丝/苏氨酸蛋白激酶Akt及其靶向药物研究进展

丝/苏氨酸蛋白激酶Akt(又名prote in k inase B)在多种人类肿瘤中存在表达或活性失调,并且Akt在调节肿瘤细胞生长、增殖,促进细胞侵袭和转移,促进新生血管生成,以及肿瘤细胞产生化疗、放疗耐受性中起着重要作用,因此,Akt已成为抗肿瘤药物的潜在靶点。以Akt为靶点的药物开发已成为当前研究的热点。目前已开发出多种针对Akt,具有抗肿瘤活性的化合物,如API-2、Akt-I-1、Akt-I-2、DC IEL。这些化合物有可能对Akt异常的肿瘤有高选择性和高疗效,具有良好的应用前景。     

哌立福新联合顺铂抑制骨肉瘤细胞U2-OS的活性研究

目的 探讨PI3K/Akt特异性抑制剂哌立福新协同化疗药物顺铂(DDP)对骨肉瘤细胞U2-OS增殖和凋亡的影响. 方法 采用四甲基偶氮唑盐(MTT)法检测哌立福新对U2-OS细胞增殖的影响;AnnexinV FITC试剂盒检测细胞凋亡;免疫印迹法检测蛋白表达水平. 结果 哌立福新能够显著抑制U2-OS细胞的增殖,并下调U2-OS细胞中Akt的磷酸化水平. 哌立福新明显增强顺铂对U2-OS细胞的抑制作用,并通过活化胱天蛋白酶家族成员来诱导U2-OS细胞发生凋亡. 结论 PI3K/Akt 抑制剂哌立福新能够显著抑制人骨肉瘤细胞U2-OS的生长;哌立福新和顺铂协同抑制U2-OS 细胞的增殖并诱导其凋亡,其机制可能与共同调节胱天蛋白酶家族因子的活性相关.     

微管蛋白活性抑制剂研究进展

由微管蛋白聚集而成的微管是组成纺锤体的主要成分．微管蛋白聚集或微管解聚的抑制将导致细胞有丝分裂中止．很多天然产物通过结合在微管蛋白的ＣＬＣ部位或ＶＬＢ部位而抑制其聚集；少数化合物通过抑制微管的解聚而使细胞有丝分裂中止．本文对近年来微管活性抑制剂的研究进展进行了总结，着重讨论了化合物结构和活性的关系以及新的抑制微管活性化合物．大多数微管活性抑制剂都是抗肿瘤活性化合物．以微管蛋白为靶点筛选抗肿瘤药物是有效的途径之一．     

人参皂甙的抗肿瘤作用及其机制

人参皂甙的抗肿瘤作用机制较为广泛，主要表现为直接作用于癌细胞，通过诱导细胞凋亡抑制肿瘤生长或诱导细胞分化使其逆转；作用于肿瘤侵袭的多个环节抑制其转移；逆转肿瘤的耐药性提高化疗药物的抗肿瘤活性；调节免疫功能增强机体抗肿瘤能力；影响细胞连接通讯或抑制酶的活性及拮抗致癌剂的作用等。     

双肾上腺皮质激素样激酶1小分子抑制剂的研究进展

双肾上腺皮质激素样激酶1 (DCLK1)的过表达与多种恶性肿瘤的发生发展密切相关,抑制DCLK1活性,可以有效发挥抗肿瘤作用,已经成为抗肿瘤药物研发的热门领域。目前已有多个DCLK1小分子抑制剂表现出优秀的体内外抗肿瘤活性,有望为肿瘤治疗提供全新策略。基于此,本文综述了DCLK1小分子抑制剂的发现、结构类型、结构优化、生物活性及作用机制等方面的研究进展,以期为开发基于DCLK1的新型抗肿瘤小分子抑制剂提供借鉴和参考。     

木犀草素抗肿瘤血管生成作用机制的研究进展

血管生成是恶性肿瘤的标志之一,涉及血管内皮细胞的增殖、迁移和细胞外基质分解等多种途径。血管内皮生长因子（VEGF）靶向抗肿瘤血管生成是临床肿瘤治疗的有效方法。木犀草素为黄酮类化合物,具有抗肿瘤活性,可通过抑制VEGF及相关信号通路、抑制磷脂酰肌醇3-激酶/蛋白激酶B(PI3K/Akt)信号通路、抑制血管新生分子、抑制孕激素活性、靶向刺激Wnt信号通路、阻断生长停滞特异性蛋白6(Gas6)/受体酪氨酸激酶（Axl）信号通路而发挥抗肿瘤的血管生成作用。归纳了木犀草素抗肿瘤血管生成的作用机制,以期为木犀草素的临床应用提供参考。     

靶向硫氧还蛋白系统抗肿瘤药物的研究进展

硫氧还蛋白（Trx）/硫氧还蛋白还原酶（TrxR）在许多人原发性肿瘤中和肿瘤病人的血样中是高表达的.其在促进肿瘤细胞增殖、抑制细胞凋亡、促进肿瘤耐药发生等事件中起到关键的推动作用,通过化疗药物抑制TrxR的活性已成为有效的癌症靶向治疗策略.国内外都开展了硫氧还蛋白系统抑制剂的探索工作,目前国际上进入临床研究的硫氧还蛋白系统的靶向药物只有三种,本文针对临床在研的这三种药物进行总结,以期开发出新型更高效的抗肿瘤新药.     

组蛋白去乙酰化酶抑制剂抗肿瘤作用机制研究进展

组蛋白去乙酰化酶抑制剂可通过阻滞细胞周期、诱导细胞凋亡、抑制血管新生、诱导自我吞噬等多种途径发挥抗肿瘤作用。此外,与其他抗肿瘤化合物联合应用时也表现出良好的抗肿瘤活性,具有极大的临床开发潜力。     

LZ-106诱导人肺癌NCI-H2228细胞凋亡的研究

目的 研究LZ-106对间变性淋巴瘤激酶（ALK）激酶活性的抑制作用,及对ALK阳性细胞的生长抑制作用。方法 采用分子对接模拟LZ-106与ALK的结合,通过体外激酶活性实验检测其对ALK激酶活性的影响,通过CCK-8实验检测其对H2228细胞的生长抑制作用,通过Annexin V/PI细胞凋亡实验检测其对H2228细胞的凋亡作用,通过Western blotting检测其对H2228细胞p-ALK及下游信号通路关键激酶表达的影响。结果 LZ-106能抑制ALK激酶活性,半数抑制浓度（IC₅₀）为（15.51±2.09）nmol/L,其能显著抑制H2228细胞存活率,并能浓度相关性地诱导细胞凋亡。Western blotting实验显示LZ-106可以显著抑制p-ALK、p-蛋白激酶B（Akt）及p-信号转导因子和转录激活因子3（STAT3）的表达,且Akt及STAT3激活剂可以明显削弱LZ-106的凋亡诱导作用。结论 LZ-106显著抑制ALK激酶活性,诱导ALK阳性细胞凋亡,激活Akt及STAT3可以逆转LZ-106所致的细胞凋亡。     

选择性组蛋白去乙酰化酶 SIRT2抑制剂的合成及活性研究

目的设计合成新型选择性人沉默调节蛋白2(SIRT2)抑制剂并评价其抗肿瘤活性。方法首先以非典型组蛋白去乙酰化酶SIRT2作为靶标,在前期研究基础上,设计合成了6个N-(3-或4-取代苯基)-2-(芳基杂基)乙酰胺衍生物,并测试其体外对SIRT2的抑制活性;对活性最佳的化合物测试其对SIRT1和SIRT3的抑制活性从而评价其选择性;采用MTT法评价优选化合物1c对10种肿瘤细胞的抑制活性。结果与结论 6个目标化合物对SIRT2均有抑制作用,其中化合物1c活性最好,在50、5μmol·L~(-1)的抑制率分别为95%、71%,且该化合物对SIRT2具有较好的选择性;细胞水平抗肿瘤活性测试表明,化合物1c对肝癌细胞HUH7有较好的抑制作用,在50、25μmol·L~(-1)时的抑制率分别为92%和78%。该研究为特异性SIRT2小分子抑制剂的开发及靶向SIRT2的抗肿瘤药物研究奠定了一定基础。     

Recent progress in the development of ATP-competitive and allosteric Akt kinase inhibitors

This article describes recent advances in the development and biological evaluation of small molecule inhibitors for the serine/threonine kinase Akt (PKB). Akt plays a pivotal role in cell survival and proliferation through a number of downstream effectors. Recent studies indicate that unregulated activation of the PI3K/Akt pathway is a prominent feature of many human cancers and Akt is over-expressed or activated in all major cancers. Akt is considered an attractive target for cancer therapy and inhibition of Akt alone or in combination with standard cancer chemotherapeutics has been postulated to reduce the apoptotic threshold and preferentially kill cancer cells. The development of specific and potent inhibitors will allow this hypothesis to be tested in animals. Recently, several series of small molecule, ATP-competitive inhibitors have been reported with a range of Akt potencies and selectivities. Phosphatidylinositol (PI) analogs have been reported to inhibit Akt, but these inhibitors may also have specificity problems with respect to other pleckstrin homology (PH) domain containing proteins and may have poor bioavailability. In addition, novel allosteric inhibitors have been reported which are PH domain dependent, exhibit selectivity for the individual Akt isozymes and inhibit the activity and the activation of Akt. Compounds within these classes Akt inhibitors have sufficient potency and specificity to test for tumor efficacy in animal models and recently reported preliminary experiments are reviewed.     

The Akt/PKB family of protein kinases: a review of small molecule inhibitors and progress towards target validation

This article describes recent advances in the development and biological evaluation of small molecule inhibitors for the serine/threonine kinase Akt (PKB). Akt plays a pivotal role in cell survival and proliferation through a number of downstream effectors. Recent studies indicate that unregulated activation of the PI3K/Akt pathway is a prominent feature of many human cancers and Akt is over-expressed or activated in all major cancers. Akt is considered an attractive target for chemotherapy and it has been postulated that inhibition of Akt alone or in combination with standard cancer chemotherapeutics will reduce the apoptotic threshold and preferentially kill cancer cells. The development of specific and potent inhibitors will allow this hypothesis to be tested in animals. The majority of small molecule inhibitors in this nascent field are classic ATP-competitive inhibitors which provide little specificity. Phosphatidylinositol (PI) analogs have been reported to inhibit Akt, but these inhibitors may also have specificity problems with respect to other PH domain containing proteins and may have poor bioavailability. None of the inhibitors in these classes have been reported to have Akt isozyme specificity. Recently, novel allosteric inhibitors have been reported which are pleckstrin homology domain dependent and exhibit Akt isozyme selectivity. Inhibitors in this class may have sufficient potency and specificity to test for tumor efficacy in animal models and recently reported preliminary experiments are reviewed.     

Developments in selective small molecule ATP-targeting the serine/threonine kinase Akt/PKB

The serine/threonine kinase Akt, also known as protein kinase B (PKB), plays a key role in cell survival and proliferation through a number of downstream effectors. Recent studies indicate that unregulated activation of the Phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a prominent feature of many human cancers and Akt is overexpressed or activated in all major cancers. For these reasons, Akt is considered as an attractive target for cancer therapy. In the past few years, several series of compounds with diverse structural features have been reported as Akt inhibitors, such as, ATP-competitive inhibitors, Phosphatidylinositol (PI) analogs, and allosteric inhibitors. Although most of the inhibitors exhibited potent inhibitory activities at nanomolar concentrations against Akt, some of them have shown unfavorable selectivity against other protein kinases especially PKA and PKC. This review will focus on the recent advances in the development and biological evaluation of selective ATP-competitive inhibitors for Akt. We will summarize the novel approaches toward the developments of selective ATP-competitive inhibitors, expecting to give information to design new ATP-competitive inhibitors with high selectivity, bioavailability, and potency.     

Resistance to epidermal growth factor receptor-targeted therapy.

The epidermal growth factor receptor (EGFR) has been a major target of molecular anticancer therapy. Two approaches have been developed, involving monoclonal antibodies and receptor tyrosine kinase inhibitors, and both have demonstrated benefit in clinical trials. However, evidence of resistance to these drugs has been described. Cellular levels of EGFR do not always correlate with response to the EGFR tyrosine kinase inhibitors, indicating acquired resistance to these drugs. Since EGFR antagonists interfere with the activation of several intracellular pathways that control cell proliferation, survival, apoptosis, angiogenesis, invasion and metastasis, acquired resistance can occur as a result of several different molecular mechanisms: autocrine/paracrine production of ligand, receptor mutation, constitutive activation of the downstream pathway and activation of alternative pathways. We will describe here potential mechanisms that can cause resistance to EGFR-targeted drugs. Combinations of EGFR antagonists with inhibitors targeting different signaling mechanism(s) - such as insulin-like growth factor receptor and vascular endothelial growth factor receptor - that share the same downstream mediator (e.g., phosphatidylinositol 3-kinase/Akt, mitogen-activated protein kinase), may circumvent or delay the development of resistance to EGFR antagonists resulting in enhanced antitumor activities.     

Evidence that Akt mediates platelet-derived growth factor-dependent increases in activity and surface expression of the neuronal glutamate transporter, EAAC1

Previously we have shown that platelet-derived growth factor (PDGF) rapidly increases the activity of the neuronal glutamate transporter, EAAC1. This increase in activity is associated with a rapid (within minutes) redistribution of transporter from a subcellular compartment to the plasma membrane and is blocked by inhibitors of phosphatidylinositol 3-kinase (PI3K). Similar effects of PI3K inhibitors have been observed for insulin-dependent up-regulation of the GLUT4 subtype of glucose transporter. Although GLUT4 regulation also depends on the serine-threonine kinase (Akt/protein kinase B), a downstream target of PI3K, the downstream effectors responsible of PDGF-dependent regulation of EAAC1 have not been identified. In the present study, PDGF increased the level of Akt phosphorylation (Ser 473) in C6 glioma cells, a cell line that has been used to study regulated trafficking of endogenous EAAC1. Two inhibitors of PI3K blocked this effect. In transient transfection studies, a dominant negative mutant of Akt-1 blocked PDGF-induced redistribution of epitope-tagged EAAC1 (myc-EAAC1). Conversely, constitutively active Akt-1 (CA Akt-1) increased the cell surface expression of myc-EAAC1. A lentiviral vector engineered to express CA Akt-1 increased Akt activation, cell surface expression of endogenous EAAC1, and Na(+)-dependent glutamate transport activity. Together, these studies suggest that Akt is required for PDGF-induced regulation of EAAC1.     

Cyclosporin A suppresses prostate cancer cell growth through CaMKKβ/AMPK-mediated inhibition of mTORC1 signaling

Cyclosporin A (CsA) has antitumor effects on various cancers including prostate cancer. However, its antitumor mechanism is poorly understood. In this study, we showed that AMP-activated protein kinase (AMPK) mediates the antitumor effect of CsA on prostate cancer cells. CsA attenuated cell growth by inducing a G1 arrest through the inhibition of mTOR complex 1 (mTORC1) signaling. In this context, Akt was paradoxically activated downstream of the EGF receptor (EGFR)-mediated increase in phosphatidylinositol 3,4,5-trisphosphate (PIP₃) production. However, CsA also caused a Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ)-dependent activation of AMPK, which inhibits mTORC1 signaling; this led to ineffective Akt signaling. An EGFR or Akt inhibitor increased the growth suppressive activity of CsA, whereas the combination of an AMPK inhibitor and CsA markedly rescued cells from the G1 arrest and increased cell growth. These results provide novel insights into the molecular mechanisms of CsA on cancer signaling pathways.     

Recent progress in the discovery of Akt inhibitors as anticancer agents

Akt, also referred to as protein kinase B (PKB) or Related to A and C (RAC), is one of the major direct downstream targets of phosphoinositide 3-kinase (PI3K). As it plays a central role in promoting cancer cell proliferation and survival through a growing list of key substrates, intense efforts are underway to find inhibitors of Akt for the treatment of cancer. Discovery of potent and novel inhibitors of Akt has been facilitated greatly by the availability of the X-ray structure of the active form of Akt and by its structural similarity with other serine/threonine kinases. In this review, new Akt inhibitors for the treatment of cancer are comprehensively reviewed, with emphasis on small molecule inhibitors that bind to the ATP-binding site, allosteric sites and the PH domains. Inhibitors of pseudosubstrates and antisense oligonucleotides, as well as Akt inhibitors with unknown mechanism of actions, are also reviewed. Results of clinical trials of several Akt drug candidates are briefly discussed. A brief summary of Akt structure and regulation and the evidences supporting Akt as a cancer target is provided as well. The patent literature is surveyed through July 2007.     

Inhibition of Akt signaling in hepatoma cells induces apoptotic cell death independent of Akt activation status

The serine/threonine kinase Akt, a downstream effector of phosphatidylinositol 3-kinase (PI3K), is involved in cell survival and anti-apoptotic signaling. Akt has been shown to be constitutively expressed in a variety of human tumors including hepatocellular carcinoma (HCC). In this report we analyzed the status of Akt pathway in three HCC cell lines, and tested cytotoxic effects of Akt pathway inhibitors LY294002, Wortmannin and Inhibitor VIII. In Mahlavu human hepatoma cells Akt was constitutively activated, as demonstrated by its Ser473 phosphorylation, downstream hyperphosphorylation of BAD on Ser136, and by a specific cell-free kinase assay. In contrast, Huh7 and HepG2 did not show hyperactivation when tested by the same criteria. Akt enzyme hyperactivation in Mahlavu was associated with a loss of PTEN protein expression. Akt signaling was inhibited by the upstream kinase inhibitors, LY294002, Wortmannin, as well as by the specific Akt Inhibitor VIII in all three hepatoma cell lines. Cytotoxicity assays with Akt inhibitors in the same cell lines indicated that they were all sensitive, but with different IC50 values as assayed by RT-CES. We also demonstrated that the cytotoxic effect was through apoptotic cell death. Our findings provide evidence for its constitutive activation in one HCC cell line, and that HCC cell lines, independent of their Akt activation status respond to Akt inhibitors by apoptotic cell death. Thus, Akt inhibition may be considered as an attractive therapeutic intervention in liver cancer.     

Homocysteine induces cell cycle G1 arrest in endothelial cells through the PI3K/Akt/FOXO signaling pathway

OBJECTIVE: High levels of homocysteine (Hcy) induce a sustained injury on arterial endothelial cells, which accelerates the development of thrombosis and atherosclerosis. Hcy specifically inhibits the growth of endothelial cells. The present study investigated the signaling pathways underlying this cell-cycle effect. METHODS: Human umbilical venous endothelial cells were treated with Hcy, and/or LY294002, okadaic acid, peroxovanadate (PV), antisense Akt, phosphorylation of Akt and FKHRL1 proteins. p27(kip1) protein levels were measured with Western blotting, and Akt kinase activity and cell cycle were measured with immunoprecipitation and flow cytometry, respectively. RESULTS: We demonstrate that Hcy induces dephosphorylation of Akt and FKHRL1 and upregulates the cyclin-dependent kinase inhibitors p27(kip1) in a time- and dose-dependent manner. Phosphatidylinositol-3 kinase (PI3K) activator PV and phosphatase 2A inhibitor okadaic acid could reverse it, which suggests it was dependent on PI3K activity. Moreover, Hcy induces cell cycle G1 phase arrest prevented by pretreatment with PV and okadaic acid. Transfection with specific antisense oligonucleotides to Akt further proves the observations. CONCLUSIONS: The studies implied that a novel signaling pathway, PI3K/Akt/FOXO, might play an important role in mediating cell cycle G1 arrest in endothelial cells.