Detection of dendritic cell subsets in the tumor microenvironment by multiplex immunohistochemistry

Dendritic cells (DCs) are essential in antitumor immunity. In humans, three main DC subsets are defined: two types of conventional DCs (cDC1s and cDC2s) and plasmacytoid DCs (pDCs). To study DC subsets in the tumor microenvironment (TME), it is important to correctly identify them in tumor tissues. Tumor-derived DCs are often analyzed in cell suspensions in which spatial information about DCs which can be important to determine their function within the TME is lost. Therefore, we developed the first standardized and optimized multiplex immunohistochemistry panel, simultaneously detecting cDC1s, cDC2s, and pDCs within their tissue context. We report on this panel's development, validation, and quantitative analysis. A multiplex immunohistochemistry panel consisting of CD1c, CD303, X-C motif chemokine receptor 1, CD14, CD19, a tumor marker, and DAPI was established. The ImmuNet machine learning pipeline was trained for the detection of DC subsets. The performance of ImmuNet was compared with conventional cell phenotyping software. Ultimately, frequencies of DC subsets within several tumors were defined. In conclusion, this panel provides a method to study cDC1s, cDC2s, and pDCs in the spatial context of the TME, which supports unraveling their specific roles in antitumor immunity.

Pseudobudding: ruptured glands do not represent true tumor buds

Tumor budding (TB) is a strong biomarker of poor prognosis in colorectal cancer and other solid cancers. TB is defined as isolated single cancer cells or clusters of up to four cancer cells at the invasive tumor front. In areas with a large inflammatory response at the invasive front, single cells and cell clusters surrounding fragmented glands are observed appearing like TB. Occurrence of these small groups is referred to as pseudobudding (PsB), which arises due to external influences such as inflammation and glandular disruption. Using a combination of orthogonal approaches, we show that there are clear biological differences between TB and PsB. TB is representative of active invasion by presenting features of epithelial-mesenchymal transition and exhibiting increased deposition of extracellular matrix within the surrounding tumor microenvironment (TME), whereas PsB represents a reactive response to heavy inflammation where increased levels of granulocytes within the surrounding TME are observed. Our study provides evidence that areas with a strong inflammatory reaction should be avoided in the routine diagnostic assessment of TB. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Multiplex Immunohistochemical Analysis of the Spatial Immune Cell Landscape of the Tumor Microenvironment

The immune cell landscape of the tumor microenvironment potentially contains information for the discovery of prognostic and predictive biomarkers. Multiplex immunohistochemistry is a valuable tool to visualize and identify different types of immune cells in tumor tissues while retaining its spatial information. Here we provide detailed protocols to analyze lymphocyte, myeloid, and dendritic cell populations in tissue sections. Starting from cutting formalin-fixed paraffin-embedded sections, automatic multiplex staining procedures on an automated platform, scanning of the slides on a multispectral imaging microscope, to the analysis of images using an in-house-developed machine learning algorithm ImmuNet. These protocols can be applied to a variety of tumor specimens by simply switching tumor markers to analyze immune cells in different compartments of the sample (tumor versus invasive margin) and apply nearest-neighbor analysis. This analysis is not limited to tumor samples but can also be applied to other (non-)pathogenic tissues. Improvements to the equipment and workflow over the past few years have significantly shortened throughput times, which facilitates the future application of this procedure in the diagnostic setting.

Direct In Vivo Activation of T Cells with Nanosized Immunofilaments Inhibits Tumor Growth and Metastasis

Adoptive T cell therapy has successfully been implemented for the treatment of cancer. Nevertheless, ex vivo expansion of T cells by artificial antigen-presenting cells (aAPCs) remains cumbersome and can compromise T cell functionality, thereby limiting their therapeutic potential. We propose a radically different approach aimed at direct expansion of T cells in vivo, thereby omitting the need for large-scale ex vivo T cell production. We engineered nanosized immunofilaments (IFs), with a soluble semiflexible polyisocyanopeptide backbone that presents peptide-loaded major histocompatibility complexes and costimulatory molecules multivalently. IFs readily activated and expanded antigen-specific T cells like natural APCs, as evidenced by transcriptomic analyses of T cells. Upon intravenous injection, IFs reach the spleen and lymph nodes and induce antigen-specific T cell responses in vivo. Moreover, IFs display strong antitumor efficacy resulting in inhibition of the formation of melanoma metastases and reduction of primary tumor growth in synergy with immune checkpoint blockade. In conclusion, nanosized IFs represent a powerful modular platform for direct activation and expansion of antigen-specific T cells in vivo, which can greatly contribute to cancer immunotherapy.

Tumor microenvironment shows an immunological abscopal effect in patients with NSCLC treated with pembrolizumab-radiotherapy combination

Background

Immunotherapy is currently part of the standard of care for patients with advanced-stage non-small cell lung cancer (NSCLC). However, many patients do not respond to this treatment, therefore combination strategies are being explored to increase clinical benefit. The PEMBRO-RT trial combined the therapeutic programmed cell death 1 (PD-1) antibody pembrolizumab with stereotactic body radiation therapy (SBRT) to increase the overall response rate and study the effects on the tumor microenvironment (TME).

Methods

Here, immune infiltrates in the TME of patients included in the PEMBRO-RT trial were investigated. Tumor biopsies of patients treated with pembrolizumab alone or combined with SBRT (a biopsy of the non-irradiated site) at baseline and during treatment were stained with multiplex immunofluorescence for CD3, CD8, CD20, CD103 and FoxP3 for lymphocytes, pan-cytokeratin for tumors, and HLA-ABC expression was determined.

Results

The total number of lymphocytes increased significantly after 6 weeks of treatment in the anti-PD-1 group (fold change: 1.87, 95% CI: 1.06 to 3.29) and the anti-PD-1+SBRT group (fold change: 2.29, 95% CI: 1.46 to 3.60). The combination of SBRT and anti-PD-1 induced a 4.87-fold increase (95% CI: 2.45 to 9.68) in CD103⁺ cytotoxic T-cells 6 weeks on treatment and a 2.56-fold increase (95% CI: 1.03 to 6.36) after anti-PD-1 therapy alone. Responders had a significantly higher number of lymphocytes at baseline than non-responders (fold difference 1.85, 95% CI: 1.04 to 3.29 for anti-PD-1 and fold change 1.93, 95% CI: 1.08 to 3.44 for anti-PD-1+SBRT).

Conclusion

This explorative study shows that that lymphocyte infiltration in general, instead of the infiltration of a specific lymphocyte subset, is associated with response to therapy in patients with NSCLC.

Furthermore, anti-PD-1+SBRT combination therapy induces an immunological abscopal effect in the TME represented by a superior infiltration of cytotoxic T cells as compared with anti-PD-1 monotherapy.

Abstract LB140: The genomic landscape of primary and secondary angiosarcomas, a rare heterogenous group of soft tissue sarcomas

Background: Angiosarcomas (AS) are a rare heterogenous group of soft tissue sarcomas (STS) that form in the lining of blood vessels or lymphatic vessels. They comprise of primary (de novo) AS and secondary AS. The etiology of primary AS is unknown. Secondary AS arise due to DNA damaging factors like prior radiotherapy (RT), ultraviolet (UV) light exposure or chronic lymphedema (Stewart Treves syndrome). Treatment options are limited and their prognosis is poor. Development of new treatment strategies is difficult due to the rarity of these subgroups of STS. Genomic profiling of primary and secondary AS may provide a rationale for targeted treatment strategies.

Method: Tumor samples were retrospectively collected from patients diagnosed with AS in the Netherlands. Patients were categorized as primary/secondary AS. Genomic profiles were analyzed using “TruSight Oncology 500”, a Next Generation Sequencing panel that analyzes variants in 523 cancer relevant genes.

Results: Tumor DNA from 51 treatment naive AS patients was analyzed. The cohort comprised of 26 patients with a primary AS, divided in 5 subgroups: Heart (n=5, 10%), primary breast (n=5, 10%), skin not UV associated (n=4, 8%), soft tissue (n=5, 10%) and visceral (n=7, 14%) AS. The other 25 patients had a secondary AS, subdivided in RT-associated (n=13, 25%), Stewart Treves (n=5, 10%) and UV-associated (n=7, 14%) AS. Mean Tumor Mutational Burden (TMB) was 7.1 mutations per Mb for all patients (4.2 mut/Mb in primary AS vs 10.1 in secondary AS, p = 0.91). High TMB (≥10 mut/Mb) was found in 6 patients (12%) divided over 3 subgroups: UV associated AS (n=3/7 (43%)), visceral AS (n=2/7 (28%)) and skin not UV associated AS (n=1/4 (25%)). No patients were microsatellite instable. A pathogenic mutation, amplification or deletion was identified in 82% of all patients (n=42, 70% of primary AS vs 100% of secondary AS (p=<0.01)). In 36 patients (71%) at least one (likely) pathogenic mutation was detected (54% primary vs 88% secondary AS, (p=0,013)). In 20 patients (39%) a mutation in the DNA damage response (DDR) pathway was detected (12% primary vs 68% secondary AS (p=<0.01)). The most frequently found mutations were TP53 (10%), BRAF (6%), ERCC4 (6%), PTPRD (6%), WETD2 (6%), SETD2 (6%) and PIK3CA (4%). Amplifications were found in 49% (n=25) of all patients (15% primary vs 84% secondary AS, (p=<0,01)). MYC amplifications were detected in 41% of all patients (15% of primary vs 68% of secondary AS), including 100% of Stewart Treves AS, 92% of RT associated AS and 75% of skin not UV associated AS. FLT4 (20%) and CRKL (12%) amplifications occurred only in secondary AS. FLT4 was seen in 31% of RT-associated AS.

Conclusion: We showed a clear distinction in genomic profiles of AS subgroups with specific pathogenic alterations. Especially secondary AS may benefit from treatment with ICI based on frequent MYC amplifications, DDR mutations, and high TMB. These data show clear evidence for the development of future treatment strategies with targeted therapy and ICI for this rare heterogeneous group of STS.

Citation Format: Stefan G. van Ravensteijn, Yvonne M. Versleijen-Jonkers, Melissa H. Hillebrandt-Roeffen, Maikel Nederkoorn, Mark A. Gorris, Kiek Verrijp, Leonie I. Kroeze, Tessa J. de Bitter, Richarda M. de Voer, Uta E. Flucke, Ingrid M. Desar. The genomic landscape of primary and secondary angiosarcomas, a rare heterogenous group of soft tissue sarcomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB140.

Which angiosarcoma subtypes may benefit from immunotherapy?

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Background: Angiosarcomas (AS) are aggressive mesenchymal tumors arising from cells with endothelial properties. They include de novo primary AS (pAS), and secondary AS (sAS) due to prior radiotherapy, UV exposure or chronic lymphedema. Treatment options are limited and their prognosis is poor. Development of new treatment strategies is difficult due to the heterogeneity and rarity of AS. We hypothesize that immunological and genomic profiles are significantly different between pAS and sAS and may result in different immune checkpoint inhibition (ICI) based treatment strategies. Methods: Tumor samples from AS patients were retrospectively collected. Patients were categorized as pAS or sAS. Lymphocytes were analyzed using multiplex immunohistochemistry on tissue microarrays. Genomic profiling was performed in a selected subgroup with “TruSight Oncology 500”, a Next Generation Sequencing panel containing 523 cancer related genes. Results: Immunological data were analyzed from 257 AS patients. The cohort comprised 80 pAS patients and 177 sAS patients. The median density of CD3+ T cells was 250 cells/mm2 in pAS vs 452 cells/mm2 in sAS (p< 0.001). Median CD4+ T helper cell density was 128 cells/mm2 in pAS vs 246 cells/mm2 in secondary AS (p< 0.001). The median density of CD8+ cytotoxic T cells was 85 cells/mm2 in pAS vs 111 cells/mm2 in sAS ( p= 0.057). Density of FoxP3+ T regulatory cells was higher in sAS (median 42 cells/mm2) compared to pAS (median 23 cells/mm2) (p< 0.001). The median count of CD20+ B cells in pAS was 24 cells/mm2 compared to 32 cells/mm2 in sAS ( p= 0.533). Genomic analysis was performed on tumor DNA from 51 patients (25 pAS and 26 sAS). Median tumor mutational burden (TMB) was 3.2 (range 0.8-11.9) mutations per megabase (mut/Mb) in pAS vs 3.9 (range 0.0-99.6) in sAS ( p= 0.485). No microsatellite instability was detected. A pathogenic mutation, gene amplification or gene loss was identified in 82% of all patients (n = 42, 70% of pAS vs 100% of sAS ( p< 0.01)). In 36 patients (71%) at least one (likely) pathogenic mutation was detected (54% pAS vs 88% sAS, ( p= 0.013)). In 20 patients (39%) mutations in the DNA damage response (DDR) pathway were detected (12% pAS vs 68% sAS ( p< 0.01)). The most frequently found mutated genes were TP53 (10%), BRAF (6%), ERCC4 (6%), PTPRD (6%), WETD2 (6%) and SETD2 (6%). Amplifications were found in 49% (n = 25) of all patients (15% pAS vs 84% sAS, ( p< 0,01)). MYC amplifications were most common and were detected in 15% of pAS and 68% of sAS. Immune profiles of the 51 genomically characterized patients are currently under further investigation. Conclusions: We showed a clear distinction in immunological and genomic profiles between pAS and sAS. The potential benefit of ICI seems to be most promising in sAS with a T cell inflamed tumor microenvironment, frequent MYC amplifications, DDR mutations, and high mutational load, while in pAS boosting strategies to enhance susceptibility to ICI might be interesting for further investigation.

Paired primary and metastatic lesions of patients with ipilimumab-treated melanoma: high variation in lymphocyte infiltration and HLA-ABC expression whereas tumor mutational load is similar and correlates with clinical outcome

BACKGROUND

Immune checkpoint inhibitors (ICI) can lead to long-term responses in patients with metastatic melanoma. Still many patients with melanoma are intrinsically resistant or acquire secondary resistance. Previous studies have used primary or metastatic tumor tissue for biomarker assessment. Especially in melanoma, metastatic lesions are often present at different anatomical sites such as skin, lymph nodes, and visceral organs. The anatomical site may directly affect the tumor microenvironment (TME). To evaluate the impact of tumor evolution on the TME and on ICI treatment outcome, we directly compared paired primary and metastatic melanoma lesions for tumor mutational burden (TMB), HLA-ABC status, and tumor infiltrating lymphocytes (TILs) of patients that received ipilimumab.

METHODS

TMB was analyzed by sequencing primary and metastatic melanoma lesions using the TruSight Oncology 500 assay. Tumor tissues were subjected to multiplex immunohistochemistry to assess HLA-ABC status and for the detection of TIL subsets (B cells, cytotoxic T cells, helper T cells, and regulatory T cells), by using a machine-learning algorithm.

RESULTS

While we observed a very good agreement between TMB of matched primary and metastatic melanoma lesions (intraclass coefficient=0.921), such association was absent for HLA-ABC status, TIL density, and subsets thereof. Interestingly, analyses of different metastatic melanoma lesions within a single patient revealed that TIL density and composition agreed remarkably well, rejecting the hypothesis that the TME of different anatomical sites affects TIL infiltration. Similarly, the HLA-ABC status between different metastatic lesions within patients was also comparable. Furthermore, high TMB, of either primary or metastatic melanoma tissue, directly correlated with response to ipilimumab, whereas lymphocyte density or composition did not. Loss of HLA-ABC in the metastatic lesion correlated to a shorter progression-free survival on ipilimumab.

CONCLUSIONS

We confirm the link between TMB and HLA-ABC status and the response to ipilimumab-based immunotherapy in melanoma, but no correlation was found for TIL density, neither in primary nor metastatic lesions. Our finding that TMB between paired primary and metastatic melanoma lesions is highly stable, demonstrates its independency of the time point and location of acquisition. TIL and HLA-ABC status in metastatic lesions of different anatomical sites are highly similar within an individual patient.

The tumour microenvironment shapes dendritic cell plasticity in a human organotypic melanoma culture

The tumour microenvironment (TME) forms a major obstacle in effective cancer treatment and for clinical success of immunotherapy. Conventional co-cultures have shed light onto multiple aspects of cancer immunobiology, but they are limited by the lack of physiological complexity. We develop a human organotypic skin melanoma culture (OMC) that allows real-time study of host-malignant cell interactions within a multicellular tissue architecture. By co-culturing decellularized dermis with keratinocytes, fibroblasts and immune cells in the presence of melanoma cells, we generate a reconstructed TME that closely resembles tumour growth as observed in human lesions and supports cell survival and function. We demonstrate that the OMC is suitable and outperforms conventional 2D co-cultures for the study of TME-imprinting mechanisms. Within the OMC, we observe the tumour-driven conversion of cDC2s into CD14+ DCs, characterized by an immunosuppressive phenotype. The OMC provides a valuable approach to study how a TME affects the immune system.

The Importance of Wall Apposition in Flow Diverters

BACKGROUND

It is assumed that high pore densities in flow diverters (FDs) are beneficial for intracranial aneurysm (IA) healing. However, various animal studies are not conclusive on the issue, suggesting that other factors are in play. One important factor might be wall apposition.

OBJECTIVE

To (1) determine the relationship between FD pore density and aneurysm occlusion, and (2) determine the relationship between FD wall apposition and aneurysm occlusion.

METHODS

Saccular aneurysms were microsurgically created in the aorta of 36 Wistar rats. Twelve rats received a low pore density FD (10 pores/mm2), 12 rats received a high pore density FD (23 pores/mm2), and the remaining 12 rats served as a control group. Six animals from each group were sacrificed 1 and 3 mo after surgery. We determined aneurysm occlusion, the number of struts not in contact with the aorta wall, and the average distance from malapposed struts to aorta wall through histology.

RESULTS

No significant differences were found in aneurysm occlusion between the low pore density and high pore density groups (P > .05) after 1 and 3 mo of follow-up. The average number of malapposed struts was lower for the occluded aneurysm group (4.4 ± 1.9) compared to the nonoccluded aneurysm group (7.7 ± 2.6, P < .01). The average distance between malapposed struts and parent artery wall was lower for the occluded aneurysm group (33.9 μm ± 11.5 μm) than for the nonoccluded aneurysm group (48.7 μm ± 18.8 μm, P < .05).

CONCLUSION

Wall apposition is more important than pore density for aneurysm occlusion.

Isocitrate dehydrogenase 1-mutated human gliomas depend on lactate and glutamate to alleviate metabolic stress

Diffuse gliomas often carry point mutations in isocitrate dehydrogenase ( IDH1^mut), resulting in metabolic stress. Although IDH^mut gliomas are difficult to culture in vitro, they thrive in the brain via diffuse infiltration, suggesting brain-specific tumor-stroma interactions that can compensate for IDH-1 deficits. To elucidate the metabolic adjustments in clinical IDH^mut gliomas that contribute to their malignancy, we applied a recently developed method of targeted quantitative RNA next-generation sequencing to 66 clinical gliomas and relevant orthotopic glioma xenografts, with and without the endogenous IDH-1^R132H mutation. Datasets were analyzed in R using Manhattan plots to calculate distance between expression profiles, Ward's method to perform unsupervised agglomerative clustering, and the Mann Whitney U test and Fisher's exact tests for supervised group analyses. The significance of transcriptome data was investigated by protein analysis, in situ enzymatic activity mapping, and in vivo magnetic resonance spectroscopy of orthotopic IDH1^mut- and IDH^wt-glioma xenografts. Gene set enrichment analyses of clinical IDH1^mut gliomas strongly suggest a role for catabolism of lactate and the neurotransmitter glutamate, whereas, in IDH^wt gliomas, processing of glucose and glutamine are the predominant metabolic pathways. Further evidence of the differential metabolic activity in these cancers comes from in situ enzymatic mapping studies and preclinical in vivo magnetic resonance spectroscopy imaging. Our data support an evolutionary model in which IDH^mut glioma cells exist in symbiosis with supportive neuronal cells and astrocytes as suppliers of glutamate and lactate, possibly explaining the diffuse nature of these cancers. The dependency on glutamate and lactate opens the way for novel approaches in the treatment of IDH^mut gliomas.-Lenting, K., Khurshed, M., Peeters, T. H., van den Heuvel, C. N. A. M., van Lith, S. A. M., de Bitter, T., Hendriks, W., Span, P. N., Molenaar, R. J., Botman, D., Verrijp, K., Heerschap, A., ter Laan, M., Kusters, B., van Ewijk, A., Huynen, M. A., van Noorden, C. J. F., Leenders, W. P. J. Isocitrate dehydrogenase 1-mutated human gliomas depend on lactate and glutamate to alleviate metabolic stress.

In vivo phage display screening for tumor vascular targets in glioblastoma identifies a llama nanobody against dynactin-1-p150Glued

Diffuse gliomas are primary brain cancers that are characterised by infiltrative growth. Whereas high-grade glioma characteristically presents with perinecrotic neovascularisation, large tumor areas thrive on pre-existent vasculature as well. Clinical studies have revealed that pharmacological inhibition of the angiogenic process does not improve survival of glioblastoma patients. Direct targeting of tumor vessels may however still be an interesting therapeutic approach as it allows pinching off the blood supply to tumor cells. Such tumor vessel targeting requires the identification of tumor-specific vascular targeting agents (TVTAs).

Here we describe a novel TVTA, C-C7, which we identified via in vivo biopanning of a llama nanobody phage display library in an orthotopic mouse model of diffuse glioma. We show that C-C7 recognizes a subpopulation of tumor blood vessels in glioma xenografts and clinical glioma samples. Additionally, C-C7 recognizes macrophages and activated endothelial cells in atherosclerotic lesions. By using C-C7 as bait in yeast-2-hybrid (Y2H) screens we identified dynactin-1-p150Glued as its binding partner. The interaction was confirmed by co-immunostainings with C-C7 and a commercial anti-dynactin-1-p150Glued antibody, and via co-immunoprecipitation/western blot studies. Normal brain vessels do not express dynactin-1-p150^Glued and its expression is reduced under anti-VEGF therapy, suggesting that dynactin-1-p150^Glued is a marker for activated endothelial cells.

In conclusion, we show that in vivo phage display combined with Y2H screenings provides a powerful approach to identify tumor-targeting nanobodies and their binding partners. Using this combination of methods we identify dynactin-1-p150^Glued as a novel targetable protein on activated endothelial cells and macrophages.

Selective MET Kinase Inhibition in MET-Dependent Glioma Models Alters Gene Expression and Induces Tumor Plasticity

The receptor tyrosine kinase (RTK) MET represents a promising tumor target in a subset of glioblastomas. Most RTK inhibitors available in the clinic today, including those inhibiting MET, affect multiple targets simultaneously. Previously, it was demonstrated that treatment with cabozantinib (MET/VEGFR2/RET inhibitor) prolonged survival of mice carrying orthotopic patient-derived xenografts (PDX) of the MET-addicted glioblastoma model E98, yet did not prevent development of recurrent and cabozantinib-resistant tumors. To exclude VEGFR2 inhibition-inflicted blood-brain barrier normalization and diminished tumor distribution of the drug, we have now investigated the effects of the novel MET-selective inhibitor Compound A in the orthotopic E98 xenograft model. In vitro, Compound A proved a highly potent inhibitor of proliferation of MET-addicted cell lines. In line with its target selectivity, Compound A did not restore the leaky blood-brain barrier and was more effective than cabozantinib in inhibiting MET phosphorylation in vivo Compound A treatment significantly prolonged survival of mice carrying E98 tumor xenografts, but did not prevent eventual progression. Contrasting in vitro results, the Compound A-treated xenografts displayed high levels of AKT phosphorylation despite the absence of phosphorylated MET. Profiling by RNA sequencing showed that in vivo transcriptomes differed significantly from those in control xenografts.Implications: Collectively, these findings demonstrate the plasticity of paracrine growth factor receptor signaling in vivo and urge for prudency with in vitro drug-testing strategies to validate monotherapies. Mol Cancer Res; 15(11); 1587-97. ©2017 AACR.

Abstract 2077: Selective MET kinase inhibition in MET-dependent glioma models

Background - Grade IV diffuse gliomas (glioblastomas) are notoriously difficult to treat. Many studies aim at targeting tumor-specific aberrations, such as mutations in genes encoding oncogenic receptor tyrosine kinases (RTKs). Of high interest as a tumor target in diffuse glioma is the RTK MET, which is amplified in a significant proportion of glioblastomas, and a number of MET inhibitors have been developed. However, most RTK inhibitors available in the clinic today, including those inhibiting MET, are not entirely selective and inhibit additional kinases at the doses used. They therefore may induce potentially undesired off-target effects, such as blood-brain barrier normalization in the case of concomitant VEGFR2 inhibition.

Methods – We studied the effects of the novel, selective MET-kinase inhibitor (Compound A) and the combined VEGFR2/RET/MET inhibitor cabozantinib on MET activation and proliferation in the MET-amplified E98 astrocytoma cell line in vitro, using western blot analysis and MTT proliferation assays. Effects of compound A were also studied in mice carrying orthotopic xenografts of the same E98 cell line. Survival was monitored and effects of MET inhibition were investigated by immunohistochemistry using phospho-specific antibodies.

Results – E98 cells were highly sensitive to treatment with Compound A in vitro (IC50~9.4 nM). Furthermore, Compound A effectively inhibited phosphorylation of MET in orthotopic E98 xenografts. In contrast, we have previously shown that after treatment with cabozantinib in the same model the high levels of phosphorylated MET were maintained. While treatment with Compound A significantly prolonged the survival of E98-xenograft bearing mice, tumors still developed and showed extensive AKT phosphorylation in the absence of MET phopshorylation, suggesting in vivo therapy resistance mechanisms. Interestingly, resistance to Compound A was not seen in vitro in an E98 cell line derived from Compound A-resistant tumor xenografts.

Conclusions – Compound A is a promising, highly selective MET kinase inhibitor with activity against gliomas with constitutive MET signaling. Selective MET kinase inhibitors may be more suited for treatment of glioma than combined VEGFR2/MET inhibitors, as the latter may induce vessel

normalization resulting in poor tumor penetration. Similar to clinical experience, E98 tumor-bearing mice ultimately develop resistance to TKIs. Combination therapies targeting both MET and potential resistance pathways may be required to allow long-term tumor treatment.

Citation Format: Corina van den Heuvel, Anna Navis, Houshang Amiri, Kiek Verrijp, Arend Heerschap, Karen Rex, Isabelle Dussault, Sean Caenepeel, Angela Coxon, Pieter Wesseling, William Leenders. Selective MET kinase inhibition in MET-dependent glioma models [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 2077. doi:10.1158/1538-7445.AM2017-2077

Comprehensive protein tyrosine phosphatase mRNA profiling identifies new regulators in the progression of glioma

The infiltrative behavior of diffuse gliomas severely reduces therapeutic potential of surgical resection and radiotherapy, and urges for the identification of new drug-targets affecting glioma growth and migration. To address the potential role of protein tyrosine phosphatases (PTPs), we performed mRNA expression profiling for 91 of the 109 known human PTP genes on a series of clinical diffuse glioma samples of different grades and compared our findings with in silico knowledge from REMBRANDT and TCGA databases. Overall PTP family expression levels appeared independent of characteristic genetic aberrations associated with lower grade or high grade gliomas. Notably, seven PTP genes (DUSP26, MTMR4, PTEN, PTPRM, PTPRN2, PTPRT and PTPRZ1) were differentially expressed between grade II-III gliomas and (grade IV) glioblastomas. For DUSP26, PTEN, PTPRM and PTPRT, lower expression levels correlated with poor prognosis, and overexpression of DUSP26 or PTPRT in E98 glioblastoma cells reduced tumorigenicity. Our study represents the first in-depth analysis of PTP family expression in diffuse glioma subtypes and warrants further investigations into PTP-dependent signaling events as new entry points for improved therapy.

Identification of a novel inactivating mutation in Isocitrate Dehydrogenase 1 (IDH1-R314C) in a high grade astrocytoma

The majority of low-grade and secondary high-grade gliomas carry heterozygous hotspot mutations in cytosolic isocitrate dehydrogenase 1 (IDH1) or the mitochondrial variant IDH2. These mutations mostly involve Arg132 in IDH1, and Arg172 or Arg140 in IDH2. Whereas IDHs convert isocitrate to alpha-ketoglutarate (α-KG) with simultaneous reduction of NADP⁺ to NADPH, these IDH mutants reduce α-KG to D-2-hydroxyglutarate (D-2-HG) while oxidizing NADPH. D-2-HG is a proposed oncometabolite, acting via competitive inhibition of α-KG-dependent enzymes that are involved in metabolism and epigenetic regulation. However, much less is known about the implications of the metabolic stress, imposed by decreased α-KG and NADPH production, for tumor biology. We here present a novel heterozygous IDH1 mutation, IDH1^R314C, which was identified by targeted next generation sequencing of a high grade glioma from which a mouse xenograft model and a cell line were generated. IDH1^R314C lacks isocitrate-to-α-KG conversion activity due to reduced affinity for NADP⁺, and differs from the IDH1^R132 mutants in that it does not produce D-2-HG. Because IDH1^R314C is defective in producing α-KG and NADPH, without concomitant production of the D-2-HG, it represents a valuable tool to study the effects of IDH1-dysfunction on cellular metabolism in the absence of this oncometabolite.

Elevated levels of polymorphonuclear myeloid-derived suppressor cells in patients with glioblastoma highly express S100A8/9 and arginase and suppress T cell function

BACKGROUND

Gliomas are primary brain tumors that are associated with a poor prognosis. The introduction of new treatment modalities (including immunotherapy) for these neoplasms in the last 3 decades has resulted in only limited improvement in survival. Gliomas are known to create an immunosuppressive microenvironment that hampers the efficacy of (immuno)therapy. One component of this immunosuppressive environment is the myeloid-derived suppressor cell (MDSC).

METHODS

We set out to analyze the presence and activation state of MDSCs in blood (n = 41) and tumor (n = 20) of glioma patients by measuring S100A8/9 and arginase using flow cytometry and qPCR. Inhibition of T cell proliferation and cytokine production after stimulation with anti-CD3/anti-CD28 coated beads was used to measure in vitro MDSC suppression capacity.

RESULTS

We report a trend toward a tumor grade-dependent increase of both monocytic (M-) and polymorphonuclear (PMN-) MDSC subpopulations in the blood of patients with glioma. M-MDSCs of glioma patients have increased levels of intracellular S100A8/9 compared with M-MDSCs in healthy controls (HCs). Glioma patients also have increased S100A8/9 serum levels, which correlates with increased arginase activity in serum. PMN-MDSCs in both blood and tumor tissue demonstrated high expression of arginase. Furthermore, we assessed blood-derived PMN-MDSC function and showed that these cells have potent T cell suppressive function in vitro.

CONCLUSIONS

These data indicate a tumor grade-dependent increase of MDSCs in the blood of patients with a glioma. These MDSCs exhibit an increased activation state compared with MDSCs in HCs, independent of tumor grade.

Intracellular and extracellular domains of protein tyrosine phosphatase PTPRZ-B differentially regulate glioma cell growth and motility

Gliomas are primary brain tumors for which surgical resection and radiotherapy is difficult because of the diffuse infiltrative growth of the tumor into the brain parenchyma. For development of alternative, drug-based, therapies more insight in the molecular processes that steer this typical growth and morphodynamic behavior of glioma cells is needed. Protein tyrosine phosphatase PTPRZ-B is a transmembrane signaling molecule that is found to be strongly up-regulated in glioma specimens. We assessed the contribution of PTPRZ-B protein domains to tumor cell growth and migration, via lentiviral knock-down and over-expression using clinically relevant glioma xenografts and their derived cell models. PTPRZ-B knock-down resulted in reduced migration and proliferation of glioma cells in vitro and also inhibited tumor growth in vivo. Interestingly, expression of only the PTPRZ-B extracellular segment was sufficient to rescue the in vitro migratory phenotype that resulted from PTPRZ-B knock-down. In contrast, PTPRZ-B knock-down effects on proliferation could be reverted only after re-expression of PTPRZ-B variants that contained its C-terminal PDZ binding domain. Thus, distinct domains of PTPRZ-B are differentially required for migration and proliferation of glioma cells, respectively. PTPRZ-B signaling pathways therefore represent attractive therapeutic entry points to combat these tumors.

Increased mitochondrial activity in a novel IDH1-R132H mutant human oligodendroglioma xenograft model: in situ detection of 2-HG and α-KG

Background

Point mutations in genes encoding NADP⁺-dependent isocitrate dehydrogenases (especially IDH1) are common in lower grade diffuse gliomas and secondary glioblastomas and occur early during tumor development. The contribution of these mutations to gliomagenesis is not completely understood and research is hampered by the lack of relevant tumor models. We previously described the development of the patient-derived high-grade oligodendroglioma xenograft model E478 that carries the commonly occurring IDH1-R132H mutation. We here report on the analyses of E478 xenografts at the genetic, histologic and metabolic level.

Results

LC-MS and in situ mass spectrometric imaging by LESA-nano ESI-FTICR revealed high levels of the proposed oncometabolite D-2-hydroxyglutarate (D-2HG), the product of enzymatic conversion of α-ketoglutarate (α-KG) by IDH1-R132H, in the tumor but not in surrounding brain parenchyma. α-KG levels and total NADP⁺-dependent IDH activity were similar in IDH1-mutant and -wildtype xenografts, demonstrating that IDH1-mutated cancer cells maintain α-KG levels. Interestingly, IDH1-mutant tumor cells in vivo present with high densities of mitochondria and increased levels of mitochondrial activity as compared to IDH1-wildtype xenografts. It is not yet clear whether this altered mitochondrial activity is a driver or a consequence of tumorigenesis.

Conclusions

The oligodendroglioma model presented here is a valuable model for further functional elucidation of the effects of IDH1 mutations on tumor metabolism and may aid in the rational development of novel therapeutic strategies for the large subgroup of gliomas carrying IDH1 mutations.

Autosomal recessive dilated cardiomyopathy due to DOLK mutations results from abnormal dystroglycan O-mannosylation

Genetic causes for autosomal recessive forms of dilated cardiomyopathy (DCM) are only rarely identified, although they are thought to contribute considerably to sudden cardiac death and heart failure, especially in young children. Here, we describe 11 young patients (5-13 years) with a predominant presentation of dilated cardiomyopathy (DCM). Metabolic investigations showed deficient protein N-glycosylation, leading to a diagnosis of Congenital Disorders of Glycosylation (CDG). Homozygosity mapping in the consanguineous families showed a locus with two known genes in the N-glycosylation pathway. In all individuals, pathogenic mutations were identified in DOLK, encoding the dolichol kinase responsible for formation of dolichol-phosphate. Enzyme analysis in patients' fibroblasts confirmed a dolichol kinase deficiency in all families. In comparison with the generally multisystem presentation in CDG, the nonsyndromic DCM in several individuals was remarkable. Investigation of other dolichol-phosphate dependent glycosylation pathways in biopsied heart tissue indicated reduced O-mannosylation of alpha-dystroglycan with concomitant functional loss of its laminin-binding capacity, which has been linked to DCM. We thus identified a combined deficiency of protein N-glycosylation and alpha-dystroglycan O-mannosylation in patients with nonsyndromic DCM due to autosomal recessive DOLK mutations.

Mild muscular features in tenascin-X knockout mice, a model of Ehlers-danlos syndrome

INTRODUCTION

Tenascin-X (TNX) is an extracellular matrix (ECM) glycoprotein, the absence of which in humans leads to a recessive form of Ehlers-Danlos syndrome (EDS), a group of inherited connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. A mouse model of TNX-deficient type EDS has been used to characterize the dermatological, orthopedic, and obstetrical features. The growing insight in the clinical overlap between myopathies and inherited connective tissue disorders asks for a study of the muscular characteristics of inherited connective tissue diseases. Therefore, this study aims to define the muscular phenotype of TNX knockout (KO) mice.

MATERIALS AND METHODS

We performed a comprehensive study on the muscular phenotype of these TNX KO mice, consisting of standardized clinical assessment, muscle histology, and gene expression profiling of muscle tissue. Furthermore, peripheral nerve composition was studied by histology and electron microscopy.

RESULTS

The main findings are the presence of mild muscle weakness, mild myopathic features on histology, and functional upregulation of genes encoding proteins involved in ECM degradation and synthesis. Additionally, sciatic nerve samples showed mildly reduced collagen fibril density of endoneurium.

DISCUSSION

The muscular phenotype of TNX KO mice consists of mild muscle weakness with histological signs of myopathy and of increased turnover of the ECM in muscle. Furthermore, mildly reduced diameter of myelinated fibers and reduction of collagen fibril density of endoneurium may correspond with polyneuropathy in TNX-deficient EDS patients. This comprehensive assessment can serve as a starting point for further investigations on neuromuscular function in TNX KO mice.

Urinary dopamine in aromatic L-amino acid decarboxylase deficiency: the unsolved paradox

INTRODUCTION

In aromatic L-amino acid decarboxylase (AADC) deficiency, a neurotransmitter biosynthesis defect, paradoxical normal or increased levels of urinary dopamine have been reported. Genotype/phenotype correlations or alternative metabolic pathways may explain this remarkable finding, but were never studied systematically.

METHODS

We studied the mutational spectrum and urinary dopamine levels in 20 patients with AADC-deficiency. Experimental procedures were designed to test for alternative metabolic pathways of dopamine production, which included alternative substrates (tyramine and 3-methoxytyrosine) and alternative enzymes (tyrosinase and CYP2D6).

RESULTS/DISCUSSION

In 85% of the patients the finding of normal or increased urinary levels of dopamine was confirmed, but a relation with AADC genotype could not be identified. Renal microsomes containing CYP2D were able to convert tyramine into dopamine (3.0 nmol/min/g protein) but because of low plasma levels of tyramine this is an unlikely explanation for urinary dopamine excretion in AADC-deficiency. No evidence was found for the production of dopamine from 3-methoxytyrosine. Tyrosinase was not expressed in human kidney.

CONCLUSION

Normal or increased levels of urinary dopamine are found in the majority of AADC-deficient patients. This finding can neither be explained by genotype/phenotype correlations nor by alternative metabolic pathways, although small amounts of dopamine may be formed via tyramine hydroxylation by renal CYP2D6. CYP2D6-mediated conversion of tyramine into dopamine might be an interesting target for the development of new therapeutic strategies in AADC-deficiency.

Circulating tumour tissue fragments in patients with pulmonary metastasis of clear cell renal cell carcinoma

Tumour metastasis is the result of a complex sequence of events, including migration of tumour cells through stroma, proteolytic degradation of stromal and vessel wall elements, intravasation, transport through the circulation, extravasation and outgrowth at compatible sites in the body (the 'seed and soil' hypothesis). However, the high incidence of metastasis from various tumour types in liver and lung may be explained by a stochastic process as well, based on the anatomical relationship of the primary tumour with the circulation and mechanical entrapment of metastatic tumour cells in capillary beds. We previously reported that constitutive VEGF-A expression in tumour xenografts facilitates this type of metastatic seeding by promoting shedding of multicellular tumour tissue fragments, surrounded by vessel wall elements, into the circulation. After transport through the vena cava, such fragments may be trapped in pulmonary arteries, allowing them to expand to symptomatic lesions. Here we tested whether this process has clinical relevance for clear cell renal cell carcinoma (ccRCC), a prototype tumour in the sense of high constitutive VEGF-A expression. To this end we collected and analysed outflow samples from the renal vein, directly after tumour nephrectomy, in 42 patients diagnosed with ccRCC. Tumour fragments in venous outflow were observed in 33% of ccRCC patients and correlated with the synchronous presence or metachronous development of pulmonary metastases (p < 0.001, Fisher's exact test). In patients with tumours that, in retrospect, were not of the VEGF-A-expressing clear cell type, tumour fragments were never observed in the renal outflow. These data suggest that, in ccRCC, a VEGF-A-induced phenotype promotes a release of tumour cell clusters into the circulation that may contribute to pulmonary metastasis.

Isolation of targeting nanobodies against co-opted tumor vasculature

Tumor vasculature is in general highly heterogeneous. This characteristic is most prominent in high-grade gliomas, which present with areas of angiogenic growth, next to large areas of diffuse infiltrative growth in which tumor cells thrive on pre-existent brain vasculature. This limits the effectiveness of anti-angiogenic compounds as these will not affect more matured and co-opted vessels. Therefore, additional destruction of existing tumor vasculature may be a promising alternative avenue to effectively deprive tumors from blood. This approach requires the identification of novel tumor vascular targeting agents, which have broad tumor vessel specificities, ie are not restricted to newly formed vessels. Here, we describe the generation of a phage library displaying nanobodies that were cloned from lymphocytes of a Llama which had been immunized with clinical glioma tissue. In vivo biopanning with this library in the orthotopic glioma xenograft models E98 and E434 resulted in the selection of various nanobodies which specifically recognized glioma vessels in corresponding glioma xenografts. Importantly, also nanobodies were isolated which discriminated incorporated pre-existent vessels in highly infiltrative cerebral E434 xenografts from normal brain vessels. Our results suggest that the generation of nanobody-displaying immune phage libraries and subsequent in vivo biopanning in appropriate animal models is a promising approach for the identification of novel vascular targeting agents.

Plexin D1 is ubiquitously expressed on tumor vessels and tumor cells in solid malignancies

BACKGROUND

Plexin D1 is expressed on both tumor-associated endothelium and malignant cells in a number of clinical brain tumors. Recently we demonstrated that Plexin D1 expression is correlated with tumor invasion level and metastasis in a human melanoma progression series. The objective of this study was to examine whether Plexin D1 might be clinically useful as a pan-tumor vessel and pan-tumor cell target in solid tumors.

METHODS

We examined Plexin D1 expression in clinical solid tumors (n = 77) of different origin, a selection of pre-malignant lesions (n = 29) and a variety of non-tumor related tissues (n = 52) by immunohistochemistry. Signals were verified in a selection of tissues via mRNA in situ hybridization.

RESULTS

Plexin D1 is abundantly expressed on both activated established tumor vasculature and malignant cells in the majority of primary and metastatic clinical tumors, as well as on macrophages and fibroblasts. Importantly, in non-tumor related tissues Plexin D1 expression is restricted to a subset of, presumably activated, fibroblasts and macrophages.

CONCLUSION

We demonstrate that Plexin D1 is in general ubiquitously expressed in tumor but not normal vasculature, as well as in malignant cells in a wide range of human tissues. This expression profile highlights Plexin D1 as a potentially valuable therapeutic target in clinical solid tumors, enabling simultaneous targeting of different tumor compartments.

Deficiency of Dol-P-Man synthase subunit DPM3 bridges the congenital disorders of glycosylation with the dystroglycanopathies

Alpha-dystroglycanopathies such as Walker Warburg syndrome represent an important subgroup of the muscular dystrophies that have been related to defective O-mannosylation of alpha-dystroglycan. In many patients, the underlying genetic etiology remains unsolved. Isolated muscular dystrophy has not been described in the congenital disorders of glycosylation (CDG) caused by N-linked protein glycosylation defects. Here, we present a genetic N-glycosylation disorder with muscular dystrophy in the group of CDG type I. Extensive biochemical investigations revealed a strongly reduced dolichol-phosphate-mannose (Dol-P-Man) synthase activity. Sequencing of the three DPM subunits and complementation of DPM3-deficient CHO2.38 cells showed a pathogenic p.L85S missense mutation in the strongly conserved coiled-coil domain of DPM3 that tethers catalytic DPM1 to the ER membrane. Cotransfection experiments in CHO cells showed a reduced binding capacity of DPM3(L85S) for DPM1. Investigation of the four Dol-P-Man-dependent glycosylation pathways in the ER revealed strongly reduced O-mannosylation of alpha-dystroglycan in a muscle biopsy, thereby explaining the clinical phenotype of muscular dystrophy. This mild Dol-P-Man biosynthesis defect due to DPM3 mutations is a cause for alpha-dystroglycanopathy, thereby bridging the congenital disorders of glycosylation with the dystroglycanopathies.

Semaphorin 3E expression correlates inversely with Plexin D1 during tumor progression

Plexin D1 (PLXND1) is broadly expressed on tumor vessels and tumor cells in a number of different human tumor types. Little is known, however, about the potential functional contribution of PLXND1 expression to tumor development. Expression of semaphorin 3E (Sema3E), one of the ligands for PLXND1, has previously been correlated with invasive behavior and metastasis, suggesting that the PLXND1-Sema3E interaction may play a role in tumor progression. Here we investigated PLXND1 and Sema3E expression during tumor progression in cases of melanoma. PLXND1 was not expressed by melanocytic cells in either naevi or melanomas in situ, whereas expression increased with invasion level, according to Clark's criteria. Furthermore, 89% of the metastatic melanomas examined showed membranous PLXND1-staining of tumor cells. Surprisingly, expression of Sema3E was inversely correlated with tumor progression, with no detectable staining in melanoma metastasis. To functionally assess the effects of Sema3E expression on tumor development, we overexpressed Sema3E in a xenograft model of metastatic melanoma. Sema3E expression dramatically decreased metastatic potential. These results show that PLXND1 expression during tumor development is strongly correlated with both invasive behavior and metastasis, but exclude Sema3E as an activating ligand.

Imaging liver metastases of colorectal cancer patients with radiolabelled bevacizumab: Lack of correlation with VEGF-A expression

AIM OF THE STUDY

To investigate the correlation between tumour accumulation of In-111-bevacizumab and VEGF-A expression in patients with colorectal liver metastases.

METHODS

Two weeks before resection of the liver metastases 12 patients were intravenously injected with In-111-labelled bevacizumab. Ten minutes and 7 d after injection a whole body scan was acquired. Seven days after the injection, 3D acquisition SPECT of the liver was performed.

RESULTS

Enhanced uptake of In-111-bevacizumab in the liver metastases was observed in 9 of the 12 patients. The level of antibody accumulation in these lesions varied considerably. There was no correlation between the level of In-111-antibody accumulation and the level of VEGF-A expression in the tissue as determined by in situ hybridisation and ELISA.

CONCLUSIONS

In this study, we investigated the correlation between tumour accumulation of radiolabelled bevacizumab and VEGF-A expression in patients with colorectal liver metastases. No clear-cut correlation between the level of antibody accumulation and expression of VEGF-A was found.

Delayed intrauterine repair of an experimental spina bifida with a collagen biomatrix

BACKGROUND/PURPOSE

The aim of the study was to evaluate whether a collagen biomatrix is useful for delayed intrauterine coverage of a surgically created spina bifida in a fetal lamb.

METHODS

In 20 fetal lambs, surgery was performed at 72 or 79 days' gestation. In 15 lambs a spina bifida was created surgically. In 8 lambs it was covered with a collagen biomatrix 2 weeks later and in 7 lambs it was left uncovered. Five lambs served as sham operated controls. Neurological examination was performed at 1 week of age and afterwards the lambs were sacrificed for further histological evaluation.

RESULTS

None of the 5 surviving lambs with the defect covered showed loss of spinal function and the architecture of the spinal cord was preserved in 4 of the 5 lambs. In the uncovered group, 1 of the 4 surviving lambs had loss of spinal function, 5 lambs were available for histological evaluation and 4 of them showed disturbance of the architecture of the spinal cord.

CONCLUSIONS

Collagen biomatrices can be used for intrauterine coverage of an experimental spina bifida and can preserve the architecture of the spinal cord. Neurological outcome is not different between fetuses with their spinal cord covered and fetuses with uncovered cords.

Micronodular transformation as a novel mechanism of VEGF-A-induced metastasis

How and why tumors metastasize is still a matter of debate. The assumption is that mutations render tumor cells with a metastatic phenotype, enabling entrance in and transport through lymph or blood vessels. Distant outgrowth is thought to occur only in a suitable microenvironment (the seed and soil hypothesis). However, the anatomical location of most metastases in cancer patients suggests entrapment of tumor cells in the first microcapillary bed that is encountered. We here investigated how vascular endothelial growth factor-A (VEGF-A) attributes to the metastatic process. We describe here that VEGF-A enhances spontaneous metastasis by inducing intravasation of heterogeneous tumor cell clusters, surrounded by vessel wall elements, via an invasion-independent mechanism. These tumor clusters generate metastatic tissue embolisms in pulmonary arteries. Treatment of tumor-bearing mice with the antiangiogenic compound ZD6474 prevented the development of this metastatic phenotype. This work shows that tumors with high constitutive VEGF-A expression metastasize via the formation of tumor emboli and provides an alternative rationale for anti-VEGF-A therapy, namely to inhibit metastasis formation.

Development of the tumor vascular bed in response to hypoxia-induced VEGF-A differs from that in tumors with constitutive VEGF-A expression

Tumors arise initially as avascular masses in which central hypoxia induces expression of vascular endothelial growth factor-A (VEGF-A) and subsequently tumor vascularization. However, VEGF-A can also be constitutively expressed as a result of genetic events. VEGF-A is alternatively spliced to yield at least 6 different isoforms. Of these, VEGF-A(121) is freely diffusible whereas basically charged domains in the larger isoforms confer affinity for cell surface or extracellular matrix components. We previously reported that in a mouse brain metastasis model of human melanoma, VEGF-A(121) induced a qualitatively different tumor vascular phenotype than VEGF-A(165) and VEGF-A(189): in contrast to the latter ones, and VEGF-A(121) did not induce a neovascular bed but rather led to leakage and dilatation of preexistent brain vessels. Here, we correlate vascular phenotypes with spatial VEGF-A expression profiles in clinical brain tumors (low grade gliomas; n = 6, melanoma metastases; n = 4, adenocarcinoma metastases; n = 4, glioblastoma multiforme; n = 3, sarcoma metastasis; n = 1, renal cell carcinoma metastasis; n = 1). We show that tumors that constitutively express VEGF-A present with different vascular beds than tumors in which VEGF-A is expressed as a response to central hypoxia. This phenotypic difference is consistent with a model where in tumors with constitutive VEGF-A expression, all isoforms exert their effects on vasculature, resulting in a classical angiogenic phenotype. In tumors where only central parts express hypoxia-induced VEGF-A, the larger angiogenic isoforms are retained by extracellular matrix, leaving only freely diffusible VEGF-A(121) to exert its dilatation effects on distant vessels.

Plexin D1 Expression Is Induced on Tumor Vasculature and Tumor Cells: A Novel Target for Diagnosis and Therapy?

We previously reported that during mouse embryogenesis, plexin D1 (plxnD1) is expressed on neuronal and endothelial cells. Endothelial cells gradually loose plxnD1 expression during development. Here we describe, using in situ hybridization, that endothelial plxnD1 expression is regained during tumor angiogenesis in a mouse model of brain metastasis. Importantly, we found PLXND1 expression also in a number of human brain tumors, both of primary and metastatic origin. Apart from the tumor vasculature, abundant expression was also found on tumor cells. Via panning of a phage display library, we isolated two phages that carry single-domain antibodies with specific affinity towards a PLXND1-specific peptide. Immunohistochemistry with these single-domain antibodies on the same tumors that were used for in situ hybridization confirmed PLXND1 expression on the protein level. Furthermore, both these phages and the derived antibodies specifically homed to vessels in brain lesions of angiogenic melanoma in mice after i.v. injection. These results show that PLXND1 is a clinically relevant marker of tumor vasculature that can be targeted via i.v. injections.

Antiangiogenic therapy of cerebral melanoma metastases results in sustained tumor progression via vessel co-option

PURPOSE

In the brain, tumors may grow without inducing angiogenesis, via co-option of the dense pre-existent capillary bed. The purpose of this study was to investigate how this phenomenon influences the outcome of antiangiogenic therapy.

EXPERIMENTAL DESIGN

Mice carrying brain metastases of the human, highly angiogenic melanoma cell line Mel57-VEGF-A were either or not treated with different dosages of ZD6474, a vascular endothelial growth factor (VEGF) receptor 2 tyrosine kinase inhibitor with additional activity against epidermal growth factor receptor. Effect of treatment was evaluated using contrast-enhanced magnetic resonance imaging (CE- MRI) and (immuno)morphologic analysis.

RESULTS

Placebo-treated Mel57-VEGF-A brain metastases evoked an angiogenic response and were highlighted in CE-MRI. After treatment with ZD6474 (100 mg/kg), CE-MRI failed to detect tumors in either prevention or therapeutic treatment regimens. However, (immuno)histologic analysis revealed the presence of numerous, small, nonangiogenic lesions. Treatment with 25 mg/kg ZD6474 also resulted in efficient blockade of vessel formation, but it did not fully inhibit vascular leakage, thereby still allowing visualization in CE-MRI scans.

CONCLUSIONS

Our data show that, although angiogenesis can be effectively blocked by ZD6474, in vessel-dense organs this may result in sustained tumor progression via co-option, rather than in tumor dormancy. Importantly, blocking VEGF-A may result in undetectability of tumors in CE-MRI scans, leading to erroneous conclusions about therapeutic efficacy during magnetic resonance imaging follow-up. The maintenance of VEGF-A-induced vessel leakage in the absence of neovascularization at lower ZD6474 doses may be exploited to improve delivery of chemotherapeutic agents in combined treatment regimens of antiangiogenic and chemotherapeutic compounds.

Differential effects of vascular endothelial growth factor A isoforms in a mouse brain metastasis model of human melanoma

We reported previously that vascular endothelial growth factor isoform A (VEGF-A) expression by Mel57 human melanoma cells led to tumor progression in a murine brain metastasis model in an angiogenesis-independent fashion by dilation of co-opted, pre-existing vessels and concomitant enhanced blood supply (B. Kusters et al., Cancer Res., 62: 341-345, 2002). Here, we compare the activities of the 121, 165, and 189 VEGF-A isoforms in this model by transfecting Mel57 cells with the respective cDNAs and by injecting the resulting stably transfected cell lines in the internal carotid arteries of nude mice (n = 10 for each isoform). Although the three isoforms had similar potency to induce endothelial cell proliferation, VEGF(121) expression did not result in sprouting angiogenesis but rather led to extensive vasodilation and increased permeability of pre-existing, predominantly peritumoral vessels. Sometimes, proliferating endothelial cells accumulated in vessel lumina, giving these a microvascular, glomeruloid, proliferation-like appearance. Expression of VEGF(165) or VEGF(189) was associated with induction of an intratumoral neovascular bed. In VEGF(165)-expressing tumors, daughter endothelial cells were distributed among newly formed vessels that were extensively dilated. This also occurred in VEGF(189) tumors, but there, vasodilation was less pronounced. Using contrast-enhanced magnetic resonance imaging, the different vascular phenotypes were visualized on characteristic radiological images. VEGF(165) expression was the most unfavorable of the three. Mice carrying VEGF(165) tumors became moribund earlier than those carrying VEGF(121)-expressing tumors (16 +/- 4 days versus 22 +/- 3 days). Our data demonstrate that VEGF-A isoforms differ in angiogenic properties that can be visualized by contrast-enhanced magnetic resonance imaging.

Vascular endothelial growth factor-A(165) induces progression of melanoma brain metastases without induction of sprouting angiogenesis

We investigated the mechanisms of vascularization in a brain metastases model of malignant melanoma. Parenchymal metastases expressing little vascular endothelial growth factor-A (VEGF-A) co-opted the preexistent brain vasculature, leading to an infiltrative phenotype. Metastases of the human melanoma cell line Mel57, engineered to express recombinant VEGF-A(165), showed accelerated growth in a combined expansive and infiltrative pattern with marked central necrosis. This difference in growth profile was accompanied by dilation of co-opted intra- and peritumoral vessels with concomitant induction of vascular permeability. Our data show that modulation of preexistent vasculature can contribute to malignant progression without induction of sprouting angiogenesis.

Cytopress: automated slide preparation of cytologic material from suspension

This paper describes a new automated system to prepare slides of cytological material from suspension. The system collects material on a filter tape by filtration and transfers it to glass slides by means of pressure-fixation. Using cervical cells as a model, results show that a well-defined cell number is evenly deposited over a standardized area, while a small number of cells is retained on the tape and a negligible number lost in the filtrate. Contamination is very small. Application of the system to other cytological material (fine needle aspirations, monolayer and cell suspension cultures, agar cultures, and isolated nuclei) is shown. In general, more than one slide can be made from one sample. Several histological staining procedures as well as immunofluorescence labeling protocols can be applied to the preparations obtained in this way. This system thus introduces a method that will standardize specimen preparation, is quick, saves operator time, and can be used for both diagnostic and research applications.