and efficacy. Embryonic and induced pluripotent stem cells may be considered as sources of NSC because NSC is difficult to harvest, and ethical issues have been raised. Mesenchymal stem cells are alternative candidates for cellular vehicle and are easily harvested from the bone marrow. In addition, a new type of nonlytic, amphotropic retroviral replicating vector encoding suicide gene has shown efficacy in patients with recurrent high-grade glioma in a clinical trial. This replicating viral capacity is another possible candidate as delivery vehicle to tackle gliomas. Herein, we review the concept of suicide gene therapy, as well as recent progress in preclinical and clinical studies in this field.

Biological intratumoral therapy for the high-grade glioma part II: vector- and cell-based therapies and radioimmunotherapy

Management of high-grade gliomas (HGGs) remains a complex challenge with an overall poor prognosis despite aggressive multimodal treatment. New translational research has focused on maximizing tumor cell eradication through improved tumor cell targeting while minimizing collateral systemic side effects. In particular, biological intratumoral therapies have been the focus of novel translational research efforts due to their inherent potential to be both dynamically adaptive and target specific. This two part review will provide an overview of biological intratumoral therapies that have been evaluated in human clinical trials in HGGs, and summarize key advances and remaining challenges in the development of these therapies as a potential new paradigm in the management of HGGs. Part II discusses vector-based therapies, cell-based therapies and radioimmunotherapy.

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.

Preclinical And Clinical Development Of Oncolytic Adenovirus For The Treatment Of Malignant Glioma

Replication conditional oncolytic human adenovirus has long been considered a promising biological therapeutic to target high-grade gliomas (HGG), a group of essentially lethal primary brain cancer. The last decade has witnessed initiation and some completion of a number of Phase I and II clinical investigations of oncolytic adenovirus for HGG in the US and Europe. Results of these trials in patients are pivotal for not only federal approval but also filling an existing knowledge gap that primarily derives from the stark differences in permissivity to human adenovirus between humans and preclinical mouse models. DNX-2401 (Delta-24-RGD), the current mainstream oncolytic adenovirus with modifications in E1A and the fiber, has been shown to induce impressive objective response and long-term survival (>3 years) in a fraction of patients with recurrent HGG. Responders exhibited initial enlargement of the treated lesions for a few months post treatment, followed by shrinkage and near complete resolution. In accord with preclinical research, post-treatment specimens revealed virus-mediated alteration of the immune tumor microenvironment as evidenced by infiltration of CD8+ T cells and M1-polarized macrophages. These findings are encouraging and together with further information from ongoing studies have a potential to make oncolytic adenovirus a viable option for clinical management of HGG. This review deals with this timely topic; we will describe both preclinical and clinical development of oncolytic adenovirus therapy for HGG, summarize updated knowledge on clinical trials and discuss challenges that the field currently faces.

Preclinical investigation of combined gene-mediated cytotoxic immunotherapy and immune checkpoint blockade in glioblastoma

Background

Combined immunotherapy approaches are promising cancer treatments. We evaluated anti-programmed cell death protein 1 (PD-1) treatment combined with gene-mediated cytotoxic immunotherapy (GMCI) performed by intratumoral injection of a prodrug metabolizing nonreplicating adenovirus (AdV-tk), providing in situ chemotherapy and immune stimulation.

Methods

The effects of GMCI on PD ligand 1 (PD-L1) expression in glioblastoma were investigated in vitro and in vivo. The efficacy of the combination was investigated in 2 syngeneic mouse glioblastoma models (GL261 and CT-2A). Immune infiltrates were analyzed by flow cytometry.

Results

GMCI upregulated PD-L1 expression in vitro and in vivo. Both GMCI and anti-PD-1 increased intratumoral T-cell infiltration. A higher percentage of long-term survivors was observed in mice treated with combined GMCI/anti-PD-1 relative to single treatments. Long-term survivors were protected from tumor rechallenge, demonstrating durable memory antitumor immunity. GMCI led to elevated interferon gamma positive T cells and a lower proportion of exhausted double positive PD1+TIM+CD8+ T cells. GMCI also increased PD-L1 levels on tumor cells and infiltrating macrophages/microglia. Our data suggest that anti-PD-1 treatment improves the effectiveness of GMCI by overcoming interferon-induced PD-L1-mediated inhibitory signals, and GMCI improves anti-PD-1 efficacy by increasing tumor-infiltrating T-cell activation.

Conclusions

Our data show that the GMCI/anti-PD-1 combination is well tolerated and effective in glioblastoma mouse models. These results support evaluation of this combination in glioblastoma patients.

Viral and other therapies for recurrent glioblastoma: is a 24-month durable response unusual?

A phase I trial of an engineered poliovirus for the treatment of recurrent glioblastoma (GBM) has attracted attention due to 8 survivors reaching the 24-month and 5 reaching the 36-month survival landmarks.1 Genetically engineered viruses (oncolytic viruses) have been in trials for GBM for almost two decades.2 These replication-competent (tumor-selective, oncolytic, replication-conditional) viruses or replication-defective viral vectors (gene therapy) deliver cytotoxic payloads to tumors, leading to immunogenic death and intratumoral inflammatory responses. This transforms the tumor microenvironment from immunologically naïve ("cold") to inflamed ("hot"), increasing immune cell recognition of tumor antigens and the durable responses observed in virotherapy.3,4 Several current and past virotherapy trials have reported a "tail" of apparent responders at the 24-month landmark. Other modalities have also reported a "tail" of seemingly long-term survivors. These trials seem to show that these responder "tails" characterize a defined subset of GBM patients.

Immunotherapy for glioblastoma: going viral

Intratumoral infusion of a nonpathogenic replication-competent recombinant polio-rhinovirus chimera for recurrent glioblastoma demonstrates safety and promising preliminary treatment responses.

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.

Immunotherapy and gene therapy as novel treatments for cancer

The immune system interacts closely with tumors during the disease development and progression to metastasis. The complex communication between the immune system and the tumor cells can prevent or promote tumor growth. New therapeutic approaches harnessing protective immunological mechanisms have recently shown very promising results. This is performed by blocking inhibitory signals or by activating immunological effector cells directly. Immune checkpoint blockade with monoclonal antibodies directed against the inhibitory immune receptors CTLA-4 and PD-1 has emerged as a successful treatment approach for patients with advanced melanoma. Ipilimumab is an anti-CTLA-4 antibody which demonstrated good results when administered to patients with melanoma. Gene therapy has also shown promising results in clinical trials. Particularly, Herpes simplex virus (HSV)-mediated delivery of the HSV thymidine kinase (TK) gene to tumor cells in combination with ganciclovir (GCV) may provide an effective suicide gene therapy for destruction of glioblastomas, prostate tumors and other neoplasias by recruiting tumor-infiltrating lymphocytes into the tumor. The development of new treatment strategies or combination of available innovative therapies to improve cell cytotoxic T lymphocytes trafficking into the tumor mass and the production of inhibitory molecules blocking tumor tissue immune-tolerance are crucial to improve the efficacy of cancer therapy.

Exogenous p53 and ASPP2 expression enhances rAdV-TK/ GCV-induced death in hepatocellular carcinoma cells lacking functional p53

Suicide gene therapy using herpes simplex virus-1 thymidine kinase (HSV-TK) in combination with ganciclovir (GCV) has emerged as a potential new method for treating cancer. We hypothesize that the efficacy of HSV-TK/GCV therapy is at least partially dependent on p53 status in hepatocellular carcinoma (HCC) patients. Using recombinant adenoviral vectors (rAdV), TK, p53, and ASPP2 were overexpressed individually and in combination in Hep3B (p53 null) and HepG2 (p53 wild-type) cell lines and in primary HCC tumor cells. p53 overexpression induced death in Hep3B cells, but not HepG2 cells. ASPP2 overexpression increased rAdV-TK/GCV-induced HepG2 cell death by interacting with endogenous p53. Similarly, ASPP2 reduced survival in rAdV-TK/GCV-treated primary HCC cells expressing p53 wild-type but not a p53 R249S mutant. Mutated p53 was unable to bind to ASPP2, suggesting that the increase in rAdV-TK/GCV-induced cell death resulting from ASPP2 overexpression was dependent on its interaction with p53. Additionally, γ-H2AX foci, ATM phosphorylation, Bax, and p21 expression increased in rAdV-TK/GCV-treated HepG2 cells as compared to Hep3B cells. This suggests that the combined use of HSV-TK, GCV, rAdV-p53 and rAdV-ASPP2 may improve therapeutic efficacy in HCC patients lacking functional p53.

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.

Combined delivery of temozolomide and the thymidine kinase gene for treatment of glioblastoma

Glioblastoma is the most malignant form of brain tumor. In this study, combination therapy with temozolomide (TMZ) and the herpes simplex virus thymidine kinase (HSVtk) gene was evaluated in glioblastoma models. The R7L10 peptide was used as a carrier of TMZ and the HSVtk gene. TMZ was loaded into R7L10 micelles using the oil-in-water emulsion/solvent evaporation method. The TMZ-loaded R7L10 (R7L10-TMZ) micelles formed a complex with the HSVtk gene, pHSVtk. The formation of the R7L10-TMZ/pHSVtk complex was confirmed by gel retardation and heparin competition assays. An in vitro transfection assay demonstrated that the transfection efficiency of R7L10-TMZ was similar to that of R7L10 in C6 glioblastoma cells. R7L10-TMZ had greater anti-tumor effects than TMZ alone in C6 cells in vitro, suggesting that R7L10 is an efficient carrier of TMZ. The in vivo efficacy of the R7L10-TMZ/pHSVtk complex was evaluated in the intracranial glioblastoma model. HSVtk expression in tumors was confirmed by immunohistochemistry. Furthermore, a greater anti-tumor effect was observed in the R7L10-TMZ/pHSVtk group compared with the TMZ or R7L10/pHSVtk single injection group. In conclusion, combined delivery of TMZ and the HSVtk gene using R7L10 peptides may be useful for the treatment of glioblastoma.

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.

Phase II multicenter study of gene-mediated cytotoxic immunotherapy as adjuvant to surgical resection for newly diagnosed malignant glioma

BACKGROUND

Despite aggressive standard of care (SOC) treatment, survival of malignant gliomas remains very poor. This Phase II, prospective, matched controlled, multicenter trial was conducted to assess the safety and efficacy of aglatimagene besadenovec (AdV-tk) plus valacyclovir (gene-mediated cytotoxic immunotherapy [GMCI]) in combination with SOC for newly diagnosed malignant glioma patients.

METHODS

Treatment cohort patients received SOC + GMCI and were enrolled at 4 institutions from 2006 to 2010. The preplanned, matched-control cohort included all concurrent patients meeting protocol criteria and SOC at a fifth institution. AdV-tk was administered at surgery followed by SOC radiation and temozolomide. Subset analyses were preplanned, based on prognostic factors: pathological diagnosis (glioblastoma vs others) and extent of resection.

RESULTS

Forty-eight patients completed SOC + GMCI, and 134 met control cohort criteria. Median overall survival (OS) was 17.1 months for GMCI + SOC versus 13.5 months for SOC alone (P = .0417). Survival at 1, 2, and 3 years was 67%, 35%, and 19% versus 57%, 22%, and 8%, respectively. The greatest benefit was observed in gross total resection patients: median OS of 25 versus 16.9 months (P = .0492); 1, 2, and 3-year survival of 90%, 53%, and 32% versus 64%, 28% and 6%, respectively. There were no dose-limiting toxicities; fever, fatigue, and headache were the most common GMCI-related symptoms.

CONCLUSIONS

GMCI can be safely combined with SOC in newly diagnosed malignant gliomas. Survival outcomes were most notably improved in patients with minimal residual disease after gross total resection. These data should help guide future immunotherapy studies and strongly support further evaluation of GMCI for malignant gliomas.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov NCT00589875.

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.

Gene-mediated cytotoxic immunotherapy as adjuvant to surgery or chemoradiation for pancreatic adenocarcinoma

BACKGROUND

While surgical resection of pancreatic adenocarcinoma provides the only chance of cure, long-term survival remains poor. Immunotherapy may improve outcomes, especially as adjuvant to local therapies. Gene-mediated cytotoxic immunotherapy (GMCI) generates a systemic anti-tumor response through local delivery of an adenoviral vector expressing the HSV-tk gene (aglatimagene besadenovec, AdV-tk) followed by anti-herpetic prodrug. GMCI has demonstrated synergy with standard of care (SOC) in other tumor types. This is the first application in pancreatic cancer.

METHODS

Four dose levels (3 × 10(10) to 1 × 10(12) vector particles) were evaluated as adjuvant to surgery for resectable disease (Arm A) or to 5-FU chemoradiation for locally advanced disease (Arm B). Each patient received two cycles of AdV-tk + prodrug.

RESULTS

Twenty-four patients completed therapy, 12 per arm, with no dose-limiting toxicities. All Arm A patients were explored, eight were resected, one was locally advanced and three had distant metastases. CD8(+) T cell infiltration increased an average of 22-fold (range sixfold to 75-fold) compared with baseline (p = 0.0021). PD-L1 expression increased in 5/7 samples analyzed. One node-positive resected patient is alive >66 months without recurrence. Arm B RECIST response rate was 25 % with a median OS of 12 months and 1-year survival of 50 %. Patient-reported quality of life showed no evidence of deterioration.

CONCLUSIONS

AdV-tk can be safely combined with pancreatic cancer SOC without added toxicity. Response and survival compare favorably to expected outcomes and immune activity increased. These results support further evaluation of GMCI with more modern chemoradiation and surgery as well as PD-1/PD-L1 inhibitors in pancreatic cancer.

Polymeric nanoparticles for nonviral gene therapy extend brain tumor survival in vivo

Biodegradable polymeric nanoparticles have the potential to be safer alternatives to viruses for gene delivery; however, their use has been limited by poor efficacy in vivo. In this work, we synthesize and characterize polymeric gene delivery nanoparticles and evaluate their efficacy for DNA delivery of herpes simplex virus type I thymidine kinase (HSVtk) combined with the prodrug ganciclovir (GCV) in a malignant glioma model. We investigated polymer structure for gene delivery in two rat glioma cell lines, 9L and F98, to discover nanoparticle formulations more effective than the leading commercial reagent Lipofectamine 2000. The lead polymer structure, poly(1,4-butanediol diacrylate-co-4-amino-1-butanol) end-modified with 1-(3-aminopropyl)-4-methylpiperazine, is a poly(β-amino ester) (PBAE) and formed nanoparticles with HSVtk DNA that were 138 ± 4 nm in size and 13 ± 1 mV in zeta potential. These nanoparticles containing HSVtk DNA showed 100% cancer cell killing in vitro in the two glioma cell lines when combined with GCV exposure, while control nanoparticles encoding GFP maintained robust cell viability. For in vivo evaluation, tumor-bearing rats were treated with PBAE/HSVtk infusion via convection-enhanced delivery (CED) in combination with systemic administration of GCV. These treated animals showed a significant benefit in survival (p = 0.0012 vs control). Moreover, following a single CED infusion, labeled PBAE nanoparticles spread completely throughout the tumor. This study highlights a nanomedicine approach that is highly promising for the treatment of malignant glioma.

Trial watch: DNA vaccines for cancer therapy

The foundation of modern vaccinology dates back to the 1790s, when the English physician Edward Jenner uncovered the tremendous medical potential of prophylactic vaccination. Jenner’s work ignited a wave of nationwide vaccination campaigns abating the incidence of multiple life-threatening infectious diseases and culminating with the eradication of natural smallpox virus, which was definitively certified by the WHO in 1980. The possibility of using vaccines against cancer was first proposed at the end of the 19th century by Paul Ehrlich and William Coley. However, it was not until the 1990s that such a hypothesis began to be intensively investigated, following the realization that the immune system is not completely unresponsive to tumors and that neoplastic cells express immunogenic tumor-associated antigens (TAAs). Nowadays, anticancer vaccines are rapidly moving from the bench to the bedside, and a few prophylactic and therapeutic preparations have already been approved by FDA for use in humans. In this setting, one interesting approach is constituted by DNA vaccines, i.e., TAA-encoding circularized DNA constructs, often of bacterial origin, that are delivered to patients as such or by means of specific vectors, including (but not limited to) liposomal preparations, nanoparticles, bacteria and viruses. The administration of DNA vaccines is most often performed via the intramuscular or subcutaneous route and is expected to cause (1) the endogenous synthesis of the TAA by myocytes and/or resident antigen-presenting cells; (2) the presentation of TAA-derived peptides on the cell surface, in association with MHC class I molecules; and (3) the activation of potentially therapeutic tumor-specific immune responses. In this Trial Watch, we will summarize the results of recent clinical trials that have evaluated/are evaluating DNA vaccines as therapeutic interventions against cancer.

MUC1 Promoter-Driven DTA as a Targeted Therapeutic Strategy against Pancreatic Cancer

Mucin1 (MUC1) is overexpressed in pancreatic ductal adenocarcinoma (PDA) and is associated with tumor aggressiveness, suggesting that MUC1 is a promising therapeutic target for promoter-driven diphtheria toxin A (DTA). Endogenous MUC1 transcript levels were analyzed by quantitative PCR (qPCR) in multiple PDA cells (Capan1, HPAFII, Su.86.86, Capan2, Hs766T, MiaPaCa2, and Panc1). Expression levels were correlated with luciferase activity and cell death after transfection with MUC1 promoter-driven luciferase and DTA constructs. MUC1-positive (+) cells had significantly elevated MUC1 mRNA expression compared with MUC1-negative (-) cells. Luciferase activity was significantly higher in MUC1(+) cells when transfected with MUC1 promoter-driven luciferase and MUC1(+) cells underwent enhanced cell death after transfection with a single dose of MUC1 promoter-driven DTA. IFNγ pretreatment enhanced MUC1 expression in MUC1(-) cells and induced sensitivity to MUC1-DTA therapy. Matched primary and metastatic tumor lesions from clinical specimens revealed similar MUC1 IHC labeling patterns, and a tissue microarray of human PDA biopsies revealed increased immunolabeling with a combination of MUC1 and mesothelin (MSLN) antibodies, compared with either antibody alone. Combining MUC1 with MSLN-targeted DTA enhanced drug efficacy in an in vitro model of heterogeneous PDA. These data demonstrate that MUC1 promoter-driven DTA preferentially kills MUC1-expressing PDA cells and drugs that enhance MUC1 expression sensitize PDA cells with low MUC1 expression.

IMPLICATIONS

MUC1 expression in primary and metastatic lesions provides a rationale for the development of a systemic MUC1 promoter-driven DTA therapy that may be further enhanced by combination with other promoter-driven DTA constructs.

Stem cell in alternative treatments for brain tumors: potential for gene delivery

Despite ongoing research efforts and attempts to bring new drugs into trial, the prognosis for brain tumors remains poor. Patients with the most common and lethal intracranial neoplasia, glioblastoma multiforme (GBM), have an average survival of one year with combination of surgical resection, radiotherapy and temozolomide. One of the main problems in the treatment of GBM is getting drugs across the blood brain barrier (BBB) efficiently. In an attempt to solve this problem, there are ongoing experimental and clinical trials to deliver drugs within stem cells. The purpose for this method is the ease by which stem cells home to the brain. This review discusses the experimental and clinical applications of stem cells for GBM. We also discuss the different properties of stem cells. This information is important to understand why one stem cell would be advantageous over another in cell therapy. We provide an overview of the different drug delivery methods, gene-based treatments and cancer vaccines for GBM, including the stem cell subset.

Stem cell in alternative treatments for brain tumors: potential for gene delivery

Despite ongoing research efforts and attempts to bring new drugs into trial, the prognosis for brain tumors remains poor. Patients with the most common and lethal intracranial neoplasia, glioblastoma multiforme (GBM), have an average survival of one year with combination of surgical resection, radiotherapy and temozolomide. One of the main problems in the treatment of GBM is getting drugs across the blood brain barrier (BBB) efficiently. In an attempt to solve this problem, there are ongoing experimental and clinical trials to deliver drugs within stem cells. The purpose for this method is the ease by which stem cells home to the brain. This review discusses the experimental and clinical applications of stem cells for GBM. We also discuss the different properties of stem cells. This information is important to understand why one stem cell would be advantageous over another in cell therapy. We provide an overview of the different drug delivery methods, gene-based treatments and cancer vaccines for GBM, including the stem cell subset.

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.

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.

Trial Watch: DNA vaccines for cancer therapy

During the past 2 decades, the possibility that preparations capable of eliciting tumor-specific immune responses would mediate robust therapeutic effects in cancer patients has received renovated interest. In this context, several approaches to vaccinate cancer patients against their own malignancies have been conceived, including the administration of DNA constructs coding for one or more tumor-associated antigens (TAAs). Such DNA-based vaccines conceptually differ from other types of gene therapy in that they are not devised to directly kill cancer cells or sensitize them to the cytotoxic activity of a drug, but rather to elicit a tumor-specific immune response. In spite of an intense wave of preclinical development, the introduction of this immunotherapeutic paradigm into the clinical practice is facing difficulties. Indeed, while most DNA-based anticancer vaccines are well tolerated by cancer patients, they often fail to generate therapeutically relevant clinical responses. In this Trial Watch, we discuss the latest advances on the use of DNA-based vaccines in cancer therapy, discussing the literature that has been produced around this topic during the last 13 months as well as clinical studies that have been launched in the same time frame to assess the actual therapeutic potential of this intervention.

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.

A designed equine herpes thymidine kinase (EHV4 TK) variant improves ganciclovir-induced cell-killing

The limitations of the ganciclovir (GCV)/herpes simplex virus thymidine kinase (HSV1 TK: EC 2.7.1.21) system as a suicide gene therapy approach have been extensively studied over the years. In our study, we focused on improving the cytotoxic profile of the GCV/equine herpes virus-4 thymidine kinase (EHV4 TK: EC 2.7.1.21) system. Our approach involved the structure-guided mutagenesis of EHV4 TK in order to switch its ability to preferentially phosphorylate the natural substrate deoxythymidine (dT) to that of GCV. We performed steady-state kinetic analysis, genetic complementation in a thymidine kinase-deficient Escherichia coli strain, isothermal titration calorimetry, and analysis of GCV-induced cell killing through generation of HEK 293 stable cell-lines expressing EHV4 TK mutants and wild-type EHV4 TK. We found that the EHV4 TK S144H-GFP mutant preferentially phosphorylates GCV and confers increased GCV-induced cytotoxicity compared to wild-type EHV4 TK.