Department of Neurological Surgery, The Ohio State University Medical Center, Columbus, Ohio, United States of America.
Department of Neurological Surgery, The Ohio State University Medical Center, Columbus, Ohio, United States of America; Departments of Neurosurgery, Beijing Sanbo Brain Hospital, Capital Medical University, Beijing, China.
PLoS One. 2014 Apr 16;9(4):e92546. doi: 10.1371/journal.pone.0092546. eCollection 2014.
Glioblastoma multiforme (GBM) is a highly lethal brain tumor. Due to resistance to current therapies, patient prognosis remains poor and development of novel and effective GBM therapy is crucial. Glioma stem cells (GSCs) have gained attention as a therapeutic target in GBM due to their relative resistance to current therapies and potent tumor-initiating ability. Previously, we identified that the mitotic kinase maternal embryonic leucine-zipper kinase (MELK) is highly expressed in GBM tissues, specifically in GSCs, and its expression is inversely correlated with the post-surgical survival period of GBM patients. In addition, patient-derived GSCs depend on MELK for their survival and growth both in vitro and in vivo. Here, we demonstrate evidence that the role of MELK in the GSC survival is specifically dependent on its kinase activity. With in silico structure-based analysis for protein-compound interaction, we identified the small molecule Compound 1 (C1) is predicted to bind to the kinase-active site of MELK protein. Elimination of MELK kinase activity was confirmed by in vitro kinase assay in nano-molar concentrations. When patient-derived GSCs were treated with C1, they underwent mitotic arrest and subsequent cellular apoptosis in vitro, a phenotype identical to that observed with shRNA-mediated MELK knockdown. In addition, C1 treatment strongly induced tumor cell apoptosis in slice cultures of GBM surgical specimens and attenuated growth of mouse intracranial tumors derived from GSCs in a dose-dependent manner. Lastly, C1 treatment sensitizes GSCs to radiation treatment. Collectively, these data indicate that targeting MELK kinase activity is a promising approach to attenuate GBM growth by eliminating GSCs in tumors.
多形性胶质母细胞瘤（GBM）是一种高度致命的脑肿瘤。由于对现有治疗方法的耐药性，患者的预后仍然很差，因此开发新的有效的 GBM 治疗方法至关重要。神经胶质瘤干细胞（GSCs）由于对现有治疗方法的相对耐药性和强大的肿瘤起始能力，已成为 GBM 的治疗靶点。以前，我们发现有丝分裂激酶母源性胚胎亮氨酸拉链激酶（MELK）在 GBM 组织中高度表达，特别是在 GSCs 中，其表达与 GBM 患者手术后的生存时间呈负相关。此外，患者来源的 GSCs 在体外和体内都依赖 MELK 来生存和生长。在这里，我们证明了 MELK 在 GSC 存活中的作用特别依赖于其激酶活性。通过基于结构的蛋白质-化合物相互作用的计算机模拟分析，我们鉴定出小分子化合物 1（C1）被预测与 MELK 蛋白的激酶活性位点结合。在纳摩尔浓度下通过体外激酶测定证实了 MELK 激酶活性的消除。当患者来源的 GSCs 用 C1 处理时，它们在体外经历有丝分裂停滞和随后的细胞凋亡，这与 shRNA 介导的 MELK 敲低观察到的表型相同。此外，C1 处理强烈诱导 GBM 手术标本切片培养中的肿瘤细胞凋亡，并以剂量依赖性方式减弱源自 GSCs 的小鼠颅内肿瘤的生长。最后，C1 处理使 GSCs 对放射治疗敏感。总之，这些数据表明，靶向 MELK 激酶活性是通过消除肿瘤中的 GSCs 来减弱 GBM 生长的一种很有前途的方法。
