Search for Novel Anti-cancer Drugs Targetting DNA Replication and Repair

我们使用无细胞系统对放线菌和真菌菌进行SV40 DNA复制和紫外照射SV40小染色体核苷酸切除修复（NER）的培养上清液进行筛选，获得DNA复制和修复的抑制剂或刺激物。作为这些筛选的结果，我们获得了一些复制抑制剂和NER抑制剂的样品。纯化了其中一个复制抑制剂RK606，其结构鉴定为大豆皂苷（soyasaponin II）的一种。RK606还可以抑制SV40 DNA与纯化蛋白的复制，因此，我们研究了RK606对单个酶和蛋白的影响。结果表明，RK606特异性抑制sv40t抗原的DNA解旋酶活性。有趣的是，细胞DNA解旋酶未被该化合物抑制，这表明RK606可能是T抗原解旋酶的特异性抑制剂。据我们所知，这是除ATP类似物外的第一个DNA解旋酶抑制剂。研究了其中一种修复抑制剂RK679在不同pH下的稳定性和几种溶剂的可萃取性。修复抑制剂的行为与某些酪氨酸激酶抑制剂染料木素和大豆苷元的行为相似，因此，我们检查了这些酪氨酸激酶抑制剂对无细胞NER的影响。然而，我们没有发现这些化合物对NER有任何影响，这表明RK679既不是染料木素也不是大豆苷元，而是不同的化合物。

We have screened more than one hundred of culture supernatants of Actinomycetes and Eumycetes using cell-free systems for SV40 DNA replication and the nucleotide excision repair (NER) with UV-irradiated SV40 minichromosomes to obtain either inhibitors or stimulators for DNA replication and repair. As s result of these screening, we obtained a couple of samples for replication inhibitors and NER inhibitors.One of the replication inhibitors (RK606) was purified, and its structure was identified as a kind of soybean saponin (soyasaponin II). RK606 also inhibited SV40 DNA replication with purified proteins, therefore, we examined the effect of RK606 on individual enzymes and proteins. It turned out that RK606 specifically inhibited DNA helicase activity of SV40 T antigen. Interestingly, a cellular DNA helicase was not inhibited by this compound, indicating that RK606 might be a specific inhibitor of T antigen helicase. To our knowledge, this is the first inhibitor besides ATP analogues for any DNA helicase.One of the repair inhibitors (RK679) was examined for its stability at different pH and for its extractability by several solvents. The behaviors of the repair inhibitor were similar to those of some kinds of tyrosine kinase inhibitors, genistein and daizein, therefore, we checked the effect of these tyrosine kinase inhibitors on cell-free NER assay. However, we could not find any effect of these compounds on NER,suggesting that RK679 is not either genistein or daizein but is rather different compound.