Limited Effects of Class II Transactivator-Based Immunotherapy in Murine and Human Glioblastoma.

BACKGROUND: The major histocompatibility complex type II is downregulated in glioblastoma (GB) due to the silencing of the major transcriptional regulator class II transactivator (CIITA). We investigated the pro-immunogenic potential of CIITA overexpression in mouse and human GB. METHODS: The intracerebral growth of wildtype GL261-WT cells was assessed following contralateral injection of GL261-CIITA cells or flank injections with GL261-WT or GL261-CIITA cells. Splenocytes obtained from mice implanted intracerebrally with GL261-WT, GL261-CIITA cells or phosphate buffered saline (PBS) were transferred to other mice and subsequently implanted intracerebrally with GL261-WT. Human GB cells and (syngeneic) GB-infiltrating immune cells were isolated from surgical samples and co-cultured with GB cells expressing CIITA or not, followed by RT-qPCR assessment of the expression of key immune regulators. RESULTS: Intracerebral vaccination of GL261-CIITA significantly reduced the subsequent growth of GL261-WT cells implanted contralaterally. Vaccination with GL261-WT or -CIITA subcutaneously, however, equivalently retarded the intracerebral growth of GL261 cells. Adoptive cell transfer experiments showed a similar antitumor potential of lymphocytes harvested from mice implanted intracerebrally with GL261-WT or -CIITA. Human GB-infiltrating myeloid cells and lymphocytes were not activated when cultured with CIITA-expressing GB cells. Tumor-infiltrating NK cells remained mostly inactivated when in co-culture with GB cells, regardless of CIITA. CONCLUSION: these results question the therapeutic potential of CIITA-mediated immunotherapy in glioblastoma.

MKP1 phosphatase is recruited by CXCL12 in glioblastoma cells and plays a role in DNA strand breaks repair.

Glioblastoma (GBM) is the most frequent and aggressive primary tumor in the central nervous system. Previously, the secretion of CXCL12 in the brain subventricular zones has been shown to attract GBM cells and protect against irradiation. However, the exact molecular mechanism behind this radioprotection is still unknown. Here, we demonstrate that CXCL12 modulates the phosphorylation of MAP kinases and their regulator, the nuclear MAP kinase phosphatase 1 (MKP1). We further show that MKP1 is able to decrease GBM cell death and promote DNA repair after irradiation by regulating major apoptotic players, such as Jun-N-terminal kinase, and by stabilizing the DNA repair protein RAD51. Increases in MKP1 levels caused by different corticoid treatments should be reexamined for GBM patients, particularly during their radiotherapy sessions, in order to prevent or to delay the relapses of this tumor.

Aurora A plays a dual role in migration and survival of human glioblastoma cells according to the CXCL12 concentration.

Primary glioblastoma is the most frequent human brain tumor in adults and is generally fatal due to tumor recurrence. We previously demonstrated that glioblastoma-initiating cells invade the subventricular zones and promote their radio-resistance in response to the local release of the CXCL12 chemokine. In this work, we show that the mitotic Aurora A kinase (AurA) is activated through the CXCL12-CXCR4 pathway in an ERK1/2-dependent manner. Moreover, the CXCL12-ERK1/2 signaling induces the expression of Ajuba, the main cofactor of AurA, which allows the auto-phosphorylation of AurA.We show that AurA contributes to glioblastoma cell survival, radio-resistance, self-renewal, and proliferation regardless of the exogenous stimulation with CXCL12. On the other hand, AurA triggers the CXCL12-mediated migration of glioblastoma cells in vitro as well as the invasion of the subventricular zone in xenograft experiments. Moreover, AurA regulates cytoskeletal proteins (i.e., Actin and Vimentin) and favors the pro-migratory activity of the Rho-GTPase CDC42 in response to CXCL12. Altogether, these results show that AurA, a well-known kinase of the mitotic machinery, may play alternative roles in human glioblastoma according to the CXCL12 concentration.

Phosphatases and solid tumors: focus on glioblastoma initiation, progression and recurrences.

Phosphatases and cancer have been related for many years now, as these enzymes regulate key cellular functions, including cell survival, migration, differentiation and proliferation. Dysfunctions or mutations affecting these enzymes have been demonstrated to be key factors for oncogenesis. The aim of this review is to shed light on the role of four different phosphatases (PTEN, PP2A, CDC25 and DUSP1) in five different solid tumors (breast cancer, lung cancer, pancreatic cancer, prostate cancer and ovarian cancer), in order to better understand the most frequent and aggressive primary cancer of the central nervous system, glioblastoma.

CXCL12 mediates glioblastoma resistance to radiotherapy in the subventricular zone.

BACKGROUND: Patients with glioblastoma (GBM) have an overall median survival of 15 months despite multimodal therapy. These catastrophic survival rates are to be correlated to systematic relapses that might arise from remaining glioblastoma stem cells (GSCs) left behind after surgery. In this line, it has recently been demonstrated that GSCs are able to escape the tumor mass and preferentially colonize the adult subventricular zone (SVZ). At a distance from the initial tumor site, these GSCs might therefore represent a high-quality model of clinical resilience to therapy and cancer relapses as they specifically retain tumor-initiating abilities. METHOD: While relying on recent findings that have validated the existence of GSCs in the human SVZ, we questioned the role of the SVZ niche as a potential GSC reservoir involved in therapeutic failure. RESULTS: Our results demonstrate that (i) GSCs located in the SVZ are specifically resistant to radiation in vivo, (ii) these cells display enhanced mesenchymal roots that are known to be associated with cancer radioresistance, (iii) these mesenchymal traits are specifically upregulated by CXCL12 (stromal cell-derived factor-1) both in vitro and in the SVZ environment, (iv) the amount of SVZ-released CXCL12 mediates GBM resistance to radiation in vitro, and (v) interferes with the CXCL12/CXCR4 signalling system, allowing weakening of the tumor mesenchymal roots and radiosensitizing SVZ-nested GBM cells. CONCLUSION: Together, these data provide evidence on how the adult SVZ environment, through the release of CXCL12, supports GBM therapeutic failure and potential tumor relapse.

The Unexpected Roles of Aurora A Kinase in Gliobastoma Recurrences.

The main obstacle for the cure of glioblastoma (GBM) is systematic tumor recurrence after treatment. More than 90 % of GBM tumors are indeed recurrent within 5 years after diagnosis and treatment. We urgently need new therapies to specifically address these deadly relapses. A major advance in the understanding of GBM recurrence is the identification of GBM-Initiating Cells (GIC), characterized by their abilities for self-renewal, multilineage differentiation, and proliferation. It appears that these features of GIC could be modulated by the mitotic kinase Aurora A (AurA). Indeed, besides its role in mitosis, AurA has recently been identified to regulate alternative functions like cell polarity, asymmetric cell division, and epithelial to mesenchymal transition. All these properties may help explain GBM therapeutic resistance and recurrence. In this review, we make the hypothesis that AurA could significantly contribute to GBM recurrences and we focus on the possible roles of AurA in GIC.

New role of osteopontin in DNA repair and impact on human glioblastoma radiosensitivity.

Glioblastoma (GBM) represents the most aggressive and common solid human brain tumor. We have recently demonstrated the importance of osteopontin (OPN) in the acquisition/maintenance of stemness characters and tumorigenicity of glioma initiating cells. Consultation of publicly available TCGA database indicated that high OPN expression correlated with poor survival in GBM patients. In this study, we explored the role of OPN in GBM radioresistance using an OPN-depletion strategy in U87-MG, U87-MG vIII and U251-MG human GBM cell lines. Clonogenic experiments showed that OPN-depleted GBM cells were sensitized to irradiation. In comet assays, these cells displayed higher amounts of unrepaired DNA fragments post-irradiation when compared to control. We next evaluated the phosphorylation of key markers of DNA double-strand break repair pathway. Activating phosphorylation of H2AX, ATM and 53BP1 was significantly decreased in OPN-deficient cells. The addition of recombinant OPN prior to irradiation rescued phospho-H2AX foci formation thus establishing a new link between DNA repair and OPN expression in GBM cells. Finally, OPN knockdown improved mice survival and induced a significant reduction of heterotopic human GBM xenograft when combined with radiotherapy. This study reveals a new function of OPN in DNA damage repair process post-irradiation thus further confirming its major role in GBM aggressive disease.

Constitutive activation of casein kinase 2 in glioblastomas: Absence of class restriction and broad therapeutic potential.

Casein kinase II contributes to the growth and survival of malignant gliomas and attracts increasing attention as a therapeutic target in these tumors. Several reports have suggested that this strategy might be most relevant for specific subgroups of patients, namely Verhaak's classical and TP53 wild-type tumors. Using kinase assays and microarray genetic profiling in a series of 27 proprietary fresh frozen surgical glioma samples, we showed that constitutive CK2 kinase activation is not restricted to tumors that present increased copy numbers or mRNA expression of its catalytic or regulatory subunits, and can result from a functional activation by various cytokines from the glioma microenvironment. Using corresponding primary tumor and human astrocyte cell cultures as well as glioma cell lines, we confirmed that CK2 inhibition is selectively toxic to malignant glial tumors, without any restriction to tumor class or to TP53 status. We finally showed that while the contribution of CK2 to the constitutive NF-κB hyperactivation in malignant gliomas is at best moderate, a delayed activation of NF-κB may associate with the therapeutic resistance of glioma cells to CK2 inhibition.

Adult mouse subventricular zones stimulate glioblastoma stem cells specific invasion through CXCL12/CXCR4 signaling.

BACKGROUND: Patients with glioblastoma multiforme (GBM) have an overall median survival of 15 months. This catastrophic survival rate is the consequence of systematic relapses that could arise from remaining glioblastoma stem cells (GSCs) left behind after surgery. We previously demonstrated that GSCs are able to escape the tumor mass and specifically colonize the adult subventricular zones (SVZs) after transplantation. This specific localization, away from the initial injection site, therefore represents a high-quality model of a clinical obstacle to therapy and relapses because GSCs notably retain the ability to form secondary tumors. METHOD: In this work, we questioned the role of the CXCL12/CXCR4 signaling in the GSC-specific invasion of the SVZs. RESULTS: We demonstrated that both receptor and ligand are respectively expressed by different GBM cell populations and by the SVZ itself. In vitro migration bio-assays highlighted that human U87MG GSCs isolated from the SVZs (U87MG-SVZ) display stronger migratory abilities in response to recombinant CXCL12 and/or SVZ-conditioned medium (SVZ-CM) compared with cancer cells isolated from the tumor mass (U87MG-TM). Moreover, in vitro inhibition of the CXCR4 signaling significantly decreased the U87MG-SVZ cell migration in response to the SVZ-CM. Very interestingly, treating U87MG-xenografted mice with daily doses of AMD3100, a specific CXCR4 antagonist, prevented the specific invasion of the SVZ. Another in vivo experiment, using CXCR4-invalidated GBM cells, displayed similar results. CONCLUSION: Taken together, these data demonstrate the significant role of the CXCL12/CXCR4 signaling in this original model of brain cancer invasion.

Glioblastoma-initiating cells: relationship with neural stem cells and the micro-environment.

Glioblastoma multiforme (GBM, WHO grade IV) is the most common and lethal subtype of primary brain tumor with a median overall survival of 15 months from the time of diagnosis. The presence in GBM of a cancer population displaying neural stem cell (NSC) properties as well as tumor-initiating abilities and resistance to current therapies suggests that these glioblastoma-initiating cells (GICs) play a central role in tumor development and are closely related to NSCs. However, it is nowadays still unclear whether GICs derive from NSCs, neural progenitor cells or differentiated cells such as astrocytes or oligodendrocytes. On the other hand, NSCs are located in specific regions of the adult brain called neurogenic niches that have been shown to control critical stem cell properties, to nourish NSCs and to support their self-renewal. This "seed-and-soil" relationship has also been adapted to cancer stem cell research as GICs also require a specific micro-environment to maintain their "stem cell" properties. In this review, we will discuss the controversies surrounding the origin and the identification of GBM stem cells and highlight the micro-environment impact on their biology.