Vascular heterogeneity and targeting: the role of YKL-40 in glioblastoma vascularization.

Malignant glioblastomas (GBM) are highly malignant brain tumors that have extensive and aberrant tumor vasculature, including multiple types of vessels. This review focuses on recent discoveries that the angiogenic factor YKL-40 (CHI3L1) acts on glioblastoma-stem like cells (GSCs) to drive the formation of two major forms of tumor vascularization: angiogenesis and vasculogenic mimicry (VM). GSCs possess multipotent cells able to transdifferentiate into vascular pericytes or smooth muscle cells (PC/SMCs) that either coordinate with endothelial cells (ECs) to facilitate angiogenesis or assemble in the absence of ECs to form blood-perfused channels via VM. GBMs express high levels of YKL-40 that drives the divergent signaling cascades to mediate the formation of these distinct microvascular circulations. Although a variety of anti-tumor agents that target angiogenesis have demonstrated transient benefits for patients, they often fail to restrict tumor growth, which underscores the need for additional therapeutic tools. We propose that targeting YKL-40 may compliment conventional anti-angiogenic therapies to provide a substantial clinical benefit to patients with GBM and several other types of solid tumors.

Anti-YKL-40 antibody and ionizing irradiation synergistically inhibit tumor vascularization and malignancy in glioblastoma.

Chemo/radiotherapies are the most common adjuvant modality treated for patients with glioblastoma (GBM) following surgery. However, the overall therapeutic benefits are still uncertain, as the mortality remains high. Elevated expression of YKL-40 in GBM was correlated with increases in mural cell-associated vessel coverage, stability and density, and decreases in vessel permeability and disease survival. To explore the potential role of YKL-40 in mural cell-mediated tumor vascularization, we employed an anti-YKL-40 neutralizing antibody (mAY) and ionizing irradiation (IR) in xenografted brain tumor models. Although single treatment with mAY or IR partially increased mouse survival, their combination led to dramatic inhibition in tumor growth and increases in mouse survival. mAY blocked mural cell-mediated vascular stability, integrity and angiogenesis; whereas IR merely promoted tumor cell and vascular cell apoptosis. Vascular radioresistance is at least partially attributed to expression of YKL-40 in mural cells. These divergent effects were also recapitulated in cultured systems using endothelial cells and mural cells differentiated from glioblastoma stem-like cells (GSCs). Dysfunction of intercellular contact N-cadherin was found to mediate mAY-inhibited vascularization. Collectively, the data suggest that the conjunction therapy with mAY and IR synergistically inhibit tumor vascularization and progression. The evidence may shed light on a new adjuvant therapy in clinic.

Transdifferentiation of glioblastoma stem-like cells into mural cells drives vasculogenic mimicry in glioblastomas.

Recent evidence has shown that glioblastoma stem-like cells (GSCs) can transdifferentiate into endothelial cells and vascular-like tumor cells. The latter pattern of vascularization indicates an alternative microvascular circulation known as vasculogenic mimicry (VM). However, it remains to be clarified how the GSC-driven VM makes a significant contribution to tumor vasculature. Here, we investigated 11 cases of glioblastomas and found that most of them consisted of blood-perfused vascular channels that coexpress mural cell markers smooth muscle α-actin and platelet-derived growth factor receptor ß, epidermal growth factor receptor, and vascular endothelial growth factor receptor 2 (Flk-1), but not CD31 or VE-cadherin. This microvasculature coexisted with endothelial cell-associated vessels. GSCs derived from patients with glioblastomas developed vigorous mural cell-associated vascular channels but few endothelial cell vessels in orthotopic animal models. Suppression of Flk-1 activity and gene expression abrogated GSC transdifferentiation and vascularization in vitro, and inhibited VM in animal models. This study establishes mural-like tumor cells differentiated from GSCs as a significant contributor to microvasculature of glioblastoma and points to Flk-1 as a potential target for therapeutic intervention that could complement current anti-angiogenic treatment.

Glioblastoma-derived tumor cells induce vasculogenic mimicry through Flk-1 protein activation.

Glioblastoma (GBM) is extremely aggressive and essentially incurable. Its malignancy is characterized by vigorous microvascular proliferations. Recent evidence has shown that tumor cells display the ability to drive blood-perfused vasculogenic mimicry (VM), an alternative microvascular circulation independent of endothelial cell angiogenesis. However, molecular mechanisms underlying this vascular pathogenesis are poorly understood. Here, we found that vascular channels of VM in GBM were composed of mural-like tumor cells that strongly express VEGF receptor 2 (Flk-1). To explore a potential role of Flk-1 in the vasculogenesis, we investigated two glioblastoma cell lines U87 and GSDC, both of which express Flk-1 and exhibit a vascular phenotype on Matrigel. Treatment of both cell lines with either Flk-1 gene knockdown or Flk-1 kinase inhibitor SU1498 abrogated Flk-1 activity and impaired vascular function. Furthermore, inhibition of Flk-1 activity suppressed intracellular signaling cascades, including focal adhesion kinase and mitogen-activated protein kinase ERK1/2. In contrast, blockade of VEGF activity by the neutralizing antibody Bevacizumab failed to recapitulate the impact of SU1498, suggesting that Flk-1-mediated VM is independent of VEGF. Xenotransplantation of SCID/Beige mice with U87 cells and GSDCs gave rise to tumors harboring robust mural cell-associated vascular channels. Flk-1 shRNA restrained VM in tumors and subsequently inhibited tumor development. Collectively, all the data demonstrate a central role of Flk-1 in the formation of VM in GBM. This study has shed light on molecular mechanisms mediating tumor aggressiveness and also provided a therapeutic target for patient treatment.

Role of YKL-40 in the angiogenesis, radioresistance, and progression of glioblastoma.

Glioblastoma is one of the most fatal cancers, characterized by a strong vascularized phenotype. YKL-40, a secreted glycoprotein, is overexpressed in patients with glioblastomas and has potential as a novel tumor biomarker. The molecular mechanisms of YKL-40 in glioblastoma development, however, are poorly understood. Here, we aimed to elucidate the role YKL-40 plays in the regulation of VEGF expression, tumor angiogenesis, and radioresistance. YKL-40 up-regulated VEGF expression in glioblastoma cell line U87, and both YKL-40 and VEGF synergistically promote endothelial cell angiogenesis. Interestingly, long term inhibition of VEGF up-regulated YKL-40. YKL-40 induced coordination of membrane receptor syndecan-1 and integrin αvß5, and triggered a signaling cascade through FAK(397) to ERK-1 and ERK-2, leading to elevated VEGF and enhanced angiogenesis. In addition, γ-irradiation of U87 cells increased YKL-40 expression that protects cell death through AKT activation and also enhances endothelial cell angiogenesis. Blockade of YKL-40 activity or expression decreased tumor growth, angiogenesis, and metastasis in xenografted animals. Immunohistochemical analysis of human glioblastomas revealed a correlation between YKL-40, VEGF, and patient survival. These findings have shed light on the mechanisms by which YKL-40 promotes tumor angiogenesis and malignancy, and thus provide a therapeutic target for tumor treatment.

Postpartum granulomatous hypophysitis with sphenoid sinus involvement: a case study.

OBJECTIVE: To report an unusual case of granulomatous hypophysitis with sphenoid sinus involvement in a woman presenting with headaches and visual field deficits approximately 2 weeks after a normal delivery. METHODS: We present the history, physical findings, hormonal assay results, pituitary imaging, surgical findings, and pathology findings at presentation and then follow-up data at several times encompassing 1 year of observation. We also performed a literature review on granulomatous hypophysitis. RESULTS: A 29-year-old woman presented with headache and visual disturbances 11 days after childbirth. Magnetic resonance imaging revealed a sellar mass with suprasellar extension, compression of the optic chiasm, possible invasion of the cavernous sinuses, and sinus mucosal thickening. A subtotal resection was performed through the transsphenoidal route. Histologic examination demonstrated extensive nonvasculitic granulomatous tissue in pituitary and sphenoid mucosal samples. Investigation for known causes of granulomatous hypophysitis was negative. She required desmopressin and levothyroxine replacement postoperatively. Sequential follow-up revealed spontaneous resolution of the residual mass in 5 months. CONCLUSION: Unique features of this case include the concomitant presence of granulomatous lesions in the pituitary gland and the sphenoid sinus, its manifestation in the early postpartum period, and the spontaneous resolution of the residual granulomatous lesions in both the sphenoid sinus and the sella turcica.