The PTEN/PI3K/AKT signalling pathway in cancer, therapeutic implications

PTEN/PI3K/AKT constitutes an important pathway regulating the signaling of multiple biological processes such as apoptosis, metabolism, cell proliferation and cell growth. PTEN is a dual protein/lipid phosphatase which main substrate is the phosphatidyl-inositol,3,4,5 triphosphate (PIP3), the product of PI3K. Increase in PIP3 recruits AKT to the membrane where it is activated by other kinases also dependent on PIP3. Many components of this pathway have been described as causal forces in cancer. PTEN activity is lost by mutations, deletions or promoter methylation silencing at high frequency in many primary and metastatic human cancers. Germ line mutations of PTEN are found in several familial cancer predisposition syndromes. Activating mutations which have been reported for PI3K and AKT, in tumours are able to confer tumourigenic properties in several cellular systems. Additionally, the binding of PI3K to oncogenic ras is essential for the transforming properties of ras. In summary, the data strongly support the view of the PTEN/PI3K/AKT pathway as an important target for drug discovery.     

The anti-tumor effect of pachymic acid on osteosarcoma cells by inducing PTEN and Caspase 3/7-dependent apoptosis

Pachymic acid (PA) is a lanostane type triterpenoid isolated from Poria cocos, which possesses an anti-tumor effect in breast cancer, prostate cancer, lung cancer, and bladder cancer cells. In this study, we investigated the effect of PA on the growth and apoptosis of human immortalized cell line (HOS) and primary osteosarcoma cells by a Cell Counting Kit-8 (CCK-8) and Annexin V and propidium iodide (PI) staining, respectively. Western blot was used to measure the expression of cleaved Caspase 3, PTEN, and AKT, as well as the AKT phosphorylation. The Caspase 3 activity was determined using the Caspase-3 Colorimetric Assay Kit. From the results, PA significantly reduced cell proliferation in a concentration- and time-dependent manner. PA also induced cell apoptosis in a dose-dependent fashion. PA treatment led to increased Caspase 3 activation and PTEN expression, as well as reduced AKT phosphorylation. Moreover, Ac-DEVD-CHO (a Caspase 3/7 inhibitor) pre-treatment or PTEN knockdown partially blocked the effects of PA on cell proliferation and apoptosis. Caspase 3/7 inhibitor had an additive effect with PTEN knockdown. Collectively, our results suggested that induction of apoptosis by PA was mediated in part by PTEN/AKT signaling and Caspase 3/7 activity. This study provides evidence that PA might be useful in the treatment of human osteosarcoma.     

Targeting the AKT pathway in glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant brain tumor in adults. The treatment options for patients diagnosed with GBM are limited and the current median survival is 14-16 months following diagnosis. Genetic mutations have been identified that act as drivers of GBM growth and these should be considered as a basis for identifying novel therapeutic strategies. AKT is a downstream serine/threonine kinase in the RTK/PTEN/PI3K pathway and large scale genomic analysis of GBM has demonstrated that this pathway is mutated in the majority of GBMs. This RTK/PTEN/PI3K pathway leads to activated AKT and phospho-AKT levels are elevated in the majority of GBM tumor samples and cell lines, which studies show help glioma cells grow uncontrolled, evade apoptosis, and enhance tumor invasion. AKT represents a nodal point in this pathway which allows for amplification of growth signals, thereby making inhibition of AKT an attractive target for GBM therapy. Many different classes of AKT inhibitors exist, however, few have been tested sufficiently to demonstrate in vivo efficacy. This article will summarize the key components of the Akt pathway with special attention to gliomas, the genetic alterations driving this pathway in gliomas, and the studies evaluating inhibitors of this pathway. Inhibitors of the Akt pathway represent a potential treatment option against GBM and additional research efforts are required to fully explore and develop this possible treatment strategy.     

PTEN/mTOR通路在高糖诱导的人绒毛膜滋养层细胞HTR-8/SVneo凋亡中的作用机制探讨 #br#

目的 探讨高糖诱导人绒毛膜滋养层细胞HTR-8/SVneo凋亡的相关机制。方法 体外培养人绒毛膜滋 养层细胞HTR-8/SVneo,分为空白对照组、高糖组、NC组（阴性对照组）、第10号染色体缺失的磷酸酶及张力蛋白同 源物基因（PTEN）-siRNA 组（抑制 PTEN 表达组）及哺乳动物雷帕霉素靶蛋白（mTOR）通路抑制剂（GDC-0349）组。 四甲基偶氮唑蓝（MTT）法检测HTR-8/SVneo细胞增殖能力;流式细胞仪检测细胞凋亡情况;蛋白免疫印迹法检测凋 亡相关蛋白及PTEN/mTOR通路相关蛋白表达情况。结果 与空白对照组比较,高糖组HTR-8/SVneo细胞增殖抑制 率、凋亡率及Bcl-2相关X蛋白（Bax）、活化的含半胱氨酸的天冬氨酸蛋白水解酶3（cleaved caspase-3）、PTEN蛋白表 达水平均显著升高（P＜0.05）,B淋巴细胞瘤-2（Bcl-2）、磷酸化磷脂酰肌醇-3激酶（p-PI3K）/PI3K、磷酸化蛋白激酶B （p-AKT）/AKT、磷酸化 mTOR（p-mTOR）/mTOR 蛋白表达水平显著降低（P＜0.05）;与高糖组、NC 组比较,PTENsiRNA组HTR-8/SVneo细胞增殖抑制率、凋亡率及Bax、cleaved caspase-3、PTEN蛋白表达水平均显著降低,Bcl-2、pPI3K/PI3K、p-AKT/AKT、p-mTOR/mTOR 蛋白表达水平显著升高（P＜0.05）;与 PTEN-siRNA 组比较,GDC-0349 组 HTR-8/SVneo细胞增殖抑制率、凋亡率及Bax、cleaved caspase-3蛋白表达水平均显著升高,Bcl-2、p-PI3K/PI3K、pAKT/AKT、p-mTOR/mTOR 蛋白表达水平显著降低（P＜0.05）。结论 高糖可抑制人绒毛膜滋养层细胞 HTR-8/ SVneo增殖能力,诱导其凋亡,可能是通过上调PTEN表达、抑制PI3K/AKT/mTOR通路活化实现的。     

Deregulation of the Akt pathway in human cancer

Akt (protein kinase B) is a serine/threonine kinase which is a central regulator of widely divergent cellular processes including proliferation, differentiation, migration, survival and metabolism. Akt is activated by a variety of stimuli, through growth factor receptors, in phosphatidylinositol 3-kinase (PI3K)-dependent manner. Akt is also negatively regulated by the tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN). A disruption of normal Akt/PKB/PTEN signaling frequently occurs in many human cancers, which plays an important role in cancer development, progression and therapeutic resistance. Numerous studies have revealed the blockage of Akt signaling to result in apoptosis and growth inhibition of tumor cells. Therefore, this signaling pathway, including both upstream and downstream of Akt, has recently attracted considerable attention as a new target for effective cancer therapeutic strategies. In fact, many inhibitors of Akt pathway have been identified and clinical studies of some agents are ongoing. In this review, we describe Akt signaling pathway components and its cellular functions as well as the alterations in human cancers and the therapeutic approaches for targeting the Akt pathway in cancer.     

三种蛋白在上皮性卵巢癌中的表达及意义

目的 检测PIK3CA、AKT2、FFEN在上皮性卵巢癌中的表达情况,分析其与临床病理参数的关系,探讨三者在上皮性卵巢癌发生发展中的可能作用机制.方法 采用免疫组织化学S-P法及半定量分析法检测29例正常卵巢及64例上皮性卵巢癌组织中PIK3CA、AKT2、PTEN蛋白的表达情况,分析在上皮性卵巢癌中三者与临床病理特征之间的关系以及三者之间的相关性.结果 PIK3CA蛋白表达部位主要在细胞质内.在正常卵巢组织及上皮性卵巢癌组织中灰度值分别为(85.21±4.74)、(46.68±10.22),差异有统计学意义(P<0.01).AKT2蛋白表达部位主要在细胞质内.在正常卵巢组织及上皮性卵巢癌组织中灰度值分别为(85.72±4.29)、(46.17±9.29),差异有统计学意义(P<0.01).PTEN阳性染色主要定位于细胞质,有少量定位于细胞核.在正常卵巢组织及上皮性卵巢癌组织中灰度值分别为(41.49±4.67)、(73.74±11.33),差异有统计学意义(P<0.01).PIK3CA与AKT2蛋白在上皮性卵巢癌中的表达均高于正常卵巢组织,PTEN蛋白表达低于正常卵巢组织,差异均有统计学意义(P<0.01);上皮性卵巢癌中,PIK3CA与AKT2蛋白在中低分化及Ⅲ～Ⅳ期组织中表达高于高分化及Ⅰ～Ⅱ期,差异有统计学意义(P<0.05),PTEN蛋白在中低分化及Ⅲ～Ⅳ期组织中表达低于高分化及Ⅰ～Ⅱ期,差异有统计学意义(P<0.05),三者在患者的年龄、组织学类型分组中表达差异无统计学意义(P>0.05);上皮性卵巢癌中,PIK3CA与AKT2蛋白表达呈正相关(r=0.674,P<0.01),PIK3CA与PTEN表达呈负相关(r=-0.514,P<0.01),AKT2与PTEN表达呈负相关(r=-0.589,P<0.01).结论 PIK3CA、AKT2蛋白的表达升高和PTEN蛋白表达降低在卵巢癌的发生、发展中起重要作用,P13K/AKT信号通路参与卵巢癌的演进过程.联合检测PIK3CA、AKT2、PTEN有助于卵巢癌的临床早期诊断和治疗,为生物靶向治疗提供新的线索.

Abstract：

Objective To investigate the expression of PIK3CA, AKT2 and PTEN in epithelial ovarian cancer, to analyze their relation to clinical and pathologic features and prognosis of epithelial ovarian cancer. Methods The expression of PIK3CA, AKT2 and PTEN protein were studied by immunohisto chemical methods in 29 normal o-vary tissues and 64 epithelial ovarian carcinoma. The correlation between clinical and pathologic features in ovarian cancer was also analyzed. Results The expression of PIK3CA and AKT2 protein in epithelial ovarian cancer was significantly higher than that in normal ovary tissues ( P <0. 01). In epithelial ovarian cancer, the expression of PIK3CA and AKT2 protein in mid and low histological grade and Ⅲ-Ⅳ clinical stage was significantly higher than that in high histological grade and Ⅰ-Ⅱ clinical stage (P <0. 05). In epithelial ovarian cancer, the expressions were not related with age and histological type(P >0.05). The expression of PIK3CA protein was positively correlated with the expression of AKT2 protein (r =0.674, P <0.01). The expression of PTEN was negatively correlated with the expression of PIK3CA(r= -0.514, P<0.01)and the expression of PTEN was negatively correlated with the expression of AKT2 (r =- 0.589, P < 0.01). Conclusions The high expression of PIK3CA and AKT2 protein as well as the low expression of PTEN protein are closely related to the occurrence and development of ovarian cancer. PI3K/AKT signal pathway takes part in the evolvement process of ovarian cancer. To-investigate the expression of PIK3CA, AKT2 and PTEN protein are helpful for the clinical diagnosis and treatment of ovarian cancer.     

AKT signaling in regulating angiogenesis

AKT is a central signaling molecule in regulating cell survival, proliferation, tumor growth and angiogenesis. Upstream components of AKT signaling pathway such as PI3K, PTEN, and Ras are commonly mutated in many human cancers. Recently it is found that AKT plays an important role in regulating normal vascularization and pathological angiogenesis. Angiogenesis is required for tumor growth and metastasis when tumor reaches more than 1 mm in diameter. This review focuses on the role and potential mechanism of AKT signaling in regulating angiogenesis. Recent studies have shown that AKT activation is necessary and sufficient to regulate VEGF and HIF-1 expression in human cancer cells. VEGF and HIF-1 are potent inducers of angiogenesis. It was found that AKT activation induces VEGF and HIF-1 expression through its two downstream molecules HDM2 and p70S6K1. On the other hand, AKT transmits the upstream signals from growth factors, cytokines, heavy metals, and oncogenes for regulating VEGF and HIF-1 expression in human cancer cells. AKT activation and VEGF expression can be inhibited by different natural compounds used for cancer prevention. Thus, inhibition of AKT and its downstream targets offers a new approach for targeting angiogenesis, which could be important for the development of new cancer therapeutics in the future.     

PTEN mediates serum deprivation-induced cytotoxicity in H9c2 cells via the PI3K/AKT signaling pathway

The pathogenesis of acute myocardial infarction (AMI) is associated with cardiomyocyte necrosis and apoptosis. Numerous studies have determined the regulatory effects of Phosphatase and tensin homolog (PTEN) cell proliferation and apoptosis in other cell types. However, the potential role of PTEN in cardiomyocyte is unclear. In this study, we used H9c2 cells cultured under serum deprivation to simulate the apoptosis process of myocardial infarction. Small interference RNA (siRNA) of PTEN was used to knock down the expression of PTEN. Cell viability was determined by CCK-8. Cell proliferation was examined by Edu staining, and the protein expression was analyzed by Western blot. We also evaluated the generation of ROS, the degree of DNA damage, and cell apoptosis using immunofluorescence assay. As a result, we observed that serum deprivation in H9c2 cells increased PTEN expression. Functionally, the PTEN knockdown experiment using siRNA inhibited serum deprivation-induced cell apoptosis, ROS production, and DNA damage, whereas increased cell proliferation. All these effects could be reversed by phosphatidylinositol 3-kinase (PI3K) inhibitor, which indicated the PI3K/protein kinase B (AKT) might be the critical component of the PTEN effects during serum deficiency. In conclusion, our study indicated the role of the PTEN/PI3K/AKT pathway in serum deprivation-induced cytotoxicity in H9c2 cells.     

miR-552通过PTEN/AKT信号通路促进非小细胞肺癌A549细胞的恶性生物学行为

目的 探讨miR-552通过调控PTEN/AKT信号通路促进人非小细胞肺癌A549细胞的恶性生物学行为及其相关机制。方法 通过qRT-PCR检测人肺癌组织样本和人非小细胞肺癌A549细胞系中miR-552、PTEN mRNA的表达情况;通过Western blotting检测PTEN、AKT、p-AKT蛋白的表达情况;通过CCK-8检测miR-552表达对A549细胞增殖能力的影响;通过Transwell小室检测miR-552表达对A549细胞迁移和侵袭能力的影响;通过流式细胞术检测miR-552表达对A549细胞凋亡能力的影响。结果 miR-552在肺癌组织和A549细胞中的表达显著上调。过表达miR-552可显著促进A549细胞的增殖、迁移和侵袭,并抑制细胞凋亡,而抑制其表达则结果相反。与癌旁组织相比,肺癌组织中PTEN表达显著下调。过表达miR-552可下调PTEN蛋白表达,上调p-AKT蛋白表达,对AKT蛋白无影响,而抑制其表达则结果相反。结论 miR-552可能通过PTEN/AKT信号通路促进人非小细胞肺癌A549细胞的恶性生物学行为。     

Ursolic acid-induced apoptosis in K562 cells involving upregulation of PTEN gene expression and inactivation of the PI3K/Akt pathway

Ursolic acid (UA), a pentacyclic triterpenoid derived from a variety of medicinal plants, exhibits potent anticancer activity against many types of cancer cells. However, the anticancer mechanism of UA is not clearly understood. Suppression of phosphatase and a tensin homolog deleted on chromosome 10 (PTEN) gene expression leading to activation of the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway has been observed in many cancers including leukemia, making the PTEN gene and PI3K/Akt pathway a central target for cancer therapy. Here, we demonstrated that UA was able to inhibit growth, induce apoptosis in a human chronic myelogenous leukemia cell line (K562 cells) via upregulation of PTEN gene expression, inhibit Akt kinase activity, change mitochondrial transmembrane potential and reduce the release of cytochrome c and the activity of caspases. These results suggest that UA may elicit its strong antitumor effects via upregulation of the PTEN gene and inhibition of the PI3K/Akt pathway.     

The complexity of PTEN: mutation, marker and potential target for therapeutic intervention

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase that removes phosphates primarily from lipids. It has also been called mutated in multiple advanced cancers 1 and transforming growth factor-beta regulated epithelial cell-enriched phosphatase 1. The best described substrate of PTEN is phosphatidyliniositol (3,4,5)-tris-phosphate [PtdIns(3,4,5)P3]. PTEN removes the phosphate in PtdIns(3,4,5)P(3) to generate PtdIns(4,5)P(2). PTEN serves to counter-balance the effects of phosphoinositide 3' kinase, which normally adds a phosphate to PtdIns(4,5)P(2) to generate PtdIns(3,4,5)P(3). PtdIns(3,4,5)P(3) recruits kinases such as phosphoinositide-dependent kinase 1, which in turn phosphorylate Akt, which phosphorylates other downstream proteins involved in regulation of apoptosis and cell-cycle progression. PTEN removal of the phosphate from PtdIns(3,4,5)P(3) inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane. Alterations of the PTEN gene are associated with cancer and other diseases. Novel therapeutic approaches have been developed to counteract the deletion/mutation of PTEN in human cancer. This review will discuss the role of PTEN in signal transduction and cancer as well as pharmacological approaches to combat PTEN loss in human cancer.     

TP53基因沉默介导PI3K/PTEN/AKT信号通路对肾透明细胞癌侵袭转移的调控机制

目的探讨肿瘤蛋白p53基因(TP53)沉默介导PI3K/PTEN/AKT信号通路对肾透明细胞癌侵袭转移的调控机制。方法取60例肾透明细胞癌组织标本,免疫组化分析TP53蛋白在肾透明细胞癌组织中的表达;取人肾透明细胞癌细胞株RLC-310进行细胞培养;细胞转染表达载体分为空白组(A组)、阴性对照组(B组)、sh TP53组(C组)、PTEN抑制剂bpv组(D组)、phen+sh TP53组(E组)。采用实时荧光定量PCR(qRT-PCR)和Western Blot检测各组细胞TP53、同源性磷酸酶-张力蛋白(PTEN)、磷脂酰肌醇-3-激酶(PI3K)、AKT的m RNA和蛋白表达水平;CCK-8法检测各组细胞增殖能力;划痕愈合试验检测各组细胞的迁移能力;Transwell侵袭试验检测各组细胞的侵袭能力。结果TP53蛋白在肾透明细胞癌组织中高表达(P<0.05);与A组和B组相比,C组的TP53,PI3K,AKT m RNA和蛋白表达水平显著下降,PTEN m RNA和蛋白表达水平均显著上升,且细胞增殖能力、迁移率、侵袭率均显著下降(P<0.05);D组TP53,PI3K,AKT m RNA和蛋白表达水平显著上升,PTEN m RNA和蛋白表达水平显著下降,且细胞增殖能力、迁移率、侵袭率均显著上升(P<0.05);同时,E组TP53下降(P<0.05),而其他指标与A组和B组相当(P>0.05)。结论沉默TP53基因抑制PI3K/PTEN/AKT信号通路,从而抑制肾透明细胞癌细胞浸润转移功能,并可逆转phen诱导的肾透明细胞癌细胞浸润转移。     

基于PI3K/AKT通路探究柚皮素改善多囊卵巢综合征大鼠胰岛素抵抗的作用机制

目的　基于磷脂酰肌醇3激酶（PI3K）/蛋白激酶B（AKT）通路,初步探究柚皮素防治大鼠多囊卵巢综合征（PCOS）胰岛素抵抗的分子机制。方法　SD大鼠颈背部每日皮下注射脱氢表雄酮建立PCOS模型,将造模成功的大鼠采用随机数字表法分为模型组、柚皮素组、PI3K抑制剂组、柚皮素+PI3K抑制剂组,每组15只;相同时间段取SD大鼠15只,于颈背部皮下注射油剂2 mL/kg,作为正常对照组。检测各组大鼠血糖、胰岛素、血脂、生殖激素水平,计算胰岛素抵抗指数;HE染色观察卵巢形态;免疫组化法检测磷酸化PI3K（p-PI3K）阳性表达;Western blot法检测PI3K/AKT通路磷酸化蛋白及通路相关蛋白胰岛素受体底物-1（IRS-1）、糖原合成酶激酶-3β（GSK-3β）、葡萄糖转运蛋白因子-4（GLUT4）、人第10号染色体上磷酸酶和张力蛋白同源缺失基因（PTEN）蛋白表达。结果　与正常对照组相比,模型组大鼠卵巢组织出现卵泡囊性扩张、黄体数量及颗粒细胞层减少、闭锁卵泡增多等病理损伤症状,血脂、血糖、胰岛素水平升高,胰岛素抵抗增加,生殖激素分泌紊乱,PI3K/AKT通路磷酸化蛋白及通路相关蛋白IRS-1、GSK-3β磷酸化蛋白表达、GLUT4蛋白表达降低,PTEN蛋白表达升高（P＜0.05）。柚皮素可减轻卵泡囊性扩张等病理损伤,促进PI3K/AKT通路及通路相关蛋白IRS-1、GSK-3β磷酸化蛋白及GLUT4蛋白表达,改善生殖激素分泌紊乱现象,减轻胰岛素抵抗,降低血糖、血脂水平及PTEN蛋白表达（P＜0.05）。PI3K抑制剂可减弱柚皮素的上述作用（P＜0.05）。结论　柚皮素可通过促进PI3K/AKT通路活化,降低血糖、血脂水平及胰岛素抵抗,改善PCOS大鼠生殖激素紊乱及卵巢多囊改变。     

Targeting the PI3K/AKT/mTOR Signaling Axis in Children with Hematologic Malignancies

The phosphatidylinositiol 3-kinase (PI3K), AKT, mammalian target of rapamycin (mTOR) signaling pathway (PI3K/AKT/mTOR) is frequently dysregulated in disorders of cell growth and survival, including a number of pediatric hematologic malignancies. The pathway can be abnormally activated in childhood acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), and chronic myelogenous leukemia (CML), as well as in some pediatric lymphomas and lymphoproliferative disorders. Most commonly, this abnormal activation occurs as a consequence of constitutive activation of AKT, providing a compelling rationale to target this pathway in many of these conditions. A variety of agents, beginning with the rapamycin analogue (rapalog) sirolimus, have been used successfully to target this pathway in a number of pediatric hematologic malignancies. Rapalogs demonstrate significant preclinical activity against ALL, which has led to a number of clinical trials. Moreover, rapalogs can synergize with a number of conventional cytotoxic agents and overcome pathways of chemotherapeutic resistance for drugs commonly used in ALL treatment, including methotrexate and corticosteroids. Based on preclinical data, rapalogs are also being studied in AML, CML, and non-Hodgkin's lymphoma. Recently, significant progress has been made using rapalogs to treat pre-malignant lymphoproliferative disorders, including the autoimmune lymphoproliferative syndrome (ALPS); complete remissions in children with otherwise therapy-resistant disease have been seen. Rapalogs only block one component of the pathway (mTORC1), and newer agents are under preclinical and clinical development that can target different and often multiple protein kinases in the PI3K/AKT/mTOR pathway. Most of these agents have been tolerated in early-phase clinical trials. A number of PI3K inhibitors are under investigation. Of note, most of these also target other protein kinases. Newer agents are under development that target both mTORC1 and mTORC2, mTORC1 and PI3K, and the triad of PI3K, mTORC1, and mTORC2. Preclinical data suggest these dual- and multi-kinase inhibitors are more potent than rapalogs against many of the aforementioned hematologic malignancies. Two classes of AKT inhibitors are under development, the alkyl-lysophospholipids (APLs) and small molecule AKT inhibitors. Both classes have agents currently in clinical trials. A number of drugs are in development that target other components of the pathway, including eukaryotic translation initiation factor (eIF) 4E (eIF4E) and phosphoinositide-dependent protein kinase 1 (PDK1). Finally, a number of other key signaling pathways interact with PI3K/AKT/mTOR, including Notch, MNK, Syk, MAPK, and aurora kinase. These alternative pathways are being targeted alone and in combination with PI3K/AKT/mTOR inhibitors with promising preclinical results in pediatric hematologic malignancies. This review provides a comprehensive overview of the abnormalities in the PI3K/AKT/mTOR signaling pathway in pediatric hematologic malignancies, the agents that are used to target this pathway, and the results of preclinical and clinical trials, using those agents in childhood hematologic cancers.     

The complexity of PTEN: mutation,marker and potential target for therapeutic intervention

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase that removes phosphates primarily from lipids. It has also been called mutated in multiple advanced cancers 1 and transforming growth factor-β regulated epithelial cell-enriched phosphatase 1. The best described substrate of PTEN is phosphatidyliniositol (3,4,5)-tris-phosphate [PtdIns(3,4,5)P3]. PTEN removes the phosphate in PtdIns(3,4,5)P₃ to generate PtdIns(4,5)P₂. PTEN serves to counter-balance the effects of phosphoinositide 3′ kinase, which normally adds a phosphate to PtdIns(4,5)P₂ to generate PtdIns(3,4,5)P₃. PtdIns(3,4,5)P₃ recruits kinases such as phosphoinositide-dependent kinase 1, which in turn phosphorylate Akt, which phosphorylates other downstream proteins involved in regulation of apoptosis and cell-cycle progression. PTEN removal of the phosphate from PtdIns(3,4,5)P₃ inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane. Alterations of the PTEN gene are associated with cancer and other diseases. Novel therapeutic approaches have been developed to counteract the deletion/mutation of PTEN in human cancer. This review will discuss the role of PTEN in signal transduction and cancer as well as pharmacological approaches to combat PTEN loss in human cancer.     

The phosphoinositide 3-kinase signaling pathway as a therapeutic target in grade IV brain tumors

Brain tumors comprise a wide variety of neoplasia classified according to their cellular origin and their morphological and histological characteristics. The transformed phenotype of brain tumor cells has been extensively studied in the past years, achieving a significant progress in our understanding of the molecular pathways leading to tumorigenesis. It has been reported that the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway is frequently altered in grade IV brain tumors resulting in uncontrolled cell growth, survival, proliferation, angiogenesis, and migration. This aberrant activation can be explained by oncogenic mutations in key components of the pathway or through abnormalities in its regulation. These alterations include overexpression and mutations of receptor tyrosine kinases (RTKs), mutations and deletions of the phosphatase and tensin homologue deleted on chromosome 10 (PTEN) tumor suppressor gene, encoding a lipid kinase that directly antagonized PI3K activity, and alterations in Ras signaling. Due to promising results of preclinical studies investigating the PI3K/AKT pathway in grade IV brain tumors like glioblastoma and medulloblastoma, the components of this pathway have emerged as promising therapeutic targets to treat these malignant brain tumors. Although an arsenal of small molecule inhibitors that target specific components of this signaling pathway is being developed, its successful application in the clinics remains a challenge. In this article we will review the molecular basis of the PI3K/AKT signaling pathway in malignant brain tumors, mainly focusing on glioblastoma and medulloblastoma, and we will further discuss the current status and potential of molecular targeted therapies.     

人脑胶质瘤PTEN及PI3K/AKT/GSK3相关蛋白的表达

目的探讨人脑胶质瘤及正常脑组织中PTEN及AKT、pAKT、GSK3、pGSK3的表达差异。方法将组织标本分为正常脑组织、低级别胶质瘤、高级别胶质瘤三组,采用Western blot方法检测PTEN、AKT、pAKT、GSK3、pGSK3的表达。结果 PTEN在正常脑组织中表达量最高,在低级别胶质瘤中表达量居中,在高级别胶质瘤中表达量最低(P<0.05)。pAKT及pGSK3则在高级别胶质瘤中表达量最高,低级别胶质瘤中表达量居中,正常脑组织中表达量最低(P<0.05)。AKT及GSK3在三种标本中表达量没有明显差别(P>0.05)。结论 PTEN、pAKT、pGSK3蛋白的表达水平与胶质瘤病理分级具有相关性。随着胶质瘤级别的增高,PTEN蛋白的表达量明显降低,pAKT、pGSK3的表达量明显增高。     

A novel PI3K inhibitor displays potent preclinical activity against an androgen-independent and PTEN-deficient prostate cancer model established from the cell line PC3

Recent studies demonstrated that targeting the phosphatidylinositide 3-kinase (PI3K)/AKT signaling pathway is a major strategy for the treatment of androgen-independent prostate cancer. In the present study, we developed an analog BENC-511 from a recently reported PI3K inhibitor S14161 by structural optimization. Using PC3 and DU145 as the model cell lines, we found PTEN-deficient PC3 cells were more sensitive than PTEN-expressing DU145 ones in terms of cell proliferation, apoptosis, and caspase-3 activation. These findings were consistent with the inhibition on PI3K/AKT signals. BENC-511 preferably suppressed AKT activation in PC3 over DU145 cells. Notably, PTEN restoration attenuated BENC-511 induced apoptosis. Moreover, BENC-511 displayed great therapeutic efficacy in a PC3-derived prostate cancer model in nude mice. With an oral dosage of 50 mg/kg, BENC-511 decreased tumor growth more than 50% in 27 days, which was accompanied with PARP cleavage, but did not show overt toxicity. This study lays a solid rationale for the development of BENC-511 as a drug for the treatment of PTEN-deficient and androgen-independent prostate cancers.     

Akt as a therapeutic target in cancer

Background: The phosphatidylinositol 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/v-akt murine thymoma viral oncogene homolog (Akt)/mammalian target of rapamycin (mTOR) pathway is central in the transmission of growth regulatory signals originating from cell surface receptors. Objective: This review discusses how mutations occur that result in elevated expression the PI3K/PTEN/Akt/mTOR pathway and lead to malignant transformation, and how effective targeting of this pathway may result in suppression of abnormal growth of cancer cells. Methods: We searched the literature for articles which dealt with altered expression of this pathway in various cancers including: hematopoietic, melanoma, non-small cell lung, pancreatic, endometrial and ovarian, breast, prostate and hepatocellular. Results/conclusions: The PI3K/PTEN/Akt/mTOR pathway is frequently aberrantly regulated in various cancers and targeting this pathway with small molecule inhibitors and may result in novel, more effective anticancer therapies.