Cheng A, Balczon R, Zuo Z, Koons J S, Walsh A H, Honkanen R E
Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile 36688, USA.
Cancer Res. 1998 Aug 15;58(16):3611-9.
Fostriecin, a structurally unique phosphate ester, is presently under evaluation in clinical trials to determine its potential use as an antitumor drug in humans. Fostriecin has been reported as having inhibitory activity against DNA topoisomerase type II and protein phosphatases implicated in cell-cycle control. However, the relative contribution of these mechanisms to the antitumor activity of fostriecin has not yet been elucidated. In this study, after confirming that fostriecin is a potent inhibitor of serine/threonine protein phosphatase type 2A and a weak inhibitor of serine/threonine protein phosphatase type 1, we show that fostriecin inhibits approximately 50% of the divalent cation independent serine/threonine protein phosphatase (PPase) activity contained in whole cell homogenates of Chinese hamster ovary cells at concentrations associated with antitumor activity (1-20 microM). Investigations into the cellular effects produced by fostriecin treatment reveal that 1-20 microM fostriecin induces a dose-dependent arrest of cell growth during the G2-M phase of the cell cycle. Immunostaining of treated cells indicates that growth arrest occurs before the completion of mitosis and that fostriecin-induced growth arrest is associated with the aberrant amplification of centrosomes, which results in the formation of abnormal mitotic spindles. The "mitotic block" induced by fostriecin is reversible if treatment is discontinued in <24 h. However, after approximately 24-30 h of continuous treatment, growth arrest is not reversible, and treated cells die even when placed in fostriecin-free media. Correlative studies conducted with established PPase inhibitors reveal that, when applied at concentrations that inhibit PPase activity to a comparable extent, both okadaic acid and cantharidin also induce aberrant centrosome replication, the appearance of multiple aberrant mitotic spindles, and G2-M-phase growth arrest. These studies add additional support to the concept that PPase inhibition underlies the antitumor activity of fostriecin and suggest that other type-selective PPase inhibitors should be evaluated for potential antitumor activity.
福司曲星是一种结构独特的磷酸酯，目前正在进行临床试验，以确定其作为人类抗肿瘤药物的潜在用途。据报道，福司曲星对参与细胞周期调控的DNA拓扑异构酶II和蛋白磷酸酶具有抑制活性。然而，这些机制对福司曲星抗肿瘤活性的相对贡献尚未阐明。在本研究中，在确认福司曲星是丝氨酸/苏氨酸蛋白磷酸酶2A的有效抑制剂和丝氨酸/苏氨酸蛋白磷酸酶1的弱抑制剂后，我们表明，在与抗肿瘤活性相关的浓度（1-20 microM）下，福司曲星可抑制中国仓鼠卵巢细胞全细胞匀浆中约50%的二价阳离子非依赖性丝氨酸/苏氨酸蛋白磷酸酶（PPase）活性。对福司曲星处理产生的细胞效应的研究表明，1-20 microM福司曲星在细胞周期的G2-M期诱导剂量依赖性的细胞生长停滞。对处理过的细胞进行免疫染色表明，生长停滞发生在有丝分裂完成之前，并且福司曲星诱导的生长停滞与中心体的异常扩增有关，这导致异常有丝分裂纺锤体的形成。如果在<24小时内停止治疗，福司曲星诱导的“有丝分裂阻滞”是可逆的。然而，在连续治疗约24-30小时后，生长停滞是不可逆的，并且即使将处理过的细胞置于无福司曲星的培养基中，它们也会死亡。与已建立的PPase抑制剂进行的相关研究表明，当以同等程度抑制PPase活性的浓度应用时，冈田酸和斑蝥素都会诱导中心体异常复制、多个异常有丝分裂纺锤体的出现以及G2-M期生长停滞。这些研究进一步支持了PPase抑制是福司曲星抗肿瘤活性基础的概念，并表明应评估其他类型选择性PPase抑制剂的潜在抗肿瘤活性。
