Dimer-specific immunoprecipitation of active caspase-2 identifies TRAF proteins as novel activators.

Caspase-2 has been shown to initiate apoptotic cell death in response to specific intracellular stressors such as DNA damage. However, the molecular mechanisms immediately upstream of its activation are still poorly understood. We combined a caspase-2 bimolecular fluorescence complementation (BiFC) system with fluorophore-specific immunoprecipitation to isolate and study the active caspase-2 dimer and its interactome. Using this technique, we found that tumor necrosis factor receptor-associated factor 2 (TRAF2), as well as TRAF1 and 3, directly binds to the active caspase-2 dimer. TRAF2 in particular is necessary for caspase-2 activation in response to apoptotic cell death stimuli. Furthermore, we found that dimerized caspase-2 is ubiquitylated in a TRAF2-dependent manner at K15, K152, and K153, which in turn stabilizes the active caspase-2 dimer complex, promotes its association with an insoluble cellular fraction, and enhances its activity to fully commit the cell to apoptosis. Together, these data indicate that TRAF2 positively regulates caspase-2 activation and consequent cell death by driving its activation through dimer-stabilizing ubiquitylation.

Humanized chondroitinase ABC sensitizes glioblastoma cells to temozolomide.

BACKGROUND: Malignant gliomas (glioblastomas; GBMs) are extremely aggressive and have a median survival of approximately 15 months. Current treatment modalities, which include surgical resection, radiation and chemotherapy, have done little to prolong the lives of GBM patients. Chondroitin sulfate proteoglycans (CSPG) are critical for cell-cell and cell-extracellular matrix (ECM) interactions and are implicated in glioma growth and invasion. Chondroitinase (Chase) ABC is a bacterial enzyme that cleaves chondroitin sulfate disaccharide chains from CSPGs in the tumor ECM. Wild-type Chase ABC has limited stability and/or activity in mammalian cells; therefore, we created a mutant humanized version (Chase M) with enhanced function in mammalian cells. METHODS: We hypothesized that disruption of cell-cell and cell-ECM interactions by ChaseM and temozolomide (TMZ) will enhance the chemotherapeutic availability and sensitivity of glioma cells. RESULTS: Utilizing primary patient-derived neurospheres, we found that ChaseM decreases glioma neurosphere aggregation in vitro. Furthermore, an oncolytic HSV-1 virus expressing secreted ChaseM (OV-ChaseM) enhanced viral spread and glioma cell killing compared to OV-Control, in vitro. OV-ChaseM plus TMZ combinatorial treatment resulted in a significant synergistic enhancement of glioma cell killing accompanied by an increase in apoptotic cell death. Intracellular flow cytometric analysis revealed a significant reduction in the phosphorylation of the pro-survival AKT protein following OV-ChaseM plus TMZ treatment. Lastly, in nude mice bearing intracranial GBM30 glioma xenografts, intratumoral OV-ChaseM plus TMZ (10 mg/kg by oral gavage) combination therapy resulted in a significant (p < 0.02) enhancement of survival compared to each individual treatment alone. CONCLUSIONS: These data reveal that OV-ChaseM enhances glioma cell viral susceptibility and sensitivity to TMZ.

BAI1 Orchestrates Macrophage Inflammatory Response to HSV Infection-Implications for Oncolytic Viral Therapy.

Purpose: Brain angiogenesis inhibitor (BAI1) facilitates phagocytosis and bacterial pathogen clearance by macrophages; however, its role in viral infections is unknown. Here, we examined the role of BAI1, and its N-terminal cleavage fragment (Vstat120) in antiviral macrophage responses to oncolytic herpes simplex virus (oHSV).Experimental Design: Changes in infiltration and activation of monocytic and microglial cells after treatment of glioma-bearing mice brains with a control (rHSVQ1) or Vstat120-expressing (RAMBO) oHSV was analyzed using flow cytometry. Co-culture of infected glioma cells with macrophages or microglia was used to examine antiviral signaling. Cytokine array gene expression and Ingenuity Pathway Analysis (IPA) helped evaluate changes in macrophage signaling in response to viral infection. TNFα-blocking antibodies and macrophages derived from Bai1-/- mice were used.Results: RAMBO treatment of mice reduced recruitment and activation of macrophages/microglia in mice with brain tumors, and showed increased virus replication compared with rHSVQ1. Cytokine gene expression array revealed that RAMBO significantly altered the macrophage inflammatory response to infected glioma cells via altered secretion of TNFα. Furthermore, we showed that BAI1 mediated macrophage TNFα induction in response to oHSV therapy. Intracranial inoculation of wild-type/RAMBO virus in Bai1-/- or wild-type non-tumor-bearing mice revealed the safety of this approach.Conclusions: We have uncovered a new role for BAI1 in facilitating macrophage anti-viral responses. We show that arming oHSV with antiangiogenic Vstat120 also shields them from inflammatory macrophage antiviral response, without reducing safety. Clin Cancer Res; 23(7); 1809-19. ©2016 AACR.

Bortezomib Treatment Sensitizes Oncolytic HSV-1-Treated Tumors to NK Cell Immunotherapy.

PURPOSE: Both the proteasome inhibitor bortezomib and an oncolytic herpes simplex virus-1 (oHSV)-expressing GM-CSF are currently FDA approved. Although proteasome blockade can increase oHSV replication, immunologic consequences, and consequent immunotherapy potential are unknown. In this study, we investigated the impact of bortezomib combined with oHSV on tumor cell death and sensitivity to natural killer (NK) cell immunotherapy. EXPERIMENTAL DESIGN: Western blot, flow cytometry, and caspase 3/7 activity assays were used to evaluate the induction of apoptosis/autophagy and/or necroptotic cell death. Cellular and mitochondrial reactive oxygen species (ROS) production was measured using CellROX and MitoSOX. Inhibitors/shRNA-targeting ROS, JNK and RIP1 kinase (RIPK1) were used to investigate the mechanism of cell killing. The synergistic interaction between oHSV and bortezomib was calculated using a Chou-Talalay analysis. NK cells isolated from normal human blood were co-cultured with tumor cells to evaluate cellular interactions. Q-PCR, ELISA, and FACS analysis were used to evaluate NK cell activation. Intracranial tumor xenografts were used to evaluate antitumor efficacy. RESULTS: Combination treatment with bortezomib- and oHSV-induced necroptotic cell death and increased the production of mitochondrial ROS and JNK phosphorylation. Inhibitors/shRNA of RIPK1 and JNK rescued synergistic cell killing. Combination treatment also significantly enhanced NK cell activation and adjuvant NK cell therapy of mice treated with bortezomib and oHSV improved antitumor efficacy. CONCLUSIONS: This study provides a significant rationale for triple combination therapy with bortezomib, oHSV, and NK cells to improve efficacy, in glioblastoma patients. Clin Cancer Res; 22(21); 5265-76. ©2016 AACRSee related commentary by Suryadevara et al., p. 5164.

How to train glioma cells to die: molecular challenges in cell death.

The five-year survival rate for patients with malignant glioma is less than 10%. Despite aggressive chemo/radiotherapy these tumors have remained resistant to almost every interventional strategy evaluated in patients. Resistance to these agents is attributed to extrinsic mechanisms such as the tumor microenvironment, poor drug penetration, and tumoral heterogeneity. In addition, genetic and molecular examination of these tumors has revealed defective apoptotic regulation, enhanced pro-survival autophagy signaling, and a propensity for necrosis that aids in the adaptation to environmental stress and resistance to treatment. The combination of extrinsic and intrinsic hallmarks in glioma contributes to the multifaceted resistance to traditional anti-tumor agents. Here we describe the biology of the disease relevant to therapeutic resistance, with a specific focus on molecular deregulation of cell death pathways. Emerging studies investigating the targeting of these pathways including BH3 mimetics and autophagy inhibitors that are being evaluated in both the preclinical and clinical settings are discussed. This review highlights the pathways exploited by glioblastoma cells that drive their hallmark pro-survival predisposition and makes therapy development such a challenge.

Metabolic control of Ca2+/calmodulin-dependent protein kinase II (CaMKII)-mediated caspase-2 suppression by the B55ß/protein phosphatase 2A (PP2A).

High levels of metabolic activity confer resistance to apoptosis. Caspase-2, an apoptotic initiator, can be suppressed by high levels of nutrient flux through the pentose phosphate pathway. This metabolic control is exerted via inhibitory phosphorylation of the caspase-2 prodomain by activated Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). We show here that this activation of CaMKII depends, in part, on dephosphorylation of CaMKII at novel sites (Thr(393)/Ser(395)) and that this is mediated by metabolic activation of protein phosphatase 2A in complex with the B55ß targeting subunit. This represents a novel locus of CaMKII control and also provides a mechanism contributing to metabolic control of apoptosis. These findings may have implications for metabolic control of the many CaMKII-controlled and protein phosphatase 2A-regulated physiological processes, because both enzymes appear to be responsive to alterations in glucose metabolized via the pentose phosphate pathway.

SapC-DOPS-induced lysosomal cell death synergizes with TMZ in glioblastoma.

SapC-DOPS is a novel nanotherapeutic that has been shown to target and induce cell death in a variety of cancers, including glioblastoma (GBM). GBM is a primary brain tumor known to frequently demonstrate resistance to apoptosis-inducing therapeutics. Here we explore the mode of action for SapC-DOPS in GBM, a treatment being developed by Bexion Pharmaceuticals for clinical testing in patients. SapC-DOPS treatment was observed to induce lysosomal dysfunction of GBM cells characterized by decreased glycosylation of LAMP1 and altered proteolytic processing of cathepsin D independent of apoptosis and autophagic cell death. We observed that SapC-DOPS induced lysosomal membrane permeability (LMP) as shown by LysoTracker Red and Acridine Orange staining along with an increase of sphingosine, a known inducer of LMP. Additionally, SapC-DOPS displayed strong synergistic interactions with the apoptosis-inducing agent TMZ. Collectively our data suggest that SapC-DOPS induces lysosomal cell death in GBM cells, providing a new approach for treating tumors resistant to traditional apoptosis-inducing agents.

Aurora-A inhibition offers a novel therapy effective against intracranial glioblastoma.

Glioblastoma remains a devastating disease for which novel therapies are urgently needed. Here, we report that the Aurora-A kinase inhibitor alisertib exhibits potent efficacy against glioblastoma neurosphere tumor stem-like cells in vitro and in vivo. Many glioblastoma neurosphere cells treated with alisertib for short periods undergo apoptosis, although some regain proliferative activity upon drug removal. Extended treatment, however, results in complete and irreversible loss of tumor cell proliferation. Moreover, alisertib caused glioblastoma neurosphere cells to partially differentiate and enter senescence. These effects were also observed in glioma cells treated with the Aurora-A inhibitor TC-A2317 or anti-Aurora-A siRNA. Furthermore, alisertib extended median survival of mice bearing intracranial human glioblastoma neurosphere tumor xenografts. Alisertib exerted similar effects on glioblastoma neurosphere cells in vivo and resulted in markedly reduced activated phosphoThr288Aurora-A and increased abnormal mitoses and cellular ploidy, consistent with on-target activity. Our results offer preclinical proof-of-concept for alisertib as a new therapeutic for glioma treatment.

Genetic validation of the protein arginine methyltransferase PRMT5 as a candidate therapeutic target in glioblastoma.

Glioblastoma is the most common and aggressive histologic subtype of brain cancer with poor outcomes and limited treatment options. Here, we report the selective overexpression of the protein arginine methyltransferase PRMT5 as a novel candidate theranostic target in this disease. PRMT5 silences the transcription of regulatory genes by catalyzing symmetric dimethylation of arginine residues on histone tails. PRMT5 overexpression in patient-derived primary tumors and cell lines correlated with cell line growth rate and inversely with overall patient survival. Genetic attenuation of PRMT5 led to cell-cycle arrest, apoptosis, and loss of cell migratory activity. Cell death was p53-independent but caspase-dependent and enhanced with temozolomide, a chemotherapeutic agent used as a present standard of care. Global gene profiling and chromatin immunoprecipitation identified the tumor suppressor ST7 as a key gene silenced by PRMT5. Diminished ST7 expression was associated with reduced patient survival. PRMT5 attenuation limited PRMT5 recruitment to the ST7 promoter, led to restored expression of ST7 and cell growth inhibition. Finally, PRMT5 attenuation enhanced glioblastoma cell survival in a mouse xenograft model of aggressive glioblastoma. Together, our findings defined PRMT5 as a candidate prognostic factor and therapeutic target in glioblastoma, offering a preclinical justification for targeting PRMT5-driven oncogenic pathways in this deadly disease.

Systemic delivery of SapC-DOPS has antiangiogenic and antitumor effects against glioblastoma.

Saposin C-dioleoylphosphatidylserine (SapC-DOPS) nanovesicles are a nanotherapeutic which effectively target and destroy cancer cells. Here, we explore the systemic use of SapC-DOPS in several models of brain cancer, including glioblastoma multiforme (GBM), and the molecular mechanism behind its tumor-selective targeting specificity. Using two validated spontaneous brain tumor models, we demonstrate the ability of SapC-DOPS to selectively and effectively cross the blood-brain tumor barrier (BBTB) to target brain tumors in vivo and reveal the targeting to be contingent on the exposure of the anionic phospholipid phosphatidylserine (PtdSer). Increased cell surface expression of PtdSer levels was found to correlate with SapC-DOPS-induced killing efficacy, and tumor targeting in vivo was inhibited by blocking PtdSer exposed on cells. Apart from cancer cell killing, SapC-DOPS also exerted a strong antiangiogenic activity in vitro and in vivo. Interestingly, unlike traditional chemotherapy, hypoxic cells were sensitized to SapC-DOPS-mediated killing. This study emphasizes the importance of PtdSer exposure for SapC-DOPS targeting and supports the further development of SapC-DOPS as a novel antitumor and antiangiogenic agent for brain tumors.

NK cells impede glioblastoma virotherapy through NKp30 and NKp46 natural cytotoxicity receptors.

The role of the immune response to oncolytic Herpes simplex viral (oHSV) therapy for glioblastoma is controversial because it might enhance or inhibit efficacy. We found that within hours of oHSV infection of glioblastomas in mice, activated natural killer (NK) cells are recruited to the site of infection. This response substantially diminished the efficacy of glioblastoma virotherapy. oHSV-activated NK cells coordinated macrophage and microglia activation within tumors. In vitro, human NK cells preferentially lysed oHSV-infected human glioblastoma cell lines. This enhanced killing depended on the NK cell natural cytotoxicity receptors (NCRs) NKp30 and NKp46, whose ligands are upregulated in oHSV-infected glioblastoma cells. We found that HSV titers and oHSV efficacy are increased in Ncr1(-/-) mice and a Ncr1(-/-) NK cell adoptive transfer model of glioma, respectively. These results demonstrate that glioblastoma virotherapy is limited partially by an antiviral NK cell response involving specific NCRs, uncovering new potential targets to enhance cancer virotherapy.

Copper chelation enhances antitumor efficacy and systemic delivery of oncolytic HSV.

PURPOSE: Copper in serum supports angiogenesis and inhibits replication of wild-type HSV-1. Copper chelation is currently being investigated as an antiangiogenic and antineoplastic agent in patients diagnosed with cancer. Herpes simplex virus-derived oncolytic viruses (oHSV) are being evaluated for safety and efficacy in patients, but several host barriers limit their efficacy. Here, we tested whether copper inhibits oHSV infection and replication and whether copper chelation would augment therapeutic efficacy of oHSV. EXPERIMENTAL DESIGN: Subcutaneous and intracranial tumor-bearing mice were treated with oHSV ± ATN-224 to evaluate tumor burden and survival. Virus replication and cell killing was measured in the presence or absence of the copper chelating agent ATN-224 and in the presence or absence of copper in vitro. Microvessel density and changes in perfusion were evaluated by immunohistochemistry and dynamic contrast enhanced MRI (DCE-MRI). Serum stability of oHSV was measured in mice fed with ATN-224. Tumor-bearing mice were injected intravenously with oHSV; tumor burden and amount of virus in tumor tissue were evaluated. RESULTS: Combination of systemic ATN-224 and oHSV significantly reduced tumor growth and prolonged animal survival. Immunohistochemistry and DCE-MRI imaging confirmed that ATN-224 reduced oHSV-induced blood vessel density and vascular leakage. Copper at physiologically relevant concentrations inhibited oHSV replication and glioma cell killing, and this effect was rescued by ATN-224. ATN-224 increased serum stability of oHSV and enhanced the efficacy of systemic delivery. CONCLUSION: This study shows that combining ATN-224 with oHSV significantly increased serum stability of oHSV and greatly enhanced its replication and antitumor efficacy.

Extracellular matrix protein CCN1 limits oncolytic efficacy in glioma.

Oncolytic viral therapy has been explored widely as an option for glioma treatment but its effectiveness has remained limited. Cysteine rich 61 (CCN1) is an extracellular matrix (ECM) protein elevated in cancer cells that modulates their adhesion and migration by binding cell surface receptors. In this study, we examined a hypothesized role for CCN1 in limiting the efficacy of oncolytic viral therapy for glioma, based on evidence of CCN1 induction that occurs in this setting. Strikingly, we found that exogenous CCN1 in glioma ECM orchestrated a cellular antiviral response that reduced viral replication and limited cytolytic efficacy. Gene expression profiling and real-time PCR analysis revealed a significant induction of type-I interferon responsive genes in response to CCN1 exposure. This induction was accompanied by activation of the Jak/Stat signaling pathway, consistent with induction of an innate antiviral cellular response. Both effects were mediated by the binding of CCN1 to the cell surface integrin α6ß1, activating its signaling and leading to rapid secretion of interferon-α, which was essential for the innate antiviral effect. Together, our findings reveal how an integrin signaling pathway mediates activation of a type-I antiviral interferon response that can limit the efficacy of oncolytic viral therapy. Furthermore, they suggest therapeutic interventions to inhibit CCN1-integrin α6 interactions to sensitize gliomas to viral oncolysis.

Impact of tumor microenvironment on oncolytic viral therapy.

Interactions between tumor cells and their microenvironment have been shown to play a very significant role in the initiation, progression, and invasiveness of cancer. These tumor-stromal interactions are capable of altering the delivery and effectiveness of therapeutics into the tumor and are also known to influence future resistance and re-growth after treatment. Here we review recent advances in the understanding of the tumor microenvironment and its response to oncolytic viral therapy. The multifaceted environmental response to viral therapy can influence viral infection, replication, and propagation within the tumor. Recent studies have unveiled the complicated temporal changes in the tumor vasculature post-oncolytic virus (OV) treatment, and their impact on tumor biology. Similarly, the secreted extracellular matrix in solid tumors can affect both infection and spread of the therapeutic virus. Together, these complex changes in the tumor microenvironment also modulate the activation of the innate antiviral host immune response, leading to quick and efficient viral clearance. In order to combat these detrimental responses, viruses have been combined with pharmacological adjuvants and "armed" with therapeutic genes in order to suppress the pernicious environmental conditions following therapy. In this review we will discuss the impact of the tumor environment on viral therapy and examine some of the recent literature investigating methods of modulating this environment to enhance oncolysis.