Novel agents targeting the IGF-1R/PI3K pathway impair cell proliferation and survival in subsets of medulloblastoma and neuroblastoma

The receptor tyrosine kinase (RTK)/phosphoinositide 3-kinase (PI3K) pathway is fundamental for cancer cell proliferation and is known to be frequently altered and activated in neoplasia, including embryonal tumors. Based on the high frequency of alterations, targeting components of the PI3K signaling pathway is considered to be a promising therapeutic approach for cancer treatment. Here, we have investigated the potential of targeting the axis of the insulin-like growth factor-1 receptor (IGF-1R) and PI3K signaling in two common cancers of childhood: neuroblastoma, the most common extracranial tumor in children and medulloblastoma, the most frequent malignant childhood brain tumor. By treating neuroblastoma and medulloblastoma cells with R1507, a specific humanized monoclonal antibody against the IGF-1R, we could observe cell line-specific responses and in some cases a strong decrease in cell proliferation. In contrast, targeting the PI3K p110α with the specific inhibitor PIK75 resulted in broad anti-proliferative effects in a panel of neuro- and medulloblastoma cell lines. Additionally, sensitization to commonly used chemotherapeutic agents occurred in neuroblastoma cells upon treatment with R1507 or PIK75. Furthermore, by studying the expression and phosphorylation state of IGF-1R/PI3K downstream signaling targets we found down-regulated signaling pathway activation. In addition, apoptosis occurred in embryonal tumor cells after treatment with PIK75 or R1507. Together, our studies demonstrate the potential of targeting the IGF-1R/PI3K signaling axis in embryonal tumors. Hopefully, this knowledge will contribute to the development of urgently required new targeted therapies for embryonal tumors.

Development of Drugs Targeting the PI3K Signalling Pathway in Leukaemias and Lymphomas

The phosphoinositide 3-kinase (PI3K) family of signalling enzymes play a key role in the transduction of signals from activated cell surface receptors controlling cell growth and proliferation, survival, metabolism, and migration. The intracellular signalling pathway from activated receptors to PI3K and its downstream targets v-akt murine thymoma viral oncogene homolog (Akt) and mechanistic target of rapamycin (mTOR) is very frequently deregulated by genetic and epigenetic mechanisms in human cancer, including leukaemia and lymphoma. In the past decade, an arsenal of small molecule inhibitors of key enzymes in this pathway has been developed and evaluated in pre-clinical studies and clinical trials in cancer patients. These include pharmacological inhibitors of Akt, mTOR, and PI3K, some of which are approved for the treatment of leukaemia and lymphoma. The PI3K family comprises eight different catalytic isoforms in humans, which have been subdivided into three classes. Class I PI3K isoforms have been extensively studied in the context of human cancer, and the isoforms p110α and p110δ are validated drug targets. The recent approval of a p110δ-specific PI3K inhibitor (idelalisib/Zydelig®) for the treatment of selected B cell malignancies represents the first success in developing these molecules into anti-cancer drugs. In addition to PI3K inhibitors, mTOR inhibitors are intensively studied in leukaemia and lymphoma, and temsirolimus (Torisel®) is approved for the treatment of a type of lymphoma. Based on these promising results it is hoped that additional novel PI3K pathway inhibitors will in the near future be further developed into new drugs for leukaemia and lymphoma.

Targeting phosphoinositide 3-kinase signalling in lung cancer

Lung cancer is the leading cause of cancer-related mortality worldwide and more than 1 million people annually die in consequence of lung cancer. Although an improvement in lung cancer treatment could be achieved, especially in the last decade, the development of additional therapeutic strategies is urgently required in order to provide improved survival benefit for patients. Lung cancer formation is caused by genetic modifications commonly caused by tobacco smoking. Numerous studies have demonstrated the role of extracellular growth factors in lung cancer cell proliferation, metastasis, and chemoresistance. Mutations and amplifications in molecules related to receptor tyrosine signalling, such as EGFR, ErbB2, c-Met, c-Kit, VEGFR, PI3K, and PTEN are only some of the alterations known to contribute to the development of lung cancer. The phosphoinositide 3-kinase (PI3K) pathway, fundamental for cell development, growth, and survival, is known to be frequently altered in neoplasia, including carcinomas of the lung. Based on the high frequency of alterations, which include mutations and amplifications, leading to over-activation of certain upstream/downstream mediators, targeting components of the PI3K signalling pathway is considered to be a promising therapeutic approach in cancer treatment. In this article we will summarize the current knowledge about the involvement of PI3K signalling in lung cancer and discuss the development of targeted therapies involving PI3K pathway inhibitors.

Phosphatidylinositol 3-kinase isoforms as novel drug targets

Phosphatidylinositol 3-kinases (PI3Ks) are key molecules in the signal transduction pathways initiated by the binding of extracellular signals to their cell surface receptors. The PI3K family of enzymes comprises eight catalytic isoforms subdivided into three classes and control a variety of cellular processes including proliferation, growth, apoptosis, migration and metabolism. Deregulation of the PI3K pathway has been extensively investigated in connection to cancer, but is also involved in other commonly occurring diseases such as chronic inflammation, autoimmunity, allergy, atherosclerosis, cardiovascular and metabolic diseases. The fact that the PI3K pathway is deregulated in a large number of human diseases, and its importance for different cellular responses, makes it an attractive drug target. Pharmacological PI3K inhibitors have played a very important role in studying cellular responses involving these enzymes. Currently, a wide range of selective PI3K inhibitors have been tested in preclinical studies and some have entered clinical trials in oncology. However, due to the complexity of PI3K signaling pathways, developing an effective anti-cancer therapy may be difficult. The biggest challenge in curing cancer patients with various signaling pathway abnormalities is to target multiple components of different signal transduction pathways with mechanism-based combinatorial treatments. In this article we will give an overview of the complex role of PI3K isoforms in human diseases and discuss their potential as drug targets. In addition, we will describe the drugs currently used in clinical trials, as well as promising emerging candidates.

Targeting the phosphoinositide 3-kinase p110-α isoform impairs cell proliferation, survival, and tumor growth in small cell lung cancer

The phosphoinositide 3-kinase (PI3K) pathway is fundamental for cell proliferation and survival and is frequently altered and activated in neoplasia, including carcinomas of the lung. In this study, we investigated the potential of targeting the catalytic class I(A) PI3K isoforms in small cell lung cancer (SCLC), which is the most aggressive of all lung cancer types.

Involvement of autophagy in the response of tumor cells to PtdIns3K inhibitors: therapeutic implications

The phosphoinositide 3-kinase (PI3K) pathway plays a crucial role in cell proliferation and survival and is frequently activated by genetic and epigenetic alterations in human cancer. An arsenal of pharmacological inhibitors of key signaling enzymes in this pathway, including class I(A) PI3K isoforms, has been developed in the past decade and several compounds have entered clinical testing in cancer patients. The PIK3CA/p110α isoform is the most studied enzyme of the family and a validated cancer target. The induction of autophagy by PI3K pathway inhibitors has been documented in various cancers, although a clear picture about the significance of this phenomenon is still missing, especially in the in vivo situation. A better understanding of the contribution of autophagy to the action of PI3K inhibitors on tumors cells is important, since it may limit or enhance the action of these compounds, depending on the cellular context.

The Phosphoinositide 3-Kinase p110α Isoform Regulates Leukemia Inhibitory Factor Receptor Expression via c-Myc and miR-125b to Promote Cell Proliferation in Medulloblastoma.

Medulloblastoma (MB) is the most common malignant brain tumor in childhood and represents the main cause of cancer-related death in this age group. The phosphoinositide 3-kinase (PI3K) pathway has been shown to play an important role in the regulation of medulloblastoma cell survival and proliferation, but the molecular mechanisms and downstream effectors underlying PI3K signaling still remain elusive. The impact of RNA interference (RNAi)-mediated silencing of PI3K isoforms p110α and p110δ on global gene expression was investigated by DNA microarray analysis in medulloblastoma cell lines. A subset of genes with selectively altered expression upon p110α silencing in comparison to silencing of the closely related p110δ isoform was revealed. Among these genes, the leukemia inhibitory factor receptor α (LIFR α) was validated as a novel p110α target in medulloblastoma. A network involving c-Myc and miR-125b was shown to be involved in the control of LIFRα expression downstream of p110α. Targeting the LIFRα by RNAi, or by using neutralizing reagents impaired medulloblastoma cell proliferation in vitro and induced a tumor volume reduction in vivo. An analysis of primary tumors revealed that LIFRα and p110α expression were elevated in the sonic hedgehog (SHH) subgroup of medulloblastoma, indicating its clinical relevance. Together, these data reveal a novel molecular signaling network, in which PI3K isoform p110α controls the expression of LIFRα via c-Myc and miR-125b to promote MB cell proliferation.

Secretin receptor promotes the proliferation of endocrine tumor cells via the PI3K/AKT pathway

The secretin receptor (SR), a G protein-coupled receptor, mediates the effects of the gastrointestinal hormone secretin on digestion and water homeostasis. Recently, high SR expression has been observed in pancreatic ductal adenocarcinomas, cholangiocellular carcinomas, gastrinomas, and bronchopulmonary carcinoid tumors. Receptor overexpression associates with enhanced secretin-mediated signaling, but whether this molecule plays an independent role in tumorigenesis is currently unknown. We recently discovered that pheochromocytomas developing in rats affected by the MENX (multiple endocrine neoplasia-like) syndrome express at very high-level Sctr, encoding SR. We here report that SR are also highly abundant on the membranes of rat adrenal and extraadrenal pheochromocytoma, starting from early stages of tumor development, and are functional. PC12 cells, the best characterized in vitro pheochromocytoma model, also express Sctr at high level. Thus, we used them as model to study the role of SR in neoplastic transformation. Small interfering RNA-mediated knockdown of Sctr decreases PC12 cells proliferation and increases p27 levels. The proproliferative effect of SR in PC12 cells is mediated, in part, by the phosphatidylinositol 3 kinase (PI3K)/serine-threonine protein kinase (AKT) pathway. Transfection of Sctr in Y1 adrenocortical carcinoma cells, expressing low endogenous levels of Sctr, stimulates cell proliferation also, in part, via the PI3K/AKT signaling cascade. Because of the link between SR and PI3K/AKT signaling, tumor cells expressing high levels of the receptor (MENX-associated primary pheochromocytoma and NCI-H727 human bronchopulmonary carcinoid cells) respond well and in a SR-dependent manner to PI3K inhibitors, such as NVP-BEZ235. The association between SR levels and response to PI3K inhibition might open new avenues for the treatment of tumors overexpressing this receptor.

Biosynthesis and expression of VE-cadherin is regulated by the PI3K/mTOR signaling pathway

Vascular endothelial (VE)-cadherin is an essential protein of adherens junctions of endothelial cells and plays a pivotal role in vascular homeostasis. Mammalian target of rapamycin complex 2 (mTORC2) deficient mice display defects in fetal vascular development. Blocking mTOR or the upstream kinase phosphoinositide 3-kinase (PI3K) led to a dose-dependently decrease of the VE-cadherin mRNA and protein expression. Immunofluorescent staining showed a strongly decreased expression of VE-cadherin at the interface of human umbilical endothelial cells (HUVECs) followed by intercellular gap formation. Herewith, we demonstrated that the expression of VE-cadherin is dependent on mTOR and PI3K signaling.

A phosphoinositide 3-kinase (PI3K)-serum- and glucocorticoid-inducible kinase 1 (SGK1) pathway promotes Kv7.1 channel surface expression by inhibiting Nedd4-2 protein

Epithelial cell polarization involves several kinase signaling cascades that eventually divide the surface membrane into an apical and a basolateral part. One kinase, which is activated during the polarization process, is phosphoinositide 3-kinase (PI3K). In MDCK cells, the basolateral potassium channel Kv7.1 requires PI3K activity for surface-expression during the polarization process. Here, we demonstrate that Kv7.1 surface expression requires tonic PI3K activity as PI3K inhibition triggers endocytosis of these channels in polarized MDCK. Pharmacological inhibition of SGK1 gave similar results as PI3K inhibition, whereas overexpression of constitutively active SGK1 overruled it, suggesting that SGK1 is the primary downstream target of PI3K in this process. Furthermore, knockdown of the ubiquitin ligase Nedd4-2 overruled PI3K inhibition, whereas a Nedd4-2 interaction-deficient Kv7.1 mutant was resistant to both PI3K and SGK1 inhibition. Altogether, these data suggest that a PI3K-SGK1 pathway stabilizes Kv7.1 surface expression by inhibiting Nedd4-2-dependent endocytosis and thereby demonstrates that Nedd4-2 is a key regulator of Kv7.1 localization and turnover in epithelial cells.

Targeting the PI3K/AKT/mTOR signaling pathway in medulloblastoma

Medulloblastoma is the most common malignant childhood brain tumor and is associated with a poor outcome. There is an urgent need to develop novel targeted therapeutic approaches for medulloblastoma, which will arise from an enhanced understanding of the disease at the molecular level. Medulloblastoma has been recognized to be a heterogeneous disease, and no recurrent cancer gene mutations have been found, although many of the mutations described so far affect key intracellular signaling pathways, such as sonic hedgehog (SHH) and Wnt/β-catenin. The PI3K/AKT/mTOR (PAM) signaling pathway controls key cellular responses, such as cell growth and proliferation, survival, migration and metabolism. Over the last decades, it has been recognized that this intracellular signaling pathway is frequently activated by genetic and epigenetic alterations in malignant brain tumors, including medulloblastoma. Clinical trials have started to evaluate the safety and efficacy of agents targeting this pathway in malignant brain tumors. Due to the complexity of the PAM signaling pathway, there remain significant difficulties in the development of novel therapeutic approaches. The future challenges in developing effective treatments for cancer patients include the development of predictive biomarkers and combinatorial approaches to effectively target multiple signal transduction pathways. In this review article, we will summarize the current knowledge about the role of PAM signaling in medulloblastoma and discuss the strategies that are currently being evaluated with targeted agents against this pathway.

A novel TNFR1-triggered apoptosis pathway mediated by class IA PI3Ks in neutrophils

The most common form of neutrophil death is apoptosis. In the present study, we report surprising differences in the molecular mechanisms used for caspase activation between FAS/CD95-stimulated and TNF receptor 1 (TNFR1)-stimulated neutrophils. Whereas FAS-induced apoptosis was followed by caspase-8 activation and required Bid to initiate the mitochondrial amplification loop, TNF-?-induced apoptosis involved class IA PI3Ks, which were activated by MAPK p38. TNF-?-induced PI3K activation resulted in the generation of reactive oxygen species, which activated caspase-3, a mechanism that did not operate in neutrophils without active NADPH oxidase. We conclude that in neutrophils, proapoptotic pathways after TNFR1 stimulation are initiated by p38 and PI3K, but not by caspase-8, a finding that should be considered in anti-inflammatory drug-development strategies.

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.

Targeting survivin via PI3K but not c-akt/PKB by anticancer drugs in immature neutrophils

Myelosuppression is the most common unwanted side effect associated with the administration of anticancer drugs, and infections remain a common cause of death in chemotherapy-treated patients. Several mechanisms of the cytotoxicity of these drugs have been proposed and may synergistically operate in a given cell. Survivin expression has been associated with cancer, but recent reports suggest that this molecule is also expressed in several immature and mature hematopoietic cells. Here, we provide evidence that treatment of immature neutrophils with anticancer drugs reduced endogenous survivin levels causing apoptosis. The anticancer drugs did not directly target survivin, instead they blocked the activity of phosphatidylinositol-3-OH kinase, which regulated survivin expression and apoptosis in these cells. Strikingly, and in contrast to other cells, this pathway did not involve the serine/threonine kinase c-akt/PKB. Moreover, in combination with anticancer drug therapy, rapamycin did not induce increased myelosuppression in an experimental lymphoma mouse model. These data suggest that drugs that block either c-akt/PKB or signaling molecules located distal to c-akt/PKB may preferentially induce apoptosis of cancer cells as they exhibit no cytotoxicity for immature neutrophils.

Targeting class IA PI3K isoforms selectively impairs cell growth, survival, and migration in glioblastoma.

The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is frequently activated in human cancer and plays a crucial role in glioblastoma biology. We were interested in gaining further insight into the potential of targeting PI3K isoforms as a novel anti-tumor approach in glioblastoma. Consistent expression of the PI3K catalytic isoform PI3K p110α was detected in a panel of glioblastoma patient samples. In contrast, PI3K p110β expression was only rarely detected in glioblastoma patient samples. The expression of a module comprising the epidermal growth factor receptor (EGFR)/PI3K p110α/phosphorylated ribosomal S6 protein (p-S6) was correlated with shorter patient survival. Inhibition of PI3K p110α activity impaired the anchorage-dependent growth of glioblastoma cells and induced tumor regression in vivo. Inhibition of PI3K p110α or PI3K p110β also led to impaired anchorage-independent growth, a decreased migratory capacity of glioblastoma cells, and reduced the activation of the Akt/mTOR pathway. These effects were selective, because targeting of PI3K p110δ did not result in a comparable impairment of glioblastoma tumorigenic properties. Together, our data reveal that drugs targeting PI3K p110α can reduce growth in a subset of glioblastoma tumors characterized by the expression of EGFR/PI3K p110α/p-S6.