The integrated landscape of driver genomic alterations in glioblastoma

Glioblastoma is one of the most challenging forms of cancer to treat. Here we describe a computational platform that integrates the analysis of copy number variations and somatic mutations and unravels the landscape of in-frame gene fusions in glioblastoma. We found mutations with loss of heterozygosity in LZTR1, encoding an adaptor of CUL3-containing E3 ligase complexes. Mutations and deletions disrupt LZTR1 function, which restrains the self renewal and growth of glioma spheres that retain stem cell features. Loss-of-function mutations in CTNND2 target a neural-specific gene and are associated with the transformation of glioma cells along the very aggressive mesenchymal phenotype. We also report recurrent translocations that fuse the coding sequence of EGFR to several partners, with EGFR-SEPT14 being the most frequent functional gene fusion in human glioblastoma. EGFR-SEPT14 fusions activate STAT3 signaling and confer mitogen independence and sensitivity to EGFR inhibition. These results provide insights into the pathogenesis of glioblastoma and highlight new targets for therapeutic intervention.

Affinity-matured recombinant immunotoxin targeting gangliosides 3'-isoLM1 and 3',6'-isoLD1 on malignant gliomas

About 60 percent of glioblastomas highly express the gangliosides 3'-isoLM1 and 3',6'-isoLD1 on the cell surface, providing ideal targets for brain tumor immunotherapy. A novel recombinant immunotoxin, DmAb14m-(scFv)-PE38KDEL (DmAb14m-IT), specific for the gangliosides 3'-isoLM1 and 3',6'-isoLD1, was constructed with improved affinity and increased cytotoxicity for immunotherapeutic targeting of glioblastoma. We isolated an scFv parental clone from a previously established murine hybridoma, DmAb14, that is specific to both 3'-isoLM1 and 3',6'-isoLD1. We then performed in vitro affinity maturation by CDR hotspot random mutagenesis. The binding affinity and specificity of affinity-matured DmAb14m-IT were measured by surface-plasmon resonance, flow cytometry, and immunohistochemical analysis. In vitro cytotoxicity of DmAb14m-IT was measured by protein synthesis inhibition and cell death assays in human cell lines expressing gangliosides 3'-isoLM1 and 3',6'-isoLD1 (D54MG and D336MG) and xenograft-derived cells (D2224MG). As a result, the KD of DmAb14m-IT for gangliosides 3'-isoLM1 and 3',6'-isoLD1 was 2.6 × 10(-9)M. Also, DmAb14m-IT showed a significantly higher internalization rate in cells expressing 3'-isoLM1 and 3',6'-isoLD1. The DmAb14m-IT IC 50 was 80 ng/mL (1194 pM) on the D54MG cell line, 5 ng/ml (75 pM) on the D336MG cell line, and 0.5 ng/ml (7.5 pM) on the D2224MG xenograft-derived cells. There was no cytotoxicity on ganglioside-negative HEK293 cells. Immunohistochemical analysis confirmed the specific apparent affinity of DmAb14m-IT with 3'-isoLM1 and 3',6'-isoLD1. In conclusion, DmAb14m-IT showed specific binding affinity, a significantly high internalization rate, and selective cytotoxicity on glioma cell lines and xenograft-derived cells expressing 3'-isoLM1 and 3',6'-isoLD1, thereby displaying robust therapeutic potential for testing the antitumor efficacy of DmAb14m-IT at the preclinical level and eventually in the clinical setting.

Construction of an immunotoxin, D2C7-(scdsFv)-PE38KDEL, targeting EGFRwt and EGFRvIII for brain tumor therapy

PURPOSE

The EGF receptor gene (EGFR) is most frequently amplified and overexpressed, along with its deletion mutant, EGFRvIII, in glioblastoma. We tested the preclinical efficacy of the recombinant immunotoxin, D2C7-(scdsFv)-PE38KDEL, which is reactive with a 55-amino acid (AA) region present in the extracellular domain of both EGFRwt (583-637 AAs) and EGFRvIII (292-346 AAs) proteins.

EXPERIMENTAL DESIGN

The binding affinity and specificity of D2C7-(scdsFv)-PE38KDEL for EGFRwt and EGFRvIII were measured by surface-plasmon resonance and flow cytometry. In vitro cytotoxicity of D2C7-(scdsFv)-PE38KDEL was measured by inhibition of protein synthesis in human EGFRwt-transfected NR6 (NR6W), human EGFRvIII-transfected NR6 (NR6M), EGFRwt-overexpressing A431-epidermoid-carcinoma, and glioblastoma xenograft cells (43, D08-0493MG, D2159MG, and D270MG). In vivo antitumor efficacy of D2C7-(scdsFv)-PE38KDEL was evaluated using 43, NR6M, and D270MG orthotopic tumor models.

RESULTS

The KD of D2C7-(scdsFv)-PE38KDEL for EGFRwt and EGFRvIII was 1.6×10(-9) mol/L and 1.3×10(-9) mol/L, respectively. Flow cytometry with NR6W and NR6M cells confirmed the specificity of D2C7-(scdsFv)-PE38KDEL for EGFRwt and EGFRvIII. The D2C7-(scdsFv)-PE38KDEL IC50 was 0.18 to 2.5 ng/mL on cells expressing EGFRwt (NR6W, A431, 43, and D08-0493MG). The D2C7-(scdsFv)-PE38KDEL IC50 was approximately 0.25 ng/mL on EGFRvIII-expressing cells (NR6M) and on EGFRwt- and EGFRvIII-expressing glioblastoma xenograft cells (D2159MG and D270MG). Significantly, in intracranial tumor models of 43, NR6M, and D270MG, treatment with D2C7-(scdsFv)-PE38KDEL by convection-enhanced delivery prolonged survival by 310% (P=0.006), 28% (P=0.002), and 166% (P=0.001), respectively.

CONCLUSIONS

In preclinical studies, the D2C7-(scdsFv)-PE38KDEL immunotoxin exhibited significant potential for treating brain tumors expressing EGFRwt, EGFRvIII, or both.

Rational design and generation of recombinant control reagents for bispecific antibodies through CDR mutagenesis

Developments in the field of bispecific antibodies have progressed rapidly in recent years, particularly in their potential role for the treatment of malignant disease. However, manufacturing stable molecules has proven to be costly and time-consuming, which in turn has hampered certain aspects of preclinical evaluation including the unavailability of appropriate "negative" controls. Bispecific molecules (e.g., bispecific tandem scFv) exhibit two specificities, often against a tumor antigen as well as an immune-activation ligand such as CD3. While for IgG antibodies, isotype-matched controls are well accepted, when considering smaller antibody fragments it is not possible to adequately control for their biological activity through the use of archetypal isotypes, which differ dramatically in affinity, size, structure, and design. Here, we demonstrate a method for the rapid production of negative control tandem scFvs through complementarity determining region (CDR) mutagenesis, using a recently described bispecific T-cell engager (BiTE) targeting a tumor-specific mutation of the epidermal growth factor receptor (EGFRvIII) as an example. Four independent control constructs were developed by this method through alteration of residues spanning individual CDR domains. Importantly, while target antigen affinity was completely impaired, CD3 binding affinity was conserved in each molecule. These results have a potential to enhance the sophistication by which bispecific antibodies can be evaluated in the preclinical setting and may have broader applications for an array of alternative antibody-derived therapeutic platforms.

Convection enhanced delivery of macromolecules for brain tumors

The blood brain barrier (BBB) poses a significant challenge for drug delivery of macromolecules into the brain. Convection-enhanced delivery (CED) circumvents the BBB through direct intracerebral infusion using a hydrostatic pressure gradient to transfer therapeutic compounds. The efficacy of CED is dependent on the distribution of the therapeutic agent to the targeted region. Here we present a review of convection enhanced delivery of macromolecules, emphasizing the role of tracers in enabling effective delivery anddiscuss current challenges in the field.

Phase II trial for patients with newly diagnosed glioblastoma (GBM) treated with carmustine wafers followed by concurrent radiation therapy (RT), temozolomide (TMZ), and bevacizumab (BV), then followed by TMZ and BV post-RT

e13015^

Background: Standard treatment for GBM includes RT and TMZ, followed by six cycles of TMZ, for a median overall survival (OS) and progression-free survival (PFS) of 14.6 and 6.9 months, respectively. BV is FDA approved for recurrent GBM and carmustine wafers are approved for newly diagnosed and recurrent GBM. We evaluated the safety and efficacy of carmustine wafers insertion followed by concurrent RT, TMZ and BV, followed by TMZ and BV for newly diagnosed GBM patients. Methods: Treatment consisted of: Part A- carmustine wafers insertion at resection followed by RT and TMZ at 75 mg/m2/day. BV at 10 mg/kg every two weeks started at least 28 days post-operatively. Part B- Patients received 12 cycles of TMZ (200 mg/m2on days 1-5 of a 28-day cycle) and BV every two weeks (day 1 and 15). Results: Forty one patients of a planned accrual of 72 were enrolled. The study was closed early due to six grade 4-5 toxicities related to study intervention, which met the safety criteria to discontinue the trial. Three patients had grade 4 cerebral edema and one each had grade 4 fatigue, wound infection and meningitis. Median age was 56 years (range, 27-77 years) and 28 patients were men. Of 41 patients, 36 completed part A and 31 started part B. Eleven patients are still on study and 4 have completed part B. Twenty six patients are off study due to progression (n = 16), adverse events (n = 8) and consent withdrawal (n = 2). At a median follow-up of 12.6 months (95% CI: 10.8-15.6 months) the median PFS is 11.3 months (95% CI: 9.2-12.9 months) and the median OS is 16.1 months (95% CI: 15.8 months- ∞). Grade 3-5 toxicities so far include: thrombocytopenia (grade 3, n = 2; grade 4, n = 2), stroke (grade 3, n = 1; grade 5, n = 1), infection (grade 3, n = 2), meningitis (grade 3, n = 1; grade 4, n=1), venous thromboembolic events (grade 3, n = 5), cerebral edema (grade 4, n = 3), fatigue (grade 4, n = 1), enterocolitis (grade 3, n = 1), and wound infection (grade 3, n = 2; grade 4, n = 1). Conclusions: For the patients who did well post carmustine wafers insertion, the treatment was tolerable and median PFS and OS has improved. Updated survival and toxicity results will be presented. Clinical trial information: NT01186406.

Dose-finding and safety study of an oncolytic polio/rhinovirus recombinant against recurrent glioblastoma

2094

Background: Current therapies for glioblastoma are limited by ineffective delivery beyond the blood-brain barrier, limited diffusion of macromolecules, and lack of tumor specificity. Sustained direct intracerebral infusion at slow flow rates [convection-enhanced delivery (CED)] can overcome delivery barriers. PVSRIPO is the live attenuated, oral (SABIN) serotype 1 poliovirus vaccine containing a heterologous internal ribosomal entry site stemming from human rhinovirus type 2. PVSRIPO recognizes nectin-like molecule-5, an oncofetal cell adhesion molecule and tumor antigen widely expressed ectopically in malignancy. We report the results of an ongoing phase I study evaluating PVSRIPO when delivered by CED. Methods: Eligible on study are adult patients with: 1-5 cm of measurable supratentorial recurrent glioblastoma ≥1cm away from the ventricles; ≥4 weeks after chemotherapy, bevacizumab or study drug; adequate organ function; KPS ≥70%; and positive anti-poliovirus titer. PVSRIPO is delivered intratumorally by CED over 6.5 hours. PVSRIPO dose escalation is accomplished by increasing agent concentration, allowing flow-rate and infusion volume to remain constant. Two-step continual reassessment method is used for dose escalation, with one patient each treated on dose levels 1-4, and a possibility of up to 13 patients on dose level 5. Results: Thus far, a total of five patients have been treated on study. No related or unrelated grade 3 or higher adverse events have been observed. Grade 1 adverse events possibly related to the study drug or procedure include one each of fever, cough, nasal congestion, vomiting, headache, hemiparesis, and lethargy. Grade 2 adverse events include one each of diarrhea and seizure. Patient #1 had failed bevacizumab prior to enrollment and remains disease free more than 9 months post PVSRIPO. Two more patients are disease free 8+ and 2+ months post treatment, respectively. One patient had pathology confirmed disease recurrence two months post treatment and one patient came off study due to clinical decline four months post treatment. Conclusions: Infusion of PVSRIPO via CED is safe thus far and encouraging efficacy results are observed. Updated results will be presented. Clinical trial information: NCT 01491893.

Recombinant anti-podoplanin (NZ-1) immunotoxin for the treatment of malignant brain tumors

Our study demonstrates the glioma tumor antigen podoplanin to be present at very high levels (>90%) in both glioblastoma (D2159MG, D08-0308MG and D08-0493MG) and medulloblastoma (D283MED, D425MED and DAOY) xenografts and cell line. We constructed a novel recombinant single-chain antibody variable region fragment (scFv), NZ-1, specific for podoplanin from the NZ-1 hybridoma. NZ-1-scFv was then fused to Pseudomonas exotoxin A, carrying a C-terminal KDEL peptide (NZ-1-PE38KDEL). The immunotoxin (IT) was further stabilized by a disulfide (ds) bond between the heavy-chain and light-chain variable regions as the construct NZ-1-(scdsFv)-PE38KDEL. NZ-1-(scdsFv)-PE38KDEL exhibited significant reactivity to glioblastoma and medulloblastoma cells. The affinity of NZ-1-(scdsFv), NZ-1-(scdsFv)-PE38KDEL and NZ-1 antibody for podoplanin peptide was 2.1 × 10(-8) M, 8.0 × 10(-8) M and 3.9 × 10(-10) M, respectively. In a protein stability assay, NZ-1-(scdsFv)-PE38KDEL retained 33-98% of its activity, whereas that of NZ-1-PE38KDEL declined to 13% of its initial levels after incubation at 37°C for 3 days. In vitro cytotoxicity of the NZ-1-(scdsFv)-PE38KDEL was measured in cells isolated from glioblastoma xenografts, D2159MG, D08-0308MG and D08-0493MG, and in the medulloblastoma D283MED, D425MED and DOAY xenografts and cell line. The NZ-1-(scdsFv)-PE38KDEL IT was highly cytotoxic, with an 50% inhibitory concentration in the range of 1.6-29 ng/ml. Significantly, NZ-1-(scdsFv)-PE38KDEL demonstrated tumor growth delay, averaging 24 days (p < 0.001) and 21 days (p < 0.001) in D2159MG and D283MED in vivo tumor models, respectively. Crucially, in the D425MED intracranial tumor model, NZ-1-(scdsFv)-PE38KDEL caused a 41% increase in survival (p ≤ 0.001). In preclinical studies, NZ-1-(scdsFv)-PE38KDEL exhibited significant potential as a targeting agent for malignant brain tumors.

BLyS levels correlate with vaccine-induced antibody titers in patients with glioblastoma lymphodepleted by therapeutic temozolomide

B lymphocyte stimulator (BLyS) is a cytokine involved in differentiation and survival of follicular B cells along with humoral response potentiation. Lymphopenia is known to precipitate dramatic elevation in serum BLyS; however, the use of this effect to enhance humoral responses following vaccination has not been evaluated. We evaluated BLyS serum levels and antigen-specific antibody titers in 8 patients undergoing therapeutic temozolomide (TMZ)-induced lymphopenia, with concomitant vaccine against a tumor-specific mutation in the epidermal growth factor receptor (EGFRvIII). Our studies demonstrate that TMZ-induced lymphopenia corresponded with spikes in serum BLyS that directly preceded the induction of anti-EGFRvIII antigen-specific antibody titers, in some cases as high as 1:2,000,000. Our data are the first clinical observation of BLyS serum elevation and greatly enhanced humoral immune responses as a consequence of chemotherapy-induced lymphopenia. These observations should be considered for the development of future vaccination strategies in the setting of malignancy.

Abstract 2079: Antitumoral activity of INC280 against adult glioblastoma brain tumors xenografts

INTRODUCTION: INC280 is an oral, highly selective c-Met receptor tyrosine kinase inhibitor. The hepatocyte growth factor (HGF)-c-Met pathway is one of the most frequently dysregulated pathways in human cancers. Aberrant HGF-c-Met signaling has been documented in a wide range of human malignancies. The c-Met pathway can be activated by abnormal HGF and c-Met expression levels, c-Met activating mutations and gene amplifications. At this time, INC280 is in development for the treatment of solid tumors with activation of the c-Met pathway. As a part of this study, we looked at the antitumoral activity of INC280 in adult glioblastoma (GBM) brain tumor xenografts with elevated levels of Met or HGF expression.

METHODS: Met expression and copy number was determined by ELISA and qPCR, HGF mRNA by RT-qPCR. Adult GBM tumor xenografts were grown subcutaneously in athymic BALB/c mice. After tumor size reached 200-500 mm3 subcutaneously, groups of 10 mice were randomly treated with either drug vehicle/control or INC280 (10mg/kg BID) PO for 30 days. Tumor responses for subcutaneous xenografts were assessed by tumor growth delay and regression.

RESULTS: Based on activation of the c-Met pathway, the following two xenograft lines were selected for treatment with INC280: D-09-0337 MG and D-09-0477 MG. As a single agent, INC280 demonstrated statistically significant (p&lt;0.001) growth delays of 40.23 and 30.13 days in D-09-0337 MG and D-09-0477 MG, respectively. In addition, when treated with INC280, tumors implanted with D-09-0337 MG (10 out of 10) or D-09-0477 MG (4 out of 10) regressed.

CONCLUSION: Our results demonstrate the therapeutic efficacy of the inhibition of a c-Met receptor tyrosine kinase in adult brain tumor xenografts with activation of the c-Met pathway. These results warrant further exploration of INC280 in clinical trials for the treatment of adult brain tumor patients with dysregulated proto-oncogene c-Met and its ligand HGF.

Citation Format: Stephen T. Keir, Martin A. Roskoski, Sabrina Wagner, Ralph Tiedt, Darell D. Bigner, Henry S. Friedman. Antitumoral activity of INC280 against adult glioblastoma brain tumors xenografts. [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 2079. doi:10.1158/1538-7445.AM2013-2079

Abstract 4322: Efficacy of Sym004, a novel anti-EGFR antibody mixture, against EGFRvIII positive glioblastoma xenografts

INTRODUCTION

Glioblastoma (GBM) is the most common intracranial cancer in adults but despite recent advances in therapy the overall survival remains about 20 months. The epidermal growth factor receptor variant III (EGFRvIII) is a truncated, constitutively active, and highly oncogenic form of the EGFR expressed on approximately 30% of GBMs. Sym004 is a recombinant IgG1 antibody mixture consisting of two antibodies against domain III of the epidermal growth factor receptor (EGFR). Like anti-EGFR monoclonal antibodies, Sym004 inhibits cancer cell growth and survival by blocking ligand-binding and receptor signaling. However, unlike the monoclonal antibodies, Sym004 induces a rapid and efficient internalization and degradation of the EGFR. Here, we examine whether the more efficient removal of the EGFR and the constitutive active EGFRvIII by Sym004 would translate into increased tumor growth inhibition of EGFRvIII GBM xenografts.

METHODS

Both subcutaneous (sc) and intracranial (ic) adult brain tumor xenografts were grown in athymic BALB/c mice. After tumor size reached 200-500 mm3 subcutaneously or 3 days after intracranial implantation, groups of 10 mice were randomly treated with either drug vehicle, Sym004 (50 mg/kg) or cetuximab (50 mg/kg) IP twice weekly for 5 weeks. Tumor responses for sc xenografts were assessed by tumor growth delay and regression and for ic xenografts by difference in median survival. Xenograft lines utilized for this study expressed either primarily EGFR wildtype (D-54 MG) or mutant EGFRvIII (D-270 MG and D-317 MG).

RESULTS AND DISCUSSION

The sc results for D-54 MG did not demonstrate statistically significant growth delays for either Sym004 or cetuximab. In sc EGFRvIII models, however, Sym004 produced statistically significant (p&lt;0.001) growth delays of 7.8 and 76.5 days and outperformed cetuximab by 4.6 and 71.9 days in D-270 MG and D-317 MG, respectively. Intracranially, Sym004 produced statistically significant (p&lt;0.001) increases in survival of 39% and 163% and outperformed cetuximab by 27% and 115% in D-270 MG and D-317 MG, respectively. We speculate that the superior effect of the Sym004 antibody mixture compared to the monoclonal antibody cetuximab in the EGFRvIII models is due to a more efficient internalization and degradation - and thereby shutdown - of the constitutively active EGFRvIII. Histological examination of the receptor status in the tumors following treatment is ongoing.

CONCLUSIONS

The novel strategy to target EGFR demonstrates the significant anti-tumor activity of Sym004 against adult glioblastoma xenografts that express EGFRvIII. These results warrant further exploration of Sym004 in clinical trials for the treatment of EGFRvIII positive brain tumors.

Funding for these studies was provided by Symphogen and the Tisch Preclinical Therapy Screening Program

Citation Format: Stephen T. Keir, Martin A. Roskoski, Michael Kragh, Mikkel W. Pederson, Helle J. Jacobsen, Ivan D. Horak, Henry S. Friedman, Darell D. Bigner. Efficacy of Sym004, a novel anti-EGFR antibody mixture, against EGFRvIII positive glioblastoma xenografts. [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 4322. doi:10.1158/1538-7445.AM2013-4322

Isocitrate dehydrogenase 1: what it means to the neurosurgeon: a review

Isocitrate dehydrogenase 1 (IDH1) mutations have been discovered to be frequent and highly conserved in secondary glioblastoma multiforme and lower-grade gliomas. Although IDH1 mutations confer a unique genotype that has been associated with a favorable prognosis, the role of the mutated IDH1 enzyme and its metabolites in tumor initiation and maintenance remains unresolved. However, given that IDH1 mutations are homogeneously expressed and are limited solely to tumor tissue, targeting this mutation could potentially yield novel treatment strategies for patients with glioblastoma multiforme.

Decoupling of DNA damage response signaling from DNA damages underlies temozolomide resistance in glioblastoma cells

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor in adults. Current therapy includes surgery, radiation and chemotherapy with temozolomide (TMZ). Major determinants of clinical response to TMZ include methylation status of the O6-methylguanine-DNA methyltransferase (MGMT) promoter and mismatch repair (MMR) status. Though the MGMT promoter is methylated in 45% of cases, for the first nine months of follow-up, TMZ does not change survival outcome. Furthermore, MMR deficiency makes little contribution to clinical resistance, suggesting that there exist unrecognized mechanisms of resistance. We generated paired GBM cell lines whose resistance was attributed to neither MGMT nor MMR. We show that, responding to TMZ, these cells exhibit a decoupling of DNA damage response (DDR) from ongoing DNA damages. They display methylation-resistant synthesis in which ongoing DNA synthesis is not inhibited. They are also defective in the activation of the S and G2 phase checkpoint. DDR proteins ATM, Chk2, MDC1, NBS1 and gammaH2AX also fail to form discrete foci. These results demonstrate that failure of DDR may play an active role in chemoresistance to TMZ. DNA damages by TMZ are repaired by MMR proteins in a futile, reiterative process, which activates DDR signaling network that ultimately leads to the onset of cell death. GBM cells may survive genetic insults in the absence of DDR. We anticipate that our findings will lead to more studies that seek to further define the role of DDR in ultimately determining the fate of a tumor cell in response to TMZ and other DNA methylators.

Myeloablative temozolomide enhances CD8⁺ T-cell responses to vaccine and is required for efficacy against brain tumors in mice

Temozolomide (TMZ) is an alkylating agent shown to prolong survival in patients with high grade glioma and is routinely used to treat melanoma brain metastases. A prominent side effect of TMZ is induction of profound lymphopenia, which some suggest may be incompatible with immunotherapy. Conversely, it has been proposed that recovery from chemotherapy-induced lymphopenia may actually be exploited to potentiate T-cell responses. Here, we report the first demonstration of TMZ as an immune host-conditioning regimen in an experimental model of brain tumor and examine its impact on antitumor efficacy of a well-characterized peptide vaccine. Our results show that high-dose, myeloablative (MA) TMZ resulted in markedly reduced CD4(+), CD8(+) T-cell and CD4(+)Foxp3(+) TReg counts. Adoptive transfer of naïve CD8(+) T cells and vaccination in this setting led to an approximately 70-fold expansion of antigen-specific CD8(+) T cells over controls. Ex vivo analysis of effector functions revealed significantly enhanced levels of pro-inflammatory cytokine secretion from mice receiving MA TMZ when compared to those treated with a lower lymphodepletive, non-myeloablative (NMA) dose. Importantly, MA TMZ, but not NMA TMZ was uniquely associated with an elevation of endogenous IL-2 serum levels, which we also show was required for optimal T-cell expansion. Accordingly, in a murine model of established intracerebral tumor, vaccination-induced immunity in the setting of MA TMZ-but not lymphodepletive, NMA TMZ-led to significantly prolonged survival. Overall, these results may be used to leverage the side-effects of a clinically-approved chemotherapy and should be considered in future study design of immune-based treatments for brain tumors.

Mutant IDH1 is required for IDH1 mutated tumor cell growth

Frequent somatic hotspot mutations in isocitrate dehydrogenase 1 (IDH1) have been identified in gliomas, acute myeloid leukemias, chondrosarcomas, and other cancers, providing a likely avenue for targeted cancer therapy. However, whether mutant IDH1 protein is required for maintaining IDH1 mutated tumor cell growth remains unknown. Here, using a genetically engineered inducible system, we report that selective suppression of endogenous mutant IDH1 expression in HT1080, a fibrosarcoma cell line with a native IDH1^R132C heterozygous mutation, significantly inhibits cell proliferation and decreases clonogenic potential. Our findings offer insights into changes that may contribute to the inhibition of cell proliferation and offer a strong preclinical rationale for utilizing mutant IDH1 as a valid therapeutic target.

Rindopepimut: anti-EGFRvIII peptide vaccine, oncolytic

Glioblastoma, the most common primary malignant brain tumor, is among the most difficult cancers to treat. Despite the aggressive standard of care, including surgical removal followed by radiotherapy with concomitant and adjuvant chemotherapy, the often sudden onset, diffuse infiltrating nature and highly malignant features of the lesion result in a median overall survival of < 15 months. Currently employed standard- of-care therapy for glioblastoma is nonspecific, leading to premature withdrawal of treatment due to off-target toxicity. Rindopepimut is a peptide-based vaccine that elicits a potent humoral and cellular immune response specifically against cells expressing EGFRvIII, a rearranged, cell-surface tyrosine kinase receptor present exclusively in glioblastoma and other common neoplasms. Several phase I and phase II clinical trials have demonstrated that vaccination with rindopepimut is safe, well tolerated and produces a highly potent immune response that effectively eradicates EGFRvIII-expressing tumor cells, leading to a 73% increase in survival among patients with newly diagnosed glioblastoma. Furthermore, temozolomide-induced lymphopenia enhances the rindopepimut-induced immune response against EGFRvIII, allowing for enhanced vaccination responses in the context of standard-of-care chemotherapy. Rindopepimut is currently undergoing evaluation in a phase III international trial for newly diagnosed glioblastoma and is under clinical investigation for recurrent glioblastoma and pediatric brain stem gliomas.

Reversing the Warburg effect as a treatment for glioblastoma

Glioblastoma multiforme (GBM), like most cancers, possesses a unique bioenergetic state of aerobic glycolysis known as the Warburg effect. Here, we documented that methylene blue (MB) reverses the Warburg effect evidenced by the increasing of oxygen consumption and reduction of lactate production in GBM cell lines. MB decreases GBM cell proliferation and halts the cell cycle in S phase. Through activation of AMP-activated protein kinase, MB inactivates downstream acetyl-CoA carboxylase and decreases cyclin expression. Structure-activity relationship analysis demonstrated that toluidine blue O, an MB derivative with similar bioenergetic actions, exerts similar action in GBM cell proliferation. In contrast, two other MB derivatives, 2-chlorophenothiazine and promethazine, exert no effect on cellular bioenergetics and do not inhibit GBM cell proliferation. MB inhibits cell proliferation in both temozolomide-sensitive and -insensitive GBM cell lines. In a human GBM xenograft model, a single daily dosage of MB does not activate AMP-activated protein kinase signaling, and no tumor regression was observed. In summary, the current study provides the first in vitro proof of concept that reversal of Warburg effect might be a novel therapy for GBM.

Disruption of wild-type IDH1 suppresses D-2-hydroxyglutarate production in IDH1-mutated gliomas

Point mutations at Arg132 of the cytoplasmic NADP(+)-dependent isocitrate dehydrogenase 1 (IDH1) occur frequently in gliomas and result in a gain of function to produce the "oncometabolite" D-2-hydroxyglutarate (D-2HG). The mutated IDH1 allele is usually associated with a wild-type IDH1 allele (heterozygous) in cancer. Here, we identify 2 gliomas that underwent loss of the wild-type IDH1 allele but retained the mutant IDH1 allele following tumor progression from World Health Organization (WHO) grade III anaplastic astrocytomas to WHO grade IV glioblastomas. Intratumoral D-2HG was 14-fold lower in the glioblastomas lacking wild-type IDH1 than in glioblastomas with heterozygous IDH1 mutations. To characterize the contribution of wild-type IDH1 to cancer cell D-2HG production, we established an IDH1-mutated astrocytoma (IMA) cell line from a WHO grade III anaplastic astrocytoma. Disruption of the wild-type IDH1 allele in IMA cells by gene targeting resulted in an 87-fold decrease in cellular D-2HG levels, showing that both wild-type and mutant IDH1 alleles are required for D-2HG production in glioma cells. Expression of wild-type IDH1 was also critical for mutant IDH1-associated D-2HG production in the colorectal cancer cell line HCT116. These insights may aid in the development of therapeutic strategies to target IDH1-mutated cancers.

Mibefradil, a novel therapy for glioblastoma multiforme: cell cycle synchronization and interlaced therapy in a murine model

Glioblastoma multiforme (GBM) is a devastating disease with a dismal prognosis and a very limited response to treatment. The current standard of care for GBM usually consists of surgery, radiation and chemotherapy with the alkylating agent temozolomide, although resistance to this drug is common. The predominant mechanism of action of temozolomide is methylation of guanine residues although this can be reversed by methylguanine methyltransferase (MGMT) as well as other DNA repair systems. The presence of methylguanine causes abortive DNA synthesis with subsequent apoptosis. This suggests that the closer a particular cell is to S phase when it is exposed to temozolomide the more likely it is to die since repair enzymes will have had less time to reverse the damage. T type calcium channel inhibitors can stop the entry of extracellular calcium that is necessary for transit past the G1/S boundary. As a result, T type calcium channel blockers can slow the growth of cancer cells, but do not generally kill them. Though slowing the growth of cancer cells is important in its own right, it also provides a therapeutic strategy in which a T type channel blocker is administered then withdrawn followed by the administration of temozolomide. We show here that imposing this cell cycle restriction increases the efficacy of subsequently administered temozolomide in immunodeficient mice bearing various human GBM xenograft lines. We also present data that MGMT expressing GBM tumors, which are temozolomide resistant, may be rendered more sensitive by this strategy.

Subgroup-specific structural variation across 1,000 medulloblastoma genomes

Medulloblastoma, the most common malignant paediatric brain tumour, is currently treated with nonspecific cytotoxic therapies including surgery, whole-brain radiation, and aggressive chemotherapy. As medulloblastoma exhibits marked intertumoural heterogeneity, with at least four distinct molecular variants, previous attempts to identify targets for therapy have been underpowered because of small samples sizes. Here we report somatic copy number aberrations (SCNAs) in 1,087 unique medulloblastomas. SCNAs are common in medulloblastoma, and are predominantly subgroup-enriched. The most common region of focal copy number gain is a tandem duplication of SNCAIP, a gene associated with Parkinson's disease, which is exquisitely restricted to Group 4α. Recurrent translocations of PVT1, including PVT1-MYC and PVT1-NDRG1, that arise through chromothripsis are restricted to Group 3. Numerous targetable SCNAs, including recurrent events targeting TGF-β signalling in Group 3, and NF-κB signalling in Group 4, suggest future avenues for rational, targeted therapy.

A heterozygous IDH1R132H/WT mutation induces genome-wide alterations in DNA methylation

Monoallelic point mutations of the NADP⁺-dependent isocitrate dehydrogenases IDH1 and IDH2 occur frequently in gliomas, acute myeloid leukemias, and chondromas, and display robust association with specific DNA hypermethylation signatures. Here we show that heterozygous expression of the IDH1^R132H allele is sufficient to induce the genome-wide alterations in DNA methylation characteristic of these tumors. Using a gene-targeting approach, we knocked-in a single copy of the most frequently observed IDH1 mutation, R132H, into a human cancer cell line and profiled changes in DNA methylation at over 27,000 CpG dinucleotides relative to wild-type parental cells. We find that IDH1^R132H/WT mutation induces widespread alterations in DNA methylation, including hypermethylation of 2010 and hypomethylation of 842 CpG loci. We demonstrate that many of these alterations are consistent with those observed in IDH1-mutant and G-CIMP+ primary gliomas and can segregate IDH wild-type and mutated tumors as well as those exhibiting the G-CIMP phenotype in unsupervised analysis of two primary glioma cohorts. Further, we show that the direction of IDH1^R132H/WT-mediated DNA methylation change is largely dependent upon preexisting DNA methylation levels, resulting in depletion of moderately methylated loci. Additionally, whereas the levels of multiple histone H3 and H4 methylation modifications were globally increased, consistent with broad inhibition of histone demethylation, hypermethylation at H3K9 in particular accompanied locus-specific DNA hypermethylation at several genes down-regulated in IDH1^R132H/WT knock-in cells. These data provide insight on epigenetic alterations induced by IDH1 mutations and support a causal role for IDH1^R132H/WT mutants in driving epigenetic instability in human cancer cells.

Central nervous system

Several different types of tumors, benign and malignant, have been identified in the central nervous system (CNS). The prognoses for these tumors are related to several factors, such as the age of the patient and the location and histology of the tumor. In adults, about half of all CNS tumors are malignant, whereas in pediatric patients, more than 75% are malignant. For most benign CNS tumors that require treatment, neurosurgeons can offer curative resections or at least provide significant relief from mass effect. Unfortunately, we still lack effective treatments for most primary and secondary malignant CNS tumors. However, the past decade has witnessed an explosion in the understanding of the early molecular events in malignant primary CNS tumors, and for the first time in history, oncologists are seeing that a plethora of new therapies targeting these molecular events are being tested in clinical trials. There is hope on the horizon for the fight against these deadly tumors. The distribution of CNS tumors by location has remained constant for numerous years. The majority of primary CNS tumors arise in the major cortical lobes. Twenty nine percent of primary CNS tumors arise from the dural meninges that encase the CNS structures. The vast majority of these are meningiomas, of which over 90% are benign. About 10% of primary CNS tumors are found in the sella turcica region, where the pituitary gland resides. Other much less common sites of primary CNS tumors include the pineal region, ventricular system, cerebellum, brain stem, cranial nerves, and spinal cord. The distribution of CNS tumors by histology has seen a slight increase in more malignant tumors over the past decade, possibly due to increased neuroimaging practices or environmental exposures. Arising from glial cells, gliomas represent over 36% of all primary CNS tumors and consist of astrocytomas, oligodendrogliomas, ependymomas, mixed gliomas, and neuroepithelial tumors. The benign meningiomas make up 32% of primary CNS tumors, followed by nerve sheath tumors and pituitary tumors. Primary CNS lymphomas, embryonal tumors, and craniopharyngiomas are uncommon. The most common gliomas are astrocytomas, and these tumors are typically classified by the World Health Organization (WHO) as Grades I through IV. Grade IV, the most malignant grade of astrocytoma, includes glioblastoma multiforme (GBM), the most common malignant primary CNS glioma in adults, which represents 51% of all CNS gliomas. GBM is unfortunately the most challenging to effectively treat and has the worst patient survival. This chapter is therefore primarily devoted to the current understanding of this topic. Here we describe the molecular and cellular events associated with malignant glioma initiation and progression. We also review the importance of glioma stem cell biology and tumor immunology in early gliomagenesis. In addition, we present a brief description of the most common malignant primary CNS glioma in pediatric patients - medulloblastoma, as well as familial cancer syndromes that include gliomas as part of the syndrome.

Frequent ATRX, CIC, FUBP1 and IDH1 mutations refine the classification of malignant gliomas

Mutations in the critical chromatin modifier ATRX and mutations in CIC and FUBP1, which are potent regulators of cell growth, have been discovered in specific subtypes of gliomas, the most common type of primary malignant brain tumors. However, the frequency of these mutations in many subtypes of gliomas, and their association with clinical features of the patients, is poorly understood. Here we analyzed these loci in 363 brain tumors. ATRX is frequently mutated in grade II-III astrocytomas (71%), oligoastrocytomas (68%), and secondary glioblastomas (57%), and ATRX mutations are associated with IDH1 mutations and with an alternative lengthening of telomeres phenotype. CIC and FUBP1 mutations occurred frequently in oligodendrogliomas (46% and 24%, respectively) but rarely in astrocytomas or oligoastrocytomas ( more than 10%). This analysis allowed us to define two highly recurrent genetic signatures in gliomas: IDH1/ATRX (I-A) and IDH1/CIC/FUBP1 (I-CF). Patients with I-CF gliomas had a significantly longer median overall survival (96 months) than patients with I-A gliomas (51 months) and patients with gliomas that did not harbor either signature (13 months). The genetic signatures distinguished clinically distinct groups of oligoastrocytoma patients, which usually present a diagnostic challenge, and were associated with differences in clinical outcome even among individual tumor types. In addition to providing new clues about the genetic alterations underlying gliomas, the results have immediate clinical implications, providing a tripartite genetic signature that can serve as a useful adjunct to conventional glioma classification that may aid in prognosis, treatment selection, and therapeutic trial design.

Aberrant Otx2 expression enhances migration and induces ectopic proliferation of hindbrain neuronal progenitor cells

Dysregulation of Otx2 is a hallmark of the pediatric brain tumor medulloblastoma, yet its functional significance in the establishment of these tumors is unknown. Here we have sought to determine the functional consequences of Otx2 overexpression in the mouse hindbrain to characterize its potential role in medulloblastoma tumorigenesis and identify the cell types responsive to this lineage-specific oncogene. Expression of Otx2 broadly in the mouse hindbrain resulted in the accumulation of proliferative clusters of cells in the cerebellar white matter and dorsal brainstem of postnatal mice. We found that brainstem ectopia were derived from neuronal progenitors of the rhombic lip and that cerebellar ectopia were derived from granule neuron precursors (GNPs) that had migrated inwards from the external granule layer (EGL). These hyperplasias exhibited various characteristics of medulloblastoma precursor cells identified in animal models of Shh or Wnt group tumors, including aberrant localization and altered spatiotemporal control of proliferation. However, ectopia induced by Otx2 differentiated and dispersed as the animals reached adulthood, indicating that factors restricting proliferative lifespan were a limiting factor to full transformation of these cells. These studies implicate a role for Otx2 in altering the dynamics of neuronal progenitor cell proliferation.

Abstract 3352: The medulloblastoma oncogene Otx2 enhances migration and permits ectopic proliferation of neuronal progenitor cells of the cerebellum and brainstem

Medulloblastoma is the most common malignant brain tumor in children. Despite a thorough understanding of the genetic underpinnings of this tumor, the pathogenesis of some variants of medulloblastoma, in particular the non-Shh/non-Wnt subtypes, is poorly understood. One of the most common genetic aberrations in non-Shh/non-Wnt medulloblastomas is copy number gain of the homeobox transcription factor OTX2. Here we have characterized mice engineered to ectopically express Otx2 in the hindbrain to identify the functional consequences of this subtype-specific genetic insult. Otx2 expression induced accumulation of proliferative hyperplasias in the cerebellar white matter and dorsal brainstem that were reminiscent of preneoplastic cells identified in other animal models of medulloblastoma. These hyperplasias were comprised of neuronal progenitor cells that had migrated away from their mitogenic niches. As animals reached adulthood, ectopic cells exited the cell cycle and differentiated, indicating that factors limiting proliferative lifespan prevented full transformation by Otx2. Comparison of the effect of Otx2 with activation of the Shh or Wnt pathways, which occur in distinct subtypes of medulloblastoma, revealed overlap of responsive cell types but distinct developmental processes involved. While activation of the Shh or Wnt pathways give rise to sustained proliferation of neuronal progenitor cells at their mitogenic niches, we found that Otx2 permitted or enhanced migration of these cells away from these niches and induced ectopic proliferation. These findings identify a role for Otx2 overexpression in altering spatiotemporal control of neuronal progenitor cell proliferation and implicate a relationship between the cells of origin of non-Shh/non-Wnt medulloblastomas and those of other medulloblastoma subtypes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3352. doi:1538-7445.AM2012-3352