Glioblastoma stem cells exploit the αvβ8 integrin-TGFβ1 signaling axis to drive tumor initiation and progression

Glioblastoma (GBM) is a primary brain cancer that contains populations of stem-like cancer cells (GSCs) that home to specialized perivascular niches. GSC interactions with their niche influence self-renewal, differentiation and drug resistance, although the pathways underlying these events remain largely unknown. Here, we report that the integrin αvβ8 and its latent transforming growth factor β1 (TGFβ1) protein ligand have central roles in promoting niche co-option and GBM initiation. αvβ8 integrin is highly expressed in GSCs and is essential for self-renewal and lineage commitment in vitro. Fractionation of β8^high cells from freshly resected human GBM samples also reveals a requirement for this integrin in tumorigenesis in vivo. Whole-transcriptome sequencing reveals that αvβ8 integrin regulates tumor development, in part, by driving TGFβ1-induced DNA replication and mitotic checkpoint progression. Collectively, these data identify the αvβ8 integrin-TGFβ1 signaling axis as crucial for exploitation of the perivascular niche and identify potential therapeutic targets for inhibiting tumor growth and progression in patients with GBM.

Oncolytic Adenovirus and Tumor-Targeting Immune Modulatory Therapy Improve Autologous Cancer Vaccination

Oncolytic viruses selectively lyse tumor cells, disrupt immunosuppression within the tumor, and reactivate antitumor immunity, but they have yet to live up to their therapeutic potential. Immune checkpoint modulation has been efficacious in a variety of cancer with an immunogenic microenvironment, but is associated with toxicity due to nonspecific T-cell activation. Therefore, combining these two strategies would likely result in both effective and specific cancer therapy. To test the hypothesis, we first constructed oncolytic adenovirus Delta-24-RGDOX expressing the immune costimulator OX40 ligand (OX40L). Like its predecessor Delta-24-RGD, Delta-24-RGDOX induced immunogenic cell death and recruit lymphocytes to the tumor site. Compared with Delta-24-RGD, Delta-24-RGDOX exhibited superior tumor-specific activation of lymphocytes and proliferation of CD8+ T cells specific to tumor-associated antigens, resulting in cancer-specific immunity. Delta-24-RGDOX mediated more potent antiglioma activity in immunocompetent C57BL/6 but not immunodeficient athymic mice, leading to specific immune memory against the tumor. To further overcome the immune suppression mediated by programmed death-ligand 1 (PD-L1) expression on cancer cells accompanied with virotherapy, intratumoral injection of Delta-24-RGDOX and an anti-PD-L1 antibody showed synergistic inhibition of gliomas and significantly increased survival in mice. Our data demonstrate that combining an oncolytic virus with tumor-targeting immune checkpoint modulators elicits potent in situ autologous cancer vaccination, resulting in an efficacious, tumor-specific, and long-lasting therapeutic effect. Cancer Res; 77(14); 3894-907. ©2017 AACR.

Efficacy of Onalespib, a Long-Acting Second-Generation HSP90 Inhibitor, as a Single Agent and in Combination with Temozolomide against Malignant Gliomas

Purpose: HSP90, a highly conserved molecular chaperone that regulates the function of several oncogenic client proteins, is altered in glioblastoma. However, HSP90 inhibitors currently in clinical trials are short-acting, have unacceptable toxicities, or are unable to cross the blood-brain barrier (BBB). We examined the efficacy of onalespib, a potent, long-acting novel HSP90 inhibitor as a single agent and in combination with temozolomide (TMZ) against gliomas in vitro and in vivoExperimental Design: The effect of onalespib on HSP90, its client proteins, and on the biology of glioma cell lines and patient-derived glioma-initiating cells (GSC) was determined. Brain and plasma pharmacokinetics of onalespib and its ability to inhibit HSP90 in vivo were assessed in non-tumor-bearing mice. Its efficacy as a single agent or in combination with TMZ was assessed in vitro and in vivo using zebrafish and patient-derived GSC xenograft mouse glioma models.Results: Onalespib-mediated HSP90 inhibition depleted several survival-promoting client proteins such as EGFR, EGFRvIII, and AKT, disrupted their downstream signaling, and decreased the proliferation, migration, angiogenesis, and survival of glioma cell lines and GSCs. Onalespib effectively crossed the BBB to inhibit HSP90 in vivo and extended survival as a single agent in zebrafish xenografts and in combination with TMZ in both zebrafish and GSC mouse xenografts.Conclusions: Our results demonstrate the long-acting effects of onalespib against gliomas in vitro and in vivo, which combined with its ability to cross the BBB support its development as a potential therapeutic agent in combination with TMZ against gliomas. Clin Cancer Res; 23(20); 6215-26. ©2017 AACR.

Post-operative stereotactic radiosurgery versus observation for completely resected brain metastases: a single-centre, randomised, controlled, phase 3 trial

Background

After brain metastasis resection, whole-brain radiation therapy (WBRT) decreases local recurrence but may cause cognitive decline. We performed this study to determine if stereotactic radiosurgery (SRS) to the surgical cavity improved local tumor tumor-free recurrence rates compared to surgical resection alone as an alternative to the need for immediate WBRT.

Methods

The main entry criteria for the study included patients >3 years of age, with a Karnofsky Performance Score ≥ 70, who were able to undergo an MRI scan and who had a complete resection of 1–3 brain metastases (the maximum diameter of the resection cavity had to be ≤4cm). Patients were assigned randomly to either SRS treatment of the resection cavity (within 30 days of surgery) or observation (OBS). Patients were stratified by histology, tumor size, and number of metastases. Patients were recruited at a single tertiary cancer center. The primary endpoint was time to local recurrence in the resection cavity assessed by blinded central review of brain MRI scans in the intention-to-treat population. The trial was registered at clinicaltrials.gov (Trial NCT00950001, status: closed to new participants).

Findings

Between 8/13/2009 and 2/16/2016, 132 patients were randomized to OBS (N=68) or SRS (N=64), with 128 patients available for analysis. We stratified by metastasis size (maximum diameter of ≥3 cm vs. <3 cm), histology (melanoma vs. other), and number of metastases (one vs. two or three). The 12-month local tumor recurrence-free rate was 43% (OBS) (95% CI 31%–59%) and 72% (SRS) (95% CI 60%–87%) (hazard ratio [HR] 0.46, 95% confidence interval [CI] 0.24–0.88, p=0.015).

Interpretation

This prospective randomized trial of patients undergoing surgical resection for 1–3 brain metastases indicates that SRS administered to the resection cavity significantly lowers local recurrence compared to observation alone. Thus, the use of SRS after brain metastasis resection is an alternative to WBRT.

Interrogating Metabolism in Brain Cancer

This article reviews existing and emerging techniques of interrogating metabolism in brain cancer from well-established proton magnetic resonance spectroscopy to the promising hyperpolarized metabolic imaging and chemical exchange saturation transfer and emerging techniques of imaging inflammation. Some of these techniques are at an early stage of development and clinical trials are in progress in patients to establish the clinical efficacy. It is likely that in vivo metabolomics and metabolic imaging is the next frontier in brain cancer diagnosis and assessing therapeutic efficacy; with the combined knowledge of genomics and proteomics a complete understanding of tumorigenesis in brain might be achieved.

Phase 1b open-label randomized study of the oncolytic adenovirus DNX-2401 administered with or without interferon gamma for recurrent glioblastoma

2002

Background: DNX-2401 is a replication-competent, tumor-selective, oncolytic adenovirus with enhanced infectivity that causes durable tumor control by killing tumor cells and eliciting antitumor immunity. To increase immune activation, a phase 1b randomized study of intratumoral DNX-2401 alone versus DNX-2401 with interferon gamma (IFN) was conducted. Methods: A total of 27 patients with biopsy-confirmed glioblastoma at first or second recurrence received a single intratumoral injection of 3e10 vp DNX-2401. Patients were randomized in a 2:1 ratio to receive 50 mcg/m2 of subcutaneous IFN (Actimmune) Q3W initiated 14 days after DNX-2401 or to be followed without further treatment for safety and survival. Results: Twenty-seven (27) patients were enrolled following first (59%) or second (41%) recurrence having previously failed surgery, radiation, and temozolomide (100%). The median longest tumor diameter was 40 mm (range 20-77 mm). Patients were randomized to DNX-2401 followed by IFN (n = 18) or to DNX-2401 alone (n = 9). Due to the poor tolerability of IFN, the median duration of treatment was only 6 weeks (range 0-30 weeks), and two patients did not initiate treatment as scheduled due to early clinical deterioration. The most frequent grade 3-4 AEs across treatment groups were fatigue, headache, and seizures consistent with pre-existing symptoms, underlying disease and/or surgery. Based upon a preliminary intent-to-treat analysis, IFN did not appear to provide additional benefit. However, OS-12 and OS-18 for all patients enrolled was 33% and 22%, respectively regardless of treatment assignment. Three patients remain alive at 19, 21, and 22 months (DNX-2401, n = 1; DNX-2401 + IFN, n = 2). Interestingly, 50% of patients with a baseline tumor diameter of ≤ 42 mm survived beyond 12 months, potentially identifying a sub-population of patients that may live longer following intratumoral DNX-2401. Conclusions: DNX-2401 was well tolerated as monotherapy. Although the addition of IFN did not improve survival, clinical activity following a single injection of DNX-2401 is encouraging and supports an ongoing Phase II study of DNX-2401 for recurrent glioblastoma. Clinical trial information: NCT02197169.

Ionizing radiation augments glioma tropism of mesenchymal stem cells

OBJECTIVE Mesenchymal stem cells (MSCs) have been shown to localize to gliomas after intravascular delivery. Because these cells home to areas of tissue injury, the authors hypothesized that the administration of ionizing radiation (IR) to tumor would enhance the tropism of MSCs to gliomas. Additionally, they sought to identify which radiation-induced factors might attract MSCs. METHODS To assess the effect of IR on MSC migration in vitro, transwell assays using conditioned medium (CM) from an irradiated commercially available glioma cell line (U87) and from irradiated patient-derived glioma stem-like cells (GSCs; GSC7-2 and GSC11) were employed. For in vivo testing, green fluorescent protein (GFP)-labeled MSCs were injected into the carotid artery of nude mice harboring orthotopic U87, GSC7-2, or GSC17 xenografts that were treated with either 0 or 10 Gy of IR, and brain sections were quantitatively analyzed by immunofluorescence for GFP-positive cells. These GSCs were used because GSC7-2 is a weak attractor of MSCs at baseline, whereas GSC17 is a strong attractor. To determine the factors implicated in IR-induced tropism, CM from irradiated GSC7-2 and from GSC11 was assayed with a cytokine array and quantitative ELISA. RESULTS Transwell migration assays revealed statistically significant enhanced MSC migration to CM from irradiated U87, GSC7-2, and GSC11 compared with nonirradiated controls and in a dose-dependent manner. After their intravascular delivery into nude mice harboring orthotopic gliomas, MSCs engrafted more successfully in irradiated U87 (p = 0.036), compared with nonirradiated controls. IR also significantly increased the tropism of MSCs to GSC7-2 xenografts (p = 0.043), which are known to attract MSCs only poorly at baseline (weak-attractor GSCs). Ionizing radiation also increased the engraftment of MSCs in strong-attractor GSC17 xenografts, but these increases did not reach statistical significance. The chemokine CCL2 was released by GSC7-2 and GSC11 after irradiation in a dose-dependent manner and mediated in vitro transwell migration of MSCs. Immunohistochemistry revealed increased CCL2 in irradiated GSC7-2 gliomas near the site of MSC engraftment. CONCLUSIONS Administering IR to gliomas enhances MSC localization, particularly in GSCs that attract MSCs poorly at baseline. The chemokine CCL2 appears to play a crucial role in the IR-induced tropism of MSCs to gliomas.

Mesenchymal stromal cells for the delivery of oncolytic viruses in gliomas

Mesenchymal stromal cells (MSCs) are a type of adult stem cell that has been exploited for the treatment of a variety of diseases, including cancer. In particular, MSCs have been studied extensively for their ability to treat glioblastoma (GBM), the most common and deadly form of brain cancer in adults. MSCs are attractive therapeutics because they can be obtained relatively easily from patients, are capable of being expanded numerically in vitro, can be easily engineered and are inherently capable of homing to tumors, making them ideal vehicles for delivering biological antitumoral agents. Oncolytic viruses are promising biological therapeutic agents that have been used in the treatment of GBMs, and MSCs are currently being explored as a means of delivering these viruses. Here we review the role of MSCs in the treatment of GBMs, focusing on the intersection of MSCs and oncolytic viruses.

Preclinical Evaluation of Sequential Combination of Oncolytic Adenovirus Delta-24-RGD and Phosphatidylserine-Targeting Antibody in Pancreatic Ductal Adenocarcinoma

Delta-24-RGD (DNX-2401) is a conditional replication-competent oncolytic virus engineered to preferentially replicate in and lyse tumor cells with abnormality of p16/RB/E2F pathway. In a phase I clinical trial, Delta-24-RGD has shown favorable safety profile and promising clinical efficacy in brain tumor, which prompted us to evaluate its anticancer activity in pancreatic ductal adenocarcinoma (PDAC), which also has high frequency of homozygous deletion and promoter methylation of CDKN2A encoding the p16 protein. Our results demonstrate that Delta-24-RGD can induce dramatic cytotoxicity in a subset of PDAC cell lines with high cyclin D1 expression. Induction of autophagy and apoptosis by Delta-24-RGD in sensitive PDAC cells was confirmed with LC3B-GFP autophagy reporter and acridine orange staining as well as Western blotting analysis of LC3B-II expression. Notably, we found that Delta-24-RGD induced phosphatidylserine exposure in infected cells independent of cells' sensitivity to Delta-24-RGD, which renders a rationale for combination of Delta-24-RGD viral therapy and phosphatidylserine targeting antibody for PDAC. In a mouse PDAC model derived from a liver metastatic pancreatic cancer cell line, Delta-24-RGD significantly inhibited tumor growth compared with control (P < 0.001), and combination of phosphatidylserine targeting antibody 1N11 further enhanced its anticancer activity (P < 0.01) possibly through inducing synergistic anticancer immune responses. Given that these 2 agents are currently in clinical evaluation, our study warrants further clinical evaluation of this novel combination strategy in pancreatic cancer therapy. Mol Cancer Ther; 16(4); 662-70. ©2016 AACR.

The Cytoskeletal Adapter Protein Spinophilin Regulates Invadopodia Dynamics and Tumor Cell Invasion in Glioblastoma

Glioblastoma is a primary brain cancer that is resistant to all treatment modalities. This resistance is due, in large part, to invasive cancer cells that disperse from the main tumor site, escape surgical resection, and contribute to recurrent secondary lesions. The adhesion and signaling mechanisms that drive glioblastoma cell invasion remain enigmatic, and as a result there are no effective anti-invasive clinical therapies. Here we have characterized a novel adhesion and signaling pathway comprised of the integrin αvβ8 and its intracellular binding partner, Spinophilin (Spn), which regulates glioblastoma cell invasion in the brain microenvironment. We show for the first time that Spn binds directly to the cytoplasmic domain of β8 integrin in glioblastoma cells. Genetically targeting Spn leads to enhanced invasive cell growth in preclinical models of glioblastoma. Spn regulates glioblastoma cell invasion by modulating the formation and dissolution of invadopodia. Spn-regulated invadopodia dynamics are dependent, in part, on proper spatiotemporal activation of the Rac1 GTPase. Glioblastoma cells that lack Spn showed diminished Rac1 activities, increased numbers of invadopodia, and enhanced extracellular matrix degradation. Collectively, these data identify Spn as a critical adhesion and signaling protein that is essential for modulating glioblastoma cell invasion in the brain microenvironment.

IMPLICATIONS

Tumor cell invasion is a major clinical obstacle in glioblastoma and this study identifies a new signaling pathway regulated by Spinophilin in invasive glioblastoma. Mol Cancer Res; 14(12); 1277-87. ©2016 AACR.

Abstract 1646: A glioblastoma methylation assay (GaMA) developedfrom genomic analysis of glioma spheroid cultures predicts response toradiation therapy in patients with glioblastoma

Radiation therapy (RT) remains one of the most effective treatments for patients with GBM and has been repeatedly demonstrated to improve survival; yet response to RT is variable. We explored the relationship between methylation status and radiation response to develop a predictor of RT response using the epigenetic data of glioma sphere-forming cells (GSCs). The DNA methylomes of 42 GSCs were profiled using Illumina Infinium 450K methylation bead arrays. 15 GSCs were irradiated with 2-, 4-, and 6-Gy RT and response determined using clonogenic assays. We discovered 168 CpG probes capable of distinguishing sensitive from resistant GSCs. To validate, we analyzed 362 TCGA GBM samples, 272 that received standard 60Gy RT and 90 treated with low or no RT. Using the glioblastoma methylation assay (GaMA) signature, we classified the samples as either RT sensitive or resistant. Survival was significantly different between the predicted sensitive vs resistant patients for those treated with standard RT (median 21.0m vs 14.7m, p&lt;0.005). GaMA did not predict a survival difference among patients receiving no/low-dose RT, suggesting a predictive, but not prognostic, role for the signature. Using the ENCODE ChIP-Seq Significance Tool, we observed that the transcription factor EZH2 was significantly associated with the radiation resistant promoters in the GaMA signature. Among the hypermethylated genes with EZH2 binding sites, the NR2F2 promoter had the greatest number of hypermethylated CpG sites correlated to RT resistance. NR2F2 has previously been identified as negatively associated with activation of the wnt/β-catenin, a pathway associated with RT resistance of mammary progenitor cells. Expression of WNT1 in TCGA GBM cohort was negatively associated with NR2F2 expression. Our GSC RT response-based methylome analysis corroborates this association and provides a rationale for the methylation signature as a predictive biomarker of radiation response.

Citation Format: Qianghu Wang, Ravesanker Ezhilarasan, Eskil Eskilsson, Joy Gumin, Jie Yang, Mona Jaffari, Ming Tang, Kenneth D. Aldape, Frederick F. Lang, Roel G.W. Verhaak, Erik P. Sulman. A glioblastoma methylation assay (GaMA) developedfrom genomic analysis of glioma spheroid cultures predicts response toradiation therapy in patients with glioblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1646.

Abstract 2668: The exosomes derived from BM-hMSCs home to glioma and deliver synthetic microRNA mimics after systemic administration

Glioblastoma is the most malignant type of glioma (World Health Organization grade 4) and has a median survival time of only 14.6 months even after the standard treatment of surgical resection followed by radiotherapy with concomitant and adjuvant temozolomide administration. Although some novel and promising anti-glioma agents have been developed, therapeutic advancement has remained disappointing due to the lack of efficient delivery tools. Here we focused on exosomes derived from mesenchymal stem cells (MSCs) as carriers to deliver biological therapeutic agents for the treatment of gliomas. These exosomes are expected to cross the blood-brain barrier and selectively home to the glioma tissue, similar to the parental cells (MSCs). Additionally, MSCs could produce sufficient amounts of exosomes on a clinically applicable scale. Thus, MSC exosomes present a potentially ideal cell-free delivery vehicle for glioma therapy.

We hypothesized that exosomes derived from human bone marrow-derived MSCs (BM-hMSCs) can target gliomas and can be used as delivery vehicles following systemic administration. In this study, we employed microRNA (miR-128) as the therapeutic cargo, and exosomes were isolated from a cultured media of BM-hMSCs using ultracentrifugation. At first, exosomes labeled with fluorescent dye were incubated with glioma cells, and exosomes taken up by glioma cells were evaluated by confocal fluorescence microscopy and flow cytometry. Labeled exosomes were also systemically injected into a glioma xenograft model and the ability to home to glioma tissue was evaluated by an in vivo imaging system and histological study. The results showed that MSC exosomes can be taken up by glioma cells and can home to glioma tissues. Next, we cultured miR-128-enriched MSC exosomes with glioma cells. To check the function of miR-128 delivered to glioma cells by MSC exosomes, the down-regulation of the BMI-1 target gene of miR128 was evaluated using real-time polymerase chain reaction and western blot analyses. We also systemically injected these exosomes into glioma xenograft models and evaluated the function of miR-128 by analyzing the downregulation of BMI-1 at the tumor site and the animal survival time in vivo. We confirmed that miR-128 delivered by MSC exosomes could function at the target site both in vitro and in vivo.

These results indicate that MSC exosomes may be an ideal delivery vehicle for the treatment of gliomas, especially for microRNA replacement therapy.

Citation Format: Shinji Yamashita, Tal Shahar, Anwar Hossain, Brittany Parker Kerrigan, Joy Gumin, Shoudong Li, Feng Gao, Kouji Yamasaki, Yuzaburo Shimizu, Frederick F. Lang. The exosomes derived from BM-hMSCs home to glioma and deliver synthetic microRNA mimics after systemic administration. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2668.

TIE2-mediated tyrosine phosphorylation of H4 regulates DNA damage response by recruiting ABL1

DNA repair pathways enable cancer cells to survive DNA damage induced after genotoxic therapies. Tyrosine kinase receptors (TKRs) have been reported as regulators of the DNA repair machinery. TIE2 is a TKR overexpressed in human gliomas at levels that correlate with the degree of increasing malignancy. Following ionizing radiation, TIE2 translocates to the nucleus, conferring cells with an enhanced nonhomologous end-joining mechanism of DNA repair that results in a radioresistant phenotype. Nuclear TIE2 binds to key components of DNA repair and phosphorylates H4 at tyrosine 51, which, in turn, is recognized by the proto-oncogene ABL1, indicating a role for nuclear TIE2 as a sensor for genotoxic stress by action as a histone modifier. H4Y51 constitutes the first tyrosine phosphorylation of core histones recognized by ABL1, defining this histone modification as a direct signal to couple genotoxic stress with the DNA repair machinery.

Endoplasmic reticulum stress-inducing drugs sensitize glioma cells to temozolomide through downregulation of MGMT, MPG, and Rad51

BACKGROUND

Endoplasmic reticulum (ER) stress results from protein misfolding imbalance and has been postulated as a therapeutic strategy. ER stress activates the unfolded protein response which leads to a complex cellular response, including the upregulation of aberrant protein degradation in the ER, with the goal of resolving that stress. O(6)-methylguanine DNA methyltransferase (MGMT), N-methylpurine DNA glycosylase (MPG), and Rad51 are DNA damage repair proteins that mediate resistance to temozolomide in glioblastoma. In this work we sought to evaluate whether ER stress-inducing drugs were able to downmodulate DNA damage repair proteins and become candidates to combine with temozolomide.

METHODS

MTT assays were performed to evaluate the cytotoxicity of the treatments. The expression of proteins was evaluated using western blot and immunofluorescence. In vivo studies were performed using 2 orthotopic glioblastoma models in nude mice to evaluate the efficacy of the treatments. All statistical tests were 2-sided.

RESULTS

Treatment of glioblastoma cells with ER stress-inducing drugs leads to downregulation of MGMT, MPG, and Rad51. Inhibition of ER stress through pharmacological treatment resulted in rescue of MGMT, MPG, and Rad51 protein levels. Moreover, treatment of glioblastoma cells with salinomycin, an ER stress-inducing drug, and temozolomide resulted in enhanced DNA damage and a synergistic antitumor effect in vitro. Of importance, treatment with salinomycin/temozolomide resulted in a significant antiglioma effect in 2 aggressive orthotopic intracranial brain tumor models.

CONCLUSIONS

These findings provide a strong rationale for combining temozolomide with ER stress-inducing drugs as an alternative therapeutic strategy for glioblastoma.

Suppression of RAF/MEK or PI3K synergizes cytotoxicity of receptor tyrosine kinase inhibitors in glioma tumor-initiating cells

Background

The majority of glioblastomas have aberrant receptor tyrosine kinase (RTK)/RAS/phosphoinositide 3 kinase (PI3K) signaling pathways and malignant glioma cells are thought to be addicted to these signaling pathways for their survival and proliferation. However, recent studies suggest that monotherapies or inappropriate combination therapies using the molecular targeted drugs have limited efficacy possibly because of tumor heterogeneities, signaling redundancy and crosstalk in intracellular signaling network, indicating necessity of rationale and methods for efficient personalized combination treatments. Here, we evaluated the growth of colonies obtained from glioma tumor-initiating cells (GICs) derived from glioma sphere culture (GSC) in agarose and examined the effects of combination treatments on GICs using targeted drugs that affect the signaling pathways to which most glioma cells are addicted.

Methods

Human GICs were cultured in agarose and treated with inhibitors of RTKs, non-receptor kinases or transcription factors. The colony number and volume were analyzed using a colony counter, and Chou-Talalay combination indices were evaluated. Autophagy and apoptosis were also analyzed. Phosphorylation of proteins was evaluated by reverse phase protein array and immunoblotting.

Results

Increases of colony number and volume in agarose correlated with the Gompertz function. GICs showed diverse drug sensitivity, but inhibitions of RTK and RAF/MEK or PI3K by combinations such as EGFR inhibitor and MEK inhibitor, sorafenib and U0126, erlotinib and BKM120, and EGFR inhibitor and sorafenib showed synergy in different subtypes of GICs. Combination of erlotinib and sorafenib, synergistic in GSC11, induced apoptosis and autophagic cell death associated with suppressed Akt and ERK signaling pathways and decreased nuclear PKM2 and β-catenin in vitro, and tended to improve survival of nude mice bearing GSC11 brain tumor. Reverse phase protein array analysis of the synergistic treatment indicated involvement of not only MEK and PI3K signaling pathways but also others associated with glucose metabolism, fatty acid metabolism, gene transcription, histone methylation, iron transport, stress response, cell cycle, and apoptosis.

Conclusion

Inhibiting RTK and RAF/MEK or PI3K could induce synergistic cytotoxicity but personalization is necessary. Examining colonies in agarose initiated by GICs from each patient may be useful for drug sensitivity testing in personalized cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0803-2) contains supplementary material, which is available to authorized users.

Genetic, epigenetic, and molecular landscapes of multifocal and multicentric glioblastoma

Ten to twenty percent of newly diagnosed glioblastoma (GBM) patients initially present with multiple lesions, termed multifocal or multicentric GBM (M-GBM). The prognosis of these patients is poorer than that of solitary GBM (S-GBM) patients. However, it is unknown whether multifocality has a genetic, epigenetic, or molecular basis. Here, we identified the genetic and epigenetic characteristics of M-GBM by performing a comprehensive analysis of multidimensional data, including imaging, genetic, epigenetic, and gene expression profiles, from 30 M-GBM cases in The Cancer Genome Atlas database and comparing the results with those of 173 S-GBM cases. We found that M-GBMs had no IDH1, ATRX, or PDGFRA mutations and were significantly associated with the mesenchymal subtype. We also identified the CYB5R2 gene to be hypo-methylated and overexpressed in M-GBMs. The expression level of CYB5R2 was significantly associated with patient survival in two major independent GBM cohorts, totaling 758 cases. The IDH1 mutation was markedly associated with CYB5R2 promoter methylation, but the survival influence of CYB5R2 was independent of IDH1 mutation status. CYB5R2 expression was significantly associated with collagen maturation and the catabolic process and immunoregulation pathways. These results reveal that M-GBMs have some underlying genetic and epigenetic characteristics that are associated with poor prognosis and that CYB5R2 is a new epigenetic marker for GBM prognosis.

Integrated Transcriptomic and Glycomic Profiling of Glioma Stem Cell Xenografts

Bone marrow-derived human mesenchymal stem cells (BM-hMSCs) have the innate ability to migrate or home toward and engraft in tumors such as glioblastoma (GBM). Because of this unique property of BM-hMSCs, we have explored their use for cell-mediated therapeutic delivery for the advancement of GBM treatment. Extravasation, the process by which blood-borne cells—such as BM-hMSCs—enter the tissue, is a highly complex process but is heavily dependent upon glycosylation for glycan-glycan and glycan-protein adhesion between the cell and endothelium. However, in a translationally significant preclinical glioma stem cell xenograft (GSCX) model of GBM, BM-hMSCs demonstrate unequal tropism toward these tumors. We hypothesized that there may be differences in the glycan compositions between the GSCXs that elicit homing ("attractors") and those that do not ("non-attractors") that facilitate or impede the engraftment of BM-hMSCs in the tumor. In this study, glycotranscriptomic analysis revealed significant heterogeneity within the attractor phenotype and the enrichment of high mannose type N-glycan biosynthesis in the non-attractor phenotype. Orthogonal validation with topical PNGase F deglycosylation on the tumor regions of xenograft tissue, followed by nLC-ESI-MS, confirmed the presence of increased high mannose type N-glycans in the non-attractors. Additional evidence provided by our glycomic study revealed the prevalence of terminal sialic acid-containing N-glycans in non-attractors and terminal galactose and N-acetyl-glucosamine N-glycans in attractors. Our results provide the first evidence for differential glycomic profiles in attractor and non-attractor GSCXs and extend the scope of molecular determinates in BM-hMSC homing to glioma.

Abstract 280: Delta-24-RGDOX: making cancer more “visible” to the immune system

Emerging evidence indicates that host immunity is critical for successful cancer virotherapy. We found that oncolytic adenovirus Delta-24-RGD elicited antiglioma immunity in an immunocompetent murine model. Recent studies suggested that the therapeutic efficacy of immune checkpoint blockade in cancer patients could be enhanced by strategies inducing tumor inflammation. We hypothesized that highly immunogenic adenovirus combined with targeting immune co-stimulator would result in better anti-tumor efficiency. Thus, we used the backbone of Delta-24-RGD to express the mouse OX40 ligand to increase the recognition of tumor-associated antigens by immune cells. The resulting Delta-24-RGDOX adenovirus maintained the oncolytic potency of Delta-24-RGD and efficiently expressed OX40 ligand on infected cells. More importantly, compared to Delta-24-RGD, Delta-24-RGDOX induced higher antiglioma activity in immunocompetent glioma models but not in an immunodeficient model, and accordingly mediated greater lymphocyte infiltration at tumor sites and stronger lymphocyte antitumor activity. While blocking or stimulating immune checkpoints with antibodies currently dominates the clinical applications, our data demonstrate that intratumoral injection of oncolyticviruses carrying immune co-stimulatory ligands may constitute a powerful alternative to the use of antibodies and other strategies targeting immune checkpoints in cancer therapy.

Note: This abstract was not presented at the meeting.

Citation Format: Hong Jiang, Xuejun Fan, Karen Clise-Dwyer, Laura Bover, Joy Gumin, Kathryn E. Ruisaard, Farah J. Mukheef, Frederick F. Lang, Candelaria Gomez-Manzano, Juan Fueyo. Delta-24-RGDOX: making cancer more “visible” to the immune system. [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 280. doi:10.1158/1538-7445.AM2015-280

Abstract 3483: Synergistic combination therapy with molecular targeted drugs in glioma stem-like cells

[Introduction] The prognosis of patients with malignant gliomas is poor despite multimodality therapies underscoring the need for novel therapeutic strategies. The majority of glioblastomas have aberrant receptor tyrosine kinase (RTK)/RAS/phosphoinositide 3 kinase (PI3K) signaling pathways and malignant glioma cells are thought to be addicted to these aberrant signaling pathways for their survival and proliferation. However, a large number of clinical trials have demonstrated that monotherapies have limited efficacy. Tumor heterogeneities and signaling redundancy and crosstalk in intracellular signaling network may imply necessity of combination treatments. Recent studies also suggested that effective methods to personalize antitumor therapy are required. However, drug sensitivity testing using tumor cells from each patient, which is one of the potent methods for personalized tumor therapy, has been unsuccessful. One possible reason of this is a technical issue regarding evaluation of clonogenicity of glioma stem-like cells (GSCs) that are thought to be key players in gliomagenesis and the disease progression and recurrence and thus targets of glioma therapy. We previously presented an effective method to evaluate clonogenicity of GSCs by using agarose-based culture system. In this study, we tested the therapeutic effects of combination treatments on GSCs using targeted drugs that affect the signaling pathways to which most glioma cells are thought to be addicted.

[Materials and Methods] Human GSCs were cultured in agarose and treated with inhibitors of RTKs, non-receptor kinase or transcription factor. The colony number and volume were analyzed using GelCountTM colony counter system (Oxford Optronix Inc., UK) and Chou-Talalay combination index was analyzed. Phosphorylation of proteins was evaluated by reverse phase protein array and immunoblotting.

[Results] While GSCs showed diverse sensitivity to targeted therapies even in the cells of the same glioma subtype, combinations of EGFR inhibitors with sorafenib, EGFR inhibitors with MEK inhibitors, Sorafenib with U0126, and erlotinib with BKM120 showed synergy in different GSC lines, indicating effectiveness of suppressing RTK and its downstream molecule. Combination of erlotinib with sorafenib, synergistic in the GSC11 cells, induced apoptosis and autophagic cell death associated with synergistic suppression of Akt and ERK signaling pathways and with decreased nuclear PKM2 and beta-catenin in vitro, and significantly improved survival of nude mice bearing GSC11 brain tumors compared with control and monotherapy groups.

[Conclusions] Inhibition of RTK and its downstream molecule induced synergistic antitumor effects but sensitivity of GSC lines to therapies was diverse. Examining colonies initiated by GSCs obtained from individual patients may be useful for drug sensitivity testing in personalized cancer therapy.

Citation Format: Takashi Shingu, Lindsay Holmes, Verlene Henry, Khatri Latha, Anupama E. Gururaj, Laura A. Gibson, Tiffany Doucette, Frederick F. Lang, Ganesh Rao, Liang Yuan, Erik P. Sulman, Nicholas P. Farrell, Waldemar Priebe, Kenneth R. Hess, Yaoqi A. Wang, Jian Hu, Oliver Bogler. Synergistic combination therapy with molecular targeted drugs in glioma stem-like cells. [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 3483. doi:10.1158/1538-7445.AM2015-3483

Abstract 4795: A novel gene fusion in glioblastoma and a radiation response methylation signature identified by genomic characterization of glioma sphere-forming cells

Purpose: High fidelity models of the lethal primary brain tumor glioblastoma (GBM) are essential to develop new therapies. Glioma sphere-forming cells (GSCs) are derived from surgical specimens and are thought to play important roles in tumor maintenance and treatment resistance. We performed genomic characterization of the largest reported panel of GSCs. We hypothesized that GSCs would recapitulate the genomic alterations of their GBMs of origin while identifying novel changes identifiable only in a pure tumor cell population.

Methods: All GSCs were obtained at the time of surgical resection and all analyses were conducted at early passage. We performed exome and transcriptome sequencing, DNA methylation profiling (Illumina Infinium 450K Bead Arrays) and DNA copy number determination (Affymetrix OncoScan). Radiation (RT) sensitivity was determined by clonogenic survival and in vivo survival by orthotopic xenograft.

Results: We analyzed 43 GSCs, 40 of which had tissue available from their tumors of origin. Somatically mutated genes previously described in GBM, such as TP53, EGFR, PTEN, NF1, PIK3CA and RB1, were found at similar mutation frequencies. Likewise, DNA copy number variations were similar to their matched tumor and those reported by the TCGA, with novel or more pronounced alterations, such as MYC application and QKI deletion, identified in the GSCs. GSCs were classified into TCGA GBM subtypes by expression signatures, identifying a subset of GSCs with a subtype differing from their matched tumors that correlated to decreased stromal enrichment. GSCs exhibited upregulation of self-renewal pathways, such as MYC, WNT, and NOTCH, and of stem-cell factors, such as MSI1, NESTIN, OLIG2, and SOX2, consistent with the stem-like phenotype attributed to GSCs. Transcript analyses identified the previously reported FGFR3-TACC3 and EGFR-SEPT14 gene fusions as well as a novel KIF1B-KMT2A (MLL) fusion, which was found to have been retained in the matching recurrent GBM as well as the GSC derived from the recurrence. A signature derived by the differential methylation pattern of RT sensitive vs. resistant GSCs was applied to the subset of TCGA cases that received upfront RT. Survival by methylation class in this subset was significantly different (median survival 84 vs. 61 weeks; HR 1.64 adjusting for patient age, p-value&lt;0.008), suggesting this signature is predictive of clinical RT response.

Conclusions: Based on genomic analyses, GSCs are robust models of GBM which can be used for therapeutic development. We have identified a novel gene fusion involving MLL with a predicted driving role suggesting a new mode of gliomagenesis. A methylation signature predictive of RT response may have potential for personalizing RT treatment of GBM patients and provides insights into RT sensitivity phenotypes.

Citation Format: Qianghu Wang, Ravesanker Ezhilarasan, Lindsey D. Goodman, Joy Gumin, Siyuan Zheng, Kosuke Yoshihara, Peng Sun, Jie Yang, Tim Heffernan, Giulio Draetta, Kenneth D. Aldape, Frederick F. Lang, Roel G.W. Verhaak, Erik P. Sulman. A novel gene fusion in glioblastoma and a radiation response methylation signature identified by genomic characterization of glioma sphere-forming cells. [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 4795. doi:10.1158/1538-7445.AM2015-4795

Mesenchymal Stem Cells Isolated From Human Gliomas Increase Proliferation and Maintain Stemness of Glioma Stem Cells Through the IL-6/gp130/STAT3 Pathway

Although mesenchymal stem cells (MSCs) have been implicated as stromal components of several cancers, their ultimate contribution to tumorigenesis and their potential to drive cancer stem cells, particularly in the unique microenvironment of human brain tumors, remain largely undefined. Consequently, using established criteria, we isolated glioma-associated-human MSCs (GA-hMSCs) from fresh human glioma surgical specimens for the first time. We show that these GA-hMSCs are nontumorigenic stromal cells that are phenotypically similar to prototypical bone marrow-MSCs. Low-passage genomic sequencing analyses comparing GA-hMSCs with matched tumor-initiating glioma stem cells (GSCs) suggest that most GA-hMSCs (60%) are normal cells recruited to the tumor (group 1 GA-hMSCs), although, rarely (10%), GA-hMSCs may differentiate directly from GSCs (group 2 GA-hMSCs) or display genetic patterns intermediate between these groups (group 3 GA-hMSCs). Importantly, GA-hMSCs increase proliferation and self-renewal of GSCs in vitro and enhance GSC tumorigenicity and mesenchymal features in vivo, confirming their functional significance within the GSC niche. These effects are mediated by GA-hMSC-secreted interleukin-6, which activates STAT3 in GSCs. Our results establish GA-hMSCs as a potentially new stromal component of gliomas that drives the aggressiveness of GSCs, and point to GA-hMSCs as a novel therapeutic target within gliomas.

ESI-MS/MS and MALDI-IMS Localization Reveal Alterations in Phosphatidic Acid, Diacylglycerol, and DHA in Glioma Stem Cell Xenografts

Glioblastoma (GBM) is the most common adult primary brain tumor. Despite aggressive multimodal therapy, the survival of patients with GBM remains dismal. However, recent evidence has demonstrated the promise of bone marrow-derived mesenchymal stem cells (BM-hMSCs) as a therapeutic delivery vehicle for anti-glioma agents due to their ability to migrate or home to human gliomas. While several studies have demonstrated the feasibility of harnessing the homing capacity of BM-hMSCs for targeted delivery of cancer therapeutics, it is now also evident, based on clinically relevant glioma stem cell (GSC) models of GBMs, that BM-hMSCs demonstrate variable tropism toward these tumors. In this study, we compared the lipid environment of GSC xenografts that attract BM-hMSCs (N = 9) with those that do not attract (N = 9) to identify lipid modalities that are conducive to homing of BM-hMSC to GBMs. We identified lipids directly from tissue by matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) and electrospray ionization-tandem mass spectrometry (ESI-MS/MS) of lipid extracts. Several species of signaling lipids, including phosphatidic acid (PA 36:2, PA 40:5, PA 42:5, and PA 42:7) and diacylglycerol (DAG 34:0, DAG 34:1, DAG 36:1, DAG 38:4, DAG 38:6, and DAG 40:6), were lower in attracting xenografts. Molecular lipid images showed that PA (36:2), DAG (40:6), and docosahexaenoic acid (DHA) were decreased within tumor regions of attracting xenografts. Our results provide the first evidence for lipid signaling pathways and lipid-mediated tumor inflammatory responses in the homing of BM-hMSCs to GSC xenografts. Our studies provide new fundamental knowledge on the molecular correlates of the differential homing capacity of BM-hMSCs toward GSC xenografts.