Horiguchi T, Tanida S
Discovery Research Laboratories II, Takeda Chemical Industries, Ltd., Osaka, Japan.
Biochem Pharmacol. 1995 May 17;49(10):1395-401. doi: 10.1016/0006-2952(95)00081-a.
TAN-1518 A is a cytotoxic agent with suppressive activity against Meth A fibrosarcoma in vivo. This compound inhibits calf thymus DNA topoisomerase I (Topo I) but does not stimulate cleavable complex formation in the nuclei of Chinese hamster ovary (CHO)-K1 cells, suggesting that it inhibits Topo I in a manner different from that of camptothecin (CPT). To clarify the mode of action of TAN-1518 A, we examined its effects on the eukaryotic microorganism Schizosaccharomyces pombe (S. pombe), which does not require Topo I as an essential factor for growth. TAN-1518 A inhibited purified S. pombe Topo I as potently as did CPT. TAN-1518 A, unlike CPT, did not stimulate Topo I-induced DNA cleavage; instead, it inhibited CPT-induced cleavable complex formation. We constructed a S. pombe strain, IR9, that produced excess Topo I. IR9 was hypersensitive to CPT, but its growth was not affected by TAN-1518 A. The CPT-mediated death of IR9 cells was reduced dramatically in the presence of TAN-1518 A. These findings clearly demonstrate that TAN-1518 A is a specific inhibitor of Topo I in eukaryotic cells and also suggest that this agent inhibits some earlier step(s) that occurs before the formation of cleavable complex on DNA strands in the catalytic cycle of this enzyme.
TAN - 1518 A是一种在体内对Meth A纤维肉瘤具有抑制活性的细胞毒性剂。该化合物抑制小牛胸腺DNA拓扑异构酶I（Topo I），但不刺激中国仓鼠卵巢（CHO）-K1细胞核中可裂解复合物的形成，这表明它以不同于喜树碱（CPT）的方式抑制Topo I。为了阐明TAN - 1518 A的作用模式，我们研究了它对真核微生物粟酒裂殖酵母（S. pombe）的影响，该微生物生长并不需要Topo I作为必需因子。TAN - 1518 A抑制纯化的粟酒裂殖酵母Topo I的能力与CPT相当。与CPT不同，TAN - 1518 A不刺激Topo I诱导的DNA切割；相反，它抑制CPT诱导的可裂解复合物的形成。我们构建了一个产生过量Topo I的粟酒裂殖酵母菌株IR9。IR9对CPT高度敏感，但其生长不受TAN - 1518 A的影响。在TAN - 1518 A存在的情况下，IR9细胞由CPT介导的死亡显著减少。这些发现清楚地表明TAN - 1518 A是真核细胞中Topo I的特异性抑制剂，也表明该药物抑制了该酶催化循环中在DNA链上形成可裂解复合物之前发生的一些早期步骤。
