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Self-renewal is a crucial property of glioblastoma cells that is enabled by the choreographed functions of chromatin regulators and transcription factors. Identifying targetable epigenetic mechanisms of self-renewal could therefore represent an important step toward developing effective treatments for this universally lethal cancer. Here we uncover an epigenetic axis of self-renewal mediated by the histone variant macroH2A2. With omics and functional assays deploying patient-derived in vitro and in vivo models, we show that macroH2A2 shapes chromatin accessibility at enhancer elements to antagonize transcriptional programs of self-renewal. macroH2A2 also sensitizes cells to small molecule-mediated cell death via activation of a viral mimicry response. Consistent with these results, our analyses of clinical cohorts indicate that high transcriptional levels of this histone variant are associated with better prognosis of high-grade glioma patients. Our results reveal a targetable epigenetic mechanism of self-renewal controlled by macroH2A2 and suggest additional treatment approaches for glioblastoma patients.

Purpose: Glioblastoma is one of the most lethal cancers in humans, and with existing therapy, survival remains at 14.6 months. Current barriers to successful treatment include their infiltrative behavior, extensive tumor heterogeneity, and the presence of a stem-like population of cells, termed brain tumor–initiating cells (BTIC) that confer resistance to conventional therapies.Experimental Design: To develop therapeutic strategies that target BTICs, we focused on a repurposing approach that explored already-marketed (clinically approved) drugs for therapeutic potential against patient-derived BTICs that encompass the genetic and phenotypic heterogeneity of glioblastoma observed clinically.Results: Using a high-throughput in vitro drug screen, we found that montelukast, clioquinol, and disulfiram (DSF) were cytotoxic against a large panel of patient-derived BTICs. Of these compounds, disulfiram, an off-patent drug previously used to treat alcoholism, in the presence of a copper supplement, showed low nanomolar efficacy in BTICs including those resistant to temozolomide and the highly infiltrative quiescent stem-like population. Low dose DSF-Cu significantly augmented temozolomide activity in vitro, and importantly, prolonged in vivo survival in patient-derived BTIC models established from both newly diagnosed and recurrent tumors. Moreover, we found that in addition to acting as a potent proteasome inhibitor, DSF-Cu functionally impairs DNA repair pathways and enhances the effects of DNA alkylating agents and radiation. These observations suggest that DSF-Cu inhibits proteasome activity and augments the therapeutic effects of DNA-damaging agents (temozolomide and radiation).Conclusions: DSF-Cu should be considered as an adjuvant therapy for the treatment of patients with glioblastoma in both newly diagnosed and recurrent settings. Clin Cancer Res; 22(15); 3860–75. ©2016 AACR.

Purpose: Rhabdoid tumors are highly aggressive pediatric tumors that are usually refractory to available treatments. The purpose of this study was to evaluate the therapeutic potential of two oncolytic viruses, myxoma virus (MV) and an attenuated vesicular stomatitis virus (VSVΔM51), in experimental models of human rhabdoid tumor.Experimental Design: Four human rhabdoid tumor cell lines were cultured in vitro and treated with live or inactivated control virus. Cytopathic effect, viral gene expression, infectious viral titers, and cell viability were examined at various time points after infection. To study viral oncolysis in vivo, human rhabdoid tumor cells were implanted s.c. in the hind flank or intracranially in CD-1 nude mice and treated with intratumoral (i.t.) or i.v. injections of live or UV-inactivated virus. Viral distribution and effects on tumor size and survival were assessed.Results: All rhabdoid tumor cell lines tested in vitro were susceptible to productive lethal infections by MV and VSVΔM51. I.t. injection of live MV or VSVΔM51 dramatically reduced the size of s.c. rhabdoid tumor xenografts compared with control animals. I.v. administration of VSVΔM51 or i.t. injection of MV prolonged the median survival of mice with brain xenografts compared with controls (VSVΔM51: 25 days versus 21 days, log-rank test, P = 0.0036; MV: median survival not reached versus 21 days, log-rank test, P = 0.0007). Most of the MV-treated animals (4 of 6; 66.7%) were alive and apparently “cured” when the experiment was arbitrarily ended (>180 days).Conclusions: These results suggest that VSVΔM51 and MV could be novel effective therapies against human rhabdoid tumor.

Figure S1: Preclinical assessment of clioquinol. Figure S2: Preclinical assessment of montelukast. Figure S3: Secondary validation of compounds identified via HTS. Figure S4: Sensitivity of BTICs to TMZ. Figure S5: Copper is required for Disulfiram-mediated cell killing. Figure S6: Cell Viability and Apoptosis in the presence of DSF-Cu. Figure S7: Efficacy to DSF-Cu is independent of MGMT expression. Figure S8: Inhibition of proteasome activity by DSF-Cu. Figure S9: DSF-Cu in combination with TMZ prolongs survival in vivo. Figure S10: DSF-Cu mediated apoptosis in vivo. Table S1: Summary of BTIC Molecular Characterization. Table S2: Summary of Compound Priortization. Table S3: Down regulation of DNA repair genes by DSF-Cu.

Supplementary Figure S1 from Oncolytic Efficacy of Recombinant Vesicular Stomatitis Virus and Myxoma Virus in Experimental Models of Rhabdoid Tumors

Supplementary Figures 1-7 from Myxoma Virus Virotherapy for Glioma in Immunocompetent Animal Models: Optimizing Administration Routes and Synergy with Rapamycin

Legend for Supplementary Figures S1-S10.

Immunophenotyping of the K1492 glioma microenvironment in response to sterile injury (S1); Immunophenotyping of the K1492 glioma microenvironment after Myxoma virus treatment (S2); Virus infected areas of K1492 tumours are accompanied by polymorphonuclear cell infiltration (S3); K1861 and Spontaneous NPcis gliomas in C57Bl/6 mice have significant microglia and/or GIM recruitment (S4); Non-tumour bearing CCR2-deficient animals are only slightly impaired in clearing MYXV (S5); CCR2-deficient mice have an exaggerated recruitment of NK and T cells to the K1492 glioma in response to Myxoma treatment (S6); Minocycline administration mimics CCR2-null viral clearance kinetics but does not result in a survival advantage (S7); K1492 tumours in IL2Rγ mice are significantly depleted of NK and T cell populations (S8); Non-tumour bearing IL2Rγ-deficient animals are impaired in clearing MYXV (S9); Single low-dose cyclophosphamide combined with Myxoma treatment did result in improved treatment efficacy or viral infection (S10).

Supplementary Figure Legends 1-7 from Myxoma Virus Virotherapy for Glioma in Immunocompetent Animal Models: Optimizing Administration Routes and Synergy with Rapamycin

Central nervous system (CNS) atypical teratoid/rhabdoid tumor (AT/RT) is a rare, aggressive tumor that most often affects very young children. The common decisive molecular defect in AT/RT has been shown to be a single genetic alteration, i.e., the loss of hSNF5 gene that encodes for a subunit of the SWI/SNF complex that modulates chromatin remodeling activities. As a result, AT/RT cells display unregulated cell proliferation due to the dysfunction of an important epigenetic control. We have previously demonstrated the preclinical efficacy of the oncolytic double-deleted vaccinia virus (VVDD) against AT/RT. Here we report the establishment of a modified VVDD engineered to express wild type hSNF5 gene. We show that this reconstructed vaccinia virus retains comparable infectivity and in vitro cytotoxicity of the parent strain. However, in addition, hSNF5-arming of VVDD results in a decreased cell cycle S phase population and down-regulation of cyclin D1. These findings suggest that hSNF5-arming of VVDD may increase the efficacy in the treatment of AT/RT and validates, as a proof-of-concept, an experimental approach to enhance the effective use of novel modified oncolytic viruses in the treatment of tumors with loss of a tumor suppressor gene function.

Sarcomas are a heterogeneous group of cancers occurring in tissues derived from the mesenchyme. Despite improved treatment strategies that include surgery and broad-based chemotherapeutics, survival of patients with sarcoma remains unchanged in the last 40 years with 5-year overall survival less than 25%. In part, this high rate of mortality can be attributed to the development of pulmonary metastases, a process that occurs in up to 50% of patients. We propose that preventing the occurrence or growth of lung metastases can improve the outcome for many of these patients. Our growing understanding of the dynamic relationship between inflammation and cancer has led to the investigation of anti-inflammatory approaches to treat cancer, including metastasis. Specifically, recent studies suggest a role for neutrophils in cancer metastasis, identifying a promising target for therapeutic intervention. The aim of the present study is to investigate the role of myeloid cells in the metastatic process, and their potential to act as therapeutic targets during the development of lung metastases. Herein we used human and syngeneic osteosarcoma lung metastatic models together with in vitro assays to assess the role of neutrophils in this process. Our results demonstrate that neutrophils are essential to facilitate the development of osteosarcoma pulmonary metastases and that treatment with the novel anti-inflammatory agent GM1-targeted linoleate-containing TLR2 ligand (GML), known to inhibit neutrophil recruitment, diminishes their occurrence. Overall, our results suggest that neutrophils play a role in mediating osteosarcoma lung metastasis and reveal GML as a potential anti-metastatic drug therapy. Citation Format: Liane Babes, Lauren A. Wierenga, Ngoc-Ha Dan, Xueqing Lun, Kimberly-Ann R. Goring, Stephen M. Robbins, Donna L. Senger. The novel anti-inflammatory agent GML (GM1-targeted linoleate-containing TLR2 ligand) inhibits sarcoma metastasis to the lung [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A014.

Alveolar soft part sarcoma (ASPS) is a rare pediatric malignancy which has characteristically poor clinical outcomes due to a propensity to metastasize along with a complete lack of chemotherapeutic options. One additional difficulty of this rare tumor is an absence of established in vivo models. Here, we describe the establishment of a patient derived xenograft model (PDX), and corresponding cell line, from the lung metastases of a 14-year-old female diagnosed with ASPS. Using this model, we performed a drug screen, from which the proteasome inhibitor carfilzomib inhibited tumor cell viability and growth in vitro and in vivo. To further elucidate factors implicated in tumor progression and chemotherapy resistance, we characterized the microenvironment and secretome of the ASPS PDX. In keeping with recent literature showing large numbers of tumor associated macrophage (TAMs) in ASPS, we found that 96% of the myeloid cells present in the PDX were TAMS, with 35% taking on a pro-tumor phenotype. Further, factors secreted by the tumor microenvironment largely support immune cell recruitment and pro-tumor phenotypes. Interestingly, in vivo assessment demonstrates that Iba1+ macrophage populations decrease by 60% with carfilzomib treatment. This prompted investigation into the potential impact of TAMs on ASPS growth and progression, and if they are implicated in the therapeutic response to carfilzomib. Based on preliminary findings that carfilzomib targets the pro-tumor phenotypic states of bone marrow derived macrophage in vitro, we hypothesize that carfilzomib alters the recruitment and phenotype of TAMs, decreasing tumor cell viability in vitro, and thus tumor burden in vivo. Citation Format: Alexis M. Philippot, Ngoc Ha Dang, Shyam V. Menon, Jennifer Bourdage, Xueqing Lun, Bo Young Ahn, Stephen M. Robbins, Donna L. Senger. Defining the microenvironment of alveolar soft part sarcoma & it’s role in therapeutic outcomes [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A006.

SUMMARYSelf-renewal is a crucial property of glioblastoma cells and is enabled by the choreographed function of chromatin regulators and transcription factors. Identifying targetable epigenetic mechanisms of self-renewal could represent an important step toward developing new and effective treatments for this universally lethal cancer. Here we uncover a targetable epigenetic axis of self-renewal mediated by the histone variant macroH2A2. Using patient-derived in vitro and in vivo models, we show that macroH2A2 has a direct role in shaping chromatin accessibility at enhancer elements to antagonize transcriptional programs of self-renewal. Pharmaceutical inhibition of the chromatin remodeler Menin increased macroH2A2 levels and repressed self- renewal. Our results reveal a targetable epigenetic mechanism of self-renewal controlled by macroH2A2 and suggest new treatment approaches for glioblastoma patients.SIGNIFICANCEGlioblastoma is an incurable brain cancer. Malignant self-renewing cells have been shown to drive tumor growth, to be refractory to current treatment approaches and to seed relapses, which ultimately prove lethal. Identifying new and targetable mechanisms associated with self-renewal could be a fundamental first step in designing effective therapies that slow or prevent glioblastoma relapses. Using patient-derived models of glioblastoma, we deployed epigenomic approaches and functional assays to define the role of the histone variant macroH2A2 in repressing self-renewal. We identified compounds that increase macroH2A2 levels and repress self-renewal, including a Menin inhibitor. As Menin inhibitors are being tested in clinical trials, these compounds could be used in new therapeutic paradigms to target self-renewing cell populations in glioblastoma.

Glioblastoma remains one of the most fatal cancers in humans. Despite the advent of optimal surgical resection, guided radiotherapy, and the addition of chemotherapy (temozolomide; TMZ) average survival remains at a dismal 14.6 months with very few long-term survivors. In this chapter we will discuss the various mouse and human glioma model systems that are used and the generation of in vivo selected models that recapitulate TMZ resistance together with the promise of repurposing disulfiram in the setting of relapsed glioblastoma. In addition, we will move beyond the sole targeting of the glioma cells and discuss the impact of the tumor microenvironment both at the level of the normal cellular repertoire that includes resident and recruited immune cells and the molecular and biophysical properties that contribute to gliomagenesis and therapeutic resistance where exciting new and novel therapeutic options are emerging.

Glioblastoma multiforme (GBM) is the most deadly brain tumor, and currently lacks effective treatment options. Brain tumor-initiating cells (BTICs) and orthotopic xenografts are widely used in investigating GBM biology and new therapies for this aggressive disease. However, the genomic characteristics and molecular resemblance of these models to GBM tumors remain undetermined. We used massively parallel sequencing technology to decode the genomes and transcriptomes of BTICs and xenografts and their matched tumors in order to delineate the potential impacts of the distinct growth environments. Using data generated from whole-genome sequencing of 201 samples and RNA sequencing of 118 samples, we show that BTICs and xenografts resemble their parental tumor at the genomic level but differ at the mRNA expression and epigenomic levels, likely due to the different growth environment for each sample type. These findings suggest that a comprehensive genomic understanding of in vitro and in vivo GBM model systems is crucial for interpreting data from drug screens, and can help control for biases introduced by cell-culture conditions and the microenvironment in mouse models. We also found that lack of MGMT expression in pretreated GBM is linked to hypermutation, which in turn contributes to increased genomic heterogeneity and requires new strategies for GBM treatment.

OBJECTIVEThe aim of this study was to demonstrate the in vivo safety and antitumor effect of a novel recombinant vesicular stomatitis virus (VSV): G protein less (GLESS)–fusion-associated small transmembrane (FAST)–VSV.METHODSViral infection efficiency and cell proliferation were detected using an inverted fluorescence microscope and alarmaBlue assay, respectively. To evaluate the safety of the virus, different doses of GLESS-FAST-VSV and a positive control virus (VSV∆M51) were injected into normal F344 rats and C57BL/6 mice, and each animal’s weight, survival time, and pathological changes were examined on the following day. To evaluate the efficacy of the virus, RG2 and GL261 cells were used to construct rat and mouse glioma models, respectively, via a stereotactic method. After multiple intratumoral injections of the virus, tumor growth (size) and the survival time of the animals were observed.RESULTSIn vitro experiments showed that GLESS-FAST-VSV could infect and kill brain tumor cells and had less toxic effects on normal cells. After direct injection of GLESS-FAST-VSV into the animal brains, all animals tolerated the virus well, and no animal death, encephalitis, or ventriculitis was observed. In contrast, all animals that received brain injections of VSV∆M51 in the brain died. Moreover, multiple injections of GLESS-FAST-VSV in brain tumors significantly prolonged the survival of normal-immunity animals harboring brain tumors.CONCLUSIONSGLESS-FAST-VSV exhibited little neurotoxicity and could be injected directly into the tumor to effectively inhibit tumor growth and prolong the survival of normal-immunity animals, laying a theoretical foundation for the early application of such viruses in clinical trials.

Purpose: Glioblastoma is one of the most lethal cancers in humans, and with existing therapy, survival remains at 14.6 months. Current barriers to successful treatment include their infiltrative behavior, extensive tumor heterogeneity, and the presence of a stem-like population of cells, termed brain tumor–initiating cells (BTIC) that confer resistance to conventional therapies. Experimental Design: To develop therapeutic strategies that target BTICs, we focused on a repurposing approach that explored already-marketed (clinically approved) drugs for therapeutic potential against patient-derived BTICs that encompass the genetic and phenotypic heterogeneity of glioblastoma observed clinically. Results: Using a high-throughput in vitro drug screen, we found that montelukast, clioquinol, and disulfiram (DSF) were cytotoxic against a large panel of patient-derived BTICs. Of these compounds, disulfiram, an off-patent drug previously used to treat alcoholism, in the presence of a copper supplement, showed low nanomolar efficacy in BTICs including those resistant to temozolomide and the highly infiltrative quiescent stem-like population. Low dose DSF-Cu significantly augmented temozolomide activity in vitro, and importantly, prolonged in vivo survival in patient-derived BTIC models established from both newly diagnosed and recurrent tumors. Moreover, we found that in addition to acting as a potent proteasome inhibitor, DSF-Cu functionally impairs DNA repair pathways and enhances the effects of DNA alkylating agents and radiation. These observations suggest that DSF-Cu inhibits proteasome activity and augments the therapeutic effects of DNA-damaging agents (temozolomide and radiation). Conclusions: DSF-Cu should be considered as an adjuvant therapy for the treatment of patients with glioblastoma in both newly diagnosed and recurrent settings. Clin Cancer Res; 22(15); 3860–75. ©2016 AACR.

Despite extensive molecular characterization, human glioblastoma remains a fatal disease with survival rates measured in months. Little improvement is seen with standard surgery, radiotherapy and chemotherapy. Clinical progress is hampered by the inability to detect and target glioblastoma disease reservoirs based on a diffuse invasive pattern and the presence of molecular and phenotypic heterogeneity. The goal of this study was to target the invasive and stem-like glioblastoma cells that evade first-line treatments using agents capable of delivering imaging enhancers or biotherapeutic cargo. To accomplish this, a combinatorial phage display library was biopanned against glioblastoma cell model systems that accurately recapitulate the intra- and inter-tumor heterogeneity and infiltrative nature of the disease. Candidate peptides were screened for specificity and ability to target glioblastoma cells in vivo. Cargo-conjugated peptides delivered contrast-enhancing agents to highly infiltrative tumor populations in intracranial xenograft models without the obvious need for blood brain barrier disruption. Simultaneous use of five independent targeting peptides provided greater coverage of this complex tumor and selected peptides have the capacity to deliver a therapeutic cargo (oncolytic virus VSVΔM51) to the tumor cells in vivo. Herein, we have identified a series of peptides with utility as an innovative platform to assist in targeting glioblastoma for the purpose of diagnostic or prognostic imaging, image-guided surgery, and/or improved delivery of therapeutic agents to glioblastoma cells implicated in disease relapse.

Small-molecule inhibitor of apoptosis (IAP) antagonists, called Smac mimetic compounds (SMCs), sensitize tumours to TNF-α-induced killing while simultaneously blocking TNF-α growth-promoting activities. SMCs also regulate several immunomodulatory properties within immune cells. We report that SMCs synergize with innate immune stimulants and immune checkpoint inhibitor biologics to produce durable cures in mouse models of glioblastoma in which single agent therapy is ineffective. The complementation of activities between these classes of therapeutics is dependent on cytotoxic T-cell activity and is associated with a reduction in immunosuppressive T-cells. Notably, the synergistic effect is dependent on type I IFN and TNF-α signalling. Furthermore, our results implicate an important role for TNF-α-producing cytotoxic T-cells in mediating the anti-cancer effects of immune checkpoint inhibitors when combined with SMCs. Overall, this combinatorial approach could be highly effective in clinical application as it allows for cooperative and complimentary mechanisms in the immune cell-mediated death of cancer cells., Smac mimetics sensitize cancer cells to the extrinsic cell death pathway and stimulate anti-tumour immunity. In this study, the authors show that Smac mimetics can synergize with immune checkpoint inhibitors to control tumour growth in mouse cancer models, including aggressive CNS tumours, in a cytotoxic CD8+ T-cell- and TNFα-dependent manner.

Oncolytic virus therapy is being evaluated in clinical trials for human glioma. While it is widely assumed that the immune response of the patient to the virus infection limits the utility of the therapy, investigations into the specific cell type(s) involved in this response have been performed using nonspecific pharmacologic inhibitors or allogeneic models with compromised immunity. To identify the immune cells that participate in clearing an oncolytic infection in glioma, we used flow cytometry and immunohistochemistry to immunophenotype an orthotopic glioma model in immunocompetent mice after Myxoma virus (MYXV) administration. These studies revealed a large resident microglia and macrophage population in untreated tumors, and robust monocyte, T-, and NK cell infiltration 3 days after MYXV infection. To determine the role on the clinical utility of MYXV therapy for glioma, we used a combination of knockout mouse strains and specific immunocyte ablation techniques. Collectively, our experiments identify an important role for tumor-resident myeloid cells and overlapping roles for recruited NK and T cells in the clearance and efficacy of oncolytic MYXV from gliomas. Using a cyclophosphamide regimen to achieve lymphoablation prior and during MYXV treatment, we prevented treatment-induced peripheral immunocyte recruitment and, surprisingly, largely ablated the tumor-resident macrophage population. Virotherapy of cyclophosphamide-treated animals resulted in sustained viral infection within the glioma as well as a substantial survival advantage. This study demonstrates that resistance to MYXV virotherapy in syngeneic glioma models involves a multifaceted cellular immune response that can be overcome with cyclophosphamide-mediated lymphoablation. Cancer Res; 74(24); 7260–73. ©2014 AACR.

Background. Intratumoral heterogeneity in glioblastoma multiforme (GBM) poses a significant barrier to therapy in certain subpopulation such as the tumorinitiating cell population, being shown to be refractory to conventional therapies. Oncolytic virotherapy has the potential to target multiple compartments within the tumor and thus circumvent some of the barriers facing conventional therapies. In this study, we investigate the oncolytic potential of myxoma virus (MYXV) alone and in combination with rapamycin in vitro and in vivo using human brain tumor‐initiating cells (BTICs). Methods. We cultured fresh GBM specimens as neurospheres and assayed their growth characteristics in vivo. We then tested the susceptibility of BTICs to MYXV infection with or without rapamycin in vitro and assessed viral biodistribution/survival in vivo in orthotopic xenografts. Results. The cultured neurospheres were found to retain stem cell markers in vivo, and they closely resembled human infiltrative GBM. In this study we determined that (i) all patient-derived BTICs tested, including those resistant to temozolomide, were susceptible to MYXV replication and killing in vitro; (ii) MYXV replicated within BTICs in vivo, and intratumoral administration of MYXV significantly prolonged survival of BTIC-bearing mice; (iii) combination therapy with MYXV and rapamycin improved antitumor activity, even in mice bearing “advanced” BTIC tumors; (iv) MYXV treatment decreased expression of stem cell markers in vitro and in vivo. Conclusions. Our study suggests that MYXV in combination with rapamycin infects and kills both the BTICs and the differentiated compartments of GBM and may be an effective treatment even in TMZ-resistant patients.

Background Malignant glioma still has a poor prognosis and remains incurable. Although temozolomide (TMZ) has demonstrated antitumor activity, its use recently has been halted because of some patients’ resistance to this drug. New treatments are desperately needed. An oncolytic virus (virotherapy) is being developed as a novel cancer therapy. We have previously reported that recombinant Vesicular Stomatitis Virus (VSV-ΔM51) and double deleted Vaccinia Virus (vvDD) infected and killed glioma cell lines in vitro and prolonged survival in animal glioma models. As a proposed ex vivo test, the oncolytic potential of VSV-ΔM51 and vvDD in the established human brain tumor stem cells (BTSCs) and the differentiated cells from fresh brain tumor tissues in vitro were further investigated. Methods BTSCs from fresh surgical glioblastoma multiforme (GBM) specimens were isolated and cultured, and the characterization of BTSCs were tested. The sensitivity of BTSCs to TMZ and the susceptibility of TMZ resistant BTSCs and their differentiated cells to both oncolytic viruses were examined. Results The BTSC spheres cultured had all the characteristics of stem cells. The GFP-labeled VSV-ΔM51 and vvDD could infect TMZ resistant BTSCs and cause cytopathic effects. The VSV-ΔM51and vvDD inhibited the self-renewal activity of TMZ resistant BTSCs. And the VSV-ΔM51and vvDD also infected and caused cytopathic effects in differentiated BTSCs. Conclusion VSV-ΔM51and vvDD could infect and kill both the TMZ resistant BTSCs and the differentiated compartments of GBMs in vitro, suggesting that they may be an effective treatment supplement for GBM therapy, particularly for TMZ resistant GBM patients.

The purpose of this study was to investigate the oncolytic potential of the recombinant, granulocyte macrophage colony-stimulating factor (GM-CSF)-expressing vaccinia virus (VV) JX-594 in experimental malignant glioma (MGs) in vitro and in immunocompetent rodent models. We have found that JX-594 killed all MG cell lines tested in vitro. Intratumoral (i.t.) administration of JX-594 significantly inhibited tumor growth and prolonged survival in rats-bearing RG2 intracranial (i.c.) tumors and mice-bearing GL261 brain tumors. Combination therapy with JX-594 and rapamycin significantly increased viral replication and further prolonged survival in both immunocompetent i.c. MG models with several animals considered “cured” (three out of seven rats >120 days, terminated experiment). JX-594 infected and killed brain tumor-initiating cells (BTICs) from patient samples grown ex vivo, and did so more efficiently than other oncolytic viruses MYXV, Reovirus type-3, and VSVΔM51. Additional safety/toxicity studies in nontumor-bearing rodents treated with a supratherapeutic dose of JX-594 demonstrated GM-CSF-dependent inflammation and necrosis. These results suggest that i.c. administered JX-594 triggers a predictable GM-CSF-mediated inflammation in murine models. Before proceeding to clinical trials, JX-594 should be evaluated in the brains of nonhuman primates and optimized for the viral doses, delivery routes as well as the combination agents (e.g., mTOR inhibitors).

The concept of oncolytic viral therapy has a century-old history, but only within the last 20 years have oncolytic viruses been considered for the treatment of brain cancers. Viruses such as herpes, measles, and vaccinia have all been known to cause devastating cases of neurological disease in humans, yet these 'scourges' are now being harnessed in such a way that they prove very useful as cancer therapeutics. There have been 8 formal clinical trials and 3 case studies using oncolytic viruses to treat malignant glioma patients. Although some success has been reached with oncolytic therapy, overall it has fallen short of expectations. In this review we analyze the results of these trials and bring to light some of the limitations and pitfalls of this therapy, as well as present some promising preclinical work that has been proposed to circumvent such problems.

Primary glial tumors of the central nervous system, most commonly glioblastoma multiforme (GBM), are aggressive lesions with a dismal prognosis. Despite identification and isolation of human brain tumor stem cells (BTSCs), characteristics that distinguish BTSCs from neural stem cells remain to be elucidated. We cultured cells isolated from gliomas, using the neurosphere culture system, to understand their growth requirements. Both CD133+ and CD133− adult GBM BTSCs proliferated in the absence of exogenous mitogenic stimulation and gave rise to multipotent GBM spheres that were capable of self-renewal. Epidermal growth factor (EGF) and fibroblast growth factor-2 enhanced GBM BTSC survival, proliferation, and subsequent sphere size. Blockade of EGF receptor (EGFR) signaling reduced exogenous mitogen-independent GBM sphere growth. Implantation of as few as 10 exogenous mitogen-independent GBM BTSCs led to the formation of highly invasive intracranial tumors, which closely resembled human GBMs, in immunocompromised mice. These results demonstrate that exogenous mitogen independence, mediated in part through EGFR signaling, is one characteristic that distinguishes CD133+ and CD133− GBM BTSCs from neural stem cells. This novel experimental system will permit the elucidation of additional constitutively activated mechanisms that promote GBM BTSC survival, self-renewal, and proliferation. Disclosure of potential conflicts of interest is found at the end of this article.

Myxoma virus, a poxvirus previously considered rabbit specific, can replicate productively in a variety of human tumor cells in culture. The purpose of this study was to determine if there was efficacy or toxicities of this oncolytic virus against experimental models of human malignant gliomas in vitro, in vivo, and ex vivo in malignant glioma specimens. In vitro, the majority of glioma cell lines tested (7 of 8, 87.5%) were fully permissive for myxoma virus replication and killed by infection. In vivo, intracerebral (i.c.) myxoma virus inoculation was well tolerated and produced only minimal focal inflammatory changes at the site of viral inoculation. U87 and U251 orthotopic xenograft models were used to assess myxoma virus efficacy in vivo. A single intratumoral injection of myxoma virus dramatically prolonged median survival compared with treatment with UV-inactivated myxoma virus. Median survival was not reached in myxoma virus-treated groups versus 47.3 days (U87; P = 0.0002) and 50.7 days (U251; P = 0.0027) in UV-inactivated myxoma virus-treated groups. Most myxoma virus-treated animals (12 of 13, 92%) were alive and apparently “cured” when the experiment was finished (>130 days). Interestingly, we found a selective and long-lived myxoma virus infection in gliomas in vivo. This is the first demonstration of the oncolytic activity of myxoma virus in vivo. The nonpathogenic nature of myxoma virus outside of the rabbit host, its capacity to be genetically modified, its ability to produce a long-lived infection in human tumor cells, and the lack of preexisting antibodies in the human population suggest that myxoma virus may be an attractive oncolytic agent against human malignant glioma.

Purpose: Human reovirus type 3 has been proposed to kill cancer cells with an activated Ras signaling pathway. The purpose of this study was to investigate the efficacy of reovirus in immunocompetent glioma animal models and safety/toxicity in immunocompetent animals, including nonhuman primates. Experimental Design: Racine glioma cells 9L and RG2 were implanted s.c. or intracranially in Fisher 344 rats with or without reovirus antibodies, followed by treatment of reovirus. To study whether reovirus kills contralateral tumors in the brain and to determine viral distribution, we established an in situ dual tumor model followed by reovirus intratumoral inoculation only into the ipsilateral tumor. To evaluate neurotoxicity/safety of reovirus, Cynomolgus monkeys and immunocompetent rats were given intracranially with reovirus, and pathological examination and/or behavioral studies were done. Viral shedding and clinical biochemistry were systematically studied in monkeys. Results: Intratumorally given reovirus significantly suppressed the growth of both s.c. and intracranially tumors and significantly prolonged survival. The presence of reovirus-neutralizing antibodies did not abort the reovirus’ antitumor effect. Reovirus inhibited glioma growth intracranially in the ipsilateral but not the contralateral tumors; viral load in ipsilateral tumors was 15 to 330-fold higher than the contralateral tumors. No encephalitis or behavioral abnormalities were found in monkeys and rats given reovirus intracranially. No treatment-related clinical biochemistry changes or diffuse histopathological abnormality were found in monkeys inoculated intracranially with Good Manufacturing Practice prepared reovirus. Microscopic changes were confined to the region of viral inoculation and were dose related, suggesting reovirus intracranially was well tolerated in nonhuman primates. Conclusions: These data show the efficacy and safety of reovirus when it is used in the treatment of gliomas in immunocompetent hosts. Inoculation of reovirus into the brain of nonhuman primates did not produce significant toxicities.

Brain and leptomeningeal metastases are common in breast cancer patients and our current treatments are ineffective. Reovirus type 3 is a replication competent, naturally occurring virus that usurps the activated Ras-signaling pathway (or an element thereof) of tumor cells and lyses them but leaves normal cells relatively unaffected. In this study we evaluated reovirus as an experimental therapeutic in models of central nervous system (CNS) metastasis from breast cancer. We found all breast cancer cell lines tested were susceptible to reovirus, with > 50% of these cells lysed within 72 h of infection. In vivo neurotoxicity studies showed only mild local inflammation at the injection site and mild communicating hydrocephalus with neither diffuse encephalitis nor behavioral abnormalities at the therapeutically effective dose of reovirus (intracranial) (ie 10(7) plaque-forming units) or one dose level higher. In vivo, a single intratumoral administration of reovirus significantly reduced the size of tumors established from two human breast cancer cell lines and significantly prolonged survival. Intrathecal administration of reovirus also remarkably prolonged survival in an immunocompetent racine model of leptomeningeal metastases. These data suggest that the evaluation of reovirus as an experimental therapeutic for CNS metastases from breast cancer is warranted.

Previous studies have shown successful antitumor effects of systemically delivered double-deleted vaccinia virus (vvDD) against a number of adult tumor models, including glioma, colon and ovarian cancers. The purpose of this study was to investigate the oncolytic potential of vvDD against a panel of cell lines representative of pediatric solid tumors that are currently difficult to cure.Cell lines derived from central nervous system atypical teratoid rhabdoid tumor (AT/RT) (BT12, BT16 and KCCF1), sarcoma (143B, HOS, RD and RH30), and neuroblastoma (SKNAS, SKNBE2, IMR-5 and IMR-32) were examined for vvDD mediated cytotoxicity defined by virus expansion followed by loss of tumor cell viability. The normal human fibroblast cell line HS68 was used as a control. Next, relevant orthotopic, subcutaneous and lung metastasis xenograft models were treated with intravenous doses of live vvDD or killed virus controls (DV). Tumor growth inhibition and viral replication were quantified and survival outcomes of these animals were assessed.vvDD was able to infect and kill nine of eleven of the pediatric tumor cells (81.8%) in vitro. In xenograft models, intravenous administration of a single dose of vvDD significantly inhibited the growth of tumors and prolonged the survival of intracranial and metastatic tumors.Oncolytic vvDD administered i.v. shows activity in preclinical models of pediatric malignancies that are resistant to many currently available treatments. Our data support further evaluation of vvDD virotherapy for refractory pediatric solid tumors.

Despite intensifying multimodal treatments, children with central nervous system atypical teratoid/rhabdoid tumor (CNS ATRT) continue to endure unacceptably high mortality rates. At present, concerted efforts are focusing on understanding the characteristic INI1 mutation and its implications for the growth and survival of these tumors. Additionally, pharmaceutical pipeline libraries constitute a significant source of potential agents that can be taken to clinical trials in a timely manner. However, this process requires efficient target validation and relevant preclinical studies. As an initial screening approach, a panel of 129 small molecule inhibitors from multiple pharmaceutical pipeline libraries was tested against three ATRT cell lines by in vitro cytotoxicity assays. Based on these data, agents that have strong activity and corresponding susceptible cellular pathways were identified. Target modulation, antibody array analysis, drug combination and in vivo xenograft studies were performed on one of the pathway inhibitors found in this screening. Approximately 20% of agents in the library showed activity with IC(50) values of 1 μM or less and many showed IC(50) values less than 0.05 μM. Intra cell line variability was also noted among some of the drugs. However, it was determined that agents capable of affecting pathways constituting ErbB2, mTOR, proteasomes, Hsp90, Polo like kinases and Aurora kinases were universally effective against the three ATRT cell lines. The first target selected for further analysis, the inhibition of ErbB2-EGFR pathway by the small molecule inhibitor lapatinib, indicated inhibition of cell migration properties and the initiation of apoptosis. Synergy between lapatinib and IGF-IR inhibition was also demonstrated by combination index (CI) values. Xenograft studies showed effective antitumor activity of lapatinib in vivo. We present an experimental approach to identifying agents and drug combinations for future clinical trials and provide evidence for the potential of lapatinib as an effective agent in the context of the biology and heterogeneity of its targets in ATRT.

The multifunctional signaling protein p75 neurotrophin receptor (p75NTR) is a central regulator and major contributor to the highly invasive nature of malignant gliomas. Here, we show that neurotrophin-dependent regulated intramembrane proteolysis (RIP) of p75NTR is required for p75NTR-mediated glioma invasion, and identify a previously unnamed process for targeted glioma therapy. Expression of cleavage-resistant chimeras of p75NTR or treatment of animals bearing p75NTR-positive intracranial tumors with clinically applicable γ-secretase inhibitors resulted in dramatically decreased glioma invasion and prolonged survival. Importantly, proteolytic processing of p75NTR was observed in p75NTR-positive patient tumor specimens and brain tumor initiating cells. This work highlights the importance of p75NTR as a therapeutic target, suggesting that γ-secretase inhibitors may have direct clinical application for the treatment of malignant glioma., Author Summary Despite technical advances, clinical prognosis of patients with malignant glioma, with an average survival of less than one year, has not changed. The highly invasive nature of these tumors, together with the recently identified brain tumor-initiating cells, provide disease reservoirs that render these tumors incurable by conventional therapies. Here, we present the first evidence to our knowledge that regulated intramembrane proteolysis of the neurotrophin receptor p75NTR is a critical regulator of glioma invasion. Inhibition of this process by clinically relevant γ-secretase inhibitors dramatically impairs the highly invasive nature of genetically distinct glioblastomas and brain tumor-initiating cells and prolongs survival. These data highlight regulated intramembrane proteolysis as a therapeutic target of malignant glioma and implicate the application of γ-secretase inhibitors in the treatment of these devastating tumors., Gamma-secretase inhibitors in clinical trials for patients with Alzheimer disease can be used to block the highly invasive behavior of malignant glioma and prolong survival.

Purpose: Rhabdoid tumors are highly aggressive pediatric tumors that are usually refractory to available treatments. The purpose of this study was to evaluate the therapeutic potential of two oncolytic viruses, myxoma virus (MV) and an attenuated vesicular stomatitis virus (VSVΔM51), in experimental models of human rhabdoid tumor. Experimental Design: Four human rhabdoid tumor cell lines were cultured in vitro and treated with live or inactivated control virus. Cytopathic effect, viral gene expression, infectious viral titers, and cell viability were examined at various time points after infection. To study viral oncolysis in vivo, human rhabdoid tumor cells were implanted s.c. in the hind flank or intracranially in CD-1 nude mice and treated with intratumoral (i.t.) or i.v. injections of live or UV-inactivated virus. Viral distribution and effects on tumor size and survival were assessed. Results: All rhabdoid tumor cell lines tested in vitro were susceptible to productive lethal infections by MV and VSVΔM51. I.t. injection of live MV or VSVΔM51 dramatically reduced the size of s.c. rhabdoid tumor xenografts compared with control animals. I.v. administration of VSVΔM51 or i.t. injection of MV prolonged the median survival of mice with brain xenografts compared with controls (VSVΔM51: 25 days versus 21 days, log-rank test, P = 0.0036; MV: median survival not reached versus 21 days, log-rank test, P = 0.0007). Most of the MV-treated animals (4 of 6; 66.7%) were alive and apparently “cured” when the experiment was arbitrarily ended (>180 days). Conclusions: These results suggest that VSVΔM51 and MV could be novel effective therapies against human rhabdoid tumor.

Human reovirus type 3 has been proposed to kill cancer cells with an activated Ras signaling pathway. The purpose of this study was to investigate the efficacy of reovirus in immunocompetent glioma animal models and safety/toxicity in immunocompetent animals, including nonhuman primates.Racine glioma cells 9L and RG2 were implanted s.c. or intracranially in Fisher 344 rats with or without reovirus antibodies, followed by treatment of reovirus. To study whether reovirus kills contralateral tumors in the brain and to determine viral distribution, we established an in situ dual tumor model followed by reovirus intratumoral inoculation only into the ipsilateral tumor. To evaluate neurotoxicity/safety of reovirus, Cynomolgus monkeys and immunocompetent rats were given intracranially with reovirus, and pathological examination and/or behavioral studies were done. Viral shedding and clinical biochemistry were systematically studied in monkeys.Intratumorally given reovirus significantly suppressed the growth of both s.c. and intracranially tumors and significantly prolonged survival. The presence of reovirus-neutralizing antibodies did not abort the reovirus' antitumor effect. Reovirus inhibited glioma growth intracranially in the ipsilateral but not the contralateral tumors; viral load in ipsilateral tumors was 15 to 330-fold higher than the contralateral tumors. No encephalitis or behavioral abnormalities were found in monkeys and rats given reovirus intracranially. No treatment-related clinical biochemistry changes or diffuse histopathological abnormality were found in monkeys inoculated intracranially with Good Manufacturing Practice prepared reovirus. Microscopic changes were confined to the region of viral inoculation and were dose related, suggesting reovirus intracranially was well tolerated in nonhuman primates.These data show the efficacy and safety of reovirus when it is used in the treatment of gliomas in immunocompetent hosts. Inoculation of reovirus into the brain of nonhuman primates did not produce significant toxicities.

BACKGROUND: Brain tumour initiating cells (BTICs) are stem-like cells hypothesized to mediate tumorigenesis and recurrence in glioblastoma multiforme (GBM). Patient-derived BTICs represent highly relevant preclinical GBM models, forming aggressive, infiltrative tumours in nude mice that closely recapitulate the phenotypic heterogeneity of patient GBMs. BTICs have also been shown to possess mechanisms mediating both chemo- and radio-resistance. Recently, success has been demonstrated in treating BTICs with oncolytic virotherapy (OV), which uses replication-competent viruses to specifically target and kill malignant cells. Myxoma virus (MyxV) is a promising oncolytic candidate, which our lab has shown to be highly efficacious in preclinical GBM models, effectively curing GBM xenografts with a single intra-cranial injection. By contrast, long-term survival is not obtained in MyxV-treated, BTIC-tumour-bearing mice, though survival is prolonged. HYPOTHESIS: We hypothesize that MyxV treatment of BTICs can be improved by utilizing clinically relevant chemotherapeutics identified via high-throughput pharmacoviral screens. RESULTS: We utilized a diverse, comprehensive panel of 80 small molecule inhibitors with preclinical and clinical anti-cancer efficacy to screen for synergy with MyxV treatment in vitro. Multiple candidates have been identified and are currently being validated for synergy (Chou-Talalay method) using a panel of genetically distinct, patient-derived BTICs. Our results implicate multiple potential targets for OV combination therapy, including topoisomerase I and the PI-3K/Akt/mTOR pathway. Target validation is currently underway using shRNA knockdowns and additional targeted inhibitors of these pathways. Further, the mechanism of synergistic cell death during these combination treatments is being explored. In vivo experiments utilizing the dual-pronged pharmacoviral approach are also underway. SIGNIFICANCE: We describe the nature and identity of compounds that carry the potential to sensitize BTICs to MyxV infection. Our findings offer an effective avenue to elucidate resistance mechanisms and develop efficacious combination therapies for targeting disease reservoirs within highly refractory GBMs. 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 LB-140. doi:1538-7445.AM2012-LB-140

Innovative biotherapeutic approaches for experimental malignant gliomas (MGs) and brain tumor stem cells (BTSCs) include using oncolytic viruses such as Myxoma Virus (Myxv) or immune cells such as Natural Killer (NK) cells. In this study, we combined the individual strengths of using NK cells and Myxv to treat MGs with a view of overcoming the potential limitations posed when each is used as monotherapy. All MGs (U87, U251) and BTSCs (25EF and 48EF) investigated expressed varying levels of NK ligands including inhibitory MHC-I, activating ULBP1-3, MICA/B, and co-activating nectin-2, poliovirus receptor. Infection of MGs and BTSCs with Myxv resulted in the downregulation of MHC-I expression both on the cell surface and intracellularly. No effect was observed on the expression of NK activating ligands except for the downregulation of nectin-2. The downregulation of MHC-I and nectin-2 by Myxv was specifically mediated by M153 gene of Myxv as loss of M153 restored MHC-I and nectin-2 expression. Subsequently, NK cell degranulation and killing of MGs was enhanced in Myxv-infected cells. Loss of M153 inhibited NK degranulation and lysis of MGs. In vivo, using luciferase-expressing U87 cells in a mouse intracranial model, Myxv accelerated tumor size reduction/clearance by NK cell lysis. Combined intratumoral treatment with Myxv and NK of established U87 tumor accelerated tumor clearance when compared with single treatment with Myxv or NK. Tumor in 66% of mice (4 out of 6 mice) were cleared or significantly reduced within 14 days following combination treatment with Myxv and NK. No significant effect was observed in Myxv or NK singly-treated mice within the same time frame. Clearance of tumors was only first observed in 50% (2 out of 4) of Myxv-treated mice after 25 days Myxv treatment. In NK treated mice, the tumor size rather increased. The enhanced tumor clearance in the combined Myxv and NK treated mice was possibly due to the down-regulation of MHC-I by Myxv since combined treatment with NK cells and mutant Myxv (gene M153 which is responsible for MHC-I down-regulation was deleted) did not result in clearance of tumors. 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 1558. doi:1538-7445.AM2012-1558

Oncolytic viruses constitute a promising therapy against malignant gliomas (MGs). However, virus-induced type-I interferon (IFN) greatly limits its clinical application. The kinase mTOR (mammalian target of rapamycin) stimulates type-I IFN production via phosphorylation of its effector proteins, 4E-BPs and S6Ks. Here we show that both mouse embryonic fibroblasts (MEFs) and mice lacking S6K1 and S6K2, are susceptible to Vesicular Stomatitis Virus (VSV) infection due to an impaired type-I interferon response. We used this knowledge to employ a pharmacoviral approach to treat MGs. The highly specific inhibitor of mTOR, rapamycin, in combination with an IFN-sensitive VSV-mutant strain (VSVΔM51), dramatically increased the survival of immunocompetent rats bearing MGs. More importantly, VSVΔM51 selectively killed tumor, but not normal cells, in MG-bearing rats, which were treated with rapamycin. These results demonstrate that reducing type-I IFNs through inhibition of mTOR is an effective strategy to augment the therapeutic activity of VSVΔM51. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5349.

Introduction: Malignant gliomas (MGs) still has a poor prognosis and remain largely incurable because their extremely invasive nature, even with significant improvements in surgery, chemotherapy and radiotherapy. Although temozolomide (TMZ) improved the survival of some GBM patients, but recently TMZ resistant became a significantly problem. So new treatments could overcome the TMZ resistant desperately needed. Recently, cells with stem cell qualities have been identified in brain malignancies and have demonstrated brain tumor initiating cells (BTICs) responsible for the initiation of brain tumors and recurrence, as well as chemotherapy and radiotherapy resistant. Therefore, to development of new therapeutic strategies targeting BTICs may provide more effective approach. Oncolytic viruses may represent an effective therapeutic approach to target BTICs because their unique and multiple mechanism of action. We have previously reported that Myxoma Virus (MYXV) “cures” most intracranial brain tumors models in CD-1 nude mice, and significantly improved the efficacy in immunocompetent hosts when combined with rapamycin. Here we further investigated the oncolytic potential of MYXV, alone or in combination with rapamycin in vitro and in animal models established using human BTICs, special for TMZ resistant BTIC lines. Experimental procedure: First, we isolated and cultured BTICs from fresh operative glioblastoma (GBM) specimens, and these cells have all the characteristic of BTICs and form tumors in vivo that very closely resemble human infiltrative GBM. Then, we test the sensitivity to TMZ and we used TMZ resistant BTICs to test the susceptibility to MYXV infection in vitro and in vivo. Results: We found that: 1) All we tested TMZ resistant BTICs susceptible to MV infection and killing in vitro, 2) MYXV replication within TMZ resistant BTICs tumor of the brain and intratumoral administration of MYXV significantly prolongs survival of SCID mice bearing invasive BTICs tumor. 3) And more importantly we found that MYXV Combination treatment with rapamycin further improved the efficacy, even significantly prolongs survival of SCID mice bearing “late-stage” invasive and TMZ resistant BTICs tumor, and this result further confirmed using MRI and bioluminescence image before and after treatment. Conclusion: Our results show for the first time that MYXV alone or in combination treatment with rapamycin significantly inhibited tumor growth and prolongs survival in TMZ resistant BTICs bearing SCID mice models. These observations suggest that MYXV alone or in combination therapy with rapamycin could be an effective therapy for extremely infiltrative GBM, as well as the important TMZ adjuvant therapy for GBM in the future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4283.