血小板型12-脂加氧酶与肿瘤

花生四烯酸通过脂加氧酶(lipoxygenase，LOX)途径代谢产生多种生物活性脂类，这些脂类在炎症、血栓形成和肿瘤演进过程中发挥着重要的作用。LOX按照组织分布被分为5-、8-、12-、15-LOX4个家族．血小板型12-LOX是LOX的一种，催化花生四烯酸转化为廿碳四烯酸。血小板型12-LOX在正常组织中主要分布在血小板、人皮肤表皮细胞细胞质和微粒体中。近来研究发现，在多种肿瘤组织和肿瘤细胞系中不仅可检测到血小板型12-LOX的表达，且随着肿瘤级别的增高．瘤细胞表达增强。血小板型12-LOX催化的代谢产物，如12(S)-羟廿碳四烯酸，已被证明涉及肿瘤细胞凋亡、肿瘤血管形成．因此血小板型12-LOX也成为肿瘤治疗的潜在目标。多项研究表明，血小板型12-LOX的抑制剂能有效抑制肿瘤，如去甲二氢愈创木酸能有效抑制胶质瘤。对血小板型12-LOX与肿瘤细胞增殖、凋亡和血管生成之间的关系以及其机制进行讨论，另外，对血小板型12-LOX抑制剂预防和治疗肿瘤予以综述。     

p12-LOX与肿瘤相关性的研究进展

花生四烯酸通过脂加氧酶（lipoxygenase,LOX）途径代谢产生多种生物活性脂类,这些脂类在炎症、血栓形成和肿瘤演进过程中发挥着重要的作用。LOX按照组织分布被分为5-、8-、12-、15-LOX 4个家族,血小板型12-LOX是LOX的一种,其催化的代谢产物如12(S)-HETE,已被证实涉及肿瘤细胞的增殖、凋亡、肿瘤血管的形成及肿瘤的侵袭与转移等过程。本文重点阐述血小板型12-LOX与肿瘤的细胞增殖、凋亡、血管生成及侵袭转移之间的关系及其与乳腺癌的相关研究进展。     

脂加氧酶在肿瘤中的研究进展

脂加氧酶（LOX）可以催化游离花生四烯酸使之成为有生物活性的类花生酸类物质,这一代谢过程可调节细胞增殖、分化、凋亡及衰老。15-LOX对结直肠癌、食管癌及前列腺癌等有抑制作用,其他LOXs的抑制剂在一系列实验模型中也显示了其致癌作用和对肿瘤生长的调控作用。不同的LOX亚型具有不同的作用机制且在肿瘤中表达不同。全文旨在分子水平上讨论LOX的分布,研究其对肿瘤细胞的增殖、凋亡、血管生成及转移等的影响,展望LOX抑制剂在临床中的靶向治疗策略,阐明其在不同类型的恶性肿瘤治疗中的研究进展。     

5-LOX及其抑制剂对肿瘤影响的研究进展

脂氧合酶（LOX）家族蛋白在恶性肿瘤演进中发挥重要作用,其亚型5-LOX 在多种肿瘤组织和细胞中呈高表达,且与淋巴结转移、患者的生存期有关,可通过诱导Src 的磷酸化、选择性抑制p53 依赖的促凋亡基因转录、促进肿瘤血管形成、刺激上皮-间质转化、形成转移前微环境等,促进肿瘤细胞增殖和转移、抑制凋亡,参与调控肿瘤的恶性演进过程。基于5-LOX及其激活蛋白ALOX5AP的促癌作用,已开发出直接、间接两类抑制剂及COX-2/5-LOX 双重抑制剂,有望通过降低5-LOX 活性或阻断5-LOX代谢途径发挥抗肿瘤作用。本文概述5-LOX在肿瘤中的调控作用以及5-LOX和其激活蛋白抑制剂的研究现状,以期为后续抗肿瘤药物的开发及临床应用提供参考及新的理论依据。     

15-LOX-1和PPARγ间的相互作用及其与肿瘤的关系

15-脂加氧酶1(15-LOX-1)表达于人的多种组织细胞中,是催化不饱和脂肪酸代谢的关键酶之一,可以将亚油酸、花生四烯酸分别代谢为13-羟基十八碳二烯酸和15-羟基二十碳四烷酸,这些不饱和脂肪酸及其代谢衍生物是过氧化物酶增殖激活受体γ(PPARγ)的天然配体.研究发现,PPARγ以非活性状态在多种肿瘤组织中高表达,其与配体结合活化后,可诱导肿瘤细胞凋亡或者分化,发挥潜在的抗肿瘤作用.以15-LOX-1和PPARγ/为靶向的肿瘤防治及其临床应用具有广阔前景.     

环氧化酶-2在肿瘤发生发展中的研究

环氧化酶-2(COX-2)是催化花生四烯酸转化为前列腺素类物质的限速酶，除与炎症反应有关外，还可通过刺激细胞增殖，抑制细胞凋亡，诱导肿瘤血管形成等促进肿瘤发生发展。近年大量研究表明，在消化系统、呼吸系统、泌尿生殖统系等多种器官恶性肿瘤组织中COX-2mRNA与其蛋白表达水平均明显增高。     

脂肪酸合成酶在肿瘤细胞中的作用

脂肪酸合成酶( fatty acid synthase,FASN)是重要的生物合成酶,是肿瘤脂质生成的一种关键酶,在催化脂肪酸合成的过程中发挥重要作用。FASN在许多肿瘤细胞中过表达而在相应的正常细胞中却不表达。有证据表明FASN是一个代谢性癌基因,在癌细胞中高表达,在肿瘤生长和存活中有重要的作用。最初发现的肿瘤细胞特殊代谢表型称Warburg效应。异常脂肪酸代谢与肿瘤生长、存活及侵袭相关,表明异常脂肪酸代谢为肿瘤生长提供了至关重要的物质和能量来源。FASN的过度表达与肿瘤的发生、演变、侵袭和预后有关。在多种肿瘤中观察到脂肪酸代谢途径中FASN的表达和活性提高,并且与不良预后密切相关,通过下调这些代谢酶的表达或利用特异性抑制剂抑制代谢酶活性,可抑制肿瘤的生长。研究发现,利用FASN抑制剂可明显抑制肿瘤的复发和转移。通过抑制FASN的酶活性而导致肿瘤细胞脂类饥饿,从而有效地抑制癌细胞增殖,促使其脱离恶性分裂周期并走向凋亡。正确认识FASN在肿瘤细胞中的表达调节,研究新的FASN抑制剂,可为肿瘤治疗提供新的方案。本文就脂肪酸合成酶及脂肪酸合成酶抑制剂在肿瘤细胞中的作用作一综述。     

环氧化酶-2及其抑制剂与卵巢癌相关性的研究

环氧化酶（cyclooxygenase,COX）是催化花生四烯酸（arachidonic acid,AA）合成前列腺素（prostaglandins,PGS）的限速酶。其中COX-2的过表达与卵巢癌细胞生长、凋亡、肿瘤浸润转移、肿瘤血管生成及肿瘤化疗耐药产生相关。COX-2及其抑制剂与卵巢癌的关系是目前国内外学者研究的热点之一。     

环氧化酶-2与前列腺癌研究进展

环氧化酶-2(COX-2)是花生四烯酸合成前列腺素的限速酶,在人类许多肿瘤中过表达。近年来研究表明,COX-2通过促进肿瘤细胞增殖、抑制肿瘤细胞凋亡、促进肿瘤血管生成以及降低机体免疫力等机制在前列腺癌变过程中发挥着重要作用。现就其研究新进展作一综述。     

环氧化酶-2与前列腺癌研究进展

环氧化酶-2（COX-2）是花生四烯酸合成前列腺素的限速酶，在人类许多肿瘤中过表达。近年来研究表明，COX-2通过促进肿瘤细胞增殖、抑制肿瘤细胞凋亡、促进肿瘤血管生成以及降低机体免疫力等机制在前列腺癌变过程中发挥着重要作用。现就其研究新进展作一综述。     

Mechanisms controlling cell cycle arrest and induction of apoptosis after 12-lipoxygenase inhibition in prostate cancer cells

Extensive studies have implicated the role of dietary fatty acids in prostatecancer progression. Platelet-type 12-Lipoxygenase (12-LOX) has beenshown to regulate growth, metastasis, and angiogenesis of prostate cancer. The effect of two 12-LOX inhibitors, Baicalein and N-benzyl-N-hydroxy-5-phenylpentamide (BHPP), on the mechanisms controlling cell cycle progression and apoptosis were examined in two prostate cancer cell lines, PC3 and DU-145. Treatment with Baicalein or BHPP resulted in a dose-dependent decrease in cell proliferation, as measured by BrdUrd incorporation. This growth arrest was shown to be because of cell cycle inhibition at G0/G1, and was associated with suppression of cyclin D1 and D3 protein levels. PC3 cells also showed a strong decrease in phosphorylated retinoblastoma (pRB) protein, whereas the other retinoblastoma-associated proteins, p107 and p130, were inhibited in DU-145 cells. Treatment with 12-hydroxyeicosatetraenoic acid in the presence of Baicalein blocked loss of pRB, whereas 12(S)-HETE alone induced pRB expression. Treatment with either Baicalein or BHPP resulted in significant apoptosis in both cell lines as measured by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling. DU-145 cells underwent apoptosis more rapidly than PC-3 cells. The mechanisms involved were decreased phosphorylation of Akt, loss of survivin and subsequent activation of caspase-3 and caspase-7 in each cell line, decreased Bcl-2 and Bcl-X(L) expression in DU-145, and a shift in Bcl-2/Bax levels favoring apoptosis in PC-3 cells. Addition of 12(S)-HETE protected both cell lines from Baicalein-induced apoptosis, whereas other LOX metabolites, 5(S)-HETE, or 15(S)-HETE did not. These results show that the 12-LOX pathway is a critical regulator of prostate cancer progression and apoptosis, by affecting various proteins regulating these processes. Therefore, inhibition of 12-LOX is a potential therapeutic agent in the treatment of prostate cancer.     

Overexpression of leukocyte-type 12-lipoxygenase promotes W256 tumor cell survival by enhancing alphavbeta5 expression

The metabolism of arachidonic acid (AA) leads to the generation of biologically active metabolites that have been implicated in cell growth and proliferation, as well as survival and apoptosis. We have previously demonstrated that rat Walker 256 (W256) carcinosarcoma cells express the platelet-type 12-lipoxygenase (12-LOX) and synthesize 12(S)- and 15(S)-HETE as their major LOX metabolites. Here we show that Walker 256 cells also express leukocyte-type 12-LOX and that its overexpression in these cells significantly extends their survival and delays apoptosis when cells are cultured under serum-free conditions. Under serum-free conditions, the expression of leukocyte-type 12-LOX is upregulated. 12-LOX-transfected W256 cells had a more spread morphology in culture compared with wild-type or mock-transfected cells. Examination of W256 cells showed that the cells expressed a number of integrins on their surface. Overexpression of 12-LOX enhanced the surface expression and focal adhesion localization of integrin alphavbeta5, while not affecting other integrins. Also, the 12-LOX-transfected W256 cells exhibited higher levels of microfilament content. Treatment of cells with monoclonal antibody to alphavbeta5 or cytochalasin B (a microfilament-disrupting agent), but not antibodies to other integrin receptors, resulted in significant apoptosis, characterized by rapid rounding up and detachment from the substratum. These results show that the 12-LOX pathway is a regulator of cell survival and apoptosis, by affecting the expression and localization of the alphavbeta5 integrin and actin microfilaments in Walker 256 cells.     

Overexpression of platelet-type 12-lipoxygenase promotes tumor cell survival by enhancing alpha(v)beta(3) and alpha(v)beta(5) integrin expression

Arachidonic acid metabolism leads to the generation of biologically active metabolites that regulate cell growth and proliferation, as well as survival and apoptosis. We have demonstrated previously that platelet-type 12-lipoxygenase (LOX) regulates the growth and survival of a number of cancer cells. In this study, we show that overexpression of platelet-type 12-LOX in prostate cancer PC3 cells or epithelial cancer A431 cells significantly extended their survival and delayed apoptosis when cultured under serum-free conditions. These effects were shown to be a result of enhanced surface integrin expression, resulting in a more spread morphology of the cells in culture. PC3 cells transfected with 12-LOX displayed increased alpha(v)beta(3) and alpha(v)beta(5) integrin expression, whereas other integrins were unaltered. Transfected A431 cells did not express alpha(v)beta(3); however, alpha(v)beta(5) integrin expression was increased. Treatment of both transfected cell lines with monoclonal antibody to alpha(v)beta(5) (and in the case of PC3 cells, anti-alpha(v)beta(3)) resulted in significant apoptosis. In addition, treatment with 100 nM 12(S)-hydroxy-eicosatetraenoic acid, the end product of platelet-type 12-LOX, but not other hydroxy-eicosatetraenoic acids, enhanced the survival of wild-type PC3 and A431 cells and resulted in increased expression of alpha(v)beta(5). Furthermore, Baicalein or N-benzyl-N-hydroxy-5-phenylpentamide, specific 12-LOX inhibitors, significantly decreased alpha(v)beta(5)-mediated adhesion and survival in 12-LOX-overexpressing cells. The results show that 12-LOX regulates cell survival and apoptosis by affecting the expression and localization of the vitronectin receptors, alpha(v)beta(3) and alpha(v)beta(5), in two cancer cell lines.     

Zyflamend-mediated inhibition of human prostate cancer PC3 cell proliferation: effects on 12-LOX and Rb protein phosphorylation

The multiherb anti-inflammatory product Zyflamend was investigated for its antiproliferative effects on PC3 human prostate cancer cells and eicosanoid metabolism in this prostate cancer cell line. Zyflamend produced a concentration-dependent inhibition of cloned COX-1, COX-2, and 5-LOX enzyme activities, with inhibition of 5-HETE production being greater than that of PGE(2) formation. Applied to intact PC3 cells, Zyflamend was found to be most potent against 12-LOX, followed by 5-LOX and then COX activities. The concentration-dependent inhibition of PC3 cell proliferation was associated with a selective G(2)/M arrest of the cell cycle and induction of apoptosis, as evidenced by flow cytometric staining of PC3 cells with annexin V. Zyflamend also produced a concentration-dependent down-regulation of 5-LOX and 12-LOX expression. Determination of cell signal transduction proteins demonstrated that Zyflamend produced an increase in p21 phosphorylation but down-regulated phosphorylation of retinoblastoma (Rb) protein. The decrease in pRb protein was shown to be due to 12-LOX inhibition and a decline in 12-HETE levels in the cells. Replenishing 12-HETE in Zyflamend-treated cells overcame the ability of this multiple herb product to inhibit cell proliferation, and concordantly, 12-HETE blocked Zyflamend's ability to down-regulate phosphorylation of Rb protein. We conclude that the effective control of human prostate cancer cell proliferation with Zyflamend is multi-mechanistic but, in part, involves regulation of aberrant tumor cell eicosanoid metabolism, especially on 5- and 12-LOX, as well as restoration of Rb tumor suppressor protein function through regulation of its phosphorylation status.     

5-Lipoxygenase inhibitors attenuate growth of human renal cell carcinoma and induce apoptosis through arachidonic acid pathway

The metabolism of arachidonic acid by either the cyclooxygenase or lipoxygenase (LOX) pathway is believed to play an important role in tumor promotion. We investigated the expression of 5- and 12-LOX in renal cell carcinoma (RCC), as well as the effects of their inhibitors on cell proliferation in 2 RCC cell lines (Caki-1 and A498). Expression of 5- and 12-LOX was detected by immunohistochemistry and RT-PCR. Effects of LOX inhibitors on RCC cell growth were examined by MTT assay, and Hoechst staining was used to determine whether or not the LOX inhibitors induce apoptosis. While 5- and 12-LOX expression levels were slightly detected in NK tissues, marked expressions of 5- and 12-LOX were detected in RCC tissues. 5-LOX inhibitors caused marked reduction of RCC cells in a concentration- and time-dependent manner. The effect of the 5-LOX inhibitor was stronger than the 12-LOX inhibitor. Furthermore, the 5-LOX inhibitor caused a marked reduction of RCC cells through apoptosis. LOX, especially 5-LOX, is induced in RCC, and the results suggest that the 5-LOX inhibitor may mediate potent anti-proliferative effects against RCC cells. Thus, 5-LOX may become a new target in treatment of RCC.     

12-Lipoxygenase inhibition induced apoptosis in human gastric cancer cells

Arachidonic acid release from membrane phospholipids is essential for tumour cell proliferation. Lipoxygenases constitute a pathway for arachidonate metabolism. The present study investigated the expression of 12-lipoxygenase and its effect on cell proliferation as well as survival in two human gastric cancer cell lines (AGS and MKN-28). RT-PCR and western blots, respectively, showed 12-LOX mRNA and protein expression in both AGS and MKN-28 cell lines. Treatment with a 12-LOX inhibitor, baicalein, significantly inhibited cancer cell proliferation, but a metabolite of 12-LOX activity, 12 hydroxyeicosatetraenoic acid (12-HETE) reversed baicalein-induced growth inhibition. Furthermore, the blockade of the 12-LOX pathway through a 12-LOX inhibitor and antisense induced apoptosis of gastric cancer cell lines. The biochemical characteristics of apoptosis were p53-independent combined with a decrease in bcl-2 expression. Caspase-7 was proteolytically activated and responsible for the apoptosis execution.     

Expression, subcellular localization and putative function of platelet-type 12-lipoxygenase in human prostate cancer cell lines of different metastatic potential

The involvement of 12-lipoxygenase (12-LOX) expression and function in tumor metastasis has been demonstrated in several murine tumor cell lines. In addition, 12-LOX expression was detected in human prostatic tumors and correlated to the clinical stage of disease. Here we provide data that human prostate cancer cell lines express the platelet-type isoform of 12-LOX at both the mRNA and protein levels, and immunohistochemistry revealed 12-LOX expression in human prostate tumors. The enzyme was localized to the plasma membrane, cytoplasmic organelles and nucleus in non-metastatic cells (PC-3 nm) and to the cytoskeleton and nucleus in metastatic cells (DU-145). After orthotopic/intraprostatic injection of tumor cells into SCID mice, the metastatic prostate carcinoma cells (DU-145) expressed 12-LOX at a significantly higher level compared with the non-metastatic counterparts, PC-3nm. The functional involvement of 12-LOX in the metastatic process was demonstrated when DU-145 cells were pretreated in vitro with the 12-LOX inhibitors N-benzyl-N-hydroxy-5-phenylpentamide (BHPP) or baicalein, the use of which significantly inhibited lung colonization. These data suggest a potential involvement of 12-LOX in the progression of human prostate cancer.