SCF as a Novel CNS and Glioma-Derived Angiogenic Factor and SC Chemotaxic Factor

在正常情况下，正常大脑中很少或没有检测到SCF表达; 然而，我们发现它在神经胶质瘤细胞系和神经胶质瘤中均以高水平表达 与非肿瘤脑相比。此外，在统计学上， 高级别胶质瘤与低级别胶质瘤中SCF表达水平的比较。由于高等级 神经胶质瘤的特征在于与神经胶质瘤相比， 在低级别胶质瘤中，SCF的表达与胶质瘤级别的增加呈正相关， 与SCF在胶质瘤相关血管生成中的潜在作用一致。我们有 表明SCF受体c-Kit表达于所有内皮细胞表面， 细胞（EC）检测，并在基础培养基中暴露于SCF的BMVEC-b，HUVEC和HMVEC-d 导致胸苷掺入和细胞增殖在所有3个EC系中， 剂量依赖性方式，即使在低浓度下，在没有其他细胞因子， VEGF。SCF还在体外伤口愈合试验中诱导EC迁移和分化， 毛细管形成测定。这些数据表明SCF能够诱导 BMVEC-b的增殖、迁移和分化。接下来我们皮下注射 将浸渍有SCF、b-FGF（阳性对照）或单独的载体的基质胶植入到 成年SCID小鼠。结果表明，SCF在体内可促进血管生成。通过 我们也用类似的技术证明了在胶质瘤细胞中抑制SCF会导致 显著抑制体内胶质瘤诱导的血管生成。接下来，我们评估了 SCF的抑制将影响患有颅内胶质瘤的动物的存活。U373/as-SCF 或U373/vector细胞立体定向植入成年大鼠大脑皮层下， 无胸腺nu/nu小鼠。Kaplan-Meier生存曲线的对数秩分析表明， 与U373/载体相比，携带U373/as-SCF的小鼠具有显著的存活优势 对照荷瘤动物（P 0.05），尽管两者的生长率< 体外培养的细胞类型相同。为了在实际肿瘤样本中证实这些结果， 胶质母细胞瘤多例手术标本免疫组化分析 发现SCF在脑胶质瘤细胞继发浸润的大脑皮层中有大量表达， 与肿瘤和神经元相关的SCF表达有关。总之，SCF表达似乎 在浸润性胶质瘤的侵袭性前部最为突出，表明其作用 在肿瘤的发展过程中。鉴于我们的数据表明SCF在肿瘤和宿主中的重要性， 细胞诱导的血管生成，我们假设，以前未被认识到，但主要的抗肿瘤 Gleevec的作用机制可能是作为一种抗血管生成剂， 抑制c-kit信号传导。因此，我们开始了一系列的体内实验， 在我们的原位胶质瘤模型中，研究格列卫对胶质瘤介导的血管生成的影响。 因此，我们将着手进行一系列临床前研究，评估格列卫与 与特异性VEGF抑制剂（LY317615，Avastin等）。格列卫渗透性差 然而，通过完整的血脑屏障，也将迫使我们筛选其他酪氨酸 具有抗c-kit活性但可能具有更有利的 药代动力学

Under normal conditions, little or no SCF expression is detectable in normal cerebrum; however we found it to be expressed at high levels both in glioma cells lines and in gliomas when compared to non-tumor brain. Additionally, there was a statistically significant higher level of SCF expression in high-grade gliomas compared to low-grade gliomas. Since high-grade gliomas are characterized by a much greater amount of tumor-associated angiogenesis compared to low-grade gliomas, the positive correlation of SCF expression with increasing glioma grade is consistent with a potential role for SCF in glioma-associated angiogenesis. We have demonstrated that the SCF receptor, c-Kit, is expressed on the surface of all endothelial cells (ECs) examined and that exposure of BMVEC-b, HUVEC and HMVEC-d in basal medium to SCF resulted in thymidine incorporation and cellular proliferation in all 3 EC lines in a dose-dependent manner even at low concentrations in the absence of other cytokines such as VEGF. SCF also induced EC migration and differentiation in an in vitro wound healing assay and capillary tube formation assay. These data demonstrated the ability of SCF to induce proliferation, migration and differentiation of BMVEC-b in vitro. We next subcutaneously implanted Matrigel impregnated with SCF, b-FGF (positive control) or vehicle alone into the adult SCID mice. The data obtained demonstrated that SCF can promote angiogenesis in vivo. By a similar technology we also demonstrated that suppression of SCF in glioma cells results in significant inhibition of glioma-induced angiogenesis in vivo. We next evaluated whether suppression of SCF would effect the survival of animals with intracranial gliomas. U373/as-SCF or U373/vector cells were stereotactically implanted to the cerebral subcortex of adult athymic nu/nu mice. Log-rank analysis of the Kaplan-Meier survival curves demonstrated a significant survival advantage for the U373/as-SCF bearing mice compared to the U373/vector control bearing animals (P<0.05), despite the fact that the growth rate of both cells types in vitro was identical. To confirm these results in actual tumor samples, immunohistochemical analysis of multiple surgical specimens from patients with glioblastoma revealed profound expression of SCF in cerebral cortex infiltrated by glioma cells secondary to both tumor-and neuronal-associated SCF expression. In summary, SCF expression appears to reside most prominently in the invasive front of the infiltrating glioma, suggesting its roles in the tumor progression. Given our data demonstrating the importance of SCF in tumor and host cell-induced angiogenesis, we hypothesize that a previously unrecognized, but major anti-tumor mechanism of Gleevec may be as an anti-angiogenic agent through its ability to potently inhibit c-kit signaling. We have therefore embarked on a series of in vivo experiments to look at the effects of Gleevec on glioma-mediated angiogenesis in our orthotopic glioma models. Thus, we will embark on a series of preclinical studies evaluating the combination of Gleevec with specific VEGF inhibitors (LY317615, Avastin, etc.). The poor penetration of Gleevec through an intact blood-brain barrier, however, will also force us to screen other tyrosine kinase inhibitors that have activity against c-kit but may have more favorable pharmacokinetics.