Design,Synthesis And Antitumor Activity Of Natural Product-like Inhibitors Of DNA Topoisomerase Ⅱα

DNA topoisomerases are enzymes that regulate the topological structure of DNA and are required for important cellular life processes. The main families of mammalian DNA topoisomerases are topoisomerase Ⅰ (TopoI) and topoisomerase Ⅱ (TopoⅡ). In both cases, enzymes are subclassified into two groups, ⅠA/B and Ⅱα/β, according to their specific structures and mechanisms of action. Monomeric type Ⅰ enzymes modify DNA topology in an ATP independent fashion by creating single strand breaks in DNA. Multimeric type Ⅱ enzymes engender DNA double-strand breaks (DSBs) in an ATP-dependent fashion. Because of the high level and cycle-regulated of TopoⅡ expression in cancer cells, TopoⅡ represents an important target for cancer chemotherapy. TopoⅡ inhibitors such as etoposide (VP16) and doxorubicin (ADR) are clinically effective and routinely used in the treatment of human malignancies. TopoⅡα was highly expressed in tumor cells and related to the development of breast cancer, lung cancer, stomach cancer, lymphoma, colorectal cancer, liver cancer, ovarian cancer and so on, whereas, inhibitory of TopoⅡβ was associated with incidences of life-threatening toxic side effects, including cardiotoxicity and development of secondary malignancies such as leukemia. Novel strategies to target TopoⅡ could represent an efficient approach to the treatment of certain forms of cancers with lower side effects. Therefore, TopoⅡα is an important target for cancer chemotherapy, and the search for novel small molecules directed against TopoⅡα remains an active domain in oncopharmacology.Natural products are continuing sources of new drugs and novel durg leads over years. In our previous study,8 p-terphenyl compounds isolated from the marine fungal strain Aspergillus sp. AF119 were found showing cytotoxicity against MDA-MB-435 cell line. At the same time,5 p-terphenyl compounds were isolated from the marine defense strain Streptomyces sp. LZ35. These nature p-terphenyls showed potent antiproliferative activity and inhibited the catalytic activity of DNA topoisomerases and induced cell-cycle arrest in MDA-MB-435 cells. Therefor, eight new p-terphenyl derivatives H1-H8 were successfully synthesized and their antitumor activities have been evaluated. Biological studies showed that these abbreviate analogues had more potent activities and the activites was directly related with the inhibition of Topo.Based on the above researchs,2-phenylnaphthalenoids was designed through molecular modeling and scaffold hopping principle, using the natural active compounds as templates. Besides,2-phenylbenzofurans and arylnaphthalene lignans were designed and synthesized from 2-phenylnaphthalenoids through scaffold hopping. First, SRB assay was applied to evaluate the antitumor activity of these compounds against various cancer cell lines. To investigate the topoisomerase inhibition activity of these compounds, pBR322 DNA relaxation, kDNA decatenation, DNA intercalation and stabilization of the cleavage complex were employed. And futher distinct mechanisms were studied using western blot assays. Among these compounds, compound A5 induced cell-cycle arrest at G2/M phase prior and showed potent antiproliferative activity against MDA-MB-231 cells and inhibitory activity on TopoIIa as a Topo poison. Further, in vivo antitumor study with xenograft nude mice indicated that compound A5 inhibited the growth of MDA-MB-231 cells and showed lower toxicity than etoposide (VP16). Compound B11 was a dual inhibitor of TopoⅠ and TopoIIa, and showed potent antiproliferative activity. Arylnaphthalene lignans had strong cytotoxic activity, but rarely any Topo inhibitory activities. Their cytotoxic activity was determined by the configuration of lactone ring, the the antero-form ones are moer potent than the retro-form ones. Its targets need to be futher explored.In our previous study, Lycogarubrin C was found showing cytotoxicity and TopoII inhibitory activities. Therefor, several abbreviate analogues were designed and synthesized. The compound D22 was a TopoIIa poison, and showed mild cytotoxic activity.In summary, we successfully designed and synthesized 4 series 162 compounds in this study. And their in vitro cytotoxicities against the proliferations of difference cell lines and inhibitory activities on DNA topoisomerase were evaluated. The outstanding compounds of each series were chosen for further cellular level and in vivo study. This study provides a novel rationale for the development of topoisomerase inhibitors.