抗肿瘤药物---拓扑异构酶I抑制剂的作用机制研究及新型结构设计

DNA topoisomerase I (Topo I) is a promising target of antineoplastic drug research in recent years. The inhibitors acting on this enzyme can selectively inhibit the replication of DNA in the phase of proliferation of tumor cells, and thus kill the tumor cells. Currently, Topo I inhibitors were regarded as one of the six important anticancer drugs in the computerized system of drug mechanism by National Cancer Institute (NCI) in USA. The classical inhibitors of Topo I is camptothecin (CPT) and its derivatives. Previous structural modification studies were performed with the aim to improve the poor solubility and lower toxicity and side effects. Several CPT derivatives have already come into market or clinical trials, such as Topotecan and Irinotecan have already been successfully applied into therapy of many kinds of tumors. However, due to the lack of the understanding of the binding mode of Topo I, DNA and CPT drugs, it is difficult for us to design novel better CPT derivatives. Besides, several specific Topo I inhibitors have already been reported recent years; many studies have confirmed that they share quite different binding site and inhibitory mode. These facts demonstrated further work are in great need in the field of Topo I inhibitors. Based on these facts described above, we systematically sort the currently reported Topo I inhibitors according to drug mechanism and binding site, and performed studies in the two main aspects: 1. The conformation of CPT was optimized by ab initio calculations at the Hartree-Fock level (HF/3-21G and HF/6-31G) as well as by semi-empirical AM1、PM3 calculations and was also compared with X-ray crystallographic studies, which provides a strong methodological basis for the conformational space studies of CPT and structure-activity relationships of its derivatives. Based on these findings, the conformational space of CPT was explored and the importance of intramolecular hydrogen bond existed in the hydroxyl lactone of CPT was elucidated. We have also developed a general model for the ternary drug-DNA-TopoI complex for the CPT derivatives using flexible docking techniques, which is significantly consistent with the current knowledge of experimental mutations that render CPT resistant and structure-activity relationships of CPT derivatives, etc. Quantitative structure-activity relationship (QSAR) studies of A-ring substituted CPT derivatives were examined using both the combination of genetic algorithm and partial least squares (PLS) and modified artificial neural networks, indicating there may exist p~p charge transfer interaction between CPT derivatives and Topo I-DNA complex. The understanding of mechanism of action of CPT with TopoI-DNA complex will benefit future design of novel potent antitumor camptothecin derivatives. Up to date, a series of novel highly potent CPT derivatives have already been designed and synthesized. The synthetic procedure was also optimized. Further synthetic work and the determination of their antineoplastic activity are still in progress. 2. The model of action of several Topo I inhibitors were investigated using molecular docking techniques. Novel selective interaction site for such drugs was obtained using multiple copy simultaneous search (MCSS), etc. Based on these findings, large scale database searching was performed to discover novel lead compounds acting on DNA topoisomerase I. And several drug-like compounds were discovered to have stronger binding with Topo I-DNA complex. Further determination of their inhibitory activity on the target enzyme will aid to elucidate their value in the development of novel antineoplastic drugs. Our work will surely provide a strong basis for the development of novel highly potent, less toxic anticancer drugs.

本实验拟利用计算机辅助药物设计技术对人拓扑异构酶I与DNA复合物的晶体结构进行研究，探讨药物、酶与DNA相互作用机制，确定酶的活性位点，并以此为靶标进行大规模的分子数菘馑蜒凹叭路肿由杓疲贸鲂碌南鹊蓟衔铮铣刹⒔幸置讣翱怪琢龌钚匝橹ぁ