c-Met-mediated endothelial plasticity drives aberrant vascularization and chemoresistance in glioblastoma

Endothelial-to-Mesenchymal Transition in Cancer

Cancer is one of the most important causes of morbidity and mortality worldwide. Tumor cells grow in a complex microenvironment constituted of immune, stromal, and vascular cells that supports growth, angiogenesis, and metastasis. Endothelial cells (ECs) are major components of the vascular microenvironment. These cells have been described for their plasticity and potential to transdifferentiate into mesenchymal cells through a process known as endothelial-to-mesenchymal transition (EndMT). This complex process is controlled by various factors, by which ECs convert into a phenotype characterized by mesenchymal protein expression and motile, contractile morphology. Initially described in normal heart development, EndMT is now identified in several pathologies, and especially in cancer. In this review, we highlight the process of EndMT in the context of cancer and we discuss it as an important adaptive process of the tumor microenvironment that favors tumor growth and dissemination but also resistance to treatment. Thus, we underline targeting of EndMT as a potential therapeutic strategy.

LncRNA MIR155HG Promotes Temozolomide Resistance by Activating the Wnt/β-Catenin Pathway Via Binding to PTBP1 in Glioma

Temozolomide (TMZ) is widely used for glioma therapy in the clinic. Currently, the development of TMZ resistance has largely led to poor prognosis. However, very little is understood about the role of MIR155HG, as a long noncoding RNA, in TMZ resistance. In our study, MIR155HG level was markedly higher in glioma patients than in normal controls and that poor survival was positively correlated with MIR155HG expression. It was apparent that TMZ sensitivity was promoted by downregulation of MIR155HG, and this could be reversed by MIR155HG overexpression in vivo and in vitro. Furthermore, polypyrimidine tract binding protein 1 (PTBP1) was proven to bind with MIR155HG and to regulate MIR155HG-related TMZ resistance. Mechanistic investigation showed that the expression levels of both MIR155HG and PTBP1 influenced the expression of relevant proteins in the Wnt/β-catenin pathway. Collectively, the study demonstrated that the knockdown of MIR155HG increased glioma sensitivity to TMZ by inhibiting Wnt/β-catenin pathway activation via potently downregulating PTBP1.

Endothelial-to-mesenchymal transition in anticancer therapy and normal tissue damage

Endothelial-to-mesenchymal transition (EndMT) involves the phenotypic conversion of endothelial-to-mesenchymal cells, and was first discovered in association with embryonic heart development. EndMT can regulate various processes, such as tissue fibrosis and cancer. Recent findings have shown that EndMT is related to resistance to cancer therapy, such as chemotherapy, antiangiogenic therapy, and radiation therapy. Based on the known effects of EndMT on the cardiac toxicity of anticancer therapy and tissue damage of radiation therapy, we propose that EndMT can be targeted as a strategy for overcoming tumor resistance while reducing complications, such as tissue damage. In this review, we discuss EndMT and its roles in damaging cardiac and lung tissues, as well as EndMT-related effects on tumor vasculature and resistance in anticancer therapy. Modulating EndMT in radioresistant tumors and radiation-induced tissue fibrosis can especially increase the efficacy of radiation therapy. In addition, we review the role of hypoxia and reactive oxygen species as the main stimulating factors of tissue damage due to vascular damage and EndMT. We consider drugs that may be clinically useful for regulating EndMT in various diseases. Finally, we argue the importance of EndMT as a therapeutic target in anticancer therapy for reducing tissue damage.

A process of cellular conversion known as endothelial-to-mesenchymal transition (EndMT) may offer a valuable target for treating cancer and other diseases. In EndMT, the cells lining blood vessels undergo a striking change in shape and physiology, acquiring features of cells called fibroblasts. Fibroblasts form the body’s connective tissue, but also produce scar tissue that impairs organ function. Researchers led by Yoon-Jin Lee of the Korea Institute of Radiological & Medical Sciences in Seoul, South Korea, have reviewed the impact of this transformation on human disease. EndMT is seen as a prelude to heart failure, in lung tissue affected by pulmonary fibrosis, and within tumors, where the process recruits cells that further stimulate cancer progression. The authors highlight the potential of using drugs that target EndMT to bolster the efficacy and safety of tumor therapy.

Dual functionalized brain-targeting nanoinhibitors restrain temozolomide-resistant glioma via attenuating EGFR and MET signaling pathways

Activation of receptor tyrosine kinase (RTK) protein is frequently observed in malignant progression of gliomas. In this study, the crosstalk activation of epidermal growth factor receptor (EGFR) and mesenchymal-epithelial transition factor (MET) signaling pathways is demonstrated to contribute to temozolomide (TMZ) resistance, resulting in an unfavorable prognosis for patients with glioblastoma. To simultaneously mitigate EGFR and MET activation, a dual functionalized brain-targeting nanoinhibitor, BIP-MPC-NP, is developed by conjugating Inherbin3 and cMBP on the surface of NHS-PEG₈-Mal modified MPC-nanoparticles. In the presence of BIP-MPC-NP, DNA damage repair is attenuated and TMZ sensitivity is enhanced via the down-regulation of E2F1 mediated by TTP in TMZ resistant glioma. In vivo magnetic resonance imaging (MRI) shows a significant repression in tumor growth and a prolonged survival of mice after injection of the BIP-MPC-NP and TMZ. These results demonstrate the promise of this nanoinhibitor as a feasible strategy overcoming TMZ resistance in glioma.

Fibronectin in malignancy: Cancer-specific alterations, protumoral effects, and therapeutic implications

Initial studies on cancer primarily focused on malignant cells themselves. The overarching narrative of cancer revolved around unchecked and rapidly proliferating cells. Special attention was given to the molecular, genetic, and metabolic profiles of isolated cancer cells in hopes of elucidating a critical factor in malignancy. However, the scope of cancer research has broadened over the past few decades to include the local environment around cancer. It has become increasingly apparent that the immune cells, vascular networks, and the extracellular matrix all have a part in cancer progression. The impact of the extracellular matrix is particularly fascinating and key stromal changes have been identified in various cancers. Pioneering work studying laminin and hyaluronate has shown that these molecules have vital roles in cancer progression. More recently, fibronectin has been included as an extracellular driver of malignancy. Fibronectin is thought to play a considerable, albeit poorly understood, role in cancer pathogenesis. In this review, we present fundamental studies that have investigated the impact of fibronectin in cancer. As an abundant component of the extracellular matrix, understanding the effect of this molecule has the potential to elucidate cancer biology.

A phase 1 and randomized, placebo-controlled phase 2 trial of bevacizumab plus dasatinib in patients with recurrent glioblastoma: Alliance/North Central Cancer Treatment Group N0872

BACKGROUND

Src signaling is markedly upregulated in patients with invasive glioblastoma (GBM) after the administration of bevacizumab. The Src family kinase inhibitor dasatinib has been found to effectively block bevacizumab-induced glioma invasion in preclinical models, which led to the hypothesis that combining bevacizumab with dasatinib could increase bevacizumab efficacy in patients with recurrent GBM.

METHODS

After the completion of the phase 1 component, the phase 2 trial (ClinicalTrials.gov identifier NCT00892177) randomized patients with recurrent GBM 2:1 to receive 100 mg of oral dasatinib twice daily (arm A) or placebo (arm B) on days 1 to 14 of each 14-day cycle combined with 10 mg/kg of intravenous bevacizumab on day 1 of each 14-day cycle. The primary endpoint was 6-month progression-free survival (PFS6).

RESULTS

In the 121 evaluable patients, the PFS6 rate was numerically, but not statistically, higher in arm A versus arm B (28.9% [95% CI, 19.5%-40.0%] vs 18.4% [95% CI, 7.7%-34.4%]; P = .22). Similarly, there was no significant difference in the median overall survival noted between the treatment arms (7.3 months and 7.7 months, respectively; P = .93). The objective response rate was 15.7% in arm A and 26.3% in arm B (P = .52), but with a significantly longer duration in patients treated on arm A (16.3 months vs 2 months). The incidence of grade ≥3 toxicity was comparable between treatment arms, with hematologic toxicities occurring more frequently in arm A versus arm B (15.7% vs 7.9%) (adverse events were assessed as per the National Cancer Institute Common Terminology Criteria for Adverse Events [version 4.0]). Correlative tissue analysis demonstrated an association between pSRC/LYN signaling in patient tumors and outcome.

CONCLUSIONS

Despite upregulation of Src signaling in patients with GBM, the combination of bevacizumab with dasatinib did not appear to significantly improve the outcomes of patients with recurrent GBM compared with bevacizumab alone.

MET in glioma: signaling pathways and targeted therapies

Gliomas represent the most common type of malignant brain tumor, among which, glioblastoma remains a clinical challenge with limited treatment options and dismal prognosis. It has been shown that the dysregulated receptor tyrosine kinase (RTK, including EGFR, MET, PDGFRα, ect.) signaling pathways have pivotal roles in the progression of gliomas, especially glioblastoma. Increasing evidence suggests that expression levels of the RTK MET and its specific stimulatory factors are significantly increased in glioblastomas compared to those in normal brain tissues, whereas some negative regulators are found to be downregulated. Mutations in MET, as well as the dysregulation of other regulators of cross-talk with MET signaling pathways, have also been identified. MET and its ligand hepatocyte growth factor (HGF) play a critical role in the proliferation, survival, migration, invasion, angiogenesis, stem cell characteristics, and therapeutic resistance and recurrence of glioblastomas. Therefore, combined targeted therapy for this pathway and associated molecules could be a novel and attractive strategy for the treatment of human glioblastoma. In this review, we highlight progress made in the understanding of MET signaling in glioma and advances in therapies targeting HGF/MET molecules for glioma patients in recent years, in addition to studies on the expression and mutation status of MET.

Vascular Detransformation for Cancer Therapy

Angiogenesis is a hallmark of cancer. However, current antivascular therapies that primarily target angiogenic factors have faced difficulties and failures in treating most cancers. It is proposed that endothelial transformation acts as an alternative driver of excessive and abnormal vascularity that fuels cancer progression and immunosuppression, and also induces resistance to therapy. Thus, vascular detransformation may serve as a promising therapeutic strategy against cancer.

Verbascoside suppresses the migration and invasion of human glioblastoma cells via targeting c-Met-mediated epithelial-mesenchymal transition

Verbascoside (VB), a glycosylated phenylpropanoid compound, is derived from the plant Syringa vulgaris (Oleaceae) and has been shown to have antitumor effects in multiple human cancers, including glioblastoma (GBM); however, the underlying mechanism has not been completely elucidated. Epithelial-to-mesenchymal transition (EMT) is the pivotal event in tumor progression. c-Met, a receptor tyrosine kinase, plays an important role in GBM aggressiveness via promoting EMT. The current study aimed to explore whether VB suppresses c-Met-induced EMT and investigated the mechanism of c-Met degradation. We found that VB inhibited GBM cell growth and downregulated c-Met and the EMT markers (snail, vimentin, and zeb1) in vitro and in an orthotopic xenograft mouse model. In addition, overexpressing c-Met in glioblastoma cells abolished the effects of VB on EMT. We also used a microscale thermophoresis (MST) assay to show that VB could directly bind to the c-Met protein, and we showed that VB degraded the c-Met protein via the ubiquitination-proteasome pathway. Our study is the first to identify a new mechanism for the anticancer effects of VB, namely, the inhibition of EMT by directly targeting c-Met; the inhibition of EMT results in c-Met protein degradation through the ubiquitination-proteasome pathway. Our current research indicates that VB is a potential agent to treat GBM via the ubiquitin-mediated degradation of c-Met.

Lnc-TALC promotes O6-methylguanine-DNA methyltransferase expression via regulating the c-Met pathway by competitively binding with miR-20b-3p

Long noncoding RNAs (lncRNAs) have emerged as new regulatory molecules implicated in diverse biological processes, including therapeutic resistance. However, the mechanisms underlying lncRNA-mediated temozolomide (TMZ) resistance in glioblastoma (GBM) remain largely unknown. To illustrate the role of lncRNA in TMZ resistance, we induce TMZ-resistant GBM cells, perform a lncRNA microarray of the parental and TMZ-resistant cells, and find an unreported lncRNA in GBM, lnc-TALC (temozolomide-associated lncRNA in glioblastoma recurrence), correlated with TMZ resistance via competitively binding miR-20b-3p to facilitate c-Met expression. A phosphorylated AKT/FOXO3 axis regulated lnc-TALC expression in TMZ-resistant GBM cells. Furthermore, lnc-TALC increased MGMT expression by mediating the acetylation of H3K9, H3K27 and H3K36 in MGMT promoter regions through the c-Met/Stat3/p300 axis. In clinical patients, lnc-TALC is required for TMZ resistance and GBM recurrence. Our results reveal that lnc-TALC in GBM could serve as a therapeutic target to overcome TMZ resistance, enhancing the clinical benefits of TMZ chemotherapy.

Temozolomide resistance in glioblastoma is associated with MGMT overexpression. Here, the authors identify a lncRNA that is a competitive endogenous RNA for miR-20b-3p, which causes c-Met activation to modulate acetylation of histone H3 on MGMT promoter through Stat3/p300 complex to increase MGMT expression and temozolomide resistance.

c-Met Expression Is a Useful Marker for Prognosis Prediction in IDH-Mutant Lower-Grade Gliomas and IDH-Wildtype Glioblastomas

OBJECTIVE

c-Met has been shown to be associated with tumor growth in several human cancers. This study aims to evaluate the correlation between the c-Met expression and histopathologic/clinical characteristics.

METHODS

A total of 153 patients with histologically defined World Health Organization grade II-IV diffuse astrocytic and oligodendroglial tumors were analyzed.

RESULTS

For each histopathologic diagnosis, the number of cases and positive rate of c-Met expression are as follows: oligodendroglioma, IDH-mutant, and 1p19q codeletion (OD): 16 cases, 6.3%; anaplastic oligodendroglioma, IDH-mutant, and 1p19q codeletion (AO): 11 cases, 36.4%; diffuse astrocytoma (DA), IDH-mutant: 21 cases, 28.6%; anaplastic astrocytoma (AA), IDH- mutant: 15 cases, 20%; glioblastoma, IDH-mutant: 2, 100%, DA, IDH-wildtype: 9 cases, 33.3%; AA, IDH-wildtype: 20 cases, 30.0%; and glioblastoma, IDH-wildtype: 59 cases, 52.5%. c-Met expression was correlated with progression-free survival in oligodendroglial tumors and glioblastoma, IDH-wildtype. Furthermore, it was correlated with overall survival in AO, oligodendroglial tumors, DA, IDH-mutant, DA, IDH-wildtype, and glioblastoma, IDH-wildtype, and tend to be correlated with overall survival in IDH-mutant lower-grade astrocytic tumors.

CONCLUSIONS

c-Met expression was revealed to be a useful marker for prognosis prediction in IDH-mutant lower-grade gliomas and glioblastoma, IDH-wildtype, representing a new independent prognostic marker that can be easily measured.

Cancer stem-like cells directly participate in vasculogenic mimicry channels in triple-negative breast cancer

Objective

Vasculogenic mimicry (VM) channels that are lined by tumor cells are a functional blood supply in malignant tumors. However, the role of VM-initiating cells remains poorly understood. Cancer stem-like cells (CSCs) are positively correlated with VM. In this study, triple-negative breast cancer (TNBC) enriched with CSCs was used to investigate the relationship between VM and CSCs.

Methods

The expression of several CSC markers was detected by immunohistochemistry in 100 human breast cancer samples. The clinical significance of CSC markers and the relationship between VM, CSCs, breast cancer subtypes, and VM-associated proteins were analyzed. CD133+ and ALDH+ human and mouse TNBC cells were isolated by FACS to examine the ability of VM formation and the spatial relationship between VM and CSCs.

Results

CSCs were associated with TNBC subtype and VM in human invasive breast cancer. CSCs in TNBC MDA-MB-231 cells formed more VM channels and expressed more molecules promoting VM than the non-TNBC MCF-7 cells in vitro. MDA-MB-231 cells that encircled VM channels on Matrigel expressed CD133. Moreover, CSCs were located near VM channels in the 3D reconstructed blood supply system in human TNBC grafts. The CD133+ and ALDH+ cells isolated from TA2 mouse breast cancer formed more VM channels in vivo.

Conclusions

CSCs line VM channels directly. Additionally, CSCs provide more VM-related molecules to synergize VM formation. The signaling pathways that control CSC differentiation may also be potential treatment targets for TNBC.

NEO212, a conjugate of temozolomide and perillyl alcohol, blocks the endothelial-to-mesenchymal transition in tumor-associated brain endothelial cells in glioblastoma

As the endothelial-to-mesenchymal transition (EndMT) supports the pro-angiogenic and invasive characteristics of glioblastoma multiforme (GBM), blocking this process would be a promising approach to inhibit tumor progression and recurrence. Here, we demonstrate that glioma stem cells (GSC) induce EndMT in brain endothelial cells (BEC). TGF-β signaling is necessary, but not sufficient to induce this EndMT process. Cell-to-cell contact and the contribution of Notch signaling are also required. NEO212, a conjugate of temozolomide and perillyl alcohol, blocks EndMT induction and reverts the mesenchymal phenotype of tumor-associated BEC (TuBEC) by blocking TGF-β and Notch pathways. Consequently, NEO212 reduces the invasiveness and pro-angiogenic properties associated with TuBEC, without affecting control BEC. Intracranial co-implantation of BEC and GSC in athymic mice showed that EndMT occurs in vivo, and can be blocked by NEO212, supporting the potential clinical value of NEO212 for the treatment of GBM.

Mutational Landscape of Secondary Glioblastoma Guides MET-Targeted Trial in Brain Tumor

Low-grade gliomas almost invariably progress into secondary glioblastoma (sGBM) with limited therapeutic option and poorly understood mechanism. By studying the mutational landscape of 188 sGBMs, we find significant enrichment of TP53 mutations, somatic hypermutation, MET-exon-14-skipping (METex14), PTPRZ1-MET (ZM) fusions, and MET amplification. Strikingly, METex14 frequently co-occurs with ZM fusion and is present in ∼14% of cases with significantly worse prognosis. Subsequent studies show that METex14 promotes glioma progression by prolonging MET activity. Furthermore, we describe a MET kinase inhibitor, PLB-1001, that demonstrates remarkable potency in selectively inhibiting MET-altered tumor cells in preclinical models. Importantly, this compound also shows blood-brain barrier permeability and is subsequently applied in a phase I clinical trial that enrolls MET-altered chemo-resistant glioma patients. Encouragingly, PLB-1001 achieves partial response in at least two advanced sGBM patients with rarely significant side effects, underscoring the clinical potential for precisely treating gliomas using this therapy.

Circulating Glioma Cells Exhibit Stem Cell-like Properties

: Circulating tumor cells (CTC) are known to be present in the blood of patients with glioblastoma (GBM). Here we report that GBM-derived CTC possess a cancer stem cell (CSC)-like phenotype and contribute to local tumorigenesis and recurrence by the process of self-seeding. Genetic probes showed that mouse GBM-derived CTC exhibited Sox2/ETn transcriptional activation and expressed glioma CSC markers, consistent with robust expression of stemness-associated genes including SOX2, OCT4, and NANOG in human GBM patient-derived samples containing CTC. A transgenic mouse model demonstrated that CTC returned to the primary tumor and generated new tumors with enhanced tumorigenic capacity. These CTCs were resistant to radiotherapy and chemotherapy and to circulation stress-induced cell apoptosis. Single-cell RNA-seq analysis revealed that Wnt activation induced stemness and chemoresistance in CTC. Collectively, these findings identify GBM-derived CTC as CSC-like cells and suggest that targeting Wnt may offer therapeutic opportunities for eliminating these treatment-refractory cells in GBM. SIGNIFICANCE: These findings identify CTCs as an alternative source for in situ tumor invasion and recurrence through local micrometastasis, warranting eradication of systemic "out-of-tumor" CTCs as a promising new therapeutic opportunity for GBM.

PDGF-mediated mesenchymal transformation renders endothelial resistance to anti-VEGF treatment in glioblastoma

Angiogenesis is a hallmark of cancer. However, most malignant solid tumors exhibit robust resistance to current anti-angiogenic therapies that primarily target VEGF pathways. Here we report that endothelial-mesenchymal transformation induces glioblastoma (GBM) resistance to anti-angiogenic therapy by downregulating VEGFR-2 expression in tumor-associated endothelial cells (ECs). We show that VEGFR-2 expression is markedly reduced in human and mouse GBM ECs. Transcriptome analysis verifies reduced VEGFR-2 expression in ECs under GBM conditions and shows increased mesenchymal gene expression in these cells. Furthermore, we identify a PDGF/NF-κB/Snail axis that induces mesenchymal transformation and reduces VEGFR-2 expression in ECs. Finally, dual inhibition of VEGFR and PDGFR eliminates tumor-associated ECs and improves animal survival in GBM-bearing mice. Notably, EC-specific knockout of PDGFR-β sensitizes tumors to VEGF-neutralizing treatment. These findings reveal an endothelial plasticity-mediated mechanism that controls anti-angiogenic therapy resistance, and suggest that vascular de-transformation may offer promising opportunities for anti-vascular therapy in cancer.

Resistance to anti-angiogenic therapies often occurs in patients. Here, the authors demonstrate the role of PDGF signaling in GBM resistance to anti-VEGF treatment via a mechanism that involves endothelial-mesenchymal transformation and transcriptional regulation of VEGFR-2.

SHP2 protects endothelial cell barrier through suppressing VE-cadherin internalization regulated by MET-ARF1

Vascular endothelial (VE)-cadherin junctional localization is known to play a central role in vascular development, endothelial barrier integrity, and homeostasis. The sarcoma homology domain containing protein tyrosine phosphatase (SHP)2 has been shown to be involved in regulating endothelial barrier function; however, the mechanisms remain largely unknown. In this work SHP2 knockdown in an HUVEC monolayer increased VE-cadherin internalization and endothelial barrier permeability. Loss of SHP2 specifically augmented the GTPase activity of ADP-ribosylation factor (ARF)-1. ARF1 knockdown or inhibition of its guanine nucleotide exchange factors (GEFs) markedly attenuated VE-cadherin internalization and barrier hyperpermeability induced by SHP2 deficiency. SHP2 knockdown increased the total and phosphorylated levels of MET, whose activity was necessary for ARF1 activation and VE-cadherin internalization. Furthermore, constitutive endothelium-specific deletion of Shp2 in mice led to disrupted endothelial cell junctions, massive hemorrhage, and lethality in embryos. Induced and endothelium-specific deletion of Shp2 in adult mice resulted in lung hyperpermeability. Inhibitors for ARF1-GEF or MET used in pregnant mice prevented the vascular leakage in endothelial Shp2-deleted embryos. Together, our findings define a novel role of SHP2 in stabilizing junctional VE-cadherin in the resting endothelial barrier through suppressing MET and ARF1 activation.-Zhang, J., Huang, J., Qi, T., Huang, Y., Lu, Y., Zhan, T., Gong, H., Zhu, Z., Shi, Y., Zhou, J., Yu, L., Zhang, X., Cheng, H., Ke, Y. SHP2 protects endothelial cell barrier through suppressing VE-cadherin internalization regulated by MET-ARF1.

EndMT: A promising and controversial field

The endothelial to mesenchymal transition (EndMT) is the process by which endothelial cells lose a portion of their cellular features and obtain certain characteristics of mesenchymal cells, including loss of tight junctions, increased motility, and increased secretion of extracellular matrix proteins. EndMT is involved in cardiac development and a variety of diseases processes, such as vascular or tissue fibrosis and tumor. However, its role in specific diseases remains under debate. This review summarizes EndMT-related diseases, existing controversies, different types of EndMT, and molecules and signaling pathways associated with the process.

Oligosaccharyltransferase Inhibition Reduces Receptor Tyrosine Kinase Activation and Enhances Glioma Radiosensitivity

PURPOSE

Parallel signaling reduces the effects of receptor tyrosine kinase (RTK)-targeted therapies in glioma. We hypothesized that inhibition of protein N-linked glycosylation, an endoplasmic reticulum co- and posttranslational modification crucial for RTK maturation and activation, could provide a new therapeutic approach for glioma radiosensitization.Experimental Design: We investigated the effects of a small-molecule inhibitor of the oligosaccharyltransferase (NGI-1) on EGFR family receptors, MET, PDGFR, and FGFR1. The influence of glycosylation state on tumor cell radiosensitivity, chemotherapy-induced cell toxicity, DNA damage, and cell-cycle arrest were determined and correlated with glioma cell receptor expression profiles. The effects of NGI-1 on xenograft tumor growth were tested using a nanoparticle formulation validated by in vivo molecular imaging. A mechanistic role for RTK signaling was evaluated through the expression of a glycosylation-independent CD8-EGFR chimera.

RESULTS

NGI-1 reduced glycosylation, protein levels, and activation of most RTKs. NGI-1 also enhanced the radiosensitivity and cytotoxic effects of chemotherapy in those glioma cells with elevated ErbB family activation, but not in cells without high levels of RTK activation. NGI-1 radiosensitization was associated with increases in both DNA damage and G₁ cell-cycle arrest. Combined treatment of glioma xenografts with fractionated radiotherapy and NGI-1 significantly reduced tumor growth compared with controls. Expression of the CD8-EGFR eliminated the effects of NGI-1 on G₁ arrest, DNA damage, and cellular radiosensitivity, identifying RTK inhibition as the principal mechanism for the NGI-1 effect.

CONCLUSIONS

This study suggests that oligosaccharyltransferase inhibition with NGI-1 is a novel approach to radiosensitize malignant gliomas with enhanced RTK signaling.See related commentary by Wahl and Lawrence, p. 455.

MiR-206 inhibits epithelial ovarian cancer cells growth and invasion via blocking c-Met/AKT/mTOR signaling pathway

BACKGROUND

MicroRNAs play important roles in the pathogenesis of various kinds of tumors. However, there are few studies on the expression profile and function of miRNAs in epithelial ovarian cancer. In this study, we performed microRNA array to compare the expression profile of microRNA in ovarian cancer tissues with noncancerous tissues.

METHODS

qRT-PCR was used to further confirm the microRNA expression levels in epithelial ovarian cancer tissues and cell lines. The function of microRNA was analyzed by overexpressing microRNA mimics followed by the analysis of cell cycle, proliferation, and metastasis. The downstream target of miR-206 was found and western blot analysis was performed to measure the activation of the downstream signaling pathway.

RESULTS

In this study, we found the expression of miR-206 was significantly down-regulated in epithelial ovarian cancer tissues and epithelial ovarian cancer cell lines. In epithelial ovarian cancer patients, downregulation of miR-206 was associated with metastasis and poor prognosis. In epithelial ovarian cancer cell lines, miR-206 contributed to the cell cycle regulation, cell apoptosis, and cancer cell metastasis. MiR-206 mimics inhibited cancer cell proliferation and metastasis, and induced cell apoptosis. Moreover, our results demonstrated that miR-206 directly targeted c-Met and repressed the activation of downstream AKT/mTOR signaling pathway.

CONCLUSION

Our results demonstrated that miR-206 was down-regulated in epithelial ovarian cancer tissues and cell lines. MiR-206 inhibits the development of epithelial ovarian cancer cell by directly targeting c-Met and inhibiting the c-Met/AKT/mTOR signaling pathway.

The role of tumor microenvironment in therapeutic resistance

Cancer cells undergo unlimited progression and survival owing to activation of oncogenes. However, support of the tumor microenvironment is essential to the formation of clinically relevant tumors. Recent evidence indicates that the tumor microenvironment is a critical regulator of immune escape, progression, and distant metastasis of cancer. Moreover, the tumor microenvironment is known to be involved in acquired resistance of tumors to various therapies. Despite significant advances in chemotherapy and radiotherapy, occurrence of therapeutic resistance leads to reduced efficacy. This review highlights myeloid cells, cancer-associated fibroblasts, and mesenchymal stem cells consisting of the tumor microenvironment, as well as the relevant signaling pathways that eventually render cancer cells to be therapeutically resistant.

Autophagy mediates glucose starvation-induced glioblastoma cell quiescence and chemoresistance through coordinating cell metabolism, cell cycle, and survival

Metabolic reprogramming is pivotal to sustain cancer growth and progression. As such dietary restriction therapy represents a promising approach to starve and treat cancers. Nonetheless, tumors are dynamic and heterogeneous populations of cells with metabolic activities modulated by spatial and temporal contexts. Autophagy is a major pathway controlling cell metabolism. It can downregulate cell metabolism, leading to cancer cell quiescence, survival, and chemoresistance. To understand treatment dynamics and provide rationales for better future therapeutic strategies, we investigated whether and how autophagy is involved in the chemo-cytotoxicity and -resistance using two commonly used human glioblastoma (GBM) cell lines U87 and U251 together with primary cancer cells from the GBM patients. Our results suggest that autophagy mediates chemoresistance through reprogramming cancer cell metabolism and promoting quiescence and survival. Further unbiased transcriptome profiling identified a number of clinically relevant pathways and genes, strongly correlated with TCGA data. Our analyses have not only reported many well-known tumor players, but also uncovered a number of genes that were not previously implicated in cancers and/or GBM. The known functions of these genes are highly suggestive. It would be of high interest to investigate their potential involvement in GBM tumorigenesis, progression, and/or drug resistance. Taken together, our results suggest that autophagy inhibition could be a viable approach to aid GBM chemotherapy and combat drug resistance.

Temporal DNA-PK activation drives genomic instability and therapy resistance in glioma stem cells

Cancer stem cells (CSCs) - known to be resistant to genotoxic radiation and chemotherapy - are fundamental to therapy failure and cancer relapse. Here, we reveal that glioma CSCs are hypersensitive to radiation, but a temporal DNA repair mechanism converts the intrinsic sensitivity to genomic instability and treatment resistance. Transcriptome analysis identifies DNA-dependent protein kinase (DNA-PK) as a predominant DNA repair enzyme in CSCs. Notably, DNA-PK activity is suppressed after irradiation when ROS induce the dissociation of DNA-PKcs with Ku70/80, resulting in delayed DNA repair and radiosensitivity; subsequently, after ROS clearance, the accumulated DNA damage and robust activation of DNA-PK induce genomic instability, facilitated by Rad50-mediated cell-cycle arrest, leading to enhanced malignancy, CSC overgrowth, and radioresistance. Finally, we show a requisite in vivo role for DNA-PK in CSC-mediated radioresistance and glioma progression. These findings identify a time-sensitive mechanism controlling CSC resistance to DNA-damaging treatments and suggest DNA-PK/Rad50 as promising targets for CSC eradication.

Vascular niche IL-6 induces alternative macrophage activation in glioblastoma through HIF-2α

Spatiotemporal regulation of tumor immunity remains largely unexplored. Here we identify a vascular niche that controls alternative macrophage activation in glioblastoma (GBM). We show that tumor-promoting macrophages are spatially proximate to GBM-associated endothelial cells (ECs), permissive for angiocrine-induced macrophage polarization. We identify ECs as one of the major sources for interleukin-6 (IL-6) expression in GBM microenvironment. Furthermore, we reveal that colony-stimulating factor-1 and angiocrine IL-6 induce robust arginase-1 expression and macrophage alternative activation, mediated through peroxisome proliferator-activated receptor-γ-dependent transcriptional activation of hypoxia-inducible factor-2α. Finally, utilizing a genetic murine GBM model, we show that EC-specific knockout of IL-6 inhibits macrophage alternative activation and improves survival in the GBM-bearing mice. These findings illustrate a vascular niche-dependent mechanism for alternative macrophage activation and cancer progression, and suggest that targeting endothelial IL-6 may offer a selective and efficient therapeutic strategy for GBM, and possibly other solid malignant tumors.

TGF-β induces oncofetal fibronectin that, in turn, modulates TGF-β superfamily signaling in endothelial cells

Gene splicing profiles are frequently altered in cancer, and the splice variants of fibronectin (FN) that contain the extra-domains A (EDA) or B (EDB), referred to as EDA+FN or EDB+FN, are highly upregulated in tumor vasculature. Transforming growth factor β (TGF-β) signaling has been attributed a pivotal role in glioblastoma, with TGF-β promoting angiogenesis and vessel remodeling. By using immunohistochemistry staining, we observed that the oncofetal FN isoforms EDA+FN and EDB+FN are expressed in glioblastoma vasculature. Ex vivo single-cell gene expression profiling of tumors by using CD31 and α-smooth muscle actin (αSMA) as markers for endothelial cells, and pericytes and vascular smooth muscle cells (VSMCs), respectively, confirmed the predominant expression of FN, EDA+FN and EDB+FN in the vascular compartment of glioblastoma. Specifically, within the CD31-positive cell population, we identified a positive correlation between the expression of EDA+FN and EDB+FN, and of molecules associated with TGF-β signaling. Further, TGF-β induced EDA+FN and EDB+FN in human cerebral microvascular endothelial cells and glioblastoma-derived endothelial cells in a SMAD3- and SMAD4-dependent manner. In turn, we found that FN modulated TGF-β superfamily signaling in endothelial cells via the EDA and EDB, pointing towards a bidirectional influence of oncofetal FN and TGF-β superfamily signaling.

Role and Therapeutic Targeting of the HGF/MET Pathway in Glioblastoma

Glioblastoma (GBM) is a lethal brain tumor with dismal prognosis. Current therapeutic options, consisting of surgery, chemotherapy and radiation, have only served to marginally increase patient survival. Receptor tyrosine kinases (RTKs) are dysregulated in approximately 90% of GBM; attributed to this, research has focused on inhibiting RTKs as a novel and effective therapy for GBM. Overexpression of RTK mesenchymal epithelial transition (MET), and its ligand, hepatocyte growth factor (HGF), in GBM highlights a promising new therapeutic target. This review will discuss the role of MET in cell cycle regulation, cell proliferation, evasion of apoptosis, cell migration and invasion, angiogenesis and therapeutic resistance in GBM. It will also discuss the modes of deregulation of HGF/MET and their regulation by microRNAs. As the HGF/MET pathway is a vital regulator of multiple pro-survival pathways, efforts and strategies for its exploitation for GBM therapy are also described.

Tumor angiogenesis revisited: Regulators and clinical implications

Since Judah Folkman hypothesized in 1971 that angiogenesis is required for solid tumor growth, numerous studies have been conducted to unravel the angiogenesis process, analyze its role in primary tumor growth, metastasis and angiogenic diseases, and to develop inhibitors of proangiogenic factors. These studies have led in 2004 to the approval of the first antiangiogenic agent (bevacizumab, a humanized antibody targeting vascular endothelial growth factor) for the treatment of patients with metastatic colorectal cancer. This approval launched great expectations for the use of antiangiogenic therapy for malignant diseases. However, these expectations have not been met and, as knowledge of blood vessel formation accumulates, many of the original paradigms no longer hold. Therefore, the regulators and clinical implications of angiogenesis need to be revisited. In this review, we discuss recently identified angiogenesis mediators and pathways, new concepts that have emerged over the past 10 years, tumor resistance and toxicity associated with the use of currently available antiangiogenic treatment and potentially new targets and/or approaches for malignant and nonmalignant neovascular diseases.

EMT- and MET-related processes in nonepithelial tumors: importance for disease progression, prognosis, and therapeutic opportunities

The epithelial-to mesenchymal (EMT) process is increasingly recognized for playing a key role in the progression, dissemination, and therapy resistance of epithelial tumors. Accumulating evidence suggests that EMT inducers also lead to a gain in mesenchymal properties and promote malignancy of nonepithelial tumors. In this review, we present and discuss current findings, illustrating the importance of EMT inducers in tumors originating from nonepithelial/mesenchymal tissues, including brain tumors, hematopoietic malignancies, and sarcomas. Among these tumors, the involvement of mesenchymal transition has been most extensively investigated in glioblastoma, providing proof for cell autonomous and microenvironment-derived stimuli that provoke EMT-like processes that regulate stem cell, invasive, and immunogenic properties as well as therapy resistance. The involvement of prominent EMT transcription factor families, such as TWIST, SNAI, and ZEB, in promoting therapy resistance and tumor aggressiveness has also been reported in lymphomas, leukemias, and sarcomas. A reverse process, resembling mesenchymal-to-epithelial transition (MET), seems particularly relevant for sarcomas, where (partial) epithelial differentiation is linked to less aggressive tumors and a better patient prognosis. Overall, a hybrid model in which more stable epithelial and mesenchymal intermediates exist likely extends to the biology of tumors originating from sources other than the epithelium. Deeper investigation and understanding of the EMT/MET machinery in nonepithelial tumors will shed light on the pathogenesis of these tumors, potentially paving the way toward the identification of clinically relevant biomarkers for prognosis and future therapeutic targets.

Suppression of p53-inducible gene 3 is significant for glioblastoma progression and predicts poor patient prognosis

Glioblastoma is the most malignant and invasive brain tumor with extremely poor prognosis. p53-inducible gene 3, a downstream molecule of the tumor suppressor p53, has been found involved in apoptosis and oxidative stress response. However, the functions of p53-inducible gene 3(PIG3) in cancer are far from clear including glioblastoma. In this study, we found that p53-inducible gene 3 expression was suppressed in glioblastoma tissues compared with normal tissues. And the expression of p53-inducible gene 3 was significantly associated with the World Health Organization grade. Patients with high p53-inducible gene 3 expression have a significantly longer median survival time (15 months) than those with low p53-inducible gene 3 expression (8 months). According to Cox regression analysis, p53-inducible gene 3 was an independent prognostic factor with multivariate hazard ratio of 0.578 (95% confidence interval, 0.352-0.947; p = 0.030) for overall survival. Additionally, gain and loss of function experiments showed that knockdown of p53-inducible gene 3 significantly increased the proliferation and invasion ability of glioblastoma cells while overexpression of p53-inducible gene 3 inhibited the proliferation and invasion ability. The results of in vivo glioblastoma models further confirmed that p53-inducible gene 3 suppression promoted glioblastoma progression. Altogether, our data suggest that high expression of p53-inducible gene 3 is significant for glioblastoma inhibition and p53-inducible gene 3 independently indicates good prognosis in patients, which might be a novel prognostic biomarker or potential therapeutic target in glioblastoma.

Dual inhibition of Akt and c-Met as a second-line therapy following acquired resistance to sorafenib in hepatocellular carcinoma cells

Sorafenib displays a limited efficacy for advanced hepatocellular carcinoma (HCC). Some patients with HCC initially respond to sorafenib, but eventually succumb to the disease, indicating that the acquired resistance to sorafenib reduces its beneficial effects. No alternative drugs are available after the failure of sorafenib therapy. Therefore, investigation of the mechanisms underlying the acquired resistance and development of second-line treatments for sorafenib-resistant HCC are urgently required. In this study, sorafenib-resistant HCC cells generated from sorafenib-sensitive human HCC cells were shown to overproduce hepatocyte growth factor (HGF) and overexpress c-Met kinase and its phosphorylated form, leading to the activation of Akt and ERK (extracellular signaling-regulated kinase) pathways. Use of specific c-Met inhibitors enhanced the effects of sorafenib by inhibiting the growth of sorafenib-resistant HCC cells. Akt inhibitors, a class of second-line therapeutic drugs under investigation for treating HCC in clinical trials, enhanced the effects of sorafenib, but also activated the c-Met pathway in sorafenib-resistant cells. Dual inhibition of Akt and c-Met by their respective inhibitors, MK2206 and capmatinib, additively or synergistically suppressed sorafenib-resistant HCC cells in vitro and sorafenib-resistant HCC xenografts in mice. The anticancer activities of MK2206 mainly rely on its ability to induce cell apoptosis and autophagic death, while capmatinib treatment leads to cell cycle arrest at phase G1. These results provide strong evidence for further investigation on the clinical utility of dual inhibition of Akt and c-Met, particularly MK2206 and capmatinib, as a second-line therapy for advanced HCC that has acquired resistance to sorafenib.

The Pleiotropic Role of L1CAM in Tumor Vasculature

Angiogenesis, the formation of new vessels, is a key step in the development, invasion, and dissemination of solid tumors and, therefore, represents a viable target in the context of antitumor therapy. Indeed, antiangiogenic approaches have given promising results in preclinical models and entered the clinical practice. However, in patients, the results obtained so far with antiangiogenic drugs have not completely fulfilled expectations, especially because their effect has been transient with tumors developing resistance and evasion mechanisms. A better understanding of the mechanisms that underlie tumor vascularization and the functional regulation of cancer vessels is a prerequisite for the development of novel and alternative antiangiogenic treatments. The L1 cell adhesion molecule (L1CAM), a cell surface glycoprotein previously implicated in the development and plasticity of the nervous system, is aberrantly expressed in the vasculature of various cancer types. L1CAM plays multiple pro-angiogenic roles in the endothelial cells of tumor-associated vessels, thus emerging as a potential therapeutic target. In addition, L1CAM prevents the maturation of cancer vasculature and its inhibition promotes vessel normalization, a process that is thought to improve the therapeutic response of tumors to cytotoxic drugs. We here provide an overview on tumor angiogenesis and antiangiogenic therapies and summarize the current knowledge on the biological role of L1CAM in cancer vasculature. Finally, we highlight the clinical implications of targeting L1CAM as a novel antiangiogenic and vessel-normalizing approach.

Fine-tuning vascular fate during endothelial-mesenchymal transition

In the heart and other organs, endothelial-mesenchymal transition (EndMT) has emerged as an important developmental process that involves coordinated migration, differentiation, and proliferation of the endothelium. In multiple disease states including cancer angiogenesis and cardiovascular disease, the processes that regulate EndMT are recapitulated, albeit in an uncoordinated and dysregulated manner. Members of the transforming growth factor beta (TGFβ) superfamily are well known to impart cellular plasticity during EndMT by the timely activation (or repression) of transcription factors and miRNAs in addition to epigenetic regulation of gene expression. On the other hand, fibroblast growth factors (FGFs) are reported to augment or oppose TGFβ-driven EndMT in specific contexts. Here, we have synthesized the currently understood roles of TGFβ and FGF signalling during EndMT and have provided a new, comprehensive paradigm that delineates how an autocrine and paracrine TGFβ/FGF axis coordinates endothelial cell specification and plasticity. We also provide new guidelines and nomenclature that considers factors such as endothelial cell heterogeneity to better define EndMT across different vascular beds. This perspective should therefore help to clarify why TGFβ and FGF can both cooperate with or oppose one another during the complex process of EndMT in both health and disease. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.