Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA.
Mol Pharmacol. 2012 Mar;81(3):431-9. doi: 10.1124/mol.111.075838. Epub 2011 Dec 14.
Bioassay-guided fractionation was used to isolate the lignan polygamain as the microtubule-active constituent in the crude extract of the Mountain torchwood, Amyris madrensis. Similar to the effects of the crude plant extract, polygamain caused dose-dependent loss of cellular microtubules and the formation of aberrant mitotic spindles that led to G(2)/M arrest. Polygamain has potent antiproliferative activities against a wide range of cancer cell lines, with an average IC(50) of 52.7 nM. Clonogenic studies indicate that polygamain effectively inhibits PC-3 colony formation and has excellent cellular persistence after washout. In addition, polygamain is able to circumvent two clinically relevant mechanisms of drug resistance, the expression of P-glycoprotein and the βIII isotype of tubulin. Studies with purified tubulin show that polygamain inhibits the rate and extent of purified tubulin assembly and displaces colchicine, indicating a direct interaction of polygamain within the colchicine binding site on tubulin. Polygamain has structural similarities to podophyllotoxin, and molecular modeling simulations were conducted to identify the potential orientations of these compounds within the colchicine binding site. These studies suggest that the benzodioxole group of polygamain occupies space similar to the trimethoxyphenyl group of podophyllotoxin but with distinct interactions within the hydrophobic pocket. Our results identify polygamain as a new microtubule destabilizer that seems to occupy a unique pharmacophore within the colchicine site of tubulin. This new pharmacophore will be used to design new colchicine site compounds that might provide advantages over the current agents.
生物测定指导的分离被用于从山桐子（Amyris madrensis）粗提物中分离出木脂素聚 gamain，它是微管活性成分。与粗提植物提取物的作用相似，聚 gamain 导致细胞微管剂量依赖性丧失和形成异常有丝分裂纺锤体，导致 G2/M 期阻滞。聚 gamain 对广泛的癌细胞系具有很强的抗增殖活性，平均 IC50 为 52.7 nM。集落形成实验表明，聚 gamain 能有效地抑制 PC-3 集落形成，并且在洗脱后仍具有极好的细胞持久性。此外，聚 gamain 能够规避两种临床相关的耐药机制，即 P-糖蛋白的表达和βIII 微管蛋白同工型。用纯化的微管蛋白进行的研究表明，聚 gamain 抑制纯化的微管蛋白组装的速率和程度，并取代秋水仙碱，表明聚 gamain 与微管蛋白上的秋水仙碱结合位点直接相互作用。聚 gamain 与鬼臼毒素具有结构相似性，进行了分子建模模拟以确定这些化合物在秋水仙碱结合位点内的潜在取向。这些研究表明，聚 gamain 的苯并二恶烷基团占据与鬼臼毒素的三甲氧基苯基基团相似的空间，但在疏水性口袋内具有不同的相互作用。我们的研究结果表明，聚 gamain 是一种新的微管不稳定化剂，它似乎在微管蛋白的秋水仙碱结合位点占据独特的药效团。这个新的药效团将用于设计新的秋水仙碱结合位点化合物，这些化合物可能比现有药物具有优势。
