Emel Akgun

Endovascular treatment increases but gamma knife radiosurgery decreases angiogenic activity of arteriovenous malformations: an in vivo experimental study using a rat cornea model.

OBJECTIVETo compare the angiogenic potentials of embolized, gamma knife–treated or untreated cerebral arteriovenous malformations (AVMs), using a rat cornea angiogenesis model. METHODSTissue samples from cerebral AVM patients who were either untreated or had previously been treated with embolization or gamma knife radiosurgery and who had undergone operations for hemorrhage at the Neurosurgery Department or the Neurological Sciences Institute of Marmara University were used. For the macroscopic evaluation of angiogenesis, tissue samples were inoculated in a micropocket created on the rat eye, and the level of angiogenic activity was graded macroscopically for 15 days, with glioblastoma multiforme and normal brain artery tissues serving as positive and negative controls, respectively. For the other part of the experiment, eyes of another set of rats were inoculated with the study samples only using the same cornea angiogenesis model, in which microvessel count and vascular endothelial growth factor assessment was done at days 3, 7, 11, and 15. RESULTSBased on our macroscopic findings in the cornea angiogenesis model, embolized AVMs exhibited the highest angiogenic activity, followed by untreated AVMs and gamma knife–treated AVMs. Evaluations of vascular endothelial growth factor expression and microvessel counts showed a similar relation among the 3 tissue groups with regard to the level of angiogenic activity, supporting the results of macroscopic examinations. CONCLUSIONThis study, for the first time, provides experimental semiquantitative data to compare the angiogenic potentials of embolized and gamma knife–treated AVM tissues. Embolization may increase angiogenic activity, and gamma knife radiosurgery may decrease it when compared with activity in previously untreated AVMs. These data can be useful to understand why recurrence of AVMs after angiographically demonstrated endovascular occlusion is common but after gamma knife occlusion is rare.

Expression of angiogenic factors in craniopharyngiomas: implications for tumor recurrence.

BACKGROUNDThe primary treatment for craniopharyngiomas is total excision, but recurrence is common. However, current knowledge on the mechanisms of recurrence is limited. OBJECTIVEWe hypothesized that recurrence is linked to the angiogenesis of the tumor. Recurrent and nonrecurrent tumor samples were compared with regard to expression of angiogenesis-related factors and angiogenic capacity in a corneal angiogenesis model. METHODSSpecimens of 4 recurrent and 6 nonrecurrent tumors were selected from 57 patients with adamantinomatous craniopharyngiomas. Sections were immunohistochemically stained with antibodies for vascular endothelial growth factor (VEGF), fibronectin, fibroblast growth factor (FGF)-2, platelet-derived growth factor (PDGF)-A, PDGF-B, platelet-derived growth factor receptor (PDGFR)-α, and PDGFR-β. Expression levels were graded using a 4-point scoring system and were compared. For corneal angiogenesis assay, tissue samples were inoculated in a micropocket created on the rat eye, and microvessels were counted on days 3, 5, 7, and 9 to evaluate angiogenic potential. RESULTSExpression of PDGFR-α and FGF-2 were significantly higher for recurrent tumors (P = .02 and P = .01). However, recurrent and nonrecurrent tumors did not differ in the expressions of other ligands and receptors (PDGF-A, PDGF-B, and PDGFR-β). Recurrent tumors displayed a higher angiogenic potential starting from the fifth day of corneal angiogenesis assay. CONCLUSIONThese findings suggest a relationship between recurrence of craniopharyngiomas and angiogenesis. New treatment modalities with selective PDGFR-α blockers may represent a novel and effective therapeutic option for the treatment of craniopharyngiomas.

Identification of novel neutralizing single-chain antibodies against vascular endothelial growth factor receptor 2.

Human vascular endothelial growth factor (VEGF) and its receptor (VEGFR‐2/kinase domain receptor [KDR]) play a crucial role in angiogenesis, which makes the VEGFR‐2 signaling pathway a major target for therapeutic applications. In this study, a single‐chain antibody phage display library was constructed from spleen cells of mice immunized with recombinant human soluble extracellular VEGFR‐2/KDR consisting of all seven extracellular domains (sKDR D1–7) to obtain antibodies that block VEGF binding to VEGFR‐2. Two specific single‐chain antibodies (KDR1.3 and KDR2.6) that recognized human VEGFR‐2 were selected; diversity analysis of the clones was performed by BstNI fingerprinting and nucleotide sequencing. The single‐chain variable fragments (scFvs) were expressed in soluble form and specificity of interactions between affinity purified scFvs and VEGFR‐2 was confirmed by ELISA. Binding of the recombinant antibodies for VEGFR‐2 receptors was investigated by surface plasmon resonance spectroscopy. In vitro cell culture assays showed that KDR1.3 and KDR2.6 scFvs significantly suppressed the mitogenic response of human umbilical vein endothelial cells to recombinant human VEGF165 in a dose‐dependent manner, and reduced VEGF‐dependent cell proliferation by 60% and 40%, respectively. In vivo analysis of these recombinant antibodies in a rat cornea angiogenesis model revealed that both antibodies suppressed the development of new corneal vessels (p < 0.05). Overall, in vitro and in vivo results disclose strong interactions of KDR1.3 and KDR2.6 scFvs with VEGFR‐2. These findings indicate that KDR1.3 and KDR2.6 scFvs are promising antiangiogenic therapeutic agents.

Relationship of angiogenic potential with clinical features in cranial meningiomas: a corneal angiogenesis study.

BACKGROUND: Intracranial meningiomas constitute approximately one fourth of all primary intracranial tumors. The invention of cranial angiographic techniques has led to the recognition of the angiogenic potential of meningiomas, which has been the subject of extensive research. OBJECTIVE: To test the relationship between the angiogenetic potential of intracranial meningiomas and clinical/prognostic features such as World Health Organization (WHO) grade, peritumoral edema, tumor border shape, and recurrence using rat corneal angiogenesis assay. METHODS: Fifteen WHO grade I (typical), 10 WHO grade II (atypical), and 5 WHO grade III (malignant) meningioma samples were implanted in the micropockets formed on rat corneas, and the number of developed vessels were counted on days 5, 10, 15, and 20. Normal brain and glioblastoma multiforme tissues served as negative and positive controls, respectively. Patients were evaluated by magnetic resonance imaging preoperatively and every 6 months thereafter. RESULTS: The angiogenic potential of WHO grade II tumors was significantly lower than that of grade III tumors and higher than that of grade I tumors throughout the experiment. Tumors with a smooth border shape and nonrecurrent tumors exhibited significantly lower angiogenic activity compared with the tumors with irregular border shape and recurrent tumors, respectively. No association was found between angiogenic activity and peritumoral edema. However, multivariate analysis identified WHO grade, recurrence, and peritumoral edema as significant predictors of a high angiogenic potential. CONCLUSION: Our findings, based on a dynamic in vivo model to examine angiogenesis, demonstrate that the angiogenic potential of meningiomas is correlated with WHO grade, recurrence, and possibly with tumor border shape and peritumoral edema. Angiogenesis seems to be an important factor in the natural course of meningiomas, suggesting that inhibition of angiogenesis may be an option, particularly in the treatment of meningiomas with an aggressive course.

Assessment of antiangiogenic effect of imatinib mesylate on vestibular schwannoma tumors using in vivo corneal angiogenesis assay

OBJECT Angiogenesis and the platelet-derived growth factor (PDGF) pathway are active in the pathogenesis of vestibular schwannomas (VSs). The purpose of this study was to test whether imatinib mesylate (Gleevec), a PDGF receptor (PDGFR) blocker, reduces angiogenic capacity in sporadic VS and in VS associated with neurofibromatosis Type 2 (NF2) using a corneal angiogenesis assay. METHODS From 121 VS tissue samples stored in the tumor bank at the Marmara University Institute of Neurological Sciences, 10 samples (6 from sporadic cases, 4 from NF2-associated cases) were selected at random for use in this study. Expression of PDGF-A and PDGF-B and their receptors was evaluated in sporadic and NF2-associated VS as well as in glioblastoma (GBM) and normal brain tissue by means of immunohistochemistry and Western blot analysis. Corneal angiogenesis assay was then used to evaluate the angiogenic capacity of tissue specimens from sporadic and NF2-associated VS with and without imatinib treatment as well as positive and negative controls (GBM and normal brain tissue). RESULTS The angiogenic potential of the sporadic and NF2-associated VS tumor tissue differed significantly from that of the positive and negative control tissues (p <0.05). Furthermore, NF2-associated VS showed significantly lower angiogenic potential than sporadic VS (p <0.05). Imatinib treatment significantly reduced the angiogenic potential in both the sporadic VS and the NF2-associated VS groups. The level of PDGF-A and PDGFR-α as well as PDGF-B and PDGFR-β expression in sporadic VS and NF2-associated VS also differed significantly (p <0.05) from the levels in controls. Additionally the level of PDGFR-β was significantly higher in sporadic VS than in NF2-associated VS (p <0.05). CONCLUSIONS The findings of this study indicate that NF2-associated VS has significantly more angiogenic potential than sporadic VS and normal brain tissue. Additionally, imatinib reduces the angiogenic activity of both sporadic and NF2-associated VS. The authors conclude that imatinib may be a potential treatment for VS, especially for NF2-associated lesions that cannot be cured with resection or radiosurgery.

Abstract A30: Investigation of imatinib mesylate effect on vestibular schwannoma tumor by using in vivo corneal angiogenesis model

Objective: Vestibular schwannomas (VSs) are histologically benign, encapsulated, and slow growing tumors that arise from Schwann cells of the vestibular branch of eighth of twelve cranial nerves (Vestibulo-cochlear nerve) that is located next to porus acusticus internus. The tested hypothesis was that gleevec reduces angiogenic capacity in patients with VSs and NF-2 associated schwannomas by using corneal angiogenesis assay. This in vivo therapeutic efficacy might induce new clinical trials in the treatment of VSs and add a medical treatment option in the armamentarium. Methods: A total of 121 patients were treated by microsurgical VS resection at the School of Medicine, Neurosurgery Department and Institute of Neurological Sciences of Marmara University, Istanbul, Turkey between 1988–2009. Randomly selected 10 (6 sporadic VS, 4 NF-2 associated VS) samples were used. Angiogenic potential of VS and NF-2 associated VSs tumors in response to imatinib were compared with the healthy subjects by using immunohistochemistry, western blot and corneal angiogenesis assay. Results: Positive and negative control tissues showed significantly higher and lower angiogenic potential (p Conclusion: The results of the present study indicate that NF-2 associated VSs showed significantly higher angiogenic potential than sporadic VSs. Moreoever, both sporadic and NF-2 associated VSs had significantly higher angiogenic potential compared with normal brain tissue. We conclude that, in the treatment of VS and NF-2 tumors, imatinib is an alternative approach to surgical resection and radiosurgery. Citation Information: Cancer Prev Res 2011;4(10 Suppl):A30.

Abstract B48: Inhibition of recurrence of craniopharyngiomas with imatinib mesylate-loaded poly(lactide-co-glycolide) (PLGA) microspheres

Background: Recurrence is highly seen in craniopharyngiomas. Due to their close proximity to the vital structures, gross-total resection, which is thought to be the major determinant of the recurrence, is not always possible for craniopharyngiomas. So, post-operative long-term effective therapy approaches are needed to prevent the recurrence. Besides, our recent studies showed that there is a positive correlation between the recurrence and angiogenic potential of craniopharyngioma through over activation of PDGF (platelet-derived growth factor) signaling pathway. Objective: In this study, we aimed to investigate the inhibitory potential of local, long-term delivery of imatinib mesylate (PDGFR-B blocker) on recurrence of adult craniopharyngiomas via PLGA-type biodegradable microspheres. Methods: Imatinib mesylate containing PLGA polymers composed of different lactic/glycolic acid concentrations, molecular weights and drug compositions were synthesized by modified double emulsion/solvent evaporation technique. After in vitro characterization of protein holding, surface morphology, entrapment efficiency and drug release kinetics, inhibitory potential of microspheres on neovascularization was tested on craniopharyngioma tumor samples implanted in rat cornea. Results: Imatinib containing PLGA microspheres in different LA:GA ratios (LA:GA, 50:50 (M38); 75:25(M70); 85:15(M71)) considerably reduced the neovascularization induced by recurrent tumor samples in an in vivo rat cornea angiogenesis model, p Conclusion: Long-term, local delivery of imatinib mesylate to the post-surgical tumoral cavity using biodegradable microspheres is promising approach to prevent the recurrence of craniopharyngiomas. Citation Information: Cancer Prev Res 2011;4(10 Suppl):B48.