Dhanalakshmi S, Singh R P, Agarwal C, Agarwal R
Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Health Sciences Center, Denver, Colorado, CO 80262, USA.
Oncogene. 2002 Mar 7;21(11):1759-67. doi: 10.1038/sj.onc.1205240.
Prostate cancer (PCA) is one of the most common invasive malignancies of men in the US, however, there have been limited successes so far in its therapy. Even most potent agents (e.g. TNFalpha) are ineffective in killing human PCA cells possibly due to constitutive activation of NF-kappaB that subsequently activates a large number of anti-apoptotic genes. In such a scenario, strong apoptotic agent TNFalpha, further induces NF-kappaB activation rather than inducing apoptosis. In several recent studies, we have demonstrated both cancer preventive and anti-cancer efficacy of silymarin and its constituent silibinin in a variety of experimental tumor models and cell culture systems. Here we examined whether silibinin is effective in inhibiting constitutive NF-kappaB activation in human PCA cells, which would help in overcoming TNFalpha-insensitivity. Our studies reveal that silibinin effectively inhibits constitutive activation of NF-kappaB in advanced human prostate carcinoma DU145 cells. Consistent with this, nuclear levels of p65 and p50 sub-units of NF-kappaB were also reduced. In the studies assessing molecular mechanism of this effect, silibinin treatment resulted in a significant increase in the level of IkappaBalpha with a concomitant decrease in phospho-IkappaBalpha. Kinase assays revealed that silibinin dose-dependently decreases IKKalpha kinase activity. The effect of silibinin on IKKalpha seemed to be direct as evidenced by the in vitro kinase assay, where immunoprecipitated IKKalpha was incubated with silibinin. This shows that silibinin does not necessarily need an upstream event to bring about its inhibitory effect on IKKalpha and downstream effectors. Additional studies showed that silibinin also inhibits TNFalpha-induced activation of NF-kappaB via IkappaBalpha pathway and subsequently sensitizes DU145 cells to TNFalpha-induced apoptosis. These results indicate that silibinin could be used to enhance the effectiveness of TNFalpha-based chemotherapy in advanced PCA.
前列腺癌（PCA）是美国男性中最常见的侵袭性恶性肿瘤之一，然而，到目前为止其治疗成效有限。即使是最有效的药物（如肿瘤坏死因子α）在杀死人前列腺癌细胞方面也无效，这可能是由于核因子κB的组成性激活，随后激活了大量抗凋亡基因。在这种情况下，强大的凋亡诱导剂肿瘤坏死因子α进一步诱导核因子κB激活，而不是诱导细胞凋亡。在最近的几项研究中，我们已经在多种实验性肿瘤模型和细胞培养系统中证明了水飞蓟素及其成分水飞蓟宾的癌症预防和抗癌功效。在此，我们研究了水飞蓟宾是否能有效抑制人前列腺癌细胞中组成性核因子κB的激活，这将有助于克服肿瘤坏死因子α不敏感性。我们的研究表明，水飞蓟宾能有效抑制晚期人前列腺癌DU145细胞中核因子κB的组成性激活。与此一致的是，核因子κB的p65和p50亚基的核水平也降低了。在评估这种效应分子机制的研究中，水飞蓟宾处理导致IκBα水平显著升高，同时磷酸化IκBα水平降低。激酶分析表明，水飞蓟宾剂量依赖性地降低IKKα激酶活性。水飞蓟宾对IKKα的作用似乎是直接的，体外激酶分析证明了这一点，即将免疫沉淀的IKKα与水飞蓟宾一起孵育。这表明水飞蓟宾不一定需要上游事件来对IKKα和下游效应器产生抑制作用。额外的研究表明，水飞蓟宾还通过IκBα途径抑制肿瘤坏死因子α诱导的核因子κB激活，随后使DU145细胞对肿瘤坏死因子α诱导的细胞凋亡敏感。这些结果表明，水飞蓟宾可用于提高晚期前列腺癌中基于肿瘤坏死因子α的化疗效果。
