Studies on the Anti-tumor Activities and Action Mechanisms of Banlangen Alkaloids on Human Neuroblastoma Cells

Neuroblastoma, a tumor of the sympathetic nervous system, is the most common extracranial solid cancer in childhood. It accounts for 8% to 10% of all childhood cancers and for approximately 15% of cancer deaths in children. The use of new promising therapeutic compounds derived from natural products or Chinese herbs have attracted much attention of scientist as an alternative strategy in cancer treatment. In my PhD project, the possible anti-tumor activities and action mechanisms of Banlangen alkaloids, including I3M and tryptanthrin, on human neuroblastoma cells were investigated.;Firstly, the anti-cancer effects of I3M on human neuroblastoma cells and the underlying mechanisms were investigated. I3M was found to inhibit the growth of the human neuroblastoma LA-N-1, SH-SY5Y and SK-N-DZ cells in a concentration- and time-dependent manner, but exhibited little, if any, direct cytotoxicity on normal cells. Mechanistic studies showed that I3M specifically decreased the expression of mitochondrial regulators ERRgamma and PGC-1beta and resulted in decreased mitochondrial mass and altered mitochondrial function characterized by reduction in mitochondrial membrane potential and elevation of reactive oxygen species (ROS) level in LA-N-1 cells. The results, when taken together, suggest that I3M might exert its anti-tumor activity by causing mitochondrial dysfunction which led to cell cycle arrest in LA-N-1 cells and resulted in cycle arrest and apoptosis in SH-SY5Y cells.;The anti-tumor effects and action mechanisms of tryptanthrin on the human neuroblastoma cells were also examined. Our results showed that tryptanthrin inhibited the growth of the human neuroblastoma LA-N-1, SH-SY5Y and SK-N-DZ cells in a concentration- and time-dependent manner, but exhibited little, if any, direct cytotoxicity on normal cells. Mechanistic studies indicated that tryptanthrin significantly reduced the protein levels of cyclin D1, cyclin D3, CDK4 and CDK6 leading to cell cycle arrest at G0/G1 phase. In addition, tryptanthrin activated caspase 8, caspase 9 and caspase 3/7 resulting in apoptosis of the human neuroblastoma LA-N-1 cells. These results indicate that tryptanthrin might exert its anti-tumor activity on the human neuroblastoma LA-N-1 cells by inducing cell cycle arrest, apoptosis and neuronal differentiation. It might be exploited as a potential therapeutic candidate for the treatment of high-risk neuroblastomas with N-myc-amplification.;Moreover, the anti-angiogenic activities of I3M and tryptanthrin were studied. Our results showed that I3M and tryptanthrin inhibited the proliferation, migration, and tube formation of the human microvascular endothelial HMEC-1 cells in vitro in a concentration-dependent manner but exhibited no significant cytotoxicity on these cells. Moreover, I3M and tryptanthrin markedly suppressed the in vivo angiogenesis in Matrigel plugs in mice. Mechanistic studies indicated that I3M down-regulated the expression of Ang-1 and MMP2 and up-regulated the expression of Ang-2. Our results demonstrated that I3M and tryptanthrin exhibited anti-angiogenic activity both in vitro and in vivo by specifically targeting the VEGFR2-mediated signaling pathways and might be exploited as potential therapeutic candidates for the treatment of angiogenesis-related diseases.;In conclusion, our findings indicate that I3M and tryptanthrin might exert their growth-inhibitory effect on the human neuroblastoma cells by causing cell cycle arrest, inducing apoptosis or inducing neuronal differentiation. However, they exhibited minimal cytotoxicity towards the normal cells. Moreover, I3M and tryptanthrin were found to possess anti-angiogenic activities by targeting the VEGFR2-mediated signaling pathways. In the future, investigations should be focused on further elucidation of the molecular action mechanisms of I3M and tryptanthrin on human neuroblastoma cells and to test the anti-tumor efficacy of I3M and tryptanthrin in animal models, using human neuroblastoma xenografts in nude mice. (Abstract shortened by UMI.).