McDaid H M, Bhattacharya S K, Chen X T, He L, Shen H J, Gutteridge C E, Horwitz S B, Danishefsky S J
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Cancer Chemother Pharmacol. 1999;44(2):131-7. doi: 10.1007/s002800050957.
Eleutherobin, a natural product, is an antimitotic agent that promotes the polymerization of stable microtubules. Although its mechanism of action is similar to that of Taxol, its structure is distinct. A structure-activity profile of synthetic eleutherobin derivatives that have modifications at C3, C8 and C15 was undertaken to define the structural requirements for microtubule stabilization and cross-resistance in Taxol-resistant cell lines.
The biological activity of five eleutherobin analogs was assessed using three techniques: (1) cytotoxicity and drug-resistance in three paired Taxol-sensitive and -resistant cell lines; (2) polymerization of microtubule protein in vitro in the absence of GTP and (3) induction of microtubule bundle formation in NIH3T3 cells.
Eleutherobin had an IC50 value comparable to that of Taxol, whereas neoeleutherobin, which has a carbohydrate domain that is enantiomeric with that of the parent compound, was less cytotoxic and had 69% of the maximum microtubule polymerization ability of eleutherobin. Both of these compounds exhibited cross-resistance in MDRI-expressing cell lines. Removal or replacement of the C15 sugar moiety resulted in reduced microtubule polymerization and cytotoxicity compared to eleutherobin and loss of cross-resistance in the cell lines SKVLB and J7-T3-1.6, both of which express high levels of P-glycoprotein. By contrast, removal of the urocanic acid group at C8 resulted in virtually complete abrogation of biological activity. The compound lost its ability to polymerize microtubules, and its cytotoxicity was reduced by a minimum of 2000-fold in lung carcinoma A549 cells.
Removal or modification of the sugar moiety alters the cytotoxic potency of eleutherobin and its pattern of cross-resistance in Taxol-resistant cells, although such compounds retain a small percentage of the microtubule-stabilizing activity of eleutherobin. The N(1)-methylurocanic acid moiety of eleutherobin, or perhaps some other substituent at the C8 position, is essential for Taxol-like activity. These findings will be important for the future design and the synthesis of new and more potent eleutherobin derivatives.
天然产物刺参苷是一种抗有丝分裂剂，可促进稳定微管的聚合。尽管其作用机制与紫杉醇相似，但其结构不同。对在C3、C8和C15处有修饰的合成刺参苷衍生物进行结构 - 活性分析，以确定在耐紫杉醇细胞系中微管稳定和交叉耐药的结构要求。
使用三种技术评估了五种刺参苷类似物的生物活性：（1）在三对紫杉醇敏感和耐药细胞系中的细胞毒性和耐药性；（2）在无GTP的情况下体外微管蛋白的聚合；（3）在NIH3T3细胞中诱导微管束形成。
刺参苷的IC50值与紫杉醇相当，而新刺参苷具有与母体化合物对映体的碳水化合物结构域，其细胞毒性较小，微管聚合最大能力为刺参苷的69%。这两种化合物在表达MDRI的细胞系中均表现出交叉耐药性。与刺参苷相比，去除或取代C15糖部分导致微管聚合和细胞毒性降低，并且在SKVLB和J7 - T3 - 1.6细胞系中失去交叉耐药性，这两种细胞系均高表达P - 糖蛋白。相比之下，去除C8处的尿刊酸基团导致生物活性几乎完全丧失。该化合物失去了聚合微管的能力，并且在肺癌A549细胞中其细胞毒性至少降低了2000倍。
糖部分的去除或修饰改变了刺参苷在耐紫杉醇细胞中的细胞毒性效力及其交叉耐药模式，尽管此类化合物保留了刺参苷微管稳定活性的一小部分。刺参苷的N(1)-甲基尿刊酸部分，或者可能是C8位置的一些其他取代基，对于紫杉醇样活性至关重要。这些发现对于未来设计和合成新的、更有效的刺参苷衍生物将具有重要意义。
