Meclofenamate causes loss of cellular tethering and decoupling of functional networks in glioblastoma

BACKGROUND

Glioblastoma cells assemble to a syncytial communicating network based on tumor microtubes (TMs) as ultra-long membrane protrusions. The relationship between network architecture and transcriptional profile remains poorly investigated. Drugs that interfere with this syncytial connectivity such as meclofenamate (MFA) may be highly attractive for glioblastoma therapy.

METHODS

In a human neocortical slice model using glioblastoma cell populations of different transcriptional signatures, three-dimensional tumor networks were reconstructed, and TM-based intercellular connectivity was mapped on the basis of two-photon imaging data. MFA was used to modulate morphological and functional connectivity; downstream effects of MFA treatment were investigated by RNA sequencing and fluorescence-activated cell sorting (FACS) analysis.

RESULTS

TM-based network morphology strongly differed between the transcriptional cellular subtypes of glioblastoma and was dependent on axon guidance molecule expression. MFA revealed both a functional and morphological demolishment of glioblastoma network architectures which was reflected by a reduction of TM-mediated intercellular cytosolic traffic as well as a breakdown of TM length. RNA sequencing confirmed a downregulation of NCAM and axon guidance molecule signaling upon MFA treatment. Loss of glioblastoma communicating networks was accompanied by a failure in the upregulation of genes that are required for DNA repair in response to temozolomide (TMZ) treatment and culminated in profound treatment response to TMZ-mediated toxicity.

CONCLUSION

The capacity of TM formation reflects transcriptional cellular heterogeneity. MFA effectively demolishes functional and morphological TM-based syncytial network architectures. These findings might pave the way to a clinical implementation of MFA as a TM-targeted therapeutic approach.

Astrocytes enhance glioblastoma growth

Glioblastoma (GBM) is a deadly disease with a need for deeper understanding and new therapeutic approaches. The microenvironment of glioblastoma has previously been shown to guide glioblastoma progression. In this study, astrocytes were investigated with regard to their effect on glioblastoma proliferation through correlative analyses of clinical samples and experimental in vitro and in vivo studies. Co-culture techniques were used to investigate the GBM growth enhancing potential of astrocytes. Cell sorting and RNA sequencing were used to generate a GBM-associated astrocyte signature and to investigate astrocyte-induced GBM genes. A NOD scid GBM mouse model was used for in vivo studies. A gene signature reflecting GBM-activated astrocytes was associated with poor prognosis in the TCGA GBM dataset. Two genes, periostin and serglycin, induced in GBM cells upon exposure to astrocytes were expressed at higher levels in cases with high "astrocyte signature score". Astrocytes were shown to enhance glioblastoma cell growth in cell lines and in a patient-derived culture, in a manner dependent on cell-cell contact and involving increased cell proliferation. Furthermore, co-injection of astrocytes with glioblastoma cells reduced survival in an orthotopic GBM model in NOD scid mice. In conclusion, this study suggests that astrocytes contribute to glioblastoma growth and implies this crosstalk as a candidate target for novel therapies.

Abstract 2928: Bortezomib sensitizes glioblastoma with unmethylated MGMT promoter to temozolomide-chemotherapy through MGMT depletion and abrogated autophagy flux

Background: Glioblastoma with unmethylated O6-methyl guanine DNA methyltransferase (MGMT) promoter is highly resistant to temozolomide (TMZ) chemotherapy. Strategies that ameliorate drug resistance are sorely needed. Recent trials of the proteasome inhibitor bortezomib (BTZ) (Velcade) in combination with various drugs failed due to inappropriate schedule timing and dosing. We hypothesized that pretreatment with BTZ prior to TMZ administration may sensitize glioblastoma cell to TMZ chemotherapy.

Methods: We investigated treatment efficacy through DNA damage, apoptosis and autophagy flux by flow cytometry, western blotting, long-lived protein degradation assays, electron and fluorescence microscopy in cell lines (U87, T98G, HF66) and patient biopsy-derived cells (P3, 2012-18, BG5 and BG7). Treatment efficacy and tolerability was investigated in vivo in mice implanted orthotopically with patient-derived GBM xenografts and subsequently treated with human equivalent dose (HED) of BTZ 1.3 mg/m2 on days 1, 4, 8 and 11 for two cycles during TMZ 82 mg/m2 or 164 mg/m2 by oral gavage 5 days/week for 5 weeks. MRI, mouse survival times, tandem LC-MS/MS and clinical chemistry were used to monitor tumor growth and evaluate tissue and blood samples for biomarkers of treatment efficacy and toxicity.

Results: Patient-derived glioblastoma cells were universally more sensitive to BTZ than carfilzomib or MG-132 (P<0.0001), while their sensitivity to TMZ was strongly associated with MGMT promoter methylation status (P<0.0001). BTZ depleted MGMT protein (P<0.001) and mRNA (P<0.0001) in TMZ resistant tumor cells and sensitized to chemotherapy through induction of prominent DNA damage, G2-S phase cell cycle arrest and apoptosis with half the IC50 doses for both drugs. BTZ simultaneously abrogated TMZ-induced autophagic flux indicated by p62 accumulation, inhibition of utophagosome fusion and degradation of long-lived proteins. Human equivalent doses of BTZ 1.3 mg/m2 and TMZ 164 mg/m2 prolonged progression free and overall survival (P<0.0001), through diminished tumor growth (P<0.05), angiogenesis (P<0.01) and proliferation (P<0.05). Loss of structural and catalytic proteasomal subunits confirmed target inhibition at the therapeutically effective dose (P<0.01). Peroxiredoxin, thioredoxin and catalase antioxidant enzymes (P<0.01), alanine aminotransferase (P<0.05) and MGMT mRNA expression (P<0.01) were downregulated in combination treated animals, serving as accessible biomarkers of response.

Conclusion: Pretreatment with BTZ chemo-sensitized resistant glioblastoma through aborted autophagic flux and MGMT depletion to augment DNA damage, apoptosis and prolonged survival. Our findings warrant a controlled investigation of the treatment schedule in selected patients.

Citation Format: Mohummad A. Rahman, Andrea G. Navarro, Jorunn Brekke, Christian Bindesbøll, Agnete Engelsen, Shahin Sarowar, Marzieh Bahador, Bjørn T. Gjertsen, Dorota Goplen, Per Ø. Enger, Frode Selheim, Anne Simonsen, Martha Chekenya. Bortezomib sensitizes glioblastoma with unmethylated MGMT promoter to temozolomide-chemotherapy through MGMT depletion and abrogated autophagy flux [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2928.

Surgical debulking promotes recruitment of macrophages and triggers glioblastoma phagocytosis in combination with CD47 blocking immunotherapy

Surgical resection is a standard component of treatment in the clinical management of patients with glioblastoma multiforme (GBM). However, experimental therapies are rarely investigated in the context of tumor debulking in preclinical models. Here, a surgical debulking GBM xenograft model was developed in nude rats, and was used in combination with CD47 blocking immunotherapy, a novel treatment strategy that triggers phagocytosis of tumor cells by macrophages in diverse cancer types including GBM. Orthotopic patient-derived xenograft tumors expressing CD47 were resected at 4 weeks after implantation and immediately thereafter treated with anti-CD47 or control antibodies injected into the cavity. Debulking prolonged survival (median survival, 68.5 vs 42.5 days, debulking and non-debulking survival times, respectively; n = 6 animals/group; P = 0.0005). Survival was further improved in animals that underwent combination treatment with anti-CD47 mAbs (median survival, 81.5 days vs 69 days, debulking + anti-CD47 vs debulking + control IgG, respectively; P = 0.0007). Immunohistochemistical staining of tumor sections revealed an increase in recruitment of cells positive for CD68, a marker for macrophages/immune cell types, to the surgical site (50% vs 10%, debulking vs non-debulking, respectively). Finally, analysis of tumor protein lysates on antibody microarrays demonstrated an increase in pro-inflammatory cytokines, such as CXCL10, and a decrease in angiogenic proteins in debulking + anti-CD47 vs non-debulking + IgG tumors. The results indicated that surgical resection combined with anti-CD47 blocking immunotherapy promoted an inflammatory response and prolonged survival in animals, and is therefore an attractive strategy for clinical translation.

Dactolisib (NVP-BEZ235) toxicity in murine brain tumour models

Background

Glioblastomas (GBMs) are highly malignant brain tumours with a poor prognosis, and current cytotoxic regimens provide only a limited survival benefit. The PI3K/Akt/mTOR pathway has been an attractive target for therapy due to its high activation in GBMs as well as other cancers. The dual pan-PI3K/mTOR kinase inhibitor dactolisib (NVP-BEZ235) is an anti-neoplastic compound currently under investigation. However, little is known about its efficacy in human GBMs. We aimed at evaluating the efficacy of dactolisib in human glioblastoma cells, as well as in murine models carrying human GBM xenografts.

Methods

To assess the effect of dactolisib in vitro, MTS assay, manual cell count, BrdU incorporation and Annexin V staining experiments were used to observe growth and apoptosis. Furthermore, Akt phosphorylation (S473), a downstream target of PI3K, was explored by western blotting. Animal studies utilizing orthotopic xenograft models of glioblastoma were performed in nude rats and NOD/SCID mice to monitor survival benefit or inhibition of tumor growth.

Results

We found that dactolisib in vitro shows excellent dose dependent anti-growth properties and increase in apoptosis. Moreover, dose dependent inhibition of Akt phosphorylation (S473), a downstream effect of PI3K, was observed by western blotting. However, in two independent animal studies utilizing nude rats and NOD/SCID mice in orthotopic xenograft models of glioblastoma, we observed no survival benefit or inhibition of tumour growth. Severe side effects were observed, such as elevated levels of blood glucose and the liver enzyme alanine transaminase (ALT), in addition to diarrhoea, hair loss (alopecia), skin rash and accumulation of saliva in the oral cavity.

Conclusion

Taken together, our results suggest that despite the anti-neoplastic efficacy of dactolisib in glioma treatment in vitro, its utility in vivo is questionable due to toxicity.

Treatment with the PI3K inhibitor buparlisib (NVP-BKM120) suppresses the growth of established patient-derived GBM xenografts and prolongs survival in nude rats

Glioblastomas (GBMs) are aggressive brain tumours with a dismal prognosis, despite combined surgery, radio- and chemotherapy. Close to 90 % of all GBMs harbour a deregulated PI3K pathway, which is essential in regulating central cellular functions such as proliferation, cell growth, motility and survival. Thus, PI3K represents a potential target for molecular therapy in GBM. We investigated the anti-tumour efficacy of the PI3K inhibitor buparlisib (NVP-BKM120) in GBM cell lines in vitro and in vivo, when treatment was initiated after MRI-confirmed tumour engraftment. We found that buparlisib inhibited glioma cell proliferation in a dose dependent manner, demonstrated by MTS assay, manual cell count and BrdU incorporation. A dose dependent increase in apoptosis was observed through flow cytometric analysis. Furthermore, by immunocytochemistry and western blot, we found a dose dependent inhibition of Akt phosphorylation. Moreover, buparlisib prolonged survival of nude rats harboring human GBM xenografts in three independent studies and reduced the tumours’ volumetric increase, as determined by MRI. In addition, histological analyses of xenograft rat brains showed necrotic areas and change in tumour cell nuclei in buparlisib-treated animals. The rats receiving buparlisib maintained their weight, activity level and food- and water intake. In conclusion, buparlisib effectively inhibits glioma cell proliferation in vitro and growth of human GBM xenografts in nude rats. Moreover, the compound is well tolerated when administered at doses providing anti-tumour efficacy. Thus, buparlisib may have a future role in glioma therapy, and further studies are warranted to validate this compound for human use.

Abstract 1331: Targeting CD47 triggers macrophage-dependent brain tumor destruction in a clinical relevant model

Glioblastoma multiform (GMB), as a major unsolved clinical challenge, remains among the most aggressive malignancies in human brain with poor prognosis around 10-14.6 months survival. Due to their infiltrative character in the limited space, it is very difficult to be completely resected surgically. Although radiotherapy and chemotherapy that were given to patients after surgery may improve overall survival, the treatment outcomes in general are poor. The tumors eventually recur. Thus, new therapeutic strategy for GBM is urgently needed. It has been shown that CD47, a tumor cell surface marker, through binding its receptor SIRPα on macrophages plays as “don't eat me signal” and thus, by blocking the interaction of CD47 with SIRPα could lead to tumor destruction. So, we developed a standardized protocol for a novel xenograft surgical resection model which mimicked the process of operation in clinic. We hypothesized that the mechanical surgical procedure of tumor resection may create an inflammatory tumor environment, leading to recruitment of immune cells including macrophages. We believed the presence of these macrophages was needed to mediate the anti-tumor effects of the CD47 antibody which we administered postoperatively. The aims of the project are: 1) Translating brain tumour immunotherapy from the lab bench via preclinical studies to the clinic; 2) Establishing a novel xenograft surgical resection model to mimic the clinical setting of tumour recurrence in patients. Specifically, we will: 1) In vitro quantify and functionally characterize tumour-associated macrophages from treated vs. untreated tumours; 2) Using our clinical relevant animal models we want to determine the efficacy of targeting CD47 therapy.

In this study, we have developed a standardized protocol for a novel xenograft surgical resection model to parallel the treatment seen in glioma patients. The model accounts for the therapeutic benefit of surgical resection in pre-clinical models and demonstrates that recurrent tumors show higher proliferation and angiogenesis comparing to non-resected tumors. Moreover, the resection site is highly infiltrated by both CD68 and pSTAT1 positive macrophages. CD47 antibody treatment group has longer survival time than other groups.

Citation Format: Huaiyang Zhu, Ning Yang, Lina Leiss, Cecilie B Rygh, Siddhartha S Mitra, Samuel H Cheshier, Bin Huang, Rolf Bjerkvig, Per Ø Enger, Irving L Weissman, Xingang Li, Jian Wang. Targeting CD47 triggers macrophage-dependent brain tumor destruction in a clinical relevant model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1331. doi:10.1158/1538-7445.AM2015-1331

Drug repurposing: sulfasalazine sensitizes gliomas to gamma knife radiosurgery by blocking cystine uptake through system Xc-, leading to glutathione depletion

Glioblastomas (GBMs) are aggressive brain tumors that always recur after radiotherapy. Cystine, mainly provided by the system X(c)(-) antiporter, is a requirement for glioma cell synthesis of glutathione (GSH) which has a critical role in scavenging free radicals, for example, after radiotherapy. Thus, we hypothesized that the X(c)(-)-inhibitor sulfasalazine (SAS) could potentiate the efficacy of radiotherapy against gliomas. Here, we show that the catalytic subunit of system X(c)(-), xCT, was uniformly expressed in a panel of 30 human GBM biopsies. SAS treatment significantly reduced cystine uptake and GSH levels, whereas it significantly increased the levels of reactive oxygen species (ROS) in glioma cells in vitro. Furthermore, SAS and radiation synergistically increased DNA double-strand breaks and increased glioma cell death, whereas adding the antioxidant N-acetyl-L-cysteine (NAC) reversed cell death. Moreover, SAS and gamma knife radiosurgery (GKRS) synergistically prolonged survival in nude rats harboring human GBM xenografts, compared with controls or either treatment alone. In conclusion, SAS effectively blocks cystine uptake in glioma cells in vitro, leading to GSH depletion and increased ROS levels, DNA damage and cell death. Moreover, it potentiates the anti-tumor efficacy of GKRS in rats with human GBM xenografts, providing a survival benefit. Thus, SAS may have a role as a radiosensitizer to enhance the efficacy of current radiotherapies for glioma patients.

Abstract LB-332: Purified ex vivo expanded and activated human Natural Killer cells efficiently kill glioblastoma cells in a dose- and donor-dependent manner

Glioblastoma (GBM) is the most malignant and frequent brain tumor. Despite combined surgery, chemo- and radiotherapy, GBM patients' survival remains very low, emphasizing the need for further development of novel therapies. The promising strategy is adoptive cellular immunotherapy. Studies investigating purified Natural Killer (NK) cells in adoptive transfer therapies for solid tumors are sparse. Most clinical trials in GBM patients have used Lymphokine Activated Killer (LAK) cells that are composed of T-lymphocytes and NK cells, where the former can contribute to Graft vs Host Disease (GvHD) and inhibit NK cytotoxicity. We hypothesized that purified allogeneic NK cells may be potent effectors for adoptive transfer in GBM patients due to their cytotoxicity, cytokine production and immunomodulatory properties.

We performed in vitro cytotoxicity experiments using patient-derived GBM cells co-cultured with resting or ex vivo expanded and activated NK cells isolated from healthy donors or LAK cells derived from the same donors. We also investigated the role of Killer Immunoglobulin-like Receptor (KIR) versus Human Leucocyte Antigen (HLA) ligand mismatch in determining potency of NK cell-mediated cytotoxicity in vitro and in vivo in human GBM-bearing Nod-Scid mice, treated with activated human NK cells isolated from 2 different donors with or without KIR-HLA ligand mismatch. The primary end points were animals' survival, NK persistence in vivo and mechanisms of therapeutic efficacy. All GBM tumors investigated for cytotoxicity expressed variable levels of MHC class I, MICA/B, ULBP1-3 as evaluated by flow cytometry. High resolution HLA-typing of the GBM cells and KIR-typing of donors was performed at genomic level. Resting and activated NK cells were also characterized for expression levels of NKp46, NKG2D/A and KIRs by flow cytometric phenotyping.

Activated NK cells killed GBM cells more efficiently than resting NK cells and LAK cells in a dose- and donor-dependent manner. By examining tumor-donor pairs for KIR-HLA ligand mismatch we could identify the receptor-ligand combinations that determine greater cytotoxic potential in vitro in suspension cultures vs. in vivo in solid tumors in mice. We demonstrate that KIR-HLA ligand mismatch was important in killing the GBM cells by resting NK cells, however, the cytotoxicity mediated by activated NK cells was less dependent on KIR-HLA mismatch. Activated NK cells upregulated expression of particular KIRs when compared to resting NK cells from the same donor and this partially explains why activated NK cell - mediated cytotoxicity is less dependent on KIR-HLA ligand mismatch.

We conclude that purified and activated NK cells are better effectors against gliomas than LAK cells. However, the KIR-HLA mismatch in solid tumors may not be the primary determinant of activated NK potency in vitro but may have relevance in vivo.

Citation Format: Justyna Kmiecik, Andrea Gras Navarro, Per Ø. Enger, Mateusz Zelkowski, Jacques Zimmer, Martha Chekenya Enger. Purified ex vivo expanded and activated human Natural Killer cells efficiently kill glioblastoma cells in a dose- and donor-dependent manner. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-332. doi:10.1158/1538-7445.AM2013-LB-332

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Abstract 1590: Sulfasalazine sensitizes glioblastoma cells to radiation treatment

Glioblastoma (GBM) is a lethal cancer with a limited response to ionizing radiation. Recent studies suggest that Sulfasalazine (SAS), a drug used to treat inflammatory bowel disease, inhibits the Xc− antiporter system in glioma cells, thereby blocking their uptake of cystein. Since the availability of cystein is a rate limiting step in intracellular antioxidant production, we wanted to investigate whether sulfasalazine sensitizes glioma cells to radiation.

Expression of xCT, the catalytic subunit of system Xc−, was found in 30 patient GBM biopsies. SAS effect on glioma cell growth was investigated using an electric cell substrate impedance sensing (ECIS) instrument. All glioma cell lines showed altered growth curves in response to SAS treatment. To assess the effect of blocking the antiporter, intracellular levels of the antioxidant glutathione were measured. With increasing doses of SAS, glutathione levels decreased in a dose response manner. In addition, cysteine was added to the medium to see if the toxic effects of SAS could be counteracted. Furthermore, accumulation of reactive oxygen species upon SAS treatment was measured. Glioma cells were also treated with escalating doses of SAS, alone or in combination with radiation (8 Gy). The presence of double stranded breaks increased markedly in the irradiated samples and also somewhat with increasing doses with SAS. In addition, cell death, viability and clonogenicity were investigated using live/dead staining, the MTS assay and the clonogenic assay.

All treatment groups exhibited increased rates of cell death compared to untreated controls. A combination of SAS and radiation resulted in higher levels of cell death, than radiation or SAS administered alone. Furthermore we continued with implantation of human GBMs into the brain of Nude rats. These animals were treated with Gamma Knife Radiosurgery alone or in combination with SAS. SAS were administered as a pre-treatment for three days before Radiosurgery. The rats receiving the combination treatment lived significantly longer compared to either treatment alone. Interestingly, the animals only receiving pre-treatment with SAS for three days lived significantly longer compared to the untreated controls, although this was not statistically significant. We are currently preparing a clinical trial for patients with GBM recurrences combining pre-treatment with Sulfasalazine and Gamma Knife Radiosurgery.

Citation Format: Linda Sleire, Bente S. Skeie, Inger A. Netland, Jan Heggdal, Paal-Henning Pedersen, Per Ø. Enger. Sulfasalazine sensitizes glioblastoma cells to radiation treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1590. doi:10.1158/1538-7445.AM2013-1590

Gene expression in tumor cells and stroma in dsRed 4T1 tumors in eGFP-expressing mice with and without enhanced oxygenation

Background

The tumor microenvironment is pivotal in tumor progression. Thus, we aimed to develop a mammary tumor model to elucidate molecular characteristics in the stroma versus the tumor cell compartment by global gene expression. Secondly, since tumor hypoxia influences several aspects of tumor pathophysiology, we hypothesized that hyperoxia might have an inhibitory effect on tumor growth per se. Finally, we aimed to identify differences in gene expression and key molecular mechanisms, both in the native state and following treatment.

Methods

4T1 dsRed breast cancer cells were injected into eGFP expressing NOD/SCID mice. Group 1 was exposed to 3 intermittent HBO treatments (Day 1, 4 and 7), Group 2 to 7 daily HBO treatments (both 2.5bar, 100% O₂, à 90 min), whereas the controls were exposed to a normal atmosphere. Tumor growth, histology, vascularisation, cell proliferation, cell death and metastasis were assessed. Fluorescence-activated cell sorting was used to separate tumor cells from stromal cells prior to gene expression analysis.

Results

The purity of sorted cells was verified by fluorescence microscopy. Gene expression profiling demonstrated that highly expressed genes in the untreated tumor stroma included constituents of the extracellular matrix and matrix metalloproteinases. Tumor growth was significantly inhibited by HBO, and the MAPK pathway was found to be significantly reduced. Immunohistochemistry indicated a significantly reduced microvessel density after intermittent HBO, whereas daily HBO did not show a similar effect. The anti-angiogenic response was reflected in the expression trends of angiogenic factors.

Conclusions

The present in vivo mammary tumor model enabled us to separate tumor and stromal cells, and demonstrated that the two compartments are characterized by distinct gene expressions, both in the native state and following HBO treatments. Furthermore, hyperoxia induced a significant tumor growth-inhibitory effect, with significant down-regulation of the MAPK pathway. An anti-angiogenic effect after intermittent HBO was observed, and reflected in the gene expression profile.

Expression of the progenitor marker NG2/CSPG4 predicts poor survival and resistance to ionising radiation in glioblastoma

Glioblastoma (GBM) is a highly aggressive brain tumour, where patients respond poorly to radiotherapy and exhibit dismal survival outcomes. The mechanisms of radioresistance are not completely understood. However, cancer cells with an immature stem-like phenotype are hypothesised to play a role in radioresistance. Since the progenitor marker neuron-glial-2 (NG2) has been shown to regulate several aspects of GBM progression in experimental systems, we hypothesised that its expression would influence the survival of GBM patients. Quantification of NG2 expression in 74 GBM biopsies from newly diagnosed and untreated patients revealed that 50% express high NG2 levels on tumour cells and associated vessels, being associated with significantly shorter survival. This effect was independent of age at diagnosis, treatment received and hypermethylation of the O(6)-methylguanine methyltransferase (MGMT) DNA repair gene promoter. NG2 was frequently co-expressed with nestin and vimentin but rarely with CD133 and the NG2 positive tumour cells harboured genetic aberrations typical for GBM. 2D proteomics of 11 randomly selected biopsies revealed upregulation of an antioxidant, peroxiredoxin-1 (PRDX-1), in the shortest surviving patients. Expression of PRDX-1 was associated with significantly reduced products of oxidative stress. Furthermore, NG2 expressing GBM cells showed resistance to ionising radiation (IR), rapidly recognised DNA damage and effectuated cell cycle checkpoint signalling. PRDX-1 knockdown transiently slowed tumour growth rates and sensitised them to IR in vivo. Our data establish NG2 as an important prognostic factor for GBM patient survival, by mediating resistance to radiotherapy through induction of ROS scavenging enzymes and preferential DNA damage signalling.

Abstract 4320: Separate analysis of the cancer and stroma cell populations from orthotopically implanted cancer cell lines in fluorescent mice

The tumour microenvironment is increasingly recognised as important in most aspects of tumourigenesis, from tumor formation, growth and invasion, to metastasis and priming of distant metastatic sites. It has been estimated that around 50% of a solid tumor mass may be of stromal origin, including cells of the immune system, endothelial cells and fibroblasts, with the latter being the most abundant. The fibroblasts recruited to a tumor are commonly known as cancer associated fibroblasts (CAFs), and are characterized by their heterogeneity of marker expression and origin, making them a challenge to study.

Therefore, we have developed a new strain of mice for the analysis of the tumour microenvironment in xenograft models. The strain was created by crossbreeding dsRed positive mice with severe combined immunodeficient (SCID) mice, and backcrossing on a SCID background until we obtained a homozygous dsRed-SCID inbred strain. As the tumor cells implanted are non-fluorescent, whereas the stromal contributions to the growing tumors are dsRed positive, the two compartments were successfully separated by Fluorescence-activated cell sorting (FACS) after mechanical and enzymatic dissociation.

The dsRed phenotype is visibly red with the naked eye, and fluoresces under a 488 nm dark reader lamp light. The organs have been confirmed dsRed positive by imaging and further confirmed and quantified by RT-PCR. The SCID phenotype was confirmed by immune phenotyping, using markers for B, T, Tc, Th and NK cells. Furthermore, the mice were confirmed immune deficient when they were orthotopicaly grafted with breast (4T1) and lung (A549) cancer cell lines.

Fibroblast enriched populations were isolated from primary A549 tumours, 4T1 tumours and 4T1 tumour metastasis to the lungs, by subsorting the dsRed positive stromal compartment, excluding cells of the immune system and endothelial cells. Preliminary data clearly show distinct tumor and stroma populations in primary breast and lung cancer, as well as in lung metastasis from breast cancer xenografts. Furthermore, when investigating the breast cancers dissociated at different time points from implantation, it is clear that the percentage of stromal cells in the overall tumour mass decreases as the tumour grows. The fibroblasts were further analyzed for marker expression, cell cycle phase distribution and in vitro growth properties. We conclude that this model provides a valuable tool for investigating the stromal compartment of xenograft tumours.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4320. doi:10.1158/1538-7445.AM2011-4320

αB-crystallin is elevated in highly infiltrative apoptosis-resistant glioblastoma cells

We have previously established two distinct glioma phenotypes by serial xenotransplantation of human glioblastoma (GBM) biopsies in nude rats. These tumors undergo a gradual transition from a highly invasive nonangiogenic to a less-invasive angiogenic phenotype. In a protein screen to identify molecular markers associated with the infiltrative phenotype, we identified α-basic-crystallin (αBc), a small heat-shock protein with cytoprotective properties. Its increased expression in the infiltrative phenotype was validated by immunohistochemistry and Western blots, confirming its identity to be tumor-derived and not from the host. Stereotactic human GBM biopsies taken from MRI-defined areas verified stronger αBc expression in the infiltrative edge compared to the tumor core. Cell migration assays and immunofluorescence staining showed αBc to be expressed by migrating cells in vitro. To determine αBc function, we altered its expression levels. αBc siRNA depletion caused a loss of migrating tumor cells from biopsy spheroids and delayed monolayer wound closure. In contrast, glioma cell migration in a Boyden chamber assay was unaffected by either αBc knockdown or overexpression, indicating that αBc is not functionally linked to the cell migration machinery. However, after siRNA αBc depletion, a significant sensitization of cells to various apoptotic inducers was observed (actinomycin, tumor necrosis factor α, and TNF-related apoptosis-inducing ligand [TRAIL]). In conclusion, αBc is overexpressed by highly migratory glioma cells where it plays a functional role in apoptosis resistance.

A reproducible brain tumour model established from human glioblastoma biopsies

Background

Establishing clinically relevant animal models of glioblastoma multiforme (GBM) remains a challenge, and many commonly used cell line-based models do not recapitulate the invasive growth patterns of patient GBMs. Previously, we have reported the formation of highly invasive tumour xenografts in nude rats from human GBMs. However, implementing tumour models based on primary tissue requires that these models can be sufficiently standardised with consistently high take rates.

Methods

In this work, we collected data on growth kinetics from a material of 29 biopsies xenografted in nude rats, and characterised this model with an emphasis on neuropathological and radiological features.

Results

The tumour take rate for xenografted GBM biopsies were 96% and remained close to 100% at subsequent passages in vivo, whereas only one of four lower grade tumours engrafted. Average time from transplantation to the onset of symptoms was 125 days ± 11.5 SEM. Histologically, the primary xenografts recapitulated the invasive features of the parent tumours while endothelial cell proliferations and necrosis were mostly absent. After 4-5 in vivo passages, the tumours became more vascular with necrotic areas, but also appeared more circumscribed. MRI typically revealed changes related to tumour growth, several months prior to the onset of symptoms.

Conclusions

In vivo passaging of patient GBM biopsies produced tumours representative of the patient tumours, with high take rates and a reproducible disease course. The model provides combinations of angiogenic and invasive phenotypes and represents a good alternative to in vitro propagated cell lines for dissecting mechanisms of brain tumour progression.

Highly infiltrative brain tumours show reduced chemosensitivity associated with a stem cell-like phenotype

AIMS

Cancer stem-like cells might have important functions in chemoresistance. We have developed a model where highly infiltrative brain tumours with a stem-like phenotype were established by orthotopic transplantation of human glioblastomas to immunodeficient rats. Serial passaging gradually transformed the tumours into a less invasive and more angiogenic phenotype (high-generation tumours). The invasive phenotype (low-generation tumours) was characterized by an increase in stem cell markers and increased phosphorylation of kinases in the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. These markers were reduced in the serially passaged vascular tumours. The present study was aimed at investigating how the two phenotypes responded in vitro to doxorubicin, a clinically potent cytotoxic drug for solid tumours.

METHODS

Biopsy spheroids were implanted and passaged intracranially in nude rats. Gene expression and protein analyses were performed, and drug sensitivity was assessed.

RESULTS

Microarray analysis revealed gene ontology categories connected to developmental aspects and negative regulators of differentiation, especially in the infiltrative stem cell-like tumours. The highly invasive stem-like phenotype was chemoresistant compared with the angiogenic phenotype. By interfering with the PI3K it was possible to sensitize tumour spheroids to chemotherapy. Real-time quantitative polymerase chain reaction showed downregulation of the stem cell markers Nestin and Musashi-1 in low-generation biopsy spheroids following PI3K inhibition.

CONCLUSIONS

Highly invasive tumours with a stem-like phenotype are more chemoresistant than angiogenic tumours derived from the same patients. We suggest that treatment resistance in glioblastomas can be related to PI3K/AKT activity in stem-like tumour cells, and that targeted interference with the PI3K/AKT pathway might differentiate and sensitize this subpopulation to chemotherapy.

The progenitor cell marker NG2/MPG promotes chemoresistance by activation of integrin-dependent PI3K/Akt signaling

Chemoresistance represents a major problem in the treatment of many malignancies. Overcoming this obstacle will require improved understanding of the mechanisms responsible for this phenomenon. The progenitor cell marker NG2/melanoma proteoglycan (MPG) is aberrantly expressed by various tumors, but its role in cell death signaling and its potential as a therapeutic target are largely unexplored. We have assessed cytotoxic drug-induced cell death in glioblastoma spheroids from 15 patients, as well as in five cancer cell lines that differ with respect to NG2/MPG expression. The tumors were treated with doxorubicin, etoposide, carboplatin, temodal, cisplatin and tumor necrosis factor (TNF)alpha. High NG2/MPG expression correlated with multidrug resistance mediated by increased activation of alpha3beta1 integrin/PI3K signaling and their downstream targets, promoting cell survival. NG2/MPG knockdown with shRNAs incorporated into lentiviral vectors attenuated beta1 integrin signaling revealing potent antitumor effects and further sensitized neoplastic cells to cytotoxic treatment in vitro and in vivo. Thus, as a novel regulator of the antiapoptotic response, NG2/MPG may represent an effective therapeutic target in several cancer subtypes.

CD133 negative glioma cells form tumors in nude rats and give rise to CD133 positive cells

CD133 is a cell surface marker expressed on progenitors of haematopoietic and endothelial cell lineages. Moreover, several studies have identified CD133 as a marker of brain tumor-initiating cells. In this study, human glioblastoma multiforme biopsies were engrafted intracerebrally into nude rats. The resulting tumors were serially passaged in vivo, and monitored by magnetic resonance imaging. CD133 expression was analyzed at various passages. Tumors initiated directly from the biopsies expressed little or no CD133, and showed no contrast enhancement suggesting an intact blood-brain barrier. During passaging, the tumors gradually displayed more contrast enhancement, increased angiogenesis and a shorter survival. Real-time qPCR and immunoblots showed that this was accompanied by increased CD133 expression. Primary biopsy spheroids and xenograft tumors were subsequently dissociated and flow sorted into CD133 negative and CD133 positive cell populations. Both populations incorporated BrdU in cell culture, and expressed the neural precursor marker nestin. Notably, CD133 negative cells derived from 6 different patients were tumorgenic when implanted into the rat brains. For 3 of these patients, analysis showed that the resulting tumors contained CD133 positive cells. In conclusion, we show that CD133 negative glioma cells are tumorgenic in nude rats, and that CD133 positive cells can be obtained from these tumors. Upon passaging of the tumors in vivo, CD133 expression is upregulated, coinciding with the onset of angiogenesis and a shorter survival. Thus, our findings do not suggest that CD133 expression is required for brain tumor initiation, but that it may be involved during brain tumor progression.

CD133 negative glioma cells form tumors in nude rats and give rise to CD133 positive cells

CD133 is a cell surface marker expressed on progenitors of haematopoietic and endothelial cell lineages. Moreover, several studies have identified CD133 as a marker of brain tumor-initiating cells. In this study, human glioblastoma multiforme biopsies were engrafted intracerebrally into nude rats. The resulting tumors were serially passaged in vivo, and monitored by magnetic resonance imaging. CD133 expression was analyzed at various passages. Tumors initiated directly from the biopsies expressed little or no CD133, and showed no contrast enhancement suggesting an intact blood-brain barrier. During passaging, the tumors gradually displayed more contrast enhancement, increased angiogenesis and a shorter survival. Real-time qPCR and immunoblots showed that this was accompanied by increased CD133 expression. Primary biopsy spheroids and xenograft tumors were subsequently dissociated and flow sorted into CD133 negative and CD133 positive cell populations. Both populations incorporated BrdU in cell culture, and expressed the neural precursor marker nestin. Notably, CD133 negative cells derived from 6 different patients were tumorgenic when implanted into the rat brains. For 3 of these patients, analysis showed that the resulting tumors contained CD133 positive cells. In conclusion, we show that CD133 negative glioma cells are tumorgenic in nude rats, and that CD133 positive cells can be obtained from these tumors. Upon passaging of the tumors in vivo, CD133 expression is upregulated, coinciding with the onset of angiogenesis and a shorter survival. Thus, our findings do not suggest that CD133 expression is required for brain tumor initiation, but that it may be involved during brain tumor progression.

Protein disulfide isomerase expression is related to the invasive properties of malignant glioma

By serial transplantation of human glioblastoma biopsies into the brain of immunodeficient nude rats, two different tumor phenotypes were obtained. Initially, the transplanted xenografts displayed a highly invasive phenotype that showed no signs of angiogenesis. By serial transplantation in animals, the tumors changed to a less invasive, predominantly angiogenic phenotype. To identify novel proteins related to the invasive phenotype, the xenografts were analyzed using a global proteomics approach. One of the identified proteins was protein disulfide isomerase (PDI) A6 precursor. PDI is a chaperone protein that mediates integrin-dependent cell adhesion. It is both present in the cytosol and at the cell surface. We show that PDI is strongly expressed on invasive glioma cells, in both xenografts and at the invasive front of human glioblastomas. Using an in vitro migration assay, we also show that PDI is expressed on migrating glioma cells. To determine the functional significance of PDI in cell migration, we tested the effect of a PDI inhibitor, bacitracin, and a PDI monoclonal antibody on glioma cell migration and invasion in vitro. Both tumor spheroids derived from human glioblastoma xenografts in nude rat brain and cell line spheroids were used. The PDI antibody, as well as bacitracin, inhibited tumor cell migration and invasion. The anti-invasive effect of bacitracin was reversible after withdrawal of the inhibitor, indicating a specific, nontoxic effect. In conclusion, using a global proteomics approach, PDI was identified to play an important role in glioma cell invasion, and its action was effectively inhibited by bacitracin.

Primary glioma spheroids maintain tumourogenicity and essential phenotypic traits after cryopreservation

Tumour spheroids initiated from glioma biopsy specimens provide a valuable three-dimensional cell culture system that share several biological features of malignant brain tumours in situ. Upon xenotransplantation in immunodeficient rats, tumours derived from such spheroids exhibit a highly infiltrative growth. Successful cryopreservation of spheroid specimens therefore represents an excellent tool for future comparative studies of tumour growth and progression. Thus, if frozen stocks of human glioma spheroids can be established, similar to those obtained from cancer cell lines, it would ease the planning of biopsy-based experiments. In this context, it is crucial that cryopreservation does not alter the biological behaviour of the tumour spheroids. The biopsy spheroids were frozen to -40 degrees Celsius, stored for 1 week at -196 degrees Celsius, thawed rapidly and cultured for 1 week. The viability of the spheroids was compared against controls using a two-colour fluorescence assay, which demonstrated that cryopreservation was well tolerated. Using an in vitro invasion assay, it is shown that the freezing procedures did not affect the spheroids ability to invade a collagen gel. Cryopreserved and control tumour spheroids were equally tumourogenic, and produced overlapping survival curves when transplanted into the brains of immunocompromised rats. Immunohistochemical analyses showed no significant changes regarding microvessel density or proliferation index. Furthermore, gene expression profiling using a macroarray system detected no significant changes following cryopreservation. The present data show that cryopreservation is well tolerated, and represent a methodologically reliable storage method for biopsy spheroids that can be used in experimental studies at later time points.

Shunt revisions in children--can they be avoided? Experiences from a population-based study

BACKGROUND

Shunt failure is by far the most frequent problem in children with shunts, and most of them will experience this condition at some point in their lives. In order to identify causes of shunt failure, and to compare multi-component and one-piece shunt systems, we analyzed retrospectively all pediatric shunt procedures in our Department during an 11-year period. The study does not deal with shunt infections.

METHODS

We reviewed the records of all pediatric shunting procedures between January 1986 and December 1996.

RESULTS

The study included 161 children operated for hydrocephalus with a total of 431 procedures. The procedures included 124 (29%) primary insertions, 10 (2%) reinsertions and 297 (69%) revisions; 206 (69%) of the revisions were due to shunt failures, of which 74 (36%) were caused by the failure of the surgical technique (misplaced ventricular catheters, disconnected shunts, or misplaced peritoneal catheters).

CONCLUSIONS

Improvement of the surgical technique may reduce the incidence of shunt failures and revisions. The results obtained in a small department like ours do not seem to differ substantially from those obtained in more specialized departments with a larger patient group. Practical measures that may reduce the risk of shunt failures are suggested.

NG2 expression regulates vascular morphology and function in human brain tumours

Tumour angiogenesis is a tightly regulated process involving cross-talk between tumour cells and the host tissue. The underlying mechanisms that regulate such interactions remain largely unknown. NG2 is a transmembrane proteoglycan whose presence on transformed cells has been demonstrated to increase proliferation in vitro and angiogenesis in vivo. To study the effects of NG2 during tumour growth and progression, we engineered an NG2 positive human glioma cell line (U251-NG2) from parental NG2 negative cells (U251-WT) and implanted both cell types stereotactically into immunodeficient nude rat brains. The tumours were longitudinally monitored in vivo using multispectral MRI employing two differently sized contrast agents (Gd-DTPA-BMA and Gadomer) to assess vascular leakiness, vasogenic oedema, tumour volumes and necrosis. Comparisons of Gd-DTPA-BMA and Gadomer revealed differences in their spatial distribution in the U251-NG2 and U251-WT tumours. The U251-NG2 tumours exhibited a higher leakiness of the larger molecular weight Gadomer and displayed a stronger vasogenic oedema (69.9 +/- 15.2, P = 0.018, compared to the controls (10.7 +/- 7.7). Moreover, immunohistochemistry and electron microscopy revealed that the U251-NG2 tumours had a higher microvascular density (11.81 +/- 0.54; P = 0.0010) compared to controls (5.76 +/- 0.87), with vessels that displayed larger gaps between the endothelial cells. Thus, tumour cells can regulate both the function and structure of the host-derived tumour vasculature through NG2 expression, suggesting a role for NG2 in the cross-talk between tumour-host compartments.

CSF shunt infections in children: experiences from a population-based study

The objective was to identify risk factors for shunt infections, and establish the rate of infection for shunt procedures carried out under standardized conditions in a well-defined population. All (407) paediatric shunt operations (primary and revisions) performed within a total population of 630000 inhabitants between January 1, 1986 and December 31, 1996, were analysed retrospectively. 11 shunt infections were diagnosed in 10 patients, giving an overall infection rate of 2.7% per procedure and 6.2% per patient. Infections were significantly correlated with age, type of operation, and a etiology of hydrocephalus. Thus, infections occurred more frequently during the first 6 months of life, more often following primary shunt insertions compared with revisions, and children with myelomeningocele had a higher infection risk than children with hydrocephalus due to other causes. There was a highly significant male preponderance in the patient material.

CONCLUSION

The overall infection rate was relatively low. The risk factors for shunt infections appear to relate to epidemiological characteristics rather than to surgical factors.

The glial precursor proteoglycan, NG2, is expressed on tumour neovasculature by vascular pericytes in human malignant brain tumours

Glial precursor cells express NG2 and GD3 in the developing brain. These antigens are both over-expressed during neoplasia, which suggests they may have specific functions in the malignant progression of human brain tumours. This study describes the expression of NG2 and GD3 in 28 paediatric and adult brain tumours. Glioblastoma biopsy spheroids were also implanted into nude rats to assess the regional distribution of the molecules within the tumour. These xenografts showed extensive infiltration and growth that mimicked the growth patterns of human gliomas in situ. NG2 was identified in 20 out of 28 brain tumours, where the expression was confined to the main mass of the tumour, and was reduced towards the tumour periphery. NG2 was mainly associated with blood vessels on both the pericyte and basement membrane components of the tumour vasculature. Ki67 (MIB-1) labelling indicated that NG2 expression was associated with areas of high cellular proliferation. Conversely, all the tumours expressed GD3, which was present both in the tumour main mass and throughout the periphery. Thus, the expression of NG2 may be indicative of tumour progression and might be an amenable target for future therapeutic interventions.