for highly malignant gliomas (World Health Organization grade III and IV) there is no successful treatment; patients have an average survival time of approximately 1 y after diagnosis. Glioma cells are highly invasive and infiltrate normal brain tissue, and as a result, surgical resection is always incomplete. Degradation of ECM by membrane-bound and secreted metalloproteases facilitates glioma invasion. In particular, the membrane-bound metalloproteases are pivotal for tumor invasion as they very efficiently digest extracellular matrix proteins and also activate secreted metalloproteases (1) like matrix metalloproteinase-2 (MMP-2, also known as gelatinase A), which is one of the major proteases involved in glioma invasion in mouse models (2) and probably also in humans (3). Hence, membrane-inserted metalloproteases like membrane type 1 matrix metalloproteinase (MT1-MMP) can enable gliomas to invade the brain parenchyma as single cells (4).Microglia are the intrinsic immune cells of the brain; they control the innate and the adaptive immune response in the CNS and are activated by inflammatory or other pathological stimuli (5). Activation of microglial toll-like receptors (TLRs) triggers the innate immune response and can initiate host-defense and tissue repair mechanisms, but also CNS inflammation, neurodegeneration, and trauma (5, 6). As microglial cells are attracted toward glioma in large numbers-glioma tissue consists of as much as 30% microglial cells-and because microglia density in gliomas positively correlates with malignancy, invasiveness, and grading of the tumors (7-9), we investigated if microglia may actively contribute to glioma expansion. Here, we show that soluble factors released from glioma stimulate microglial TLRs, resulting in microglial MT1-MMP expression via the TLR downstream signaling molecules MyD88 and p38 MAPK. In turn, MT1-MMP expression and activity in these immune cells promotes glioma cell invasion and tumor expansion. ResultsGlioma Associated Microglia Over-Express MT1-MMP. We analyzed the expression pattern of the matrix protease MT1-MMP in mouse and human gliomas and found the enzyme to be expressed predominantly in microglial cells closely associated with the tumors. Whereas tumor-free human brain samples showed virtually no MT1-MMP expression, we detected intense MT1-MMP labeling, especially in higher-grade gliomas. Importantly, in human samples, immunolabeling for the microglial marker Iba1 and for MT1-MMP largely overlapped [supporting information (SI) Fig. S1 A-D and Table S1]. Likewise, after injection of a human glioma cell line (U373 cells) into immunodeficient mice, we detected that microglia represent the predominant cell type contributing intratumoral MT1-MMP expression (see Fig. S1E).In our in vivo mouse model, the glioma cells were identified by stable expression of EGFP and microglial cells by immunolabeling for Iba1. In sections obtained from mice 2 weeks after intracerebral injection with isogenic glioma cells (GL261 cells), we found an increased density of mic...

Purpose: CEA TCB is a novel IgG-based T-cell bispecific (TCB) antibody for the treatment of CEA-expressing solid tumors currently in phase I clinical trials (NCT02324257). Its format incorporates bivalent binding to CEA, a head-to-tail fusion of CEA- and CD3e-binding Fab domains and an engineered Fc region with completely abolished binding to FcγRs and C1q. The study provides novel mechanistic insights into the activity and mode of action of CEA TCB. Experimental Design: CEA TCB activity was characterized on 110 cell lines in vitro and in xenograft tumor models in vivo using NOG mice engrafted with human peripheral blood mononuclear cells. Results: Simultaneous binding of CEA TCB to tumor and T cells leads to formation of immunologic synapses, T-cell activation, secretion of cytotoxic granules, and tumor cell lysis. CEA TCB activity strongly correlates with CEA expression, with higher potency observed in highly CEA-expressing tumor cells and a threshold of approximately 10,000 CEA-binding sites/cell, which allows distinguishing between high- and low-CEA–expressing tumor and primary epithelial cells, respectively. Genetic factors do not affect CEA TCB activity confirming that CEA expression level is the strongest predictor of CEA TCB activity. In vivo, CEA TCB induces regression of CEA-expressing xenograft tumors with variable amounts of immune cell infiltrate, leads to increased frequency of activated T cells, and converts PD-L1 negative into PD-L1–positive tumors. Conclusions: CEA TCB is a novel generation TCB displaying potent antitumor activity; it is efficacious in poorly infiltrated tumors where it increases T-cell infiltration and generates a highly inflamed tumor microenvironment. Clin Cancer Res; 22(13); 3286–97. ©2016 AACR.

IntroductionThe hypoxia-inducible factor (HIF)-1 pathway can stimulate tumor cell migration and metastasis. Furthermore, hypoxic tumors are associated with a poor prognosis. Besides the HIF-1 pathway, the unfolded protein response (UPR) is also induced by hypoxic conditions. The PKR-like ER kinase (PERK)/activating transcription factor 4 (ATF4)-arm of the UPR induces expression of lysosomal-associated membrane protein 3 (LAMP3), a factor that has been linked to metastasis and poor prognosis in solid tumors. In this study the role of UPR-induced LAMP3 in hypoxia-mediated migration of breast cancer cells was examined.MethodsA number of in vitro metastasis models were used to study the migration and invasion of MDA-MB-231 breast cancer cells under hypoxic conditions. PERK, ATF4 and their downstream factor LAMP3 were knocked down to examine their role in cell migration. In addition, multicellular tumor spheroids were used to study the involvement of the tumor microenvironment in invasion.ResultsUsing transwell assays, migration of different breast cancer cell lines was assessed. A direct correlation was found between cell migration and baseline LAMP3 expression. Furthermore, moderate hypoxia (1% O2) was found to be optimal in stimulating migration of MDA-MB-231 cells. siRNA mediated knockdown of PERK, ATF4 and LAMP3 reduced migration of cells under these conditions. Using gap closure assays, similar results were found. In a three-dimensional invasion assay into collagen, LAMP3 knockdown cells showed a diminished capacity to invade compared to control cells when collectively grown in multicellular spheroids.ConclusionsThus, the PERK/ATF4/LAMP3-arm of the UPR is an additional pathway mediating hypoxia-induced breast cancer cell migration.

Cancer metastases arise from a multi-step process that requires metastasizing tumor cells to adapt to signaling input from varying tissue environments [1]. As an early metastatic event, cancer cell dissemination occurs through different migration programs, including multicellular, collective, and single-cell mesenchymal or amoeboid migration [2-4]. Migration modes can interconvert based on changes in cell adhesion, cytoskeletal mechanotransduction [5], and/or proteolysis [6], most likely under the control of transcriptional programs such as the epithelial-to-mesenchymal transition (EMT) [7, 8]. However, how plasticity of tumor cell migration and EMT is spatiotemporally controlled and connected upon challenge by the tumor microenvironment remains unclear. Using 3D cultures of collectively invading breast and head and neck cancer spheroids, here we identify hypoxia, a hallmark of solid tumors [9], as an inducer of the collective-to-amoeboid transition (CAT), promoting the dissemination of amoeboid-moving single cells from collective invasion strands. Hypoxia-induced amoeboid detachment was driven by hypoxia-inducible factor 1 (HIF-1), followed the downregulation of E-cadherin, and produced heterogeneous cell subsets whose phenotype and migration were dependent (∼30%) or independent (∼70%) of Twist-mediated EMT. EMT-like and EMT-independent amoeboid cell subsets showed stable amoeboid movement over hours as well as leukocyte-like traits, including rounded morphology, matrix metalloproteinase (MMP)-independent migration, and nuclear deformation. Cancer cells undergoing pharmacological stabilization of HIFs retained their constitutive ability for early metastatic seeding in an experimental model of lung metastasis, indicating that hypoxia-induced CAT enhances cell release rather than early organ colonization. Induced by metabolic challenge, amoeboid movement may thus constitute a common endpoint of both EMT-dependent and EMT-independent cancer dissemination programs.