Denbinobin, Moscatilin 及 Cucurbitacin B 在人類結腸直腸癌引起細胞凋亡作用機轉之探討

Abstract

Natural products and their bio-active chemical derivatives have historically been invaluable as a source of novel cancer therapeutic agents. In recent decades, almost half of small-molecule New Chemical Entities (NCEs) were originally from natural products and their derivatives. To use natural products as a rich source of new drug development is a potential trend in the worldwide. In this thesis, we found denbinobin and moscatilin, isolated form traditional Chinese medicine - Herba dendrobii, were effective against the human colorectal cancer cells in vitro and in vivo. Cucurbitacin B, isolated from Begonia nantoensis, can induce apoptosis in human colorectal HT-29 cells. In this thesis, we study if these natural components can be new drugs against human colorectal cancer. Denbinobin, a phenanthraquinone derivative isolated from the stems of Ephemerantha lonchophylla, induces apoptosis in human colon cancer HCT-116 cells. Interestingly, denbinobin induces apoptosis via caspase-independent pathway in HCT-116 cells. Denbinobin triggered the translocation of apoptosis-inducing factor (AIF) from the mitochondria into the nucleus. Denbinobin treatment also caused DNA damage, activation of the p53 tumor suppressor gene, and upregulation of numerous downstream effectors. A HCT-116 xenograft model demonstrated the in vivo efficacy and low toxicity of denbinobin. Taken together, our findings suggest that denbinobin induces apoptosis of human colorectal cancer HCT-116 cells via DNA damage and an AIF-mediated pathway. These results indicate that denbinobin has potential as a novel anti-cancer agent. Moscatilin, purified from the stem of the orchid (Dendrobrium loddigesii), induces apoptosis of human colorectal cancer HCT-116 cells. Moscatilin induced arrest of the cell-cycle at G2/M, with an associated decrease in cells at the G1 and an increase of cells at subG1. In addition, Moscatilin inhibited tubulin polymerization, suggesting that that it might bind to tubulins. Moscatilin also induced the phosphorylation of JNK1/2 and c-Jun, and this may contribute to caspase-dependent apoptosis signaling. Moreover, moscatilin induces DNA damage, activation of p53, and activation of the downstream effector p21WAF1/CIP1. A HCT-116 xenograft model demonstrated the in vivo efficacy and low toxicity of moscatilin. In summary, our results suggest that moscatilin induces apoptosis of colorectal HCT-116 cells via tubulin depolymerization and DNA damage stress and that this leads to the activation of JNK and mitochondria-involved intrinsic apoptosis pathway. These results indicate that moscatilin has potential as a novel anti-cancer agent. Cucurbitacin B, a triterpenoid isolated from Begonia nantoensis, induces apoptosis of human colorectal cancer HT-29 cells at low concentration. Cucurbitacin B reduced mitochondrial membrane potential, induced Bcl-xL phosphorylation, and reduced expression of Mcl-1. Cucurbitacin B-induced apoptosis of HT-29 cells was dependent on activation of the extrinsic and intrinsic apoptosis pathways, as indicated by its activation and processing of procaspase-8, -9, -3, -6 and PARP. Cucurbitacin B blocked HT-29 cells at the G1 phase, elevated the levels of p21WAF1/CIP1 and p27KIP1, and suppressed expression of CDK2, CDK4, and cyclin E. Cucurbitacin B significantly activated MAPKs (ERK, p38, JNK) and Akt, but inhibited STAT3 phosphorylation. Taken together, the results of our studies of HT-29 cells provide insight to the cucurbitacin B-induced arrest of cells at the G1 phase and the apoptosis of these cells.