Perivascular Tumor Cells Research Articles

Intelligent Responsive Nanoparticles with Multilevel Triggered Drug Penetration for Tumor Photochemotherapy.

Nanomedicines have contradictory size requirements to overcome systemic barriers and penetrate the tumor extracellular matrix (ECM). Larger-sized nanoparticles (50-200 nm) exhibit prolonged blood circulation half-life and improved tumor enrichment, while small-sized nanoparticles (4-20 nm) easily penetrate deep tumor tissues. Therefore, the development of intelligent responsive nanomedicine systems can not only increase nanodrug tumor accumulation but also improve their penetration into the ECM. Herein, we propose an intelligent responsive nanoparticle triggered by near-infrared light (NIR). The nanoparticle was constructed by a temperature-sensitive liposome (TSL) encapsulating ultrasmall melanin nanoparticles (MNPs) loaded with doxorubicin (MNP/doxorubicin (DOX)@TSL). When exposed to NIR irradiation, the tailor-made nanoparticles not only effectively ablated the tumor cells around blood vessels but also destroyed the structural integrity and released loaded ultrasmall MNP/DOX (<10 nm) to promote deep tumor penetration and enhance interior tumor cell killing. This NIR-triggered intelligent nanoparticle successfully integrated photothermal therapy (PTT) for perivascular tumor cells and chemotherapy for deep tumor cell inhibition. The in vivo results showed remarkable tumor regression in 4T1 breast tumor-bearing mice by 74.2%. This controllable size switchable nanosystem with efficient tumor accumulation and penetration has shown great potential in improving synergistic antitumor effects of photochemotherapy.

L1CAM deployed perivascular tumor niche promotes vessel wall invasion of tumor thrombus and metastasis of renal cell carcinoma

The survival of tumor cells in the bloodstream, and vasculature adhesion at metastatic sites are crucial for tumor metastasis. Perivascular invasion aids tumor cell self-renewal, survival, and formation of metastases by facilitating readily available oxygen, nutrients, and endothelial-derived paracrine factors. Renal cell carcinoma (RCC) is among the most prevalent tumors of the urinary system, and the formation of venous tumor thrombus (VTT) is a characteristic feature of RCC. We observed high expression of L1CAM in the VTT with vessel wall invasion. L1CAM promotes the adhesion, migration, and invasion ability of RCC and enhances metastasis by interacting with ITGA5, which elicits activation of signaling downstream of integrin α5β1. L1CAM promotes ADAM17 transcription to facilitate transmembrane ectodomain cleavage and release of soluble L1CAM. In response to soluble L1CAM, vascular endothelial cells release several cytokines and chemokines. Endothelial-derived CXCL5 and its receptor CXCR2 promote the migration and intravasation of RCC toward endothelial cells suggesting that crosstalk between endothelial cells and tumor cells has a direct guiding role in driving the metastatic spread of RCC. LICAM plays a crucial role in the invasive ability of RCC, and regulation of L1CAM expression may contribute therapeutically to preventing RCC progression.

Identification of vascular cues contributing to cancer cell stemness and function.

Glioblastoma stem cells (GSCs) reside close to blood vessels (BVs) but vascular cues contributing to GSC stemness and the nature of GSC-BVs cross talk are not fully understood. Here, we dissected vascular cues influencing GSC gene expression and function to perfusion-based vascular cues, as well as to those requiring direct GSC-endothelial cell (EC) contacts. In light of our previous finding that perivascular tumor cells are metabolically different from tumor cells residing further downstream, cancer cells residing within a narrow, < 60µm wide perivascular niche were isolated and confirmed to possess a superior tumor-initiation potential compared with those residing further downstream. To circumvent reliance on marker expression, perivascular GSCs were isolated from the respective locales based on their relative state of quiescence. Combined use of these procedures uncovered a large number of previously unrecognized differentially expressed GSC genes. We show that the unique metabolic milieu of the perivascular niche dominated by the highly restricted zone of mTOR activity is conducive for acquisition of GSC properties, primarily in the regulation of genes implicated in cell cycle control. A complementary role of vascular cues including those requiring direct glioma/EC contacts was revealed using glioma/EC co-cultures. Outstanding in the group of glioma cells impacted by nearby ECs were multiple genes responsible for maintaining GSCs in an undifferentiated state, a large fraction of which also relied on Notch-mediated signaling. Glioma-EC communication was found to be bidirectional, evidenced by extensive Notch-mediated EC reprogramming by contacting tumor cells, primarily metabolic EC reprogramming.

Malignant gastrointestinal neuroectodermal tumor: Cytologic, histologic, immunohistochemical, and molecular pitfalls

Malignant gastrointestinal neuroectodermal tumor (GNET) is a rare malignant primary gastrointestinal mesenchymal tumor which can be diagnosed via fine-needle aspiration (FNA) cytology. In the context of FNA, the diagnosis requires a cell block and the use of significant resources including immunohistochemical stains and molecular testing. The differential diagnosis of GNET includes clear cell sarcoma (CCS), gastrointestinal stromal tumor (GIST), gastric schwannoma, metastatic melanoma, malignant perivascular epithelioid cell tumor (PEComa) and granular cell tumor, among others. Here we describe a case which was initially diagnosed as malignant granular cell tumor by FNA which was later revised to GNET following the finding of an EWSR1-ATF1 fusion gene rearrangement.

The MEMIC is an ex vivo system to model the complexity of the tumor microenvironment.

ABSTRACTThere is an urgent need for accurate, scalable and cost-efficient models of the tumor microenvironment. Here, we detail how to fabricate and use the metabolic microenvironment chamber (MEMIC) – a 3D-printed ex vivo model of intratumoral heterogeneity. A major driver of the cellular and molecular diversity in tumors is accessibility to the blood stream. Whereas perivascular tumor cells have direct access to oxygen and nutrients, cells further from the vasculature must survive under progressively more ischemic environments. The MEMIC simulates this differential access to nutrients, allow co-culturing any number of cell types, and it is optimized for live imaging and other microscopy-based analyses. Owing to a modular design and full experimental control, the MEMIC provides insights into the tumor microenvironment that would be difficult to obtain via other methods. As proof of principle, we show that cells sense gradual changes in metabolite concentration leading to predictable molecular and cellular spatial patterns. We propose the MEMIC as a complement to standard in vitro and in vivo experiments, diversifying the tools available to accurately model, perturb and monitor the tumor microenvironment.

Aggregative Perivascular Tumor Cell Growth Pattern of Primary Central Nervous System Lymphomas Is Associated with Hypoxia-Related Endoplasmic Reticulum Stress.

Primary central nervous system lymphomas (PCNSLs) often present a unique histopathological feature of aggregative perivascular tumor cells (APVT). Our previous studies showed that patients of PCNSL with APVTs exhibited poor long-term outcomes and increased expression of the endoplasmic reticulum stress (ERS) factor X-box-binding protein (XBP1). However, very little is known about molecular mechanism of the APVT formation in PCNSLs. The aim of this study is to determine if hypoxia-induced ERS is related to the APVT formation in PCNSLs. In this study, cell culture was used to observe the interplay between diffuse large B cell lymphoma (DLBCL) tumor cells and human brain microvascular endothelial cells (HBMECs) in different oxygen conditions. The expression of XBP1, CXCR and CD44 was manipulated by molecular cloning and siRNA technology. Mouse in vivo experiments and clinical studies were conducted to confirm our hypothesis. Our results showed that activated B-cell type-DLBCL cells easily migrated and invaded, and expressed high levels of XBP1 and stromal molecules CXCR4 and CD44 during hypoxia-induced ERS and dithiothreitol unfolded protein response (UPR). The gene upregulation (using overexpression vector) and downregulation (siRNA gene knock-out) in cultured cells and in mouse models further confirmed a close relation of the expression of XBP1, CXCR4, and CD44 with APVT formation, which is coincided with our clinical observation that increased expression of XBP1, CXCR4, and CD44 in the APVT cells in PCNSLs were associated with poor clinical outcomes. The results suggest that hypoxia-induced ERS and UPR might be associated with APVTs formation in PCNSL and its poor clinical outcomes. The results will help us better understand the progression of PCNSL with APVTs feature in daily pathological work and could be valuable for future target treatment of PCNSLs.

Intercellular delivery of bioorthogonal chemical receptors for enhanced tumor targeting and penetration

Targeted drug delivery using biological ligands can improve the precision of cancer therapy. However, this active targeting strategy is limited in tumor targeting and penetration abilities due to the paucity and heterogeneous distribution of targeted receptors in tumor cells, thus compromising the treatment outcomes. In this study, we developed an alternative active targeting strategy for enhanced tumor targeting and penetration through synthetic nanoparticle-mediated metabolic tumor ligand labeling for intercellular delivery of bioorthogonal chemical receptors combined with in vivo bioorthogonal click chemistry. Briefly, artificial azide-containing ligands were first labeled on perivascular tumor cells by nanoscale metabolic precursors (Az-NPs) via the enhanced permeability and retention (EPR) effect and metabolic engineering of the tumor cells. Through transport by extracellular vesicles (EVs) secreted by perivascular tumor cells, the azide-containing ligands can be autonomously transported intercellularly to adjacent cells and further spread throughout tumor tissues and label bioorthogonal ligands on cells that are not in proximity to blood vessels. Then, water-soluble dibenzocyclooctyne-modified chlorin e6 (DBCO-Ce6) was intravenously injected to react selectively, efficiently and irreversibly with the azide groups on the cell surface through an in vivo bioorthogonal click reaction. Enhanced tumor accumulation and penetration of DBCO-Ce6 was achieved through this strategy, resulting in improved therapeutic efficiency with laser irradiation for photodynamic therapy. Therefore, the artificial azide-containing ligand targeting strategy by nanoparticle-mediated metabolic labeling through the EPR effect combined with bioorthogonal click chemistry may provide an alternative strategy for enhanced tumor targeting and penetration with broad applications.

Perivascular Neuropilin-1 expression is an independent marker of improved survival in renal cell carcinoma.

Renal cell carcinoma (RCC) treatment has improved in the last decade with the introduction of drugs targeting tumor angiogenesis. However, the 5‐year survival of metastatic disease is still only 10–15%. Here, we explored the prognostic significance of compartment‐specific expression of Neuropilin 1 (NRP1), a co‐receptor for vascular endothelial growth factor (VEGF). NRP1 expression was analyzed in RCC tumor vessels, in perivascular tumor cells, and generally in the tumor cell compartment. Moreover, complex formation between NRP1 and the main VEGF receptor, VEGFR2, was determined. Two RCC tissue microarrays were used; a discovery cohort consisting of 64 patients and a validation cohort of 314 patients. VEGFR2/NRP1 complex formation in cis (on the same cell) and trans (between cells) configurations was determined by in situ proximity ligation assay (PLA), and NRP1 protein expression in three compartments (endothelial cells, perivascular tumor cells, and general tumor cell expression) was determined by immunofluorescent staining. Expression of NRP1 in perivascular tumor cells was explored as a marker for RCC survival in the two RCC cohorts. Results were further validated using a publicly available gene expression dataset of clear cell RCC (ccRCC). We found that VEGFR2/NRP1 trans complexes were detected in 75% of the patient samples. The presence of trans VEGFR2/NRP1 complexes or perivascular NRP1 expression was associated with a reduced tumor vessel density and size. When exploring NRP1 as a biomarker for RCC prognosis, perivascular NRP1 and general tumor cell NRP1 protein expression correlated with improved survival in the two independent cohorts, and significant results were obtained also at the mRNA level using the publicly available ccRCC gene expression dataset. Only perivascular NRP1 expression remained significant in multivariable analysis. Our work shows that perivascular NRP1 expression is an independent marker of improved survival in RCC patients, and reduces tumor vascularization by forming complexes in trans with VEGFR2 in the tumor endothelium. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Sequential depletion of myeloid-derived suppressor cells and tumor cells with a dual-pH-sensitive conjugated micelle system for cancer chemoimmunotherapy

Myeloid-derived suppressor cells(MDSCs)are one of the most important immunosuppressive cells in tumor microenvironment, which also promote the development and progression of tumor cells. Nevertheless, due to the different distribution features of MDSCs and tumor cells, selective elimination of MDSCs and tumor cells in tumor microenvironment remain a great challenge. Here we have designed a dual-pH-sensitivity conjugated micelle system (PAH/RGX-104@PDM/PTX) that could deliver liver-X nuclear receptor (LXR) agonist RGX-104 and paclitaxel (PTX) to the perivascular region and tumor cells, respectively. Upon arrival at the acidic tumor microenvironment, the PAH/RGX-104@PDM/PTX undergo structure disintegration and capacitate coinstantaneous release of RGX-104 in the perivascular regions, leaving the intact PTX containing micelles PDM/PTX for tumor deep penetration. The released RGX-104 can be preferentially taken up by leukocytes, endothelial cells and macrophages which are nicely enriched in perivascular regions to active the LXR, and further reduces immunosuppressive MDSC levels. The remained small micelles carrying PTX enable deep tumor penetration as well as rapid specific drug release in the endosomal/lysosomal to kill tumor cells. PAH/RGX-104@PDM/PTX exhibits superior tumor accumulation as well as tumor penetration, and suppresses 74.88% in vivo tumor growth. More importantly, PAH/RGX-104@PDM/PTX has significantly alleviated tumor immunosuppression by eliminating MDSCs and increasing cytotoxic T lymphocytes infiltration. Our studies suggest that the dual-pH-sensitive codelivery nanocarrier not only cause apoptosis of cancer cells but also regulate the tumor immune environment to ultimately enhance the antitumor effect of CTLs through MDSCs depletion.

Clinicopathological study of BCOR rearrangement in high grade endometrial stromal sarcoma

Objective: To investigate clinicopathological, cytogenetic features and differential diagnoses of high grade endometrial stromal sarcoma (HGESS) with BCOR gene rearrangement. Methods: Five cases of HGESS with BCOR rearrangement were collected from consultant files (2016-2018) at Fudan University Shanghai Cancer Center. Interphase FISH was performed using a dual color break-apart probe. The clinical data, histologic features and immunohistochemical findings were reviewed. Results: All 5 cases occurred in adult women with a median age of 48 (range, 45-55) years. Abdominal pain and abnormal vaginal bleeding were the most common symptoms. Microscopically, the tumors showed mainly tongue-like and/or intersecting myometrial invasion. Stromal myxoid matrix and/or collagen plaques were prominent in all the cases. Most tumors consisted of uniform, haphazard fascicles of short spindle cells with mild to moderate nuclear atypia. Mitotic figures and necrosis were easily identified. Significant nuclear pleomorphism was not seen. Most tumors were rich in thick-walled small vessels. Prominent perivascular tumor cell whorling seen in conventional low-grade endometrial stromal sarcoma was not seen. All tumors expressed CD10 with only focal or absent desmin, SMA and/or h-caldesmon staining. ER or PR expression was seen in 4 tumors and 1 tumor showed both marker expression. Diffuse cyclin D1 was present in 2 tumors. BCOR immunoreactivity was present with strong staining in 3 cases and moderate staining in 1 case respectively. Ki-67 index ranged from 10% to 30%. Fluorescence in situ hybridization confirmed chromosomal aberration of BCOR gene in all tumors, that were previously diagnosed as myxoid leiomyosarcoma (2 cases), spindle cell uterine sarcoma (2 cases) and low-grade endometrial stromal sarcoma (1 case). Limited follow-up information revealed that 3/5 patients developed tumor recurrence, metastasis or death within one year. Conclusion: BCOR rearranged HGESS has distinct morphological features and aggressive clinical behavior. In the presence of significant overlapping morphologic features between BCOR rearranged HGESS and other myxoid uterine mesenchymal tumors, especially myxoid leiomyosarcoma, molecular analysis is essential for accurate diagnoses.

Blood Vessel Proximity Shapes Cancer Cell Metabolism

Cancer cells are highly heterogeneous, and their features markedly vary within different areas of the tumor microenvironment. In this issue, Kumar etal. (2019) identified perivascular tumor cells, derived from mouse glioblastoma xenografts, as the fraction that displays the highest mTOR-dependent anabolic metabolism, aggressiveness, and resistance to therapy.

Cytomegalovirus promotes murine glioblastoma growth via pericyte recruitment and angiogenesis.

Cytomegalovirus (CMV) has been implicated in glioblastoma (GBM); however, a mechanistic connection in vivo has not been established. The purpose of this study is to characterize the effects of murine CMV (MCMV) on GBM growth in murine models. Syngeneic GBM models were established in mice perinatally infected with MCMV. We found that tumor growth was markedly enhanced in MCMV+ mice, with a significant reduction in overall survival compared with that of controls (P < 0.001). We observed increased angiogenesis and tumor blood flow in MCMV+ mice. MCMV reactivation was observed in intratumoral perivascular pericytes and tumor cells in mouse and human GBM specimens, and pericyte coverage of tumor vasculature was strikingly augmented in MCMV+ mice. We identified PDGF-D as a CMV-induced factor essential for pericyte recruitment, angiogenesis, and tumor growth. The antiviral drug cidofovir improved survival in MCMV+ mice, inhibiting MCMV reactivation, PDGF-D expression, pericyte recruitment, and tumor angiogenesis. These data show that MCMV potentiates GBM growth in vivo by increased pericyte recruitment and angiogenesis due to alterations in the secretome of CMV-infected cells. Our model provides evidence for a role of CMV in GBM growth and supports the application of antiviral approaches for GBM therapy.

Expression of GLUT1 in Pseudopalisaded and Perivascular Tumor Cells Is an Independent Prognostic Factor for Patients With Glioblastomas.

Glioblastomas are highly aggressive brain tumors with a particularly poor prognosis. Glucose transporter-1 (GLUT1/SLC2A1), a uniporter that is expressed by various carcinomas and may be involved in malignant neoplasm glycometabolism, may also be related to prognosis in glioblastomas. GLUT1 is essential to central nervous system glycometabolism. To clarify the exact role of GLUT1 in glioblastoma, we assessed the expression and localization of GLUT1 in patient samples by immunohistochemistry and in situ RNA hybridization. This revealed that GLUT1 was mainly expressed on perivascular and pseudopalisaded tumor cell membranes. All samples expressed GLUT1 to some degree, with 30.8% showing stronger staining. On the basis of these data, samples were divided into high and low expression groups, although SLC2A1 mRNA expression was also higher in the high GLUT1 expression group. Kaplan-Meier survival curves revealed that high GLUT1 expression associated with lower overall survival (log-rank test, p = 0.001) and worse patient prognoses (p = 0.001). Finally, MIB-1 staining was stronger in high GLUT1 expression samples (p = 0.0004), suggesting a link with proliferation. We therefore hypothesize that GLUT1 expression in glioblastomas may enhance glycolysis, affecting patient prognosis. Examination of GLUT1 in patients with glioblastomas may provide a new prognostic tool to improve outcome.

Macropinocytosis of Bevacizumab by Glioblastoma Cells in the Perivascular Niche Affects their Survival.

Purpose: Bevacizumab, a humanized monoclonal antibody to VEGF, is used routinely in the treatment of patients with recurrent glioblastoma (GBM). However, very little is known regarding the effects of bevacizumab on the cells in the perivascular space in tumors.Experimental Design: Established orthotopic xenograft and syngeneic models of GBM were used to determine entry of monoclonal anti-VEGF-A into, and uptake by cells in, the perivascular space. Based on the results, we examined CD133+ cells derived from GBM tumors in vitro Bevacizumab internalization, trafficking, and effects on cell survival were analyzed using multilabel confocal microscopy, immunoblotting, and cytotoxicity assays in the presence/absence of inhibitors.Results: In the GBM mouse models, administered anti-mouse-VEGF-A entered the perivascular tumor niche and was internalized by Sox2+/CD44+ tumor cells. In the perivascular tumor cells, bevacizumab was detected in the recycling compartment or the lysosomes, and increased autophagy was found. Bevacizumab was internalized rapidly by CD133+/Sox2+-GBM cells in vitro through macropinocytosis with a fraction being trafficked to a recycling compartment, independent of FcRn, and a fraction to lysosomes. Bevacizumab treatment of CD133+ GBM cells depleted VEGF-A and induced autophagy thereby improving cell survival. An inhibitor of lysosomal acidification decreased bevacizumab-induced autophagy and increased cell death. Inhibition of macropinocytosis increased cell death, suggesting macropinocytosis of bevacizumab promotes CD133+ cell survival.Conclusions: We demonstrate that bevacizumab is internalized by Sox2+/CD44+-GBM tumor cells residing in the perivascular tumor niche. Macropinocytosis of bevacizumab and trafficking to the lysosomes promotes CD133+ cell survival, as does the autophagy induced by bevacizumab depletion of VEGF-A. Clin Cancer Res; 23(22); 7059-71. ©2017 AACR.

Significance of perivascular tumour cells defined by CD109 expression in progression of glioma.

In the progression of glioma, tumour cells often exploit the perivascular microenvironment to promote their survival and resistance to conventional therapies. Some of these cells are considered to be brain tumour stem cells (BTSCs); however, the molecular nature of perivascular tumour cells has not been specifically clarified because of the complexity of glioma. Here, we identified CD109, a glycosylphosphatidylinositol-anchored protein and regulator of multiple signalling pathways, as a critical regulator of the progression of lower-grade glioma (World Health Organization grade II/III) by clinicopathological and whole-genome sequencing analysis of tissues from human glioma. The importance of CD109-positive perivascular tumour cells was confirmed not only in human lower-grade glioma tissues but also in a mouse model that recapitulated human glioma. Intriguingly, BTSCs isolated from mouse glioma expressed high levels of CD109. CD109-positive BTSCs exerted a proliferative effect on differentiated glioma cells treated with temozolomide. These data reveal the significance of tumour cells that populate perivascular regions during glioma progression, and indicate that CD109 is a potential therapeutic target for the disease. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract 3276: The tissue and cellular destination of therapeutic IgGs in glioblastoma

Abstract Most patients with recurrent glioblastoma (GBM) are treated with bevacizumab, a humanized monoclonal antibody (mAb) that binds VEGF-A and inhibits its binding to VEGFR. Approximately 30% of GBM patients are non-responsive to bevacizumab and the underlying mechanism for the lack of response is not known. It has been assumed that bevacizumab solely targets circulating VEGF-A in blood. We hypothesized that bevacizumab and human IgGs in general gain access to the perivascular niche that contains cancer stem cells (CSCs) in GBM. We found that bevacizumab gains access to the perivascular tumor area through leaky blood vessels and was internalized by tumor cells in an orthotopic xenograft mouse model of GBM. In vitro, CSCs (CD133+) from GBM rapidly internalized either bevacizumab or human IgG into membrane protrusions that contained actin and internalization was significantly inhibited by a macropinocytosis inhibitor (EIPA), suggesting CSCs internalize bevacizumab or human IgG via macropinocytosis. Furthermore, bevacizumab or human IgG was largely detected in the Rab4+ “fast” recycling compartment at 5 min, and both were largely detected in the LAMP1+ compartment (late endosome/lysosome) at 3 hr in the CSCs. CSCs (CD133+) from GBM do not express the neonatal Fc receptor, the canonical pathway for recycling of IgG. Administration of bevacizumab to an orthotopic xenograft mouse model of established GBM showed that bevacizumab was partially co-localized with Rab4+ or with LAMP1+ in perivascular tumor cells, consistent with our in vitro findings. Taken together, our data show that in GBM, humanized IgG, including bevacizumab, gains access to the perivascular tumor space and is then macropinocytosed by CSCs and trafficked to a recycling compartment or to the late endosome/lysosome. These data suggest that alterations in endocytosis or recycling in the CSCs could impact the fate of therapeutic IgGs like bevacizumab and ultimately influence a patients’ response to GBM therapy. Citation Format: Gaelle Muller-Greven, Cathleen Carlin, Steven Toms, Manmeet Ahluwalia, Markus Bredel, Justin Lathia, Jeremy Rich, Petra Hamerlik, Candece L. Gladson. The tissue and cellular destination of therapeutic IgGs in glioblastoma. [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 3276.

Abstract 3380: Direct contact with perivascular tumor cells enhances integrin αvβ3 signaling and migration of endothelial cells

Abstract The secretion of soluble pro-angiogenic factors by tumor cells and stromal cells in the perivascular niche promotes the aggressive angiogenesis that is typical of glioblastoma (GBM), which requires endothelial cell (EC) migration. Here, we show that angiogenesis can also be promoted by a direct interaction between brain tumor cells, including tumor cells with cancer stem-like properties (CSCs), and ECs. The direct interaction between CSCs and ECs was mediated by binding of integrin αvβ3 expressed on ECs to the RGD-peptide in L1CAM expressed on CSCs. Using in vitro assays, we found that this interaction increased network formation and migration-associated signaling events in ECs, including activation of integrin αvβ3, FAK, bone marrow tyrosine kinase on chromosome X (BMX), p130CAS, ERK and JNK. Comparison of the effects of co-culturing CSCs with ECs versus the effects of conditioned media from CSCs co-cultured with ECs indicated that upstream and downstream effector activation was not attributed to a secreted factor(s). Activation of αvβ3 and BMX was required for migration stimulated by direct binding but not for migration stimulated by soluble factors. RGD-peptide treatment of mice with established intracerebral GBM xenografts significantly reduced the percentage of Sox2-positive tumor cells (consistent with CSCs) in close proximity to ECs, decreased integrin αvβ3 and BMX activation and p130CAS phosphorylation in the ECs, and reduced the vessel surface area. These results show that direct interactions between CSCs and ECs have potent effects on EC migration and reveal a previously unrecognized aspect of the regulation of angiogenesis in GBM that can impact therapeutic anti-angiogenic targeting. Citation Format: Monica Burgett, Justin Lathia, Patrick Roth, Amy Nowacki, Elena Pugacheva, Ping Huang, Amit Vasanji, Li Meizhang, Tatiana Byzova, Tom Mikkelsen, Shideng Bao, Jeremy Rich, Michael Weller, Candece Gladson. Direct contact with perivascular tumor cells enhances integrin αvβ3 signaling and migration of endothelial cells. [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 3380.

Direct contact with perivascular tumor cells enhances integrin αvβ3 signaling and migration of endothelial cells.

The secretion of soluble pro-angiogenic factors by tumor cells and stromal cells in the perivascular niche promotes the aggressive angiogenesis that is typical of glioblastoma (GBM). Here, we show that angiogenesis also can be promoted by a direct interaction between brain tumor cells, including tumor cells with cancer stem-like properties (CSCs), and endothelial cells (ECs). As shown in vitro, this direct interaction is mediated by binding of integrin αvβ3 expressed on ECs to the RGD-peptide in L1CAM expressed on CSCs. It promotes both EC network formation and enhances directed migration toward basic fibroblast growth factor. Activation of αvβ3 and bone marrow tyrosine kinase on chromosome X (BMX) is required for migration stimulated by direct binding but not for migration stimulated by soluble factors. RGD-peptide treatment of mice with established intracerebral GBM xenografts significantly reduced the percentage of Sox2-positive tumor cells and CSCs in close proximity to ECs, decreased integrin αvβ3 and BMX activation and p130CAS phosphorylation in the ECs, and reduced the vessel surface area. These results reveal a previously unrecognized aspect of the regulation of angiogenesis in GBM that can impact therapeutic anti-angiogenic targeting.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer.

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Highlights of This Issue

Marketed EGFR antibodies are unsuitable for antibody–drug conjugate (ADC) development because their significant binding to normal tissue causes on-target toxicities. ABT-414, an ADC that selectively targets tumor cells and shows minimal binding to normal tissues, potently inhibits the growth of EGFR-positive xenograft tumors, including those expressing the EGFRde2-7 mutant form common to glioblastoma multiforme. ABT-414 combines with standard-of-care treatment radiation/temozolomide providing significant therapeutic benefit in a glioblastoma xenograft model. ABT-414 has now advanced to phase I/II clinical trials in glioblastoma patients and objective responses have been observed in a disease setting where novel treatments are urgently needed.Constitutive activation of the RAS–ERK pathway is frequently observed in human cancers and is associated with high rates of cancer cell proliferation. Recently, new ERK inhibitors were identified and shown to be active in cancer cell lines with activated RAS–ERK pathway. Here, Jha, Morris, and colleagues found that prolonged treatment of HCT-116 with SCH772984, a selective ERK inhibitor, induced acquired resistance to SCH772984 through acquisition of a mutation in ERK. Interestingly, the mutation was not in the “gatekeeper” residue, as commonly found with other kinase inhibitor–resistant models. These findings suggest potential mechanisms of resistance to ERK inhibitors that are currently in clinical trials.Targeting angiogenesis is a promising therapeutic strategy, but the available therapies grant only modest improvement in patients' survival. One of the main setbacks of antiangiogenic therapies is an induction of hypoxic signaling in the treated tumors. Hypoxic signaling and its main regulator, hypoxia-inducible factor-1 (HIF-1), negatively affect tumor progression, drug resistance, and tumor angiogenesis. Here, Szablowski and colleagues show that a DNA-binding molecule can impair the hypoxic signaling in tumors, inhibit angiogenesis, reduce perivascular tumor cell survival, and inhibit prometastatic and proangiogenic gene expression.Discovery of new drugs that directly target cancerous cells and tumor tissues is highly desirable. A new class of non–platinum-based compounds, discovered through studies in femtomedicine (FMD), recently has been found to be effective in inhibiting cancer cell growth in vitro and in vivo. This study further reveals the radiosensitizing effects of these FMD compounds on various preclinical cancer models when combined with ionizing radiation. Importantly, the compounds themselves induce no or little radiotoxicity toward normal cells or tissues. These compounds are therefore effective hypoxic radiosensitizers that have the potential to be translated into clinical trials for targeted radiotherapy of multiple cancers.