An autophagy program that promotes T cell egress from the lymph node controls responses to immune checkpoint blockade

Lymphatic endothelial cells (LECs) of the lymph node (LN) parenchyma orchestrate leukocyte trafficking and peripheral T cell dynamics. T cell responses to immunotherapy largely rely on peripheral T cell recruitment in tumors. Yet, a systematic and molecular understanding of how LECs within the LNs control T cell dynamics under steady-state and tumor-bearing conditions is lacking. Intravital imaging combined with immune phenotyping shows that LEC-specific deletion of the essential autophagy gene Atg5 alters intranodal positioning of lymphocytes and accrues their persistence in the LNs by increasing the availability of the main egress signal sphingosine-1-phosphate. Single-cell RNA sequencing of tumor-draining LNs shows that loss of ATG5 remodels niche-specific LEC phenotypes involved in molecular pathways regulating lymphocyte trafficking and LEC-T cell interactions. Functionally, loss of LEC autophagy prevents recruitment of tumor-infiltrating T and natural killer cells and abrogates response to immunotherapy. Thus, an LEC-autophagy program boosts immune-checkpoint responses by guiding systemic T cell dynamics.

The ins and outs of microglial cells in brain health and disease

Microglia are the brain's resident macrophages that play pivotal roles in immune surveillance and maintaining homeostasis of the Central Nervous System (CNS). Microglia are functionally implicated in various cerebrovascular diseases, including stroke, aneurysm, and tumorigenesis as they regulate neuroinflammatory responses and tissue repair processes. Here, we review the manifold functions of microglia in the brain under physiological and pathological conditions, primarily focusing on the implication of microglia in glioma propagation and progression. We further review the current status of therapies targeting microglial cells, including their re-education, depletion, and re-population approaches as therapeutic options to improve patient outcomes for various neurological and neuroinflammatory disorders, including cancer.

Tumor endothelial cell autophagy is a key vascular-immune checkpoint in melanoma

Tumor endothelial cells (TECs) actively repress inflammatory responses and maintain an immune-excluded tumor phenotype. However, the molecular mechanisms that sustain TEC-mediated immunosuppression remain largely elusive. Here, we show that autophagy ablation in TECs boosts antitumor immunity by supporting infiltration and effector function of T-cells, thereby restricting melanoma growth. In melanoma-bearing mice, loss of TEC autophagy leads to the transcriptional expression of an immunostimulatory/inflammatory TEC phenotype driven by heightened NF-kB and STING signaling. In line, single-cell transcriptomic datasets from melanoma patients disclose an enriched InflammatoryHigh /AutophagyLow TEC phenotype in correlation with clinical responses to immunotherapy, and responders exhibit an increased presence of inflamed vessels interfacing with infiltrating CD8+ T-cells. Mechanistically, STING-dependent immunity in TECs is not critical for the immunomodulatory effects of autophagy ablation, since NF-kB-driven inflammation remains functional in STING/ATG5 double knockout TECs. Hence, our study identifies autophagy as a principal tumor vascular anti-inflammatory mechanism dampening melanoma antitumor immunity.

Multiomics and spatial mapping characterizes human CD8+ T cell states in cancer

Clinically relevant immunological biomarkers that discriminate between diverse hypofunctional states of tumor-associated CD8⁺ T cells remain disputed. Using multiomics analysis of CD8⁺ T cell features across multiple patient cohorts and tumor types, we identified tumor niche-dependent exhausted and other types of hypofunctional CD8⁺ T cell states. CD8⁺ T cells in "supportive" niches, like melanoma or lung cancer, exhibited features of tumor reactivity-driven exhaustion (CD8⁺ T_EX). These included a proficient effector memory phenotype, an expanded T cell receptor (TCR) repertoire linked to effector exhaustion signaling, and a cancer-relevant T cell-activating immunopeptidome composed of largely shared cancer antigens or neoantigens. In contrast, "nonsupportive" niches, like glioblastoma, were enriched for features of hypofunctionality distinct from canonical exhaustion. This included immature or insufficiently activated T cell states, high wound healing signatures, nonexpanded TCR repertoires linked to anti-inflammatory signaling, high T cell-recognizable self-epitopes, and an antiproliferative state linked to stress or prodeath responses. In situ spatial mapping of glioblastoma highlighted the prevalence of dysfunctional CD4⁺:CD8⁺ T cell interactions, whereas ex vivo single-cell secretome mapping of glioblastoma CD8⁺ T cells confirmed negligible effector functionality and a promyeloid, wound healing-like chemokine profile. Within immuno-oncology clinical trials, anti-programmed cell death protein 1 (PD-1) immunotherapy facilitated glioblastoma's tolerogenic disparities, whereas dendritic cell (DC) vaccines partly corrected them. Accordingly, recipients of a DC vaccine for glioblastoma had high effector memory CD8⁺ T cells and evidence of antigen-specific immunity. Collectively, we provide an atlas for assessing different CD8⁺ T cell hypofunctional states in immunogenic versus nonimmunogenic cancers.

High endothelial venules in cancer: Regulation, function, and therapeutic implication

The lack of sufficient intratumoral CD8⁺ T lymphocytes is a significant obstacle to effective immunotherapy in cancer. High endothelial venules (HEVs) are organ-specific and specialized postcapillary venules uniquely poised to facilitate the transmigration of lymphocytes to lymph nodes (LNs) and other secondary lymphoid organs (SLOs). HEVs can also form in human and murine cancer (tumor HEVs [TU-HEVs]) and contribute to the generation of diffuse T cell-enriched aggregates or tertiary lymphoid structures (TLSs), which are commonly associated with a good prognosis. Thus, therapeutic induction of TU-HEVs may provide attractive avenues to induce and sustain the efficacy of immunotherapies by overcoming the major restriction of T cell exclusion from the tumor microenvironment. In this review, we provide current insight into the commonalities and discrepancies of HEV formation and regulation in LNs and tumors and discuss the specific function and significance of TU-HEVs in eliciting, predicting, and aiding anti-tumoral immunity.

Identification, validation and biological characterisation of novel glioblastoma tumour microenvironment subtypes: implications for precision immunotherapy

BACKGROUND

New precision medicine therapies are urgently required for glioblastoma (GBM). However, to date, efforts to subtype patients based on molecular profiles have failed to direct treatment strategies. We hypothesised that interrogation of the GBM tumour microenvironment (TME) and identification of novel TME-specific subtypes could inform new precision immunotherapy treatment strategies.

MATERIALS AND METHODS

A refined and validated microenvironment cell population (MCP) counter method was applied to >800 GBM patient tumours (GBM-MCP-counter). Specifically, partition around medoids (PAM) clustering of GBM-MCP-counter scores in the GLIOTRAIN discovery cohort identified three novel patient clusters, uniquely characterised by TME composition, functional orientation markers and immune checkpoint proteins. Validation was carried out in three independent GBM-RNA-seq datasets. Neoantigen, mutational and gene ontology analysis identified mutations and uniquely altered pathways across subtypes. The longitudinal Glioma Longitudinal AnalySiS (GLASS) cohort and three immunotherapy clinical trial cohorts [treatment with neoadjuvant/adjuvant anti-programmed cell death protein 1 (PD-1) or PSVRIPO] were further interrogated to assess subtype alterations between primary and recurrent tumours and to assess the utility of TME classifiers as immunotherapy biomarkers.

RESULTS

TME^High tumours (30%) displayed elevated lymphocyte, myeloid cell immune checkpoint, programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated protein 4 transcripts. TME^High/mesenchymal+ patients featured tertiary lymphoid structures. TME^Med (46%) tumours were enriched for endothelial cell gene expression profiles and displayed heterogeneous immune populations. TME^Low (24%) tumours were manifest as an 'immune-desert' group. TME subtype transitions upon recurrence were identified in the longitudinal GLASS cohort. Assessment of GBM immunotherapy trial datasets revealed that TME^High patients receiving neoadjuvant anti-PD-1 had significantly increased overall survival (P = 0.04). Moreover, TME^High patients treated with adjuvant anti-PD-1 or oncolytic virus (PVSRIPO) showed a trend towards improved survival.

CONCLUSIONS

We have established a novel TME-based classification system for application in intracranial malignancies. TME subtypes represent canonical 'termini a quo' (starting points) to support an improved precision immunotherapy treatment approach.

Cancer immunotherapies transition endothelial cells into HEVs that generate TCF1+ T lymphocyte niches through a feed-forward loop

The lack of T cell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLLSs), which are the local site of humoral and cellular immune responses against cancers, is associated with good prognosis, and they have recently been detected in immune checkpoint blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing single-cell transcriptomics, endothelial fate mapping, and functional multiplex immune profiling, we demonstrate that antiangiogenic immune-modulating therapies evoke transdifferentiation of postcapillary venules into inflamed high-endothelial venules (HEVs) via lymphotoxin/lymphotoxin beta receptor (LT/LTβR) signaling. In turn, tumor HEVs boost intratumoral lymphocyte influx and foster permissive lymphocyte niches for PD1^- and PD1⁺TCF1⁺ CD8 T cell progenitors that differentiate into GrzB⁺PD1⁺ CD8 T effector cells. Tumor-HEVs require continuous CD8 and NK cell-derived signals revealing that tumor HEV maintenance is actively sculpted by the adaptive immune system through a feed-forward loop.

Abstract A34: Therapeutic induction of High Endothelial Venules in cancer generates TCF1+ lymphocyte niches

The lack of T-cell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLS), which are the local site of humoral and cellular immune responses against cancers, are associated with good prognosis and have recently been detected in Immune Checkpoint Blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing scRNA sequencing, endothelial fate mapping, and multiplex immunohistochemistry, we demonstrate that antiangiogenic immune-modulating therapies evoke the transition of postcapillary venules into inflamed high endothelial venules (HEV), which predominantly generate permissive TA-TLS-like lymphocyte niches. These HEV+ immune niches entail PD1neg and PD1+TCF1+CD8+ progenitor cells that differentiate into cytotoxic TCF1neg TIM3+ PD1+ CD8 effector cells and migrate into the tumor core. Congruently, TU-HEV signatures correlate with response to ICB therapies in several human tumor types. In line with these observations, TU-HEVs require continuous CD8 and NK cell-derived lymphotoxin signals revealing that tumor-HEV maintenance is actively sculpted by the immune system through a feed-forward loop.

Citation Format: Gerlanda Vella, Yichao Hua, Florian Rambow, Elizabeth Allen, Asier Antoranz Martinez, Pascal Merchiers, Francesca Bosisio, Giuseppe Floris, Akira Takeda, Sirpa Jalkanen, Maija Hollmén, Jean-Christophe Marine, Susan Schlenner, Gabriele Bergers. Therapeutic induction of High Endothelial Venules in cancer generates TCF1+ lymphocyte niches [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr A34.

TMIC-10. IDENTIFICATION, VALIDATION AND BIOLOGICAL CHARACTERIZATION OF NOVEL GLIOBLASTOMA TUMOUR MICROENVIRONMENT SUBTYPES: IMPLICATIONS FOR PRECISION IMMUNOTHERAPY

New precision medicine therapies are urgently required for glioblastoma (GBM). However, to date, efforts to subtype patients based on molecular profiles, have failed to direct treatment strategies. We hypothesized that interrogation of the GBM tumor microenvironment (TME) and identification of novel TME-specific subtypes could inform new precision treatment strategies. To this end, a refined and validated microenvironment cell population (MCP)-counter method was applied to > 800 GBM patient tumours and validated by multiplex-immunohistochemistry. The MCP-counter deconvolution method interrogates the TME composition from transcriptomic data. Using this refined method, we classified the GLIOTRAIN(www.gliotrain.eu) IDHwt GBM cohort (n=123) into 3 novel clusters characterised by differences in TME composition and subsequently validated findings in the TCGA (n=69), CGGA (n=72) and DUKE (unpublished)(n=162) cohorts. TMEHigh tumours (30%) displayed elevated immune populations, functional orientation markers, immune checkpoint genes, and upregulated immunoregulatory pathways. Moreover, tertiary lymphoid structures were a feature of TMEHigh/mesenchymal+ patients. TMEMed (46%) tumours displayed heterogeneous immune populations and upregulated neuronal signalling pathways. TMELow (24%) tumours represented an ‘immune-desert’ group, high EGFR mutation frequency and upregulated EGFR signalling pathways. Longitudinal analysis of the GLASS cohort revealed TME-subtype transitions upon recurrence, influenced by TME composition changes. Finally, assessment of three GBM immunotherapy clinical trial cohorts revealed that TMEHigh patients treated with neo-adjuvant anti-PD1 have a significantly improved survival (P=0.04). Moreover, TMEHigh patients treated with anti-PD1 and an oncolytic virus (PVSRIPO) in the adjuvant setting, showed a trend towards improved survival (P=0.15 and P=0.056 respectively). Overall, we have established a novel TME-based classification system for application in intracranial malignancies. This system may be used to better inform a precision targeting approach in the brain tumour setting. For example, we hypothesise that patients bearing TMELow tumours may be amenable to neoadjuvant anti-TIM3 + EGFR inhibitor, TMEMed to anti-angiogenic immunotherapy, and TMEHigh patients to neoadjuvant anti-PD1 + anti-CTLA4.

A cellular hierarchy in melanoma uncouples growth and metastasis

Although melanoma is notorious for its high degree of heterogeneity and plasticity1,2, the origin and magnitude of cell-state diversity remains poorly understood. Equally, it is unclear whether growth and metastatic dissemination are supported by overlapping or distinct melanoma subpopulations. Here, by combining mouse genetics, single-cell and spatial transcriptomics, lineage tracing and quantitative modelling, we provide evidence of a hierarchical model of tumour growth that mirrors the cellular and molecular logic underlying the cell-fate specification and differentiation of the embryonic neural crest. We show that tumorigenic competence is associated with a spatially localized perivascular niche, a phenotype acquired through an intercellular communication pathway established by endothelial cells. Consistent with a model in which only a fraction of cells are fated to fuel growth, temporal single-cell tracing of a population of melanoma cells with a mesenchymal-like state revealed that these cells do not contribute to primary tumour growth but, instead, constitute a pool of metastatic initiating cells that switch cell identity while disseminating to secondary organs. Our data provide a spatially and temporally resolved map of the diversity and trajectories of melanoma cell states and suggest that the ability to support growth and metastasis are limited to distinct pools of cells. The observation that these phenotypic competencies can be dynamically acquired after exposure to specific niche signals warrant the development of therapeutic strategies that interfere with the cancer cell reprogramming activity of such microenvironmental cues.

GBM tumors are heterogeneous in their fatty acid metabolism and modulating fatty acid metabolism sensitizes cancer cells derived from recurring GBM tumors to temozolomide

Glioblastoma is a highly lethal grade of astrocytoma with very low median survival. Despite extensive efforts, there is still a lack of alternatives that might improve these prospects. We uncovered that the chemotherapeutic agent temozolomide impinges on fatty acid synthesis and desaturation in newly diagnosed glioblastoma. This response is, however, blunted in recurring glioblastoma from the same patient. Further, we describe that disrupting cellular fatty acid homeostasis in favor of accumulation of saturated fatty acids such as palmitate synergizes with temozolomide treatment. Pharmacological inhibition of SCD and/or FADS2 allows palmitate accumulation and thus greatly augments temozolomide efficacy. This effect was independent of common GBM prognostic factors and was effective against cancer cells from recurring glioblastoma. In summary, we provide evidence that intracellular accumulation of saturated fatty acids in conjunction with temozolomide based chemotherapy induces death in glioblastoma cells derived from patients.

Lipid droplet degradation by autophagy connects mitochondria metabolism to Prox1-driven expression of lymphatic genes and lymphangiogenesis

Autophagy has vasculoprotective roles, but whether and how it regulates lymphatic endothelial cells (LEC) homeostasis and lymphangiogenesis is unknown. Here, we show that genetic deficiency of autophagy in LEC impairs responses to VEGF-C and injury-driven corneal lymphangiogenesis. Autophagy loss in LEC compromises the expression of main effectors of LEC identity, like VEGFR3, affects mitochondrial dynamics and causes an accumulation of lipid droplets (LDs) in vitro and in vivo. When lipophagy is impaired, mitochondrial ATP production, fatty acid oxidation, acetyl-CoA/CoA ratio and expression of lymphangiogenic PROX1 target genes are dwindled. Enforcing mitochondria fusion by silencing dynamin-related-protein 1 (DRP1) in autophagy-deficient LEC fails to restore LDs turnover and lymphatic gene expression, whereas supplementing the fatty acid precursor acetate rescues VEGFR3 levels and signaling, and lymphangiogenesis in LEC-Atg5^-/- mice. Our findings reveal that lipophagy in LEC by supporting FAO, preserves a mitochondrial-PROX1 gene expression circuit that safeguards LEC responsiveness to lymphangiogenic mediators and lymphangiogenesis.

LGL1 binds to Integrin β1 and inhibits downstream signaling to promote epithelial branching in the mammary gland

Branching morphogenesis is a fundamental process by which organs in invertebrates and vertebrates form branches to expand their surface areas. The current dogma holds that directional cell migration determines where a new branch forms and thus patterns branching. Here, we asked whether mouse Lgl1, a homolog of the Drosophila tumor suppressor Lgl, regulates epithelial polarity in the mammary gland. Surprisingly, mammary glands lacking Lgl1 have normal epithelial polarity, but they form fewer branches. Moreover, we find that Lgl1 null epithelium is unable to directionally migrate, suggesting that migration is not essential for mammary epithelial branching as expected. We show that LGL1 binds to Integrin β1 and inhibits its downstream signaling, and Integrin β1 overexpression blocks epithelial migration, thus recapitulating the Lgl1 null phenotype. Altogether, we demonstrate that Lgl1 modulation of Integrin β1 signaling is essential for directional migration and that epithelial branching in invertebrates and the mammary gland is fundamentally distinct.

Ma et al. show that Lgl1 is essential for mammary gland branching morphogenesis but not epithelial polarity. Lgl1 is required for directional migration by regulating Integrin β1 signaling levels and focal adhesion strengths. Finally, branching mechanisms are distinct between mammary gland and Drosophila systems where directional migration is indispensable.

High Endothelial Venules: A Vascular Perspective on Tertiary Lymphoid Structures in Cancer

High endothelial venules (HEVs) are specialized postcapillary venules composed of cuboidal blood endothelial cells that express high levels of sulfated sialomucins to bind L-Selectin/CD62L on lymphocytes, thereby facilitating their transmigration from the blood into the lymph nodes (LN) and other secondary lymphoid organs (SLO). HEVs have also been identified in human and murine tumors in predominantly CD3⁺T cell-enriched areas with fewer CD20⁺B-cell aggregates that are reminiscent of tertiary lymphoid-like structures (TLS). While HEV/TLS areas in human tumors are predominantly associated with increased survival, tumoral HEVs (TU-HEV) in mice have shown to foster lymphocyte-enriched immune centers and boost an immune response combined with different immunotherapies. Here, we discuss the current insight into TU-HEV formation, function, and regulation in tumors and elaborate on the functional implication, opportunities, and challenges of TU-HEV formation for cancer immunotherapy.

The metabolism of cancer cells during metastasis

Metastasis formation is the major cause of death in most patients with cancer. Despite extensive research, targeting metastatic seeding and colonization is still an unresolved challenge. Only recently, attention has been drawn to the fact that metastasizing cancer cells selectively and dynamically adapt their metabolism at every step during the metastatic cascade. Moreover, many metastases display different metabolic traits compared with the tumours from which they originate, enabling survival and growth in the new environment. Consequently, the stage-dependent metabolic traits may provide therapeutic windows for preventing or reducing metastasis, and targeting the new metabolic traits arising in established metastases may allow their eradication.

Tumors vs. Chronic Wounds: An Immune Cell's Perspective

The wound repair program is tightly regulated and coordinated among different cell constituents including epithelial cells, fibroblasts, immune cells and endothelial cells following consecutive steps to ensure timely, and proper wound closure. Specifically, innate and adaptive immune cells are pivotal participants that also closely interact with the vasculature. Tumors are portrayed as wounds that do not heal because they undergo continuous stromal remodeling and vascular growth with immunosuppressive features to ensure tumor propagation; a stage that is reminiscent of the proliferative resolution phase in wound repair. There is increasing evidence from mouse model systems and clinical trials that targeting both the immune and vascular compartments is an attractive therapeutic approach to reawaken the inflammatory status in the "tumor wound" with the final goal to abrogate tumor cells and invigorate tissue homeostasis. In this review, we compare the implication of immune cells and the vasculature in chronic wounds and tumor wounds to underscore the conceptual idea of transitioning tumors into an inflammatory wound-like state with antiangiogenic immunotherapies to improve beneficial effects in cancer patients.

Where Have All the T Cells Gone?

Glioblastoma are highly immunosuppressive brain tumors that are known for their T cell paucity. In a recent issue of Nature Medicine, Chongsathidkiet et al. (2018) discovered a brain-specific mechanism of tumors to escape immunosurveillance by trapping T cells in the bone marrow through the loss of sphingosine-1-phosphate (S1P) receptor on the T cell surface.

Regulation of Blood and Lymphatic Vessels by Immune Cells in Tumors and Metastasis

Research over the last decades has provided strong evidence for the pivotal role of the tumor-associated blood and lymphatic vasculature in supporting immunoevasion and in subverting T cell-mediated immunosurveillance. Conversely, tumor blood and lymphatic vessel growth is in part regulated by the immune system, with infiltrating innate as well as adaptive immune cells providing both immunosuppressive and various angiogenic signals. Thus, tumor angiogenesis and escape of immunosurveillance are two cancer hallmarks that are tightly linked and interregulated by cell constituents from compartments secreting both chemokines and cytokines. In this review, we discuss the implication and regulation of innate and adaptive immune cells in regulating blood and lymphatic angiogenesis in tumor progression and metastases. Moreover, we also highlight novel therapeutic approaches that target the tumor vasculature as well as the immune compartment to sustain and improve therapeutic efficacy in cancer.

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

The reciprocal function and regulation of tumor vessels and immune cells offers new therapeutic opportunities in cancer

Tumor angiogenesis and escape of immunosurveillance are two cancer hallmarks that are tightly linked and reciprocally regulated by paracrine signaling cues of cell constituents from both compartments. Formation and remodeling of new blood vessels in tumors is abnormal and facilitates immune evasion. In turn, immune cells in the tumor, specifically in context with an acidic and hypoxic environment, can promote neovascularization. Immunotherapy has emerged as a major therapeutic modality in cancer but is often hampered by the low influx of activated cytotoxic T-cells. On the other hand, anti-angiogenic therapy has been shown to transiently normalize the tumor vasculature and enhance infiltration of T lymphocytes, providing a rationale for a combination of these two therapeutic approaches to sustain and improve therapeutic efficacy in cancer. In this review, we discuss how the tumor vasculature facilitates an immunosuppressive phenotype and vice versa how innate and adaptive immune cells regulate angiogenesis during tumor progression. We further highlight recent results of antiangiogenic immunotherapies in experimental models and the clinic to evaluate the concept that targeting both the tumor vessels and immune cells increases the effectiveness in cancer patients.

Vascular targeting of LIGHT normalizes blood vessels in primary brain cancer and induces intratumoural high endothelial venules

High-grade brain cancer such as glioblastoma (GBM) remains an incurable disease. A common feature of GBM is the angiogenic vasculature, which can be targeted with selected peptides for payload delivery. We assessed the ability of micelle-tagged, vascular homing peptides RGR, CGKRK and NGR to specifically bind to blood vessels in syngeneic orthotopic GBM models. By using the peptide CGKRK to deliver the tumour necrosis factor (TNF) superfamily member LIGHT (also known as TNF superfamily member 14; TNFSF14) to angiogenic tumour vessels, we have generated a reagent that normalizes the brain cancer vasculature by inducing pericyte contractility and re-establishing endothelial barrier integrity. LIGHT-mediated vascular remodelling also activates endothelia and induces intratumoural high endothelial venules (HEVs), which are specialized blood vessels for lymphocyte infiltration. Combining CGKRK-LIGHT with anti-vascular endothelial growth factor and checkpoint blockade amplified HEV frequency and T-cell accumulation in GBM, which is often sparsely infiltrated by immune effector cells, and reduced tumour burden. Furthermore, CGKRK and RGR peptides strongly bound to blood vessels in freshly resected human GBM, demonstrating shared peptide-binding activities in mouse and human primary brain tumour vessels. Thus, peptide-mediated LIGHT targeting is a highly translatable approach in primary brain cancer to reduce vascular leakiness and enhance immunotherapy. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Combined antiangiogenic and anti-PD-L1 therapy stimulates tumor immunity through HEV formation

Inhibitors of VEGF (vascular endothelial growth factor)/VEGFR2 (vascular endothelial growth factor receptor 2) are commonly used in the clinic, but their beneficial effects are only observed in a subset of patients and limited by induction of diverse relapse mechanisms. We describe the up-regulation of an adaptive immunosuppressive pathway during antiangiogenic therapy, by which PD-L1 (programmed cell death ligand 1), the ligand of the negative immune checkpoint regulator PD-1 (programmed cell death protein 1), is enhanced by interferon-γ-expressing T cells in distinct intratumoral cell types in refractory pancreatic, breast, and brain tumor mouse models. Successful treatment with a combination of anti-VEGFR2 and anti-PD-L1 antibodies induced high endothelial venules (HEVs) in PyMT (polyoma middle T oncoprotein) breast cancer and RT2-PNET (Rip1-Tag2 pancreatic neuroendocrine tumors), but not in glioblastoma (GBM). These HEVs promoted lymphocyte infiltration and activity through activation of lymphotoxin β receptor (LTβR) signaling. Further activation of LTβR signaling in tumor vessels using an agonistic antibody enhanced HEV formation, immunity, and subsequent apoptosis and necrosis in pancreatic and mammary tumors. Finally, LTβR agonists induced HEVs in recalcitrant GBM, enhanced cytotoxic T cell (CTL) activity, and thereby sensitized tumors to antiangiogenic/anti-PD-L1 therapy. Together, our preclinical studies provide evidence that anti-PD-L1 therapy can sensitize tumors to antiangiogenic therapy and prolong its efficacy, and conversely, antiangiogenic therapy can improve anti-PD-L1 treatment specifically when it generates intratumoral HEVs that facilitate enhanced CTL infiltration, activity, and tumor cell destruction.

Trimming the Vascular Tree in Tumors: Metabolic and Immune Adaptations

Angiogenesis, the formation of new blood vessels, has become a well-established hallmark of cancer. Its functional importance for the manifestation and progression of tumors has been further validated by the beneficial therapeutic effects of angiogenesis inhibitors, most notably ones targeting the vascular endothelial growth factor (VEGF) signaling pathways. However, with the transient and short-lived nature of the patient response, it has become evident that tumors have the ability to adapt to the pressures of vascular growth restriction. Several escape mechanisms have been described that adapt tumors to therapy-induced low-oxygen tension by either reinstating tumor growth by vascular rebound or by altering tumor behavior without the necessity to reinitiate revascularization. We review here two bypass mechanisms that either instigate angiogenic and immune-suppressive polarization of intratumoral innate immune cells to facilitate VEGF-independent angiogenesis or enable metabolic adaptation and reprogramming of endothelial cells and tumor cells to adapt to low-oxygen tension.

Abstract PR05: Glycoprotein-mediated tissue mechanics regulate glioblastoma aggression

Glioblastoma multiforme (GBM) is a malignant glioma whose progression is associated with rampant extracellular matrix (ECM) remodeling. We recently found that GBM ECM stiffness predicts reduced survival in human patients. Instead of collagen fibrosis, which is common in many solid tumors, we showed that GBM stiffening involves increased production of extracellular glycoproteins, glycosaminoglycans, and sugar-binding proteins. Using bioinformatics, we revealed that genes of the glycocalyx (transmembrane glycoproteins and their interacting partners) are disproportionately upregulated in GBM relative to lower grade gliomas. Further, these genes are overexpressed within GBM in the mesenchymal (MES) relative to the proneural (PRO) subtype, the former of which is associated with treatment resistance and relapse. Using mouse models of human GBM, we showed that MES tumors are more lethal than PRO, and present with elevated ECM stiffness and mechanical signaling. To test our hypothesis that mechanical signaling can drive the MES phenotype, we engineered PRO GBM cells with constitutively-elevated integrin signaling. Compared to control PRO cells, these undergo a robust MES-like transition, upregulate bulky glycoprotein expression, and result in stiffer and more lethal tumors. This phenotype was reversed by the inhibition of focal adhesion kinase in MES cells. To test whether an enhanced glycocalyx can directly elevate mechanical signaling, we decorated GBM cells with synthetic glycoprotein polymers. Indeed, this resulted in enhanced integrin-focal adhesion signaling and more aggressive tumor progression. The invasive properties and therapy resistance observed in mesenchymal tumor cells are often associated with elevated stem cell-like features. To investigate a link between the glycocalyx, tissue mechanics, and the mesenchymal-stem cell phenotype, we interfered with components of the gylcocalyx or mechanical signaling machinery and found a reduction in stem cell genes and surface proteins, as well as increased sensitivity to chemotherapy. These data support a model in which glycoprotein-mediated tissue stiffening drives GBM aggression through promotion of a mesenchymal phenotype.

This abstract is also being presented as Poster A39.

Citation Format: J. Matthew Barnes, Elliot C. Woods, Russell O. Bainer, Yekaterina A. Miroshnikova, Kan Lu, Gabriele Bergers, Carolyn Bertozzi, Valerie M. Weaver. Glycoprotein-mediated tissue mechanics regulate glioblastoma aggression. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr PR05.

Abstract 1245: RRx-001 is effective in temozolomide-sensitive and resistant GBM

Glioblastoma Multiforme (GBM) is one of the most aggressive malignancies in humans, being highly invasive and drug-resistant, limiting the effectiveness of surgery, chemotherapy and radiotherapy. Concurrent Temozolomide (TMZ) and radiation is the standard of care for newly diagnosed GBM patients, however, patients respond poorly and prognosis remains dismal. TMZ response is limited to patients with hypermethylation of the methylguanine methyltransferase (MGMT) promoter. Despite recent advances in therapeutic strategies, treating GBM is still an unsolved clinical challenge requiring the investigation of novel approaches with better responses over approved therapies. RRx-001 is a novel ROS-mediated systemically non-toxic chemo-sensitizing epigenetic agent with vascular normalizing properties under investigation in Phase II clinical trials in brain metastases and GBM.

We assessed whether RRx-001 is an effective approach for treating GBM by testing its effects alone and in combination with TMZ both in vitro as well as in GBM mouse models. RRx-001 induced cytotoxicity in human TMZ-sensitive as well as resistant patient-derived GBM cell lines. In addition, its effect in TMZ-sensitive GBM cells was greater than the one induced by TMZ alone.

We then asked whether the in vitro effects of RRx-001 translated to therapeutic efficacy in vivo. To this end, we injected mice intracranially with a TMZ-resistant murine mesenchymal GBM cells, and treated tumor-bearing mice with RRx-001 alone and in combination with TMZ. RRx-001 treatment alone modestly prolonged survival compared to control cohorts, whereas the combination of RRx-001 and TMZ substantially prolonged survival compared to controls and either treatment alone. Moreover, histological evaluation of GBM tumors revealed that combination of RRx-001 and TMZ induced vessel hyperdilation and apoptosis compared to RRx-001 alone. Thus, in vivo RRx-001 combined to TMZ may also indirectly regulate tumor growth by modifying the tumor stroma.

These data suggest that TMZ may still affect the microenvironment in TMZ-resistant tumors and that RRx-001 enhances these effects by both directly and indirectly restricting GBM growth, making it a promising therapeutic agent alone and in combination with TMZ.

Citation Format: Veronica Steri, Bryan Oronsky, Jan Scicinski, Gabriele Bergers. RRx-001 is effective in temozolomide-sensitive and resistant GBM. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1245.

Abstract 1343: P32-targeting TT1 peptide delivers nanoparticles to intracranial glioblastomas

Targeted delivery of cancer therapeutics using affinity ligands can dramatically improve antitumor efficacy. Over the years a number of homing peptides that upon systemic injection accumulate in solid tumors have been identified by in vivo peptide phage display. In a quest to find homing peptides optimally suited for drug delivery to high-grade gliomas, our laboratories are using advanced mouse models of glioblastoma (GBM) to systematically audit known tumor-homing peptides and to perform new in vivo screens using peptide phage libraries.

P32 is a mitochondrial chaperone that is aberrantly expressed on the cell surface in activated malignant and stromal cells in tumors. P32 is a receptor for widely used LypP-1 peptide and for recently identified TT1 peptide. Here we show that iron oxide nanoworms (IONW) functionalized with linear TT1 peptide (CKRGARST) strongly home to intracranial GBMs grafted in immune deficient mice. IONW are paramagnetic nanoparticles that are PEGylated to extend blood half-life, and have, because of their elongated shape, more effective targeting properties than spherical nanoparticles. Five hours after intravenous injection of IONW (7.5 mg/kg), macroscopic fluorescence imaging demonstrated robust homing of TT1-IONW in GBMs of murine origin (WT GBM and VEGF KO GBM from the G. Berger lab) and in a patient-derived glioma model (P13 model from the Bjerkvig lab). Confocal microscopy confirmed the presence of TT1 but not control IONW in gliomas, with TT1-IONW signal showing partial overlap with blood- and lymphatic vessel markers (CD31 and LYVE-1) in WT GBM and P13 gliomas, whereas lower level of colocalization with these markers was detected for mouse GBM not expressing VEGF. In addition, moderate colocalization between TT1-IONW and the macrophage marker CD11b was detected in the P13 tumors. Detailed phenotyping and functional characterization of TT1-positive macrophages is ongoing.

Our data suggest that TT1 peptide has potential applications as a glioma-targeting vehicle. Currently, we are evaluating TT1-targeted IONWs as a contrast agent for glioma MRI and as carriers for cytotoxic compounds.

Citation Format: Pille Säälik, Hedi Hunt, Allan Tobi, Anne-Mari Anton Willmore, Kadri Toome, Shweta Sharma, Ramana Kotamraju, Gabriele Bergers, Rolf Bjerkvig, Erkki Ruoslahti, Tambet Teesalu, Tambet Teesalu. P32-targeting TT1 peptide delivers nanoparticles to intracranial glioblastomas. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1343.

Glioblastoma: Defining Tumor Niches

Glioblastomas (GBM) are one of the most recalcitrant brain tumors because of their aggressive invasive growth and resistance to therapy. They are highly heterogeneous malignancies at both the molecular and histological levels. Specific histological hallmarks including pseudopalisading necrosis and microvascular proliferation distinguish GBM from lower-grade gliomas, and make GBM one of the most hypoxic as well as angiogenic tumors. These microanatomical compartments present specific niches within the tumor microenvironment that regulate metabolic needs, immune surveillance, survival, invasion as well as cancer stem cell maintenance. Here we review features and functions of the distinct GBM niches, detail the different cell constituents and the functional status of the vasculature, and discuss prospects of therapeutically targeting GBM niche constituents.

Abstract IA24: Understanding and tackling differing vascular niches in glioma

Glioblastoma multiforme (GBM) is the most belligerent adult brain tumor, which is defined by its aggressive growth due to uncontrolled cellular proliferation, resistance to apoptosis, diffuse infiltration and invasion, propensity for necrosis and hypoxia, and vigorous angiogenesis. Recurrence of these invasive tumors is inevitable despite advanced multimodal therapy with surgery followed by radiation and temozolomide treatment resulting in a dismal median survival of beyond one year. A recent milestone in glioma research has been the revelation that therapies targeting other cell types besides tumor cells; i.e., the cell constituents of the vascular niche can convey substantial improvements in radiographic response, progression-free survival, and quality of life. The changing perspective on the environment as a functional contributor represents a profound shift in the approach to biology and therapeutic decisions in GBM. Here, we describe paracrine signaling pathways of the differing vascular niches that regulate angiogenesis or tumor invasiveness and present therapeutic modalities to target those to more efficiently block diffuse and angiogenic GBM growth.

Citation Format: Gabriele Bergers. Understanding and tackling differing vascular niches in glioma. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr IA24.

Intratumoral myeloid cells regulate responsiveness and resistance to antiangiogenic therapy

Antiangiogenic therapy is commonly used in the clinic, but its beneficial effects are short-lived, leading to tumor relapse within months. Here, we found that the efficacy of angiogenic inhibitors targeting the VEGF/VEGFR pathway was dependent on induction of the angiostatic and immune-stimulatory chemokine CXCL14 in mouse models of pancreatic neuroendocrine and mammary tumors. In response, tumors reinitiated angiogenesis and immune suppression by activating PI3K signaling in all CD11b+ cells, rendering tumors nonresponsive to VEGF/VEGFR inhibition. Adaptive resistance was also associated with an increase in Gr1+CD11b+ cells, but targeting Gr1+ cells was not sufficient to further sensitize angiogenic blockade because tumor-associated macrophages (TAMs) would compensate for the lack of such cells and vice versa, leading to an oscillating pattern of distinct immune-cell populations. However, PI3K inhibition in CD11b+ myeloid cells generated an enduring angiostatic and immune-stimulatory environment in which antiangiogenic therapy remained efficient.

Intertwined regulation of angiogenesis and immunity by myeloid cells

Angiogenesis is a hallmark of cancer because its induction is indispensable to fuel an expanding tumor. The tumor microenvironment contributes to tumor vessel growth, and distinct myeloid cells recruited by the tumor have been shown not only to support angiogenesis but also to foster an immune suppressive environment that supports tumor expansion and progression. Recent findings suggest that the intertwined regulation of angiogenesis and immune modulation can offer therapeutic opportunities for the treatment of cancer. We review the mechanisms by which distinct myeloid cell populations contribute to tumor angiogenesis, discuss current approaches in the clinic that are targeting both angiogenic and immune suppressive pathways, and highlight important areas of future research.

Mechanisms of evasive resistance to anti-VEGF therapy in glioblastoma

Angiogenesis inhibitors targeting the VEGF signaling pathway have been US FDA approved for various cancers including glioblastoma (GBM), one of the most lethal and angiogenic tumors. This has led to the routine use of the anti-VEGF antibody bevacizumab in recurrent GBM, conveying substantial improvements in radiographic response, progression-free survival and quality of life. Despite these encouraging beneficial effects, patients inevitably develop resistance and frequently fail to demonstrate significantly better overall survival. Unlike chemotherapies, to which tumors exhibit resistance due to genetic mutation of drug targets, emerging evidence suggests that tumors bypass antiangiogenic therapy while VEGF signaling remains inhibited through a variety of mechanisms that are just beginning to be recognized. Because of the indirect nature of resistance to VEGF inhibitors there is promise that strategies combining angiogenesis inhibitors with drugs targeting such evasive resistance pathways will lead to more durable antiangiogenic efficacy and improved patient outcomes. Further identifying and understanding of evasive resistance mechanisms and their clinical importance in GBM relapse is therefore a timely and critical issue.

HR-MAS MRS of the pancreas reveals reduced lipid and elevated lactate and taurine associated with early pancreatic cancer

The prognosis for patients with pancreatic cancer is extremely poor, as evidenced by the disease's five-year survival rate of ~5%. New approaches are therefore urgently needed to improve detection, treatment, and monitoring of pancreatic cancer. MRS-detectable metabolic changes provide useful biomarkers for tumor detection and response-monitoring in other cancers. The goal of this study was to identify MRS-detectable biomarkers of pancreatic cancer that could enhance currently available imaging approaches. We used (1) H high-resolution magic angle spinning MRS to probe metabolite levels in pancreatic tissue samples from mouse models and patients. In mice, the levels of lipids dropped significantly in pancreata with lipopolysaccharide-induced inflammation, in pancreata with pre-cancerous metaplasia (4 week old p48-Cre;LSL-Kras(G12D) mice), and in pancreata with pancreatic intraepithelial neoplasia, which precedes invasive pancreatic cancer (8 week old p48-Cre LSL-Kras(G12D) mice), to 26 ± 19% (p = 0.03), 19 ± 16% (p = 0.04), and 26 ± 10% (p = 0.05) of controls, respectively. Lactate and taurine remained unchanged in inflammation and in pre-cancerous metaplasia but increased significantly in pancreatic intraepithelial neoplasia to 266 ± 61% (p = 0.0001) and 999 ± 174% (p < 0.00001) of controls, respectively. Importantly, analysis of patient biopsies was consistent with the mouse findings. Lipids dropped in pancreatitis and in invasive cancer biopsies to 29 ± 15% (p = 0.01) and 26 ± 38% (p = 0.02) of normal tissue. In addition, lactate and taurine levels remained unchanged in inflammation but rose in tumor samples to 244 ± 155% (p = 0.02) and 188 ± 67% (p = 0.02), respectively, compared with normal tissue. Based on these findings, we propose that a drop in lipid levels could serve to inform on pancreatitis and cancer-associated inflammation, whereas elevated lactate and taurine could serve to identify the presence of pancreatic intraepithelial neoplasia and invasive tumor. Our findings may help enhance current imaging methods to improve early pancreatic cancer detection and monitoring.

Novel target for peptide-based imaging and treatment of brain tumors

Malignant gliomas are associated with high mortality due to infiltrative growth, recurrence, and malignant progression. Even with the most efficient therapy combinations, median survival of the glioblastoma multiforme (grade 4) patients is less than 15 months. Therefore, new treatment approaches are urgently needed. We describe here identification of a novel homing peptide that recognizes tumor vessels and invasive tumor satellites in glioblastomas. We demonstrate successful brain tumor imaging using radiolabeled peptide in whole-body SPECT/CT imaging. Peptide-targeted delivery of chemotherapeutics prolonged the lifespan of mice bearing invasive brain tumors and significantly reduced the number of tumor satellites compared with the free drug. Moreover, we identified mammary-derived growth inhibitor (MDGI/H-FABP/FABP3) as the interacting partner for our peptide on brain tumor tissue. MDGI was expressed in human brain tumor specimens in a grade-dependent manner and its expression positively correlated with the histologic grade of the tumor, suggesting MDGI as a novel marker for malignant gliomas.

Escape mechanisms from antiangiogenic therapy: an immune cell's perspective

Neovascularization, the formation of new blood vessels, has become a well-established hallmark of cancer. Its functional importance for the manifestation and progression of tumors has been validated further by the beneficial therapeutic effects of angiogenesis inhibitors, most notably those targeting vascular endothelial growth factor signaling pathways. However, with the transient and short-lived nature of patient response, it has become evident that tumors have the ability to adapt to the pressures of vascular growth restriction. Observations made both in the clinic and at the bench suggest the existence of several escape mechanisms that either reestablish neovascularization in tumors or change tumor behavior to enable propagation and progression without obligate neovascularization. Some of these bypass mechanisms are regulated by low oxygen conditions (hypoxia) caused by therapy-induced vessel regression. Induction of hypoxia and hypoxia-inducible factors regulate a wide range of tumor-promoting pathways, including those of neovascularization, that can upregulate additional proangiogenic factors and drive the recruitment of various bone marrow-derived cells that have the capacity to express proangiogenic factors or directly contribute to neovasculature.

Location, location, location: macrophage positioning within tumors determines pro- or antitumor activity

Macrophages infiltrate hypoxic tumor regions, where they promote angiogenesis and immunosuppression. In this issue of Cancer Cell, Casazza and colleagues report that tumor-associated macrophage (TAM) entry into avascular tumor areas is regulated by Semaphorin 3A/Neuropilin-1 signaling; interference with this pathway entraps TAMs in oxygenated areas, preventing their tumorigenic function.

Gene expression profile identifies tyrosine kinase c-Met as a targetable mediator of antiangiogenic therapy resistance

PURPOSE

To identify mediators of glioblastoma antiangiogenic therapy resistance and target these mediators in xenografts.

EXPERIMENTAL DESIGN

We conducted microarray analysis comparing bevacizumab-resistant glioblastomas (BRG) with pretreatment tumors from the same patients. We established novel xenograft models of antiangiogenic therapy resistance to target candidate resistance mediator(s).

RESULTS

BRG microarray analysis revealed upregulation versus pretreatment of receptor tyrosine kinase c-Met, which underwent further investigation because of its prior biologic plausibility as a bevacizumab resistance mediator. BRGs exhibited increased hypoxia versus pretreatment in a manner correlating with their c-Met upregulation, increased c-Met phosphorylation, and increased phosphorylation of c-Met-activated focal adhesion kinase and STAT3. We developed 2 novel xenograft models of antiangiogenic therapy resistance. In the first model, serial bevacizumab treatment of an initially responsive xenograft generated a xenograft with acquired bevacizumab resistance, which exhibited upregulated c-Met expression versus pretreatment. In the second model, a BRG-derived xenograft maintained refractoriness to the MRI tumor vasculature alterations and survival-promoting effects of bevacizumab. Growth of this BRG-derived xenograft was inhibited by a c-Met inhibitor. Transducing these xenograft cells with c-Met short hairpin RNA inhibited their invasion and survival in hypoxia, disrupted their mesenchymal morphology, and converted them from bevacizumab-resistant to bevacizumab-responsive. Engineering bevacizumab-responsive cells to express constitutively active c-Met caused these cells to form bevacizumab-resistant xenografts.

CONCLUSION

These findings support the role of c-Met in survival in hypoxia and invasion, features associated with antiangiogenic therapy resistance, and growth and therapeutic resistance of xenografts resistant to antiangiogenic therapy. Therapeutically targeting c-Met could prevent or overcome antiangiogenic therapy resistance.

VEGF inhibits tumor cell invasion and mesenchymal transition through a MET/VEGFR2 complex

Inhibition of VEGF signaling leads to a proinvasive phenotype in mouse models of glioblastoma multiforme (GBM) and in a subset of GBM patients treated with bevacizumab. Here, we demonstrate that vascular endothelial growth factor (VEGF) directly and negatively regulates tumor cell invasion through enhanced recruitment of the protein tyrosine phosphatase 1B (PTP1B) to a MET/VEGFR2 heterocomplex, thereby suppressing HGF-dependent MET phosphorylation and tumor cell migration. Consequently, VEGF blockade restores and increases MET activity in GBM cells in a hypoxia-independent manner, while inducing a program reminiscent of epithelial-to-mesenchymal transition highlighted by a T-cadherin to N-cadherin switch and enhanced mesenchymal features. Inhibition of MET in GBM mouse models blocks mesenchymal transition and invasion provoked by VEGF ablation, resulting in substantial survival benefit.