Gene therapeutics: the future of brain tumor therapy?

Growth hormone therapy and risk of recurrence/progression in intracranial tumors: a meta-analysis

Growth hormone deficiency is common in intracranial tumors, which is usually treated with surgery and radiotherapy. A number of previous studies have investigated the relationship between the growth hormone replacement therapy (GHRT) and risk of tumor recurrence/progression; however, the evidence remains controversial. We conducted a meta-analysis of published studies to estimate the potential relation between GHRT and intracranial tumors recurrence/progression. Three comprehensive databases, PUBMED, EMBASE, and Cochrane Library, were researched with no limitations, covering all published studies till the end of July, 2014. Reference lists from identified studies were also screened for additional database. The summary relative risks (RR) and 95% confidence intervals (CI) were calculated by fixed-effects models for estimation. Fifteen eligible studies, involving more than 2232 cases and 3606 controls, were included in our meta-analysis. The results indicated that intracranial tumors recurrence/progression was not associated with GHRT (RR 0.48, 95% CI 0.39-0.56), and for children, the pooled RR was 0.44 and 95% CI was 0.34-0.54. In subgroup analysis, risks of recurrence/progression were decreased for craniopharyngioma, medulloblastoma, astrocytoma, glioma, but not for pituitary adenomas, and non-functioning pituitary adenoma (NFPA), ependymoma. Results from our analysis indicate that GHRT decreases the risk of recurrence/progression in children with intracranial tumors, craniopharyngioma, medulloblastoma, astrocytoma, or glioma. However, GHRT for pituitary adenomas, NFPA, and ependymoma was not associated with the recurrence/progression of the tumors. GH replacement seems safe from the aspect of risk of tumor progression.

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.

Current standing and frontiers of gene therapy for meningiomas

Meningiomas are among the most common intracranial tumors. The treatment of choice for these lesions is complete resection, but in 50% of cases it is not achieved due to tumor location and/or surgical morbidities. Moreover, benign meningiomas have high recurrence rates of up to 32% in long-term follow-up. Molecular analyses have begun to uncover the genetics behind meningiomas, giving rise to potential genetics-based treatments, including gene therapy. The authors performed a literature review on the most relevant genes associated with meningiomas and both current and potential gene therapy strategies to treat these tumors. Wild-type NF2 gene insertion, oncolytic viruses, and transfer of silencing RNA have all shown promising results both in vitro and in mice. These strategies have decreased meningioma cell growth, proliferation, and angiogenesis. However, no clinical trial has been done to date. Future research and trials in gene insertion, selective inhibition of oncogenes, and the use of oncolytic viruses, among other potential treatment approaches, may shape the future of meningioma management.

Advances in oncolytic virus therapy for glioma

The World Health Organization grossly classifies the various types of astrocytomas using a grade system with grade IV gliomas having the worst prognosis. Oncolytic virus therapy is a novel treatment option for GBM patients. Several patents describe various oncolytic viruses used in preclinical and clinical trials to evaluate safety and efficacy. These viruses are natural or genetically engineered from different viruses such as HSV-1, Adenovirus, Reovirus, and New Castle Disease Virus. While several anecdotal studies have indicated therapeutic advantage, recent clinical trials have revealed the safety of their usage, but demonstration of significant efficacy remains to be established. Oncolytic viruses are being redesigned with an interest in combating the tumor microenvironment in addition to defeating the cancerous cells. Several patents describe the inclusion of tumor microenvironment modulating genes within the viral backbone and in particular those which attack the tumor angiotome. The very innovative approaches being used to improve therapeutic efficacy include: design of viruses which can express cytokines to activate a systemic antitumor immune response, inclusion of angiostatic genes to combat tumor vasculature, and also enzymes capable of digesting tumor extra cellular matrix (ECM) to enhance viral spread through solid tumors. As increasingly more novel viruses are being tested and patented, the future battle against glioma looks promising.

Identifying candidate genes involved in brain tumor formation

Malignant primary brain tumors, gliomas, often overexpress both platelet-derived growth factor (PDGF) ligands and receptors providing an autocrine and/or paracrine boost to tumor growth. Glioblastoma multiforme (GBM) is the most frequent glioma. Its aggressive and infiltrative growth renders it extremely difficult to treat. Median survival after diagnosis is currently only 12-14 months. The present review describes the use of retroviral tagging to identify candidate cancer-causing genes that cooperate with PDGF in brain tumor formation. Newborn mice injected intracerebrally with a Moloney murine leukemia retrovirus carrying the sis/PDGF-B oncogene and a replication competent helper virus developed brain tumors with many characteristics of human gliomas. Analysis of proviral integrations in the brain tumors identified almost 70 common insertion sites (CISs). These CISs were named brain tumor loci and harbored known but also putative novel cancer-causing genes. Microarray analysis identified differentially expressed genes in the mouse brain tumors compared to normal brain. Known tumor genes and markers of immature cells were upregulated in the tumors. Tumors developed 13-42 weeks after injection and short latency tumors were further distinguished as fast growing and GBM-like. Long latency tumors resembled slow-growing oligodendrogliomas and contained significantly less integrations as compared to short latency tumors. Several candidate genes tagged in this retroviral screen have known functions in neoplastic transformation and oncogenesis. Some candidates with a previously unknown function in tumorigenesis were found and their putative role in brain tumor formation will be discussed in this review. The results show that proviral tagging may be a useful tool in the search for candidate glioma genes.

Effect of tumor microenvironment modulation on the efficacy of oncolytic virus therapy

BACKGROUND

The tumor microenvironment is being increasingly recognized as an important determinant of tumor progression as well as of therapeutic response. We investigated oncolytic virus (OV) therapy-induced changes in tumor blood vessels and the impact of modulating tumor vasculature on the efficacy of oncolytic virus therapy.

METHODS

Rat glioma cells (D74/HveC) were implanted intracranially in immune-competent rats. Seven days later, the rats (groups of 3-7 rats) were treated with oncolytic virus (hrR3), and, 3 days later, brains were harvested for evaluation. Some rats were treated with angiostatic cRGD peptide 4 days before oncolytic virus treatment. Some rats were treated with cyclophosphamide (CPA), an immunosuppressant, 2 days before oncolytic virus treatment. Changes in tumor vascular perfusion were evaluated by magnetic resonance imaging of live rats and by fluorescence microscopy of tumor sections from rats perfused with Texas red-conjugated lectin immediately before euthanasia. Leukocyte infiltration in tumors was evaluated by anti-CD45 immunohistochemistry, and the presence of oncolytic virus in tumors was evaluated by viral titration. Changes in cytokine gene expression in tumors were measured by quantitative real-time polymerase chain reaction-based microarrays. Survival was analyzed by the Kaplan-Meier method. All statistical tests were two-sided.

RESULTS

Oncolytic virus treatment of experimental rat gliomas increased tumor vascular permeability, host leukocyte infiltration into tumors, and intratumoral expression of inflammatory cytokine genes, including interferon gamma (IFN-gamma). The increase in vascular permeability was suppressed in rats pretreated with cyclophosphamide. Compared with rats treated with hrR3 alone, rats pretreated with a single dose of cRGD peptide before hrR3 treatment had reduced tumor vascular permeability, leukocyte infiltration, and IFN-gamma protein levels (mean IFN-gamma level for hrR3 versus hrR3 + cRGD = 203 versus 65.6 microg/mg, difference = 137 microg/mg, 95% confidence interval = 72.7 to 202.9 microg/mg, P = .006); increased viral titers in tumor tissue; and longer median survival (21 days versus 17 days, P<.001).

CONCLUSIONS

A single dose of angiostatic cRGD peptide treatment before oncolytic virus treatment enhanced the antitumor efficacy of oncolytic virus.