Vanadocene dichloride (VDC), a vanadium containing metallocene dihalide exhibits promising anticancer activity. However, its mechanism of action remains elusive as several diverse targets and pathways have been proposed for its anticancer activity. In this study, we observed that VDC inhibited the proliferation of mammalian cancer cells and induced apoptotic cell death by altering the mitochondrial membrane potential and the expression of bcl2 and bax. Probing further into its anticancer mechanism, we found that VDC caused depolymerization of interphase microtubules and blocked the cells at mitosis with considerable proportion of cells exhibiting monopolar spindles. The reassembly of cold depolymerized microtubules was strongly inhibited in the presence of 10 μM VDC. VDC perturbed the microtubule-kinetochore interactions during mitosis as indicated by the absence of cold stable spindle microtubules in the cells treated with 20 μM VDC. Using goat brain tubulin, we found that VDC inhibited the steady-state polymer mass of microtubules and bound to tubulin at a novel site with a K_d of 9.71 ± 0.19 μM and perturbed the secondary structure of tubulin dimer. In addition, VDC was also found to bind to the mitotic kinesin Eg5 and inhibit its basal as well as microtubule stimulated ATPase activity. The results suggest that disruption of microtubule assembly dynamics and inhibition of the ATPase activity of Eg5 could be a plausible mechanism for the antiproliferative and antimitotic activity of VDC.

Graphic abstract

二氯化钒（VDC）是一种含钒的二卤化茂金属，具有良好的抗癌活性。然而，它的作用机制仍然难以捉摸，因为已经提出了几种不同的靶点和途径来发挥其抗癌活性。在这项研究中，我们观察到 VDC 通过改变线粒体膜电位以及 bcl2 和 bax 的表达来抑制哺乳动物癌细胞的增殖并诱导细胞凋亡。进一步探讨其抗癌机制，我们发现VDC引起间期微管解聚并在有丝分裂时阻断细胞，相当多的细胞表现出单极纺锤体。在 10 μM VDC 存在下，冷解聚微管的重新组装受到强烈抑制。VDC 扰乱了有丝分裂期间的微管-动粒相互作用，如用 20 μM VDC 处理的细胞中不存在冷稳定纺锤体微管所表明的。使用山羊脑微管蛋白，我们发现 VDC 抑制微管的稳态聚合物质量，并在一个新位点与微管蛋白结合，具有K _d为 9.71 ± 0.19 μM，扰乱了微管蛋白二聚体的二级结构。此外，还发现 VDC 与有丝分裂驱动蛋白 Eg5 结合并抑制其基础以及微管刺激的 ATP 酶活性。结果表明，微管组装动力学的破坏和 Eg5 ATPase 活性的抑制可能是 VDC 抗增殖和抗有丝分裂活性的合理机制。

图形摘要