Inhibition of PDE3, PDE4 and PDE7 potentiates glucocorticoid-induced apoptosis and overcomes glucocorticoid resistance in CEM T leukemic cells

Cyclic nucleotide phosphodiesterases as drug targets

Cyclic nucleotides are synthesized by adenylyl and/or guanylyl cyclase, and downstream of this synthesis, the cyclic nucleotide phosphodiesterase families (PDEs) specifically hydrolyze cyclic nucleotides. PDEs control cyclic adenosine-3',5'monophosphate (cAMP) and cyclic guanosine-3',5'-monophosphate (cGMP) intracellular levels by mediating their quick return to the basal steady state levels. This often takes place in subcellular nanodomains. Thus, PDEs govern short-term protein phosphorylation, long-term protein expression, and even epigenetic mechanisms by modulating cyclic nucleotide levels. Consequently, their involvement in both health and disease is extensively investigated. PDE inhibition has emerged as a promising clinical intervention method, with ongoing developments aiming to enhance its efficacy and applicability. In this comprehensive review, we extensively look into the intricate landscape of PDEs biochemistry, exploring their diverse roles in various tissues. Furthermore, we outline the underlying mechanisms of PDEs in different pathophysiological conditions. Additionally, we review the application of PDE inhibition in related diseases, shedding light on current advancements and future prospects for clinical intervention. SIGNIFICANCE STATEMENT: Regulating PDEs is a critical checkpoint for numerous (patho)physiological conditions. However, despite the development of several PDE inhibitors aimed at controlling overactivated PDEs, their applicability in clinical settings poses challenges. In this context, our focus is on pharmacodynamics and the structure activity of PDEs, aiming to illustrate how selectivity and efficacy can be optimized. Additionally, this review points to current preclinical and clinical evidence that depicts various optimization efforts and indications.

Pan-cancer analysis of the PDE4DIP gene with potential prognostic and immunotherapeutic values in multiple cancers including acute myeloid leukemia

Phosphodiesterase 4D interacting protein (PDE4DIP) interacts with cAMP-specific phosphodiesterase 4D and its abnormal expression promotes the development of hematological malignancies, breast cancer, and pineal cell carcinoma. However, there is currently no systematic pan-cancer analysis of the association between PDE4DIP and various cancers. Thus, this study aimed to elucidate the potential functions of PDE4DIP in various cancers. Based on the multiple public databases and online websites, we conducted comprehensive analyses for PDE4DIP in various cancers, including differential expression, prognosis, genetic variation, DNA methylation, and immunity. We thoroughly analyzed the specific role of PDE4DIP in acute myeloid leukemia (LAML). The results indicated that there were differences in PDE4DIP expression in cancers, and in kidney chromophobe, LAML, pheochromocytoma and paraganglioma, thymoma, and uveal melanoma, PDE4DIP had potential prognostic value. PDE4DIP expression was also correlated with genetic variation, DNA methylation, immune cell infiltration, and immune-related genes in cancers. Functional enrichment analysis showed that PDE4DIP was mainly related to immune-related pathways in cancers, and in LAML, PDE4DIP was mainly related to immunoglobulin complexes, T-cell receptor complexes, and immune response regulatory signaling pathways. Our study systematically revealed for the first time the potential prognostic and immunotherapeutic value of PDE4DIP in various cancers, including LAML.

Integrative Analyses of Circulating mRNA and lncRNA Expression Profile in Plasma of Lung Cancer Patients

Circulating-free RNAs (cfRNAs) have been regarded as potential biomarkers for "liquid biopsy" in cancers. However, the circulating messenger RNA (mRNA) and long noncoding RNA (lncRNA) profiles of lung cancer have not been fully characterized. In this study, we profiled circulating mRNA and lncRNA profiles of 16 lung cancer patients and 4 patients with benign pulmonary nodules. Compared with benign pulmonary nodules, 806 mRNAs and 1,762 lncRNAs were differentially expressed in plasma of lung adenocarcinoma patients. For lung squamous cell carcinomas, 256 mRNAs and 946 lncRNAs were differentially expressed. A total of 231 mRNAs and 298 lncRNAs were differentially expressed in small cell lung cancer. Eleven mRNAs, 51 lncRNAs, and 207 canonical pathways were differentially expressed in lung cancer in total. Forty-five blood samples were collected to verify our findings via performing qPCR. There are plenty of meaningful mRNAs and lncRNAs that were found. MYC, a transcription regulator associated with the stemness of cancer cells, is overexpressed in lung adenocarcinoma. Transforming growth factor beta (TGFB1), which plays pleiotropic roles in cancer progression, was found to be upregulated in lung squamous carcinoma. MALAT1, a well-known oncogenic lncRNA, was also found to be upregulated in lung squamous carcinoma. Thus, this study provided a systematic resource of mRNA and lncRNA expression profiles in lung cancer plasma.

Treatment of Experimental Autoimmune Encephalomyelitis with an Inhibitor of Phosphodiesterase-8 (PDE8)

After decades of development, inhibitors targeting cyclic nucleotide phosphodiesterases (PDEs) expressed in leukocytes have entered clinical practice for the treatment of inflammatory disorders, with three PDE4 inhibitors being in clinical use as therapeutics for psoriasis, psoriatic arthritis, chronic obstructive pulmonary disease and atopic dermatitis. In contrast, the PDE8 family that is upregulated in pro-inflammatory T cells is a largely unexplored therapeutic target. We have previously demonstrated a role for the PDE8A-Raf-1 kinase complex in the regulation of myelin oligodendrocyte glycoprotein peptide 35–55 (MOG_35–55) activated CD4⁺ effector T cell adhesion and locomotion by a mechanism that differs from PDE4 activity. In this study, we explored the in vivo treatment of experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis (MS) induced in mice immunized with MOG using the PDE8-selective inhibitor PF-04957325. For treatment in vivo, mice with EAE were either subcutaneously (s.c.) injected three times daily (10 mg/kg/dose), or were implanted subcutaneously with Alzet mini-osmotic pumps to deliver the PDE8 inhibitor (15.5 mg/kg/day). The mice were scored daily for clinical signs of paresis and paralysis which were characteristic of EAE. We observed the suppression of the clinical signs of EAE and a reduction of inflammatory lesion formation in the CNS by histopathological analysis through the determination of the numbers of mononuclear cells isolated from the spinal cord of mice with EAE. The PDE8 inhibitor treatment reduces the accumulation of both encephalitogenic Th1 and Th17 T cells in the CNS. Our study demonstrates the efficacy of targeting PDE8 as a treatment of autoimmune inflammation in vivo by reducing the inflammatory lesion load.

Clinical Implication of Phosphodiesterase-4-Inhibition

The pleiotropic function of 3',5'-cyclic adenosine monophosphate (cAMP)-dependent pathways in health and disease led to the development of pharmacological phosphodiesterase inhibitors (PDE-I) to attenuate cAMP degradation. While there are many isotypes of PDE, a predominant role of PDE4 is to regulate fundamental functions, including endothelial and epithelial barrier stability, modulation of inflammatory responses and cognitive and/or mood functions. This makes the use of PDE4-I an interesting tool for various therapeutic approaches. However, due to the presence of PDE4 in many tissues, there is a significant danger for serious side effects. Based on this, the aim of this review is to provide a comprehensive overview of the approaches and effects of PDE4-I for different therapeutic applications. In summary, despite many obstacles to use of PDE4-I for different therapeutic approaches, the current data warrant future research to utilize the therapeutic potential of phosphodiesterase 4 inhibition.

miR-5701 promoted apoptosis of clear cell renal cell carcinoma cells by targeting phosphodiesterase-1B

Increasing evidence has demonstrated that microRNAs play critical roles in malignant biological behaviors, including cancerogenesis, cancer progression and metastasis, through the regulation of target genes expression. As miR-5701 has recently been identified to play roles as tumor suppressor miRNA in the development of some kinds of cancers, in this study we sought to investigate the role of miR-5701 in clear cell renal cell carcinoma (ccRCC). Colony formation, cell apoptosis and proliferation assays were employed, and the results showed that miR-5701 inhibited proliferation and promoted apoptosis of ccRCC cells. Western blotting and dual-luciferase reporter assays were used to confirm that PDE1B is a new direct target of miR-5701. Furthermore, overexpression of PDE1B attenuated the effects of miR-5701, indicating that miR-5701 inhibited proliferation and promoted apoptosis of ccRCC cells via targeting PDE1B. Taken together, the data presented here indicate that t miR-5701 is a tumor suppressor in ccRCC and PDE1B is a new target of miR-5701.

Advances in Cyclic Nucleotide Phosphodiesterase-Targeted PET Imaging and Drug Discovery

Cyclic nucleotide phosphodiesterases (PDEs) control the intracellular concentrations of cAMP and cGMP in virtually all mammalian cells. Accordingly, the PDE family regulates a myriad of physiological functions, including cell proliferation, differentiation and apoptosis, gene expression, central nervous system function, and muscle contraction. Along this line, dysfunction of PDEs has been implicated in neurodegenerative disorders, coronary artery diseases, chronic obstructive pulmonary disease, and cancer development. To date, 11 PDE families have been identified; however, their distinct roles in the various pathologies are largely unexplored and subject to contemporary research efforts. Indeed, there is growing interest for the development of isoform-selective PDE inhibitors as potential therapeutic agents. Similarly, the evolving knowledge on the various PDE isoforms has channeled the identification of new PET probes, allowing isoform-selective imaging. This review highlights recent advances in PDE-targeted PET tracer development, thereby focusing on efforts to assess disease-related PDE pathophysiology and to support isoform-selective drug discovery.

The Role of PDE8 in T Cell Recruitment and Function in Inflammation

Inhibitors targeting cyclic nucleotide phosphodiesterases (PDEs) expressed in leukocytes have entered clinical practice to treat inflammatory disorders, with three PDE4 inhibitors currently in clinical use as therapeutics for psoriasis, psoriatic arthritis, atopic dermatitis and chronic obstructive pulmonary disease. In contrast, the PDE8 family that is upregulated in pro-inflammatory T cells is a largely unexplored therapeutic target. It was shown that PDE8A plays a major role in controlling T cell and breast cancer cell motility, including adhesion to endothelial cells under physiological shear stress and chemotaxis. This is a unique function of PDE8 not shared by PDE4, another cAMP specific PDE, employed, as noted, as an anti-inflammatory therapeutic. Additionally, a regulatory role was shown for the PDE8A-rapidly accelerated fibrosarcoma (Raf)-1 kinase signaling complex in myelin antigen reactive CD4⁺ effector T cell adhesion and locomotion by a mechanism differing from that of PDE4. The PDE8A-Raf-1 kinase signaling complex affects T cell motility, at least in part, via regulating the LFA-1 integrin mediated adhesion to ICAM-1. The findings that PDE8A and its isoforms are expressed at higher levels in naive and myelin oligodendrocyte glycoprotein (MOG)_35–55 activated effector T (Teff) cells compared to regulatory T (Treg) cells and that PDE8 inhibition specifically affects MOG_35–55 activated Teff cell adhesion, indicates that PDE8A could represent a new beneficial target expressed in pathogenic Teff cells in CNS inflammation. The implications of this work for targeting PDE8 in inflammation will be discussed in this review.

Role of Phosphodiesterase 7 (PDE7) in T Cell Activity. Effects of Selective PDE7 Inhibitors and Dual PDE4/7 Inhibitors on T Cell Functions

Phosphodiesterase 7 (PDE7), a cAMP-specific PDE family, insensitive to rolipram, is present in many immune cells, including T lymphocytes. Two genes of PDE7 have been identified: PDE7A and PDE7B with three or four splice variants, respectively. Both PDE7A and PDE7B are expressed in T cells, and the predominant splice variant in these cells is PDE7A1. PDE7 is one of several PDE families that terminates biological functions of cAMP—a major regulating intracellular factor. However, the precise role of PDE7 in T cell activation and function is still ambiguous. Some authors reported its crucial role in T cell activation, while according to other studies PDE7 activity was not pivotal to T cells. Several studies showed that inhibition of PDE7 by its selective or dual PDE4/7 inhibitors suppresses T cell activity, and consequently T-mediated immune response. Taken together, it seems quite likely that simultaneous inhibition of PDE4 and PDE7 by dual PDE4/7 inhibitors or a combination of selective PDE4 and PDE7 remains the most interesting therapeutic target for the treatment of some immune-related disorders, such as autoimmune diseases, or selected respiratory diseases. An interesting direction of future studies could also be using a combination of selective PDE7 and PDE3 inhibitors.

PDE4 subtypes in cancer

Cyclic nucleotide phosphodiesterases (PDE) break down cyclic nucleotides such as cAMP and cGMP, reducing the signaling of these important intracellular second messengers. Several unique families of phosphodiesterases exist, and certain families are clinically important modulators of vasodilation. In the current work, we have summarized the body of literature that describes an emerging role for the PDE4 subfamily of phosphodiesterases in malignancy. We have systematically investigated PDE4A, PDE4B, PDE4C, and PDE4D isoforms and found evidence associating them with several cancer types including hematologic malignancies and lung cancers, among others. In this review, we compare the evidence examining the functional role of each PDE4 subtype across malignancies, looking for common signaling themes, signaling pathways, and establishing the case for PDE4 subtypes as a potential therapeutic target for cancer treatment.

Therapeutic targeting of 3',5'-cyclic nucleotide phosphodiesterases: inhibition and beyond

Phosphodiesterases (PDEs), enzymes that degrade 3',5'-cyclic nucleotides, are being pursued as therapeutic targets for several diseases, including those affecting the nervous system, the cardiovascular system, fertility, immunity, cancer and metabolism. Clinical development programmes have focused exclusively on catalytic inhibition, which continues to be a strong focus of ongoing drug discovery efforts. However, emerging evidence supports novel strategies to therapeutically target PDE function, including enhancing catalytic activity, normalizing altered compartmentalization and modulating post-translational modifications, as well as the potential use of PDEs as disease biomarkers. Importantly, a more refined appreciation of the intramolecular mechanisms regulating PDE function and trafficking is emerging, making these pioneering drug discovery efforts tractable.

Identification of hub genes and molecular mechanisms in infant acute lymphoblastic leukemia with MLL gene rearrangement

Infant acute lymphoblastic leukemia (ALL) with the mixed lineage leukemia (MLL) gene rearrangement (MLL-R) is considered a distinct leukemia from childhood or non-MLL-R infant ALL. To detect key genes and elucidate the molecular mechanisms of MLL-R infant ALL, microarray expression data were downloaded from the Gene Expression Omnibus (GEO) database, and differentially expressed genes (DEGs) between MLL-R and non-MLL-R infant ALL were identified. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were carried out. Then, we constructed a protein-protein interaction (PPI) network and identified the hub genes. Finally, drug-gene interactions were mined. A total of 139 cases of MLL-R infant ALL including 77 (55.4%) fusions with AF4, 38 (27.3%) with ENL, 14 (10.1%) with AF9, and 10 (7.2%) other gene fusions were characterized. A total of 236 up-regulated and 84 down-regulated DEGs were identified. The up-regulated DEGs were mainly involved in homophilic cell adhesion, negative regulation of apoptotic process and cellular response to drug GO terms, while down-regulated DEGs were mainly enriched in extracellular matrix organization, protein kinase C signaling and neuron projection extension GO terms. The up-regulated DEGs were enriched in seven KEGG pathways, mainly involving transcriptional regulation and signaling pathways, and down-regulated DEGs were involved in three main KEGG pathways including Alzheimer’s disease, TGF-beta signaling pathway, and hematopoietic cell lineage. The PPI network included 297 nodes and 410 edges, with MYC, ALB, CD44, PTPRC and TNF identified as hub genes. Twenty-three drug-gene interactions including four up-regulated hub genes and 24 drugs were constructed by Drug Gene Interaction database (DGIdb). In conclusion, MYC, ALB, CD44, PTPRC and TNF may be potential bio-markers for the diagnosis and therapy of MLL-R infant ALL.

Anti‑inflammatory effect of ciclamilast in an allergic model involving the expression of PDE4B

The present study aimed to investigate the potent inhibitory effects and possible biochemical basis of the novel phosphodiesterase 4 (PDE4) inhibitor ciclamilast, which is a derivative of piclamilast (RP 73401), on PDE4 and allergic inflammation. Ciclamilast was orally administered to allergic rats, their lungs and bronchoalveolar lavage fluid (BALF) were harvested, and their levels of inflammation and goblet cell hyperplasia, particularly cAMP‑PDE activity, and expression and distribution of PDE4 subtypes were determined. The results suggested that oral administration of ciclamilast significantly reduced the total leukocyte number and eosinophil number in BALF and suppressed lung histology changes, including the infiltration of inflammatory cells into the perivascular and peribronchial spaces, structural changes and goblet cell hyperplasia. For eosinophil infiltration, ciclamilast exhibited improved selectivity compared with piclamilast. Furthermore, ciclamilast significantly inhibited the upregulated activity of cAMP‑PDE and showed improved selective inhibition of the protein expression of PDE4B than piclamilast in a dose‑dependent manner. The mRNA expression of PDE4D was significantly increased in allergic rats, but PDE4B was not. PDE4B was mainly distributed in the cytoplasm, whereas PDE4D was mainly distributed in the cell membrane. The improved anti‑inflammatory activity of ciclamilast compared with piclamilast may be due to its higher level of inhibition of the activity, mRNA and protein expression of PDE4, particularly its effect on PDE4B.

PDE4a predicts poor prognosis and promotes metastasis by inducing epithelial-mesenchymal transition in hepatocellular carcinoma

Phosphodiesterases (PDEs) was found to be involved in a variety of cancer pathologies by modulating the degradation of levels of cAMP/cGMP. However, the prognostic significance and biological effect of PDE4a in hepatocellular carcinoma (HCC) have not been understood completely. In the present study, PDE4a expression was detected in a cohort of HCC and matched adjacent liver tissues (n = 210) by immunohistochemistry staining and Western immunoblotting assay, And in vitro experiments were conducted to determine the effect of PDE4a on metastatic capacity of HCC cells. The data here displayed that the majority of HCC patients had higher PDE4a expression in tumor tissues compared to matched adjacent liver tissues and enhanced PDE4a expression in tumor tissues was associated positively with HBV infection, liver cirrhosis, higher serum AFP level, advanced TNM stage, vascular embolus, intrahepatic metastases and portal vein tumor thrombus (PVTT). Survival analyses suggested that higher PDE4a was indicated the poor prognosis of HCCs after liver resection. Ectopic expression of PDE4a in Huh7 cells leaded to significant repression of E-cadherin and up-regulated the expression of N-cadherin and Vimentin, and facilitated migration and invasion abilities. Silencing PDE4a in MHCC97h cells acquired the opposite results. Taken together, PDE4a triggered EMT in HCC cells and acted as a predictive factor candidate and a potential therapeutic target for HCC.

Multiple cAMP Phosphodiesterases Act Together to Prevent Premature Oocyte Meiosis and Ovulation

Luteinizing hormone (LH) acts on the granulosa cells that surround the oocyte in mammalian preovulatory follicles to cause meiotic resumption and ovulation. Both of these responses are mediated primarily by an increase in cyclic adenosine monophosphate (cAMP) in the granulosa cells, and the activity of cAMP phosphodiesterases (PDEs), including PDE4, contributes to preventing premature responses. However, two other cAMP-specific PDEs, PDE7 and PDE8, are also expressed at high levels in the granulosa cells, raising the question of whether these PDEs also contribute to preventing uncontrolled activation of meiotic resumption and ovulation. With the use of selective inhibitors, we show that inhibition of PDE7 or PDE8 alone has no effect on the cAMP content of follicles, and inhibition of PDE4 alone has only a small and variable effect. In contrast, a mixture of the three inhibitors elevates cAMP to a level comparable with that seen with LH. Correspondingly, inhibition of PDE7 or PDE8 alone has no effect on meiotic resumption or ovulation, and inhibition of PDE4 alone has only a partial and slow effect. However, the fraction of oocytes resuming meiosis and undergoing ovulation is increased when PDE4, PDE7, and PDE8 are simultaneously inhibited. PDE4, PDE7, and PDE8 also function together to suppress the premature synthesis of progesterone and progesterone receptors, which are required for ovulation. Our results indicate that three cAMP PDEs act in concert to suppress premature responses in preovulatory follicles.

Analyses of PDE-regulated phosphoproteomes reveal unique and specific cAMP-signaling modules in T cells

Specific functions for different cyclic nucleotide phosphodiesterases (PDEs) have not yet been identified in most cell types. Conventional approaches to study PDE function typically rely on measurements of global cAMP, general increases in cAMP-dependent protein kinase (PKA), or the activity of exchange protein activated by cAMP (EPAC). Although newer approaches using subcellularly targeted FRET reporter sensors have helped define more compartmentalized regulation of cAMP, PKA, and EPAC, they have limited ability to link this regulation to downstream effector molecules and biological functions. To address this problem, we have begun to use an unbiased mass spectrometry-based approach coupled with treatment using PDE isozyme-selective inhibitors to characterize the phosphoproteomes of the functional pools of cAMP/PKA/EPAC that are regulated by specific cAMP-PDEs (the PDE-regulated phosphoproteomes). In Jurkat cells we find multiple, distinct PDE-regulated phosphoproteomes that can be defined by their responses to different PDE inhibitors. We also find that little phosphorylation occurs unless at least two different PDEs are concurrently inhibited in these cells. Moreover, bioinformatics analyses of these phosphoproteomes provide insight into the unique functional roles, mechanisms of action, and synergistic relationships among the different PDEs that coordinate cAMP-signaling cascades in these cells. The data strongly suggest that the phosphorylation of many different substrates contributes to cAMP-dependent regulation of these cells. The findings further suggest that the approach of using selective, inhibitor-dependent phosphoproteome analysis can provide a generalized methodology for understanding the roles of different PDEs in the regulation of cyclic nucleotide signaling.

Differential Expression and Function of PDE8 and PDE4 in Effector T cells: Implications for PDE8 as a Drug Target in Inflammation

Abolishing the inhibitory signal of intracellular cAMP is a prerequisite for effector T (Teff) cell function. The regulation of cAMP within leukocytes critically depends on its degradation by cyclic nucleotide phosphodiesterases (PDEs). We have previously shown that PDE8A, a PDE isoform with 40–100-fold greater affinity for cAMP than PDE4, is selectively expressed in Teff vs. regulatory T (Treg) cells and controls CD4⁺ Teff cell adhesion and chemotaxis. Here, we determined PDE8A expression and function in CD4⁺ Teff cell populations in vivo. Using magnetic bead separation to purify leukocyte populations from the lung draining hilar lymph node (HLN) in a mouse model of ovalbumin-induced allergic airway disease (AAD), we found by Western immunoblot and quantitative (q)RT-PCR that PDE8A protein and gene expression are enhanced in the CD4⁺ T cell fraction over the course of the acute inflammatory disease and recede at the late tolerant non-inflammatory stage. To evaluate PDE8A as a potential drug target, we compared the selective and combined effects of the recently characterized highly potent PDE8-selective inhibitor PF-04957325 with the PDE4-selective inhibitor piclamilast (PICL). As previously shown, PF-04957325 suppresses T cell adhesion to endothelial cells. In contrast, we found that PICL alone increased firm T cell adhesion to endothelial cells by ~20% and significantly abrogated the inhibitory effect of PF-04957325 on T cell adhesion by over 50% when cells were co-exposed to PICL and PF-04957325. Despite its robust effect on T cell adhesion, PF-04957325 was over two orders of magnitude less efficient than PICL in suppressing polyclonal Teff cell proliferation, and showed no effect on cytokine gene expression in these cells. More importantly, PDE8 inhibition did not suppress proliferation and cytokine production of myelin-antigen reactive proinflammatory Teff cells in vivo and in vitro. Thus, targeting PDE8 through PF-04957325 selectively regulates Teff cell interactions with endothelial cells without marked immunosuppression of proliferation, while PDE4 inhibition has partially opposing effects. Collectively, our data identify PF-04957325 as a novel function-specific tool for the suppression of Teff cell adhesion and indicate that PDE4 and PDE8 play unique and non-redundant roles in the control of Teff cell functions.

Traumatic Brain Injury Upregulates Phosphodiesterase Expression in the Hippocampus

Traumatic brain injury (TBI) results in significant impairments in hippocampal synaptic plasticity. A molecule critically involved in hippocampal synaptic plasticity, 3′,5′-cyclic adenosine monophosphate, is downregulated in the hippocampus after TBI, but the mechanism that underlies this decrease is unknown. To address this question, we determined whether phosphodiesterase (PDE) expression in the hippocampus is altered by TBI. Young adult male Sprague Dawley rats received sham surgery or moderate parasagittal fluid-percussion brain injury. Animals were analyzed by western blotting for changes in PDE expression levels in the hippocampus. We found that PDE1A levels were significantly increased at 30 min, 1 h and 6 h after TBI. PDE4B2 and 4D2 were also significantly increased at 1, 6, and 24 h after TBI. Additionally, phosphorylation of PDE4A was significantly increased at 6 and 24 h after TBI. No significant changes were observed in levels of PDE1B, 1C, 3A, 8A, or 8B between 30 min to 7 days after TBI. To determine the spatial profile of these increases, we used immunohistochemistry and flow cytometry at 24 h after TBI. PDE1A and phospho-PDE4A localized to neuronal cell bodies. PDE4B2 was expressed in neuronal dendrites, microglia and infiltrating CD11b⁺ immune cells. PDE4D was predominantly found in microglia and infiltrating CD11b⁺ immune cells. To determine if inhibition of PDE4 would improve hippocampal synaptic plasticity deficits after TBI, we treated hippocampal slices with rolipram, a pan-PDE4 inhibitor. Rolipram partially rescued the depression in basal synaptic transmission and converted a decaying form of long-term potentiation (LTP) into long-lasting LTP. Overall, these results identify several possible PDE targets for reducing hippocampal synaptic plasticity deficits and improving cognitive function acutely after TBI.

Exhaustive 3D-QSAR analyses as a computational tool to explore the potency and selectivity profiles of thieno[3,2-d]pyrimidin-4(3H)-one derivatives as PDE7 inhibitors

In the development of selective ligands binding to specific PDE isoforms, the ligand-based approach proved to be a useful tool to better investigate the potency and selectivity profiles of PDE7 inhibitors.

Effect of cAMP signaling on expression of glucocorticoid receptor, Bim and Bad in glucocorticoid-sensitive and resistant leukemic and multiple myeloma cells

Stimulation of cAMP signaling induces apoptosis in glucocorticoid-sensitive and resistant CEM leukemic and MM.1 multiple myeloma cell lines, and this effect is enhanced by dexamethasone in both glucocorticoid-sensitive cell types and in glucocorticoid-resistant CEM cells. Expression of the mRNA for the glucocorticoid receptor alpha (GR) promoters 1A3, 1B and 1C, expression of mRNA and protein for GR, and the BH3-only proapoptotic proteins, Bim and Bad, and the phosphorylation state of Bad were examined following stimulation of the cAMP and glucocorticoid signaling pathways. Expression levels of GR promoters were increased by cAMP and glucocorticoid signaling, but GR protein expression was little changed in CEM and decreased in MM.1 cells. Stimulation of these two signaling pathways induced Bim in CEM cells, induced Bad in MM.1 cells, and activated Bad, as indicated by its dephosphorylation on ser112, in both cell types. This study shows that leukemic and multiple myeloma cells, including those resistant to glucocorticoids, can be induced to undergo apoptosis by stimulating the cAMP signaling pathway, with enhancement by glucocorticoids, and the mechanism by which this occurs may be related to changes in Bim and Bad expression, and in all cases, to activation of Bad.

Phosphodiesterase inhibitor, pentoxifylline enhances anticancer activity of histone deacetylase inhibitor, MS-275 in human breast cancer in vitro and in vivo

MS-275, a histone deacetylase inhibitor (HDACi), is undergoing clinical trials for treatment of various cancers. Pentoxifylline, a nonselective phosphodiesterase (PDE) inhibitor, has been shown to increase the effectiveness of antitumor chemotherapy. In the present study, the potential anti-cancer activity of MS-275 in combination with pentoxifylline in panel of cell lines and human breast cancer xenograft model were examined. A Panel of cancer cell lines were treated with MS-275 and pentoxifylline to determine their impact on cellular proliferation, cell cycle regulation, apoptosis, anti-angiogenesis. The in vivo activities of MS-275 and pentoxifylline were assessed in a Matrigel plug angiogenesis model and human breast cancer (MDA-MB-231) xenograft model. Combination of MS-275 with pentoxifylline showed enhanced anti-proliferative activity in a panel of cancer cell lines (HCT 116, MCF-7, PC3 and MDA-MB-231). Apoptotic studies performed using, Hoechst staining and cell cycle analysis reveal that this combination at the lower concentrations induces apoptosis downstream of the HDAC inhibition and PDE regulation. Further, combination showed enhanced antiangiogenic activity in Matrigel tube formation assay using HUVECs and in Matrigel plug assay in vivo. A significant inhibition (P<0.001) of tumor growth was observed in mice bearing MDA-MB-231 breast cancer xenograft treated with the combination of MS-275 (5mg/kg p.o.) and pentoxifylline (60 mg/kg i.p.) than treatments alone, without much signs of toxicity. Taken together, our study demonstrated enhanced anticancer activity of MS-275 and pentoxifylline combination both in vitro and in vivo with reduced toxicity. However, further studies are required to understand the mechanism for this combination effect.

Inhibition of breast cancer cell migration by activation of cAMP signaling

Almost all deaths from breast cancer arise from metastasis of the transformed cells to other sites in the body. Hence, uncovering a means of inhibiting breast cancer cell migration would provide a significant advance in the treatment of this disease. Stimulation of the cAMP signaling pathway has been shown to inhibit migration and motility of a number of cell types. A very effective way of selectively stimulating cAMP signaling is through inhibition of cyclic nucleotide phosphodiesterases (PDEs). Therefore, we examined full expression profiles of all known PDE genes at the mRNA and protein levels in four human breast cancer cell lines and eight patients' breast cancer tissues. By these analyses, expression of almost all PDE genes was seen in both cell lines and tissues. In the cell lines, appreciable expression was seen for PDEs 1C, 2A, 3B, 4A, 4B, 4D, 5A, 6B, 6C, 7A, 7B, 8A, 9A, 10A, and 11A. In patients' tissues, appreciable expression was seen for PDEs 1A, 3B, 4A, 4B, 4C, 4D, 5A, 6B, 6C, 7A, 7B, 8A, 8B, and 9A. PDE8A mRNA in particular is prominently expressed in all cell lines and patients' tissue samples examined. We show here that stimulation of cAMP signaling with cAMP analogs, forskolin, and PDE inhibitors, including selective inhibitors of PDE3, PDE4, PDE7, and PDE8, inhibit aggressive triple negative MDA-MB-231 breast cancer cell migration. Under the same conditions, these agents had little effect on breast cancer cell proliferation. This study demonstrates that PDE inhibitors inhibit breast cancer cell migration, and thus may be valuable therapeutic targets for inhibition of breast cancer metastasis. Since PDE8A is expressed in all breast cancer samples, and since dipyridamole, which inhibits PDE8, and PF-04957325, a selective PDE8 inhibitor, both inhibit migration, it suggests that PDE8A may be a valuable novel target for treatment of this disease.

Regulatory T-cells and cAMP suppress effector T-cells independently of PKA-CREM/ICER: a potential role for Epac

cAMP signalling is both a major pathway as well as a key therapeutic target for inducing immune tolerance and is involved in Treg cell (regulatory T-cell) function. To achieve potent immunoregulation, cAMP can act through several downstream effectors. One proposed mechanism is that cAMP-mediated suppression, including immunosuppression by Treg cells, results from activation of PKA (protein kinase A) leading to the induction of the transcription factor ICER (inducible cAMP early repressor). In the present study, we examined CD4(+)CD25(-) Teff cell (effector T-cell) and CD4(+)CD25(+) Treg cell immune responses in Crem (cAMP-response-element modulator) gene-deficient mice which lack ICER (Crem(-/-)/ICER-deficient mice). ICER deficiency did not significantly alter the frequency or number of Treg cells and Teff cells. Treg cells or a pharmacological increase in cAMP suppressed Teff cells from Crem(+/+) and Crem(-/-)/ICER-deficient mice to an equivalent degree, demonstrating that ICER is dispensable in these functions. Additionally, activating the cAMP effector Epac (exchange protein directly activated by cAMP) suppressed Teff cells. Treg cells expressed low levels of all cyclic nucleotide Pde (phosphodiesterase) genes tested, but high levels of Epac. These data identify ICER as a redundant mediator of Treg cells and cAMP action on Teff cells and suggest that Epac may function as an alternative effector to promote cAMP-dependent Teff cell suppression.

Carboxyamidotriazole: a novel inhibitor of both cAMP-phosphodiesterases and cGMP-phosphodiesterases

Carboxyamidotriazole (CAI) is a non-cytotoxic anti-tumor drug, which also shows considerable anti-inflammatory effects in a variety of animal models of inflammation. The exact target and mechanism of CAI were not clearly understood yet. In the present study, we demonstrate that CAI is a non-selective phosphodiesterase (PDE) inhibitor, which provides comprehensive inhibitions of both adenosine 3',5'-cyclic monophosphate specific PDE (cAMP-PDE) and guanosine 3',5'-cyclic monophosphate specific PDE (cGMP-PDE) isolated from rat brain, mouse pulmonary tissue, primary mouse peritoneal macrophages, RAW264.7 cells, Lewis lung carcinoma (LLC) cells and lymphocytic leukemia cells (L1210) with moderate potencies (IC50≈0.5-30μM). The comprehensive elimination of PDE activities in living LLC cells by CAI results in accumulation of intracellular cAMP and cGMP, which can be visualized by fluorescence resonance energy transfer (FRET)-based cyclic nucleotide sensors. The stimulation by 30μM CAI yielded ~1.5-fold greater cGMP responses compared with 10μM sildenafil citrate, whereas the influence of 30μM CAI on cAMP levels was similar as that of 100μM 3-isobutyl-1-methylxanthine (IBMX). The non-selective inhibitory effect of CAI on cAMP-PDE and cGMP-PDE increases the likelihood for CAI to affect the balance between the levels of intracellular cyclic nucleotides cAMP and cGMP, then a variety of cellular signaling pathways that regulate cell functions and even related disease processes. When examining the widely proven anti-tumor and anti-inflammatory activities of CAI, it is important to affirm its comprehensive inhibitory effect on PDEs, which makes it superior to some selective PDE inhibitors in a way.

Phosphodiesterase 4D inhibitors limit prostate cancer growth potential

Phosphodiesterase 4D (PDE4D) has recently been implicated as a proliferation-promoting factor in prostate cancer and is overexpressed in human prostate carcinoma. However, the effects of PDE4D inhibition using pharmacologic inhibitors have not been examined in prostate cancer. These studies examined the effects of selective PDE4D inhibitors, NVP-ABE171 and cilomilast, as anti-prostate cancer therapies in both in vitro and in vivo models. The effects of PDE4D inhibitors on pathways that are critical in prostate cancer and/or downstream of cyclic AMP (cAMP) were examined. Both NVP-ABE171 and cilomilast decreased cell growth. In vitro, PDE4D inhibitors lead to decreased signaling of the sonic hedgehog (SHH), androgen receptor (AR), and MAPK pathways, but growth inhibition was best correlated to the SHH pathway. PDE4D inhibition also reduced proliferation of epithelial cells induced by paracrine signaling from cocultured stromal cells that had activated hedgehog signaling. In addition, PDE4D inhibitors decreased the weight of the prostate in wild-type mice. Prostate cancer xenografts grown in nude mice that were treated with cilomilast or NVP-ABE171 had decreased wet weight and increased apoptosis compared with vehicle-treated controls. These studies suggest the pharmacologic inhibition of PDE4D using small-molecule inhibitors is an effective option for prostate cancer therapy.

IMPLICATIONS

PDE4D inhibitors decrease the growth of prostate cancer cells in vivo and in vitro, and PDE4D inhibition has therapeutic potential in prostate cancer.

Modulation of the cAMP response by Gαi and Gβγ: a computational study of G protein signaling in immune cells

Cyclic AMP is important for the resolution of inflammation, as it promotes anti-inflammatory signaling in several immune cell lines. In this paper, we present an immune cell specific model of the cAMP signaling cascade, paying close attention to the specific isoforms of adenylyl cyclase (AC) and phosphodiesterase that control cAMP production and degradation, respectively, in these cells. The model describes the role that G protein subunits, including Gαs, Gαi, and Gβγ, have in regulating cAMP production. Previously, Gαi activation has been shown to increase the level of cAMP in certain immune cell types. This increase in cAMP is thought to be mediated by βγ subunits which are released upon Gα activation and can directly stimulate specific isoforms of AC. We conduct numerical experiments in order to explore the mechanisms through which Gαi activation can increase cAMP production. An important conclusion of our analysis is that the relative abundance of different G protein subunits is an essential determinant of the cAMP profile in immune cells. In particular, our model predicts that limited availability of βγ subunits may both (i) enable immune cells to link inflammatory Gαi signaling to anti-inflammatory cAMP production thereby creating a balanced immune response to stimulation with low concentrations of PGE2, and (ii) prohibit robust anti-inflammatory cAMP signaling in response to stimulation with high concentrations of PGE2.

cAMP protects acute promyelocytic leukemia cells from arsenic trioxide-induced caspase-3 activation and apoptosis

More recently, arsenic trioxide (ATO), was integrated into acute promyelocytic leukemia (APL) treatment, showing high efficacy and tolerability in patients with both ATRA-sensitive and ATRA-resistant APL. ATO could induce apoptosis at relatively high concentrations (0.5 to 2.0 micromol/L) and partial differentiation at low concentrations (0.1 to 0.5 micromol/L) in leukemic promyelocytes. It is known that cAMP agonists enhance low-dose ATO-induced APL cells differentiation. Less well appreciated was the possible interaction between relatively high-doses of ATO and enhanced levels of cAMP in APL cells. Here, we show that elevation of cAMP levels by forskolin inhibited ATO-mediated apoptosis in APL-derived NB4 cells, and this inhibition could be averted by cell permeable cAMP-dependent protein kinase inhibitor (14-22) amide. Inactivating phosphorylation of the proapoptotic protein Bad at Ser118 and phosphorylation of the CREB proto-oncogene at Ser133 were observed upon elevation of cAMP levels in NB4 cells. Phosphorylation of these PKA target proteins is known to promote cell survival in AML cells. The ability of cAMP to endow the APL cells with survival advantage is of particular importance when cAMP agonists may be considered as adjuncts to APL therapy.

Microwave-assisted synthesis of potent PDE7 inhibitors containing a thienopyrimidin-4-amine scaffold

Thienopyrimidin-4-amines have been synthesized, evaluated and modelled as phosphodiesterase inhibitors.

Targeting cAMP in chronic lymphocytic leukemia: a pathway-dependent approach for the treatment of leukemia and lymphoma

INTRODUCTION

Cyclic AMP (cAMP) promotes growth arrest and/or apoptosis of various types of lymphoma, in particular chronic lymphocytic leukemia (CLL). These responses have spurred the interest in developing agents that increase cAMP to treat such malignancies and to identify mechanisms of the responses.

AREAS COVERED

The murine T-lymphoma cell line S49, has provided an important, pioneering model to define mechanisms of cAMP-mediated lymphoid cell death. Studies with S49 cells demonstrated that cAMP, acting via protein kinase A (PKA), is pro-apoptotic through a mitochondria-dependent pathway and identified cAMP/PKA-regulated targets involved in apoptosis. Akin to such findings, cAMP promotes apoptosis via PKA of cells from patients with CLL. Analysis of mediators of cAMP accumulation and cAMP-promoted apoptosis in CLL cells has revealed approaches to increase cAMP and engage its pro-apoptotic action.

EXPERT OPINION

This 'pathway approach' targeted to cAMP has identified GPCR agonists/antagonists, AC activators (e.g., AC7), PDE inhibitors (e.g., PDE7B) and/or activators or inhibitors of downstream mediators (PKA and Epac, respectively), which might be utilized therapeutically in CLL. Therapy directed at such targets may prove to be clinically useful and may also provide a proof-of-principle of the utility of targeting cAMP signaling in other types of cancer.

Targeting phosphodiesterase 3B enhances cisplatin sensitivity in human cancer cells

We previously reported that human squamous cell carcinoma (SCC) cell lines refractory to cis-diaminedichloro-platinum II (cisplatin [CDDP]) had significant upregulation of the phosphodiesterase 3B gene (PDE3B), suggesting that inhibiting PDE3B suppresses CDDP resistance. shRNA-mediated PDE3B depletion in CDDP-resistant cells derived from SCC cells and Hela cells and induced CDDP sensitivity and inhibited tumor growth with elevated cyclic GMP induction resulting in upregulation of the multidrug-resistant molecule, but this did not occur in the 5-fluorouracil-resistant hepatocellular carcinoma cell lines. Furthermore, the antitumor growth effect of the combination of a PDE3B inhibitor (cilostazol) and CDDP in vivo was also greater than with either cilostazol or CDDP alone, with a significant increase in the number of apoptotic and cell growth-suppressive cancer cells in CDDP-resistance cell lines. Our results provided novel information on which to base further mechanistic studies of CDDP sensitization by inhibiting PDE3B in human cancer cells and for developing strategies to improve outcomes with concurrent chemotherapy.

Identification of biologically active PDE11-selective inhibitors using a yeast-based high-throughput screen

The biological roles of cyclic nucleotide phosphodiesterase 11 (PDE11) enzymes are poorly understood, in part due to the lack of selective inhibitors. To address the need for such compounds, we completed an ~200,000 compound high-throughput screen (HTS) for PDE11 inhibitors using a yeast-based growth assay, and identified 4 potent and selective PDE11 inhibitors. One compound, along with two structural analogs, elevates cAMP and cortisol levels in human adrenocortical cells, consistent with gene association studies that link PDE11 activity to adrenal function. As such, these compounds can immediately serve as chemical tools to study PDE11 function in cell culture, and as leads to develop therapeutics for the treatment of adrenal insufficiencies. Our results further validate this yeast-based HTS platform for the discovery of potent, selective, and biologically active PDE inhibitors.

Cyclic AMP is both a pro-apoptotic and anti-apoptotic second messenger

The second messenger cyclic AMP (cAMP) can either stimulate or inhibit programmed cell death (apoptosis). Here, we review examples of cell types that show pro-apoptotic or anti-apoptotic responses to increases in cAMP. We also show that cells can have both such responses, although predominantly having one or the other. Protein kinase A (PKA)-promoted changes in phosphorylation and gene expression can mediate pro-apoptotic responses, such as in murine S49 lymphoma cells, based on evidence that mutants lacking PKA fail to undergo cAMP-promoted, mitochondria-dependent apoptosis. Mechanisms for the anti-apoptotic response to cAMP likely involve Epac (Exchange protein activated by cAMP), a cAMP-regulated effector that is a guanine nucleotide exchange factor (GEF) for the low molecular weight G-protein, Rap1. Therapeutic approaches that activate PKA-mediated pro-apoptosis or block Epac-mediated anti-apoptotisis may provide a means to enhance cell killing, such as in certain cancers. In contrast, efforts to block PKA or stimulate Epac have the potential to be useful in diseases settings (such as heart failure) associated with cAMP-promoted apoptosis.

A genome-wide scan for common variants affecting the rate of age-related cognitive decline

Age-related cognitive decline is likely promoted by accumulated brain injury due to chronic conditions of aging, including neurodegenerative and vascular disease. Because common neuronal mechanisms may mediate the adaptation to diverse cerebral insults, we hypothesized that susceptibility for age-related cognitive decline may be due in part to a shared genetic network. We have therefore performed a genome-wide association study using a quantitative measure of global cognitive decline slope, based on repeated measures of 17 cognitive tests in 749 subjects from the Religious Orders Study. Top results were evaluated in 3 independent replication cohorts, consisting of 2279 additional subjects with repeated cognitive testing. As expected, we find that the Alzheimer's disease (AD) susceptibility locus, APOE, is strongly associated with rate of cognitive decline (P(DISC) = 5.6 × 10(-9); P(JOINT)= 3.7 × 10(-27)). We additionally discover a variant, rs10808746, which shows consistent effects in the replication cohorts and modestly improved evidence of association in the joint analysis (P(DISC) = 6.7 × 10(-5); P(REP) = 9.4 × 10(-3); P(JOINT) = 2.3 × 10(-5)). This variant influences the expression of 2 adjacent genes, PDE7A and MTFR1, which are potential regulators of inflammation and oxidative injury, respectively. Using aggregate measures of genetic risk, we find that known susceptibility loci for cardiovascular disease, type 2 diabetes, and inflammatory diseases are not significantly associated with cognitive decline in our cohort. Our results suggest that intermediate phenotypes, when coupled with larger sample sizes, may be a useful tool to dissect susceptibility loci for age-related cognitive decline and uncover shared molecular pathways with a role in neuronal injury.

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

The superfamily of cyclic nucleotide (cN) phosphodiesterases (PDEs) is comprised of 11 families of enzymes. PDEs break down cAMP and/or cGMP and are major determinants of cellular cN levels and, consequently, the actions of cN-signaling pathways. PDEs exhibit a range of catalytic efficiencies for breakdown of cAMP and/or cGMP and are regulated by myriad processes including phosphorylation, cN binding to allosteric GAF domains, changes in expression levels, interaction with regulatory or anchoring proteins, and reversible translocation among subcellular compartments. Selective PDE inhibitors are currently in clinical use for treatment of erectile dysfunction, pulmonary hypertension, intermittent claudication, and chronic pulmonary obstructive disease; many new inhibitors are being developed for treatment of these and other maladies. Recently reported x-ray crystallographic structures have defined features that provide for specificity for cAMP or cGMP in PDE catalytic sites or their GAF domains, as well as mechanisms involved in catalysis, oligomerization, autoinhibition, and interactions with inhibitors. In addition, major advances have been made in understanding the physiological impact and the biochemical basis for selective localization and/or recruitment of specific PDE isoenzymes to particular subcellular compartments. The many recent advances in understanding PDE structures, functions, and physiological actions are discussed in this review.

Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies

Phosphodiesterase (PDE) 4 inhibitors have been in development as a novel anti-inflammatory therapy for more than 20 years, with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, only one selective PDE4 inhibitor, roflumilast (Daxas (®)), has been approved for use in humans and available in Canada and the European Union in 2011 for the treatment of a specific population of patients with severe COPD. In many other cases, the development of PDE4 inhibitors of various structural classes has been discontinued due to lack of efficacy and/or dose-limiting adverse events. Indeed, for many of these compounds, it is likely that the maximum tolerated dose is either subtherapeutic or at the very bottom of the efficacy dose-response curve. Thus, a significant ongoing challenge that faces the pharmaceutical industry is to synthesize compounds with therapeutic ratios that are superior to roflumilast. Several strategies are being considered, but clinically effective compounds with an optimal pharmacophore have not, thus far, been reported. In this chapter, alternative means of harnessing the clinical efficacy of PDE4 inhibitors are described. These concepts are based on the assumption that additive or synergistic anti-inflammatory effects can be produced with inhibitors that target either two or more PDE families or with a PDE4 inhibitor in combination with other anti-inflammatory drugs such as a glucocorticoid.

Glucocorticoid-induced apoptosis of healthy and malignant lymphocytes

Glucocorticoids exert a wide range of physiological effects, including the induction of apoptosis in lymphocytes. The progression of glucocorticoid-induced apoptosis is a multi-component process requiring contributions from both genomic and cytoplasmic signaling events. There is significant evidence indicating that the transactivation activity of the glucocorticoid receptor is required for the initiation of glucocorticoid-induced apoptosis. However, the rapid cytoplasmic effects of glucocorticoids may also contribute to the glucocorticoid-induced apoptosis-signaling pathway. Endogenous glucocorticoids shape the T-cell repertoire through both the induction of apoptosis by neglect during thymocyte maturation and the antagonism of T-cell receptor (TCR)-induced apoptosis during positive selection. Owing to their ability to induce apoptosis in lymphocytes, synthetic glucocorticoids are widely used in the treatment of haematological malignancies. Glucocorticoid chemotherapy is limited, however, by the emergence of glucocorticoid resistance. The development of novel therapies designed to overcome glucocorticoid resistance will dramatically improve the efficacy of glucocorticoid therapy in the treatment of haematological malignancies.