Single-Cell Cloning of Breast Cancer Cells Secreting Specific Subsets of Extracellular Vesicles

Simple Summary

Extracellular vesicles (EVs) are a pivotal mechanism for long-distance intercellular communication and facilitate the stable transport of biological information. Conventional methods for profiling EVs are focused on the biological cargo obtained from large populations of cells and cannot map the secretion of specific subsets of EVs onto their cell of origin. We developed a high-throughput single-cell cloning method that can identify the kinetics of secretion of specific subsets of EVs. With the aid of this methodology, we illustrate that secretion of specific subsets of EVs can be an inheritable property of cancer cells. Our single-cell methodology enables the direct integration of EV secretion with multiple cellular functions and can enable new insights into cell and disease biology.

Abstract

Extracellular vesicles (EVs) mediate communication in health and disease. Conventional assays are limited in profiling EVs secreted from large populations of cells and cannot map EV secretion onto individual cells and their functional profiles. We developed a high-throughput single-cell technique that enabled the mapping of dynamics of EV secretion. By utilizing breast cancer cell lines, we established that EV secretion is heterogeneous at the single-cell level and that non-metastatic cancer cells can secrete specific subsets of EVs. Single-cell RNA sequencing confirmed that pathways related to EV secretion were enriched in the non-metastatic cells compared with metastatic cells. We established isogenic clonal cell lines from non-metastatic cells with differing propensities for CD81⁺CD63⁺EV secretion and showed for the first time that specificity in EV secretion is an inheritable property preserved during cell division. Combined in vitro and animal studies with these cell lines suggested that CD81⁺CD63⁺EV secretion can impede tumor formation. In human non-metastatic breast tumors, tumors enriched in signatures of CD81⁺CD63⁺EV have a better prognosis, higher immune cytolytic activity, and enrichment of pro-inflammatory macrophages compared with tumors with low CD81⁺CD63⁺EVs signatures. Our single-cell methodology enables the direct integration of EV secretion with multiple cellular functions and enables new insights into cell/disease biology.

Targeting the αv integrin/TGF-β axis improves natural killer cell function against glioblastoma stem cells

Glioblastoma multiforme (GBM), the most aggressive brain cancer, recurs because glioblastoma stem cells (GSCs) are resistant to all standard therapies. We showed that GSCs, but not normal astrocytes, are sensitive to lysis by healthy allogeneic natural killer (NK) cells in vitro. Mass cytometry and single-cell RNA sequencing of primary tumor samples revealed that GBM tumor-infiltrating NK cells acquired an altered phenotype associated with impaired lytic function relative to matched peripheral blood NK cells from patients with GBM or healthy donors. We attributed this immune evasion tactic to direct cell-to-cell contact between GSCs and NK cells via αv integrin-mediated TGF-β activation. Treatment of GSC-engrafted mice with allogeneic NK cells in combination with inhibitors of integrin or TGF-β signaling or with TGFBR2 gene-edited allogeneic NK cells prevented GSC-induced NK cell dysfunction and tumor growth. These findings reveal an important mechanism of NK cell immune evasion by GSCs and suggest the αv integrin/TGF-β axis as a potentially useful therapeutic target in GBM.

Abstract 2193: Small molecule inducible MyD88/CD40 (iMC) in CAR-T cells can repolarize M2 macrophage to an anti-tumor M1 phenotype

Background: Effective chimeric antigen receptor (CAR) T cell therapy against solid tumors must overcome a hostile, tumor microenvironment that includes tumor-associated macrophages (TAM). Pancreatic adenocarcinomas (PDAC) are commonly infiltrated with TAMs polarized to a tumor-promoting M2 phenotype rather than a T cell-stimulatory and tumor-inhibitory M1 phenotype. The GoCAR platform combines an inducible MyD88/CD40 (iMC) costimulation protein with a 1st generation CAR. Our previously published results demonstrated that iMC costimulation, activated by the small molecule dimerizer, rimiducid (Rim), enhanced CAR-T proliferation and anti-tumor efficacy. Here, we examined the extrinsic effects of iMC signaling on CAR-T cell immune-activating ligands, cytokine production and their ability to polarize M2 macrophage to an anti-tumor phenotype.

Methods: Macrophages were prepared from peripheral blood monocytes of four or more random blood donors from the Gulf Coast Regional Blood Center (Houston, TX) and differentiated in vitro to an M2 phenotype with TGF-β and IL-10, or an M1 phenotype (as a positive control). GoCAR-T cells targeting prostate stem cell antigen (PSCA) were prepared by retroviral transduction from the autologous donors. To test the effects of iMC activation on macrophage polarization, contact-dependent or independent (i.e., separation of cell populations with transwell inserts) coculture assays were performed with and without activation of iMC with 1 nM Rim and/or surface-bound PSCA. Anti-tumor cytotoxicity was measured by coculture with PSCA+ Panc1-GFP cells.

Results: CAR activation by PSCA antigen recognition or iMC activation with Rim decreased CD163, an M2 macrophage marker, and increased CD80, expressed on M1 macrophage. Full activation of the GoCAR-T cells with both Rim and the target antigen fully repolarized M2 macrophage to an M1 marked phenotype (CD163lowCD80high). This repolarization could be directed partially in the absence of cell-cell contact by diffusion of soluble factors through Transwell membranes. M2 macrophages repolarized by conditioning media from activated GoCAR-T cells also exhibited the functionality of M1 macrophages and acquired cytotoxicity against tumor cells. Furthermore, cultures of conditioned macrophages and limiting dilutions of GoCAR-T cells demonstrated a cooperative enhancement of the cytotoxicity of PSCA GoCAR-T cells toward Panc-1 targets. This cooperation was more effective for GoCAR-T cells than CD28- or 4-1BB-enhanced 2nd generation PSCA CAR-T cells.

Conclusions: These results predict that GoCAR-T activation with Rim will convert TAMs within a solid tumor microenvironment from T cell inhibitors to tumor-caustic agents.

Citation Format: Xiaohong Wang, Konrad Gabrusiewicz, David M. Spencer, Aaron E. Foster, J. Henri Bayle. Small molecule inducible MyD88/CD40 (iMC) in CAR-T cells can repolarize M2 macrophage to an anti-tumor M1 phenotype [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2193.

Abstract 2180: Genetically engineered chimeric antigen receptor (CAR) monocytes demonstrate targeted anti-tumor activity and differentiate into M1-polarized CAR macrophages

Despite rapid advances in cancer immunotherapy, clinical responses in metastatic solid tumors have been limited. Macrophages are the most abundant immune cell in the solid tumor microenvironment (TME) and are primarily recruited as monocytes by TME-derived chemokines. When not under the control of the TME, macrophages are potent immune effector cells capable of phagocytosis, T cell recruitment, and antigen presentation. We have previously demonstrated that CAR macrophages (CAR-M) have potent anti-tumor activity and overcome several of the barriers to success in solid tumor immunotherapy - trafficking, immunosuppression, and antigen heterogeneity.

Currently, CAR-M are generated via ex vivo differentiation of peripheral blood monocytes into macrophages prior to genetic manipulation. To more closely recapitulate normal biologic behavior, we attempted to create CAR monocytes that could traffic and differentiate into CAR macrophages upon tumor penetration. Toward that goal, we genetically engineered CD14+ human monocytes without ex vivo differentiation and with minimal cell culture. Using the chimeric adenoviral vector Ad5f35, we engineered human CAR-monocytes targeted against HER2. CAR expression and viability both exceeded 90%. Ad5f35 transduced CAR monocytes survived and maintained CAR expression ex vivo for at least 21 days. CAR monocytes efficiently differentiated into CAR-expressing macrophages when treated with GM-CSF as determined by FACS-based phenotypic characterization and Wright-Giemsa staining. Anti-HER2 CAR monocytes eradicated HER2 expressing tumor cells in a time and dose-dependent manner, and had comparable potency to anti-HER2 CAR-M. Additionally, the CAR monocyte manufacturing process offered the logistical advantage of a short manufacturing process (approximately two days).

We have previously demonstrated that CAR-M are polarized toward a pro-inflammatory M1 phenotype after transduction with Ad5f35. Similarly, CAR monocytes demonstrated elevated expression of M1 markers, and intriguingly after differentiation into CAR-expressing macrophages, HLA-DR, CD80, CD86, and other M1 markers remained elevated - suggesting that transduction prior to differentiation does not impact the pro-inflammatory impact of adenoviral vectors on myeloid cells.

Taken together, this abstract describes the successful development of CAR-monocytes with the potential for a rapid manufacturing process. In addition to direct anti-tumor activity while in the monocyte phase, CAR monocytes have the capacity to differentiate into CAR macrophages in situ, which are in turn capable of phagocytosis, T cell recruitment, TME activation, and antigen presentation. Given the previously demonstrated pre-clinical efficacy of CT-0508 (an anti-HER2 CAR macrophage), the CAR monocyte platform described herein offers a shortened manufacturing process and a potential advantage in tumor penetration, which will be directly evaluated in upcoming studies.

Citation Format: Konrad Gabrusiewicz, Maggie Schmierer, Andrew Best, Martha Zeeman, Yumi Ohtani, Linara Gabitova, Daniel Cushing, Saar Gill, Michael Klichinsky. Genetically engineered chimeric antigen receptor (CAR) monocytes demonstrate targeted anti-tumor activity and differentiate into M1-polarized CAR macrophages [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2180.

Human chimeric antigen receptor macrophages for cancer immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has shown promise in hematologic malignancies, but its application to solid tumors has been challenging^1-4. Given the unique effector functions of macrophages and their capacity to penetrate tumors⁵, we genetically engineered human macrophages with CARs to direct their phagocytic activity against tumors. We found that a chimeric adenoviral vector overcame the inherent resistance of primary human macrophages to genetic manipulation and imparted a sustained pro-inflammatory (M1) phenotype. CAR macrophages (CAR-Ms) demonstrated antigen-specific phagocytosis and tumor clearance in vitro. In two solid tumor xenograft mouse models, a single infusion of human CAR-Ms decreased tumor burden and prolonged overall survival. Characterization of CAR-M activity showed that CAR-Ms expressed pro-inflammatory cytokines and chemokines, converted bystander M2 macrophages to M1, upregulated antigen presentation machinery, recruited and presented antigen to T cells and resisted the effects of immunosuppressive cytokines. In humanized mouse models, CAR-Ms were further shown to induce a pro-inflammatory tumor microenvironment and boost anti-tumor T cell activity.

Abstract B65: CT-0508, a novel CAR macrophage product directed against HER2, promotes a proinflammatory tumor microenvironment

Despite recent advances in T cell immunotherapy for the treatment of human cancer, metastatic solid tumors remain an intractable challenge. Macrophages are usually the most abundant immune cell in the tumor microenvironment (TME) where, as immunosuppressive tumor-associated macrophages (TAMs), they participate in disease progression. The current goals of macrophage-based immunotherapies are to reduce TAM infiltration or enhance TAM phagocytosis. In contrast, we have developed a new paradigm based on the adoptive transfer of genetically engineered chimeric antigen receptor (CAR) macrophages (CAR-M) for the treatment of human cancer. CAR-M can only be produced using a unique adenoviral vector, since human macrophages are highly resistant to other methods of gene transfer. We have previously shown that the primary mechanism of action of CAR-M is phagocytosis, and that a single dose of primary human anti-HER2 CAR-M led to significantly improved overall survival in multiple xenograft models. We now establish that Ad5f35-transduced anti-HER2 CAR-M (CT-0508) adopt a unique proinflammatory and antitumor M1 phenotype. Functional evaluation and RNA sequencing revealed that CT-0508 maintain a proinflammatory M1 phenotype despite challenge with immunosuppressive environments in vitro, highlighting their resistance to subversion. By engrafting immunodeficient mice with human hematopoietic cells and human cancer cells, we established a novel xenografted human TME model. We demonstrate with single-cell resolution that CT-0508 maintain their phenotype within the human TME. Additionally, CT-0508 activated the human TME and generated an activated human dendritic cell signature. To further investigate the potential of CT-0508 for TME activation, we modeled the interaction of CT-0508 with immunosuppressive macrophages, dendritic cells, and T cells. CT-0508 shifted bystander macrophages toward a proinflammatory phenotype, induced activation and maturation markers on DCs, and recruited resting as well as activated T cells in chemotaxis assays. Lastly, CT-0508 demonstrated enhanced antigen presentation when compared to control human macrophages. These results show that in addition to direct antitumor activity, the anti-HER2 CAR macrophage cell product CT-0508 is capable of activating the solid cancer TME and promoting a proinflammatory phenotype. The safety of CT-0508 will be evaluated in an upcoming first-in-human phase I clinical trial.

Citation Format: Konrad Gabrusiewicz, Nicholas Anderson, Xueqing Lu, Xinhe Shan, Olga Shestova, Nicholas Petty, Feng Shen, Maggie Schmierer, Andrew Best, Martha Zeeman, Yumi Ohtani, Katherine Cummins, Saar Gill, Michael Klichinsky. CT-0508, a novel CAR macrophage product directed against HER2, promotes a proinflammatory tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B65.

Abstract 2907: Exosome secretion is an inheritable property of cancer cells: Single-cell profiling of exosome secretion

Decades of research on exosomes, nano-sized vesicles secreted by cells, have revealed novel roles of these vesicles in the formation of pre-metastasis niches that enhances the migration of tumor cells to those sites. Paradoxically, more recent work has suggested that these tumor-derived exosomes can also have an immunostimulatory role, depending on the model studied. The rate of secretion of exosomes by single cells is likely heterogeneous, and a deep profiling of the secretion capacity of individual tumor cells has been largely unexplored.

We have developed a high-throughput single-cell methodology to quantify the dynamic secretion of exosomes from single cells using a modified immunoassay and sought to define: (a) heterogeneity among individual cells within the tumor cell population, and (b) the nature of the cells secreting exosomes within a tumor cell population. In order to investigate these, we chose to study models of triple negative breast cancer: the metastatic tumor lines, 4T1 (mouse) and MDA-MB-231(human); and the non-metastatic lines 67NR (mouse) and MCF7 (human). Our method revealed that MDA-MB-231 single cells secreted exosomes at a rate, ~2 fold higher than MCF7 cells. Surprisingly, the non-metastatic 67NR cells showed a higher secretion rate (~1.5 fold) than metastatic 4T1 cells. Next, we performed single-cell RNA-seq on 67NR and 4T1 single cells. Consistent with our single-cell exosomal profiling results, 67NR cells were significantly (p-value < 0.01) enriched for genes correlated to exosome formation in comparison to the 4T1 cells. Next, in order to study exosomes of single cells, we isolated single cells using an automated micromanipulator which allowed us to establish monoclonal cell lines. Measurement of these monoclonal cells showed that secretor cells of 67NR secrete exosomes with ~2 fold higher rate than non-secretor cells.

Since our in vitro results clearly demonstrated that the secretor clonal cell lines had a higher frequency of exosome secreting single cells, we sought to define the in vivo relevance of these results. Consistent with the hypothesis that the exosomes from 67NR are immune-stimulatory, injection of the secretor clones into Balb/c mice led to lack of primary tumor formation (2/15 mice had tumors) whereas the injection of the non-secretor clones led to tumor formation in 7/15 mice.

In aggregate, our results show that the higher rate of secretion of exosomes from non-metastatic cells can facilitate tumor rejection in vivo. We are currently performing in vitro studies with the 67NR and MDA-MB-231 exosomes to study their impact on immune cells.

Citation Format: Mohsen Fathi, Robiya Joseph, Melisa Martinez-Paniagua, Jay R Adolacion, Xingyue An, Ankit Mahendra, Konrad Gabrusiewicz, Sujash Chatterjee, Sendurai A. Mani, Navin Varadarajan. Exosome secretion is an inheritable property of cancer cells: Single-cell profiling of exosome secretion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2907.

Knockout immune regulator FGL2 in tumor cells impairs tumor progression in the CNS by facilitating CD103+ dendritic cell differentiation

Although many studies link brain tumor progression to oncogene activation and tumor-suppressor gene inactivation in tumor cells, few studies implicate immune regulatory gene expression in tumor cells in arbitrating brain tumor progression. Here we show that fibrinogen-like protein 2 (FGL2) is highly expressed in glioma stem cells and primary glioblastoma (GBM) cells. FGL2 knockout (FGL2KO) in GL261, DBT, and LLC tumor cells did not affect tumor cell proliferation in vitro or tumor progression in immunodeficient NSG mice, but completely impaired GBM progression in immune-competent C57bl/6 mice. This impairment was reversed in mice with a defect in Batf3 (a key transcription factor for CD103+ DCs differentiation). Mechanistic studies revealed that FGL2KO in tumor cells induces CD103+ DCs differentiation in both the central nervous system (CNS) and in tumor draining lymph nodes (TDLN). The increased CD103+ DCs population in the CNS and TDLNs induce CD8+ T cells priming and activation and thereby gliomas regress. More specifically, the presence of FGL2 in tumor cells inhibited granulocyte-macrophage colony-stimulating factor (GM-CSF)–induced CD103+ DC differentiation by suppressing NF-κB, STAT1/5, and p38 activation. These findings are relevant to GBM patients because a low level of FGL2 expression with concurrent high GM-CSF expression is associated with higher CD8B expression and longer survival. These data provide a rationale for therapeutic inhibition of FGL2 in brain tumors.

Author Correction: FGL2 promotes tumor progression in the CNS by suppressing CD103+ dendritic cell differentiation

The original version of this Article contained errors in the author affiliations. Qingnan Zhao, Xueqing Xia, Longfei Huo and Shulin Li were incorrectly associated with Beijing Institute for Brain Disorders, 100069, Beijing, China.This has now been corrected in both the PDF and HTML versions of the Article.

FGL2 promotes tumor progression in the CNS by suppressing CD103+ dendritic cell differentiation

Few studies implicate immunoregulatory gene expression in tumor cells in arbitrating brain tumor progression. Here we show that fibrinogen-like protein 2 (FGL2) is highly expressed in glioma stem cells and primary glioblastoma (GBM) cells. FGL2 knockout in tumor cells did not affect tumor-cell proliferation in vitro or tumor progression in immunodeficient mice but completely impaired GBM progression in immune-competent mice. This impairment was reversed in mice with a defect in dendritic cells (DCs) or CD103+ DC differentiation in the brain and in tumor-draining lymph nodes. The presence of FGL2 in tumor cells inhibited granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced CD103+ DC differentiation by suppressing NF-κB, STAT1/5, and p38 activation. These findings are relevant to GBM patients because a low level of FGL2 expression with concurrent high GM-CSF expression is associated with higher CD8B expression and longer survival. These data provide a rationale for therapeutic inhibition of FGL2 in brain tumors.

Osteopontin mediates glioblastoma-associated macrophage infiltration and is a potential therapeutic target

Glioblastoma is highly enriched with macrophages, and osteopontin (OPN) expression levels correlate with glioma grade and the degree of macrophage infiltration; thus, we studied whether OPN plays a crucial role in immune modulation. Quantitative PCR, immunoblotting, and ELISA were used to determine OPN expression. Knockdown of OPN was achieved using complementary siRNA, shRNA, and CRISPR/Cas9 techniques, followed by a series of in vitro functional migration and immunological assays. OPN gene-deficient mice were used to examine the roles of non-tumor-derived OPN on survival of mice harboring intracranial gliomas. Patients with mesenchymal glioblastoma multiforme (GBM) show high OPN expression, a negative survival prognosticator. OPN is a potent chemokine for macrophages, and its blockade significantly impaired the ability of glioma cells to recruit macrophages. Integrin αvβ5 (ITGαvβ5) is highly expressed on glioblastoma-infiltrating macrophages and constitutes a major OPN receptor. OPN maintains the M2 macrophage gene signature and phenotype. Both tumor-derived and host-derived OPN were critical for glioma development. OPN deficiency in either innate immune or glioma cells resulted in a marked reduction in M2 macrophages and elevated T cell effector activity infiltrating the glioma. Furthermore, OPN deficiency in the glioma cells sensitized them to direct CD8+ T cell cytotoxicity. Systemic administration in mice of 4-1BB-OPN bispecific aptamers was efficacious, increasing median survival time by 68% (P < 0.05). OPN is thus an important chemokine for recruiting macrophages to glioblastoma, mediates crosstalk between tumor cells and the innate immune system, and has the potential to be exploited as a therapeutic target.

Cell surface vimentin-targeted monoclonal antibody 86C increases sensitivity to temozolomide in glioma stem cells

Glioblastoma multiforme (GBM) is the most prevalent and aggressive brain tumor. The current standard therapy, which includes radiation and chemotherapy, is frequently ineffective partially because of drug resistance and poor penetration of the blood-brain barrier. Reducing resistance and increasing sensitivity to chemotherapy may improve outcomes. Glioma stem cells (GSCs) are a source of relapse and chemoresistance in GBM; sensitization of GSCs to temozoliomide (TMZ), the primary chemotherapeutic agent used to treat GBM, is therefore integral for therapeutic efficacy. We previously discovered a unique tumor-specific target, cell surface vimentin (CSV), on patient-derived GSCs. In this study, we found that the anti-CSV monoclonal antibody 86C efficiently increased GSC sensitivity to TMZ. The combination TMZ+86C induced significantly greater antitumor effects than TMZ alone in eight of 12 GSC lines. TMZ+86C-sensitive GSCs had higher CSV expression overall and faster CSV resurfacing among CSV^- GSCs compared with TMZ+86C-resistant GSCs. Finally, TMZ+86C increased apoptosis of tumor cells and prolonged survival compared with either drug alone in GBM mouse models. The combination of TMZ+86C represents a promising strategy to reverse GSC chemoresistance.

Glioblastoma stem cell-derived exosomes induce M2 macrophages and PD-L1 expression on human monocytes

Exosomes can mediate a dynamic method of communication between malignancies, including those sequestered in the central nervous system and the immune system. We sought to determine whether exosomes from glioblastoma (GBM)-derived stem cells (GSCs) can induce immunosuppression. We report that GSC-derived exosomes (GDEs) have a predilection for monocytes, the precursor to macrophages. The GDEs traverse the monocyte cytoplasm, cause a reorganization of the actin cytoskeleton, and skew monocytes toward the immune suppresive M2 phenotype, including programmed death-ligand 1 (PD-L1) expression. Mass spectrometry analysis demonstrated that the GDEs contain a variety of components, including members of the signal transducer and activator of transcription 3 (STAT3) pathway that functionally mediate this immune suppressive switch. Western blot analysis revealed that upregulation of PD-L1 in GSC exosome-treated monocytes and GBM-patient-infiltrating CD14⁺ cells predominantly correlates with increased phosphorylation of STAT3, and in some cases, with phosphorylated p70S6 kinase and Erk1/2. Cumulatively, these data indicate that GDEs are secreted GBM-released factors that are potent modulators of the GBM-associated immunosuppressive microenvironment.

Germline polymorphisms in myeloid-associated genes are not associated with survival in glioma patients

Immune cells of myeloid origin, including microglia, macrophages, and myeloid-derived suppressor cells adopt immunosuppressive phenotypes that support gliomagenesis. Here, we tested an a priori hypothesis that single nucleotide polymorphisms (SNPs) in genes related to glioma-associated myeloid cell regulation and function are also associated with patient survival after glioma diagnosis. Subjects for this study were 992 glioma patients treated at The University of Texas MD Anderson Cancer Center in Houston, Texas between 1992 and 2008. Haplotype-tagging SNPs in 91 myeloid-associated genes were analyzed for association with survival by Cox regression. Individual SNP- and gene-based tests were performed separately in glioblastoma (WHO grade IV, n = 511) and lower-grade glioma (WHO grade II-III, n = 481) groups. After adjustment for multiple testing, no myeloid-associated gene variants were significantly associated with survival in glioblastoma. Two SNPs, rs147960238 in CD163 (p = 2.2 × 10-5) and rs17138945 in MET (p = 5.6 × 10-5) were significantly associated with survival of patients with lower-grade glioma. However, these associations were not confirmed in an independent analysis of 563 lower-grade glioma cases from the University of California at San Francisco Adult Glioma Study (p = 0.65 and p = 0.41, respectively). The results of this study do not support a role for inherited polymorphisms in myeloid-associated genes in affecting survival of patients diagnosed with glioblastoma or lower-grade glioma.

Soluble Tie2 overrides the heightened invasion induced by anti-angiogenesis therapies in gliomas

Glioblastoma recurrence after treatment with the anti–vascular endothelial growth factor (VEGF) agent bevacizumab is characterized by a highly infiltrative and malignant behavior that renders surgical excision and chemotherapy ineffective. Our group has previously reported that Tie2-expressing monocytes (TEMs) are aberrantly present at the tumor/normal brain interface after anti-VEGF therapies and their significant role in the invasive outgrowth of these tumors. Here, we aimed to further understand the mechanisms leading to this pro-invasive tumor microenvironment. Examination of a U87MG xenogeneic glioma model and a GL261 murine syngeneic model showed increased tumor expression of angiopoietin 2 (Ang2), a natural ligand of Tie2, after anti-angiogenesis therapies targeting VEGF or VEGF receptor (VEGFR), as assessed by immunohistochemical analysis, immunofluorescence analysis, and enzyme-linked immunosorbent assays of tumor lysates. Migration and gelatinolytic assays showed that Ang2 acts as both a chemoattractant of TEMs and an enhancing signal for their tumor-remodeling properties. Accordingly, in vivo transduction of Ang2 into intracranial gliomas increased recruitment of TEMs into the tumor. To reduce invasive tumor outgrowth after anti-angiogenesis therapy, we targeted the Ang-Tie2 axis using a Tie2 decoy receptor. Using syngeneic models, we observed that overexpression of soluble Tie2 within the tumor prevented the recruitment of TEMs to the tumor and the development of invasion after anti-angiogenesis treatment. Taken together, these data indicate an active role for the Ang2-Tie2 pathway in invasive glioma recurrence after anti-angiogenesis treatment and provide a rationale for testing the combined targeting of VEGF and Ang-Tie2 pathways in patients with glioblastoma.

Immune modulatory nanoparticle therapeutics for intracerebral glioma

Background

Previously we showed therapeutic efficacy of unprotected miR-124 in preclinical murine models of glioblastoma, including in heterogeneous genetically engineered murine models by exploiting the immune system and thereby negating the need for direct tumor delivery. Although these data were promising, to implement clinical trials, we required a scalable formulation that afforded protection against circulatory RNases.

Methods

We devised lipid nanoparticles that encapsulate and protect the miRs from degradation and provide enhanced delivery into the immune cell compartment and tested in vivo antitumor effects.

Results

Treatment with nanoparticle-encapsulated miR-124, LUNAR-301, demonstrated a median survival exceeding 70 days, with an associated reversal of tumor-mediated immunosuppression and induction of immune memory. In both canine and murine models, the safety profile of LUNAR-301 was favorable.

Conclusions

For the first time, we show that nanoparticles can direct a therapeutic response by targeting intracellular immune pathways. Although shown in the context of gliomas, this therapeutic approach would be applicable to other malignancies.

Abstract 2259: Evaluation of polymorphisms in myeloid-associated genes and glioma survival

BACKGROUND: Gliomas are highly infiltrated by immune cells including microglia, macrophages, and myeloid-derived suppressor cells (collectively, glioma-associated myeloid cells). These cells have been shown to be induced by the tumor to be immune-suppressive and tumor-supportive, and are a negative prognosticator for survival in mouse models. Here, we examine whether inherited variants in genes important to the function of glioma-associated myeloid cells are associated with survival following low-grade glioma diagnosis.

METHODS: Subjects for this study were 484 patients with WHO grade II or grade III glioma treated at The University of Texas MD Anderson Cancer Center in Houston, Texas between 1992 and 2008 and followed up for survival through August, 2016. We selected 100 genes for analysis including transcription factors, cytokines and chemokines, receptors, enzymes, and other genes central to the function of glioma-associated myeloid cells. Genotyping was originally performed using the Illumina Human 610-Quad Bead Chip platform and 2,040 tagging SNPs as determined by Haploview Tagger software were selected for analysis with minor allele frequency (AF) ≥ 1%. Associations between selected SNPs and survival were evaluated by Cox regression analysis under an additive allelic model adjusting for age, sex, extent of surgery (biopsy only/partial resection/gross total resection), radiotherapy (yes/no), and chemotherapy (yes/no). Models were examined to ensure that proportional hazards assumptions were not violated.

RESULTS: Median survival among low-grade glioma patients was 6.7 years. Age at diagnosis, extent of surgery, and having received radiotherapy or chemotherapy were each significantly associated with survival. Five SNPs were associated with survival at a significance level of p&lt;0.001, and two remained significantly associated with low-grade glioma survival after adjustment for multiple comparisons (FDR-adjusted p-value (q)&lt;0.10). These results indicated inferior survival for carriers of the C allele (AF=1.4%) at rs147960238 in CD163 (HR=5.47, 95% CI: 2.49-11.99, p=2.23x10-5, q=0.046) and for carriers of the G allele (AF=3.8%) at rs17138945 in MET (HR=2.27, 95% CI: 1.52-3.38, p=5.61x10-5, q=0.057). These SNPs are located in the 10th and 2nd introns of CD163 and MET, respectively.

CONCLUSIONS: Here we provide preliminary evidence of an association between polymorphisms in two genes related to glioma-associated myeloid cell function and low-grade glioma survival. CD163 is a receptor that is highly expressed on macrophages and may play a role in macrophage-mediated anti-inflammatory responses, while MET is a receptor tyrosine kinase and well-studied proto-oncogene that is also involved in the expansion of myeloid-derived suppressor cell populations. Further investigation of these associations is warranted, and validation of these findings is planned in an independent population.

Citation Format: Daniel I. Jacobs, Yanhong Liu, Konrad Gabrusiewicz, Spiridon Tsavachidis, E. Susan Amirian, Georgina N. Armstrong, Renke Zhou, Jun Wei, Cristina Ivan, George Calin, Michael Scheurer, Anna Dahlin, Terri Rice, Paige M. Bracci, Helen M. Hansen, John K. Wiencke, Margaret R. Wrensch, Beatrice Melin, Amy B. Heimberger, Melissa L. Bondy. Evaluation of polymorphisms in myeloid-associated genes and glioma survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2259. doi:10.1158/1538-7445.AM2017-2259

FGL2 promotes tumor progression via inducing TIGIT expression on T cells in tumor microenvironment of glioma

Glioblastoma multiforme (GBM) is the most common primary brain tumor with a median survival of only 14.6 months. Our previous work shows that FGL2 promotes glioma tumor growth and the expression levels of FGL2 positively correlated with glioma grade in patients. T cell Ig and ITIM domain (TIGIT) is an inhibitory receptor expressed by activated T cells, Tregs, and NK cells. Here we found that there is a statistically significant positive correlation between FGL2 and TIGIT mRNA expression level in both low grade glioma database (TCGA, provisional) and glioblastoma multiforme database (TCGA, provisional). Future, FGL2 and TIGIT are coordinately expressed by human tumor-infiltrating lymphocytes of glioma as detected by flow cytometry. In addition, TIGIT expression on T cells which suppresses their function, can be induced by initial T cell activation or FGL2 in vitro. Induced TIGIT expression upon initial T cell activation is suppressed in FGL2KO T cells which has higher tumor-killing ability than WT T cells. Therefore, our results show that FGL2 induces TIGIT expression in brain-infiltrated lymphocytes which suppresses anti-tumor immune response in glioma. By this mechanism, FGL2 promotes tumor progression of glioma.

Glioblastoma-infiltrated innate immune cells resemble M0 macrophage phenotype

Glioblastomas are highly infiltrated by diverse immune cells, including microglia, macrophages, and myeloid-derived suppressor cells (MDSCs). Understanding the mechanisms by which glioblastoma-associated myeloid cells (GAMs) undergo metamorphosis into tumor-supportive cells, characterizing the heterogeneity of immune cell phenotypes within glioblastoma subtypes, and discovering new targets can help the design of new efficient immunotherapies. In this study, we performed a comprehensive battery of immune phenotyping, whole-genome microarray analysis, and microRNA expression profiling of GAMs with matched blood monocytes, healthy donor monocytes, normal brain microglia, nonpolarized M0 macrophages, and polarized M1, M2a, M2c macrophages. Glioblastoma patients had an elevated number of monocytes relative to healthy donors. Among CD11b⁺ cells, microglia and MDSCs constituted a higher percentage of GAMs than did macrophages. GAM profiling using flow cytometry studies revealed a continuum between the M1- and M2-like phenotype. Contrary to current dogma, GAMs exhibited distinct immunological functions, with the former aligned close to nonpolarized M0 macrophages.

Macrophage Ablation Reduces M2-Like Populations and Jeopardizes Tumor Growth in a MAFIA-Based Glioma Model

Monocytes/macrophages are an influential component of the glioma microenvironment. However, understanding their diversity and plasticity constitute one of the most challenging areas of research due to the paucity of models to study these cells' inherent complexity. Herein, we analyzed the role of monocytes/macrophages in glioma growth by using a transgenic model that allows for conditional ablation of this cell population. We modeled glioma using intracranial GL261-bearing CSF-1R–GFP⁺ macrophage Fas-induced apoptosis (MAFIA) transgenic mice. Conditional macrophage ablation was achieved by exposure to the dimerizer AP20187. Double immunofluorescence was used to characterize M1- and M2-like monocytes/macrophages during tumor growth and after conditional ablation. During glioma growth, the monocyte/macrophage population consisted predominantly of M2 macrophages. Conditional temporal depletion of macrophages reduced the number of GFP⁺ cells, targeting mainly the repopulation of M2-polarized cells, and altered the appearance of M1-like monocytes/macrophages, which suggested a shift in the M1/M2 macrophage balance. Of interest, compared with control-treated mice, macrophage-depleted mice had a lower tumor mitotic index, microvascular density, and reduced tumor growth. These results demonstrated the possibility of studying in vivo the role and phenotype of macrophages in gliomas and suggested that transitory depletion of CSF-1R⁺ population influences the reconstitutive phenotypic pool of these cells, ultimately suppressing tumor growth. The MAFIA model provides a much needed advance in defining the role of macrophages in gliomas.

Tipping a favorable CNS intratumoral immune response using immune stimulation combined with inhibition of tumor-mediated immune suppression

High-grade gliomas are notoriously heterogeneous regarding antigen expression, effector responses, and immunosuppressive mechanisms. Therefore, combinational immune therapeutic approaches are more likely to impact a greater number of patients and result in longer, durable responses. We have previously demonstrated the monotherapeutic effects of miR-124, which inhibits the signal transducer and activator of transcription 3 (STAT3) immune suppressive pathway, and immune stimulatory 4-1BB aptamers against a variety of malignancies, including genetically engineered immune competent high-grade gliomas. To evaluate potential synergy, we tested an immune stimulatory aptamer together with microRNA-124 (miRNA-124), which blocks tumor-mediated immune suppression, and found survival to be markedly enhanced, including beyond that produced by monotherapy. The synergistic activity appeared to be not only secondary to enhanced CD3(+) cell numbers but also to reduced macrophage immune tumor trafficking, indicating that a greater therapeutic benefit can be achieved with approaches that both induce immune activation and inhibit tumor-mediated immune suppression within the central nervous system (CNS) tumors.

MiR-138 exerts anti-glioma efficacy by targeting immune checkpoints

BACKGROUND

Antibody therapeutic targeting of the immune checkpoints cytotoxic T-lymphocyte-associated molecule 4 (CTLA-4) and programmed cell death 1 (PD-1) has demonstrated marked tumor regression in clinical trials. MicroRNAs (miRNAs) can modulate multiple gene transcripts including possibly more than one immune checkpoint and could be exploited as immune therapeutics.

METHODS

Using online miRNA targeting prediction algorithms, we searched for miRNAs that were predicted to target both PD-1 and CTLA-4. MiR-138 emerged as a leading candidate. The effects of miR-138 on CTLA-4 and PD-1 expression and function in T cells were determined and the therapeutic effect of intravenous administration of miR-138 was investigated in both immune-competent and -incompetent murine models of GL261 glioma.

RESULTS

Target binding algorithms predicted that miR-138 could bind the 3' untranslated regions of CTLA-4 and PD-1, which was confirmed with luciferase expression assays. Transfection of human CD4+ T cells with miR-138 suppressed expression of CTLA-4, PD-1, and Forkhead box protein 3 (FoxP3) in transfected human CD4+ T cells. In vivo miR-138 treatment of GL261 gliomas in immune-competent mice demonstrated marked tumor regression, a 43% increase in median survival time (P = .011), and an associated decrease in intratumoral FoxP3+ regulatory T cells, CTLA-4, and PD-1 expression. This treatment effect was lost in nude immune-incompetent mice and with depletion of CD4+ or CD8+ T cells, and miR-138 had no suppressive effect on glioma cells when treated directly at physiological in vivo doses.

CONCLUSIONS

MiR-138 exerts anti-glioma efficacy by targeting immune checkpoints which may have rapid translational potential as a novel immunotherapeutic agent.

PD-L1 expression and prognostic impact in glioblastoma

BACKGROUND

Therapeutic targeting of the immune checkpoints cytotoxic T-lymphocyte-associated molecule-4 (CTLA-4) and PD-1/PD-L1 has demonstrated tumor regression in clinical trials, and phase 2 trials are ongoing in glioblastoma (GBM). Previous reports have suggested that responses are more frequent in patients with tumors that express PD-L1; however, this has been disputed. At issue is the validation of PD-L1 biomarker assays and prognostic impact.

METHODS

Using immunohistochemical analysis, we measured the incidence of PD-L1 expression in 94 patients with GBM. We categorized our results according to the total number of PD-L1-expressing cells within the GBMs and then validated this finding in ex vivo GBM flow cytometry with further analysis of the T cell populations. We then evaluated the association between PD-L1 expression and median survival time using the protein expression datasets and mRNA from The Cancer Genome Atlas.

RESULTS

The median percentage of PD-L1-expressing cells in GBM by cell surface staining is 2.77% (range: 0%-86.6%; n = 92), which is similar to the percentage found by ex vivo flow cytometry. The majority of GBM patients (61%) had tumors with at least 1% or more PD-L1-positive cells, and 38% had at least 5% or greater PD-L1 expression. PD-L1 is commonly expressed on the GBM-infiltrating T cells. Expression of both PD-L1 and PD-1 are negative prognosticators for GBM outcome.

CONCLUSIONS

The incidence of PD-L1 expression in GBM patients is frequent but is confined to a minority subpopulation, similar to other malignancies that have been profiled for PD-L1 expression. Higher expression of PD-L1 is correlated with worse outcome.

Abstract 5088: Glioblastoma stem cell-secreted exosomes can induce a tumor supportive M2 response

INTRODUCTION: Tumor-released exosomes have pleiotropic functions in promoting autocrine signaling to distant cells. Elucidating the mechanistic modulation of the immune system by these exosomes provides insights into potential biomarkers for detection, recurrence and response and identifies potential new therapeutic targets.

METHODS: Exosomes were isolated from human glioblastoma stem cells (GSCs) and fibroblasts (control) using differential centrifugation and characterized by nanosight technology, electron microscopy, and western blotting. Fluorescent-labeled exosomes were co-cultured with human immune cells. Confocal microscopy was used to determine the preferential uptake in various immune populations and to evaluate the intracellular trafficking. The cell-secreted exosome content was characterized by mass spectrometry and nanostring technology. The phenotypic and functional skewing of the monocyte lineage was analyzed given its propensity to take up exosomes.

RESULTS: GSC-secreted exosomes were homogenous in morphology, ranged from 50-120 nm in size, and expressed CD63 and CD9 surface molecules. The GSCs-produced exosomes were preferentially absorbed by CD14+ monocytes (precursors to macrophages) and Gr-1+ derived myeloid cells isolated from healthy volunteers and/or glioblastoma patients. When activated, CD4+ and CD8+ T cells, but not NK cells could also uptake exosomes. Longitudinal kinetic studies established that the highest uptake of PKH67-labeled GCS-secreted exosomes occurred at 48 hours after exposure. Confocal microscopy revealed that monocytes could only internalize GSC-released exosomes but not fibroblast-secreted exosomes. The exposure to GSC-secreted exosomes induced a phenotypic change in monocytes and prevented them from undergoing apoptosis. Studies of M1/M2 macrophage markers by flow cytometry revealed that GSCs-secreted exosomes, but not the fibroblast-secreted exosomes, increased expression of CD80, CD163, CD206 and decreased expression of MHC class II. This profile was similar to myeloid suppressor cells and macrophages that were obtained directly ex vivo from glioblastomas (n = 17). The GSC-secreted exosomes were preferentially enriched relative to fibroblast-secreted exosomes in transcriptional regulators that induced the M2 phenotype.

CONCLUSIONS: Monocytes demonstrate preferential uptake of GSC-secreted exosomes which then induces a glioma-supportive M2 phenotype - similar to the phenotype observed in myeloid cells and macrophages isolated from human glioblastomas. This data indicates that the GSC-secreted exosomes can be a contributing factor in the M2 skewing within the tumor microenvironment.

Citation Format: Konrad Gabrusiewicz, Yuuri Hashimoto, Jun Wei, Maiti Sourindra, John Yu, Shinji Yamashita, Anna Zal, Tomasz Zal, Laurence Cooper, Amy B. Heimberger. Glioblastoma stem cell-secreted exosomes can induce a tumor supportive M2 response. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5088. doi:10.1158/1538-7445.AM2015-5088

Abstract 3298: ABL1 is required for Tie2-mediated DNA repair in brain tumor stem cells

Glioblastoma is the most aggressive primary brain tumor and, in spite of surgery and chemoradiotherapy, invariably recurs. The poor prognosis associated with this disease, with a median survival of 15 months, is largely caused by the striking radioresistance of these tumors. The development of new therapeutic strategies for patient with brain tumors requires the identification of key molecular pathways regulating their resistant phenotype. The abnormal function of tyrosine kinase receptors (TKRs) is a hallmark of malignant gliomas. We previously reported the expression of the TKR Tie2 in brain tumor stem cells (BTSCs) and in human surgical glioma specimens in relation to malignancy. In in vivo experiments, consisting of ionizing irradiation (IR) of mice bearing intracranial BTSCs-derived xenografts showed unexpected Tie2 nuclear localization. These results were confirmed by using immunofluorescence studies using confocal microscope and subcellular fractionation followed by Western blots. Of clinical interest, the presence of Tie2 in the nucleus is associated with radioresistance, as observed after mutagenesis of a newly discovered nuclear localization signal. In addition, upon IR, we detected increased levels of Tie2 natural ligand, Angiopoietin1 (Ang1). The blocking of the Ang1/Tie2 interaction, by the use of a soluble receptor, modulated the IR-mediated Tie2 nuclear translocation, indicating Tie2 intracellular trafficking was ligand dependent. Additionally we also found that after IR treatment, Tie2 localized in the DNA-repair foci and complexed with the H2AX, the key DNA repair protein. The data presented here clearly suggested a role of Tie2 in the DNA damage repair machinery. To test our hypothesis, we used a fluorescent reporter construct in which a functional GFP gene was reconstituted following a non-homologous end joining (NHEJ) event (gift from Dr. Gorbunova, University of Rochester), and we observed that Tie2-expressing cells displayed a more efficient NHEJ repair than Tie2 negative counterparts. Based on the recently reported role of ABL1 (cAbl) in the ATM and KAT5 mediated DNA damage repair, we explored the relationship between ABL1 and the Tie2-mediated radioresistance. Our data clearly showed that DNA repair efficiency significantly and specifically decreased by using ABL1 inhibitor but not by knocking down ABL2 expression. We further analyzed the interactions between Tie2 and chromatin and, interestingly, observed that Tie2 complexes with core histones. Collectively, our results should propel the development of preclinical studies on the combination of nuclear Tie2-targeting strategies with radiotherapy for patients with glioblastomas.

Citation Format: Mohammad B. Hossain, Rehnuma Shifat, David G. Johnson, Mark T. Bedford, Mien-Chie Hung, Nahir Cortes-Santiago, Konrad Gabrusiewicz, Joy Gumin, Ravesanker Ezhilarasan, Erik P. Sulman, Frederick Lang, Raymond Sawaya, W.K. Alfred Yung, Juan Fueyo, Candelaria Gomez-Manzano. ABL1 is required for Tie2-mediated DNA repair in brain tumor stem cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3298. doi:10.1158/1538-7445.AM2015-3298

FGL2 as a Multimodality Regulator of Tumor-Mediated Immune Suppression and Therapeutic Target in Gliomas

BACKGROUND

Fibrinogen-like protein 2 (FGL2) may promote glioblastoma multiforme (GBM) cancer development by inducing multiple immune-suppression mechanisms.

METHODS

The biological significance of FGL2 expression was assessed using the The Cancer Genome Atlast (TCGA) glioma database and tumor lysates analysis. The therapeutic effects of an anti-Fgl2 antibody and the role of immune suppression regulation by Fgl2 were determined in immune-competent, NOD-scid IL2Rgammanull (NSG), and FcɣRIIB-/- mice (n = 3-18 per group). Data were analyzed with two-way analysis of variance, log-rank survival analysis, and Pearson correlation. All statistical tests were two-sided.

RESULTS

In low-grade gliomas, 72.5% of patients maintained two copies of the FGL2 gene, whereas 83.8% of GBM patients had gene amplification or copy gain. Patients with high levels of FGL2 mRNA in glioma tissues had a lower overall survival (P = .009). Protein levels of FGL2 in GBM lysates were higher relative to low-grade glioma lysates (11.48±5.75ng/mg vs 3.96±1.01ng/mg, P = .003). In GL261 mice treated with an anti-FGL2 antibody, median survival was 27 days compared with only 17 days for mice treated with an isotype control antibody (P = .01). The anti-FGL2 antibody treatment reduced CD39(+) Tregs, M2 macrophages, programmed cell death protein 1 (PD-1), and myeloid-derived suppressor cells (MDSCs). FGL2-induced increases in M2, CD39, and PD-1 were ablated in FcɣRIIB-/- mice.

CONCLUSIONS

FGL2 augments glioma immunosuppression by increasing the expression levels of PD-1 and CD39, expanding the frequency of tumor-supportive M2 macrophages via the FcγRIIB pathway, and enhancing the number of MDSCs and CD39(+) regulatory T cells. Collectively, these results show that FGL2 functions as a key immune-suppressive modulator and has potential as an immunotherapeutic target for treating GBM.

Organ specificity of cancer metastasis depends on the adaptive immune surveillance and the neuronal chemokine fractalkine (TUM10P.1030)

The phenomenon of organ specificity in cancer metastasis has been traditionally interpreted in terms of the “seed and soil” hypothesis. However, the role of the adaptive immune system in this phenomenon is largely unknown and controversial. We found that MCA-fibrosarcoma cancer cells formed lethal tumors in the lungs, but not in the brain thereby representing a model of organ-specificity of cancer metastasis. Using this model, we assessed the role of the adaptive immune system. In immune competent multi-color fluorescent reporter mice, longitudinal intravital imaging via cranial windows revealed initial engraftment and growth of MCA cancer cells that was followed by tumor regression in concordance with T cell infiltration. However, MCA cancer cells formed lethal tumors in the brains of Rag1-KO mice indicating a key role for the adaptive immune system in the organ specificity of MCA cancer cell metastasis. In contrast, T cells were recruited to pulmonary MCA lesions but were ineffective in tumor rejection in that organ. Interestingly, T cell recruitment to MCA micrometastases in the brain was dramatically impeded in mice lacking the receptor for the neuronal chemokine fractalkine, and MCA tumors progressed in the brains of those mice. Our results reveal a role for brain-specific adaptive immunity to cancer metastasis and implicate fractalkine in regulating this process thereby broadening the “seed and soil” concept.

Anti-vascular endothelial growth factor therapy-induced glioma invasion is associated with accumulation of Tie2-expressing monocytes

The addition of anti-angiogenic therapy to the few treatments available to patients with malignant gliomas was based on the fact that these tumors are highly vascularized and on encouraging results from preclinical and clinical studies. However, tumors that initially respond to this therapy invariably recur with the acquisition of a highly aggressive and invasive phenotype. Although several myeloid populations have been associated to this pattern of recurrence, a specific targetable population has not been yet identified. Here, we present evidence for the accumulation of Tie2-expressing monocytes/macrophages (TEMs) at the tumor/normal brain interface of mice treated with anti-VEGF therapies in regions with heightened tumoral invasion. Furthermore, we describe the presence of TEMs in malignant glioma surgical specimens that recurred after bevacizumab treatment. Our studies showed that TEMs enhanced the invasive properties of glioma cells and secreted high levels of gelatinase enzymatic proteins. Accordingly, Tie2⁺MMP9⁺ monocytic cells were consistently detected in the invasive tumor edge upon anti-VEGF therapies. Our results suggest the presence of a specific myeloid/monocytic subpopulation that plays a pivotal role in the mechanism of escape of malignant gliomas from anti-VEGF therapies and therefore constitutes a new cellular target for combination therapies in patients selected for anti-angiogenesis treatment.

Effect of miR-142-3p on the M2 macrophage and therapeutic efficacy against murine glioblastoma

BACKGROUND

The immune therapeutic potential of microRNAs (miRNAs) in the context of tumor-mediated immune suppression has not been previously described for monocyte-derived glioma-associated macrophages, which are the largest infiltrating immune cell population in glioblastomas and facilitate gliomagenesis.

METHODS

An miRNA microarray was used to compare expression profiles between human glioblastoma-infiltrating macrophages and matched peripheral monocytes. The effects of miR-142-3p on phenotype and function of proinflammatory M1 and immunosuppressive M2 macrophages were determined. The therapeutic effect of miR-142-3p was ascertained in immune-competent C57BL/6J mice harboring intracerebral GL261 gliomas and in genetically engineered Ntv-a mice bearing high-grade gliomas. Student t test was used to evaluate the differences between ex vivo datasets. Survival was analyzed with the log-rank test and tumor sizes with linear mixed models and F test. All statistical tests were two-sided.

RESULTS

miR-142-3p was the most downregulated miRNA (approximately 4.95-fold) in glioblastoma-infiltrating macrophages. M2 macrophages had lower miR-142-3p expression relative to M1 macrophages (P = .03). Overexpression of miR-142-3p in M2 macrophages induced selective modulation of transforming growth factor beta receptor 1, which led to subsequent preferential apoptosis in the M2 subset (P = .01). In vivo miR-142-3p administration resulted in glioma growth inhibition (P = .03, n = 5) and extended median survival (miR-142-3p-treated C57BL/6J mice vs scramble control: 31 days vs 23.5 days, P = .03, n = 10; miR-142-3p treated Ntv-a mice vs scramble control: 32 days vs 24 days, P = .03, n = 9), with an associated decrease in infiltrating macrophages (R (2) = .303).

CONCLUSIONS

These data indicate a unique role of miR-142-3p in glioma immunity by modulating M2 macrophages through the transforming growth factor beta signaling pathway.

Abstract B36: Understanding the mechanisms underlying recurrence of malignant gliomas after antiangiogenesis treatment

Anti-angiogenesis therapies, in particular bevacizumab, are currently offered to patients with malignant gliomas given strong preclinical and clinical data supporting its effectiveness. However, evidence gathered in the literature shows that upon bevacizumab treatment patients will invariably recur with highly invasive tumors resistant to all available therapies. The purpose of the study we have undertaken is to understand the underlying mechanisms involved in this enhanced malignancy with the aim to uncover new combined therapeutic strategies for these patients. Using tissue obtained from glioma bearing mice treated with bevacizumab or control treatment, we have obtained evidence that upon anti-VEGF treatment, a population of Tie2-expressing cells is recruited to the tumor particularly around areas of invasion. Further characterization of this population demonstrated that a significant proportion of these cells are of myeloid origin, Tie2-expressing monocytes or TEMs. Through the use of an M2 polarized culture as well as TEMs obtained from blood of healthy donors we have gathered data supporting that this myeloid cell population has high expression of several transcripts of molecules associated with invasion as well as a much higher secretion of MMP2 and MMP9 than their Tie2 negative counterparts. In an attempt to understand the changes within the tumor microenvironment after anti-VEGF therapy, immunohistochemical analysis for expression of several molecules associated with angiogenesis was performed. Results obtained identified angiopoietin 2 (Ang2), a Tie2 ligand, as being dramatically increased after therapy. Interestingly, our in vitro and in vivo data show that Ang2 serves as a chemo-attractant molecule to TEMs and therefore could be the main molecule responsible for their recruitment into the tumors following anti-VEGF treatment. We gathered preliminary data on the enhanced presence of TEMs as well as higher levels of MMP9 in human surgical samples after bevacizumab treatment. Our data strongly supports a strong influence of TEMs and Ang2 in the recurrent phenotype of gliomas after anti-VEGF therapy. Further studies aim to understand the extent to which targeting Ang2 specifically and the Ang/Tie2 pathway in general, in combination with anti-VEGF therapy, will lead to improved outcomes.

Citation Format: Nahir Cortes Santiago, Konrad Gabrusiewicz, Dan Liu, Mohammed B. Hossain, Charles Conrad, Juan Fueyo, Candelaria Gomez-Manzano. Understanding the mechanisms underlying recurrence of malignant gliomas after antiangiogenesis treatment. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B36.