Oncolytic herpes simplex virus expressing IL-2 controls glioblastoma growth and improves survival

BACKGROUND

Glioblastoma (GBM), a highly immunosuppressive and often fatal primary brain tumor, lacks effective treatment options. GBMs contain a subpopulation of GBM stem-like cells (GSCs) that play a central role in tumor initiation, progression, and treatment resistance. Oncolytic viruses, especially oncolytic herpes simplex virus (oHSV), replicate selectively in cancer cells and trigger antitumor immunity-a phenomenon termed the "in situ vaccine" effect. Although talimogene laherparepvec (T-VEC), an oHSV armed with granulocyte macrophage-colony stimulating factor (GM-CSF), is Food and Drug Administration (FDA)-approved for melanoma, its use in patients with GBM has not been reported. Interleukin 2 (IL-2) is another established immunotherapy that stimulates T cell growth and orchestrates antitumor responses. IL-2 is FDA-approved for melanoma and renal cell carcinoma but has not been widely evaluated in GBM, and IL-2 treatment is limited by its short half-life, minimal tumor accumulation, and significant systemic toxicity. We hypothesize that local intratumoral expression of IL-2 by an oHSV would avoid the systemic IL-2-related therapeutic drawbacks while simultaneously producing beneficial antitumor immunity.

METHODS

We developed G47Δ-mIL2 (an oHSV expressing IL-2) using the flip-flop HSV BAC system to deliver IL-2 locally within the tumor microenvironment (TME). We then tested its efficacy in orthotopic mouse GBM models (005 GSC, CT-2A, and GL261) and evaluated immune profiles in the treated tumors and spleens by flow cytometry and immunohistochemistry.

RESULTS

G47Δ-mIL2 significantly prolonged median survival without any observable systemic IL-2-related toxicity in the 005 and CT-2A models but not in the GL261 model due to the non-permissive nature of GL261 cells to HSV infection. The therapeutic activity of G47Δ-mIL2 in the 005 GBM model was associated with increased intratumoral infiltration of CD8+ T cells, critically dependent on the release of IL-2 within the TME, and CD4+ T cells as their depletion completely abrogated therapeutic efficacy. The use of anti-PD-1 immune checkpoint blockade did not improve the therapeutic outcome of G47Δ-mIL2.

CONCLUSIONS

Our findings illustrate that G47Δ-mIL2 is efficacious, stimulates antitumor immunity against orthotopic GBM, and may also target GSC. OHSV expressing IL-2 may represent an agent that merits further exploration in patients with GBM.

Photodynamic augmentation of oncolytic virus therapy for central nervous system malignancies

Oncolytic viruses (OVs) have emerged as a clinical therapeutic modality potentially effective for cancers that evade conventional therapies, including central nervous system malignancies. Rationally designed combinatorial strategies can augment the efficacy of OVs by boosting tumor-selective cytotoxicity and modulating the tumor microenvironment (TME). Photodynamic therapy (PDT) of cancer not only mediates direct neoplastic cell death but also primes the TME to sensitize the tumor to secondary therapies, allowing for the combination of two potentially synergistic therapies with broader targets. Here, we created G47Δ-KR, clinical oncolytic herpes simplex virus G47Δ that expresses photosensitizer protein KillerRed (KR). Optical properties and cytotoxic effects of G47Δ-KR infection followed by amber LED illumination (peak wavelength: 585-595 nm) were examined in human glioblastoma (GBM) and malignant meningioma (MM) models in vitro. G47Δ-KR infection of tumor cells mediated KR expression that was activated by LED and produced reactive oxygen species, leading to cell death that was more robust than G47Δ-KR without light. In vivo, we tested photodynamic-oncolytic virus (PD-OV) therapy employing intratumoral injection of G47Δ-KR followed by laser light tumor irradiation (wavelength: 585 nm) in GBM and MM xenografts. PD-OV therapy was feasible in these models and resulted in potent anti-tumor effects that were superior to G47Δ-KR alone (without laser light) or laser light alone. RNA sequencing analysis of post-treatment tumor samples revealed PD-OV therapy-induced increases in TME infiltration of variable immune cell types. This study thus demonstrated the proof-of-concept that G47Δ-KR enables PD-OV therapy for neuro-oncological malignancies and warrants further research to advance potential clinical translation.

Histone deacetylase inhibitors enhance oncolytic herpes simplex virus therapy for malignant meningioma

Approximately 20% of meningiomas are not benign (higher grade) and tend to relapse after surgery and radiation therapy. Malignant (anaplastic) meningioma (MM) is a minor subset of high-grade meningioma that is lethal with no effective treatment options currently. Oncolytic herpes simplex virus (oHSV) is a powerful anti-cancer modality that induces both direct cell death and anti-tumor immunity, and has shown activity in preclinical models of MM. However, clinically meaningful efficacy will likely entail rational mechanistic combination approaches. We here show that epigenome modulator histone deacetylase inhibitors (HDACi) increase anti-cancer effects of oHSV in human MM models, IOMM-Lee (NF2 wild-type) and CH157 (NF2 mutant). Minimally toxic, sub-micromolar concentrations of pan-HDACi, Trichostatin A and Panobinostat, substantively increased the infectability and spread of oHSV G47Δ within MM cells in vitro, resulting in enhanced oHSV-mediated killing of target cells when infected at low multiplicity of infection (MOI). Transcriptomics analysis identified selective alteration of mRNA processing and splicing modules that might underlie the potent anti-MM effects of combining HDACi and oHSV. In vivo, HDACi treatment increased intratumoral oHSV replication and boosted the capacity of oHSV to control the growth of human MM xenografts. Thus, our work supports further translational development of the combination approach employing HDACi and oHSV for the treatment of MM.

In Situ Cancer Vaccination and Immunovirotherapy Using Oncolytic HSV

Herpes simplex virus (HSV) can be genetically altered to acquire oncolytic properties so that oncolytic HSV (oHSV) preferentially replicates in and kills cancer cells, while sparing normal cells, and inducing anti-tumor immune responses. Over the last three decades, a better understanding of HSV genes and functions, and improved genetic-engineering techniques led to the development of oHSV as a novel immunovirotherapy. The concept of in situ cancer vaccination (ISCV) was first introduced when oHSV was found to induce a specific systemic anti-tumor immune response with an abscopal effect on non-injected tumors, in the process of directly killing tumor cells. Thus, the use of oHSV for tumor vaccination in situ is antigen-agnostic. The research and development of oHSVs have moved rapidly, with the field of oncolytic viruses invigorated by the FDA/EMA approval of oHSV talimogene laherparepvec in 2015 for the treatment of advanced melanoma. Immunovirotherapy can be enhanced by arming oHSV with immunomodulatory transgenes and/or using them in combination with other chemotherapeutic and immunotherapeutic agents. This review offers an overview of the development of oHSV as an agent for ISCV against solid tumors, describing the multitude of different oHSVs and their efficacy in immunocompetent mouse models and in clinical trials.

Temozolomide antagonizes oncolytic immunovirotherapy in glioblastoma

BACKGROUND

Temozolomide (TMZ) chemotherapy is a current standard of care for glioblastoma (GBM), however it has only extended overall survival by a few months. Because it also modulates the immune system, both beneficially and negatively, understanding how TMZ interacts with immunotherapeutics is important. Oncolytic herpes simplex virus (oHSV) is a new class of cancer therapeutic with both cytotoxic and immunostimulatory activities. Here, we examine the combination of TMZ and an oHSV encoding murine interleukin 12, G47Δ-mIL12, in a mouse immunocompetent GBM model generated from non-immunogenic 005 GBM stem-like cells (GSCs.

METHODS

We first investigated the cytotoxic effects of TMZ and/or G47Δ-IL12 treatments in vitro, and then the antitumor effects of combination therapy in vivo in orthotopically implanted 005 GSC-derived brain tumors. To improve TMZ sensitivity, O⁶-methylguanine DNA methyltransferase (MGMT) was inhibited. The effects of TMZ on immune cells were evaluated by flow cytometery and immunohistochemistry.

RESULTS

The combination of TMZ+G47Δ-IL12 kills 005 GSCs in vitro better than single treatments. However, TMZ does not improve the survival of orthotopic tumor-bearing mice treated with G47Δ-IL12, but rather can abrogate the beneficial effects of G47Δ-IL12 when the two are given concurrently. TMZ negatively affects intratumor T cells and macrophages and splenocytes. Addition of MGMT inhibitor O⁶-benzylguanine (O6-BG), an inactivating pseudosubstrate of MGMT, to TMZ improved survival, but the combination with G47Δ-IL12 did not overcome the antagonistic effects of TMZ treatment on oHSV therapy.

CONCLUSIONS

These results illustrate that chemotherapy can adversely affect oHSV immunovirotherapy. As TMZ is the standard of care for GBM, the timing of these combined therapies should be taken into consideration when planning oHSV clinical trials with chemotherapy for GBM.

Modification of Extracellular Matrix Enhances Oncolytic Adenovirus Immunotherapy in Glioblastoma

PURPOSE

Extracellular matrix (ECM) component hyaluronan (HA) facilitates malignant phenotypes of glioblastoma (GBM), however, whether HA impacts response to GBM immunotherapies is not known. Herein, we investigated whether degradation of HA enhances oncolytic virus immunotherapy for GBM.

EXPERIMENTAL DESIGN

Presence of HA was examined in patient and murine GBM. Hyaluronidase-expressing oncolytic adenovirus, ICOVIR17, and its parental virus, ICOVIR15, without transgene, were tested to determine if they increased animal survival and modulated the immune tumor microenvironment (TME) in orthotopic GBM. HA regulation of NF-κB signaling was examined in virus-infected murine macrophages. We combined ICOVIR17 with PD-1 checkpoint blockade and assessed efficacy and determined mechanistic contributions of tumor-infiltrating myeloid and T cells.

RESULTS

Treatment of murine orthotopic GBM with ICOVIR17 increased tumor-infiltrating CD8+ T cells and macrophages, and upregulated PD-L1 on GBM cells and macrophages, leading to prolonged animal survival, compared with control virus ICOVIR15. High molecular weight HA inhibits adenovirus-induced NF-κB signaling in macrophages in vitro, linking HA degradation to macrophage activation. Combining ICOVIR17 with anti-PD-1 antibody further extended the survival of GBM-bearing mice, achieving long-term remission in some animals. Mechanistically, CD4+ T cells, CD8+ T cells, and macrophages all contributed to the combination therapy that induced tumor-associated proinflammatory macrophages and tumor-specific T-cell cytotoxicity locally and systemically.

CONCLUSIONS

Our studies are the first to show that immune modulatory ICOVIR17 has a dual role of mediating degradation of HA within GBM ECM and subsequently modifying the immune landscape of the TME, and offers a mechanistic combination immunotherapy with PD-L1/PD-1 blockade that remodels innate and adaptive immune cells.

Characterization and oncolytic virus targeting of FAP-expressing tumor-associated pericytes in glioblastoma

Cancer-associated fibroblasts (CAFs) are activated fibroblasts constituting the major stromal components in many types of cancer. CAFs contribute to hallmarks of cancer such as proliferation, invasion and immunosuppressive tumor microenvironment, and are associated with poor prognosis of patients with cancer. However, in glioblastoma (GBM), the most common and aggressive primary malignant brain tumor, our knowledge about CAFs or CAF-like stromal cells is limited. Here, using commonly accepted CAF markers, we characterized CAF-like cell populations in clinical glioma specimens and datasets along with mouse models of GBM. We found that tumor-associated pericytes marked by co-expression of fibroblast activation protein α (FAP) and PDGFRβ represent major stromal cell subsets in both human GBM and mouse GBM models, while a fraction of mesenchymal neoplastic cells also express FAP in patient tumors. Since oncolytic viruses can kill cancer cells and simultaneously modulate the tumor microenvironment by impacting non-neoplastic populations such as immune cells and tumor vasculature, we further investigated the ability of oncolytic viruses to target GBM-associated stromal cells. An oncolytic adenovirus, ICOVIR15, carrying ∆24-E1A and an RGD-fiber, infects and depletes FAP+ pericytes as well as GBM cells in murine GBM. Our study thus identifies FAP+/PDGFRβ+ pericytes as a major CAF-like stromal cell population in GBM, and highlights the unique property of this oncolytic adenovirus to target both GBM cells and GBM-associated stromal FAP+ cells.

Oncolytic herpes simplex virus immunovirotherapy in combination with immune checkpoint blockade to treat glioblastoma

Oncolytic viruses, such as oncolytic herpes simplex virus (oHSV), are a new class of cancer therapeutic, which selectively replicate and kill cancer cells, while inducing an inflammatory microenvironment, immunovirotherapy. Recently, an oHSV (talimogene laherparepvec) has been approved for the treatment of advanced melanoma. Glioblastoma (GBM) is an almost always lethal primary tumor in the brain that is highly immunosuppressive, and posited to contain GBM stem-like cells (GSCs). Immune checkpoint blockade has revolutionized therapy for some cancers, but not GBM. We have used a syngeneic GSC-derived orthotopic GBM model (005) to develop immunotherapeutic strategies. Curative therapy required oHSV expressing IL-12 in combination with two checkpoint inhibitors, anti-PD-1 and anti-CTLA-4. This response required CD4⁺ and CD8⁺ T cells, and macrophages in a complex interplay.

Myc targeted CDK18 promotes ATR and homologous recombination to mediate PARP inhibitor resistance in glioblastoma

PARP inhibitors (PARPis) have clinical efficacy in BRCA-deficient cancers, but not BRCA-intact tumors, including glioblastoma (GBM). We show that MYC or MYCN amplification in patient-derived glioblastoma stem-like cells (GSCs) generates sensitivity to PARPi via Myc-mediated transcriptional repression of CDK18, while most tumors without amplification are not sensitive. In response to PARPi, CDK18 facilitates ATR activation by interacting with ATR and regulating ATR-Rad9/ATR-ETAA1 interactions; thereby promoting homologous recombination (HR) and PARPi resistance. CDK18 knockdown or ATR inhibition in GSCs suppressed HR and conferred PARPi sensitivity, with ATR inhibitors synergizing with PARPis or sensitizing GSCs. ATR inhibitor VE822 combined with PARPi extended survival of mice bearing GSC-derived orthotopic tumors, irrespective of PARPi-sensitivity. These studies identify a role of CDK18 in ATR-regulated HR. We propose that combined blockade of ATR and PARP is an effective strategy for GBM, even for low-Myc GSCs that do not respond to PARPi alone, and potentially other PARPi-refractory tumors.

PARP inhibitors are mainly used to treat BRCA1/2 mutated cancers. Here, the authors show that MYC amplified glioblastomas are sensitive to PARP inhibition due to CDK18 repression, which impairs ATR regulated homologous recombination repair, and that ATR inhibition sensitises glioblastomas to PARP inhibition.

Performance of a Hospital Pathway for Patients With a New Single Brain Mass

PURPOSE:

To reduce care variation and improve the management of patients with newly identified single brain masses and no history of cancer, we implemented a dedicated admission protocol.

METHODS:

We reviewed records of 206 patients who presented to our emergency department between January 2010 and May 2016 with a new single brain mass but no history of cancer. Patients admitted before the protocol implementation were designated the pre-implementation group (PRE), and those admitted after implementation were designated the post-implementation group (POST).

RESULTS:

Ninety-six patients were in the PRE group and 110 in the POST group. Length of stay for POST patients was significantly shorter than for PRE patients (6 v 7 days, respectively; P = .042), and this effect was more robust after excluding the 66 patients who were discharged to rehabilitation, skilled nursing, or hospice facilities (5 v 7 days, respectively; P = .001). Additional comparison of POST with PRE patients showed that time to surgery was significantly reduced (2.7 v 3.5 days, respectively; P = .006) and that computed tomography scans of the chest, abdomen, and pelvis were reduced (12% v 47%, respectively; P < .001). No difference was found in the 30-day readmission rates. For patients with GBM, there also was no significant difference in time to initiation of chemoradiation or in median overall survival.

CONCLUSION:

Implementation of a specialized admission pathway for patients with a new single brain mass decreased average length of hospital stay and time to surgery and reduced unnecessary diagnostic imaging tests in patients with primary brain tumors.

Author Correction: Sequestration of T cells in bone marrow in the setting of glioblastoma and other intracranial tumors

In the version of this article originally published, the figure callout in this sentence was incorrect: "Furthermore, in S1P1-KI mice themselves, whereas PD-1 blockade was ineffectual as monotherapy, the effects of 4-1BB agonism and checkpoint blockade proved additive, with the combination prolonging median survival and producing a 50% long-term survival rate (Fig. 6f)." The callout should have been to Supplementary Fig. 6b. The error has been corrected in the PDF and HTML versions of the article.

Combinatorial Effects of VEGFR Kinase Inhibitor Axitinib and Oncolytic Virotherapy in Mouse and Human Glioblastoma Stem-Like Cell Models

Purpose: Glioblastoma (GBM), a fatal brain cancer, contains a subpopulation of GBM stem-like cells (GSCs) that contribute to resistance to current therapy. Angiogenesis also plays a key role in GBM progression. Therefore, we developed a strategy to target the complex GBM microenvironment, including GSCs and tumor vasculature.Experimental Design: We evaluated the cytotoxic effects of VEFGR tyrosine kinase inhibitor (TKI) axitinib in vitro and then tested antitumor efficacy of axitinib in combination with oncolytic herpes simplex virus (oHSV) expressing antiangiogenic cytokine murine IL12 (G47Δ-mIL12) in two orthotopic GSC-derived GBM models: patient-derived recurrent MGG123 GSCs, forming vascular xenografts in immunodeficient mice; and mouse 005 GSCs, forming syngeneic tumors in immunocompetent mice.Results: GSCs form endothelial-like tubes and were sensitive to axitinib. G47Δ-mIL12 significantly improved survival, as did axitinib, while dual combinations further extended survival significantly compared with single therapies alone in both models. In MGG123 tumors, axitinib was effective only at high doses (50 mg/kg), alone and in combination with G47Δ-mIL12, and this was associated with greatly decreased vascularity, increased macrophage infiltration, extensive tumor necrosis, and PDGFR/ERK pathway inhibition. In the mouse 005 model, antiglioma activity, after single and combination therapy, was only observed in immunocompetent mice and not the T-cell-deficient athymic mice. Interestingly, immune checkpoint inhibition did not improve efficacy.Conclusions: Systemic TKI (axitinib) beneficially combines with G47Δ-mIL12 to enhance antitumor efficacy in both immunodeficient and immunocompetent orthotopic GBM models. Our results support further investigation of TKIs in combination with oHSV for GBM treatment. Clin Cancer Res; 24(14); 3409-22. ©2018 AACR.

Blockade of transforming growth factor-β signaling enhances oncolytic herpes simplex virus efficacy in patient-derived recurrent glioblastoma models

Despite the current standard of multimodal management, glioblastoma (GBM) inevitably recurs and effective therapy is not available for recurrent disease. A subset of tumor cells with stem-like properties, termed GBM stem-like cells (GSCs), are considered to play a role in tumor relapse. Although oncolytic herpes simplex virus (oHSV) is a promising therapeutic for GBM, its efficacy against recurrent GBM is incompletely characterized. Transforming growth factor beta (TGF-β) plays vital roles in maintaining GSC stemness and GBM pathogenesis. We hypothesized that oHSV and TGF-β inhibitors would synergistically exert antitumor effects for recurrent GBM. Here we established a panel of patient-derived recurrent tumor models from GBMs that relapsed after postsurgical radiation and chemotherapy, based on GSC-enriched tumor sphere cultures. These GSCs are resistant to the standard-of-care temozolomide but susceptible to oHSVs G47Δ and MG18L. Inhibition of TGF-β receptor kinase with selective targeted small molecules reduced clonogenic sphere formation in all tested recurrent GSCs. The combination of oHSV and TGF-βR inhibitor was synergistic in killing recurrent GSCs through, in part, an inhibitor-induced JNK-MAPK blockade and increase in oHSV replication. In vivo, systemic treatment with TGF-βR inhibitor greatly enhanced the antitumor effects of single intratumoral oHSV injections, resulting in cures in 60% of mice bearing orthotopic recurrent GBM. These results reveal a novel synergistic interaction of oHSV therapy and TGF-β signaling blockade, and warrant further investigations aimed at clinical translation of this combination strategy for GBM patients.

Macrophage Polarization Contributes to Glioblastoma Eradication by Combination Immunovirotherapy and Immune Checkpoint Blockade

Glioblastoma is an immunosuppressive, fatal brain cancer that contains glioblastoma stem-like cells (GSCs). Oncolytic herpes simplex virus (oHSV) selectively replicates in cancer cells while inducing anti-tumor immunity. oHSV G47Δ expressing murine IL-12 (G47Δ-mIL12), antibodies to immune checkpoints (CTLA-4, PD-1, PD-L1), or dual combinations modestly extended survival of a mouse glioma model. However, the triple combination of anti-CTLA-4, anti-PD-1, and G47Δ-mIL12 cured most mice in two glioma models. This treatment was associated with macrophage influx and M1-like polarization, along with increased T effector to T regulatory cell ratios. Immune cell depletion studies demonstrated that CD4⁺ and CD8⁺ T cells as well as macrophages are required for synergistic curative activity. This combination should be translatable to the clinic and other immunosuppressive cancers.

Rad51 Degradation: Role in Oncolytic Virus-Poly(ADP-Ribose) Polymerase Inhibitor Combination Therapy in Glioblastoma

Background

Clinical success of poly(ADP-ribose) polymerase inhibitors (PARP i ) has been limited to repair-deficient cancers and by resistance. Oncolytic herpes simplex viruses (oHSVs) selectively kill cancer cells, irrespective of mutation, and manipulate DNA damage responses (DDR). Here, we explore potential synthetic lethal-like interactions between oHSV and PARP i .

Methods

The efficacy of combining PARP i , oHSV MG18L, and G47Δ in killing patient-derived glioblastoma stem cells (GSCs) was assessed using cell viability assays and Chou-Talalay synergy analysis. Effects on DDR pathways, apoptosis, and cell cycle after manipulation with pharmacological inhibitors and lentivirus-mediated knockdown or overexpression were examined by immunoblotting and FACS. In vivo efficacy was evaluated in two GSC-derived orthotopic xenograft models (n = 7-8 per group). All statistical tests were two-sided.

Results

GSCs are differentially sensitive to PARP i despite uniform inhibition of PARP activity. oHSV sensitized GSCs to PARP i , irrespective of their PARP i sensitivity through selective proteasomal degradation of key DDR proteins; Rad51, mediating the combination effects; and Chk1. Rad51 degradation required HSV DNA replication. This synthetic lethal-like interaction increased DNA damage, apoptosis, and cell death in vitro and in vivo. Combined treatment of mice bearing PARP i -sensitive or -resistant GSC-derived brain tumors greatly extended median survival compared to either agent alone (vs olaparib: P ≤.001; vs MG18L: P  = .005; median survival for sensitive of 83 [95% CI = 77 to 86], 94 [95% CI = 75 to 107], 102 [95% CI = 85 to 110], and 131 [95% CI = 108 to 170] days and for resistant of 54 [95% CI = 52 to 58], 56 [95% CI = 52 to 61], 62 [95% CI = 56 to 72], and 75 [95% CI = 64 to 90] days for mock, PARPi, oHSV, and combination, respectively).

Conclusions

The unique oHSV property to target multiple components of DDR generates cancer selective sensitivity to PARP i . This combination of oHSV with PARP i is a new anticancer strategy that overcomes the clinical barriers of PARP i resistance and DNA repair proficiency and is applicable not only to glioblastoma, an invariably lethal tumor, but also to other tumor types.

Histopathological prognostic factors of recurrence following definitive therapy for atypical and malignant meningiomas

OBJECTIVE Patients with atypical and malignant (WHO Grade II and III) meningiomas have a worse prognosis than patients with benign (WHO Grade I) meningiomas. However, there is limited understanding of the pathological risk factors that affect long-term tumor control following combined treatment with surgery and radiation therapy. Here, the authors identify clinical and histopathological risk factors for the progression and/or recurrence (P/R) of high-grade meningiomas based on the largest series of patients with atypical and malignant meningiomas, as defined by the 2007 WHO classification. METHODS Patients diagnosed with WHO Grade II and III meningiomas between 2007 and 2014 per the WHO 2007 criteria and treated with both surgery and external beam radiation therapy were retrospectively reviewed for clinical and histopathological factors at the time of diagnosis and assessed for P/R outcomes at the last available follow-up. RESULTS A total of 76 patients met the inclusion criteria (66 Grade II meningiomas, 10 Grade III meningiomas). Median follow-up from the time of pathological diagnosis was 52.6 months. Three factors were found to predict P/R: Grade III histology, brain and/or bone invasion, and a Ki-67 proliferation rate at or above 3%. The crude P/R rate was 80% for patients with Grade III histology, 40% for those with brain and/or bone involvement (regardless of WHO tumor grade), and 20% for those with a proliferative index ≥ 3% (regardless of WHO tumor grade). The median proliferation index was significantly different between patients in whom treatment failed and those in whom it did not fail (11% and 1%, respectively). CONCLUSIONS In patients with atypical or malignant meningiomas, the presence of Grade III histology, brain and/or bone involvement, and a high mitotic index significantly predicted an increased risk of treatment failure despite combination therapy. These patients can be stratified into risk groups predicting P/R. Patients with high-risk features may benefit from more treatment and counseling than is typically offered currently.

A new patient-derived orthotopic malignant meningioma model treated with oncolytic herpes simplex virus

BACKGROUND

Higher-grade meningiomas (HGMs; World Health Organization grades II and III) pose a clinical problem due to high recurrence rates and the absence of effective therapy. Preclinical development of novel therapeutics requires a disease model that recapitulates the genotype and phenotype of patient HGM. Oncolytic herpes simplex virus (oHSV) has shown efficacy and safety in cancers in preclinical and clinical studies, but its utility for HGM has not been well characterized.

METHODS

Tumorsphere cultures and serial orthotopic xenografting in immunodeficient mice were used to establish a patient-derived HGM model. The model was pathologically and molecularly characterized by immunohistochemistry, western blot, and genomic DNA sequencing and compared with the patient tumor. Anti-HGM effects of oHSV G47Δ were assessed using cell viability and virus replication assays in vitro and animal survival analysis following intralesional injections of G47Δ.

RESULTS

We established a serially transplantable orthotopic malignant meningioma model, MN3, which was lethal within 3 months after tumorsphere implantation. MN3 xenografts exhibited the pathological hallmarks of malignant meningioma such as high Ki67 and vimentin expression. Both the patient tumor and xenografts were negative for neurofibromin 2 (merlin) and had the identical NF2 mutation. Oncolytic HSV G47Δ efficiently spread and killed MN3 cells, as well as other patient-derived HGM lines in vitro. Treatment with G47Δ significantly extended the survival of mice bearing subdural MN3 tumors.

CONCLUSIONS

We established a new patient-derived meningioma model that will enable the study of targeted therapeutic approaches for HGM. Based on these studies, it is reasonable to consider a clinical trial of G47Δ for HGM.

Transient fasting enhances replication of oncolytic herpes simplex virus in glioblastoma

Short-term nutritional restriction (fasting) has been shown to enhance the efficacy of chemotherapy by sensitizing cancer cells and protecting normal cells in a variety of cancer models, including glioblastoma (GBM). Cancer cells, unlike normal cells, respond to fasting by promoting oncogenic signaling and protein synthesis. We hypothesized that fasting would increase the replication of oncolytic herpes simplex virus (oHSV) in GBM. Patient-derived GBM cell lines were fasted by growth in glucose and fetal calf serum restricted culture medium. "Transient fasting", 24-hour fasting followed by 24-hour recovery in complete medium, increased late virus gene expression and G47Δ yields about 2-fold in GBM cells, but not in human astrocytes, and enhanced G47Δ killing of GBM cells. Mechanistically, "transient fasting" suppressed phosphorylation of the subunit of eukaryotic initiation factor 2α (eIF2α) and c-Jun N-terminal kinases (JNK) in GBM cells, but not in astrocytes. Pharmacological inhibition of JNK also increased G47Δ yield. In vivo, transient fasting (48-hour food restriction and 24-hour recovery) doubled luciferase activity after intratumoral G47Δ-US11fluc injection into orthotopic GBM xenografts. Thus, "transient fasting" increases G47Δ replication and oncolytic activity in human GBM cells. These results suggest that "transient fasting" may be effectively combined to enhance oncolytic HSV therapy of GBM.

Benign meningiomas (WHO Grade I) with atypical histological features: correlation of histopathological features with clinical outcomes

OBJECT

World Health Organization (WHO) Grade I (benign) meningiomas with atypical features may behave more aggressively than similarly graded tumors without atypical features. Here, the prognostic significance of atypical features in benign meningiomas was determined.

METHODS

Data from patients diagnosed with WHO Grade I benign meningiomas per the 2007 WHO criteria and who underwent surgery between 2002 and 2012 were retrospectively reviewed. Patients were stratified by the absence or presence of 1 to 2 atypical features with review of the clinical and histological factors.

RESULTS

A total of 148 patients met the inclusion criteria (n = 77 with atypia; n = 71 without atypia). The median follow-up duration after pathological diagnosis was 37.5 months. Thirty patients had progression/recurrence (P/R) after initial treatment, and 22 (73%) of 30 patients with P/R had 1–2 atypical features. The presence of atypical features was significantly associated with P/R (p = 0.03) and independent of the MIB-1 labeling index. The 1-year and 5-year actuarial rates of P/R were 9.6% versus 1.4% and 30.8% versus 13.8% fortumors with and without atypical features, respectively. Higher Simpson grade resection (II–IV vs I) was associated with the increased risk of P/R (p < 0.001). Stratification of patients into low-risk (Simpson Grade I), intermediate-risk (Simpson Grade II–IV with no atypical features), and high-risk groups (Simpson Grade II–IV with atypical features) was significantly correlated with increased risk of P/R (p < 0.001).

CONCLUSIONS

Patients with benign meningiomas with atypical features and those undergoing Simpson Grade II–IV resection are at significantly increased risk of P/R. Patients with these features may benefit from the consideration of additional surgery and/or radiation therapy.

Imaging and extent of surgical resection predict risk of meningioma recurrence better than WHO histopathological grade

BACKGROUND

Risk stratification of meningiomas by histopathological grade alone does not reliably predict which patients will progress/recur after treatment. We sought to determine whether preoperative imaging and clinical characteristics could predict histopathological grade and/or improve prognostication of progression/recurrence (P/R).

METHODS

We retrospectively reviewed preoperative MR and CT imaging features of 144 patients divided into low-grade (2007 WHO grade I; n = 118) and high-grade (2007 WHO grades II/III; n = 26) groups that underwent surgery between 2002 and 2013 (median follow-up of 49 months).

RESULTS

Multivariate analysis demonstrated that the risk factors most strongly associated with high-grade histopathology were male sex, low apparent diffusion coefficient (ADC), absent calcification, and high peritumoral edema. Remarkably, multivariate Cox proportional hazards analysis demonstrated that, in combination with extent of resection, ADC outperformed WHO histopathological grade for predicting which patients will suffer P/R after initial treatment. Stratification of patients into 3 risk groups based on non-Simpson grade I resection and low ADC as risk factors correlated with the likelihood of P/R (P < .001). The high-risk group (2 risk factors; n = 39) had a 45% cumulative incidence of P/R, whereas the low-risk group (0 risk factors; n = 31) had no P/R events at 5 years after treatment. Independent of histopathological grade, high-risk patients who received adjuvant radiotherapy had a lower 5-year crude rate of P/R than those without (17% vs 59%; P = .04).

CONCLUSIONS

Patients with non-Simpson grade I resection and low ADC meningiomas are at significantly increased risk of P/R and may benefit from adjuvant radiotherapy and/or additional surgery.

Vestibular schwannoma: suboccipital approach

Microsurgery via the suboccipital approach is a common treatment option for vestibular schwannomas (VS). The procedure is performed under general anesthesia with cranial nerve monitoring in the supine position. Following suboccipital craniectomy, durotomy, CSF release from the foramen magnum, and identification of cranial nerve position, the tumor is debulked internally. The internal auditory canal is drilled and dissection of the tumor progresses. Following resection, the IAC is waxed and a fat graft placed. A watertight pericranial graft is sewn in and a titanium mesh cranioplasty placed. The muscle and skin are closed in layers. The video can be found here: http://youtu.be/ialtKy3cuPU .

Single agent efficacy of the VEGFR kinase inhibitor axitinib in preclinical models of glioblastoma

Anti-angiogenic therapy is a promising therapeutic strategy for the highly vascular and malignant brain tumor, glioblastoma (GBM), although current clinical trials have failed to demonstrate an extension in overall survival. The small molecule tyrosine kinase inhibitor axitinib that targets vascular endothelial growth factor receptor, potently inhibits angiogenesis and has single-agent clinical activity in non-small cell lung, thyroid, and advanced renal cell cancer. Here we show that axitinib exerts direct cytotoxic activity against a number of patient-derived GBM stem cell (GSCs) and an endothelial cell line, and inhibits endothelial tube formation in vitro. Axitinib treatment of mice bearing hypervascular intracranial tumors generated from human U87 glioma cells, MGG4 GSCs and mouse 005 GSCs significantly extended survival that was associated with decreases in tumor-associated vascularity. We thus show for the first time the anti-angiogenic effect and survival prolongation provided by systemic single agent treatment with axitinib in preclinical orthotopic GBM models including clinically relevant GSC models. These results support further investigation of axitinib as an anti-angiogenic agent for GBM.

Treatment of orthotopic malignant peripheral nerve sheath tumors with oncolytic herpes simplex virus

BACKGROUNDS

Malignant peripheral nerve sheath tumors (MPNSTs) are an aggressive and often lethal sarcoma that frequently develops in patients with neurofibromatosis type 1 (NF1). We developed new preclinical MPNST models and tested the efficacy of oncolytic herpes simplex viruses (oHSVs), a promising cancer therapeutic that selectively replicates in and kills cancer cells.

METHODS

Mouse NF1(-) MPNST cell lines and human NF1(-) MPNST stemlike cells (MSLCs) were implanted into the sciatic nerves of immunocompetent and athymic mice, respectively. Tumor growth was followed by external measurement and sciatic nerve deficit using a hind-limb scoring system. Oncolytic HSV G47Δ as well as "armed" G47Δ expressing platelet factor 4 (PF4) or interleukin (IL)-12 were injected intratumorally into established sciatic nerve tumors.

RESULTS

Mouse MPNST cell lines formed tumors with varying growth kinetics. A single intratumoral injection of G47Δ in sciatic nerve tumors derived from human S462 MSLCs in athymic mice or mouse M2 (37-3-18-4) cells in immunocompetent mice significantly inhibited tumor growth and prolonged survival. Local IL-12 expression significantly improved the efficacy of G47Δ in syngeneic mice, while PF4 expression prolonged survival. Injection of G47Δ directly into the sciatic nerve of athymic mice resulted in only mild symptoms that did not differ from phosphate buffered saline control.

CONCLUSIONS

Two new orthotopic MPNST models are described, including in syngeneic mice, expanding the options for preclinical testing. Oncolytic HSV G47Δ exhibited robust efficacy in both immunodeficient and immunocompetent MPNST models while maintaining safety. Interleukin-12 expression improved efficacy. These studies support the clinical translation of G47Δ for patients with MPNST.

Single-cell RNA-seq highlights intratumoral heterogeneity in primary glioblastoma

Human cancers are complex ecosystems composed of cells with distinct phenotypes, genotypes, and epigenetic states, but current models do not adequately reflect tumor composition in patients. We used single-cell RNA sequencing (RNA-seq) to profile 430 cells from five primary glioblastomas, which we found to be inherently variable in their expression of diverse transcriptional programs related to oncogenic signaling, proliferation, complement/immune response, and hypoxia. We also observed a continuum of stemness-related expression states that enabled us to identify putative regulators of stemness in vivo. Finally, we show that established glioblastoma subtype classifiers are variably expressed across individual cells within a tumor and demonstrate the potential prognostic implications of such intratumoral heterogeneity. Thus, we reveal previously unappreciated heterogeneity in diverse regulatory programs central to glioblastoma biology, prognosis, and therapy.

Reconstructing and reprogramming the tumor-propagating potential of glioblastoma stem-like cells

Developmental fate decisions are dictated by master transcription factors (TFs) that interact with cis-regulatory elements to direct transcriptional programs. Certain malignant tumors may also depend on cellular hierarchies reminiscent of normal development but superimposed on underlying genetic aberrations. In glioblastoma (GBM), a subset of stem-like tumor-propagating cells (TPCs) appears to drive tumor progression and underlie therapeutic resistance yet remain poorly understood. Here, we identify a core set of neurodevelopmental TFs (POU3F2, SOX2, SALL2, and OLIG2) essential for GBM propagation. These TFs coordinately bind and activate TPC-specific regulatory elements and are sufficient to fully reprogram differentiated GBM cells to "induced" TPCs, recapitulating the epigenetic landscape and phenotype of native TPCs. We reconstruct a network model that highlights critical interactions and identifies candidate therapeutic targets for eliminating TPCs. Our study establishes the epigenetic basis of a developmental hierarchy in GBM, provides detailed insight into underlying gene regulatory programs, and suggests attendant therapeutic strategies. PAPERCLIP:

An aberrant transcription factor network essential for Wnt signaling and stem cell maintenance in glioblastoma

Glioblastoma (GBM) is thought to be driven by a subpopulation of cancer stem cells (CSCs) that self-renew and recapitulate tumor heterogeneity yet remain poorly understood. Here, we present a comparative analysis of chromatin state in GBM CSCs that reveals widespread activation of genes normally held in check by Polycomb repressors. These activated targets include a large set of developmental transcription factors (TFs) whose coordinated activation is unique to the CSCs. We demonstrate that a critical factor in the set, ASCL1, activates Wnt signaling by repressing the negative regulator DKK1. We show that ASCL1 is essential for the maintenance and in vivo tumorigenicity of GBM CSCs. Genome-wide binding profiles for ASCL1 and the Wnt effector LEF-1 provide mechanistic insight and suggest widespread interactions between the TF module and the signaling pathway. Our findings demonstrate regulatory connections among ASCL1, Wnt signaling, and collaborating TFs that are essential for the maintenance and tumorigenicity of GBM CSCs.

Expression of FMS-like tyrosine kinase 3 ligand by oncolytic herpes simplex virus type I prolongs survival in mice bearing established syngeneic intracranial malignant glioma

BACKGROUND

Glioblastoma is a fatal brain tumor in needing urgent effective therapy. Treatments with both oncolytic viruses and immunotherapy have shown preclinical efficacy and clinical promise. We sought to exploit possible synergies between oncolytic herpes simplex virus type 1 (oHSV-1) infection of intracranial gliomas and delivery of immune-stimulating fms-like tyrosine kinase 3 ligand (Flt3L) by engineering a herpes vector to express the cytokine.

OBJECTIVE

To construct an oHSV-1 vector that expresses high levels of Flt3L and examine its antiglioma efficacy in an immunocompetent murine model.

METHODS

G47Δ and a bacterial artificial chromosome system were used to generate a novel oHSV-1, termed G47Δ-Flt3L, expressing Flt3L. Cytokine expression was confirmed, and G47Δ-Flt3L was injected intratumorally into established intracranial CT-2A gliomas in syngeneic C57/Bl6 mice. Animals were followed for survival and assessed by the Kaplan-Meier method.

RESULTS

G47Δ-Flt3L expressed high levels of Flt3L in culture. Expression of Flt3L affected neither viral replication nor had a cytotoxic effect on CT2A glioma cells. Direct inoculation into intracerebral CT2A glioma cells resulted in high levels of detectable Flt3L in mouse blood and was superior to parental G47Δ in prolonging survival in glioma-bearing animals.

CONCLUSION

Treatment with G47Δ-Flt3L improves survival of glioma-bearing mice.

Combination of vinblastine and oncolytic herpes simplex virus vector expressing IL-12 therapy increases antitumor and antiangiogenic effects in prostate cancer models

Oncolytic herpes simplex virus (oHSV)-1-based vectors selectively replicate in tumor cells causing direct killing, that is, oncolysis, while sparing normal cells. The oHSVs are promising anticancer agents, but their efficacy, when used as single agents, leaves room for improvement. We hypothesized that combining the direct oncolytic and antiangiogenic activities of the interleukin (IL)-12-secreting NV1042 oHSV with microtubule disrupting agents (MDAs) would be an effective means to enhance antitumor efficacy. Vinblastine (VB) was identified among several MDAs screened, which displayed consistent and potent cytotoxic killing of both prostate cancer and endothelial cell lines. In matrigel tube-forming assays, VB was found to be highly effective at inhibiting tube formation of human umbilical vein endothelial cells. The combination of VB with NV1023 (the parental virus lacking IL-12) or NV1042 showed additive or synergistic activity against prostate cancer cell lines, and was not due to increased oHSV replication by VB. In athymic mice bearing CWR22 prostate tumors, VB in combination with NV1042 was superior to the combination of VB plus NV1023 in reducing tumor burden, appeared to be nontoxic and resulted in a statistically significant diminution in the number of CD31(+) cells as compared with other treatment groups. In human organotypic cultures using surgical samples from radical prostatectomies, both NV1023 and NV1042 were localized specifically to the epithelial cells of prostatic glands but not to the surrounding stroma. These data highlight the therapeutic advantage of combining the dual-acting antitumor and antiangiogenic activities of oHSVs and MDAs.

Postoperative imaging of vestibular schwannomas

Symptomatic vestibular schwannomas can be treated with resection (translabyrinthine, retrosigmoid [suboccipital], or middle cranial fossa approaches) or stereotactic radiosurgery. When appropriate, auditory brainstem stimulators can also be implanted in patients with current or impending hearing loss due to bilateral vestibular schwannomas. Imaging plays a prominent role in determining management following these procedures. In this article, the expected postoperative imaging appearances are depicted. The radiological features of complications are also reviewed, including recurrent tumor, fat graft necrosis, CSF leakage, infection, hydrocephalus, cerebral infarction, venous sinus thrombosis, hemorrhage, and temporal lobe and cerebellar contusions.

Multimechanistic tumor targeted oncolytic virus overcomes resistance in brain tumors

Only a subset of cancer patients inoculated with oncolytic herpes simplex virus (oHSV) type-1 has shown objective response in phase 1 and 2 clinical trials. This has raised speculations whether resistance of tumor cells to oHSV therapy may be a limiting factor. In this study, we have identified established and patient derived primary glioblastoma multiforme (GBM) stem cell lines (GSC) resistant to oHSV and also to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) that has recently shown promise in preclinical and initial clinical studies. We created a recombinant oHSV bearing a secretable TRAIL (oHSV-TRAIL) and hypothesized that oHSV-TRAIL could be used as a cancer therapeutic to target a broad spectrum of resistant tumors in a mechanism-based manner. Using the identified resistant GBM lines, we show that oHSV-TRAIL downregulates extracellular signal-regulated protein kinase (ERK)-mitogen-activated protein kinase (MAPK) and upregulates c-Jun N-terminal kinase (JNK) and p38-MAPK signaling, which primes resistant GBM cells to apoptosis via activation of caspase-8, -9, and -3. We further show that oHSV-TRAIL inhibits tumor growth and invasiveness and increases survival of mice bearing resistant intracerebral tumors without affecting the normal tissues. This study sheds new light on the mechanism by which oHSV and TRAIL function in concert to overcome therapeutic-resistance, and provides an oncolytic virus based platform to target a broad spectrum of different cancer types.

Oncolytic herpes simplex virus counteracts the hypoxia-induced modulation of glioblastoma stem-like cells

Glioblastoma (GBM), a fatal malignant brain tumor, contains abundant hypoxic regions that provide a "niche" to promote both the maintenance and enrichment of glioblastoma stem-like cells (GSCs) and confer resistance to chemo- and radiotherapy. Since GSCs, with an ability to resist conventional therapies, may be responsible for tumor recurrence, targeting GSCs located in such a hypoxic environment may be critical to improving the therapeutic outcome for GBM patients. Oncolytic viral therapies have been tested in the clinic as a promising therapeutic approach for GBM. In this study, we analyzed and compared the therapeutic effects of oncolytic herpes simplex virus (oHSV) type 1 G47Δ (γ34.5(-)ICP6(-)LacZ(+)α47(-)) in patient-derived GSCs under normoxia (21% oxygen) and hypoxia (1% oxygen). GSCs cultured in hypoxia showed an increased ability to form neurospheres and expressed higher levels of the putative stem cell marker CD133 compared with GSCs cultured in normoxia. G47Δ exhibited a comparable ability to infect, replicate, and kill GSCs in normoxia and hypoxia in vitro. Importantly, G47Δ could counteract hypoxia-mediated enhancement of the stem-like properties of GSCs, inhibiting their self-renewal and stem cell marker expression. Using orthotopic human GSC xenografts in mice, we demonstrated that intratumoral injection of G47ΔUs11fluc, a newly developed G47Δ derivative that expresses firefly luciferase driven by a true late viral promoter, led to an equivalent frequency of viral infection and replication in hypoxic and nonhypoxic tumor areas. These findings suggest that oHSV G47Δ represents a promising therapeutic strategy to target and kill GSCs, not only in normoxic areas of GBM but also within the hypoxic niche.

Oncolytic virus-mediated manipulation of DNA damage responses: synergy with chemotherapy in killing glioblastoma stem cells

BACKGROUND

Although both the alkylating agent temozolomide (TMZ) and oncolytic viruses hold promise for treating glioblastoma, which remains uniformly lethal, the effectiveness of combining the two treatments and the mechanism of their interaction on cancer stem cells are unknown.

METHODS

We investigated the efficacy of combining TMZ and the oncolytic herpes simplex virus (oHSV) G47Δ in killing glioblastoma stem cells (GSCs), using Chou-Talalay combination index analysis, immunocytochemistry and fluorescence microscopy, and neutral comet assay. The role of treatment-induced DNA double-strand breaks, activation of DNA damage responses, and virus replication in the cytotoxic interaction between G47Δ and TMZ was examined with a panel of pharmacological inhibitors and short-hairpin RNA (shRNA)-mediated knockdown of DNA repair pathways. Comparisons of cell survival and virus replication were performed using a two-sided t test (unpaired). The survival of athymic mice (n = 6-8 mice per group) bearing GSC-derived glioblastoma tumors treated with the combination of G47Δ and TMZ was analyzed by the Kaplan-Meier method and evaluated with a two-sided log-rank test.

RESULTS

The combination of G47Δ and TMZ acted synergistically in killing GSCs but not neurons, with associated robust induction of DNA damage. Pharmacological and shRNA-mediated knockdown studies suggested that activated ataxia telangiectasia mutated (ATM) is a crucial mediator of synergy. Activated ATM relocalized to HSV DNA replication compartments where it likely enhanced oHSV replication and could not participate in repairing TMZ-induced DNA damage. Sensitivity to TMZ and synergy with G47Δ decreased with O(6)-methylguanine-DNA-methyltransferase (MGMT) expression and MSH6 knockdown. Combined G47Δ and TMZ treatment extended survival of mice bearing GSC-derived intracranial tumors, achieving long-term remission in four of eight mice (median survival = 228 days; G47Δ alone vs G47Δ + TMZ, hazard ratio of survival = 7.1, 95% confidence interval = 1.9 to 26.1, P = .003) at TMZ doses attainable in patients.

CONCLUSIONS

The combination of G47Δ and TMZ acts synergistically in killing GSCs through oHSV-mediated manipulation of DNA damage responses. This strategy is highly efficacious in representative preclinical models and warrants clinical translation.

Maintenance of primary tumor phenotype and genotype in glioblastoma stem cells

The clinicopathological heterogeneity of glioblastoma (GBM) and the various genetic and phenotypic subtypes in GBM stem cells (GSCs) are well described. However, the relationship between GSCs and the corresponding primary tumor from which they were isolated is poorly understood. We have established GSC-enriched neurosphere cultures from 15 newly diagnosed GBM specimens and examined the relationship between the histopathological and genomic features of GSC-derived orthotopic xenografts and those of the respective patient tumors. GSC-initiated xenografts recapitulate the distinctive cytological hallmarks and diverse histological variants associated with the corresponding patient GBM, including giant cell and gemistocytic GBM, and primitive neuroectodermal tumor (PNET)-like components. This indicates that GSCs generate tumors that preserve patient-specific disease phenotypes. The majority of GSC-derived intracerebral xenografts (11 of 15) demonstrated a highly invasive behavior crossing the midline, whereas the remainder formed discrete nodular and vascular masses. In some cases, GSC invasiveness correlated with preoperative MRI, but not with the status of PI3-kinase/Akt pathways or O(6)-methylguanine methyltransferase expression. Genome-wide screening by array comparative genomic hybridization and fluorescence in situ hybridization revealed that GSCs harbor unique genetic copy number aberrations. GSCs acquiring amplifications of the myc family genes represent only a minority of tumor cells within the original patient tumors. Thus, GSCs are a genetically distinct subpopulation of neoplastic cells within a GBM. These studies highlight the value of GSCs for preclinical modeling of clinically relevant, patient-specific GBM and, thus, pave the way for testing novel anti-GSC/GBM agents for personalized therapy.

Enhanced antitumor efficacy of low-dose Etoposide with oncolytic herpes simplex virus in human glioblastoma stem cell xenografts

PURPOSE

Glioblastoma (GBM) inevitably recurs despite surgery, radiation, and chemotherapy. A subpopulation of tumor cells, GBM stem cells (GSC), has been implicated in this recurrence. The chemotherapeutic agent etoposide is generally reserved for treating recurrent tumors; however, its effectiveness is limited due to acute and cumulative toxicities to normal tissues. We investigate a novel combinatorial approach of low-dose etoposide with an oncolytic HSV to enhance antitumor activity and limit drug toxicity.

EXPERIMENTAL DESIGN

In vitro, human GBM cell lines and GSCs were treated with etoposide alone, oncolytic herpes simplex virus (oHSV) G47Δ alone, or the combination. Cytotoxic interactions were analyzed using the Chou-Talalay method, and changes in caspase-dependent apoptosis and cell cycle were determined. In vivo, the most etoposide-resistant human GSC, BT74, was implanted intracranially and treated with either treatment alone or the combination. Analysis included effects on survival, therapy-associated adverse events, and histologic detection of apoptosis.

RESULTS

GSCs varied in their sensitivity to etoposide by over 50-fold in vitro, whereas their sensitivity to G47Δ was similar. Combining G47Δ with low-dose etoposide was moderately synergistic in GSCs and GBM cell lines. This combination did not enhance virus replication, but significantly increased apoptosis. In vivo, the combination of a single cycle of low-dose etoposide with G47Δ significantly extended survival of mice-bearing etoposide-insensitive intracranial human GSC-derived tumors.

CONCLUSIONS

The combination of low-dose etoposide with G47Δ increases survival of mice-bearing intracranial human GSC-derived tumors without adverse side effects. These results establish this as a promising combination strategy to treat resistant and recurrent GBM.

Distinguishing inflammation from tumor and peritumoral edema by myeloperoxidase magnetic resonance imaging

PURPOSE

Inflammation occurs routinely when managing gliomas and is not easily distinguishable from tumor regrowth by current MRI methods. The lack of noninvasive technologies that monitor inflammation prevents us to understand whether it is beneficial or detrimental for the patient, and current therapies do not take this host response in consideration. We aim to establish whether a gadolinium (Gd)-based agent targeting the inflammatory enzyme myeloperoxidase (MPO) can selectively detect intra- and peritumoral inflammation as well as glioma response to treatment by MRI.

METHODS

We carried out serial Gd-bis-5-HT-DTPA (MPO-Gd) MRI before and after treating rodent gliomas with different doses of oncolytic virus (OV) and analyzed animal survival. The imaging results were compared with histopathologic and molecular analyses of the tumors for macrophage/microglia infiltration, virus persistence, and MPO levels.

RESULTS

Elevated MPO activity was observed by MRI inside the tumor and in the peritumoral cerebrum at day 1 post-OV injection, which corresponded with activation/infiltration of myeloid cells inhibiting OV intratumoral persistence. MPO activity decreased, whereas tumor size increased, as the virus and the immune cells were cleared (days 1-7 post-OV injection). A 10-fold increase in viral dose temporally decreased tumor size, but augmented MPO activity, thus preventing extension of viral intratumoral persistence.

CONCLUSIONS

MPO-Gd MRI can distinguish enhancement patterns that reflect treatment-induced spatiotemporal changes of intratumoral and intracerebral inflammation from those indicating tumor and peritumoral edema. This technology improves the posttreatment diagnosis of gliomas and will increase our understanding of the role of inflammation in cancer therapy.

A novel oncolytic herpes simplex virus that synergizes with phosphoinositide 3-kinase/Akt pathway inhibitors to target glioblastoma stem cells

PURPOSE

To develop a new oncolytic herpes simplex virus (oHSV) for glioblastoma (GBM) therapy that will be effective in glioblastoma stem cells (GSC), an important and untargeted component of GBM. One approach to enhance oHSV efficacy is by combination with other therapeutic modalities.

EXPERIMENTAL DESIGN

MG18L, containing a U(S)3 deletion and an inactivating LacZ insertion in U(L)39, was constructed for the treatment of brain tumors. Safety was evaluated after intracerebral injection in HSV-susceptible mice. The efficacy of MG18L in human GSCs and glioma cell lines in vitro was compared with other oHSVs, alone or in combination with phosphoinositide-3-kinase (PI3K)/Akt inhibitors (LY294002, triciribine, GDC-0941, and BEZ235). Cytotoxic interactions between MG18L and PI3K/Akt inhibitors were determined using Chou-Talalay analysis. In vivo efficacy studies were conducted using a clinically relevant mouse model of GSC-derived GBM.

RESULTS

MG18L was severely neuroattenuated in mice, replicated well in GSCs, and had anti-GBM activity in vivo. PI3K/Akt inhibitors displayed significant but variable antiproliferative activities in GSCs, whereas their combination with MG18L synergized in killing GSCs and glioma cell lines, but not human astrocytes, through enhanced induction of apoptosis. Importantly, synergy was independent of inhibitor sensitivity. In vivo, the combination of MG18L and LY294002 significantly prolonged survival of mice, as compared with either agent alone, achieving 50% long-term survival in GBM-bearing mice.

CONCLUSIONS

This study establishes a novel therapeutic strategy: oHSV manipulation of critical oncogenic pathways to sensitize cancer cells to molecularly targeted drugs. MG18L is a promising agent for the treatment of GBM, being especially effective when combined with PI3K/Akt pathway-targeted agents.

Abstract 2568: Combination treatment of bevacizumab and oncolytic HSV armed with angiostatin show enhanced antitumoral and antiangiogenic effects

Background: Bevacizumab (Avastin), a monoclonal antibody that inactivates VEGF, was approved by US Food and Drug Administration as a single agent for treatment of recurrent glioblastomas (GBM). It prolongs progression-free survival and controls peritumoral edema. However, its effect on prognosis and overall survival remains to be determined. Angiostatin is a naturally occurring inhibitor of angiogenesis that was shown to inhibit growth of primary and metastatic tumors, but can not be delivered efficiently to GBM. Oncolytic viruses (OV) are promising agents for the treatment of GBM, whose therapeutic potential is not fully exploited due to infiltration of anti-viral macrophages. Treatment with anti-angiogenic factors was shown to increase replication and therapeutic capacity of OV. We hypothesized that combination of Avastin with an HSV OV (G47Δ) coding for angiostatin (G47Δ-angio) would enhance GBM treatment due to increased viral spread and delivery of angiostatin.

Materials & Methods: G47Δ-angio was constructed using the “flip-flop” HSV-BAC system. Expression of angiostatin was confirmed by western blot; in vitro matrigel endothelial tube formation assay was performed to test its anti-angiogenic potential. We confirmed the capacity of this virus to infect cancer cells and inhibit tumor angiogenesis in vivo, and determined therapeutic efficacy using both a subcutaneous and an intracerebral glioma model in mice. A control virus not carrying the angiostatin gene (G47Δ-empty) served as the negative control for all experiments. Avastin (5mg/kg) was delivered by i.v injection in intracerebral glioma model, started at Day 5 and followed by twice a week for consecutive 4 weeks. Tumor angiogenesis was determined by CD31 and VEGF staining, macrophages infiltration was detected by F4/80 staining. The overall survival of intracerebral glioma mice was followed up in G47Δ-angio, Avastin and combination (G47Δ-angio + Avastin) treatments.

Results: G47Δ-angio decreased endothelial tube formation in vitro and demonstrated potent antiangiogenic effects in vivo. In our subcutaneous tumor model, G47Δ inhibited tumor growth (n=7/group, P&lt;0.05) and in the intracranial glioma model, G47Δ extended survival (n=10/group, P&lt;0.05). Furthermore, the combination treatment (G47Δ-angio + Avastin) had the most significant antitumor and antiangiogenesis efficacy compared with either treatment alone (n=10/group, P&lt;0.05).

Conclusion: Our results demonstrate that G47Δ-angio could significantly enhance antitumor and antiangiogenic efficacy. Moreover, the combination treatment could further improve the antitumor and antiangiogenic efficacy in intracerebral glioma model in vivo. Hence, “Arming” HSV with an antiangiogenic gene that targets both the tumor cells and tumor vasculature is a promising therapy for use with Avastin treatment in clinical translation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2568. doi:10.1158/1538-7445.AM2011-2568

Abstract 5389: Oncolytic herpes simplex virus expressing interleukin-12 for treating glioma stem cells

Glioblastoma multiforme (GBM) is an aggressive adult brain tumor that despite surgery, radiation and chemotherapy, inevitably recurs. This tumor recurrence is thought to be due to a subpopulation of cells with stem cell-like properties called glioma stem cells (GSCs), and specific targeting of these GSCs might improve GBM treatment. Oncolytic herpes simplex virus (oHSV) vectors are genetically engineered to selectively replicate in, and kill cancer cells, without harming normal tissue, and have been shown to be safe in glioma clinical trials. Our group has shown that oHSV G47delta (G47D) can kill human GSCs, yet its efficacy in vivo was insufficient. Moreover, it is not well understood if GSCs can be targeted effectively by an anti-tumor immune response, partly due to the lack of immune-competent mouse models of GSCs. In this study, we hypothesize that arming G47D with interleukin-12 (IL-12), a critical cytokine involved in adaptive and innate immune responses as well as anti-angiogenesis, will be more effective at targeting GSCs, and tested this using a new syngeneic mouse model of GSCs.

We characterized mouse 005 GSCs (obtained from I. Verma, UCSD) which constitutively express H-Ras and are p53-/+. They exhibit stem cells markers such as nestin and CD133, could be differentiated into neuronal and glial phenotype, and could form tumors in C57BL/6 mice with characteristic GBM necrosis, giant cells and CD31-positive vasculature. These 005 mGSCs expressed MHC/NK ligand markers, but lacked significant expression of co-stimulatory signaling molecules for T cells as observed by flow cytometry. In vitro, treatment of 005 GSCs with increasing concentrations of G47D-Empty (−E; without transgene) or G47D-IL12 resulted in increase in cytotoxicity with similar EC50 values (MOI∼0.1 at 4 days). G47D-IL12 also replicated well in 005 mGSCs leading to a significant release of IL-12 as measured by ELISA. Intracranial tumors established by implanting 005 mGSC in C57BL/6 mice were then treated with two intratumoral injections of either G47D-E or G47D-IL12 oHSV. This resulted in a significant inhibition in tumor growth with extension of survival with G47D-E (median survival 40.5 days; p&lt; 0.03) and G47D-IL12 (median survival 56 days; p&lt; 0.0001) compared with control saline-injected mice with a median survival of 37 days. Importantly, there was a significant increase in survival of mice treated with G47D-IL12 (p&lt; 0.0003) when compared with G47D-E. This increase in survival, potentially due to increased immune response and/or decrease in angiogenesis, is currently under investigation.

This is the first demonstration that GSC can be effectively targeted with oHSV-IL12 in a syngeneic GSC mouse model, showing its marked efficacy over G47D-E. This may be a promising strategy to eradicate glioma cell populations through direct oncolysis combined with enhancing anti-tumor immunity as well as altering the tumor vasculature microenvironment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5389. doi:10.1158/1538-7445.AM2011-5389

Identification of the ENT1 antagonists dipyridamole and dilazep as amplifiers of oncolytic herpes simplex virus-1 replication

Oncolytic herpes simplex virus-1 (oHSV) vectors selectively replicate in tumor cells, where they kill through oncolysis while sparing normal cells. One of the drawbacks of oHSV vectors is their limited replication and spread to neighboring cancer cells. Here, we report the outcome of a high-throughput chemical library screen to identify small-molecule compounds that augment the replication of oHSV G47Delta. Of the 2,640-screened bioactives, 6 compounds were identified and subsequently validated for enhanced G47Delta replication. Two of these compounds, dipyridamole and dilazep, interfered with nucleotide metabolism by potently and directly inhibiting the equilibrative nucleoside transporter-1 (ENT1). Replicative amplification promoted by dipyridamole and dilazep were dependent on HSV mutations in ICP6, the large subunit of ribonucleotide reductase. Our results indicate that ENT1 antagonists augment oHSV replication in tumor cells by increasing cellular ribonucleoside activity.

Oncolytic herpes simplex virus armed with xenogeneic homologue of prostatic acid phosphatase enhances antitumor efficacy in prostate cancer

Prostate cancer is one of the most prevalent cancers in men. Replication-competent oncolytic herpes simplex virus (oHSV) vectors are a powerful antitumor therapy that can exert at least two effects: direct cytocidal activity that selectively kills cancer cells and induction of antitumor immunity. In addition, oHSV vectors can also function as a platform to deliver transgenes of interest. In these studies, we have examined the expression of a xenogeneic homologue of the prostate cancer antigen, prostatic acid phosphatase (PAP), with the goal of enhancing virotherapy against PAP-expressing tumors. PAP has already been used for cancer vaccination in patients with prostate cancer. Here we show that treatment with oHSV bPDelta6 expressing xenogeneic human PAP (hPAP) significantly reduces tumor growth and increases survival of C57/BL6 mice bearing mouse TRAMP-C2 prostate tumors, whereas expression of syngeneic mouse PAP (mPAP) from the same oHSV vector did not enhance antitumor activity. Treatment of mice bearing metastatic TRAMP-C2 lung tumors with oHSV-expressing hPAP resulted in fewer tumor nodules. To our knowledge, this is the first report of oncolytic viruses being used to express xenoantigens. These data lend support to the concept of combining oncolytic and immunogenic therapies as a way to improve therapy of metastatic prostate cancer.

Analysis of genetically engineered oncolytic herpes simplex viruses in human prostate cancer organotypic cultures

Oncolytic herpes simplex viruses type 1 (oHSVs) such as G47Delta and G207 are genetically engineered for selective replication competence in cancer cells. Several factors can influence the overall effectiveness of oHSV tropism, including HSV-1 receptor expression, extracellular matrix milieu and cellular permissiveness. We have taken advantage of human prostate organ cultures derived from radical prostatectomies to investigate oHSV tropism. In this study, we show that both G47Delta and G207 specifically replicate in epithelial cells of the prostatic glands but not in the surrounding stroma. In contrast, both the epithelial and stromal cell compartments were readily infected by wild-type HSV-1. Analysis of oHSV replication in prostate surgical specimens 3 days post infection showed that G47Delta generated approximately 30-fold more viral progeny than did G207. This correlated with the enhanced expression of G47Delta-derived glycoprotein gB protein levels as compared with G207. In benign prostate tissues, G207 and G47Delta titers were notably reduced, whereas strain F titers were maintained at similar levels compared with prostate cancer specimens. Overall, our results show that these oncolytic herpes vectors show both target specificity and replication competence in human prostate cancer specimens and point to the utility of using human prostate organ cultures in assessing oHSV tropism and cellular specificity.

Abstract C176: Combining oncolytic herpes simplex virus and chemotherapy: G47 and temozolomide synergize in killing glioma stem cells

Malignant gliomas, such as glioblastoma, are amongst the most common primary brain tumors in adults. Along with debulking surgery and post-operative radiation, the alkylating agent temozolomide (TMZ) is the standard of care for glioblastoma patients. However, the benefits of TMZ are correlated with tumors having transcriptional silencing of the O6-methylguanine methyltransferase (MGMT) gene, which occurs in approximately half of tumors. Unfortunately, regardless of MGMT status, recurrence or progression are inevitable, necessitating novel therapeutic approaches. Glioma stem cells (GSCs) have been implicated as a potential perpetrator of glioma recurrence. We have established human GSCs from surgically resected glioblastomas that vary in MGMT expression and TMZ sensitivity. Five human GSC lines were examined, two of which were MGMT-positive (confirmed by western blotting). MGMT-negative GSCs were more sensitive to TMZ (IC50&lt;100 µM) than their counterparts grown in serum-containing media (representative of the bulk tumor) or established glioma cell lines such as U87 or U373. MGMT-positive GSCs were extremely resistant to TMZ (IC50&gt;1000 µM). When MGMT was inactivated by O6-Benzylguanine (O6-BG), GSC sensitivity to TMZ approximately doubled. Oncolytic viruses destroy tumor cells by different mechanisms from conventional therapeutics, including TMZ, and therefore should interact positively. We have previously reported that clinically tested oncolytic herpes simplex virus (oHSV) G207 combined with TMZ synergistically kills established glioma cell lines. However, G207 does not replicate in GSCs. Therefore, we examined a newer generation oHSV, G47, which was effective at killing GSCs regardless of MGMT status. The interaction between TMZ and G47 on GSC killing was assessed by Chou-Talalay analysis. For MGMT-negative GSCs, the combination was synergistic, while it was antagonistic for MGMT-positive GSCs. When MGMT was inactivated with O6-BG, the interaction became synergistic for MGMT-positive GSCs. Interestingly, viral replication, entry, or spread was not affected by combination treatment. For those combinations that were synergistic, there was a large increase in H2AX, indicative of DNA double-strand breaks. Finally, the effect of combination therapy was assessed in two in vivo GSC models: GBM8 (MGMT-negative) and BT74 (MGMT-positive). Intracerebral tumors were established in athymic mice and treated with chemotherapy and/or intracerebral injection of G47 on the second day of chemotherapy. TMZ + G47 was more effective than either agent alone in extending survival in mice bearing GBM8 tumors. In the BT74 model, TMZ + O6-BG + G47 was more effective than TMZ+O6-BG or G47 alone. These studies demonstrate that GSCs can be both sensitive and resistant to TMZ, correlating with their MGMT status. All GSCs were sensitive to killing by G47 and this was synergistically enhanced by TMZ or TMZ+O6-BG, depending upon the MGMT status. Importantly, the combination was very efficacious in vivo in both models, suggesting that this combination strategy be tested clinically.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C176.

Human glioblastoma-derived cancer stem cells: establishment of invasive glioma models and treatment with oncolytic herpes simplex virus vectors

Glioblastoma, the most malignant type of primary brain tumor, is one of the solid cancers where cancer stem cells have been isolated, and studies have suggested resistance of those cells to chemotherapy and radiotherapy. Here, we report the establishment of CSC-enriched cultures derived from human glioblastoma specimens. They grew as neurospheres in serum-free medium with epidermal growth factor and fibroblast growth factor 2, varied in the level of CD133 expression and very efficiently formed highly invasive and/or vascular tumors upon intracerebral implantation into immunodeficient mice. As a novel therapeutic strategy for glioblastoma-derived cancer stem-like cells (GBM-SC), we have tested oncolytic herpes simplex virus (oHSV) vectors. We show that although ICP6 (UL39)-deleted mutants kill GBM-SCs as efficiently as wild-type HSV, the deletion of gamma34.5 significantly attenuated the vectors due to poor replication. However, this was significantly reversed by the additional deletion of alpha47. Infection with oHSV G47Delta (ICP6(-), gamma34.5(-), alpha47(-)) not only killed GBM-SCs but also inhibited their self-renewal as evidenced by the inability of viable cells to form secondary tumor spheres. Importantly, despite the highly invasive nature of the intracerebral tumors generated by GBM-SCs, intratumoral injection of G47Delta significantly prolonged survival. These results for the first time show the efficacy of oHSV against human GBM-SCs, and correlate this cytotoxic property with specific oHSV mutations. This is important for designing new oHSV vectors and clinical trials. Moreover, the new glioma models described in this study provide powerful tools for testing experimental therapeutics and studying invasion and angiogenesis.