Karolien Castermans

MicroRNA-146a is a therapeutic target and biomarker for peripartum cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a life-threatening pregnancy-associated cardiomyopathy in previously healthy women. Although PPCM is driven in part by the 16-kDa N-terminal prolactin fragment (16K PRL), the underlying molecular mechanisms are poorly understood. We found that 16K PRL induced microRNA-146a (miR-146a) expression in ECs, which attenuated angiogenesis through downregulation of NRAS. 16K PRL stimulated the release of miR-146a-loaded exosomes from ECs. The exosomes were absorbed by cardiomyocytes, increasing miR-146a levels, which resulted in a subsequent decrease in metabolic activity and decreased expression of Erbb4, Notch1, and Irak1. Mice with cardiomyocyte-restricted Stat3 knockout (CKO mice) exhibited a PPCM-like phenotype and displayed increased cardiac miR-146a expression with coincident downregulation of Erbb4, Nras, Notch1, and Irak1. Blocking miR-146a with locked nucleic acids or antago-miRs attenuated PPCM in CKO mice without interrupting full-length prolactin signaling, as indicated by normal nursing activities. Finally, miR-146a was elevated in the plasma and hearts of PPCM patients, but not in patients with dilated cardiomyopathy. These results demonstrate that miR-146a is a downstream-mediator of 16K PRL that could potentially serve as a biomarker and therapeutic target for PPCM.

Anti-angiogenesis therapy can overcome endothelial cell anergy and promote leukocyte-endothelium interactions and infiltration in tumors

Tumor escape from immunity, as well as the failure of several anti‐cancer vaccination and cellular immunotherapy approaches, is suggested to be due to the angiogenesis‐mediated suppression of endothelial cell (EC) adhesion molecules involved in leukocyte‐vessel wall interactions. We hypothesized that inhibition of angiogenesis would overcome this escape from immunity. We investigated this in vivo by means of intravital microscopy and ex vivo by immunohistochemistry in two mouse tumor models. Angiogenesis inhibitors anginex, endostatin, and angiostatin, and the chemotherapeutic agent paclitaxel were found to significantly stimulate leukocyte‐vessel wall interactions by circumvention of EC anergy in vivo, i.e., by the up‐regulation of endothelial adhesion molecules in tumor vessels. This was confirmed by in vitro studies of cultured EC at the protein and mRNA levels. The new angiostatic designer peptide anginex was most potent at overcoming EC anergy; the enhanced leukocyte‐vessel interactions led to an increase in the numbers of tumor infiltrating leukocytes. While anginex inhibited tumor growth and microvessel density significantly, the amount of infiltrated leukocytes (CD45), as well as the number of CD8+ cytotoxic T lymphocytes, was enhanced markedly. The current results suggest that immunotherapy strategies can be improved by combination with anti‐angiogenesis.‐Dirkx, A. E. M., oude Egbrink, M. G. A., Castermans, K., van der Schaft, D. W. J., Thijssen, V. L. J. L., Dings, R. P. M., Kwee, L., Mayo, K. H., Wagstaff, J., Bouma‐ter Steege, J. C. A., Griffioen, A. W. Anti‐angiogenesis therapy can overcome endothelial cell anergy and promote leukocyteendothelium interactions and infiltration in tumors. FASEB J. 20, 621–630 (2006)

Tumor cell plasticity in Ewing sarcoma, an alternative circulatory system stimulated by hypoxia.

A striking feature of Ewing sarcoma is the presence of blood lakes lined by tumor cells. The significance of these structures, if any, is unknown. Here, we report that the extent of blood lakes correlates with poor clinical outcomes, whereas variables of angiogenesis do not. We also show that Ewing sarcoma cells form vessel-like tubes in vitro and express genes associated with vasculogenic mimicry. In tumor models, we show that there is blood flow through the blood lakes, suggesting that these structures in Ewing sarcoma contribute to the circulation. Furthermore, we present evidence that reduced oxygen tension may be instrumental in tube formation by plastic tumor cells. The abundant presence of these vasculogenic structures, in contrast to other tumor types, makes Ewing sarcoma the ideal model system to study these phenomena. The results suggest that optimal tumor treatment may require targeting of these structures in combination with prevention of angiogenesis.

Paramagnetic Lipid-Coated Silica Nanoparticles with a Fluorescent Quantum Dot Core : A New Contrast Agent Platform for Multimodality Imaging

Silica particles as a nanoparticulate carrier material for contrast agents have received considerable attention the past few years, since the material holds great promise for biomedical applications. A key feature for successful application of this material in vivo is biocompatibility, which may be significantly improved by appropriate surface modification. In this study, we report a novel strategy to coat silica particles with a dense monolayer of paramagnetic and PEGylated lipids. The silica nanoparticles carry a quantum dot in their center and are made target-specific by the conjugation of multiple alphavbeta3-integrin-specific RGD-peptides. We demonstrate their specific uptake by endothelial cells in vitro using fluorescence microscopy, quantitative fluorescence imaging, and magnetic resonance imaging. The lipid-coated silica particles introduced here represent a new platform for nanoparticulate multimodality contrast agents.

Molecular imaging of tumor angiogenesis using αvβ3-integrin targeted multimodal quantum dots

Molecular imaging of angiogenesis is urgently needed for diagnostic purposes such as early detection, monitoring of (angiostatic) therapy and individualized therapy. Multimodality molecular imaging is a promising and refined technique to study tumor angiogenesis, which has so far been largely unexplored due to the lack of suitable multimodal contrast agents. Here, we report on the application of a novel αvβ3-specific quantum dot-based nanoparticle, which has been optimized for both optical and magnetic resonance detection of tumor angiogenesis. Upon intravenous injection of RGD-pQDs in tumor-bearing mice, intravital microscopy allowed the detection of angiogenically activated endothelium at cellular resolution with a small scanning window and limited penetration depth, while magnetic resonance imaging was used to visualize angiogenesis at anatomical resolution throughout the entire tumor. Fluorescence imaging allowed whole-body investigation of angiogenic activity. Using these quantum dots and the aforementioned imaging modalities, the angiogenic tumor vasculature was readily detected with the highest angiogenic activity occurring in the periphery of the tumor. This nanoparticle may be employed for multimodality imaging of a variety of diseases that are accompanied by activation of endothelial cells. Furthermore, the current technology might be developed for molecular imaging of other pathophysiological processes.

Isolation of endothelial cells from fresh tissues

Here, we present a protocol for the isolation of endothelial cells (ECs) from tissues. ECs make up a minor population of cells in a tissue, but play a major role in tissue homeostasis, as well as in diverse pathologies. To understand the biology of ECs, characterization of this cell population is highly desirable, but requires the availability of purified cells. For this purpose, tissues are mechanically minced and subsequently digested enzymatically with collagenase and dispase. ECs in the resulting single-cell suspension are labeled with Abs against EC surface antigens and separated from the remainder of the cells and debris by capture with magnetic beads or by high-speed cell sorting. Purified ECs are viable and suitable for characterization of diverse cellular properties. This protocol is optimized for human tissues but can also be adapted for use with other species. Depending on the tissue, the procedure can be completed in ∼6 h.

Enhancement of T-cell–Mediated Antitumor Response: Angiostatic Adjuvant to Immunotherapy against Cancer

Purpose: Tumor-released proangiogenic factors suppress endothelial adhesion molecule (EAM) expression and prevent leukocyte extravasation into the tumor. This is one reason why immunotherapy has met with limited success in the clinic. We hypothesized that overcoming EAM suppression with angiogenesis inhibitors would increase leukocyte extravasation and subsequently enhance the effectiveness of cellular immunotherapy. Experimental Design: Intravital microscopy, multiple color flow cytometry, immunohistochemistry, and various tumor mouse (normal and T-cell deficient) models were used to investigate the temporal dynamics of cellular and molecular events that occur in the tumor microenvironment during tumor progression and angiostatic intervention. Results: We report that while EAM levels and T-cell infiltration are highly attenuated early on in tumor growth, angiostatic therapy modulates these effects. In tumor models with normal and T-cell–deficient mice, we show the active involvement of the adaptive immune system in cancer and differentiate antiangiogenic effects from antiangiogenic mediated enhancement of immunoextravasation. Our results indicate that a compromised immune response in tumors can be obviated by the use of antiangiogenic agents. Finally, with adoptive transfer studies in mice, we show that a phased combination of angiostatic therapy and T-cell transfer significantly (P < 0.0013) improves tumor growth inhibition. Conclusions: This research contributes to understand the cellular mechanism of action of angiostatic agents and the immune response within the tumor microenvironment, in particular as a consequence of the temporal dynamics of EAM levels. Moreover, our results suggest that adjuvant therapy with angiogenesis inhibitors holds promise for cellular immunotherapy in the clinic. Clin Cancer Res; 17(10); 3134–45. ©2011 AACR.

Angiostatic activity of the antitumor cytokine interleukin-21

Interleukin-21 (IL-21) is a recently described immunoregulatory cytokine. It has been identified as a very potent immunotherapeutic agent in several cancer types in animal models, and clinical studies are ongoing. IL-21 belongs to the type I cytokine family of which other members, ie, IL-2, IL-15, and IL-4, have been shown to exert activities on vascular endothelial cells (ECs). We hypothesized that IL-21, in addition to inducing the antitumor immune response, also inhibits tumor angiogenesis. In vitro experiments showed a decrease of proliferation and sprouting of activated ECs after IL-21 treatment. We found that the IL-21 receptor is expressed on vascular ECs. Furthermore, in vivo studies in the chorioallantoic membrane of the chick embryo and in mouse tumors demonstrated that IL-21 treatment disturbs vessel architecture and negatively affects vessel outgrowth. Our results also confirm the earlier suggested angiostatic potential of IL-2 in vitro and in vivo. The angiostatic effect of IL-21 is confirmed by the decrease in expression of angiogenesis-related genes. Interestingly, IL-21 treatment of ECs leads to a decrease of Stat3 phosphorylation. Our research shows that IL-21 is a very powerful antitumor compound that combines the induction of an effective antitumor immune response with inhibition of tumor angiogenesis.

Small-Molecule Inhibitors of Vascular Adhesion Protein-1 Reduce the Accumulation of Myeloid Cells into Tumors and Attenuate Tumor Growth in Mice

Vascular adhesion protein-1 (VAP-1) is an endothelial, cell surface–expressed oxidase involved in leukocyte traffic. The adhesive function of VAP-1 can be blocked by anti–VAP-1 Abs and small-molecule inhibitors. However, the effects of VAP-1 blockade on antitumor immunity and tumor progression are unknown. In this paper, we used anti–VAP-1 mAbs and small-molecule inhibitors of VAP-1 in B16 melanoma and EL-4 lymphoma tumor models in C57BL/6 mice. Leukocyte accumulation into tumors and neoangiogenesis were evaluated by immunohistochemistry, flow cytometry, and intravital videomicroscopy. We found that both anti–VAP-1 Abs and VAP-1 inhibitors reduced the number of leukocytes in the tumors, but they targeted partially different leukocyte subpopulations. Anti–VAP-1 Abs selectively inhibited infiltration of CD8-positive lymphocytes into tumors and had no effect on accumulation of myeloid cells into tumors. In contrast, the VAP-1 inhibitors significantly reduced only the number of proangiogenic Gr-1+CD11b+ myeloid cells in melanomas and lymphomas. Blocking of VAP-1 by either means left tumor homing of regulatory T cells and type 2 immune-suppressing monocytes/macrophages intact. Notably, VAP-1 inhibitors, but not anti–VAP-1 Abs, retarded the growth of melanomas and lymphomas and reduced tumor neoangiogenesis. The VAP-1 inhibitors also reduced the binding of Gr-1+ myeloid cells to the tumor vasculature. We conclude that tumors use the catalytic activity of VAP-1 to recruit myeloid cells into tumors and to support tumor progression. Small-molecule VAP-1 inhibitors therefore might be a potential new tool for immunotherapy of tumors.

A transgenic Tie2-GFP athymic mouse model; a tool for vascular biology in xenograft tumors

We report the generation of a transgenic Tie2-GFP athymic nude mouse, carrying green fluorescent blood vessels throughout the body. This transgenic mouse is a tool for studies in vascular biology, and is especially of interest for imaging of tumor angiogenesis and the study of anti-angiogenesis strategies in (human) xenografts. Intravital microscopy identified the presence of blood conducting structures that are not lined by endothelial cells. Dedifferentiation of aggressive tumor cells can lead to acquisition of endothelial characteristics. This process of tumor cell plasticity, also referred to as vasculogenic mimicry, has been suggested to contribute to the circulatory system in a tumor. In plastic EW7 Ewing sarcoma tumors in these Tie2-GFP mice, we observed blood flow in both regular blood vessels and non-fluorescent tumor cell-lined channels, visualizing in vivo hemodynamics in vasculogenic channels. These results demonstrate that the transgenic Tie2-GFP athymic mouse model is a valuable tool for vascular biology research.