Bai R L, Paull K D, Herald C L, Malspeis L, Pettit G R, Hamel E
Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1991 Aug 25;266(24):15882-9.
Data generated in the new National Cancer Institute drug evaluation program, which is based on inhibition of cell growth in 60 human tumor cell lines, were used to compare new compounds with agents of known mechanism of action in terms of their differential cytotoxicity. Two marine natural products, halichondrin B and homohalichondrin B, appeared repeatedly when the data base was probed with known antimitotic agents. We confirmed that both compounds were highly cytotoxic (IC50 values for L1210 murine leukemia cells of 0.3 and 1 nM, respectively), with accumulation of cells arrested in mitosis at toxic concentrations, that both inhibited the polymerization of purified tubulin, and that both inhibited microtubule assembly dependent on microtubule-associated proteins. Limited amounts of homohalichondrin B, the less active agent, were available, so only halichondrin B was studied in detail. Halichondrin B did not interfere with colchicine binding to tubulin, but it was a noncompetitive inhibitor of the binding of vinblastine to tubulin (apparent Ki, 5.0 microM). Halichondrin B was therefore compared with other agents which interfere with the binding of vinca alkaloids to tubulin (vinblastine, maytansine, dolastatin 10, phomopsin A, rhizoxin) in terms of its effects on tubulin polymerization, inhibition of GTP hydrolysis, inhibition of nucleotide exchange, and stabilization of tubulin, as well as the quantitative assessment of its effects on vinca alkaloid binding and inhibition of cell growth. Since halichondrin B was originally isolated from the same organism as the phosphatase inhibitor okadaic acid, and since it is about 50-fold more effective than okadaic acid as an inhibitor of L1210 cell growth, perturbations of cellular microtubules observed following treatment with okadaic acid should be interpreted cautiously.
新的美国国立癌症研究所药物评估项目所产生的数据基于对60种人类肿瘤细胞系细胞生长的抑制作用，这些数据被用于根据新化合物与已知作用机制药物的差异细胞毒性进行比较。当用已知抗有丝分裂药物探查数据库时，两种海洋天然产物——海兔毒素B和高海兔毒素B反复出现。我们证实这两种化合物均具有高度细胞毒性（对L1210小鼠白血病细胞的IC50值分别为0.3和1 nM），在毒性浓度下有细胞停滞在有丝分裂期的积累，二者均抑制纯化微管蛋白的聚合，且均抑制依赖微管相关蛋白的微管组装。活性较低的高海兔毒素B的量有限，因此仅对海兔毒素B进行了详细研究。海兔毒素B不干扰秋水仙碱与微管蛋白的结合，但它是长春碱与微管蛋白结合的非竞争性抑制剂（表观Ki为5.0 μM）。因此，就海兔毒素B对微管蛋白聚合、GTP水解抑制、核苷酸交换抑制、微管蛋白稳定作用的影响，以及对长春花生物碱结合和细胞生长抑制作用的定量评估而言，将其与其他干扰长春花生物碱与微管蛋白结合的药物（长春碱、美登素、多拉司他汀10、腐草霉素A、根赤壳菌素）进行了比较。由于海兔毒素B最初是从与磷酸酶抑制剂冈田酸相同的生物体中分离出来的，并且由于它作为L1210细胞生长抑制剂的效力比冈田酸高约50倍，因此在用冈田酸处理后观察到的细胞微管扰动应谨慎解释。
