PI 3-kinase and cancer: changing accents

Testes-specific protease 50 heightens stem-like properties and improves mitochondrial function in colorectal cancer

AIMS

The progression of colorectal cancer (CRC) is driven by a small subset of cancer stem-like cells (CSCs), and mitochondrial function is essential for maintaining their stemness. TSP50, a novel identified oncogene, has been found to promote cell proliferation in multiple cancer types. In this study, we detected the regulatory role of TSP50 in regulating CSC-like properties and mitochondrial mass in CRC.

MATERIALS AND METHODS

First, TSP50 expression and clinical relevance were analyzed via clinical databases and immunohistochemical (IHC). Subsequently, bioinformatic analyses, CRC cell lines, tumorsphere cultures, and mouse xenograft models were utilized to evaluate the relationship between TSP50 and CSC-like properties as well as mitochondrial mass. Finally, immunofluorescence, immunoprecipitation, and Western blotting were performed to dissect the regulatory mechanisms of TSP50, followed by rescue experiments conducted both in vitro and in vivo.

KEY FINDINGS

TSP50 was overexpressed in CRC tissues, correlating with poor drug response and shorter overall survival (OS). Meanwhile, TSP50 was shown to enhance CSC-like properties in both CRC cells and mouse xenograft models, while concurrently increasing mitochondrial mass and reducing ROS levels, these effects were partially reversed by inhibition of the PI3K/AKT pathway. Mechanistic investigations revealed that TSP50-induced activation of PI3K/AKT signaling is primarily mediated by the enhanced catalytic activity of PI3K p110α subunit.

SIGNIFICANCE

Collectively, TSP50 drives CRC malignancy by promoting CSC-like properties and enhancing mitochondrial function through PI3K/AKT signaling. These findings identify TSP50 as a potential therapeutic target for eliminating CSC-like cells and improving clinical outcomes in CRC treatment.

Rs12039395 Variant Influences the Expression of hsa-miR-181a-5p and PTEN Toward Colorectal Cancer Risk

BACKGROUND

Single nucleotide polymorphisms (SNPs) in microRNA (miRNA) genes could alter miRNA expression levels or processing and, thus, may contribute to colorectal cancer (CRC) development. Therefore, this study aimed to examine whether the MIR181A1 genomic sequence possesses SNPs that can affect the expression of hsa-miR-181a-5p and, subsequently, impact its targets and associate with CRC risk.

METHODS

The NCBI dbSNP database was searched for possible SNPs associated with MIR181A1. One SNP with a minor allele frequency > 5%, rs12039395 G > T was identified. In silico analyses determined the effect of the SNP on the secondary structure of the miRNA and predicted the hsa-miR-181a-5p target genes. The SNP was genotyped using allelic discrimination assay, the relative hsa-miR-181a-5p expression level was determined using quantitative real-time PCR, and immunohistochemical staining was used to detect target genes in 192 paraffin-embedded specimens collected from 160 CRC patients and 32 healthy subjects.

RESULTS

The rs6505162 SNP conferred protection against CRC, and the G-allele presence provides may provide accessibility for the transcriptional machinery. Hsa-miR-181a-5p was significantly over-expressed in the CRC group compared to controls and in samples carrying the G-allele compared to those with T-allele. PTEN, identified as the only hsa-miR-181a-5p target implicated in CRC, was significantly diminished in the CRC group compared to controls and showed an inverse relationship with hsa-miR-181a-5p expression level as well as negatively associated with the G-allele presence in CRC.

CONCLUSION

This study highlights that rs12039395 G > T may protect against CRC by influencing the expression of hsa-mir-181a-5p and its target gene, PTEN.

[Synthetic Study on Bicyclic Depsipeptides Containing an Intramolecular Disulfide Bond]

Bicyclic depsipeptide natural products containing an intramolecular disulfide bond are potent histone deacetylase (HDAC) inhibitors. Among them, FK228 (romidepsin) is approved for treating cutaneous T-cell lymphoma and peripheral T-cell lymphoma. This study focused on developing a new synthesis method for producing this class of natural products for use as HDAC inhibitors with high efficacy and low toxicity. In this paper, the total syntheses of FK228 as well as spiruchostatins A and B are described. The synthesis routes include a convergent way to assemble seco-acids via the amide condensation of amine segments with carboxylic acid segments. The syntheses of C4- and C7-modified FK228 analogs (FK-A1 to FK-A8) are also described. The evaluation of HDAC and cell growth inhibitory activities of the synthesized analogs revealed novel aspects of their structure-activity relationship. Potent and highly isoform-selective HDAC1 inhibitors were identified. Furthermore, the analogs showed phosphatidylinositol 3-kinase (PI3K) inhibitory activity. Structural optimization of the analogs as HDAC/PI3K dual inhibitors led to the identification of FK-A11 as the most potent analog.

How the structural properties of the indole derivatives are important in kinase targeted drug design?: A case study on tyrosine kinase inhibitors

Kinases are considered as important signalling enzymes that illustrate 20% of the druggable genome. Human kinase family comprises >500 protein kinases and about 20 lipid kinases. Protein kinases are responsible for the mechanism of protein phosphorylation. These are necessary for regulation of various cellular activities including proliferation, cell cycle, apoptosis, motility, growth, differentiation, etc. Their deregulation leads to disruption of many cellular processes leading to different diseases most importantly cancer. Thus, kinases are considered as valuable targets in different types of cancer as well as other diseases. Researchers around the world are actively engaged in developing inhibitors based on distinct chemical scaffolds. Indole represents as a versatile scaffold in the naturally occurring and bioactive molecules. It is also used as a privileged scaffold for the target-based drug design against different diseases. This present article aim to review the applications of indole scaffold in the design of inhibitors against different tyrosine kinases such as epidermal growth factor receptors (EGFRs), vascular endothelial growth factor receptors (VEGFRs), platelet-derived growth factor receptors (PDGFRs), etc. Important structure activity relationships (SARs) of indole derivatives were discussed. The present work is an attempt to summarize all the crucial structural information which is essential for the development of indole based tyrosine kinase inhibitors with improved potency.

The impact of microRNAs on myeloid-derived suppressor cells in cancer

Inflammation promotes cancer development. To a large extent, this can be attributed to the recruitment of myeloid-derived suppressor cells (MDSCs) to tumors. These cells are known for establishing an immunosuppressive tumor microenvironment by suppressing T cell activities. However, MDSCs also promote metastasis and angiogenesis. Critically, as small non-coding RNAs that regulate gene expression, microRNAs (miRNAs) control MDSC activities. In this review, we discuss how miRNA networks regulate key MDSC signaling pathways, how they shape MDSC development, differentiation and activation, and how this impacts tumor development. By targeting the expression of miRNAs in MDSCs, we can alter their main signaling pathways. In turn, this can compromise their ability to promote multiple hallmarks of cancer. Therefore, this may represent a new powerful strategy for cancer immunotherapy.

Romidepsin (FK228), A Histone Deacetylase Inhibitor and its Analogues in Cancer Chemotherapy

BACKGROUND

Human HDACs represent a group of enzymes able to modify histone and non-histone proteins, which interact with DNA to generate chromatin. The correlation between irregular covalent modification of histones and tumor development has been proved over the last decades. Therefore, HDAC inhibitors are considered as potential drugs in cancer treatment. Romidepsin (FK228), Belinostat (PXD-101), Vorinostat (SAHA), Panobinostat (LBH-589) and Chidamide were approved by FDA as novel antitumor agents.

OBJECTIVE

The aim of this review article is to highlight the structure-activity relationships of several FK228 analogues as HDAC inhibitors. In addition, the synergistic effects of a dual HDAC/PI3K inhibition by some derivatives have been investigated.

MATERIALS AND METHODS

PubMed, MEDLINE, CAPLUS, SciFinder Scholar database were considered by selecting articles which fulfilled the objectives of this review, dating from 2015 till present time.

RESULTS

HDAC inhibitors have a significant role in cancer pathogenesis and evolution. Class I HDAC isoforms are expressed in many tumor types, therefore, potent and selective Class I HDAC inhibitors are of great interest as candidate therapeutic agents with limited side effects. By structurebased optimization, several FK228 analogues [15 (FK-A5), 22, 23 and 26 (FK-A11)] were identified, provided with significant activity against Class I HDAC enzymes and dose dependent antitumor activity. Compound 26 was recognized as an interesting HDAC/PI3K dual inhibitor (IC₅₀ against p110α of 6.7 μM while for HDAC1 inhibitory activity IC₅₀ was 0.64 nM).

CONCLUSION

Romidepsin analogues HDAC inhibitors have been confirmed as useful anticancer agents. In addition, dual HDAC/PI3K inhibition showed by some of them exhibited synergistic effects in inducing apoptosis in human cancer cells. Further studies on FK228 analogues may positively contribute to the availability of potent agents in tumor treatment.

MiRNAs in Radiotherapy Resistance of Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is one of the most common malignant tumors of the head and neck in Southeast Asia and southern China. Although the comprehensive treatment based on intensity-modulated radiation therapy improves outcomes, the five-year survival rate of NPC patients is low, and the recurrence remains high. Radiotherapy resistance is the main cause of poor prognosis in NPC patients. MicroRNAs (miRNAs) are a class of endogenous non-coding RNAs regulating various biological functions in eukaryotes. These miRNAs can regulate the development and progression of nasopharyngeal carcinoma by affecting the proliferation, apoptosis, movement, invasion and metastasis of NPC cells. The abnormal expression of miRNAs is closely related to radiotherapy sensitivity and prognosis of NPC patients, which can affect the transmission of related signaling pathways by regulating the expression of tumor suppressor genes and / or oncogenes, and therefore participate in radiotherapy resistance in nasopharyngeal carcinoma. Here, we review the mechanisms by which miRNAs may be involved in the radiotherapy resistance of nasopharyngeal carcinoma.

For Better or Worse: The Potential for Dose Limiting the On-Target Toxicity of PI 3-Kinase Inhibitors

The hyper-activation of the phosphoinositide (PI) 3-kinase signaling pathway is a hallmark of many cancers and overgrowth syndromes, and as a result, there has been intense interest in the development of drugs that target the various isoforms of PI 3-kinase. Given the key role PI 3-kinases play in many normal cell functions, there is significant potential for the disruption of essential cellular functions by PI 3-kinase inhibitors in normal tissues; so-called on-target drug toxicity. It is, therefore, no surprise that progress within the clinical development of PI 3-kinase inhibitors as single-agent anti-cancer therapies has been slowed by the difficulty of identifying a therapeutic window. The aim of this review is to place the cellular, tissue and whole-body effects of PI 3-kinase inhibition in the context of understanding the potential for dose limiting on-target toxicities and to introduce possible strategies to overcome these.

The role of microRNAs involved in PI3-kinase signaling pathway in colorectal cancer

In recent decades, cancer has been one of the most important concerns of the human community, which affects human life from many different ways, such as breast, lung, colorectal, prostate, and other cancers. Colorectal cancer is one of the most commonly diagnosed cancers in the world that has recently been introduced as the third leading cause of cancer deaths in the world. microRNAs have a very crucial role in tumorgenesis and prevention of cancer, which plays a significant role with influencing various factors through different signaling pathways. Phosphoinositide 3 (PI3)-kinase/AKT is one of the most important signaling pathways involved in the control and growth of tumor in colorectal cancer, through important proteins of this pathway, such as PTEN and AKT, that they can perform specific influence on this process. Our effort in this study is to collect microRNAs that act as tumor suppressors and oncomirs in this cancer through PI3-kinase/AKT signaling pathway.

Prognostic role of PIK3CA and TP53 in human papillomavirus-negative oropharyngeal cancers

BACKGROUND

Human papilloma virus (HPV)-negative oropharyngeal squamous cell carcinomas (OPCs) have a poorer prognosis and best management is an unmet need. We studied the prognostic role of epidermal growth factor receptor (EGFR) and PIK3CA amplifications and TP53 functional status.

METHODS

Between 1992 and 2000, 90 consecutive patients with OPCs were treated with surgery, followed by radiotherapy in case of high-risk pathologic features. Of those, 73 cases were HPV-negative and therefore were selected for molecular analysis ( PIK3CA and EGFR fluorescent in situ hybridization [FISH] analysis and TP53 mutation analysis).

RESULTS

FISH analyses of EGFR and PIK3CA were successfully conducted on 69 and 63 of 73 tumor samples, respectively. EGFR alterations were detected in 43% of patients but just 7% showed amplification. Seven cases (11%) carried PIK3CA amplification and 18 (29%) gene gain or high polysomy. TP53 was detected as nonfunctional in 24 of 67 (36%) successfully analyzed cases. Both univariable and multivariable analysis showed statistically significantly worse disease-free survival (DFS) for patients with PIK3CA disomy compared to those with gene gain or high polysomy. No differences in overall survival or DFS for EGFR and TP53 alteration were evident. The combined evaluation of PIK3CA and TP53 showed that PIK3CA gene copy number gain separated a population with better outcome, defining an overall worse prognosis population (disomy) now clearly further divided according to TP53 functional status.

CONCLUSION

PIK3CA gene copy number increase is associated with a favorable clinical outcome in HPV-negative OPCs treated with surgery ± postoperative radiotherapy. In patients without PIK3CA alteration, TP53 nonfunctional mutations are associated with poor prognosis.

TBK1 Promote Bladder Cancer Cell Proliferation and Migration via Akt Signaling

Bladder cancer is a challenging and fatal malignancy and the improvement in prognosis is limited over years. Deep understanding the mechanism of bladder cancer tumorigenesis and progression will help to discover novel and effective treatment strategies. In this study, we identify non-canonical IkB kinase TBK1 is up-regulated in bladder cancer tissue and cell lines. Knockdown of TBK1 markedly inhibits cell proliferation and migration. Inhibition of TBK1 kinase activity by BX795 significantly attenuates bladder cancer cell proliferation and migration. Mechanistic study shows that overexpression of TBK1 promoted the phosphorylation of Akt, whereas knockdown of TBK1 reverses this action. Taken together, our data suggest that TBK1 modulates the malignant behaviors of bladder cancer cell via Akt signaling, revealing new insights in discovering new therapy target for bladder cancer.

Scaffolding Function of PI3Kgamma Emerges from Enzyme's Shadow

Traditionally, an enzyme is a protein that mediates biochemical action by binding to the substrate and by catalyzing the reaction that translates external cues into biological responses. Sequential dissemination of information from one enzyme to another facilitates signal transduction in biological systems providing for feed-forward and feed-back mechanisms. Given this viewpoint, an enzyme without its catalytic activity is generally considered to be an inert organizational protein without catalytic function and has classically been termed as pseudo-enzymes. However, pseudo-enzymes still have biological function albeit non-enzymatic like serving as a chaperone protein or an interactive platform between proteins. In this regard, majority of the studies have focused solely on the catalytic role of enzymes in biological function, overlooking the potentially critical non-enzymatic roles. Increasing evidence from recent studies implicate that the scaffolding function of enzymes could be as important in signal transduction as its catalytic activity, which is an antithesis to the definition of enzymes. Recognition of non-enzymatic functions could be critical, as these unappreciated roles may hold clues to the ineffectiveness of kinase inhibitors in pathology, which is characteristically associated with increased enzyme expression. Using an established enzyme phosphoinositide 3-kinase γ, we discuss the insights obtained from the scaffolding function and how this non-canonical role could contribute to/alter the outcomes in pathology like cancer and heart failure. Also, we hope that with this review, we provide a forum and a starting point to discuss the idea that catalytic function alone may not account for all the actions observed with increased expression of the enzyme.

[Advances in the Research of Autophagy in EGFR-TKI Treatment and Resistance in Lung Cancer]

表皮生长因子受体激酶抑制剂（epidermal growth factor receptor-tyrosine kinase inhibitor, EGFR-TKI）是一类针对肿瘤细胞中EGFR的异常活化而开发的肿瘤靶向药物，可以有效抑制带有EGFR敏感突变的肿瘤细胞的生长。然而先天性以及获得性耐药严重制约了该类药物的使用。近些年的研究发现自噬（autophagy），作为一个细胞编码的高度保守的应对压力的存活机制，其与肿瘤的发生发展及抗肿瘤药物的耐药密切相关。EGFR的激活可以通过多条通路调控自噬。EGFR-TKI也可以诱导自噬，且自噬在EGFR-TKI的治疗和产生耐药性的过程中发挥着双刃剑的作用：一方面EGFR-TKI诱导的自噬是肿瘤细胞的一个保护机制，联合使用自噬抑制剂可以增强药物的细胞毒性效果；同时还有研究证明EGFR-TKI诱导的高水平自噬可以在凋亡缺陷的细胞中造成自噬性死亡，这种情况下联合使用自噬诱导剂则可能产生更好的效果。因此，针对不同的情况通过调控自噬以提高EGFR-TKI的治疗效果是一个颇具前景的治疗方案。本文对EGFR-TKI和自噬相关的信号通路进行了阐述，并对自噬在EGFR-TKI类药物对肺癌的治疗和耐药中作用的最新研究进展进行了总结，为设计联合方案提高EGFR-TKI的抑制效果，降低耐药性提供线索。

High frequency of loss of PTEN expression in human solid salivary adenoid cystic carcinoma and its implication for targeted therapy

Salivary gland tumor (SGT) is one of the least studied cancers due to its rarity and heterogeneous histological types. Here, we reported that loss of PTEN expression was most frequently found in the poorly differentiated, high grade solid adenoid cystic carcinomas. Loss of PTEN expression correlated with activation of mTOR by increased phosphorylated S6 ribosome protein. We further functionally studied the role of PTEN in a pair of human SACC cell lines, SACC-83 and SACC-LM. Reduced PTEN level was correlated with the metastasis potential. When we knocked down PTEN in the SACC-83 cell line, we observed increased proliferation and enhanced migration/invasion in vitro, and increased tumor size in vivo. We further tested the therapeutical effect by applying a PI3K/mTOR inhibitor NVP-BEZ235 to both SACC cell lines. Decreased cell proliferation, increased apoptosis, as well as reduced cell migration/invasion were observed in both cell lines upon the NVP-BEZ235 treatment. Moreover, the NVP-BEZ235 treatment in a SGT xenograft mouse model significantly reduced primary tumor size and lung metastasis. Taken together, our results demonstrated that PTEN is a potent tumor suppressor in human SGTs, and targeting PI3K/mTOR pathway may be effective in the targeted therapy for human SGT patients with loss of PTEN expression.

Overexpression of PIK3CA in murine head and neck epithelium drives tumor invasion and metastasis through PDK1 and enhanced TGFβ signaling

Head and neck squamous cell carcinoma (HNSCC) patients have a poor prognosis, with invasion and metastasis as major causes of mortality. The phosphatidylinositol 3-kinase (PI3K) pathway regulates a wide range of cellular processes crucial for tumorigenesis, and PIK3CA amplification and mutation are among the most common genetic alterations in human HNSCC. Compared to the well-documented roles of the PI3K pathway in cell growth and survival, the roles of the PI3K pathway in tumor invasion and metastasis have not been well delineated. We generated a PIK3CA-genetically engineered mouse model (PIK3CA-GEMM) in which wildtype PIK3CA is overexpressed in head and neck epithelium. Although PIK3CA overexpression alone was not sufficient to initiate HNSCC formation, it significantly increased tumor susceptibility in an oral-carcinogenesis mouse model. PIK3CA overexpression in mouse oral epithelium increased tumor invasiveness and metastasis by increasing epithelial-mesenchymal transition and by enriching a cancer stem cell phenotype in tumor epithelial cells. In addition to these epithelial alterations, we also observed marked inflammation in tumor stroma. AKT is a central signaling mediator of the PI3K pathway. However, molecular analysis suggested that progression of PIK3CA-driven HNSCC is facilitated by PDK1 and enhanced TGFβ signaling rather than by AKT. Examination of human HNSCC clinical samples revealed that both PIK3CA and PDK1 protein levels correlated with tumor progression, highlighting the significance of this pathway. In summary, our results offer significant insight into how PIK3CA-overexpression drives HNSCC invasion and metastasis, providing a rationale for targeting PI3K/PDK1 and TGFβ signaling in advanced HNSCC patients with PIK3CA amplification.

Mutant K-RAS Promotes Invasion and Metastasis in Pancreatic Cancer Through GTPase Signaling Pathways

Pancreatic ductal adenocarcinoma is one of the most aggressive malignancies, characterized by the local invasion into surrounding tissues and early metastasis to distant organs. Oncogenic mutations of the K-RAS gene occur in more than 90% of human pancreatic cancers. The goal of this study was to investigate the functional significance and downstream effectors of mutant K-RAS oncogene in the pancreatic cancer invasion and metastasis. We applied the homologous recombination technique to stably disrupt K-RAS oncogene in the human pancreatic cell line MiaPaCa-2, which carries the mutant K-RAS (G12C) oncogene in both alleles. Using in vitro assays, we found that clones with disrupted mutant K-RAS gene exhibited low RAS activity, reduced growth rates, increased sensitivity to the apoptosis inducing agents, and suppressed motility and invasiveness. In vivo assays showed that clones with decreased RAS activity had reduced tumor formation ability in mouse xenograft model and increased survival rates in the mouse orthotopic pancreatic cancer model. We further examined molecular pathways downstream of mutant K-RAS and identified RhoA GTP activating protein 5, caveolin-1, and RAS-like small GTPase A (RalA) as key effector molecules, which control mutant K-RAS-dependent migration and invasion in MiaPaCa-2 cells. Our study provides rational for targeting RhoA and RalA GTPase signaling pathways for inhibition of pancreatic cancer metastasis.

High purity microfluidic sorting and analysis of circulating tumor cells: towards routine mutation detection

A new generation of the Ephesia cell capture technology optimized for CTC capture and genetic analysis is presented, characterized in depth and compared with the CellSearch system as a reference. This technology uses magnetic particles bearing tumour-cell specific EpCAM antibodies, self-assembled in a regular array in a microfluidic flow cell. 48,000 high aspect-ratio columns are generated using a magnetic field in a high throughput (>3 ml h(-1)) device and act as sieves to specifically capture the cells of interest through antibody-antigen interactions. Using this device optimized for CTC capture and analysis, we demonstrated the capture of epithelial cells with capture efficiency above 90% for concentrations as low as a few cells per ml. We showed the high specificity of capture with only 0.26% of non-epithelial cells captured for concentrations above 10 million cells per ml. We investigated the capture behavior of cells in the device, and correlated the cell attachment rate with the EpCAM expression on the cell membranes for six different cell lines. We developed and characterized a two-step blood processing method to allow for rapid processing of 10 ml blood tubes in less than 4 hours, and showed a capture rate of 70% for as low as 25 cells spiked in 10 ml blood tubes, with less than 100 contaminating hematopoietic cells. Using this device and procedure, we validated our system on patient samples using an automated cell immunostaining procedure and a semi-automated cell counting method. Our device captured CTCs in 75% of metastatic prostate cancer patients and 80% of metastatic breast cancer patients, and showed similar or better results than the CellSearch device in 10 out of 13 samples. Finally, we demonstrated the possibility of detecting cancer-related PIK3CA gene mutation in 20 cells captured in the chip with a good correlation between the cell count and the quantitation value Cq of the post-capture qPCR.

MicroRNA-494 promotes cervical cancer proliferation through the regulation of PTEN

The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway appears to be a key regulator in cervical carcinogenesis. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein is principally involved in the homeostatic maintenance of PI3K/Akt signaling and PTEN has been identified to play an important role in the occurrence and development of cervical cancer. MicroRNA (miRNA)-494 has been proven to be involved in the carcinogenesis and development of various types of cancer by directly targeting PTEN. However the role, mechanism and clinical significance of miR-494 in cervical cancer have not been further reported. In the present study, we analyzed the expression of miR-494 in -with PTEN expression and clinicopathological data of cervical cancer patients. The results showed that miR-494 expression was significantly upregulated in human cervical cancer cell lines and tissues. miR-494 upregulation was significantly associated with PTEN downregulation, adverse clinicopathological characteristics, poor overall and progression-free survival and poor prognosis. In vitro experiments showed that inhibition of miR-494 suppressed cell proliferation and growth by directly targeting the 3'-untranslated region (3'-UTR) of PTEN mRNA. These findings identified a novel molecular mechanism involved in the regulation of PTEN expression and cervical cancer progression. Results of the present study indicated that miR-494 may have an essential role in the carcinogenesis and progression of cervical cancer and targeting miR-494 may be a promising therapeutic strategy for the treatment of cervical cancer.

Biochemical, biological and structural properties of romidepsin (FK228) and its analogs as novel HDAC/PI3K dual inhibitors

Romidepsin (FK228, depsipeptide) is a potent histone deacetylase (HDAC) inhibitor that has FDA approval for the treatment of cutaneous and peripheral T-cell lymphomas. We have previously reported that FK228 and its analogs have an additional activity as phosphatidylinositol 3-kinase (PI3K) inhibitors, and are defined as HDAC/PI3K dual inhibitors. Because a combination of an HDAC inhibitor and a PI3K inhibitor induces apoptosis in human cancer cells in a synergistic manner, development of an HDAC/PI3K dual inhibitor will provide an attractive novel drug for cancer therapy. Using structure-based optimization of the analogs, FK-A11 was identified as the most potent analog. FK-A11 inhibited phosphorylation of AKT and accelerated histone acetylation at lower concentrations, resulting in stronger cytotoxic effects than FK228 and the other analogs in human cancer cells. In this study, we have characterized the biochemical, biological and structural properties of FK228 analogs as PI3K inhibitors. First, FK-A11 is an ATP competitive PI3K inhibitor. Second, FK-A11 is a pan-p110 isoform inhibitor. Third, FK-A11 selectively inhibits PI3K among 22 common cellular kinases. Fourth, conformational changes of FK228 analogs by reduction of an internal disulfide bond have no effect on PI3K inhibitory activity, unlike HDAC inhibitory activity. Finally, molecular modeling of PI3K-FK228 analogs and analyses of the binding affinities identified the structure that defines potency for PI3K inhibitory activity. These results prove our concept that a series of FK228 analogs are HDAC/PI3K dual inhibitors. These findings should help in the development of FK228 analogs as novel HDAC/PI3K dual inhibitors.

Role of phosphoinositide 3-OH kinase p110β in skeletal myogenesis

Phosphoinositide 3-OH kinase (PI3K) regulates a number of developmental and physiologic processes in skeletal muscle; however, the contributions of individual PI3K p110 catalytic subunits to these processes are not well-defined. To address this question, we investigated the role of the 110-kDa PI3K catalytic subunit β (p110β) in myogenesis and metabolism. In C2C12 cells, pharmacological inhibition of p110β delayed differentiation. We next generated mice with conditional deletion of p110β in skeletal muscle (p110β muscle knockout [p110β-mKO] mice). While young p110β-mKO mice possessed a lower quadriceps mass and exhibited less strength than control littermates, no differences in muscle mass or strength were observed between genotypes in old mice. However, old p110β-mKO mice were less glucose tolerant than old control mice. Overexpression of p110β accelerated differentiation in C2C12 cells and primary human myoblasts through an Akt-dependent mechanism, while expression of kinase-inactive p110β had the opposite effect. p110β overexpression was unable to promote myoblast differentiation under conditions of p110α inhibition, but expression of p110α was able to promote differentiation under conditions of p110β inhibition. These findings reveal a role for p110β during myogenesis and demonstrate that long-term reduction of skeletal muscle p110β impairs whole-body glucose tolerance without affecting skeletal muscle size or strength in old mice.

Activation of miR-21 by STAT3 induces proliferation and suppresses apoptosis in nasopharyngeal carcinoma by targeting PTEN gene

The present study is to investigate the role of microRNA-21 (miR-21) in nasopharyngeal carcinoma (NPC) and the mechanisms of regulation of PTEN by miR-21. Fifty-four tissue samples were collected from 42 patients with NPC and 12 healthy controls. Human NPC cell lines CNE-1, CNE-2, TWO3 and C666-1 were used for cell assays. To investigate the expression of miR-21, RT-PCR was employed. RT-PCR, Western blotting, and immunohistochemistry were used to measure the expression of STAT3 mRNA and STAT3 protein. To test the effect of miR-21 on the cell growth and apoptosis of NPC cells in vitro, transfection of CNE1 and CNE2 cell lines and flow cytometry were performed. TUNEL assay was used to detect DNA fragmentation. To validate whether miR-21 directly recognizes the 3'-UTRs of PTEN mRNA, luciferase reporter assay was employed. miR-21 expression was increased in NPC tissues compared with control and the same result was found in NPC cell lines. Notably, increased expression of miR-21 was directly related to advanced clinical stage and lymph node metastasis. STAT3, a transcription factor activated by IL-6, directly activated miR-21 in transformed NPC cell lines. Furthermore, miR-21 markedly inhibited PTEN tumor suppressor, leading to increased AKT activity. Both in vitro and in vivo assays revealed that miR-21 enhanced NPC cell proliferation and suppressed apoptosis. miR-21, activated by STAT3, induced proliferation and suppressed apoptosis in NPC by targeting PTEN-AKT pathway.

EGFR inhibitors and autophagy in cancer treatment

Epidermal growth factor receptor (EGFR) inhibitor treatment is a strategy for cancer therapy. However, innate and acquired resistance is a major obstacle of the efficacy. Autophagy is a self-digesting process in cells, which is considered to be associated with anti-cancer drug resistance. The activation of EGFR can regulate autophagy through multiple signal pathways. EGFR inhibitors can induce autophagy, but the specific function of the induction of autophagy by EGFR inhibitors remains biphasic. On the one hand, autophagy induced by EGFR inhibitors acts as a cytoprotective response in cancer cells, and autophagy inhibitors can enhance the cytotoxic effects of EGFR inhibitors. On the other hand, a high level of autophagy after treatment of EGFR inhibitors can also result in autophagic cell death lacking features of apoptosis, and the combination of EGFR inhibitors with an autophagy inducer might be beneficial. Thus, autophagy regulation represents a promising approach for improving the efficacy of EGFR inhibitors in the treatment of cancer patients.

miR‑494 is an independent prognostic factor and promotes cell migration and invasion in colorectal cancer by directly targeting PTEN

Accumulating evidence has shown that micro-RNAs (miRNAs) are involved in multiple processes in cancer development and progression. Upregulation of miRNA-494 (miR-494) has been identified as an oncogenic miRNA and is associated with poor prognosis in several types of human cancer. However, the specific function of miR-494 in colorectal cancer remains unclear. In this study we found that the expression of miR-494 in colorectal cancer tissues and cell lines was much higher than in normal control tissues and cells, respectively. In addition, upregulation of miR-494 more frequently occurred in tissue specimens with adverse clinical stage and the presence of distant metastasis. Moreover, multivariate survival analyses demonstrated that overexpression of miR-494 is an independent prognostic factor for both progression-free and overall survival. In addition miR-494 promoted invasion and migration in colorectal cancer cells, and miR-494 directly inhibited the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression by targeting its 3'-untranslated region (3'-UTR). Moreover, PTEN is down regulated and inversely correlated with miR-494 expression in tissues. Thus, for the first time, we provided convincing evidence that upregulation of miR-494 was associated with tumor aggressiveness and tumor metastasis and promoted cell migration and invasion by targeting PTEN gene in colorectal cancer, and miR-494 is an independent prognostic marker for colorectal cancer patients.

MiR-21 upregulation induced by promoter zone histone acetylation is associated with chemoresistance to gemcitabine and enhanced malignancy of pancreatic cancer cells

BACKGROUND AND AIMS

MicroRNA-21 (miR-21) is reported to be overexpressed and to contribute to proliferation, apoptosis and gemcitabine resistance in pancreatic ductal adenocarcinomas (PDACs). The aims of this study were to explore regulation of miR-21 expression by epigenetic change and its impact on chemoresistance and malignant properties of of pancreatic cancer.

MATERIALS AND METHODS

We retrospectively collected 41 cases of advanced pancreatic cancer patients who were sensitive or resistant to gemcitabine and assessed levels of serum circulating miR-21 for correlation with cytotoxic activity. Histone acetylation in the miR-21 promoter was also studied in gemcitabine-sensitive and gemcitabine-resistant PDAC cells. Gemcitabine-resistant HPAC and PANC-1 cells were transfected with pre-miR-21 precursors (pre-miR-21) and antisense oligonucleotides (anti-miR-21), and were treated with TSA. Finally, invasion and metastasis assays were performed and alteration in mir-21, PTEN, AKT and pAKT level was evaluated in these cells.

RESULTS

Serum miR-21 levels were increased in gemcitabine- resistant PDAC patients compared with gemcitabine-sensitive subjects. The miR-21 levels were increased in 6 PDAC cells treated with gemcitabine significantly, associated with 50% inhibitory concentrations (IC50s). Histone acetylation levels at miR-21 promoter were increased in PDAC cells after treatment with gemcitabine. Enhanced invasion and metastasis, increased miR-21 expression, decreased PTEN, elevated pAKT level were demonstrated in gemcitabine-resistant HPAC and PANC-1 cells. Pre-miR-21 transfection or TSA treatment further increased invasion and metastasis ability, decreased PTEN, and elevated pAKT levels in these two lines. In contrast, anti-miR-21 transfection could reverse invasion and metastasis, and PTEN and pAKT expressions induced by gemcitabine.

CONCLUSIONS

MiR-21 upregulation induced by histone acetylation in the promoter zone is associated with chemoresistance to gemcitabine and enhanced malignant potential in pancreatic cancer cells.

Expression profiling of exosomal miRNAs derived from human esophageal cancer cells by Solexa high-throughput sequencing

Cellular genetic materials, such as microRNAs (miRNAs), mRNAs and proteins, are packaged inside exosomes, small membrane vesicles of endocytic origin that are released into the extracellular environment. These cellular genetic materials can be delivered into recipient cells, where they exert their respective biological effects. However, the miRNA profiles and biological functions of exosomes secreted by cancer cells remain unknown. The present study explored the miRNA expression profile and distribution characteristics of exosomes derived from human esophageal cancer cells through Solexa high-throughput sequencing. Results showed that 56,421 (2.94%) unique sequences in cells and 7727 (0.63%) in exosomes matched known miRNAs. A total of 342 and 48 known miRNAs were identified in cells and exosomes, respectively. Moreover, 64 and 32 novel miRNAs were predicted in cells and exosomes, respectively. Significant differences in miRNA expression profiles were found between human esophageal cancer cells and exosomes. These findings provided new insights into the characteristics of miRNAs in exosomes derived from human esophageal cancer cells and the specific roles of miRNAs in intercellular communication mediated by exosomes in esophageal cancer.

Synthesis and structure-activity relationships of PI3K/mTOR dual inhibitors from a series of 2-amino-4-methylpyrido[2,3-d]pyrimidine derivatives

Inhibition of the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway by PI3K/mTOR dual inhibitors provides a promising new approach to the treatment of cancers. In this Letter, we identified structurally novel and potent PI3K/mTOR dual inhibitors from a series of 2-amino-4-methylpyrido[2,3-d]pyrimidine derivatives. Their synthesis and structure-activity relationships are reported.

MicroRNA-92a functions as an oncogene in colorectal cancer by targeting PTEN

BACKGROUND

Our previous studies show that microRNA-92a (miR-92a) is overexpressed in colorectal cancer (CRC) and is thought to be correlated with the development of the cancer. However, its biological role in CRC remains poorly understood.

AIMS

The aim of the study was to determine the role of miR-92a and to elucidate its regulatory mechanism in CRC.

METHODS

The expression levels of miR-92a and phosphatase and tensin homologue (PTEN) were detected by qRT-PCR and western blot. MTT, migration and invasion assays were used to examine the proliferation, migration and invasion of pre-miR-92a transfected SW480 cells, and a mouse model was used to investigate tumorigenesis. In addition, the regulation of PTEN by miR-92a was evaluated by qRT-PCR, western blot and luciferase reporter assays.

RESULTS

The expression of miR-92a was significantly up-regulated in the tissues of CRC patients with lymph node metastasis. The ectopic expression of miR-92a enhanced CRC cell proliferation, migration and invasion. Similar results were found in xenograft assay performed in nude mice. Up-regulation of miR-92a induced EMT in CRC cells. There was an inverse correlation between the levels of miR-92a and PTEN in CRC tissues. The overexpression of miR-92a in CRC cells decreased PTEN expression at the translational level, and decreased PTEN-driven luciferase-reporter activity.

CONCLUSIONS

Our results demonstrated that miR-92a induced EMT and regulated cell growth, migration and invasion in the SW480 cells, at least partially, via suppression of PTEN expression. MiR-92a may serve as a novel therapeutic target in colorectal cancer.

Down-regulation of PTEN expression modulated by dysregulated miR-21 contributes to the progression of esophageal cancer

BACKGROUND AND AIM

miR-21, a putative tumor oncomiR, is a frequently overexpressed miRNA in a variety of tumors. Because it targets tumor-suppressor genes it has been linked to tumor progression. In this study we investigated the role of miR-21 in esophageal squamous cell carcinoma (ESCC), and its possible mechanism.

METHODS

Expression of miR-21 was detected by stem-loop RT-PCR in tissue from 76 invasive ESCC at stage I-IV and in their corresponding para-cancerous histological normal tissues (PCHNT). Thirty endoscopic esophageal mucosal biopsy specimens from non-tumor patients were used as controls. Expression of PTEN in 76 paired ESCC and PCHNT was investigated by real-time RT-PCR and an immunohistochemical method, respectively. Paired tumor and PCHNT specimens of 20 ESCC cases were randomly selected for western blot analysis. The effect of miR-21 on PTEN expression was assessed in the ESCC cell line with an miR-21 inhibitor to reduce miR-21 expression. Furthermore, the roles of miR-21 in cell biology were analyzed by use of miR-21 inhibitor-transfected cells.

RESULTS

Stem-loop RT-PCR revealed miR-21 was significantly overexpressed in ESCC tissues and cell lines. Overexpression of miR-21 correlated with tumor status, lymph node metastasis, and clinical stage. We demonstrated that knockdown of miR-21 significantly increased expression of PTEN protein. Consequent PTEN expression reduced cell proliferation, invasion, and migration.

CONCLUSIONS

Our findings suggest that miR-21 could be a potential oncomiR, probably by regulation of PTEN, and a novel prognostic factor for ESCC patients.

Spatially distinct roles of class Ia PI3K isoforms in the development and maintenance of PTEN hamartoma tumor syndrome

PTEN hamartoma tumor syndrome (PHTS) comprises a collection of genetic disorders associated with germline mutations in the tumor suppressor gene PTEN. Therapeutic options and preventative measures for PHTS are limited. Using both genetically engineered mouse models and pharmacological PI3K isoform-selective inhibitors, we found that the roles of PI3K isoforms are spatially distinct in the skin: While p110α is responsible for the sustained survival of suprabasal cells of the epidermis in the absence of PTEN, p110β is important for the hyperproliferation of basal cells in PHTS. Furthermore, we identified a differential expression pattern of p110α and p110β in basal and suprabasal keratinocytes as well as differential PI3K regulation by upstream signals in the basal and suprabasal compartments of the epidermis, providing a potential molecular mechanism underlying the specific roles of PI3K isoforms in the epidermis. Finally, we demonstrate that combined inhibition of both PI3K isoforms prevents the development of PHTS and also reverses skin hamartomas that have reached advanced stages in mice. Together, these results not only advance our overall understanding of the diverse roles of PI3K isoforms, but also have the potential for meaningful translation via the clinical utilization of PI3K inhibitors for both prevention and therapy in PHTS patients.

AKT-independent PI3-K signaling in cancer - emerging role for SGK3

The phosphoinositide 3-kinase (PI3-K) signaling pathway plays an important role in a wide variety of fundamental cellular processes, largely mediated via protein kinase B/v-akt murine thymoma viral oncogene homolog (PKB/AKT) signaling. Given the crucial role of PI3-K/AKT signaling in regulating processes such as cell growth, proliferation, and survival, it is not surprising that components of this pathway are frequently dysregulated in cancer, making the AKT kinase family members important therapeutic targets. The large number of clinical trials currently evaluating PI3-K pathway inhibitors as a therapeutic strategy further emphasizes this. The serum- and glucocorticoid-inducible protein kinase (SGK) family is made up of three isoforms, SGK1, 2, and 3, that are PI3-K-dependent, serine/threonine kinases, with similar substrate specificity to AKT. Consequently, the SGK family also regulates similar cell processes to the AKT kinases, including cell proliferation and survival. Importantly, there is emerging evidence demonstrating that SGK3 plays a critical role in AKT-independent oncogenic signaling. This review will focus on the role of SGK3 as a key effector of AKT-independent PI3-K oncogenic signaling.

Oncogenic mutations of p110α isoform of PI 3-kinase upregulate its protein kinase activity

In addition to lipid kinase activity, the class-I PI 3-kinases also function as protein kinases targeting regulatory autophosphorylation sites and exogenous substrates. The latter include a recently identified regulatory phosphorylation of the GM-CSF/IL-3 βc receptor contributing to survival of acute myeloid leukaemia cells. Previous studies suggested differences in the protein kinase activity of the 4 isoforms of class-I PI 3-kinase so we compared the ability of all class-I PI 3-kinases and 2 common oncogenic mutants to autophosphorylate, and to phosphorylate an intracellular fragment of the GM-CSF/IL-3 βc receptor (βic). We find p110α, p110β and p110γ all phosphorylate βic but p110δ is much less effective. The two most common oncogenic mutants of p110α, H1047R and E545K have stronger protein kinase activity than wildtype p110α, both in terms of autophosphorylation and towards βic. Importantly, the lipid kinase activity of the oncogenic mutants is still inhibited by autophosphorylation to a similar extent as wildtype p110α. Previous evidence indicates the protein kinase activity of p110α is Mn(2+) dependent, casting doubt over its role in vivo. However, we show that the oncogenic mutants of p110α plus p110β and p110γ all display significant activity in the presence of Mg(2+). Furthermore we demonstrate that some small molecule inhibitors of p110α lipid kinase activity (PIK-75 and A66) are equally effective against the protein kinase activity, but other inhibitors (e.g. wortmannin and TGX221) show different patterns of inhibition against the lipid and protein kinases activities. These findings have implications for the function of PI 3-kinase, especially in tumours carrying p110α mutations.

Distinct and opposing roles for the phosphatidylinositol 3-OH kinase catalytic subunits p110α and p110β in the regulation of insulin secretion from rodent and human beta cells

AIMS/HYPOTHESIS

Phosphatidylinositol 3-OH kinases (PI3Ks) regulate beta cell mass, gene transcription, and function, although the contribution of the specific isoforms is unknown. As reduced type 1A PI3K signalling is thought to contribute to impaired insulin secretion, we investigated the role of the type 1A PI3K catalytic subunits α and β (p110α and -β) in insulin granule recruitment and exocytosis in rodent and human islets.

METHODS

The p110α and p110β subunits were inhibited pharmacologically or by small hairpin (sh)RNA-mediated knockdown, and were directly infused or overexpressed in mouse and human islets, beta cells and INS-1 832/13 cells. Glucose-stimulated insulin secretion (GSIS), single-cell exocytosis, Ca(2+) signalling, plasma membrane granule localisation, and actin density were monitored.

RESULTS

Inhibition or knockdown of p110α increased GSIS. This was not due to altered Ca(2+) responses, depolymerisation of cortical actin or increased cortical granule density, but to enhanced Ca(2+)-dependent exocytosis. Intracellular infusion of recombinant PI3Kα (p110α/p85β) blocked exocytosis. Conversely, knockdown (but not pharmacological inhibition) of p110β blunted GSIS, reduced cortical granule density and impaired exocytosis. Exocytosis was rescued by direct intracellular infusion of recombinant PI3Kβ (p110β/p85β) even when p110β catalytic activity was inhibited. Conversely, both the wild-type p110β and a catalytically inactive mutant directly facilitated exocytosis.

CONCLUSIONS/INTERPRETATION

Type 1A PI3K isoforms have distinct and opposing roles in the acute regulation of insulin secretion. While p110α acts as a negative regulator of beta cell exocytosis and insulin secretion, p110β is a positive regulator of insulin secretion through a mechanism separate from its catalytic activity.

MicroRNA-32 (miR-32) regulates phosphatase and tensin homologue (PTEN) expression and promotes growth, migration, and invasion in colorectal carcinoma cells

Background

Colorectal carcinoma (CRC) is one of the leading causes of cancer-related mortality worldwide. MicroRNAs (miRNAs, miRs) play important roles in carcinogenesis. MiR-32 has been shown to be upregulated in CRC. In this study, we identified the potential effects of miR-32 on some important biological properties of CRC cells, and clarified the regulation of PTEN by miR-32.

Methods

The effect of miR-32 on PTEN expression was assessed in CRC cell lines with miR-32 mimics/inhibitor to increase/decrease miR-32 expression. Furthermore, the roles of miR-32 in regulating CRC cells biological properties were analyzed with miR-32 mimics/inhibitor-transfected cells. The 3^′-untranslated region (3^′-UTR) of PTEN combined with miR-32 was verified by dual-luciferase reporter assay.

Results

Gain-of-function and loss-of-function studies showed that overexpression of miR-32 promoted SW480 cell proliferation, migration, and invasion, reduced apoptosis, and resulted in downregulation of PTEN at a posttranscriptional level. However, miR-32 knock-down inhibited these processes in HCT-116 cells and enhanced the expression of PTEN protein. In addition, we further identified PTEN as the functional downstream target of miR-32 by directly targeting the 3^′-UTR of PTEN.

Conclusions

Our results demonstrated that miR-32 was involved in tumorigenesis of CRC at least in part by suppression of PTEN.

p110δ PI3 kinase pathway: emerging roles in cancer

Class IA PI3Ks consists of three isoforms of the p110 catalytic subunit designated p110α, p110β, and p110δ which are encoded by three separate genes. Gain-of-function mutations on PIK3CA gene encoding for p110α isoform have been detected in a wide variety of human cancers whereas no somatic mutations of genes encoding for p110β or p110δ have been reported. Unlike p110α and p110β which are ubiquitously expressed, p110δ is highly enriched in leukocytes and thus the p110δ PI3K pathway has attracted more attention for its involvement in immune disorders. However, findings have been accumulated showing that the p110δ PI3K plays a seminal role in the development and progression of some hematologic malignancies. A wealth of knowledge has come from studies showing the central role of p110δ PI3K in B-cell functions and B-cell malignancies. Further data have documented that wild-type p110δ becomes oncogenic when overexpressed in cell culture models and that p110δ is the predominant isoform expressed in some human solid tumor cells playing a prominent role in these cells. Genetic inactivation of p110δ in mice models and highly-selective inhibitors of p110δ have demonstrated an important role of this isoform in differentiation, growth, survival, motility, and morphology with the inositol phosphatase PTEN to play a critical role in p110δ signaling. In this review, we summarize our understanding of the p110δ PI3K signaling pathway in hematopoietic cells and malignancies, we highlight the evidence showing the oncogenic potential of p110δ in cells of non-hematopoietic origin and we discuss perspectives for potential novel roles of p110δ PI3K in cancer.

Enhanced Akt phosphorylation and myogenic differentiation in PI3K p110β-deficient myoblasts is mediated by PI3K p110α and mTORC2

Phosphoinositide 3-kinase (PI3K) is a principal regulator of Akt activation and myogenesis; however, the function of PI3K p110β in these processes is not well defined. To address this, we investigated the role of p110β in Akt activation and skeletal muscle cell differentiation. We found that Akt phosphorylation was enhanced in p110β-deficient myoblasts in response to Insulin-like Growth Factor-I (IGF-I), epidermal growth factor, or p110α overexpression, as compared to p110β-sufficient cells. This effect was associated with increased mammalian target of rapamycin complex 2 activation, even in myoblasts deficient in mSin1 and rictor. Conversely, in response to the G-protein-coupled receptor agonist lysophosphatidic acid, Akt phosphorylation was attenuated in p110β-deficient myoblasts. Loss of p110β also enhanced the expression of myogenic markers at the myoblast stage and during the first 48 h of differentiation. These data demonstrate that reductions in p110β are associated with agonist-specific Akt hyperactivation and accelerated myogenesis, thus revealing a negative role for p110β in Akt activation and during myoblast differentiation.

microRNA-21 overexpression contributes to cell proliferation by targeting PTEN in endometrioid endometrial cancer

The aim of this study was to investigate the role of microRNA-21 (miR-21) in the regulation of phosphatase and tensin homolog deleted from chromosome-10 (PTEN) expression and proliferation of endometrioid endometrial cancer (EEC) cells. We performed a qRT-PCR assay with miR-21 and PTEN in 16 paired EEC tumor tissues and adjacent non-tumor endometrium. To investigate the regulation of PTEN by miR-21, we designed gain- and loss-of-function of miR-21 experiments in the KLE cell line by transfection with a synthetic miR-21 mimic and inhibitor. To validate the putative binding site of miR-21 in the 3' untranslated region (3'-UTR) of PTEN messenger RNA (mRNA), a dual-luciferase reporter assay was carried out. To evaluate the potential effect of miR-21 on EEC proliferation, we performed both overexpression experiments, using an miR-21 mimic, and inhibition assays, using an miR-21 inhibitor. miR-21 was overexpressed in EEC and was inversely correlated with PTEN protein expression (P<0.001). miR-21 regulated PTEN protein expression and cell proliferation in the KLE cell line and the direct binding of miR-21 to the PTEN 3'-UTR was confirmed using a dual-luciferase reporter assay. The upregulation of miR-21 led to a significant decrease in the PTEN protein expression level (P=0.007). The downregulation of miR-21 led to a significant increase in PTEN protein (P=0.002). The expression of luciferase in the wt-PTEN-3'-UTR-pGL3 group was downregulated in the presence of the miR-21 mimic (P=0.001). miR-21 was overexpressed in EEC. In conclusion, we demonstrated that the expression of PTEN protein, but not mRNA, was negatively directly regulated by miR-21 in the KLE cell line. The overexpression of miR-21 modulated EEC cell proliferation through the downregulation of PTEN.

Role of phosphatidylinositol-3-kinase pathway in head and neck squamous cell carcinoma

Activation of the phosphatidylinositol-3-kinase (PI3K) pathway is one of the most frequently observed molecular alterations in many human malignancies, including head and neck squamous cell carcinoma (HNSCC). A growing body of evidence demonstrates the prime importance of the PI3K pathway at each stage of tumorigenesis, that is, tumor initiation, progression, recurrence, and metastasis. Expectedly, targeting the PI3K pathway yields some promising results in both preclinical studies and clinical trials for certain cancer patients. However, there are still many questions that need to be answered, given the complexity of this pathway and the existence of its multiple feedback loops and interactions with other signaling pathways. In this paper, we will summarize recent advances in the understanding of the PI3K pathway role in human malignancies, with an emphasis on HNSCC, and discuss the clinical applications and future direction of this field.

Present and Future of EGFR Inhibitors for Head and Neck Squamous Cell Cancer

Although EGFR is expressed at high levels in head and neck squamous cell carcinomas (HNSCCs) and mutations are extremely rare, monotherapy with EGFR inhibitors has shown limited success. The PI3kinase/Akt pathway is responsible for cellular survival, and inhibition of phosphatidylinositol (PI) synthesis has antiproliferative, anti-invasive, and antiangiogenesis effects on HNSCC. Molecular crosstalk has been observed between EGFR and IGF1R signaling through the PI3kinase/Akt pathway in HNSCC, as has molecular crosstalk between the NFκB and STAT3 signaling pathways. Therefore, the combination of an EGFR antagonist with an agent that inhibits the activation of both Akt and NFκB may overcome resistance to EGFR antagonists in HNSCC.

Will kinase inhibitors make it as glioblastoma drugs?

Kinase inhibitors have emerged as effective cancer therapeutics in a variety of human cancers. Glioblastoma (GBM), the most common malignant brain tumor in adults, represents a compelling disease for kinase inhibitor therapy because the majority of these tumors harbor genetic alterations that result in aberrant activation of growth factor signaling pathways. Attempts to target the Ras-Phosphatidylinositol 3-kinase (PI3K)-mammalian Target of Rapamycin (mTOR) axis in GBM with first generation receptor tyrosine kinase (RTK) inhibitors and rapalogs have been disappointing. However, there is reason for renewed optimism given the now very detailed knowledge of the cancer genome in GBM and a wealth of novel compounds entering the clinic, including next generation RTK inhibitors, class I PI3K inhibitors, mTOR kinase inhibitors (TORKinibs), and dual PI3(K)/mTOR inhibitors. This chapter reviews common genetic alterations in growth factor signaling pathways in GBM, their validation as therapeutic targets in this disease, and strategies for future clinical development of kinase inhibitors for high grade glioma.

PI3 Kinase in Cancer: From Biology to Clinic

The discovery and clinical development of small-molecule inhibitors of the phosphatidylinositide 3-kinase (PI3 kinase) family of lipid kinases have marked a remarkable 20-year journey that follows the progressive developments in cancer biology over the last few decades: from hypothesis-driven, basic cancer research that began with viral oncogenesis and developed in the 1960s and 70s, through the discovery of individual mutated oncogenes and tumor suppressor genes in 1970 and 80s and the linkage of these cancer genes to signal transduction pathways in the 1990s, to all large-scale genome-wide sequencing, functional screening, and network biology efforts today. Thus, PI3 kinase research began with the discovery in 1985 of a new type of enzyme activity associated with viral oncogenesis. It benefited greatly from the discovery of wortmannin and LY294002 as PI3 kinase inhibitors and chemical tools in late 1980s to mid-90s. Alongside these tools, genetic validation of PI3 kinase as a target initially involved activation by upstream oncogenic receptor tyrosine kinases and RAS mutation, together with overexpression and amplification of the p110α catalytic isoform of PI3 kinase and frequent loss of the tumor suppressor and negative regulator of PI3 kinase activity, PTEN. As PI3 kinase drug development began, further stimulus came from the discovery through genome sequencing of mutations in PIK3CA, which encodes p110α and is the most frequently mutated kinase in the human genome. From these beginnings, there are now many PI3 kinase inhibitors in clinical trials and more in preclinical development. We review progress, current challenges, and future opportunities in this article.

The Akt signaling pathway: an emerging therapeutic target in malignant melanoma

Studies using cultured melanoma cells and patient tumor biopsies have demonstrated deregulated PI3 kinase-Akt3 pathway activity in ~70% of melanomas. Furthermore, targeting Akt3 and downstream PRAS40 has been shown to inhibit melanoma tumor development in mice. Although these preclinical studies and several other reports using small interfering RNAs and pharmacological agents targeting key members of this pathway have been shown to retard melanoma development, analysis of early Phase I and Phase II clinical trials using pharmacological agents to target this pathway demonstrate the need for (1) selection of patients whose tumors have PI3 kinase-Akt pathway deregulation, (2) further optimization of therapeutic agents for increased potency and reduced toxicity, (3) the identification of additional targets in the same pathway or in other signaling cascades that synergistically inhibit the growth and progression of melanoma, and (4) better methods for targeted delivery of pharmaceutical agents inhibiting this pathway. In this review we discuss key potential targets in PI3K-Akt3 signaling, the status of pharmacological agents targeting these proteins, drugs under clinical development, and strategies to improve the efficacy of therapeutic agents targeting this pathway.

p37δ is a new isoform of PI3K p110δ that increases cell proliferation and is overexpressed in tumors

The phosphatidylinositol 3-kinases (PI3Ks) regulate cell growth, proliferation and survival, and are frequently affected in human cancer. PI3K is composed of a catalytic subunit, p110, and a regulatory subunit, p85. The PI3K catalytic subunit p110δ is encoded by PIK3CD and contains p85- and RAS-binding domains, and a kinase domain. Here we present an alternatively spliced PIK3CD transcript encoding a previously unknown protein, p37δ, and demonstrate that this protein is expressed in human ovarian and colorectal tumors. p37δ retains the p85-binding domain and a fraction of the RAS-binding domain, lacks the catalytic domain, and has a unique carboxyl-terminal region. In contrast to p110δ, which stabilizes p85, p37δ promoted p85 sequestering. Despite the truncated RAS-binding domain, p37δ bound to RAS and we found a strong positive correlation between the protein levels of p37δ and RAS. Overexpressing p37δ, but not p110δ, increased the proliferation and invasive properties of HEK-293 cells and mouse embryonic fibroblasts. Cells overexpressing p37δ showed a quicker phosphorylation response of AKT and ERK1/2 following serum stimulation. Ubiquitous expression of human p37δ in the fruit fly increased body size, DNA content and phosphorylated ERK1/2 levels. Thus, p37δ appears to be a new tumor-specific isoform of p110δ with growth-promoting properties.

IkappaB kinase epsilon and TANK-binding kinase 1 activate AKT by direct phosphorylation

AKT activation requires phosphorylation of the activation loop (T308) by 3-phosphoinositide-dependent protein kinase 1 (PDK1) and the hydrophobic motif (S473) by the mammalian target of rapamycin complex 2 (mTORC2). We recently observed that phosphorylation of the AKT hydrophobic motif was dramatically elevated, rather than decreased, in mTOR knockout heart tissues, indicating the existence of other kinase(s) contributing to AKT phosphorylation. Here we show that the atypical IκB kinase ε and TANK-binding kinase 1 (IKKε/TBK1) phosphorylate AKT on both the hydrophobic motif and the activation loop in a manner dependent on PI3K signaling. This dual phosphorylation results in a robust AKT activation in vitro. Consistently, we found that growth factors can induce AKT (S473) phosphorylation in Rictor(-/-) cells, and this effect is insensitive to mTOR inhibitor Torin1. In IKKε/TBK1 double-knockout cells, AKT activation by growth factors is compromised. We also observed that TBK1 expression is elevated in the mTOR knockout heart tissues, and that TBK1 is required for Ras-induced mouse embryonic fibroblast transformation. Our observations suggest a physiological function of IKKε/TBK1 in AKT regulation and a possible mechanism of IKKε/TBK1 in oncogenesis by activating AKT.