孕期黄酮类化合物摄入与婴幼儿白血病相关性研究的现状

目的:探讨黄酮类化合物作为DNA拓扑异构酶Ⅱ抑制剂以及孕期黄酮类化合物摄入与婴幼儿白血病间的关系.方法:应用PubMed、万方和维普科技期刊数据库检索系统,以“黄酮类化合物、白血病和拓扑异构酶Ⅱ抑制剂”为关键词,检索1987-01-2012-09的相关文献,共检索到英文文献7条,中文文献0条,以任意2个关键词搜索,共检索到英文文献1 445条,中文文献108条.纳入标准:1)黄酮类化合物的基本资料介绍.2)婴幼儿白血病的基本资料介绍.3)拓扑异构酶及拓扑异构酶Ⅱ抑制剂的基本资料介绍.4)拓扑异构酶Ⅱ抑制剂与白血病的关系.5)黄酮类化合物与婴幼儿白血病的关系.根据纳入标准精选46篇文献,最后纳入分析32篇.结果:黄酮类化合物广泛存在于日常食物中,对人类健康有许多积极作用.但是,黄酮类化合物作为拓扑异构酶Ⅱ抑制剂也存在遗传毒性、细胞毒性,某些实体瘤患者在应用DNA拓扑异构酶Ⅱ抑制剂治疗后可继发白血病,其细胞遗传学异常多与原发急性髓系白血病(AML)有关,其中最常见的是位于染色体11q23的混合系白血病(MLL)基因异位.孕期黄酮类化合物摄入与婴幼儿某种类型白血病的发生风险增高有一定的关系.在急性婴幼儿白血病患者中,＞80％都包括位于染色体11q23的MLL基因异位或异常重组.样本量均超过200例的5个病例对照研究显示,孕期摄入大量含DNA拓扑异构酶Ⅱ抑制剂的食物(主要为含黄酮类化合物的水果和蔬菜等)后,MLL重排引起的AML的发病风险增高.结论:了解黄酮类化合物作为DNA拓扑异构酶Ⅱ抑制剂以及孕期黄酮类化合物摄入与婴幼儿白血病间的关系,有助于孕妇膳食指导及膳食指南的修订与完善.     

以DNA拓扑异构酶Ⅱ为靶点的一种抗癌药筛选的新方法

借鉴文献方法,我们以小鼠L_(1210)白血病细胞为村料,提取DNA拓扑异构酶Ⅱ,鉴别了其生物学特性,并观察了十多种已知及未知的抗癌药物对其活性的影响,初步建立了以DNA拓扑异构酶Ⅱ为靶点的新抗癌药筛选方法。实验表明DNA拓扑异构酶Ⅱ对DNA链切割反应是可逆的,并且高浓度的氯化钠对其活性有抑制作用。许多药物能促进拓扑酶Ⅱ引起的DNA链断裂如ADM、DNR、Vp16及ACM—B等,而另一些药物如萜类化合物BC_1、BC_4等则能抑制链断裂反应。     

国产盐酸拓扑替康对小细胞肺癌疗效的初步研究

盐酸拓扑替康（ topotecan）是具有抑制拓扑异构酶Ⅰ活性的抗肿瘤新药。其作用机制是拓扑异构酶Ⅰ可诱导 DNA单链可逆性断裂，使 DNA螺旋链松解。盐酸拓扑替康与拓扑异构酶Ⅰ -DNA复合物结合并阻止这些单股断链的重新连接，其细胞毒作用是在 DNA的合成中。盐酸拓扑替康、拓扑异构酶 I和 DNA形成的三元复合物与复制酶相互作用产生双股 DNA的损伤，而哺乳动物的细胞不能有效地修复这些双股 DNA链的中断。国外研究表明盐酸拓扑替康对多种肿瘤有效 [1～ 3]，本研究采用国产盐酸拓扑替康对小细胞肺癌的疗效进行临床研究，报告如下。     

肿瘤化疗的重要靶点—DNA拓扑异构酶

DNA 拓扑异构酶是近年来新发现的肿瘤化疗的重要靶点,它涉及到抗癌药作用的许多环节,如 DNA 复制、DNA 损伤与修复、基因的重组和转录、细胞有丝分裂及分化等。本文列举了一些临床上广泛使用的以 DNA 拓扑异构酶为靶点的化疗药物,着重介绍了拓扑酶抑制剂作用的分子基础及其与耐药的关系。事实证明拓扑酶抑制剂能促进酶介导的 DNA 切割复合物的形成,阻断正常基因及癌基因的表达。另一方面,对拓扑酶抑制剂耐药的细胞常表现为酶活性及酶量的下降,这种变化与拓扑酶基因的突变有关。     

拓扑异构酶与肿瘤细胞耐药性

拓扑异构酶可分为二类即拓扑异构酶Ⅰ(TOPOI)和拓扑异构酶Ⅱ(TOPOⅡ)。TOPOⅠ在细胞中DNA空间构型变化,DNA复制、重组、转录、切割、再连接、细胞染色质的组化以及有丝分裂中均起重要作用。TOPOⅡ是真核细胞生存所必不可少的核酸,它的作用涉及到核酸代谢的诸方面,包括DNA复制、mRNA加工、染色体的分离及浓缩、核基质的组成等。许多抗癌药物正是通过干扰DNA的正常代谢而发挥抗癌作用。肿瘤化疗失败的重要原因之一是耐药性的产生。耐药性的原因多种多样,最近研究表明拓扑异构酶的变化是一个不可忽视的原因,现综述如下。     

DNA拓扑酶抑制剂诱导细胞凋亡的研究

目前 ,以 DNA拓扑异构酶为靶点的抗癌药已成为临床有效的抗肿瘤一线药物 ,随着此类药物越来越多地被开发 ,其作用机制的研究受到广泛关注。迄今其诱导肿瘤细胞凋亡的机制仍有探索中 ,现作一简要综述。1　 DNA拓扑异构酶主要生理功能及其抑制剂的作用机制　　　真核细胞 DNA拓扑异构酶 (Topoi-som erase Topo)主要分为 Topo 及Topo ,其生理功能主要以两种方式体现 ,一是调节控制 DNA超螺旋状态及打结或解结 DNA的环连体状态 ;二是直接参与那些需打断并重新连接 DNA分子链的细胞过程。Topo与 DNA共价结合形成断裂复合物 ,使 DNA产…     

拓扑异构酶——癌化疗的新靶

一类具有调节DNA三维结构的核酶称为DNA拓扑异构酶(Topoisomerases),它们在细胞的翻译、转录和有丝分裂的生命过程中起重要作用。抗癌药蒽环类、鬼臼霉素类和吖啶类干扰这些酶,尤其是干扰TopoⅡ酶的活性。DNA—拓扑异构酶Ⅱ复合物是酶活性的中介体,其如果被药物所稳定则形成一种“断裂复合物”而显示药物的细胞毒作用。 拓扑异构酶有二型,即TOPOⅠ和TOPOⅡ。TOPOⅠ酶是分子量为100KD的单体,它能断裂一条     

急性白血病患者多药耐药基因和TopoⅡ的表达及临床意义

目的:探讨急性白血病患者多药耐药基因(mdr1)和DNA拓扑异构酶Ⅱ(TopoⅡ)的表达及其临床意义。方法:采用反转录—聚合酶链反应(RT-PCR)技术检测了52例急性白血病患者mdr1基因和DNA拓扑异构酶Ⅱ的表达。结果:复发难治组白血病患者mdr1阳性率83.3 %,明显高于初治组36.7 %和完全缓解组10.0 %。复发难治组TopoⅡ表达阳性率25.0 %,低于初治组43.3 %和完全缓解组70.0 %。mdr1和TopoⅡ二者表达之间无相关性(P>0.05)。mdr1(+)/TopoⅡ(-)者预后最差。结论: mdr1阳性和TopoⅡ的表达降低均是判断疗效和预后的重要指标。mdr1和TopoⅡ之间无相关性。     

抗VEGF抗体诱导K562细胞凋亡及其机制的研究

目的 观察抗VEGF抗体对K562细胞凋亡的影响,探讨VEGF抑制白血病细胞凋亡的机理.方法 采用半定量逆转录聚合酶链反应（RT-PCR）检测抗VEGF单抗对拓扑异构酶Ⅱ（TOPOⅡ）表达的影响;采用低浓度溴乙啶荧光测定法检测细胞TOPOⅡ的活性;应用琼脂糖凝胶电泳检测K562细胞凋亡的情况.结果 抗VEGF抗体能抑制K562细胞TOPOⅡ的表达,降低TOPOⅡ的活性,促进DNA解旋、断裂;抗VEGF单抗作用于K562细胞后,电泳结果显示有凋亡细胞特有的“梯状”条带.结论 抗VEGF单抗能引起白血病细胞凋亡,其原因可能是抗VEGF单抗抑制了白血病细胞TOPOⅡ基因的表达.     

DNA拓扑异构酶抑制剂与抗癌作用(摘要)

自七十年代发现了一类能控制和改变DNA拓扑异构状态(三维结构)的酶,称为DNA拓扑异构酶(DNAT、opoisomerases)。按其在反应中暂时断裂一条或二条DNA链的不同,可分为Ⅰ型和Ⅱ型DNA拓扑异构酶。这类酶在DNA的复制和转录过程中起着非常重要的作用,它们控制DNA     

Predisposition to therapy-related acute leukemia with balanced chromosomal translocations does not result from a major constitutive defect in DNA double-strand break end joining

The frequency of acute myeloid leukemia (AML) with balanced chromosomal translocations arising after anticancer therapy with DNA-damaging agents such as DNA topoisomerase II inhibitors has increased over the last two decades. However, factors that predispose to these therapy-related disorders are still poorly defined. It has been reported that DNA double-strand break (DSB) repair by the non-homologous end-joining (NHEJ) pathway is impaired in myeloid leukemia cells. This led us to hypothesize that therapy-related AML (t-AML) may result from individual differences in the repair of DSBs generated by the treatment. We show here that DSB repair is accurate, in vivo, in non-tumoral cells derived from patients who developed t-AML with t(9;11) or t(15;17) translocation after treatment for a first cancer with DNA topoisomerase II inhibitors. These results indicate that a major constitutive defect in the NHEJ pathway is unlikely to predispose to t-AML with balanced chromosomal translocations.     

Topoisomerase Inhibitors Have Potent Differentiation-inducing Activity for Human and Mouse Myeloid Leukemia Cells

DNA topoisomerase inhibitors, camptothecin and 4'-demethylepipodophyllotoxin ethylidene-jS-D-glucoside (VP16) had strong differentiation-inducing activity for all five kinds of leukemia cells examined (human HL60, U937, ML1, and K562 cells and mouse Ml cells) as judged from measurements of various differentiation markers. The characteristics that appeared as a result of differentiation induced by these inhibitors were essentially similar in every cell line. Exposure to VP16 for 2 h induced both differentiation and DNA-strand breaks in K562 cells, whereas podophyl-lotoxin, which lacks topoisomerase II inhibitory activity, induced neither differentiation nor DNA-strand breaks in these cells. These results suggest a parallelism between the induction of differentiation and that of DNA-strand breaks. The combination of VP16 and recomhinant tumor necrosis factor α (rTNFα) synergistically induced differentiation of human U937, ML1, and M1 cells and had an additive effect on HL60 cells. Simultaneous treatment with rTNFa plus camptothecin or VP16, or pretreatment with camptothecin or VP16, followed by rTNFα induced marked differentiation of Ml cells. These results indicate that inhibition of topoisomerase (either topoisomerase I or II) followed by the action of rTNFα was effective in inducing differentiation of leukemia cells.     

Cytostatic and cytotoxic effects of fostriecin on human promyelocytic HL-60 and lymphocytic MOLT-4 leukemic cells.

Exposure of exponentially growing human promyelocytic of lymphocytic leukemic cells to the putative DNA topoisomerase II inhibitor fostriecin (FST), at a concentration of 1 microM, results in the suppression of their rate of progression through the S and G2 phases of the cell cycle. At concentrations between 5 microM and 0.5 mM, FST triggers endonucleolytic DNA degradation in human promyelocytic leukemia cells, resulting in apoptotic cell death; this effect is not selective for any particular phase of the cell cycle. Little or no apoptotic cell death is observed in lymphocytic leukemic cells at any FST concentration. Because FST, unlike other inhibitors of topoisomerase II, such as teniposide (TN) or amsacrine (m-AMSA), does not stabilize cleavable DNA-topoisomerase complexes, the observed differences between the effects of FST versus TN or m-AMSA on the cell cycle may provide clues regarding the role of such complexes in the kinetic effects of these inhibitors. The present results, therefore, are compared with our earlier data on the effects of TN and m-AMSA on the same cells. The only observed difference is the loss of cell cycle phase-specific triggering of DNA degradation by FST in human promyelocytic leukemia cells, compared to the S phase-specific effects of TN and m-AMSA. Therefore, stabilization of the DNA-topoisomerase cleavable complexes may be essential in the selectivity of cell kill during S phase. However, it appears that the presence of stabilized complexes is not essential to the suppression of cell progression through S or G2 or the induction of apoptotis or necrosis, in general, by topoisomerase II inhibitors.     

Synergistic effect of inhibitors of topoisomerase I and II on chromosome damage and cell killing in cultured Chinese hamster ovary cells

Simultaneous treatment of cultured Chinese hamster ovary cells with the topoisomerase I inhibitor camptothecin and the topoisomerase II inhibitor 4-(9-acridinylamino)-methanesulfon-m-anisidide results in a clear synergistic effect on both chromosome damage detected at metaphase and loss of colony-forming ability. In contrast, the effect of combined treatment with these topoisomerase inhibitors on sister chromatid exchanges was not significantly different from that expected if the effects were additive. Taken as a whole, these results seem to support the hypothesis that topoisomerase inhibitors can lead to cell death, presumably when DNA replication forks collide with drug-stabilized cleavable complexes. Nevertheless, no evidence of apoptosis was obtained from DNA fragmentation analysis. The possible clinical implications of our findings are discussed.     

A new derivative of camptothecin, irinotecan hydrochloride (cpt-11) induces programmed cell-death in leukemia-lymphoma cell-lines

Irinotecan Hydrochloride (CPT-11) and 7-ethyl-10-hydroxycamptothecin (SN-38), which are both topoisomerase I inhibitors with potent antitumor effects in vivo and in vitro, were tested for the induction of programmed cell death (PCD) in leukemia/lymphoma cell lines. When the human T-cell leukemia cell line HUT-102 and the human promyelocytic leukemia cell line HL-60 cells were exposed to CPT-11, PCD characterized by a DNA fragmentation ladder of 180-200 bp in agarose gel electrophoresis and loss of cell viability was induced. The PCD inducing activity of SN-38, an active metabolite of CPT-11, was much more powerful than that of CPT-11. Besides inducing PCD in HUT-102 and HL-60 cells, SN-38 also induced PCD in the human erythroblast leukemia cell line K-562, which was resistant to CPT-11. Induction of PCD by SN-38 and CPT-11 was dose- and time-dependent. PCD in HUT-102 cells induced by SN-38 was prevented neither by aurintricarboxylic acid (ATA), an endonuclease inhibitor, as determine by DNA electrophoretic profiles and the number of viable cells, nor by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA). The present data suggest that the topoisomerase I inhibitors, SN-38 and CPT-11 exert antitumor activity through induction of PCD in involved cells, at least in part. The PCD-inducing activity of the topoisomerase II inhibitor VP-16 was also tested in the above three cell lines and compared with CPT-11 and SN-38.     

Diverse effects of camptothecin, an inhibitor of topoisomerase I, on the cell cycle of lymphocytic (L1210, MOLT-4) and myelogenous (HL-60, KG1) leukemic cells

Exposure of mouse lymphocytic L1210 cells to 0.02-0.5 micrograms/ml of camptothecin (CAM) causes a slowdown in the rate of cell progression through S and G2 phases of the cell cycle; the "terminal" point of CAM action is about 1 h prior to mitosis. Some cells also enter higher DNA ploidy and progress through the cycle at that ploidy. CAM exerts similar effects (S- and G2-phase arrest, entrance to higher DNA ploidy, low initial cytotoxicity) on human lymphocytic MOLT-4 leukemia cells. In contrast, treatment of human promyelocytic HL-60 cells with CAM results in the immediate (occurring as early as 2 h after treatment) death of S- and G2+M-phase cells; the dead cells exhibit decreased DNA stainability with intercalating dyes, suggestive of DNA degradation. Although CAM is less cytotoxic to another human myelogenous leukemic cell line, KG1, the latter cells also respond like HL-60, namely by selective death in S and G2. The data indicate that there may be a tissue (leukemia type) specificity in the response of cells to camptothecin and suggest that myelogenous leukemias, especially those characterized by high proliferation rates, may be especially sensitive to the cytotoxic action of this and perhaps other topoisomerase I inhibitors.     

Topoisomerase inhibitors have potent differentiation-inducing activity for human and mouse myeloid leukemia cells.

DNA topoisomerase inhibitors, camptothecin and 4'-demethylepipodophyllotoxin ethylidene-beta-D-glucoside (VP16) had strong differentiation-inducing activity for all five kinds of leukemia cells examined (human HL60, U937, ML1, and K562 cells and mouse M1 cells) as judged from measurements of various differentiation markers. The characteristics that appeared as a result of differentiation induced by these inhibitors were essentially similar in every cell line. Exposure to VP16 for 2 h induced both differentiation and DNA-strand breaks in K562 cells, whereas podophyllotoxin, which lacks topoisomerase II inhibitory activity, induced neither differentiation nor DNA-strand breaks in these cells. These results suggest a parallelism between the induction of differentiation and that of DNA-strand breaks. The combination of VP16 and recombinant tumor necrosis factor alpha (rTNF alpha) synergistically induced differentiation of human U937, ML1, and M1 cells and had an additive effect on HL60 cells. Simultaneous treatment with rTNF alpha plus camptothecin or VP16, or pretreatment with camptothecin or VP16, followed by rTNF alpha induced marked differentiation of M1 cells. These results indicate that inhibition of topoisomerase (either topoisomerase I or II) followed by the action of rTNF alpha was effective in inducing differentiation of leukemia cells.     

DNA topoisomerase I-mediated DNA cleavage and cytotoxicity of camptothecin analogues

20(S)-Camptothecin, the 20(S)-camptothecin sodium salt, and 12 analogues with substituents on the A ring differ widely in their effectiveness in the treatment of murine L1210 lymphoblastic leukemia in vivo. The drugs were screened in the following systems: System 1, the cleavage of DNA in the presence of purified topoisomerase I; System 2, drug-induced trapping of topoisomerase I in a covalent complex with DNA; and System 3, the induction of protein-associated DNA breaks in drug-treated L1210 leukemia cells. 9-Amino-20(S), 10-amino-20(RS), and 10,11-methylenedioxy-20(RS), drugs effective against murine L1210 leukemia in vivo, stabilize topoisomerase I-DNA cleavable complexes in a purified system and in cultured L1210 cells. Other analogues, inactive against L1210 leukemia in vivo, were totally ineffective in topoisomerase I-directed screens. The rest of the analogues were intermediate in terms of their antitumor and topoisomerase I-directed activities. The study shows that the drug-induced accumulation of enzyme-DNA cleavable complexes is directly proportional to drug cytotoxicity and antitumor activity.     

DNA topoisomerase II as a potential factor in drug resistance of human malignancies

The stabilization of the cleavable complex between DNA topoisomerase II and DNA by adriamycin (ADR), as well as by other topoisomerase II-targeted drugs, is an essential step in a process associated with drug cytotoxicity. Unlike many other cell types, ADR does not produce DNA cleavage in the lymphocytes of chronic lymphocytic leukemia (CLL). The CLL lymphocytes have been identified as quiescent cells with an extremely low level of topoisomerase II. The low level of this enzyme could constitute a basis for a new mechanism of drug resistance operating not only in CLL, but perhaps in any slow growing cancer with a large population of quiescent cells. Other factors contributing to drug resistance could include changes in enzyme regulation or processing of the cleavable complex, or the presence of a "mutant" enzyme which renders cancer cells unresponsive to topoisomerase II-targeted drugs. Suggested strategies in drug development, aimed at the topoisomerase II-related drug resistance, could include 1) the selection of topoisomerase I as an alternative target for cancer chemotherapy, 2) the development of ADR analogs which, unlike ADR, stabilize the topoisomerase II-DNA complex with high efficiency, and 3) the search for agents enhancing the SOS-like repair response, presumably triggered by DNA topoisomerase-targeted drugs.     

Studies on the role of topoisomerases in general, gene- and strand-specific DNA repair

Using specific inhibitors we have assessed the role of topoisomerasesI and II in DNA repair of the overall genome and in both strandsof an essential gene, the dihydrofolate reductase (DHFR) genein chinese hamster ovary (CHO) cells. In these studies we have:(1) used inhibitors of topoisomerases during the repair incubationand (2) studied the DNA repair in cells with altered levelsof topoisomerase activity. When cells were allowed to repairafter UV irradiation, the gene-specific DNA repair was not affectedby either topoisomerase I or topoisomerase II inhibitors alone.However, when topoisomerase I and topoisomerase II inhibitorswere added simultaneously the gene- and strand-specific DNArepair were markedly inhibited. In contrast, the overall genomeDNA repair was only marginally affected. This suggests thattopoisomerases are involved in gene-specific DNA repair andthat one type may substitute for the other in the repair process.That concept is further supported by our findings using a mutantcell line with a decreased level of topoisomerase I: gene-specificDNA repair can be inhibited by a topoisomerase II inhibitoralone. By analyzing the steady-state expression of the DHFRgene we find that inhibition of repair in the DHFR gene is notascribed to an obvious change in the messenger level. Furthermore,using agents other than UV, we observe that the inhibitors haveno effect on gene-specific repair of DNA damage introduced bythe chemotherapeutic agents cisplatin and nitrogen mustard.