su-1498 and Glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive type of primary brain tumor with grave prognosis. Despite the growing understanding of the complex signaling networks responsible for the initiation and progression of GBM, many experimental therapies have fallen short of their treatment goals. In the present study, we investigated the novel molecular mechanisms responsible for synergistic action of temozolomide (TMZ) and anti-VEGF therapy in GBM cells. We tested the combined effects of TMZ and VEGF blockade in four human GBM cell lines: TMZ-sensitive U251-MG and U373-MG cells, and TMZ-resistant CRT-MG and LN215-MG cells, which correlated with MGMT promoter methylation status. Treatment of TMZ along with a sublethal dosage range of SU1498, a chemical inhibitor of the VEGF receptor signaling, induced significant cell death in both TMZ-sensitive and TMZ-resistant GBM cells without changing the status of the MGMT promoter methylation. Treatment with TMZ specifically reduced the expression of NRP-1, a coreceptor of VEGF but not those of VEGF-R1 and VEGF-R2. We further confirmed the key role of NRP-1 by showing that the reduction of NRP-1 by siRNA also increased the SU1498-induced cytotoxicity of LN215-MG. These results collectively indicate that combined treatment of TMZ can sensitize GBM cells to blockade of autocrine VEGF signaling through specific down-regulation of NRP-1, which provide a rationale for further evaluation and a potential clinical trial of combinatorial therapy of TMZ and SU1498 or other VEGF inhibitors for intractable brain tumors.

Topics: Antineoplastic Agents; Cell Death; Cell Line, Tumor; Cell Survival; Cinnamates; Dacarbazine; DNA Methylation; DNA Modification Methylases; DNA Repair Enzymes; Down-Regulation; Glioblastoma; Humans; Neuropilin-1; Promoter Regions, Genetic; RNA, Small Interfering; Temozolomide; Tumor Suppressor Proteins; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-2

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.

Topics: Animals; Cell Line, Tumor; Cinnamates; Fluorescent Antibody Technique; Glioblastoma; Humans; Immunoblotting; Immunohistochemistry; Mice; Neovascularization, Pathologic; RNA, Small Interfering; Vascular Endothelial Growth Factor Receptor-2; Xenograft Model Antitumor Assays

Leptin is a pleiotropic hormone whose mitogenic and angiogenic activity has been implicated in the development and progression of several malignancies, including brain tumors. In human brain cancer, especially in glioblastoma multiforme (GBM), leptin and its receptor (ObR) are overexpressed relative to normal tissue. Until present, the potential of intratumoral leptin to exert proangiogenic effects on endothelial cells has not been addressed. Using in vitro models, we investigated if GBM can express leptin, if leptin can affect angiogenic and mitogenic potential of endothelial cells, and if its action can be inhibited with specific ObR antagonists. Leptin effects were compared with that induced by the best-characterized angiogenic regulator, VEGF.. We found that GBM cell lines LN18 and LN229 express leptin mRNA and LN18 cells secrete detectable amounts of leptin protein. Both lines also expressed and secreted VEGF. The conditioned medium (CM) of LN18 and LN 229 cultures as well as 200 ng/mL pure leptin or 50 ng/mL pure VEGF stimulated proliferation of human umbilical vein endothelial cells (HUVEC) at 24 h of treatment. Mitogenic effects of CM were ~2-fold greater than that of pure growth factors. Furthermore, CM treatment of HUVEC for 24 h increased tube formation by ~5.5-fold, while leptin increased tube formation by ~ 80% and VEGF by ~60% at 8 h. The mitogenic and angiogenic effects of both CM were blocked by Aca 1, a peptide ObR antagonist, and by SU1498, which inhibits the VEGF receptor. The best anti-angiogenic and cytostatic effects of Aca1 were obtained with 10 nM and 25 nM, respectively, while for SU1498, the best growth and angiogenic inhibition was observed at 5 μM. The combination of 5 μM SU1498 and Aca1 at 25 nM (growth inhibition) or at 10 nM (reduction of tube formation) produced superior effects compared with single agent treatments.. Our data provide the first evidence that LN18 and LN 229 human GBM cells express leptin mRNA and might produce biologically active leptin, which can stimulate tube formation and enhance proliferation of endothelial cells. Furthermore, we demonstrate for the first time that a peptide ObR antagonist inhibits proangiogenic and growth effects of leptin on endothelial cells, and that the pharmacological potential of this compound might be combined with drugs targeting the VEGF pathway.

Topics: Angiogenesis Inhibitors; Cell Division; Cell Line, Tumor; Cells, Cultured; Cinnamates; Culture Media, Conditioned; Endothelial Cells; Gene Expression Regulation, Neoplastic; Glioblastoma; Humans; In Vitro Techniques; Leptin; Morphogenesis; Neoplasm Proteins; Neovascularization, Pathologic; Oligopeptides; Receptors, Leptin; Receptors, Vascular Endothelial Growth Factor; RNA, Messenger; RNA, Neoplasm; Signal Transduction; Umbilical Cord; Up-Regulation; Vascular Endothelial Growth Factor A