Gene therapy for malignant glioma

Role of post-therapy 99mTc-MIBI single-photon emission computed tomography/computed tomography scan in predicting survival in patients with high-grade glioma

OBJECTIVE

High-grade gliomas (HGGs) carry dismal prognosis with survival typically reported as less than a year. We explored the predictive value of qualitative and quantitative evaluations of post-treatment 99m-technetium-labelled methoxyisobutylisonitrile (99mmTc-MIBI) brain single-photon emission computed tomography-computed tomography (SPECT/CT) tumor uptake in relation to overall survival (OS) in patients with HGG.

METHODS

Thirty patients with pathologically or radiologically documented high-grade glioma (HGG) were prospectively recruited for this study (24 male, 6 female; mean age 43 ± 14 years). All patients had a clinical or radiological suspicion of residual/recurrent tumor after initial therapy. 99mTc-MIBI brain SPECT/CT scanning was performed, and the scans were evaluated qualitatively on a five-point probability score (1-5, scores ≥3 considered positive for residual/recurrent tumor); and quantitively via drawing volumes of interest (VOI) on the suspected lesions and normal contralateral brain tissue. All patients were followed up for 1 year or till death.

RESULTS

Positive visual MIBI results were associated with poor survival. Among 10 patients with negative MIBI scores, only two patients died (OS = 75%), while 11/20 patients reported positive on MIBI died, with a median survival of 9 months (OS = 14.5%; P = 0.03). All patients with active isocontour volume ≤1.96 cm3 were alive at the end of the study, compared to a median survival of 9 months and OS of 12% for patients with an isocontour volume of >1.97% (P = 0.003).

CONCLUSION

In patients with HGG, post-therapy brain SPECT/CT with 99mTc-MIBI can provide useful prognostic information.

Drug and gene delivery across the blood-brain barrier with focused ultrasound

The blood-brain barrier (BBB) remains one of the most significant limitations to treatments of central nervous system (CNS) disorders including brain tumors, neurodegenerative diseases and psychiatric disorders. It is now well-established that focused ultrasound (FUS) in conjunction with contrast agent microbubbles may be used to non-invasively and temporarily disrupt the BBB, allowing localized delivery of systemically administered therapeutic agents as large as 100nm in size to the CNS. Importantly, recent technological advances now permit FUS application through the intact human skull, obviating the need for invasive and risky surgical procedures. When used in combination with magnetic resonance imaging, FUS may be applied precisely to pre-selected CNS targets. Indeed, FUS devices capable of sub-millimeter precision are currently in several clinical trials. FUS mediated BBB disruption has the potential to fundamentally change how CNS diseases are treated, unlocking potential for combinatorial treatments with nanotechnology, markedly increasing the efficacy of existing therapeutics that otherwise do not cross the BBB effectively, and permitting safe repeated treatments. This article comprehensively reviews recent studies on the targeted delivery of therapeutics into the CNS with FUS and offers perspectives on the future of this technology.

Highly compacted pH-responsive DNA nanoparticles mediate transgene silencing in experimental glioma

Complex genetic mutations are common in brain cancer, making gene therapy an attractive approach to repair or modulate altered genes and cellular pathways. Non-viral gene vectors can offer DNA delivery without the risk of immunogenicity and/or insertional mutagenesis that are common with viral vectors. We developed pH-responsive DNA nanoparticles, CH₁₂K₁₈PEG_5k, by inserting a poly-L-histidine segment between PEG and poly-L-lysine to engineer a triblock copolymer. CH₁₂K₁₈PEG_5k DNA nanoparticles trafficked through clathrin-dependent endocytosis (CME) as the primary pathway in mouse glioblastoma (GBM) cells, and protected plasmid DNA from both DNase-mediated and acidic lysosomal degradation. CH₁₂K₁₈PEG_5k DNA nanoparticles effectively silenced a tumor-specific transgene (firefly luciferase) following direct injection into mouse intracranial GBM. Toxicity and histological analysis showed no evidence of acute or delayed inflammatory responses. These results demonstrate the utility of using this DNA nanoparticle-based technology for delivering genes to tumor cells as a possible therapeutic approach for patients with brain cancer.

Maintaining and loading neural stem cells for delivery of oncolytic adenovirus to brain tumors

Despite recent advancements in the treatment of cancer, the prognosis for patients with malignant brain tumors remains poor. The success of currently available therapies has been limited in part because of the disseminated nature of these tumors. Furthermore, most of these tumors, when in a high-grade form, are resistant to chemo- and radiotherapy. Taking the above considerations into account, effective treatment of these cancers not only requires the development of new means to target tumor burdens that have dispersed significantly from their site of origin, but also therapeutic approaches which can appropriately discriminate between tumor cell and normal brain. In the past two decades, novel approaches involving the use of oncolytic adenoviruses to target -malignant brain tumors have undergone extensive investigation and proven to be an effective mode of antiglioma therapy. While the use of various oncolytic adenoviruses has been proven to be safe for local delivery in preclinical and clinical trials, the successful application of this approach in the clinic has been hampered by the host immune response against the viral vector. The discovery of the inherent tumor-tropic properties of neural stem cells (NSCs) provides a unique opportunity that employs NSCs as a cellular vehicle to track tumor cells and deliver therapeutic oncolytic virus. This presents a novel platform for targeted delivery of oncolytic adenovirus to disseminated tumors selectively while hiding the therapeutic virus from the host immune system. NSC loaded with an oncolytic adenovirus offer a more selective and effective method of targeting satellite tumor burdens and this chapter reviews the methodology associated with this unique approach.

A chimeric adenovirus with an Ad 3 fiber knob modification augments glioma virotherapy

BACKGROUND

Malignant gliomas remain refractory to treatment despite advances in chemotherapy and surgical techniques. Viral vectors developed to treat gliomas have had low transduction capabilities, limiting their use. Gliomas over-express CD46, CD80, and CD86, all of which bind adenovirus serotype 3.

METHODS

To increase the infectivity and replication of oncolytic vectors in malignant brain tumors, we created a conditionally replicating adenovirus, CRAd-Survivin-5/3, which contains a survivin promoter-driving E1A and a chimeric fiber consisting of adenovirus serotype 3 knob.

RESULTS

In vitro, this modified CRAd showed ten- to 100-fold increased cytotoxicity against glioma cells. Ex vivo analysis of primary glioblastoma multiforme samples infected with CRAd-Survivin-5/3 showed an increase in cytotoxicity of 20-30% compared to adenovirus wild-type (AdWT). In normal human astrocytes and normal brain tissues, CRAd-Survivin-5/3 exhibited 30-40% and 10-15% lower cytotoxicity than AdWT, respectively. In an intracranial xenograft model of glioma, this oncolytic virus increased tumor-free survival and overall lifespan by 50% compared to controls (p < 0.05).

CONCLUSIONS

CRAd-Survivin-5/3 represents an attractive alternative to existing vectors and should be tested further in the pre-clinical setting.

Brain-targeting gene delivery and cellular internalization mechanisms for modified rabies virus glycoprotein RVG29 nanoparticles

A 29 amino-acid peptide derived from the rabies virus glycoprotein (RVG29) was exploited as a ligand for efficient brain-targeting gene delivery. RVG29 was modified on polyamidoamine dendrimers (PAMAM) through bifunctional PEG, then complexed with DNA, yielding PAMAM-PEG-RVG29/DNA nanoparticles (NPs). The NPs were observed to be uptaken by brain capillary endothelial cells (BCECs) through a clathrin and caveolae mediated energy-depending endocytosis. The specific cellular uptake can be inhibited by free RVG29 and GABA but not by nicotinic acetylcholine receptor (nAchR) agonists/antagonists, indicating RVG29 probably relates to the GABA(B) receptor besides nAchR reported previously. PAMAM-PEG-RVG29/DNA NPs showed higher blood-brain barrier (BBB)-crossing efficiency than PAMAM/DNA NPs in an in vitro BBB model. In vivo imaging showed that the NPs were preferably accumulated in brain. The report gene expression of the PAMAM-PEG-RVG29/DNA NPs was observed in brain, and significantly higher than unmodified NPs. Thus, PAMAM-PEG-RVG29 provides a safe and noninvasive approach for the gene delivery across the BBB.

Low-dose radiation enhances survivin-mediated virotherapy against malignant glioma stem cells

To improve the efficacy and selectivity of virotherapy for malignant glioma, we designed a strategy to amplify adenoviral replication in conjunction with radiotherapy using a radioinducible promoter. First, we compared the radiation-inducible activity of FLT-1, vascular endothelial growth factor, DR5, Cox2, and survivin. We then examined the capacity of the optimal promoter to modulate transgene expression followed by E1A activity in vitro and in vivo in a glioma stem cell model. In the presence of radiation, survivin mRNA activity increased 10-fold. Luciferase transgene expression was dose dependent and optimal at 2 Gy. A novel oncolytic adenovirus, CRAd-Survivin-pk7, showed significant toxicity and replication against a panel of passaged and primary CD133(+) glioma stem cells. On delivery of radiation, the toxicity associated with CRAd-Survivin-pk7 increased by 20% to 50% (P < 0.05). At the same time, the level of E1A activity increased 3- to 10-fold. In vivo, treatment of U373MG CD133(+) stem cells with CRAd-Survivin-pk7 and radiation significantly inhibited tumor growth (P < 0.05). At the same time, the level of E1A activity was 100-fold increased versus CRAd-Survivin-pk7 alone. Selected genes linked to radioinducible promoters whose expression can be regulated by ionizing radiation may improve the therapeutic ratio of virotherapy. In this study, we have identified a new radioinducible promoter, survivin, which greatly enhances the activity of an oncolytic adenovirus in the presence of low-dose radiotherapy.

Ultrasound-mediated microbubble destruction facilitates gene transfection in rat C6 glioma cells

The goal of this study was to determine whether ultrasound (US) exposure combined with microbubble destruction could be used to enhance non-viral gene delivery in rat C6 glioma cells. Microbubbles were prepared and gently mixed with plasmid DNA. The mixture of the DNA and microbubbles was administered to cultured C6 cells under different US/microbubble conditions. Transfection efficiency and cell viability were assessed by FACS analysis, confocal laser scanning microscopy, and Trypan blue staining. The results demonstrate that microbubble with US exposure could significantly enhance the reporter gene expression as compared with other groups. No statistical significant difference was observed in the glioma cell viability between different groups. Our in vitro findings suggest that US-mediated microbubble destruction has the potential to promote safe and efficient gene transfer into C6 cells. This non-invasive gene transfer method may be useful for safe clinical gene therapy of brain cancer without a viral vector system.

Diagnosis and treatment of high-grade astrocytoma

High-grade astrocytomas include the most common adult central nervous system (CNS) tumor, glioblastoma multiforme, and anaplastic astrocytoma--a highly aggressive cancer with short median survival despite maximal multimodality therapy. Diagnosis is by clinical and radiographic findings confirmed by histopathology. Standard-of-care therapy includes surgical resection, radiotherapy, and temozolomide. Nearly all patients who have high-grade astrocytomas develop tumor recurrence or progression after this multimodality treatment. Two treatment challenges are molecular/genetic heterogeneity of tumors and limited CNS tumor delivery. It is probable that targeted therapies will be most effective in combination with one another or with cytotoxic therapies. This article discusses diagnosis and current treatment of high-grade astrocytomas.