Fulda S, Jeremias I, Steiner H H, Pietsch T, Debatin K M
University Children's Hospital, Ulm, Germany.
Int J Cancer. 1999 Jul 30;82(3):435-41. doi: 10.1002/(sici)1097-0215(19990730)82:3<435::aid-ijc18>3.0.co;2-1.
Malignant brain tumors are the most common solid tumors in children. The overall prognosis for this group of patients is still poor, emphasizing the importance of more effective therapies. Betulinic acid (Bet A) has been described as a novel cytotoxic compound active against melanoma and neuroblastoma cells. Here we report that Bet A was active against medulloblastoma and glioblastoma cell lines. In addition, Bet A exerted cytotoxic activity against primary tumor cells cultured from patients in 4 of 4 medulloblastoma-tumor samples tested and in 20 of 24 glioblastoma-tumor samples. Since a small percentage of primary-glioblastoma-tumor cells (4/24) did not respond to Bet-A treatment, resistance to Bet A might occur. Induction of apoptosis by Bet A involved mitochondrial perturbations, since inhibition of the mitochondrial permeability transition by the mitochondrion-specific inhibitor bongkrekic acid (BA) reduced Bet-A-induced apoptosis. In addition, mitochondria undergoing Bet-A-induced permeability transition triggered DNA fragmentation in isolated nuclei. Cytochrome c was released from mitochondria of Bet-A-treated cells, and might be involved in activation of caspases. Following treatment with Bet A, caspase-8, caspase-3 and PARP were proteolytically processed. Inhibition of caspase cleavage by the broad-range caspase inhibitor zVAD.fmk strongly reduced Bet-A-induced apoptosis, indicating that apoptosis was mediated by activation of caspases. Since Bet A did not exhibit cytotoxicity against murine neuronal cells in vitro, these findings suggest that Bet A may be a promising new agent for the treatment of medulloblastoma and glioblastoma cells that clearly warrants further pre-clinical and clinical evaluation.
恶性脑肿瘤是儿童中最常见的实体瘤。这组患者的总体预后仍然很差，这凸显了更有效治疗方法的重要性。桦木酸（Bet A）已被描述为一种对黑色素瘤和神经母细胞瘤细胞具有活性的新型细胞毒性化合物。在此我们报告，Bet A对髓母细胞瘤和胶质母细胞瘤细胞系具有活性。此外，在4个测试的髓母细胞瘤肿瘤样本中的4个以及24个胶质母细胞瘤肿瘤样本中的20个中，Bet A对从患者培养的原发性肿瘤细胞具有细胞毒性活性。由于一小部分原发性胶质母细胞瘤肿瘤细胞（4/24）对Bet-A治疗无反应，可能会出现对Bet A的耐药性。Bet A诱导的细胞凋亡涉及线粒体扰动，因为线粒体特异性抑制剂邦克雷酸（BA）抑制线粒体通透性转换可减少Bet-A诱导的细胞凋亡。此外，经历Bet-A诱导的通透性转换的线粒体触发了分离细胞核中的DNA片段化。细胞色素c从Bet-A处理的细胞的线粒体中释放出来，可能参与了半胱天冬酶的激活。用Bet A处理后，半胱天冬酶-8、半胱天冬酶-3和PARP被蛋白水解加工。广谱半胱天冬酶抑制剂zVAD.fmk抑制半胱天冬酶切割可强烈减少Bet-A诱导的细胞凋亡，表明细胞凋亡是由半胱天冬酶的激活介导的。由于Bet A在体外对小鼠神经元细胞未表现出细胞毒性，这些发现表明Bet A可能是一种有前途的新型药物，用于治疗髓母细胞瘤和胶质母细胞瘤细胞，显然值得进一步的临床前和临床评估。
