Orthotopic transplantation of v-src–expressing glioma cell lines into immunocompetent mice: establishment of a new transplantable in vivo model for malignant glioma

Tyrphostin A9 attenuates glioblastoma growth by suppressing PYK2/EGFR-ERK signaling pathway

PURPOSE

Glioblastoma (GBM) is a fatal primary brain tumor with extremely poor clinical outcomes. The anticancer efficiency of tyrosine kinase inhibitors (TKIs) has been shown in GBM and other cancer, with limited therapeutic outcomes. In the current study, we aimed to investigate the clinical impact of active proline-rich tyrosine kinase-2 (PYK2) and epidermal growth factor receptor (EGFR) in GBM and evaluate its druggability by a synthetic TKI-Tyrphostin A9 (TYR A9).

METHODS

The expression profile of PYK2 and EGFR in astrocytoma biopsies (n = 48) and GBM cell lines were evaluated through quantitative PCR, western blots, and immunohistochemistry. The clinical association of phospho-PYK2 and EGFR was analyzed with various clinicopathological features and the Kaplan-Meier survival curve. The phospho-PYK2 and EGFR druggability and subsequent anticancer efficacy of TYR A9 was evaluated in GBM cell lines and intracranial C6 glioma model.

RESULTS

Our expression data revealed an increased phospho-PYK2, and EGFR expression aggravates astrocytoma malignancy and is associated with patients' poor survival. The mRNA and protein correlation analysis showed a positive association between phospho-PYK2 and EGFR in GBM tissues. The in-vitro studies demonstrated that TYR A9 reduced GBM cell growth, cell migration, and induced apoptosis by attenuating PYK2/EGFR-ERK signaling. The in-vivo data showed TYR A9 treatment dramatically reduced glioma growth with augmented animal survival by repressing PYK2/EGFR-ERK signaling.

CONCLUSION

Altogether, this study report that increased phospho-PYK2 and EGFR expression in astrocytoma was associated with poor prognosis. The in-vitro and in-vivo evidence underlined translational implication of TYR A9 by suppressing PYK2/EGFR-ERK modulated signaling pathway. The schematic diagram displayed proof of concept of the current study indicating activated PYK2 either through the Ca2+/Calmodulin-dependent protein kinase II (CAMKII) signaling pathway or autophosphorylation at Tyr402 induces association to the SH2 domain of c-Src that leads to c-Src activation. Activated c-Src in turn activates PYK2 at other tyrosine residues that recruit Grb2/SOS complex and trigger ERK½ activation. Besides, PYK2 interaction with c-Src acts as an upstream of EGFR transactivator that can activate the ERK½ signaling pathway, which induces cell proliferation and cell survival by increasing anti-apoptotic proteins or inhibiting pro-apoptotic proteins. TYR A9 treatment attenuate GBM cell proliferation and migration; and induce GBM cell death by inhibiting PYK2 and EGFR-induced ERK activation.

STAT3 Enhances Sensitivity of Glioblastoma to Drug-Induced Autophagy-Dependent Cell Death

Simple Summary

Glioblastoma is the most common primary brain cancer in adults. One reason for the development and malignancy of this tumor is the misregulation of certain cellular proteins. The oncoprotein STAT3 that is frequently overactive in glioblastoma cells is associated with more aggressive disease and decreased patient survival. Autophagy is a form of cellular self digestion that normally maintains cell integrity and provides nutrients and basic building blocks required for growth. While glioblastoma is known to be particularly resistant to conventional therapies, recent research has suggested that these tumors are more sensitive to excessive overactivation of autophagy, leading to autophagy-dependent tumor cell death. Here, we show a hitherto unknown role of STAT3 in sensitizing glioblastoma cells to excessive autophagy induced with the repurposed drug pimozide. These findings provide the basis for future research aimed at determining whether STAT3 can serve as a predictor for autophagy-proficient tumors and further support the notion of overactivating autophagy for cancer therapy.

Abstract

Glioblastoma (GBM) is a devastating disease and the most common primary brain malignancy of adults with a median survival barely exceeding one year. Recent findings suggest that the antipsychotic drug pimozide triggers an autophagy-dependent, lysosomal type of cell death in GBM cells with possible implications for GBM therapy. One oncoprotein that is often overactivated in these tumors and associated with a particularly dismal prognosis is Signal Transducer and Activator of Transcription 3 (STAT3). Here, we used isogenic human and murine GBM knockout cell lines, advanced fluorescence microscopy, transcriptomic analysis and FACS-based assessment of cell viability to show that STAT3 has an underappreciated, context-dependent role in drug-induced cell death. Specifically, we demonstrate that depletion of STAT3 significantly enhances cell survival after treatment with Pimozide, suggesting that STAT3 confers a particular vulnerability to GBM. Furthermore, we show that active STAT3 has no major influence on the early steps of the autophagy pathway, but exacerbates drug-induced lysosomal membrane permeabilization (LMP) and release of cathepsins into the cytosol. Collectively, our findings support the concept of exploiting the pro-death functions of autophagy and LMP for GBM therapy and to further determine whether STAT3 can be employed as a treatment predictor for highly apoptosis-resistant, but autophagy-proficient cancers.

Rabeprazole has efficacy per se and reduces resistance to temozolomide in glioma via EMT inhibition

PURPOSE

Epithelial to mesenchymal transition (EMT) is pivotal in embryonic development and wound healing, whereas in cancer it inflicts malignancy and drug resistance. The recognition of an EMT-like process in glioma is relatively new and its clinical and therapeutic significance has, as yet, not been fully elucidated. Here, we aimed to delineate the clinical significance of the EMT-like process in glioma and its therapeutic relevance to rabeprazole.

METHODS

We investigated the expression profiles of EMT-associated proteins in primary glioma biopsies through Western blotting and immunohistochemistry, and correlated them with various clinicopathological features and data listed in the cancer genome atlas (TCGA). In addition, the anticancer efficacy of rabeprazole and its therapeutic relevance to EMT along with temozolomide chemo-sensitization were assessed using multiple cell-based assays, Western blotting and confocal imaging. For in vivo assessment, we used a stereotaxic C6-rat glioma model.

RESULTS

Expression analysis of EMT-associated proteins in glioma biopsies, in conjunction with clinicopathological and TCGA dataset analyses, revealed non-canonical expression of E/N-cadherin and upregulation of GFAP, vimentin and β-catenin. The increased expression of EMT-associated proteins may attribute to glioma malignancy and a poor patient prognosis. Subsequent in vitro studies revealed that rabeprazole treatment attenuated glioma cell growth and migration, and induced apoptosis. Rabeprazole suppressed EMT by impeding AKT/GSK3β phosphorylation and/or NF-κB signaling and sensitized temozolomide resistance. Additional in vivo studies showed restricted tumor growth and inhibited expression of EMT-associated proteins after rabeprazole treatment.

CONCLUSIONS

Our data revealed (i) a clinical association of the EMT-like process with glioma malignancy and a poor survival and (ii) an anticancer and temozolomide sensitizing effect of rabeprazole by repressing EMT.

Novel Iodine nanoparticles target vascular mimicry in intracerebral triple negative human MDA-MB-231 breast tumors

Triple negative breast cancer (TNBC), ~ 10-20% of diagnosed breast cancers, metastasizes to brain, lungs, liver. Iodine nanoparticle (INP) radioenhancers specifically localize to human TNBC MDA-MB-231 tumors growing in mouse brains after iv injection, significantly extending survival of mice after radiation therapy (RT). A prominent rim of INP contrast (MicroCT) previously seen in subcutaneous tumors but not intracerebral gliomas, provide calculated X-ray dose-enhancements up to > eightfold. Here, MDA-MB-231-cells, INPs, CD31 were examined by fluorescence confocal microscopy. Most INP staining co-localized with CD31 in the tumor center and periphery. Greatest INP/CD31 staining was in the tumor periphery, the region of increased MicroCT contrast. Tumor cells are seen to line irregularly-shaped spaces (ISS) with INP, CD31 staining very close to or on the tumor cell surface and PAS stain on their boundary and may represent a unique form of CD31-expressing vascular mimicry in intracerebral 231-tumors. INP/CD31 co-staining is also seen around ISS formed around tumor cells migrating on CD31+ blood-vessels. The significant radiation dose enhancement to the prolific collagen I containing, INP-binding ISS found throughout the tumor but concentrated in the tumor rim, may contribute significantly to the life extensions observed after INP-RT; VM could represent a new drug/NP, particularly INP, tumor-homing target.

Immunologic aspects of viral therapy for glioblastoma and implications for interactions with immunotherapies

INTRODUCTION

The treatment for glioblastoma (GBM) has remained unchanged for the past decade, with only minimal improvements in patient survival. As a result, novel treatments are needed to combat this devastating disease. Immunotherapies are treatments that stimulate the immune system to attack tumor cells and can be either local or systemically delivered. Viral treatments can lead to direct tumor cell death through their natural lifecycle or through the delivery of a suicide gene, with the potential to generate an anti-tumor immune response, making them interesting candidates for combinatorial treatment with immunotherapy.

METHODS

We review the current literature surrounding the interactions between oncolytic viruses and the immune system as well as the use of oncolytic viruses combined with immunotherapies for the treatment of GBM.

RESULTS

Viral therapies have exhibited preclinical efficacy as single-agents and are being investigated in that manner in clinical trials. Oncolytic viruses have significant interactions with the immune system, although this can also vary depending on the strain of virus. Combinatorial treatments using both oncolytic viruses and immunotherapies have demonstrated promising preclinical findings.

CONCLUSIONS

Studies combining viral and immunotherapeutic treatment modalities have provided exciting results thus far and hold great promise for patients with GBM. Additional studies assessing the clinical efficacy of these treatments as well as improved preclinical modeling systems, safety mechanisms, and the balance between treatment efficacy and immune-mediated viral clearance should be considered.

Iodine nanoparticle radiotherapy of human breast cancer growing in the brains of athymic mice

About 30% of breast cancers metastasize to the brain; those widely disseminated are fatal typically in 3-4 months, even with the best available treatments, including surgery, drugs, and radiotherapy. To address this dire situation, we have developed iodine nanoparticles (INPs) that target brain tumors after intravenous (IV) injection. The iodine then absorbs X-rays during radiotherapy (RT), creating free radicals and local tumor damage, effectively boosting the local RT dose at the tumor. Efficacy was tested using the very aggressive human triple negative breast cancer (TNBC, MDA-MB-231 cells) growing in the brains of athymic nude mice. With a well-tolerated non-toxic IV dose of the INPs (7 g iodine/kg body weight), tumors showed a heavily iodinated rim surrounding the tumor having an average uptake of 2.9% iodine by weight, with uptake peaks at 4.5%. This is calculated to provide a dose enhancement factor of approximately 5.5 (peaks at 8.0), the highest ever reported for any radiation-enhancing agents. With RT alone (15 Gy, single dose), all animals died by 72 days; INP pretreatment resulted in longer-term remissions with 40% of mice surviving 150 days and 30% surviving > 280 days.

Tumor Vessel Normalization, Immunostimulatory Reprogramming, and Improved Survival in Glioblastoma with Combined Inhibition of PD-1, Angiopoietin-2, and VEGF

Glioblastoma (GBM) is a non-T-cell-inflamed cancer characterized by an immunosuppressive microenvironment that impedes dendritic cell maturation and T-cell cytotoxicity. Proangiogenic cytokines such as VEGF and angiopoietin-2 (Ang-2) have high expression in glioblastoma in a cell-specific manner and not only drive tumor angiogenesis and vascular permeability but also negatively regulate T-lymphocyte and innate immune cell responses. Consequently, the alleviation of immunosuppression might be a prerequisite for successful immune checkpoint therapy in GBM. We here combined antiangiogenic and immune checkpoint therapy and demonstrated improved therapeutic efficacy in syngeneic, orthotopic GBM models. We observed that blockade of VEGF, Ang-2, and programmed cell death protein-1 (PD-1) significantly extended survival compared with vascular targeting alone. In the GBM microenvironment, triple therapy increased the numbers of CTLs, which inversely correlated with myeloid-derived suppressor cells and regulatory T cells. Transcriptome analysis of GBM microvessels indicated a global vascular normalization that was highest after triple therapy. Our results propose a rationale to overcome tumor immunosuppression and the current limitations of VEGF monotherapy by integrating the synergistic effects of VEGF/Ang-2 and PD-1 blockade to reinforce antitumor immunity through a normalized vasculature.

Roscovitine effectively enhances antitumor activity of temozolomide in vitro and in vivo mediated by increased autophagy and Caspase-3 dependent apoptosis

Gliomas are incurable solid tumors with extremely high relapse rate and definite mortality. As gliomas readily acquire resistance to only approved drug, temozolomide (TMZ), there is increasing need to overcome drug resistance by novel therapeutics or by repurposing the existing therapy. In the current study, we investigated antitumor efficacy of roscovitine, a Cdk inhibitor, in combination with TMZ in vitro (U87, U373, LN 18 and C6 cell lines) and in vivo (orthotopic glioma model in Wistar rats) glioma models. We observed that TMZ treatment following a pre-treatment with RSV significantly enhanced chemo-sensitivity and suppressed the growth of glioma cells by reducing Cdk-5 activity and simultaneous induction of autophagy and Caspase-3 mediated apoptosis. Additionally, reduced expression of Ki67, GFAP and markers of angiogenesis (CD31, VEGF) was observed in case of TMZ + RSV treatments. Also, presence of reactive astrocytes in peri-tumoral areas and in areas around blood vessels was completely diminished in TMZ + RSV treated brain sections. Taken together, results in the current study provide evidence that RSV in conjunction with TMZ restricts glioma growth, reduces angiogenesis and also eliminates reactive astrocytes thereby preventing the spread of glioma to adjacent healthy brain tissues and thus might be more potent therapeutic option for glioma.

Iodine nanoparticles enhance radiotherapy of intracerebral human glioma in mice and increase efficacy of chemotherapy

Gliomas and other brain tumors have evaded durable therapies, ultimately causing about 20% of all cancer deaths. Tumors are widespread in the brain at time of diagnosis, limiting surgery and radiotherapy effectiveness. Drugs are also poorly effective. Radiotherapy (RT) is limited by dose to normal tissue. However, high-atomic-number elements absorb X-rays and deposit the absorbed dose locally, even doubling (or more) the local dose. Previously we showed that gold nanoparticles (AuNPs) with RT could eradicate some brain tumors in mice and many other preclinical studies confirmed AuNPs as outstanding radioenhancers. However, impediments to clinical translation of AuNPs have been poor clearance, skin discoloration, and cost. We therefore developed iodine nanoparticles (INPs) that are almost colorless, non-toxic, lower cost, and have reasonable clearance, thus overcoming major drawbacks of AuNPs. Here we report the use of iodine nanoparticle radiotherapy (INRT) in treating advanced human gliomas (U87) grown orthotopically in nude mice resulting in a more than a doubling of median life extension compared to RT alone. Significantly, INRT also enhanced the efficacy of chemotherapy when it was combined with the chemotherapeutic agent Doxil, resulting in some longer-term survivors. While ongoing optimization studies should further improve INRT, clinical translation appears promising.

Therapeutic Targeting of Stat3 Using Lipopolyplex Nanoparticle-Formulated siRNA in a Syngeneic Orthotopic Mouse Glioma Model

Glioblastoma (GBM), WHO grade IV, is the most aggressive primary brain tumor in adults. The median survival time using standard therapy is only 12–15 months with a 5-year survival rate of around 5%. Thus, new and effective treatment modalities are of significant importance. Signal transducer and activator of transcription 3 (Stat3) is a key signaling protein driving major hallmarks of cancer and represents a promising target for the development of targeted glioblastoma therapies. Here we present data showing that the therapeutic application of siRNAs, formulated in nanoscale lipopolyplexes (LPP) based on polyethylenimine (PEI) and the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), represents a promising new approach to target Stat3 in glioma. We demonstrate that the LPP-mediated delivery of siRNA mediates efficient knockdown of Stat3, suppresses Stat3 activity and limits cell growth in murine (Tu2449) and human (U87, Mz18) glioma cells in vitro. In a therapeutic setting, intracranial application of the siRNA-containing LPP leads to knockdown of STAT3 target gene expression, decreased tumor growth and significantly prolonged survival in Tu2449 glioma-bearing mice compared to negative control-treated animals. This is a proof-of-concept study introducing PEI-based lipopolyplexes as an efficient strategy for therapeutically targeting oncoproteins with otherwise limited druggability.

Small, Long Blood Half-Life Iodine Nanoparticle for Vascular and Tumor Imaging

Standard clinical X-ray contrast agents are small iodine-containing molecules that are rapidly cleared by the kidneys and provide robust imaging for only a few seconds, thereby limiting more extensive vascular and tissue biodistribution imaging as well as optimal tumor uptake. They are also not generally useful for preclinical microCT imaging where longer scan times are required for high resolution image acquisition. We here describe a new iodine nanoparticle contrast agent that has a unique combination of properties: 20 nm hydrodynamic diameter, covalent PEG coating, 40 hour blood half-life, 50% liver clearance after six months, accumulation in tumors, and well-tolerated to at least 4 g iodine/kg body weight after intravenous administration in mice. These characteristics are unique among the other iodine nanoparticles that have been previously reported and provide extended-time high contrast vascular imaging and tumor loading. As such, it is useful for preclinical MicroCT animal studies. Potential human applications might include X-ray radiation dose enhancement for cancer therapy and vascular imaging for life-threatening situations where high levels of contrast are needed for extended periods of time.

The role of interleukin-6-STAT3 signalling in glioblastoma

Glioblastoma is the most common type of malignant brain tumor among adults and is currently a non-curable disease due primarily to its highly invasive phenotype, and the lack of successful current therapies. Despite surgical resection and post-surgical treatment patients ultimately develop recurrence of the tumour. Several signalling molecules have been implicated in the development, progression and aggressiveness of glioblastoma. The present study reviewed the role of interleukin (IL)-6, a cytokine known to be important in activating several pro-oncogenic signaling pathways in glioblastoma. The current study particularly focused on the contribution of IL-6 in recurrent glioblastoma, with particular focus on glioblastoma stem cells and resistance to therapy.

Retroviral replicating vector-mediated gene therapy achieves long-term control of tumor recurrence and leads to durable anticancer immunity

Background

Prodrug-activator gene therapy with Toca 511, a tumor-selective retroviral replicating vector (RRV) encoding yeast cytosine deaminase, is being evaluated in recurrent high-grade glioma patients. Nonlytic retroviral infection leads to permanent integration of RRV into the cancer cell genome, converting infected cancer cell and progeny into stable vector producer cells, enabling ongoing transduction and viral persistence within tumors. Cytosine deaminase in infected tumor cells converts the antifungal prodrug 5-fluorocytosine into the anticancer drug 5-fluorouracil, mediating local tumor destruction without significant systemic adverse effects.

Methods

Here we investigated mechanisms underlying the therapeutic efficacy of this approach in orthotopic brain tumor models, employing both human glioma xenografts in immunodeficient hosts and syngeneic murine gliomas in immunocompetent hosts.

Results

In both models, a single injection of replicating vector followed by prodrug administration achieved long-term survival benefit. In the immunodeficient model, tumors recurred repeatedly, but bioluminescence imaging of tumors enabled tailored scheduling of multicycle prodrug administration, continued control of disease burden, and long-term survival. In the immunocompetent model, complete loss of tumor signal was observed after only 1-2 cycles of prodrug, followed by long-term survival without recurrence for >300 days despite discontinuation of prodrug. Long-term survivors rejected challenge with uninfected glioma cells, indicating immunological responses against native tumor antigens, and immune cell depletion showed a critical role for CD4+ T cells.

Conclusion

These results support dual mechanisms of action contributing to the efficacy of RRV-mediated prodrug-activator gene therapy: long-term tumor control by prodrug conversion-mediated cytoreduction, and induction of antitumor immunity.

ASA404, a vascular disrupting agent, as an experimental treatment approach for brain tumors

Malignant brain tumors, including gliomas, brain metastases and anaplastic meningiomas, are associated with poor prognosis, and represent an unmet medical need. ASA404 (DMXAA), a vascular disrupting agent, has demonstrated promising results in several preclinical tumor models and early phase clinical trials. However, two phase III trials in non-small cell lung cancer reported insufficient results. The aim of the present study was to determine the effects of ASA404 on brain tumors. The effects of ASA404 were evaluated in vitro and in vivo using subcutaneous, and orthotopical models for malignant glioma (U-87, LN-229, U-251, LN-308 and Tu-2449), brain metastasis (HT-29) and malignant meningioma (IOMM-Lee). The acute effects of ASA404 on tumor tissue were analyzed using conventional and immunohistochemical staining techniques [hematoxylin and eosin, MIB-1 antibody/proliferation maker protein Ki-67, cleaved caspase-8, stimulator of interferon genes (STING), ionized calcium-binding adapter molecule 1]. Furthermore, the sizes of subcutaneous tumors were measured and the symptom-free survival rates of animals with intracranial tumors receiving ASA404 treatment were analyzed. ASA404 demonstrated low toxicity in vitro, but exhibited strong effects on subcutaneous tumors 24 h following a single dose of ASA404 (25 mg/kg). ASA404 induced necrosis, hemorrhages and inhibited the proliferation, and growth of tumors in the subcutaneous glioma models. However, ASA404 failed to demonstrate comparable effects in any of the intracranial tumor models examined and did not result in a prolongation of survival. Expression of STING, the molecular target of ASA404, and infiltration of macrophages, the cells mediating ASA404 activity, did not differ between subcutaneous and intracranial tumors. In conclusion, ASA404 demonstrates clear efficacy in subcutaneous tumor models, but has no relevant activity in orthotopic brain tumor models. The expression of STING and infiltration with macrophages were not determined to be involved in the differential activity observed among tumor models. It is possible that the low penetration of ASA-404 into the brain prevents concentrations sufficient enough reaching the tumor in order to exhibit acute effects in vivo.

Tumor cell resistance against targeted therapeutics: the density of cultured glioma tumor cells enhances Stat3 activity and offers protection against the tyrosine kinase inhibitor canertinib

Tumor cell resistance to drug treatment severely limits the therapeutic success of treatment.

Tumor cell resistance to drug treatment severely limits the therapeutic success of treatment. Tumor cells, exposed to chemotherapeutic drugs, have developed intricate strategies to escape the cytotoxic effects and adapt to adverse conditions. The molecular mechanisms causing drug resistance can be based upon modifications of drug transport or metabolism, structural alterations of drug targets or adaptation of cellular signaling. An important component in the transformation of cells and the emergence of drug resistance is the activation of the transcription factor Stat3. The persistent, inappropriate activation of Stat3 causes the expression of target genes which promote tumor cell proliferation, survival, invasion and immune suppression, and it is instrumental in the process of the emergence of resistance to both conventional chemotherapeutic agents and novel targeted compounds. For these reasons, Stat3 inhibition is being pursued as a promising therapeutic strategy. We have investigated the effects of the tyrosine kinase inhibitor canertinib on the glioma cell line Tu-2449. In these cells Stat3 is persistently phosphorylated and activated downstream of the oncogenic driver v-Src and its effector, the cytoplasmic tyrosine kinase Bmx. Canertinib exposure of Tu-2449 cells rapidly caused the inhibition of the Bmx kinase and the deactivation of Stat3. Prolonged exposure of the cells to canertinib caused the death of the large majority of the cells. Only a few cells became resistant to canertinib and survived in tight clusters. These cells have become drug resistant. When the canertinib resistant cells were expanded and cultured at lower cell densities, they regained their sensitivity towards canertinib. We measured the extent of Stat3 activation as a function of cell density and found that higher cell densities are accompanied by increased Stat3 activation and a higher expression of Stat3 target genes. We suggest that Stat3 induction through tight cell–cell interactions, most likely through the engagement of cadherins, can counteract the inhibitory effects exerted by canertinib on Bmx. Cell–cell interactions induced Stat3 and compensated for the suppression of Stat3 by canertinib, thus transiently protecting the cells from the cytotoxic effects of the inhibitor.

Role of STAT3 in Genesis and Progression of Human Malignant Gliomas

Signal transducer and activator of transcription 3 (STAT3) is aberrantly activated in glioblastoma and has been identified as a relevant therapeutic target in this disease and many other human cancers. After two decades of intensive research, there is not yet any approved STAT3-based glioma therapy. In addition to the canonical activation by tyrosine 705 phosphorylation, concordant reports described a potential therapeutic relevance of other post-translational modifications including mainly serine 727 phosphorylation. Such reports reinforce the need to refine the strategy of targeting STAT3 in each concerned disease. This review focuses on the role of serine 727 and tyrosine 705 phosphorylation of STAT3 in glioma. It explores their contribution to glial cell transformation and to the mechanisms that make glioma escape to both immune control and standard treatment.

Development of a transplantable glioma tumour model from genetically engineered mice: MRI/MRS/MRSI characterisation

The initial aim of this study was to generate a transplantable glial tumour model of low-intermediate grade by disaggregation of a spontaneous tumour mass from genetically engineered models (GEM). This should result in an increased tumour incidence in comparison to GEM animals. An anaplastic oligoastrocytoma (OA) tumour of World Health Organization (WHO) grade III was obtained from a female GEM mouse with the S100β-v-erbB/inK4a-Arf (+/-) genotype maintained in the C57BL/6 background. The tumour tissue was disaggregated; tumour cells from it were grown in aggregates and stereotactically injected into C57BL/6 mice. Tumour development was followed using Magnetic Resonance Imaging (MRI), while changes in the metabolomics pattern of the masses were evaluated by Magnetic Resonance Spectroscopy/Spectroscopic Imaging (MRS/MRSI). Final tumour grade was evaluated by histopathological analysis. The total number of tumours generated from GEM cells from disaggregated tumour (CDT) was 67 with up to 100 % penetrance, as compared to 16 % in the local GEM model, with an average survival time of 66 ± 55 days, up to 4.3-fold significantly higher than the standard GL261 glioblastoma (GBM) tumour model. Tumours produced by transplantation of cells freshly obtained from disaggregated GEM tumour were diagnosed as WHO grade III anaplastic oligodendroglioma (ODG) and OA, while tumours produced from a previously frozen sample were diagnosed as WHO grade IV GBM. We successfully grew CDT and generated tumours from a grade III GEM glial tumour. Freezing and cell culture protocols produced progression to grade IV GBM, which makes the developed transplantable model qualify as potential secondary GBM model in mice.

Reprogramming strategies for the establishment of novel human cancer models

Cancer comprises heterogeneous cells, ranging from highly proliferative immature precursors to more differentiated cell lineages. The emergence of the "cancer stem cell" (CSC) hypothesis that they are the cells responsible for resistance, metastasis and secondary tumor appearance identifies these populations as novel obligatory targets for the treatment of cancer. CSCs, like their normal tissue-specific stem cell counterparts, are multipotent, partially differentiated, self-sustaining, yet transformed cells. To date, most studies on CSC biology have relied on the use of murine models and primary human material. In spite of much progress, the use of primary material presents several limitations that limit our understanding of the mechanisms underlying CSC formation, the similarities between normal stem cells and CSCs and ultimately, the possibility for developing targeted therapies. Recently, different strategies for controlling cell fate have been applied to the modeling of human cancer initiation and for the generation of human CSC models. Here we will summarize recent developments in the establishment and application of reprogramming strategies for the modeling of human cancer initiation and CSC formation.

Toca 511 plus 5-fluorocytosine in combination with lomustine shows chemotoxic and immunotherapeutic activity with no additive toxicity in rodent glioblastoma models

BACKGROUND

Toca 511, a gamma retroviral replicating vector encoding cytosine deaminase, used in combination with 5-fluorocytosine (5-FC) kills tumor by local production of 5-fluorouracil (5-FU), inducing local and systemic immunotherapeutic response resulting in long-term survival after cessation of 5-FC. Toca 511 and Toca FC (oral extended-release 5-FC) are under investigation in patients with recurrent high-grade glioma. Lomustine is a treatment option for patients with high-grade glioma.

METHODS

We investigated the effects of lomustine combined with Toca 511 + 5-FC in syngeneic orthotopic glioma models. Safety and survival were evaluated in immune-competent rat F98 and mouse Tu-2449 models comparing Toca 511 + 5-FC to lomustine + 5-FC or the combination of Toca 511 + 5-FC + lomustine. After intracranial implantation of tumor, Toca 511 was delivered transcranially followed by cycles of intraperitoneal 5-FC with or without lomustine at the first or fourth cycle.

RESULTS

Coadministration of 5-FC with lomustine was well tolerated. In F98, combination Toca 511 + 5-FC and lomustine increased median survival, but "cures" were not achieved. In Tu-2449, combination Toca 511 + 5-FC and lomustine increased median survival and resulted in high numbers of cure. Rejection of tumor rechallenge occurred after treatment with Toca 511 + 5-FC or combined with lomustine, but not with lomustine + 5-FC. Mixed lymphocyte-tumor cell reactions using splenocytes from cured animals showed robust killing of target cells in an effector:target ratio-dependent manner with Toca 511 + 5-FC and Toca 511 + 5-FC + lomustine day 10.

CONCLUSION

The combination of Toca 511 + 5-FC and lomustine shows promising efficacy with no additive toxicity in murine glioma models. Immunotherapeutic responses resulting in long-term survival were preserved despite lomustine-related myelosuppression.

Withania somnifera Suppresses Tumor Growth of Intracranial Allograft of Glioma Cells

Gliomas are the most frequent type of primary brain tumor in adults. Their highly proliferative nature, complex cellular composition, and ability to escape therapies have confronted investigators for years, hindering the advancement toward an effective treatment. Agents that are safe and can be administered as dietary supplements have always remained priority to be most feasible for cancer therapy. Withania somnifera (ashwagandha) is an essential ingredient of Ayurvedic preparations and is known to eliminate cancer cells derived from a variety of peripheral tissues. Although our previous studies have addressed the in vitro anti-proliferative and differentiation-inducing properties of ashwagandha on neuronal cell lines, in vivo studies validating the same are lacking. While exploring the mechanism of its action in vitro, we observed that the ashwagandha water extract (ASH-WEX) induced the G2/M phase blockade and caused the activation of multiple pro-apoptotic pathways, leading to suppression of cyclin D1, bcl-xl, and p-Akt, and reduced the expression of polysialylated form of neural cell adhesion molecule (PSA-NCAM) as well as the activity of matrix metalloproteinases. ASH-WEX reduced the intracranial tumor volumes in vivo and suppressed the tumor-promoting proteins p-nuclear factor kappa B (NF-κB), p-Akt, vascular endothelial growth factor (VEGF), heat shock protein 70 (HSP70), PSA-NCAM, and cyclin D1 in the rat model of orthotopic glioma allograft. Reduction in glial fibrillary acidic protein (GFAP) and upregulation of mortalin and neural cell adhesion molecule (NCAM) expression specifically in tumor-bearing tissue further indicated the anti-glioma efficacy of ASH-WEX in vivo. Combining this enhanced understanding of the molecular mechanisms of ASH-WEX in glioma with in vivo model system offers new opportunities to develop therapeutic strategy for safe, specific, and effective formulations for treating brain tumors.

In vivo modeling of malignant glioma: the road to effective therapy

Despite an increased emphasis on developing new therapies for malignant gliomas, they remain among the most intractable tumors faced today as they demonstrate a remarkable ability to evade current treatment strategies. Numerous candidate treatments fail at late stages, often after showing promising preclinical results. This disconnect highlights the continued need for improved animal models of glioma, which can be used to both screen potential targets and authentically recapitulate the human condition. This review examines recent developments in the animal modeling of glioma, from more established rat models to intriguing new systems using Drosophila and zebrafish that set the stage for higher throughput studies of potentially useful targets. It also addresses the versatility of mouse modeling using newly developed techniques recreating human protocols and sophisticated genetically engineered approaches that aim to characterize the biology of gliomagenesis. The use of these and future models will elucidate both new targets and effective combination therapies that will impact on disease management.

Similarity on neural stem cells and brain tumor stem cells in transgenic brain tumor mouse models

Although it is believed that glioma is derived from brain tumor stem cells, the source and molecular signal pathways of these cells are still unclear. In this study, we used stable doxycycline-inducible transgenic mouse brain tumor models (c-myc⁺/SV40Tag⁺/Tet-on⁺) to explore the malignant trans-formation potential of neural stem cells by observing the differences of neural stem cells and brain tumor stem cells in the tumor models. Results showed that chromosome instability occurred in brain tumor stem cells. The numbers of cytolysosomes and autophagosomes in brain tumor stem cells and induced neural stem cells were lower and the proliferative activity was obviously stronger than that in normal neural stem cells. Normal neural stem cells could differentiate into glial fibrillary acidic protein-positive and microtubule associated protein-2-positive cells, which were also negative for nestin. However, glial fibrillary acidic protein/nestin, microtubule associated protein-2/nestin, and glial fibrillary acidic protein/microtubule associated protein-2 double-positive cells were found in induced neural stem cells and brain tumor stem cells. Results indicate that induced neural stem cells are similar to brain tumor stem cells, and are possibly the source of brain tumor stem cells.

Toca 511 gene transfer and 5-fluorocytosine in combination with temozolomide demonstrates synergistic therapeutic efficacy in a temozolomide-sensitive glioblastoma model

Toca 511 (vocimagene amiretrorepvec), an amphotropic retroviral replicating vector (RRV), can successfully and safely deliver a functional, optimized cytosine deaminase (CD) gene to tumors in orthotopic glioma models. This agent, in conjunction with subsequent oral extended-release 5-fluorocytosine (5-FC) (Toca FC), is currently under investigation in patients with recurrent high-grade glioma . Temozolomide (TMZ) with radiation is the most frequently used first-line treatment for patients with glioblastoma, the most common and aggressive form of primary brain cancer in adults. However, subsets of patients with certain genetic alterations do not respond well to TMZ treatment and the overall median survival for patients who respond remains modest, suggesting that combinatorial approaches may be necessary to significantly improve outcomes. We show that in vitro TMZ delays but does not prevent RRV spread, nor interfere with Toca 511+5-FC-mediated cell killing in glioma tumor cells, and in vivo there is no significant hematologic effect from the combination of 5-FC and the clinically relevant dose of TMZ. A synergistic long-term survival advantage is observed in mice bearing an orthotopic TMZ-sensitive glioma after Toca 511 administration followed by coadministration of TMZ and 5-FC. These results provide support for the investigation of this novel combination treatment strategy in patients with newly diagnosed malignant glioma.

Therapy model for advanced intracerebral B16 mouse melanoma using radiation therapy combined with immunotherapy

A reproducible therapy model for advanced intracerebral B16 melanoma is reported. Implanted tumors (D0), suppressed by a single 15 Gy radiosurgical dose of 100 kVp X-rays (D8), were further suppressed by a single ip injection of a Treg-depleting mAb given 2 days prior to the initiation (D9) of four weekly then eight bi-monthly sc injections of GMCSF-transfected, mitotically disabled B16 cells. The trends of seven independent experiments were similar to the combined result: The median (days) [SD/total N] of survival went from 15[1.09/62] (no treatment control) to 35.8[8.8/58] (radiation therapy only) to 52.5[13.5/57] (radiation therapy plus immunotherapy). Within 2 weeks after immunization, tumors in mice receiving radiation therapy plus immunotherapy were significantly smaller than tumors in mice treated only with radiosurgery. Splenocytes and lymph node cells from immunized mice showed increased interferon γ production when cultured with syngeneic tumor cells. We suggest that our model will be useful for the development and testing of novel combination therapies for brain tumors.

STAT3 silencing inhibits glioma single cell infiltration and tumor growth

BACKGROUND

Diffuse infiltration remains the fulcrum of glioblastoma's incurability, leading inevitably to recurrence. Therefore, uncovering the pathological mechanism is imperative. Because signal transducer and activator of transcription 3 (STAT3) correlates with glioma malignancy and predicts poor clinical outcome, we determined its role in glioma single cell infiltration and tumor growth.

METHODS

STAT3 was silenced in Tu-2449 glioma cells via lentiviral gene transfer. Target gene expression was measured by real-time reverse transcription PCR, Western blotting, and immunohistochemistry. Microvilli were visualized by staining with wheat germ agglutinin. Migration and invasion were measured by Scratch and Matrigel chamber assays. Diffuse infiltration was studied in 350-μm-thick organotypic tissue cultures over 14 days using cells tagged with enhanced green fluorescent protein and live confocal laser scanning microscopy. Survival of tumor-bearing syngeneic, immunocompetent B6C3F1 mice was analyzed by Kaplan-Meier plots.

RESULTS

STAT3 silencing reduced cell migration and invasion in vitro and stopped single cell infiltration ex vivo, while STAT3-expressing cells disseminated through the neuropil at ∼100 µm/day. STAT3 silencing reduced transcription of several tumor progression genes. Mice with intracranial STAT3 knockdown tumors had a significant (P< .0007) survival advantage over controls, yielding 27% long-term survival. STAT3 knockdown reduced podoplanin expression 50-fold and inhibited concurrent microvilli formation. STAT3 knockdown tumors exhibited a weaker podoplanin immunoreactivity compared with controls. Podoplanin staining was diffuse, preferentially at tumor margins, and absent in normal brain.

CONCLUSIONS

Our results show compelling evidence that STAT3 is a key driver of diffuse infiltration and glioma growth and might therefore represent a promising target for an anti-invasive therapy.

Gold nanoparticle imaging and radiotherapy of brain tumors in mice

AIM

To test intravenously injected gold nanoparticles for x-ray imaging and radiotherapy enhancement of large, imminently lethal, intracerebral malignant gliomas.

MATERIALS & METHODS

Gold nanoparticles approximately 11 nm in size were injected intravenously and brains imaged using microcomputed tomography. A total of 15 h after an intravenous dose of 4 g Au/kg was administered, brains were irradiated with 30 Gy 100 kVp x-rays.

RESULTS

Gold uptake gave a 19:1 tumor to normal brain ratio with 1.5% w/w gold in tumor, calculated to increase local radiation dose by approximately 300%. Mice receiving gold and radiation (30 Gy) demonstrated 50% long term (>1 year) tumor-free survival, whereas all mice receiving radiation only died.

CONCLUSION

Intravenously injected gold nanoparticles cross the blood-tumor barrier, but are largely blocked by the normal blood-brain barrier, enabling high-resolution computed tomography tumor imaging. Gold radiation enhancement significantly improved long-term survival compared with radiotherapy alone. This approach holds promise to improve therapy of human brain tumors and other cancers.

Review: insights gained from modelling high-grade glioma in the mouse

High-grade gliomas (HGGs) are devastating primary brain tumours with poor outcomes. Advances towards effective treatments require improved understanding of pathogenesis and relevant model systems for preclinical testing. Mouse models for HGG provide physiologically relevant experimental systems for analysis of HGG pathogenesis. There are advantages and disadvantages to the different methodologies used to generate such models, including implantation, genetic engineering or somatic gene transfer approaches. This review highlights how mouse models have provided insights into the contribution of specific mutations to tumour initiation, progression and phenotype, the influence of tumour micro-environment, and the analysis of cell types that can give rise to glioma. HGGs are a heterogeneous group of tumours, and the complexity of diverse mutations within common signalling pathways as well as the developmental and cell-type context of transformation contributes to the overall diversity of glioma phenotype. Enhanced understanding of the mutations and cell types giving rise to HGG, along with the ability to design increasingly complex mouse models that more closely simulate the process of human gliomagenesis will continue to provide improved experimental systems for dissecting mechanisms of disease pathogenesis and for preclinical testing.

Animal models for vaccine therapy

Animal models are important for defining paradigms of tumor immunology and for evaluating therapeutic efficacy of immunotherapy. Many animal models have been used for evaluating in vivo characteristics of malignant gliomas and their responses to therapy. No animal model, however, is perfect because malignant glioma has a very heterogeneous biological behavior. There are so many parallels between mouse and human immunology, but there are significant discrepancies in immune system. Animal models for vaccine therapy can be classified as transplantable tumor models and models of spontaneous tumor in genetically engineered animals. Although transplantable tumor models have been used to test immunotherapeutic efficacy and remain a mainstay in study of brain tumor immunology, a lot of tumor vaccines that look promising in experimental animals have turned out to be ineffective clinically. Recent advances of laboratory techniques and understanding of genetic and molecular characteristics of gliomas allows for animal models of gliomas with similar biologic characteristics. Well-designed glioma models that accurately reflect the biology, pathology and clinical behaviors of human gliomas can provide more useful preclinical informations to predict clinical efficacy of novel immunotherapies and cancer vaccines.

MR imaging features of high-grade gliomas in murine models: how they compare with human disease, reflect tumor biology, and play a role in preclinical trials

Murine models are the most commonly used and best investigated among the animal models of HGG. They constitute an important weapon in the development and testing of new anticancer drugs and have long been used in preclinical trials. Neuroimaging methods, particularly MR imaging, offer important advantages for the evaluation of treatment response: shorter and more reliable treatment end points and insight on tumor biology and physiology through the use of functional imaging DWI, PWI, BOLD, and MR spectroscopy. This functional information has been progressively consolidated as a surrogate marker of tumor biology and genetics and may play a pivotal role in the assessment of specifically targeted drugs, both in clinical and preclinical trials. The purpose of this Research Perspectives was to compile, summarize, and critically assess the available information on the neuroimaging features of different murine models of HGGs, and explain how these correlate with human disease and reflect tumor biology.

Brain tumor eradication and prolonged survival from intratumoral conversion of 5-fluorocytosine to 5-fluorouracil using a nonlytic retroviral replicating vector

Patients with the most common and aggressive form of high-grade glioma, glioblastoma multiforme, have poor prognosis and few treatment options. In 2 immunocompetent mouse brain tumor models (CT26-BALB/c and Tu-2449-B6C3F1), we showed that a nonlytic retroviral replicating vector (Toca 511) stably delivers an optimized cytosine deaminase prodrug activating gene to the tumor lesion and leads to long-term survival after treatment with 5-fluorocytosine (5-FC). Survival benefit is dose dependent for both vector and 5-FC, and as few as 4 cycles of 5-FC dosing after Toca 511 therapy provides significant survival advantage. In the virally permissive CT26-BALB/c model, spread of Toca 511 to other tissues, particularly lymphoid tissues, is detectable by polymerase chain reaction (PCR) over a wide range of levels. In the Tu-2449-B6C3F1 model, Toca 511 PCR signal in nontumor tissues is much lower, spread is not always observed, and when observed, is mainly detected in lymphoid tissues at low levels. The difference in vector genome spread correlates with a more effective antiviral restriction element, APOBEC3, present in the B6C3F1 mice. Despite these differences, neither strain showed signs of treatment-related toxicity. These data support the concept that, in immunocompetent animals, a replicating retroviral vector carrying a prodrug activating gene (Toca 511) can spread through a tumor mass, leading to selective elimination of the tumor after prodrug administration, without local or systemic pathology. This concept is under investigation in an ongoing phase I/II clinical trial of Toca 511 in combination with 5-FC in patients with recurrent high-grade glioma (www.clinicaltrials.gov NCT01156584).

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

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

STAT3 is required for proliferation and maintenance of multipotency in glioblastoma stem cells

Signal transducer and activator of transcription 3 (STAT3) regulates diverse cellular processes, including cell growth, differentiation, and apoptosis, and is frequently activated during tumorigenesis. Recently, putative glioblastoma stem cells (GBM-SCs) were isolated and characterized. These cells can self-renew indefinitely in culture, are highly tumorigenic, and retain the ability to differentiate in culture. We have found that treatment of GBM-SCs with two chemically distinct small molecule inhibitors of STAT3 DNA-binding inhibits cell proliferation and the formation of new neurospheres from single cells. Genetic knockdown of STAT3 using a short hairpin RNA also inhibits GBM-SC proliferation and neurosphere formation, confirming that these effects are specific to STAT3. Although STAT3 inhibition can induce apoptosis in serum-derived GBM cell lines, this effect was not observed in GBM-SCs grown in stem cell medium. Markers of neural stem cell multipotency also decrease upon STAT3 inhibition, suggesting that STAT3 is required for maintenance of the stem-like characteristics of these cells. Strikingly, even a transient inhibition of STAT3 leads to irreversible growth arrest and inhibition of neurosphere formation. These data suggest that STAT3 regulates the growth and self-renewal of GBM-SCs and is thus a potential target for cancer stem cell-directed therapy of glioblastoma multiforme.

Establishment of a new human glioblastoma multiforme cell line (WJ1) and its partial characterization

(1) A new human glioblastoma multiforme (GBM) cell line, WJ1, was established from the tissue derived from a 29-year-old patient diagnosed with a grade IV GBM. (2) The WJ1 cell line has been subcultured for more than 80 passages in standard culture media without feeder layer or collagen coatings. (3) GBM cells grow in vitro with distinct morphological appearance. Ultrastructural examination revealed large irregular nuclei and pseudo-inclusion bodies in nuclei. The cytoplasm contained numerous immature organelles and a few glia filaments. Growth kinetic studies demonstrated an approximate population doubling time of 60 h and a colony forming efficiency of 4.04%. The karyotype of the cells was hyperdiploid, with a large subpopulation of polyploid cells. Drug sensitivities of DDP, VP-16, tanshinone IIA of this cell line were assayed. They showed a dose- and time-dependent growth inhibition effect on the cells. (4) Orthotopic transplantation of GBM cells into athymic nude mice induced the formation of solid tumor masses about 6 weeks. The cells obtained from mouse tumor masses when cultivated in vitro had the same morphology and ultrastructure as those of the initial cultures. (5) This cell line may provide a useful model in vitro and in vivo in the cellular and molecular studies as well as in testing novel therapies for human glioblastoma multiforme.