Treating brain tumors with PDE4 inhibitors

Visualization and bibliometric analysis of cAMP signaling system research trends and hotspots in cancer

Cyclic adenosine monophosphate (cAMP) is an essential second messenger that widely distributed among prokaryotic and eukaryotic organisms. cAMP can regulate various biological processes, including cell proliferation, differentiation, apoptosis and immune functions. Any dysregulation or alteration of cAMP signaling may cause cell metabolic disorder, immune dysfunction and lead to disease or cancer. This study aimed to conduct a scientometric analysis of cAMP signaling system in cancer field, and explored the research trend, hotspots and frontiers from the past decade. Relevant literatures published from 2009 to 2019 were collected in the Web of Science Core Collection database. EndNote X9 was used to remove duplicate articles, and irrelevant articles were manually filtered. Bibliometric analyses were completed by CiteSpace V. A total of 4306 articles were included in this study. The number of related literatures published each year is gradually increasing. Most of them belong to “Biochemistry & Molecular Biology”, “Oncology”, “Cell Biology”, “Pharmacology & Pharmacy” and “Endocrinology & Metabolism” areas. In the past decade, USA, China, and Japan contributed the most to the research of cAMP signaling system in cancer. The frontiers and hotspots of cAMP signaling pathway system related to cancer fields mainly focused on cancer cell apoptosis, metastasis, and multiple tumors occurrence in patients with Carney complex. Intervention of the cAMP metabolic pathway may be a potential and promising therapeutic strategy for controlling clinical cancer and tumor diseases.

Elevated intracellular cAMP concentration mediates growth suppression in glioma cells

Supressed levels of intracellular cAMP have been associated with malignancy. Thus, elevating cAMP through activation of adenylyl cyclase (AC) or by inhibition of phosphodiesterase (PDE) may be therapeutically beneficial. Here, we demonstrate that elevated cAMP levels suppress growth in C6 cells (a model of glioma) through treatment with forskolin, an AC activator, or a range of small molecule PDE inhibitors with differing selectivity profiles. Forskolin suppressed cell growth in a PKA-dependent manner by inducing a G₂/M phase cell cycle arrest. In contrast, trequinsin (a non-selective PDE2/3/7 inhibitor), not only inhibited cell growth via PKA, but also stimulated (independent of PKA) caspase-3/-7 and induced an aneuploidy phenotype. Interestingly, a cocktail of individual PDE 2,3,7 inhibitors suppressed cell growth in a manner analogous to forskolin but not trequinsin. Finally, we demonstrate that concomitant targeting of both AC and PDEs synergistically elevated intracellular cAMP levels thereby potentiating their antiproliferative actions.

Targeting Cyclic AMP Signalling in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major healthcare problem worldwide, representing one of the leading causes of cancer mortality. Since there are currently no predictive biomarkers for early stage diagnosis, HCC is detected only in advanced stages and most patients die within one year, as radical tumour resection is generally performed late during the disease. The development of alternative therapeutic approaches to HCC remains one of the most challenging areas of cancer. This review focuses on the relevance of cAMP signalling in the development of hepatocellular carcinoma and identifies the modulation of this second messenger as a new strategy for the control of tumour growth. In addition, because the cAMP pathway is controlled by phosphodiesterases (PDEs), targeting these enzymes using PDE inhibitors is becoming an attractive and promising tool for the control of HCC. Among them, based on current preclinical and clinical findings, PDE4-specific inhibitors remarkably demonstrate therapeutic potential in the management of cancer outcomes, especially as adjuvants to standard therapies. However, more preclinical studies are warranted to ascertain their efficacy during the different stages of hepatocyte transformation and in the treatment of established HCC.

Rolipram optimizes therapeutic effect of bevacizumab by enhancing proapoptotic, antiproliferative signals in a glioblastoma heterotopic model

The unstable response to bevacizumab is a big dilemma in the antiangiogenic therapy of high-grade glioma that appears to be linked to an increase in the post-treatment intratumor levels of hypoxia-inducible factor 1 α (HIF1α) and active AKT. Particularly, a selective phosphodiesterase IV (PDE4) inhibitor, rolipram is capable of inhibiting HIF1α and AKT in cancer cells. Here, the effect of bevacizumab alone and in presence of rolipram on therapeutic efficacy, intratumor hypoxia levels, angiogenesis, apoptosis and proliferation mechanisms were evaluated. BALB/c mice bearing C6 glioma were received bevacizumab and rolipram either alone or combined for 30 days (n = 11/group). At the last day of treatments, apoptosis, proliferation and microvessel density, in xenografts (3/group) were detected by TUNEL staining, Ki67 and CD31 markers, respectively. Relative expression of target proteins was measured using western blotting. Bevacizumab initially hindered the tumor progression but its antitumor effect was weakened later despite the vascular regression and apoptosis induction. Unpredictably, bevacizumab-treated tumors exhibited the highest cell proliferation coupled with PDE4A, HIF1α and AKT upregulation and p53 downregulation and reversed by co-treatment with rolipram. Unlike a similar antivascular pattern to bevacizumab, rolipram consistently led to a more tumor growth suppression and proapoptotic effect versus bevacizumab. Co-treatment maximally hampered the tumor progression and elongated survival along with the major vascular regression, hypoxia, apoptosis induction, p53 and caspase activities. In conclusion, superior and persistent therapeutic efficacy of co-treatment provides a new insight into antiangiogenic therapy of malignant gliomas, suggesting to be a potential substitute in selected patients.

Emerging therapeutic potential of anti-psychotic drugs in the management of human glioma: A comprehensive review

Despite numerous advancements in the last decade, human gliomas such as astrocytoma and glioblastoma multiforme have the worst prognoses among all cancers. Anti-psychotic drugs are commonly prescribed to treat mental disorders among cancer patients, and growing empirical evidence has revealed their antitumor, anti-metastatic, anti-angiogenic, anti-proliferative, chemo-preventive, and neo-adjuvant efficacies in various in vitro, in vivo, and clinical glioma models. Anti-psychotic drugs have drawn the attention of physicians and researchers owing to their beneficial effects in the prevention and treatment of gliomas. This review highlights data on the therapeutic potential of various anti-psychotic drugs as anti-proliferative, chemopreventive, and anti-angiogenic agents in various glioma models via the modulation of upstream and downstream molecular targets involved in apoptosis, autophagy, oxidative stress, inflammation, and the cell cycle in in vitro and in vivo preclinical and clinical stages among glioma patients. The ability of anti-psychotic drugs to modulate various signaling pathways and multidrug resistance-conferring proteins that enhance the efficacy of chemotherapeutic drugs with low side-effects exemplifies their great potential as neo-adjuvants and potential chemotherapeutics in single or multimodal treatment approach. Moreover, anti-psychotic drugs confer the ability to induce glioma into oligodendrocyte-like cells and neuronal-like phenotype cells with reversal of epigenetic alterations through inhibition of histone deacetylase further rationalize their use in glioma treatment. The improved understanding of anti-psychotic drugs as potential chemotherapeutic drugs or as neo-adjuvants will provide better information for their use globally as affordable, well-tolerated, and effective anticancer agents for human glioma.

Therapeutic opportunities in colon cancer: Focus on phosphodiesterase inhibitors

Despite novel technologies, colon cancer remains undiagnosed and 25% of patients are diagnosed with metastatic colon cancer. Resistant to chemotherapeutic agents is one of the major problems associated with treating colon cancer which creates the need to develop novel agents targeting towards newer targets. A phosphodiesterase is a group of isoenzyme, which, hydrolyze cyclic nucleotides and thereby lowers intracellular levels of cAMP and cGMP leading to tumorigenic effects. Many in vitro and in vivo studies have confirmed increased PDE expression in different types of cancers including colon cancer. cAMP-specific PDE inhibitors increase intracellular cAMP that leads to activation of effector molecules-cAMP-dependent protein kinase A, exchange protein activated by cAMP and cAMP gated ion channels. These molecules regulate cellular responses and exert its anticancer role through different mechanisms including apoptosis, inhibition of angiogenesis, upregulating tumor suppressor genes and suppressing oncogenes. On the other hand, cGMP specific PDE inhibitors exhibit anticancer effects through cGMP dependent protein kinase and cGMP dependent cation channels. Elevation in cGMP works through activation of caspases, suppression of Wnt/b-catenin pathway and TCF transcription leading to inhibition of CDK and survivin. These studies point out towards the fact that PDE inhibition is associated with anti-proliferative, anti-apoptotic and anti-angiogenic pathways involved in its anticancer effects in colon cancer. Thus, inhibition of PDE enzymes can be used as a novel approach to treat colon cancer. This review will focus on cAMP and cGMP signaling pathways leading to tumorigenesis and the use of PDE inhibitors in colon cancer.

Understanding and exploiting cell signalling convergence nodes and pathway cross-talk in malignant brain cancer

In cancer, complex intracellular and intercellular signals constantly evolve for the advantage of the tumour cells but to the disadvantage of the whole organism. Decades of intensive research have revealed the critical roles of cellular signalling pathways in regulating complex cell behaviours which influence tumour development, growth and therapeutic response, and ultimately patient outcome. Most studies have focussed on specific pathways and the resulting tumour cell function in a rather linear fashion, partly due to the available methodologies and partly due to the traditionally reductionist approach to research. Advances in cancer research, including genomic technologies have led to a deep appreciation of the complex signals and pathway interactions operating in tumour cells. In this review we examine the role and interaction of three major cell signalling pathways, PI3K, MAPK and cAMP, in regulating tumour cell functions and discuss the prospects for exploiting this knowledge to better treat difficult to treat cancers, using glioblastoma, the most common and deadly malignant brain cancer, as the example disease.

Unstructured Formulation Data Analysis for the Optimization of Lipid Nanoparticle Drug Delivery Vehicles

Designing nanoparticle formulations with features tailored to their therapeutic targets in demanding timelines assumes increased importance. In this context, nanostructured lipid carriers (NLCs) offer an excellent example of a drug delivery nanosystem that has been broadly explored in the treatment of glioblastoma multiforme (GBM). Distinct fundamental NLC quality attributes can be harnessed to fit this purpose, namely particle size, size distribution, and zeta potential. These critical aspects intrinsically depend on the formulation components, influencing drug loading capacity, drug release, and stability of the NLCs. Wide variations in their composition, including the type of lipids and other surface modifier excipients, lead to differences on these parameters. NLC target product profile involves small mean particle sizes, narrow size distributions, and absolute values of zeta potential higher than 30 mV. In this work, a wealth of data previously obtained in experiments on NLC preparation, encompassing, e.g., results of preliminary studies and those of intermediate formulations, is analyzed in order to extract information useful in further optimization studies. Principal component analysis (PCA) and partial least squares (PLS) are performed to evaluate the influence of NLC composition on the respective characteristics. These methods provide a rapid and discriminatory analysis for establishing a preformulation framework, by selecting the most suitable types of lipids, surfactants, surface modifiers, and drugs, within the set of investigated variables. The results have direct implications in the optimization of formulation and processes.

Inhibitors of phosphodiesterase as cancer therapeutics

Phosphodiesterases (PDEs) are a class of enzymes that hydrolyze cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which is involved in many physiological processes including visual transduction, cell proliferation and differentiation, cell-cycle regulation, gene expression, inflammation, apoptosis, and metabolic function. PDEs are composed of 11 different families and each family contains different subtypes. The distribution, expression, regulation mode and sensitivity to inhibitors of each subtype are different, and they are involved in cancer, inflammation, asthma, depression, erectile dysfunction and other pathological processes of development. A large number of studies have shown that PDEs play an important role in the development of tumors by affecting the intracellular level of cAMP and/or cGMP and PDEs could become diagnostic markers or therapeutic targets. This review will give a brief overview of the expression and regulation of PDE families in the process of tumorigenesis and their anti-tumor inhibitors, which may guide the design of novel therapeutic drugs targeting PDEs for anticancer agent.

The G protein Gαs acts as a tumor suppressor in sonic hedgehog signaling-driven tumorigenesis

G protein-coupled receptors (GPCRs) are critical players in tumor growth and progression. The redundant roles of GPCRs in tumor development confound effective treatment; therefore, targeting a single common signaling component downstream of these receptors may be efficacious. GPCRs transmit signals through heterotrimeric G proteins composed of Gα and Gβγ subunits. Hyperactive Gαs signaling can mediate tumor progression in some tissues; however, recent work in medulloblastoma and basal cell carcinoma revealed that Gαs can also function as a tumor suppressor in neoplasms derived from ectoderm cells including neural and epidermal stem/progenitor cells. In these stem-cell compartments, signaling through Gαs suppresses self-renewal by inhibiting the Sonic Hedgehog (SHH) and Hippo pathways. The loss of GNAS, which encodes Gαs, leads to activation of these pathways, over-proliferation of progenitor cells, and tumor formation. Gαs activates the cAMP-dependent protein kinase A (PKA) signaling pathway and inhibits activation of SHH effectors Smoothened-Gli. In addition, Gαs-cAMP-PKA activation negatively regulates the Hippo pathway by blocking the NF2-LATS1/2-Yap signaling. In this review, we will address the novel function of the signaling network regulated by Gαs in suppression of SHH-driven tumorigenesis and the therapeutic approaches that can be envisioned to harness this pathway to inhibit tumor growth and progression.

Quo natas, Danio?-Recent Progress in Modeling Cancer in Zebrafish

Over the last decade, zebrafish has proven to be a powerful model in cancer research. Zebrafish form tumors that histologically and genetically resemble human cancers. The live imaging and cost-effective compound screening possible with zebrafish especially complement classic mouse cancer models. Here, we report recent progress in the field, including genetically engineered zebrafish cancer models, xenotransplantation of human cancer cells into zebrafish, promising approaches toward live investigation of the tumor microenvironment, and identification of therapeutic strategies by performing compound screens on zebrafish cancer models. Given the recent advances in genome editing, personalized zebrafish cancer models are now a realistic possibility. In addition, ongoing automation will soon allow high-throughput compound screening using zebrafish cancer models to be part of preclinical precision medicine approaches.

Development of anticancer agents targeting the Hedgehog signaling

Hedgehog signaling is an evolutionarily conserved pathway which is essential in embryonic and postnatal development as well as adult organ homeostasis. Abnormal regulation of Hedgehog signaling is implicated in many diseases including cancer. Consequently, substantial efforts have made in the past to develop potential therapeutic agents that specifically target the Hedgehog signaling for cancer treatment. Here, we review the therapeutic agents for inhibition of the Hedgehog signaling and their clinical advances in cancer treatment.

The Role of Protein Kinase B Signaling Pathway in Anti-Cancer Effect of Rolipram on Glioblastoma Multiforme: An In Vitro Study

Introduction:

The mechanism of putative cytotoxicity of 4-[3-(cyclopentyloxy)-4-methoxyphenyl]-2-pyrrolidone (rolipram), a specific phosphodiesterase-4 (PDE4) inhibitor, on glioblastoma multiforme (GBM) is almost unknown. This study aimed to investigate the role of protein kinase B (Akt) pathway in the cytotoxic effect of rolipram on human GBM U87 MG cell line and Tumor-Initiating Cells (TICs) isolated from patient’s GBM specimen.

Methods:

TICs were characterized by using flow cytometry and quantitative real-time PCR. The cells were treated with rolipram at inhibitory concentration of 50% (IC50) in the presence or absence of SC79 (4μg/mL), a specific AKT activator, for 48 hours. The cell viability and apoptosis were measured by MTT assay and TUNEL staining, respectively. The relative expression of Phospho-Akt (Ser473), matrix metalloproteinase 2 (MMP2), and vascular endothelial growth factor A (VEGFA) were detected using Western blotting.

Results:

The findings showed that rolipram could suppress cell viability in both U87MG and TICs, dose-dependently. Interestingly, the rolipram-induced cytotoxicity was significantly reduced in the presence of SC79. Nevertheless, in rolipram-treated cells, the pretreatment with SC79 significantly led to increase in U87 MG cells and TICs apoptosis and decrease in viability of U87 MG cells but not TICs relative to corresponding control. In U87 MG and TICs, rolipram-induced reduction of Phospho-Akt (Ser473) and MMP2 levels were significantly suppressed by SC79.

Conclusion:

There is a cell type-specific mechanism of anti-proliferative action of rolipram on GBM cells. The reduction of intracellular level of MMP2 but not VEGFA by rolipram is conducted through the inhibition of Akt signal. Rolipram-induced apoptosis is mediated via Akt dependent/independent mechanisms.

Increase of Intracellular Cyclic AMP by PDE4 Inhibitors Affects HepG2 Cell Cycle Progression and Survival

Type 4 cyclic nucleotide phosphodiesterases (PDE4) are major members of a superfamily of enzymes (PDE) involved in modulation of intracellular signaling mediated by cAMP. Broadly expressed in most human tissues and present in large amounts in the liver, PDEs have in the last decade been key therapeutic targets for several inflammatory diseases. Recently, a significant body of work has underscored their involvement in different kinds of cancer, but with no attention paid to liver cancer. The present study investigated the effects of two PDE4 inhibitors, rolipram and DC-TA-46, on the growth of human hepatoma HepG2 cells. Treatment with these inhibitors caused a marked increase of intracellular cAMP level and a dose- and time-dependent effect on cell growth. The concentrations of inhibitors that halved cell proliferation to about 50% were used for cell cycle experiments. Rolipram (10 μM) and DC-TA-46 (0.5 μM) produced a decrease of cyclin expression, in particular of cyclin A, as well as an increase in p21, p27 and p53, as evaluated by Western blot analysis. Changes in the intracellular localization of cyclin D1 were also observed after treatments. In addition, both inhibitors caused apoptosis, as demonstrated by an Annexin-V cytofluorimetric assay and analysis of caspase-3/7 activity. Results demonstrated that treatment with PDE4 inhibitors affected HepG2 cell cycle and survival, suggesting that they might be useful as potential adjuvant, chemotherapeutic or chemopreventive agents in hepatocellular carcinoma. J. Cell. Biochem. 118: 1401-1411, 2017. © 2016 Wiley Periodicals, Inc.

Psychiatric aspects of phosphodiesterases: An overview

Phosphodiesterases (PDE) are exciting new targets in medical sciences. These enzymes are some of the key mediators of cellular functions in the body and hence are attractive sites for drug-induced modulations. With the finding that Tofisopam, a new anxiolytic, inhibits PDEs, the authors were inspired to look into the role of PDE and drugs acting on them in psychiatry. Hence, the review was undertaken. We found several research materials available highlighting the role of PDE in cellular functions and the possible newer etiological mechanisms of neuropsychiatric illnesses such as schizophrenia, depression/anxiety disorders, and cognitive dysfunction involving PDEs. We also found that there are many molecules acting on PDEs, which have the potential to alter the way we treat mental illnesses today. This article is intended to provide an in-depth look at these enzymes so that more cost-effective therapeutic molecules may be synthesized and marketed in India for managing mental illnesses.

Intersections at the crossroads: Neurofibromatosis type 1, cAMP, sex, and glioma risk

Cancer predisposition syndromes, particularly neurofibromatosis type 1 (NF1), provide unique vantage points from which to examine the co-contributions of molecular, cellular, and tissue processes to tumor biology. Polymorphisms in adenylate cyclase 8 affect brain tumor risk in NF1 in a sex-specific fashion, illuminating novel interdependencies in brain tumorigenesis.

A phosphodiesterase 4B-dependent interplay between tumor cells and the microenvironment regulates angiogenesis in B-cell lymphoma

Angiogenesis associates with poor outcome in diffuse large B-cell lymphoma (DLBCL), but the contribution of the lymphoma cells to this process remains unclear. Addressing this knowledge gap may uncover unsuspecting proangiogenic signaling nodes and highlight alternative antiangiogenic therapies. Here we identify the second messenger cyclic-AMP (cAMP) and the enzyme that terminates its activity, phosphodiesterase 4B (PDE4B), as regulators of B-cell lymphoma angiogenesis. We first show that cAMP, in a PDE4B-dependent manner, suppresses PI3K/AKT signals to down-modulate VEGF secretion and vessel formation in vitro. Next, we create a novel mouse model that combines the lymphomagenic Myc transgene with germline deletion of Pde4b. We show that lymphomas developing in a Pde4b-null background display significantly lower microvessel density in association with lower VEGF levels and PI3K/AKT activity. We recapitulate these observations by treating lymphoma-bearing mice with the FDA-approved PDE4 inhibitor Roflumilast. Lastly, we show that primary human DLBCLs with high PDE4B expression display significantly higher microvessel density. Here, we defined an unsuspected signaling circuitry in which the cAMP generated in lymphoma cells downmodulates PI3K/AKT and VEGF secretion to negatively influence vessel development in the microenvironment. These data identify PDE4 as an actionable antiangiogenic target in DLBCL.

Not so Fast: Co-Requirements for Sonic Hedgehog Induced Brain Tumorigenesis

The Sonic hedgehog (Shh) pathway plays an integral role in cellular proliferation during normal brain development and also drives growth in a variety of cancers including brain cancer. Clinical trials of Shh pathway inhibitors for brain tumors have yielded disappointing results, indicating a more nuanced role for Shh signaling. We postulate that Shh signaling does not work alone but requires co-activation of other signaling pathways for tumorigenesis and stem cell maintenance. This review will focus on the interplay between the Shh pathway and these pathways to promote tumor growth in brain tumors, presenting opportunities for the study of combinatorial therapies.

Targeting brain tumor cAMP: the case for sex-specific therapeutics

A relationship between cyclic adenosine 3′, 5′-monophosphate (cAMP) levels and brain tumor biology has been evident for nearly as long as cAMP and its synthetase, adenylate cyclase (ADCY) have been known. The importance of the pathway in brain tumorigenesis has been demonstrated in vitro and in multiple animal models. Recently, we provided human validation for a cooperating oncogenic role for cAMP in brain tumorigenesis when we found that SNPs in ADCY8 were correlated with glioma (brain tumor) risk in individuals with Neurofibromatosis type 1 (NF1). Together, these studies provide a strong rationale for targeting cAMP in brain tumor therapy. However, the cAMP pathway is well-known to be sexually dimorphic, and SNPs in ADCY8 affected glioma risk in a sex-specific fashion, elevating the risk for females while protecting males. The cAMP pathway can be targeted at multiple levels in the regulation of its synthesis and degradation. Sex differences in response to drugs that target cAMP regulators indicate that successful targeting of the cAMP pathway for brain tumor patients is likely to require matching specific mechanisms of drug action with patient sex.

An in vivo chemical genetic screen identifies phosphodiesterase 4 as a pharmacological target for hedgehog signaling inhibition

Hedgehog (Hh) signaling plays an integral role in vertebrate development, and its dysregulation has been accepted widely as a driver of numerous malignancies. While a variety of small molecules target Smoothened (Smo) as a strategy for Hh inhibition, Smo gain-of-function mutations have limited their clinical implementation. Modulation of targets downstream of Smo could define a paradigm for treatment of Hh-dependent cancers. Here, we describe eggmanone, a small molecule identified from a chemical genetic zebrafish screen, which induced an Hh-null phenotype. Eggmanone exerts its Hh-inhibitory effects through selective antagonism of phosphodiesterase 4 (PDE4), leading to protein kinase A activation and subsequent Hh blockade. Our study implicates PDE4 as a target for Hh inhibition, suggests an improved strategy for Hh-dependent cancer therapy, and identifies a unique probe of downstream-of-Smo Hh modulation.

G-Protein Gαs controls medulloblastoma initiation by suppressing sonic hedgehog signaling

We identify Gαs as a novel tumor suppressor in medulloblastoma that functions principally by inhibition of sonic hedgehog signaling. Gαs not only stimulates cyclic adenosine monophosphate (cAMP)-dependent signaling but also inhibits ciliary trafficking of hedgehog components. Elevation of cAMP inhibits medulloblastoma growth and augments inhibition of smoothened to decrease tumor cell proliferation, thus highlighting Gαs as a potential therapeutic target.

PDE7B is a novel, prognostically significant mediator of glioblastoma growth whose expression is regulated by endothelial cells

Cell-cell interactions between tumor cells and constituents of their microenvironment are critical determinants of tumor tissue biology and therapeutic responses. Interactions between glioblastoma (GBM) cells and endothelial cells (ECs) establish a purported cancer stem cell niche. We hypothesized that genes regulated by these interactions would be important, particularly as therapeutic targets. Using a computational approach, we deconvoluted expression data from a mixed physical co-culture of GBM cells and ECs and identified a previously undescribed upregulation of the cAMP specific phosphodiesterase PDE7B in GBM cells in response to direct contact with ECs. We further found that elevated PDE7B expression occurs in most GBM cases and has a negative effect on survival. PDE7B overexpression resulted in the expansion of a stem-like cell subpopulation in vitro and increased tumor growth and aggressiveness in an in vivo intracranial GBM model. Collectively these studies illustrate a novel approach for studying cell-cell interactions and identifying new therapeutic targets like PDE7B in GBM.

The G protein α subunit Gαs is a tumor suppressor in Sonic hedgehog-driven medulloblastoma

Medulloblastoma, the most common malignant childhood brain tumor, exhibits distinct molecular subtypes and cellular origins. Genetic alterations driving medulloblastoma initiation and progression remain poorly understood. Herein, we identify GNAS, encoding the G-protein Gsα, as a potent tumor suppressor gene that defines a subset of aggressive Sonic Hedgehog (Shh)-driven human medulloblastomas. Ablation of the single Gnas gene in anatomically-distinct progenitors is sufficient to induce Shh-associated medulloblastomas, which recapitulate their human counterparts. Gsα is highly enriched at the primary cilium of granule neuron precursors and suppresses Shh-signaling by regulating both the cAMP-dependent pathway and ciliary trafficking of Hedgehog pathway components. Elevation of a Gsα effector, cAMP, effectively inhibits tumor cell proliferation and progression in Gnas mutants. Thus, our gain- and loss-of-function studies identify a previously unrecognized tumor suppressor function for Gsα that acts as a molecular link across Shh-group medulloblastomas of disparate cellular and anatomical origins, illuminating G-protein modulation as a potential therapeutic avenue.

Chronic exposure to GLP-1 increases GLP-1 synthesis and release in a pancreatic alpha cell line (α-TC1): evidence of a direct effect of GLP-1 on pancreatic alpha cells

Aims/Hypothesis

Incretin therapies, which are used to treat diabetic patients, cause a chronic supra-physiological increase in GLP-1 circulating levels. It is still unclear how the resulting high hormone concentrations may affect pancreatic alpha cells. The present study was designed to investigate the effects of chronic exposure to high GLP-1 levels on a cultured pancreatic alpha cell line.

Methods

α-TC1-6 cell line was cultured in the presence or absence of GLP-1 (100 nmol/l) for up to 72 h. In our model GLP-1 receptor (GLP-1R) was measured. After the cells were exposed to GLP-1 the levels of glucagon secretion were measured. Because GLP-1 acts on intracellular cAMP production, the function of GLP-1R was studied. We also investigated the effects of chronic GLP-1 exposure on the cAMP/MAPK pathway, Pax6 levels, the expression of prohormone convertases (PCs), glucagon gene (Gcg) and protein expression, glucagon and GLP-1 production.

Results

In our model, we were able to detect GLP-1R. After GLP-1 exposure we found a reduction in glucagon secretion. During further investigation of the function of GLP-1R, we found an activation of the cAMP/MAPK/Pax6 pathway and an increase of Gcg gene and protein expression. Furthermore we observed a significant increase in PC1/3 protein expression, GLP-1 intracellular content and GLP-1 secretion.

Conclusions/Interpretation

Our data indicate that the chronic exposure of pancreatic alpha cells to GLP-1 increases the ability of these cells to produce and release GLP-1. This phenomenon occurs through the stimulation of the transcription factor Pax6 and the increased expression of the protein convertase PC1/3.

Theobromine, the primary methylxanthine found in Theobroma cacao, prevents malignant glioblastoma proliferation by negatively regulating phosphodiesterase-4, extracellular signal-regulated kinase, Akt/mammalian target of rapamycin kinase, and nuclear factor-kappa B

Theobromine, a caffeine derivative, is the primary methylxanthine produced by Theobroma cacao. We previously showed that methylxanthines, including caffeine and theophylline, have antitumor and antiinflammatory effects, which are in part mediated by their inhibition of phosphodiesterase (PDE). A member of the PDE family, PDE4, is widely expressed in and promotes the growth of glioblastoma, the most common type of brain tumor. The purpose of this study was to determine whether theobromine could exert growth inhibitory effects on U87-MG, a cell line derived from human malignant glioma. We show that theobromine treatment elevates intracellular cAMP levels and increases the activity of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase, whereas it attenuates p44/42 extracellular signal-regulated kinase activity and the Akt/mammalian target of rapamycin kinase and nuclear factor-kappa B signal pathways. It also inhibits cell proliferation. These results suggest that foods and beverages containing cocoa bean extracts, including theobromine, might be extremely effective in preventing human glioblastoma.

Benzoquinones and terphenyl compounds as phosphodiesterase-4B inhibitors from a fungus of the order Chaetothyriales (MSX 47445)

Three bioactive compounds were isolated from an organic extract of an ascomycete fungus of the order Chaetothyriales (MSX 47445) using bioactivity-directed fractionation as part of a search for anticancer leads from filamentous fungi. Of these, two were benzoquinones [betulinan A (1) and betulinan C (3)], and the third was a terphenyl compound, BTH-II0204-207:A (2). The structures were elucidated using a set of spectroscopic and spectrometric techniques; the structure of the new compound (3) was confirmed via single-crystal X-ray diffraction. Compounds 1-3 were evaluated for cytotoxicity against a human cancer cell panel, for antimicrobial activity against Staphylococcus aureus and Candida albicans, and for phosphodiesterase (PDE4B2) inhibitory activities. The putative binding mode of 1-3 with PDE4B2 was examined using a validated docking protocol, and the binding and enzyme inhibitory activities were correlated.

Targeted activation of PKA and Epac promotes glioblastoma regression in vitro

Ras-p44/42 mitogen-activated protein kinase (MAPK) and Akt signaling are the key pathways involved in the promotion of glioblastoma formation. Notably, phosphodiesterase 4 (PDE4) is widely expressed in brain tumors and promotes their growth. PDE4 inhibitors have been reported to suppress glioblastoma growth in vitro and in vivo. The mechanisms underlying these actions, however, have yet to be elucidated. The aim of this study was to investigate whether intracellular cyclic adenosine monophosphate (cAMP) was able to suppress the Ras-p44/42 MAPK signaling pathway via protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) in U87MG human malignant glioma cells. Forskolin, an activator of adenylate cyclase, inhibited cell growth and the phosphorylation of p44/42 MAPK in U87MG cells, whereas the non-hydrolyzable cAMP analog 8-bromoadenosine 3',5'-cAMP (8-Br-cAMP) considerably suppressed cell growth and phosphorylation of p44/42 MAPK. The inhibitory effects of forskolin were partially prevented by the PKA inhibitor H89. The Epac-selective agonist 8-(4-chlorophenylthio)-2'-O-methyladenosine cAMP (8-CPT-cAMP) inhibited phosphorylation of p44/42 MAPK. These findings suggest that PKA and Epac are involved in the effect of intracellular cAMP on the Ras-p44/42 MAPK signaling pathway.

Cyclic AMP, protein kinase A, and phosphodiesterases: proceedings of an international workshop

Cyclic nucleotides cAMP and cGMP are part of almost all major cellular signaling pathways. Phosphodiesterases (PDEs) are enzymes that regulate the intracellular levels of cAMP and cGMP. Protein kinase A or cAMP-dependent protein kinase mediates most cAMP effects in the cell. Over the last 25 years, various components of this group of molecules have been involved in human diseases, both genetic and acquired. Lately, the PDEs attract more attention. The pharmacological exploitation of the PDE's ability to regulate cGMP and cAMP, and through them, a variety of signaling pathways, has led to a number of new drugs for diverse applications from the treatment of erectile dysfunction to heart failure, asthma, and chronic obstructive pulmonary disease. We present the abstracts (available online) and selected articles from the proceedings of a meeting that took place at the National Institutes of Health (NIH), Bethesda, MD, June 8-10, 2011.

Inhibition of phosphodiesterase-4 (PDE4) activity triggers luminal apoptosis and AKT dephosphorylation in a 3-D colonic-crypt model

Background

We previously established a three-dimensional (3-D) colonic crypt model using HKe3 cells which are human colorectal cancer (CRC) HCT116 cells with a disruption in oncogenic KRAS, and revealed the crucial roles of oncogenic KRAS both in inhibition of apoptosis and in disruption of cell polarity; however, the molecular mechanism of KRAS-induced these 3-D specific biological changes remains to be elucidated.

Results

Among the genes that were upregulated by oncogenic KRAS in this model, we focused on the phosphodiesterase 4B (PDE4B) of which expression levels were found to be higher in clinical tumor samples from CRC patients in comparison to those from healthy control in the public datasets of gene expression analysis. PDE4B2 was specifically overexpressed among other PDE4 isoforms, and re-expression of oncogenic KRAS in HKe3 cells resulted in PDE4B overexpression. Furthermore, the inhibition of PDE4 catalytic activity using rolipram reverted the disorganization of HCT116 cells into the normal physiologic state of the epithelial cell polarity by inducing the apical assembly of ZO-1 (a tight junction marker) and E-cadherin (an adherens junction marker) and by increasing the activity of caspase-3 (an apoptosis marker) in luminal cavities. Notably, rolipram reduced the AKT phosphorylation, which is known to be associated with the disruption of luminal cavity formation and CRC development. Similar results were also obtained using PDE4B2-shRNAs. In addition, increased expression of PDE4B mRNA was found to be correlated with relapsed CRC in a public datasets of gene expression analysis.

Conclusions

These results collectively suggested that PDE4B is upregulated by oncogenic KRAS, and also that the inhibition of PDE4 catalytic activity can induce both epithelial cell polarity and luminal apoptosis in CRC, thus highlighting the utility of our 3-D culture (3 DC) model for the KRAS-induced development of CRC in 3-D microenvironment. Indeed, using this model, we found that PDE4B is a promising candidate for a therapeutic target as well as prognostic molecular marker in CRC. Further elucidation of the signaling network of PDE4B2 in 3 DC would provide a better understanding of CRC in vivo.

Clinical utility of neuroprotective agents in neurodegenerative diseases: current status of drug development for Alzheimer's, Parkinson's and Huntington's diseases, and amyotrophic lateral sclerosis

INTRODUCTION

According to the definition of the Committee to Identify Neuroprotective Agents in Parkinson's Disease (CINAPS), "neuroprotection would be any intervention that favourably influences the disease process or underlying pathogenesis to produce enduring benefits for patients" [Meissner W, et al. Trends Pharmacol Sci 2004;25:249-253]. Preferably, neuroprotective agents should be used before or eventually during the prodromal phase of the diseases that could start decades before the appearance of symptoms. Although several symptomatic drugs are available, a disease-modifying agent is still elusive.

AREAS COVERED

The aim of the present review is to give an overview of neuroprotective agents being currently investigated for the treatment of AD, PD, HD and ALS in clinical phases.

EXPERT OPINION

Development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages, both conceptual and methodological. Novel solutions might be offered by evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multi-target approaches and network pharmacology.

Phosphodiesterase function and endocrine cells: links to human disease and roles in tumor development and treatment

Phosphodiesterases (PDEs) are enzymes that regulate the intracellular levels of cyclic adenosine monophosphate and cyclic guanosine monophosphate, and, consequently, exhibit a central role in multiple cellular functions. The pharmacological exploitation of the ability of PDEs to regulate specific pathways has led to the discovery of drugs with selective action against specific PDE isoforms. Considerable attention has been given to the development of selective PDE inhibitors, especially after the therapeutic success of PDE5 inhibitors in the treatment of erectile dysfunction. Several associations between PDE genes and genetic diseases have been described, and more recently PDE11A and PDE8B have been implicated in predisposition to tumor formation. This review focuses on the possible function of PDEs in a variety of tumors, primarily in endocrine glands, both in tumor predisposition and as potential therapeutic targets.

Mechanism of RAF isoform switching induced by oncogenic RAS in melanoma

BRAF and RAS are often mutated in cutaneous melanoma and both mutations stimulate the MAPK pathway. However the biological consequences of BRAF and NRAS mutations are different because when RAS is mutated in melanoma, cells use CRAF rather than BRAF to activate MEK/ERK. The mechanism of this BRAF to CRAF isoform switching in response to oncogenic RAS has recently been described. Activation of the MAPK pathway, which results from a mutation of NRAS, induces phosphorylation of BRAF on serine 151 by ERK which prevents its binding to NRAS. To circumvent this negative feedback inhibition of BRAF, melanoma cells containing a mutation of RAS use CRAF to activate MEK/ERK. However, because the cAMP pathway in melanocytes constitutively inhibits CRAF, RAF isoform switching in melanoma is accompanied by an inhibition of the cAMP pathway. This inhibition is due to an increase in phosphodiesterase activity, which degrades cAMP thereby preventing inhibition of CRAF by PKA. These data highlight the importance of CRAF downstream of oncogenic Ras in tumor development.