Remission of invasive, cancer stem-like glioblastoma xenografts using lentiviral vector-mediated suicide gene therapy

Transduction Efficiency of Zika Virus E Protein Pseudotyped HIV-1gfp and Its Oncolytic Activity Tested in Primary Glioblastoma Cell Cultures

The development of new tools against glioblastoma multiforme (GBM), the most aggressive and common cancer originating in the brain, remains of utmost importance. Lentiviral vectors (LVs) are among the tools of future concepts, and pseudotyping offers the possibility of tailoring LVs to efficiently transduce and inactivate GBM tumor cells. Zika virus (ZIKV) has a specificity for GBM cells, leaving healthy brain cells unharmed, which makes it a prime candidate for the development of LVs with a ZIKV coat. Here, primary GBM cell cultures were transduced with different LVs encased with ZIKV envelope variants. LVs were generated by using the pNLgfpAM plasmid, which produces the lentiviral, HIV-1-based, core particle with GFP (green fluorescent protein) as a reporter (HIVgfp). Using five different GBM primary cell cultures and three laboratory-adapted GBM cell lines, we showed that ZIKV/HIVgfp achieved a 4-6 times higher transduction efficiency compared to the commonly used VSV/HIVgfp. Transduced GBM cell cultures were monitored over a period of 9 days to identify GFP+ cells to study the oncolytic effect due to ZIKV/HIVgfp entry. Tests of GBM tumor specificity by transduction of GBM tumor and normal brain cells showed a high specificity for GBM cells.

GAP43-dependent mitochondria transfer from astrocytes enhances glioblastoma tumorigenicity

The transfer of intact mitochondria between heterogeneous cell types has been confirmed in various settings, including cancer. However, the functional implications of mitochondria transfer on tumor biology are poorly understood. Here we show that mitochondria transfer is a prevalent phenomenon in glioblastoma (GBM), the most frequent and malignant primary brain tumor. We identified horizontal mitochondria transfer from astrocytes as a mechanism that enhances tumorigenesis in GBM. This transfer is dependent on network-forming intercellular connections between GBM cells and astrocytes, which are facilitated by growth-associated protein 43 (GAP43), a protein involved in neuron axon regeneration and astrocyte reactivity. The acquisition of astrocyte mitochondria drives an increase in mitochondrial respiration and upregulation of metabolic pathways linked to proliferation and tumorigenicity. Functionally, uptake of astrocyte mitochondria promotes cell cycle progression to proliferative G2/M phases and enhances self-renewal and tumorigenicity of GBM. Collectively, our findings reveal a host-tumor interaction that drives proliferation and self-renewal of cancer cells, providing opportunities for therapeutic development.

Gene Therapy for High Grade Glioma: The Clinical Experience

INTRODUCTION

High-grade gliomas (HGG) are the most common malignant primary brain tumors in adults, with a median survival of ~18 months. The standard of care (SOC) is maximal safe surgical resection, and radiation therapy with concurrent and adjuvant temozolomide. This protocol remains unchanged since 2005, even though HGG median survival has marginally improved.

AREAS COVERED

Gene therapy was developed as a promising approach to treat HGG. Here, we review completed and ongoing clinical trials employing viral and non-viral vectors for adult and pediatric HGG, as well as the key supporting preclinical data.

EXPERT OPINION

These therapies have proven safe, and pre- and post-treatment tissue analyses demonstrated tumor cell lysis, increased immune cell infiltration, and increased systemic immune function. Although viral therapy in clinical trials has not yet significantly extended the survival of HGG, promising strategies are being tested. Oncolytic HSV vectors have shown promising results for both adult and pediatric HGG. A recently published study demonstrated that HG47Δ improved survival in recurrent HGG. Likewise, PVSRIPO has shown survival improvement compared to historical controls. It is likely that further analysis of these trials will stimulate the development of new administration protocols, and new therapeutic combinations that will improve HGG prognosis.

Pseudotyped lentiviral vectors: Ready for translation into targeted cancer gene therapy?

Gene therapy holds great promise for curing cancer by editing the deleterious genes of tumor cells, but the lack of vector systems for efficient delivery of genetic material into specific tumor sites in vivo has limited its full therapeutic potential in cancer gene therapy. Over the past two decades, increasing studies have shown that lentiviral vectors (LVs) modified with different glycoproteins from a donating virus, a process referred to as pseudotyping, have altered tropism and display cell-type specificity in transduction, leading to selective tumor cell killing. This feature of LVs together with their ability to enable high efficient gene delivery in dividing and non-dividing mammalian cells in vivo make them to be attractive tools in future cancer gene therapy. This review is intended to summarize the status quo of some typical pseudotypings of LVs and their applications in basic anti-cancer studies across many malignancies. The opportunities of translating pseudotyped LVs into clinic use in cancer therapy have also been discussed.

Comparing Tumor Cell Invasion and Myeloid Cell Composition in Compatible Primary and Relapsing Glioblastoma

Simple Summary

We established a new minimally invasive mouse model for GBM relapse. For this, we utilized orthotopical implantation of HSVTK-transduced GBM cells and pharmacological treatment with GCV. In addition, we implanted patient-derived GBM cells of primary or recurrent tumors. We found that recurrent GBM were more aggressively invasive than primary GBM. Moreover, the recurring tumors had a higher ratio of monocyte-derived macrophages among the entire population of tumor associated myeloid cells. This shift in the composition of tumor-associated immune cells appeared to be independent from cell-death signaling or surgical intervention. This model provides the means to investigate the entire process of tumor relapse and test standard as well as experimental therapeutic strategies for relapsing GBM under defined conditions.

Abstract

Glioblastoma (GBM) recurrence after treatment is almost inevitable but addressing this issue with adequate preclinical models has remained challenging. Here, we introduce a GBM mouse model allowing non-invasive and scalable de-bulking of a tumor mass located deeply in the brain, which can be combined with conventional therapeutic approaches. Strong reduction of the GBM volume is achieved after pharmacologically inducing a tumor-specific cell death mechanism. This is followed by GBM re-growth over a predictable timeframe. Pharmacological de-bulking followed by tumor relapse was accomplished with an orthotopic mouse glioma model. Relapsing experimental tumors recapitulated pathological features often observed in recurrent human GBM, like increased invasiveness or altered immune cell composition. Orthotopic implantation of GBM cells originating from biopsies of one patient at initial or follow-up treatment reproduced these findings. Interestingly, relapsing GBM of both models contained a much higher ratio of monocyte-derived macrophages (MDM) versus microglia than primary GBM. This was not altered when combining pharmacological de-bulking with invasive surgery. We interpret that factors released from viable primary GBM cells preferentially attract microglia whereas relapsing tumors preponderantly release chemoattractants for MDM. All in all, this relapse model has the capacity to provide novel insights into clinically highly relevant aspects of GBM treatment.

Current Approaches for Glioma Gene Therapy and Virotherapy

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

Retroviral gene therapy in Germany with a view on previous experience and future perspectives

Gene therapy can be used to restore cell function in monogenic disorders or to endow cells with new capabilities, such as improved killing of cancer cells, expression of suicide genes for controlled elimination of cell populations, or protection against chemotherapy or viral infection. While gene therapies were originally most often used to treat monogenic diseases and to improve hematopoietic stem cell transplantation outcome, the advent of genetically modified immune cell therapies, such as chimeric antigen receptor modified T cells, has contributed to the increased numbers of patients treated with gene and cell therapies. The advancement of gene therapy with integrating retroviral vectors continues to depend upon world-wide efforts. As the topic of this special issue is "Spotlight on Germany," the goal of this review is to provide an overview of contributions to this field made by German clinical and research institutions. Research groups in Germany made, and continue to make, important contributions to the development of gene therapy, including design of vectors and transduction protocols for improved cell modification, methods to assess gene therapy vector efficacy and safety (e.g., clonal imbalance, insertion sites), as well as in the design and conduction of clinical gene therapy trials.

Large-Scale Production of Lentiviral Vectors: Current Perspectives and Challenges

Lentiviral vectors (LVs) have gained value over recent years as gene carriers in gene therapy. These viral vectors are safer than what was previously being used for gene transfer and are capable of infecting both dividing and nondividing cells with a long-term expression. This characteristic makes LVs ideal for clinical research, as has been demonstrated with the approval of lentivirus-based gene therapies from the Food and Drug Administration and the European Agency for Medicine. A large number of functional lentiviral particles are required for clinical trials, and large-scale production has been challenging. Therefore, efforts are focused on solving the drawbacks associated with the production and purification of LVsunder current good manufacturing practice. In recent years, we have witnessed the development and optimization of new protocols, packaging cell lines, and culture devices that are very close to reaching the target production level. Here, we review the most recent, efficient, and promising methods for the clinical-scale production ofLVs.

Long-term treatment with valganciclovir improves lentiviral suicide gene therapy of glioblastoma

BACKGROUND

Suicide gene therapy for malignant gliomas has shown encouraging results in the latest clinical trials. However, prodrug application was most often restricted to short-term treatment (14 days), especially when replication-defective vectors were used. We previously showed that a substantial fraction of herpes simplex virus thymidine kinase (HSV-TK) transduced tumor cells survive ganciclovir (GCV) treatment in an orthotopic glioblastoma (GBM) xenograft model. Here we analyzed whether these TK+ tumor cells are still sensitive to prodrug treatment and whether prolonged prodrug treatment can enhance treatment efficacy.

METHODS

Glioma cells positive for TK and green fluorescent protein (GFP) were sorted from xenograft tumors recurring after suicide gene therapy, and their sensitivity to GCV was tested in vitro. GBM xenografts were treated with HSV-TK/GCV, HSV-TK/valganciclovir (valGCV), or HSV-TK/valGCV + erlotinib. Tumor growth was analyzed by MRI, and survival as well as morphological and molecular changes were assessed.

RESULTS

TK-GFP+ tumor cells from recurrent xenograft tumors retained sensitivity to GCV in vitro. Importantly, a prolonged period (3 mo) of prodrug administration with valganciclovir (valGCV) resulted in a significant survival advantage compared with short-term (3 wk) application of GCV. Recurrent tumors from the treatment groups were more invasive and less angiogenic compared with primary tumors and showed significant upregulation of epidermal growth factor receptor (EGFR) expression. However, double treatment with the EGFR inhibitor erlotinib did not increase therapeutic efficacy.

CONCLUSION

Long-term treatment with valGCV should be considered as a replacement for short-term treatment with GCV in clinical trials of HSV-TK mediated suicide gene therapy.

Suicide Gene Therapy Mediated with Exosomes Produced by Mesenchymal Stem/Stromal Cells Stably Transduced with HSV Thymidine Kinase

Mesenchymal stem/stromal cells (MSCs) prepared from various human tissues were stably transduced with the suicide gene herpes simplex virus thymidine kinase (HSVTK) by means of retrovirus infection. HSVTK-transduced MSCs express the suicide gene and in prodrug ganciclovir (GCV) presence induced cell death by intracellular conversion of GCV to GCV-triphosphate. The homogenous population of HSVTK-MSCs were found to release exosomes having mRNA of the suicide gene in their cargo. The exosomes were easily internalized by the tumor cells and the presence of ganciclovir caused their death in a dose-dependent manner. Efficient tumor cell killing of glioma cell lines and primary human glioblastoma cells mediated by HSVTK-MSC exosomes is reported. Exosomes produced by suicide gene transduced MSCs represent a new class of highly selective tumor cell targeted drug acting intracellular with curative potential.

Development of Large-Scale Downstream Processing for Lentiviral Vectors

The interest in lentiviral vectors (LVs) has increased prominently for gene therapy applications, but few have reached the later stages of clinical trials. The main challenge has remained in scaling up the manufacturing process for the fragile vector to obtain high titers for in vivo usage. We have previously scaled up the LV production to iCELLis 500, being able to produce up to 180 L of harvest material in one run with perfusion. The following challenge considers the purification and concentration of the product to meet titer and purity requirements for clinical use. We have developed a downstream process, beginning with clarification, buffer exchange, and concentration, by tangential flow filtration. This is followed by a purification step using single membrane-based anion exchange chromatography and final formulation with tangential flow filtration. Different materials and conditions were compared to optimize the process, especially for the chromatography step that has been the bottleneck in lentiviral vector purification scale-up. The final infectious titer of the lentiviral vector product manufactured using the optimized scale-up process was determined to be 1.97 × 10⁹ transducing units (TU)/mL, which can be considered as a high titer for lentiviral vectors.

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.

Lentiviral Vectors as Tools for the Study and Treatment of Glioblastoma

Glioblastoma (GBM) has the worst prognosis among brain tumors, hence basic biology, preclinical, and clinical studies are necessary to design effective strategies to defeat this disease. Gene transfer vectors derived from the most-studied lentivirus-the Human Immunodeficiency Virus type 1-have wide application in dissecting GBM specific features to identify potential therapeutic targets. Last-generation lentiviruses (LV), highly improved in safety profile and gene transfer capacity, are also largely employed as delivery systems of therapeutic molecules to be employed in gene therapy (GT) approaches. LV were initially used in GT protocols aimed at the expression of suicide factors to induce GBM cell death. Subsequently, LV were adopted to either express small noncoding RNAs to affect different aspects of GBM biology or to overcome the resistance to both chemo- and radiotherapy that easily develop in this tumor after initial therapy. Newer frontiers include adoption of LV for engineering T cells to express chimeric antigen receptors recognizing specific GBM antigens, or for transducing specific cell types that, due to their biological properties, can function as carriers of therapeutic molecules to the cancer mass. Finally, LV allow the setting up of improved animal models crucial for the validation of GBM specific therapies.

Lentiviral HSV-Tk.007-mediated suicide gene therapy is not toxic for normal brain cells

BACKGROUND

Gene therapeutic strategies with suicide genes are currently investigated in clinical trials for brain tumors. Previously, we have shown that lentiviral vectors delivering the suicide gene HSV-Tk to experimental brain tumors promote a highly significant treatment effect and thus are promising vectors for clinical translation.

METHODS

In the present study, we tested lentiviral vectors delivering the suicide gene HSV-Tk.007, a highly active mutant of HSV-Tk, to rat brains as a preclinical toxicity study. We injected 10(6) vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped functional lentiviral particles harboring the suicide gene HSV-Tk.007 into the brain of healthy, immunocompetent rats. During prodrug treatment with ganciclovir (GCV), we measured weight and assessed the behavior of the rats in an open field test. After 14 days of GCV treatment, we analyzed HSV-Tk.007 expression in different brain cell populations, as well as inflammatory responses and apoptosis.

RESULTS

During prodrug treatment with GCV, behavior experiments did not reveal differences between the treated rats and the control groups. Analysis of HSV-Tk expression in different brain cell populations showed that transduced normal brain cells survived GCV treatment. There were no statistically significant differences in the number of transduced cells between treatment and control groups. Furthermore, inflammatory responses and apoptosis of brain cells were not observed.

CONCLUSIONS

We show that HSV-Tk.007-mediated suicide gene therapy is not toxic to normal brain cells. This observation is of high relevance for the translation of lentivirus-mediated suicide gene therapies into the clinic for the treatment of brain tumor patients. Copyright © 2016 John Wiley & Sons, Ltd.

Genome Editing Reveals Glioblastoma Addiction to MicroRNA-10b

Glioblastoma (GBM) brain tumor remains among the most lethal and incurable human diseases. Oncogenic microRNA-10b (miR-10b) is strongly and universally upregulated in GBM, and its inhibition by antisense oligonucleotides (ASOs) reduces the growth of heterogeneous glioma cells; therefore, miR-10b represents a unique therapeutic target for GBM. Here we explored the effects of miR-10b gene editing on GBM. Using the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system, we investigated effects of miR-10b gene editing on the growth of cultured human glioma cells, tumor-initiating stem-like cells, and mouse GBM xenografts, as well as the oncogene-induced transformation of normal astrocytes. We show that GBM is strictly "addicted" to miR-10b and that miR-10b gene ablation is lethal for glioma cell cultures and established intracranial tumors. miR-10b loss-of-function mutations lead to the death of glioma, but not other cancer cell lines. We have not detected escaped proliferative clones of GBM cells edited in the miR-10b locus. Finally, neoplastic transformation of normal astrocytes was abolished by the miR-10b-editing vectors. This study demonstrates the feasibility of gene editing for brain tumors in vivo and suggests virus-mediated miR-10b gene ablation as a promising therapeutic approach that permanently eliminates the key regulator essential for tumor growth and survival.

Cancer suicide gene therapy: a patent review

INTRODUCTION

Cancer is considered the second leading cause of death worldwide despite the progress made in early detection and advances in classical therapies. Advancing in the fight against cancer requires the development of novel strategies, and the suicide gene transfer to tumor cells is providing new possibilities for cancer therapy.

AREAS COVERED

In this manuscript, authors present an overview of suicide gene systems and the latest innovations done to enhance cancer suicide gene therapy strategies by i) improving vectors for targeted gene delivery using tissue specific promoter and receptors; ii) modification of the tropism; and iii) combining suicide genes and/or classical therapies for cancer. Finally, the authors highlight the main challenges to be addressed in the future.

EXPERT OPINION

Even if many efforts are needed for suicide gene therapy to be a real alternative for cancer treatment, we believe that the significant progress made in the knowledge of cancer biology and characterization of cancer stem cells accompanied by the development of novel targeted vectors will enhance the effectiveness of this type of therapeutic strategy. Moreover, combined with current treatments, suicide gene therapy will improve the clinical outcome of patients with cancer in the future.

EGFRvIII mutations can emerge as late and heterogenous events in glioblastoma development and promote angiogenesis through Src activation

BACKGROUND

Amplification of the epidermal growth factor receptor (EGFR) and its mutant EGFRvIII are among the most common genetic alterations in glioblastoma (GBM), the most frequent and most aggressive primary brain tumor.

METHODS

In the present work, we analyzed the clonal evolution of these major EGFR aberrations in a small cohort of GBM patients using a unique surgical multisampling technique. Furthermore, we overexpressed both receptors separately and together in 2 patient-derived GBM stem cell lines (GSCs) to analyze their functions in vivo in orthotopic xenograft models.

RESULTS

In human GBM biopsies, we identified EGFR amplification as an early event because EGFRvIII mutations emerge from intratumoral heterogeneity later in tumor development. To investigate the biological relevance of this distinct developmental pattern, we established experimental model systems. In these models, EGFR⁺ tumor cells showed activation of classical downstream signaling pathways upon EGF stimulation and displayed enhanced invasive growth without evidence of angiogenesis in vivo. In contrast, EGFRvIII⁺ tumors were driven by activation of the prototypical Src family kinase c-Src that promoted VEGF secretion leading to angiogenic tumor growth.

CONCLUSIONS

The presented work shows that sequential EGFR amplification and EGFRvIII mutations might represent concerted evolutionary events that drive the aggressive nature of GBM by promoting invasion and angiogenesis via distinct signaling pathways. In particular, c-SRC may be an attractive therapeutic target for tumors harboring EGFRvIII as we identified this protein specifically mediating angiogenic tumor growth downstream of EGFRvIII.

Surface modification via strain-promoted click reaction facilitates targeted lentiviral transduction

As a result of their ability to integrate into the genome of both dividing and non-dividing cells, lentiviruses have emerged as a promising vector for gene delivery. Targeted gene transduction of specific cells and tissues by lentiviral vectors has been a major goal, which has proven difficult to achieve. We report a novel targeting protocol that relies on the chemoselective attachment of cancer specific ligands to unnatural glycans on lentiviral surfaces. This strategy exhibits minimal perturbation on virus physiology and demonstrates remarkable flexibility. It allows for targeting but can be more broadly useful with applications such as vector purification and immunomodulation.

Engraftment of Human Glioblastoma Cells in Immunocompetent Rats through Acquired Immunosuppression

Transplantation of glioblastoma patient biopsy spheroids to the brain of T cell-compromised Rowett (nude) rats has been established as a representative animal model for human GBMs, with a tumor take rate close to 100%. In immunocompetent littermates however, primary human GBM tissue is invariably rejected. Here we show that after repeated passaging cycles in nude rats, human GBM spheroids are enabled to grow in the brain of immunocompetent rats. In case of engraftment, xenografts in immunocompetent rats grow progressively and host leukocytes fail to enter the tumor bed, similar to what is seen in nude animals. In contrast, rejection is associated with massive infiltration of the tumor bed by leukocytes, predominantly ED1+ microglia/macrophages, CD4+ T helper cells and CD8+ effector cells, and correlates with elevated serum levels of pro-inflammatory cytokines IL-1β, IL-18 and TNF-α. We observed that in nude rat brains, an adaptation to the host occurs after several in vivo passaging cycles, characterized by striking attenuation of microglial infiltration. Furthermore, tumor-derived chemokines that promote leukocyte migration and their entry into the CNS such as CXCL-10 and CXCL-12 are down-regulated, and the levels of TGF-β2 increase. We propose that through serial in vivo passaging in nude rats, human GBM cells learn to avoid and or/ suppress host immunity. Such adapted GBM cells are in turn able to engraft in immunocompetent rats without signs of an inflammatory response.

Long non-coding RNA Linc-ITGB1 knockdown inhibits cell migration and invasion in GBC-SD/M and GBC-SD gallbladder cancer cell lines

Gallbladder cancer is a highly aggressive malignancy with a low 5-year survival rate. Despite advances in the molecular understanding of the initiation and progression in gallbladder cancer, treatment modalities such as surgery, radiotherapy, or chemotherapy in advanced cases did not yield promising outcomes. Therefore, it is of great importance to uncover new mechanism underlying gallbladder cancer growth and metastasis. In this study, we identified a differentially expressed long intergenic non-coding RNA, linc-ITGB1, in a pair of higher and lower metastatic gallbladder cancer cell sublines. Then, the potential role of linc-ITGB1 in gallbladder cancer cell proliferation, migration, and invasion was explored using a lentivirus-mediated RNA interference system. Functional analysis showed that knockdown of linc-ITGB1 significantly inhibited gallbladder cancer cell proliferation. Moreover, cell migration and invasion were reduced by over twofold in linc-ITGB1 knockdown cells probably due to upregulation of β-catenin and downregulation of vimentin, slug, and TCF8. In conclusion, linc-ITGB1 potentially promoted gallbladder cancer invasion and metastasis by accelerating the process of epithelial-to-mesenchymal transition, and the application of RNA interference targeting linc-ITGB1 might be a potential form of gallbladder cancer treatment in advanced cases.

Lentivirus-mediated TPD52L2 depletion inhibits the proliferation of liver cancer cells in vitro

Tumor protein D52-like 2, known as hD54 in previous studies (TPD52L2), is a member of TPD52 family which has been implicated in multiple human cancers. In recent reports, TPD52 proteins were indicated to be associated with several malignancies, but very little is known about the function of TPD52L2 in liver cancers. In our present study, in order to explore the role of TPD52L2 in liver cancer, TPD52L2 was knocked down in SMMC-7721 liver cancer cell line by lentivirus mediated RNA interference. The results demonstrated that depletion of TPD52L2 could remarkably inhibit proliferation and colony forming ability of cancer cell SMMC-7721. Furthermore, cell cycle in TPD52L2 depleted cells was verified to be arrested in G0/G1 phase as determined by FACS assay, in consistence with the observation of cell proliferation inhibition. These results unraveled that TPD52L2 played an important role in tumorigenesis pathways of liver cancer and might serve as a promising target in human liver cancer diagnosis and therapy.

Therapeutic effects of lentivirus-mediated shRNA targeting of cyclin D1 in human gastric cancer

Background

Gastric cancer is the second most common cause of cancer-related death in males and the fourth in females. Traditional treatment has poor prognosis because of recurrence and systemic side effects. Therefore, the development of new therapeutic strategies is an important issue. Lentivirus-mediated shRNA stably inhibits target genes and can efficiently transduce most cells. Since overexpressed cyclin D1 is closely related to human gastric cancer progression, inhibition of cyclin D1 using specific targeting could be an effective treatment method of human gastric cancer.

Methods

The therapeutic effect of lentivirus-mediated shRNA targeting of cyclin D1 (ShCCND1) was analyzed both in vitro and in vivo experiments.

Results

In vitro, NCI-N87 cells with downregulation of cyclin D1 by ShCCND1 showed significant inhibition of cell proliferation, cell motility, and clonogenicity. Downregulation of cyclin D1 in NCI-N87 cells also resulted in significantly increased G1 arrest and apoptosis. In vivo, stable NCI-N87 cells expressing ShCCND1 were engrafted into nude mice. Then, the cancer-growth inhibition effect of lentivirus was confirmed. To assess lentivirus including ShCCND1 as a therapeutic agent, intratumoral injection was conducted. Tumor growth of the lentivirus-treated group was significantly inhibited compared to growth of the control group. These results are in accordance with the in vitro data and lend support to the mitotic figure count and apoptosis analysis of the tumor mass.

Conclusion

The lentivirus-mediated ShCCND1 was constructed, which effectively inhibited growth of NCI-N87-derived cancer both in vitro and in vivo. The efficiency of shRNA knockdown and variation in the degree of inhibition is mediated by different shRNA sequences and cancer cell lines. These experimental results suggest the possibility of developing new gastric cancer therapies using lentivirus-mediated shRNA.

Tumor versus stromal cells in culture--survival of the fittest?

Two of the signature genetic events that occur in human gliomas, EGFR amplification and IDH mutation, are poorly represented in experimental models in vitro. EGFR amplification, for example, occurs in 40 to 50% of GBM, and yet, EGFR amplification is rarely preserved in cell cultures derived from human tumors. To analyze the fate of EGFR amplified and IDH mutated cells in culture, we followed the development over time of cultures derived from human xenografts in nude rats enriched for tumor cells with EGFR amplification and of cultures derived from patient samples with IDH mutations, in serum monolayer and spheroid suspension culture, under serum and serum free conditions. We observed under serum monolayer conditions, that nestin positive or nestin and SMA double positive rat stromal cells outgrew EGFR amplified tumor cells, while serum spheroid cultures preserved tumor cells with EGFR amplification. Serum free suspension culture exhibited a more variable cell composition in that the resultant cell populations were either predominantly nestin/SOX2 co-expressing rat stromal cells or human tumor cells, or a mixture of both. The selection for nestin/SMA positive stromal cells under serum monolayer conditions was also consistently observed in human oligodendrogliomas and oligoastrocytomas with IDH mutations. Our results highlight for the first time that serum monolayer conditions can select for stromal cells instead of tumor cells in certain brain tumor subtypes. This result has an important impact on the establishment of new tumor cell cultures from brain tumors and raises the question of the proper conditions for the growth of the tumor cell populations of interest.

EGFR wild-type amplification and activation promote invasion and development of glioblastoma independent of angiogenesis

Angiogenesis is regarded as a hallmark of cancer progression and it has been postulated that solid tumor growth depends on angiogenesis. At present, however, it is clear that tumor cell invasion can occur without angiogenesis, a phenomenon that is particularly evident by the infiltrative growth of malignant brain tumors, such as glioblastomas (GBMs). In these tumors, amplification or overexpression of wild-type (wt) or truncated and constitutively activated epidermal growth factor receptor (EGFR) are regarded as important events in GBM development, where the complex downstream signaling events have been implicated in tumor cell invasion, angiogenesis and proliferation. Here, we show that amplification and in particular activation of wild-type EGFR represents an underlying mechanism for non-angiogenic, invasive tumor growth. Using a clinically relevant human GBM xenograft model, we show that tumor cells with EGFR gene amplification and activation diffusely infiltrate normal brain tissue independent of angiogenesis and that transient inhibition of EGFR activity by cetuximab inhibits the invasive tumor growth. Moreover, stable, long-term expression of a dominant-negative EGFR leads to a mesenchymal to epithelial-like transition and induction of angiogenic tumor growth. Analysis of human GBM biopsies confirmed that EGFR activation correlated with invasive/non-angiogenic tumor growth. In conclusion, our results indicate that activation of wild-type EGFR promotes invasion and glioblastoma development independent of angiogenesis, whereas loss of its activity results in angiogenic tumor growth.

Current status of gene therapy for brain tumors

Glioblastoma (GBM) is the most common and deadliest primary brain tumor in adults, with current treatments having limited impact on disease progression. Therefore the development of alternative treatment options is greatly needed. Gene therapy is a treatment strategy that relies on the delivery of genetic material, usually transgenes or viruses, into cells for therapeutic purposes, and has been applied to GBM with increasing promise. We have included selectively replication-competent oncolytic viruses within this strategy, although the virus acts directly as a complex biologic anti-tumor agent rather than as a classic gene delivery vehicle. GBM is a good candidate for gene therapy because tumors remain locally within the brain and only rarely metastasize to other tissues; the majority of cells in the brain are post-mitotic, which allows for specific targeting of dividing tumor cells; and tumors can often be accessed neurosurgically for administration of therapy. Delivery vehicles used for brain tumors include nonreplicating viral vectors, normal adult stem/progenitor cells, and oncolytic viruses. The therapeutic transgenes or viruses are typically cytotoxic or express prodrug activating suicide genes to kill glioma cells, immunostimulatory to induce or amplify anti-tumor immune responses, and/or modify the tumor microenvironment such as blocking angiogenesis. This review describes current preclinical and clinical gene therapy strategies for the treatment of glioma.

Optimizing glioblastoma temozolomide chemotherapy employing lentiviral-based anti-MGMT shRNA technology

Despite treatments combining surgery, radiation-, and chemotherapy, patients affected by glioblastoma (GBM) have a limited prognosis. Addition of temozolomide (TMZ) to radiation therapy is the standard therapy in clinical application, but effectiveness of TMZ is limited by the tumor's overexpression of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). The goal of this study was to use the highly specific and efficient RNA interference (RNAi) pathway to modulate MGMT expression to increase TMZ efficiency in chemotherapy resistant GBM. Using lentiviral-based anti-MGMT small hairpin RNA (shRNA) technology we observed a specific inhibition of the MGMT expression in GBM cell lines as well as in subcutaneous tumors. Tumor growth inhibition was observed following TMZ treatment of xenografts with low MGMT expression in contrast to xenografts with high MGMT expression. Bioluminescence imaging (BLI) measurements indicated that luciferase and shRNA-expressing lentiviruses were able to efficiently transduce the GBM xenografts in vivo. Treatment combining injection of a lentivirus expressing an anti-MGMT shRNA and TMZ induced a reduction of the size of the tumors, in contrast with treatment combining the lentivirus expressing the control shRNA and TMZ. Our data suggest that anti-MGMT shRNA therapy could be used in combination with TMZ chemotherapy in order to improve the treatment of resistant GBM.

Remnant living cells that escape cell loss in late-stage tumors exhibit cancer stem cell-like characteristics

A balance between cell proliferation and cell loss is essential for tumor progression. Although up to 90% of cells are lost in late-stage carcinomas, the progression and characteristics of remnant living cells in tumor mass are unclear. Here we used molecular imaging to track the progression of living cells in a syngeneic tumor model, and ex vivo investigated the properties of this population at late-stage tumor. The piggyBac transposon system was used to stably introduce the dual reporter genes, including monomeric red fluorescent protein (mRFP) and herpes simplex virus type-1 thymidine kinase (HSV1-tk) genes for fluorescence-based and radionuclide-based imaging of tumor growth in small animals, respectively. Iodine-123-labeled 5-iodo-2′-fluoro-1-beta-𝒟-arabinofuranosyluracil was used as a radiotracer for HSV1-tk gene expression in tumors. The fluorescence- and radionuclide-based imaging using the single-photon emission computed tomography/computed tomography revealed that the number of living cells reached the maximum at 1 week after implantation of 4T1 tumors, and gradually decreased and clustered near the side of the body until 4 weeks accompanied by enlargement of tumor mass. The remnant living cells at late-stage tumor were isolated and investigated ex vivo. The results showed that these living cells could form mammospheres and express cancer stem cell (CSC)-related biomarkers, including octamer-binding transcription factor 4, SRY (sex-determining region Y)-box 2, and CD133 genes compared with those cultured in vitro. Furthermore, this HSV1-tk-expressing CSC-like population was sensitive to ganciclovir applied for the suicide therapy. Taken together, the current data suggested that cells escaping from cell loss in late-stage tumors exhibit CSC-like characteristics, and HSV1-tk may be considered a theranostic agent for targeting this population in vivo.

In vivo models of primary brain tumors: pitfalls and perspectives

Animal modeling for primary brain tumors has undergone constant development over the last 60 years, and significant improvements have been made recently with the establishment of highly invasive glioblastoma models. In this review we discuss the advantages and pitfalls of model development, focusing on chemically induced models, various xenogeneic grafts of human cell lines, including stem cell–like cell lines and biopsy spheroids. We then discuss the development of numerous genetically engineered models available to study mechanisms of tumor initiation and progression. At present it is clear that none of the current animal models fully reflects human gliomas. Yet, the various model systems have provided important insight into specific mechanisms of tumor development. In particular, it is anticipated that a combined comprehensive knowledge of the various models currently available will provide important new knowledge on target identification and the validation and development of new therapeutic strategies.

Suicide gene therapy in cancer: where do we stand now?

Suicide gene therapy is based on the introduction into tumor cells of a viral or a bacterial gene, which allows the conversion of a non-toxic compound into a lethal drug. Although suicide gene therapy has been successfully used in a large number of in vitro and in vivo studies, its application to cancer patients has not reached the desirable clinical significance. However, recent reports on pre-clinical cancer models demonstrate the huge potential of this strategy when used in combination with new therapeutic approaches. In this review, we summarize the different suicide gene systems and gene delivery vectors addressed to cancer, with particular emphasis on recently developed systems and associated bystander effects. In addition, we review the different strategies that have been used in combination with suicide gene therapy and provide some insights into the future directions of this approach, particularly towards cancer stem cell eradication.

Oncolytic virotherapy of glioma: what does it need to make it work?

Oncolytic virotherapy is a highly promising approach, with diverse viruses currently under development as therapeutic agents to treat malignant glioma. Although the first clinical trials did not show toxicity or serious adverse events related to intracerebral administration, overall the antitumor efficacy has fallen short of expectations. This article discusses multiple options on how to improve and maximize the effectiveness of oncolytic virus therapy in brain cancer, including strategies to enhance safety by attenuating neurovirulence via cancer-specific cell-targeting, increasing antitumor potency by transgene-arming and integrating the ability to trigger an effective antitumoral immune response, as well as developing optimized delivery routes in order to boost intratumoral viral distribution. Eventually, it will highlight the use of multipronged approaches, combining multiple modes of action of different agents.

Cancer suicide gene therapy with TK.007: superior killing efficiency and bystander effect

Suicide gene therapy is a promising concept in oncology. We have recently introduced a novel suicide gene, TK.007, which was shown to excel established herpes simplex virus thymidine kinase (HSVtk) variants when used for donor-lymphocyte modification in adoptive immunotherapy models. Here, the potential of TK.007 in killing cancer cells was studied. Initially, we transduced tumour cell lines derived from different neoplasias (glioblastoma, melanoma, lung cancer, colon cancer) with lentiviral LeGO vectors encoding TK.007 or the splice-corrected (sc)HSVtk together with an eGFP/Neo-marker. Based on direct in vitro comparison, we found that TK.007 facilitates more efficient tumour cell killing at significantly lower ganciclovir doses in all tumour cell lines tested. Also, using different readout systems, we found a significantly stronger bystander effect of TK.007 as compared to scHSVtk. Importantly, in vitro data were confirmed in vivo using a subcutaneous G62 glioblastoma model in NOD/SCID mice. In mice transplanted with scHSVtk-positive tumours, treatment with low (10 mg/kg) or standard (50 mg/kg) ganciclovir doses resulted only in short-term growth inhibition or transient tumour remission, respectively. In striking contrast, in the TK.007 group, all animals achieved continuous complete remission after both standard and low-dose ganciclovir. Finally, a substantial bystander effect for TK.007 was also confirmed with the G62 model in vivo, where significantly prolonged survival for mice bearing tumours containing only 10% or 50% TK.007-expressing cells was observed. In summary, our data indicate strongly improved anti-tumour activity of TK.007 as compared to conventional HSVtk. We therefore suppose that TK.007 is an excellent candidate for cancer suicide gene therapy.

Frontiers in targeting glioma stem cells

Patients with glioblastoma multiforme (GBM - WHO grade IV) seldom recover. This is due to the infiltrative nature of these tumours and the presence of cellular populations with ability to escape therapies and drive tumour recurrence and progression. In some cases, these resistant cells exhibit stem properties [glioma stem cells (GSC)]. This article aims at discussing relevant issues on GSC resistance to current therapies and outlines possible and promising avenues in regard to novel therapeutic strategies, such as pharmacological, immunological and viral interventions.

Intrathecal gene therapy for treatment of leptomeningeal carcinomatosis

Leptomeningeal carcinomatosis occurs occasionally in patients with solid malignancies and carries a poor prognosis despite treatment with systemic chemotherapy and/or radiotherapy. We describe the case of a 43 year old man who presented with leptomeningeal carcinomatosis secondary to malignant melanoma. The patient received intraventricular delivery of NIH3T3 producer cells expressing the thymidine kinase (HSV-Tk1) gene via a retroviral vector followed by intravenous ganciclovir. He experienced abrupt and severe meningeal irritation and hyperpyrexia immediately after injection of the producer cells into the ventricular CSF. Vector producer cells (VPC) survived and were detected by NeoR marker gene expression in the CSF for a week, until a single dose of ganciclovir (GCV) was followed by a decline in the copy number of the NeoR marker gene to undetectable levels over 24 h. This decline upon introduction of ganciclovir suggests effective distribution of ganciclovir to producer cells bearing the HSV-Tk gene. The patient survived 9 months after treatment. Side-effects from the treatment included acute hyperpyrexia which was short-lived and medically manageable.

Concise review: Nanoparticles and cellular carriers-allies in cancer imaging and cellular gene therapy?

Ineffective treatment and poor patient management continue to plague the arena of clinical oncology. The crucial issues include inadequate treatment efficacy due to ineffective targeting of cancer deposits, systemic toxicities, suboptimal cancer detection and disease monitoring. This has led to the quest for clinically relevant, innovative multifaceted solutions such as development of targeted and traceable therapies. Mesenchymal stem cells (MSCs) have the intrinsic ability to "home" to growing tumors and are hypoimmunogenic. Therefore, these can be used as (a) "Trojan Horses" to deliver gene therapy directly into the tumors and (b) carriers of nanoparticles to allow cell tracking and simultaneous cancer detection. The camouflage of MSC carriers can potentially tackle the issues of safety, vector, and/or transgene immunogenicity as well as nanoparticle clearance and toxicity. The versatility of the nanotechnology platform could allow cellular tracking using single or multimodal imaging modalities. Toward that end, noninvasive magnetic resonance imaging (MRI) is fast becoming a clinical favorite, though there is scope for improvement in its accuracy and sensitivity. In that, use of superparamagnetic iron-oxide nanoparticles (SPION) as MRI contrast enhancers may be the best option for tracking therapeutic MSC. The prospects and consequences of synergistic approaches using MSC carriers, gene therapy, and SPION in developing cancer diagnostics and therapeutics are discussed.

Brain tumor stem cells

Since the end of the ‘no-new-neuron’ theory, emerging evidence from multiple studies has supported the existence of stem cells in neurogenic areas of the adult brain. Along with this discovery, neural stem cells became candidate cells being at the origin of brain tumors. In fact, it has been demonstrated that molecular mechanisms controlling self-renewal and differentiation are shared between brain tumor stem cells and neural stem cells and that corruption of genes implicated in these pathways can direct tumor growth. In this regard, future anticancer approaches could be inspired by uncovering such redundancies and setting up treatments leading to exhaustion of the cancer stem cell pool. However, deleterious effects on (normal) neural stem cells should be minimized. Such therapeutic models underline the importance to study the cellular mechanisms implicated in fate decisions of neural stem cells and the oncogenic derivation of adult brain cells. In this review, we discuss the putative origins of brain tumor stem cells and their possible implications on future therapies.

Potential therapeutic implications of cancer stem cells in glioblastoma

Glioblastoma is the most common and lethal type of primary brain tumor. Despite recent therapeutic advances in other cancers, the treatment of glioblastomas remains ineffective and essentially palliative. The treatment failure is a result of a number of causes, but we and others have demonstrated that a highly tumorigenic subpopulation of cancer cells called glioblastoma stem cells (GSCs) display relative resistance to radiation and chemotherapy. GSCs also contribute to tumor growth through the stimulation of angiogenesis, which has been shown to be a useful therapeutic target in the treatment of recurrent or progressive malignant gliomas. Cancer stem cells also have been hypothesized as a contributor to systemic metastases. While glioblastomas rarely metastasize beyond the central nervous system, glioblastomas invade into brain structures to prevent surgical cure and GSCs have an extremely invasive phenotype. Collectively, these studies and others suggest that GSCs may be important therapeutic targets not only to achieve cure but even reduce tumor relapse and improve overall survival. Many recent studies suggest that GSCs share core regulatory pathways with normal embryonic and somatic stem cells, but display important distinctions that provide clues into useful treatment targets. The cancer stem cell hypothesis may also modify our approaches in tumor imaging and biomarker development, but clinical validation waits. In this review, we summarize the current understanding of GSC biology with a focus on potential anti-GSC therapies.

Vesicular stomatitis virus modified with single chain IL-23 exhibits oncolytic activity against tumor cells in vitro and in vivo

Viruses are potentially attractive agents for development as novel oncolytic agents. Reverse genetic approaches allow for the attenuation of candidate viruses and can enhance their ability to exploit inherent cellular and molecular properties of tumors, including deficiencies in interferon (IFN) signaling. Vesicular stomatitis virus (VSV) is a promising oncolytic agent for exactly these reasons. VSV infection of immunocompetent mice is usually rapidly cleared due to the virus' sensitivity to type I IFN responses. However, in tumors that are unable to activate the IFN response, VSV is able to replicate without inhibition, resulting in cell destruction. Unfortunately, when VSV is introduced into mice intranasally or systemically via therapeutic doses into tumor-bearing rodents, hosts may develop fatal encephalitis. We have previously found that a recombinant VSV expressing the pro-inflammatory cytokine interleukin-23 (IL-23) is significantly attenuated in the central nervous system (CNS). As a result of this, we hypothesized that attenuation in the CNS is partially a result of enhanced NO response as a result of IL-23 signaling. Infection of the CNS with this virus (designated VSV23) is characterized by decreased viral replication, morbidity, and mortality. We have now extended those studies which reveal that VSV23 maintains oncolytic capacity in vitro in multiple cell lines including NB41A3 neuroblastomas, L929 adipose-derived cells, immortalized BHK-21 cells, and the murine mammary derived JC cells. Additionally, in vivo VSV23 infection results in JC tumor destruction and induces enhanced memory responses against tumor cells.

Cytokine-modified VSV is attenuated for neural pathology, but is both highly immunogenic and oncolytic

Vesicular stomatitis virus (VSV), an enveloped, nonsegmented, negative-stranded RNA virus, is being tested by several laboratories as an antitumor agent. Unfortunately, viral infection of the central nervous system (CNS) has been observed by many groups following administration to tumor-bearing animals. In rodents, VSV encephalitis is characterized by weight-loss, paralysis, and high mortality. In order to provide protection from VSV infection of the CNS after therapeutic administration, we have attenuated VSV by the introduction of the gene encoding the proinflammatory cytokine interleukin (IL)-23, and designated the new virus VSV23. We hypothesize that while VSV23 is replicating within tumors, resulting in tumor destruction, the expression of IL-23 will enhance host antitumor and antiviral immune responses. In the event that the virus escapes from the tumor, the host's immune system will be activated and the virus will be rapidly cleared from healthy tissue. Experimental VSV23 infection of the CNS is characterized by decreased viral replication, morbidity, and mortality. VSV23 is capable of stimulating the enhanced production of nitric oxide in the CNS, which is critical for elimination of VSV from infected neurons. Intraperitoneal administration of VSV23 stimulates both nonspecific natural killer cell, virus-specific cytolytic T lymphocyte and memory virus-specific proliferative T cell responses against wild-type VSV in splenocytes. Furthermore, VSV23 is able to replicate in, and induce apoptosis of tumor cells in vitro. These data indicate that VSV23 is immunogenic, attenuated and suitable for testing as an efficacious and safe oncolytic agent.