A cell-based PDE4 assay in 1536-well plate format for high-throughput screening

Development of Phosphodiesterase-Protein-Kinase Complexes as Novel Targets for Discovery of Inhibitors with Enhanced Specificity

Phosphodiesterases (PDEs) hydrolyze cyclic nucleotides to modulate multiple signaling events in cells. PDEs are recognized to actively associate with cyclic nucleotide receptors (protein kinases, PKs) in larger macromolecular assemblies referred to as signalosomes. Complexation of PDEs with PKs generates an expanded active site that enhances PDE activity. This facilitates signalosome-associated PDEs to preferentially catalyze active hydrolysis of cyclic nucleotides bound to PKs and aid in signal termination. PDEs are important drug targets, and current strategies for inhibitor discovery are based entirely on targeting conserved PDE catalytic domains. This often results in inhibitors with cross-reactivity amongst closely related PDEs and attendant unwanted side effects. Here, our approach targeted PDE–PK complexes as they would occur in signalosomes, thereby offering greater specificity. Our developed fluorescence polarization assay was adapted to identify inhibitors that block cyclic nucleotide pockets in PDE–PK complexes in one mode and disrupt protein-protein interactions between PDEs and PKs in a second mode. We tested this approach with three different systems—cAMP-specific PDE8–PKAR, cGMP-specific PDE5–PKG, and dual-specificity RegA–R_D complexes—and ranked inhibitors according to their inhibition potency. Targeting PDE–PK complexes offers biochemical tools for describing the exquisite specificity of cyclic nucleotide signaling networks in cells.

Identification of Antifungal Compounds against Multidrug-Resistant Candida auris Utilizing a High-Throughput Drug-Repurposing Screen

Candida auris is an emerging fatal fungal infection that has resulted in several outbreaks in hospitals and care facilities. Current treatment options are limited by the development of drug resistance. Identification of new pharmaceuticals to combat these drug-resistant infections will thus be required to overcome this unmet medical need. We have established a bioluminescent ATP-based assay to identify new compounds and potential drug combinations showing effective growth inhibition against multiple strains of multidrug-resistant Candida auris The assay is robust and suitable for assessing large compound collections by high-throughput screening (HTS). Utilizing this assay, we conducted a screen of 4,314 approved drugs and pharmacologically active compounds that yielded 25 compounds, including 6 novel anti-Candida auris compounds and 13 sets of potential two-drug combinations. Among the drug combinations, the serine palmitoyltransferase inhibitor myriocin demonstrated a combinational effect with flucytosine against all tested isolates during screening. This combinational effect was confirmed in 13 clinical isolates of Candida auris.

Ferulic acid prevents LPS-induced up-regulation of PDE4B and stimulates the cAMP/CREB signaling pathway in PC12 cells

AIM

Phosphodiesterase 4 (PDE4) isozymes are involved in different functions, depending on their patterns of distribution in the brain. The PDE4 subtypes are distributed in different inflammatory cells, and appear to be important regulators of inflammatory processes. In this study we examined the effects of ferulic acid (FA), a plant component with strong anti-oxidant and anti-inflammatory activities, on lipopolysaccharide (LPS)-induced up-regulation of phosphodiesterase 4B (PDE4B) in PC12 cells, which in turn regulated cellular cAMP levels and the cAMP/cAMP response element binding protein (CREB) pathway in the cells.

METHODS

PC12 cells were treated with LPS (1 μg/mL) for 8 h, and the changes of F-actin were detected using laser scanning confocal microscopy. The levels of pro-inflammatory cytokines were measured suing ELISA kits, and PDE4B-specific enzymatic activity was assessed with a PDE4B assay kit. The mRNA levels of PDE4B were analyzed with Q-PCR, and the protein levels of CREB and phosphorylated CREB (pCREB) were determined using immunoblotting. Furthermore, molecular docking was used to identify the interaction between PDE4B2 and FA.

RESULTS

Treatment of PC12 cells with LPS induced thick bundles of actin filaments appearing in the F-actin cytoskeleton, which were ameliorated by pretreatment with FA (10-40 μmol/L) or with a PDE4B inhibitor rolipram (30 μmol/L). Pretreatment with FA dose-dependently inhibited the LPS-induced production of TNF-α and IL-1β in PC12 cells. Furthermore, pretreatment with FA dose-dependently attenuated the LPS-induced up-regulation of PDE4 activity in PC12 cells. Moreover, pretreatment with FA decreased LPS-induced up-regulation of the PDE4B mRNA, and reversed LPS-induced down-regulation of CREB and pCREB in PC12 cells. The molecular docking results revealed electrostatic and hydrophobic interactions between FA and PDE4B2.

CONCLUSION

The beneficial effects of FA in PC12 cells might be conferred through inhibition of LPS-induced up-regulation of PDE4B and stimulation of cAMP/CREB signaling pathway. Therefore, FA may be a potential therapeutic intervention for the treatment of neuroinflammatory diseases such as AD.

Characterization of the cellular activity of PDE 4 inhibitors using two novel PDE 4 reporter cell lines

We report here the generation and pharmacological characterization of two novel PDE 4B1 and PDE 4D3 reporter cell lines. Intracellular cAMP levels are monitored in these cells by a cAMP-sensitive biosensor. We used the recombinant PDE 4B1 and PDE 4D3 reporter cell lines to characterize the cellular effects of various competitive and allosteric PDE 4 inhibitors. In addition, we compared the cellular activity of these PDE 4 inhibitors with the in vitro inhibition of full-length PDE 4D3 and a truncated enzyme comprising the PDE 4D3 catalytic domain. Two different groups of PDE 4 inhibitors could be identified. The first group, including competitive inhibitors like roflumilast, cilomilast and piclamilast, shows similar in vitro activity on full-length and truncated PDE 4D3 and comparably low cellular activity. The second group, including the allosteric inhibitors PMNPQ, D159153, and D159404, shows much better inhibition of full-length versus truncated PDE 4D3. In addition, these compounds show high cellular activity. Our data obtained with the prototype PDE 4 inhibitor rolipram show that rolipram has properties intermediate between the two groups. The results imply that these novel PDE 4 reporter cell lines are well-suited for the characterization of the cellular activity of PDE 4 inhibitors and may also support a better understanding of the complex PDE 4 pharmacology.

A homogenous luminescence assay reveals novel inhibitors for giardia lamblia carbamate kinase

The human pathogen Giardia lamblia is an anaerobic protozoan parasite that causes giardiasis, one of the most common diarrheal diseases worldwide. Although several drugs are available for the treatment of giardisis, resistance to these drugs has been reported and is likely to increase. The Giardia carbamate kinase (glCK) plays an essential role in Giardia metabolism and has no homologs in humans, making it an attractive candidate for anti-Giardia drug development. We have developed a luminescent enzyme coupled assay to measure the activity of glCK by quantitating the amount of ATP produced by the enzyme. This assay is homogeneous and has been miniaturized into a 1536-well plate format. A pilot screen against 4,096 known compounds using this assay yielded a signal-to-basal ratio of 11.5 fold and Z’ factor of 0.8 with a hit rate of 0.9 % of inhibitors of glCK. Therefore, this Giardia lamblia carbamate kinase assay is useful for high throughput screening of large compound collection for identification of the inhibitors for drug development.

Identification of small-molecule agonists of human relaxin family receptor 1 (RXFP1) by using a homogenous cell-based cAMP assay

The relaxin hormone is involved in a variety of biological functions, including female reproduction and parturition, as well as regulation of cardiovascular, renal, pulmonary, and hepatic functions. It regulates extracellular matrix remodeling, cell invasiveness, proliferation, differentiation, and overall tissue homeostasis. The G protein-coupled receptor (GPCR) relaxin family receptor 1 (RXFP1) is a cognate relaxin receptor that mainly signals through cyclic AMP second messenger. Although agonists of the receptor could have a wide range of pharmacologic utility, until now there have been no reported small-molecule agonists for relaxin receptors. Here, we report the development of a quantitative high-throughput platform for an RXFP1 agonist screen based on homogenous cell-based HTRF cyclic AMP (cAMP) assay technology. Two small molecules of similar structure were independently identified from a screen of more than 365 677 compounds. Neither compound showed activity in a counterscreen with HEK293T cells transfected with an unrelated GPCR vasopressin 1b receptor. These small-molecule agonists also demonstrated selectivity against the RXFP2 receptor, providing a basis for future medicinal chemistry optimization of selective relaxin receptor agonists.

Unique reporter-based sensor platforms to monitor signalling in cells

Introduction

In recent years much progress has been made in the development of tools for systems biology to study the levels of mRNA and protein, and their interactions within cells. However, few multiplexed methodologies are available to study cell signalling directly at the transcription factor level.

Methods

Here we describe a sensitive, plasmid-based RNA reporter methodology to study transcription factor activation in mammalian cells, and apply this technology to profiling 60 transcription factors in parallel. The methodology uses two robust and easily accessible detection platforms; quantitative real-time PCR for quantitative analysis and DNA microarrays for parallel, higher throughput analysis.

Findings

We test the specificity of the detection platforms with ten inducers and independently validate the transcription factor activation.

Conclusions

We report a methodology for the multiplexed study of transcription factor activation in mammalian cells that is direct and not theoretically limited by the number of available reporters.

A Homogeneous Fluorescent Assay for cAMP-Phosphodiesterase Enzyme Activity

Cyclic adenosine monophosphate–phosphodiesterases (cAMP-PDEs) regulate the cellular level of cAMP by selectively catalyzing the hydrolysis of the phosphodiester bond in the cAMP molecule. They play important roles in modulating cellular and physiological functions. There is a growing interest in the study of cAMP-PDEs as therapeutic targets. We describe a novel method for measuring the enzyme activity of cAMP-PDEs that is based on a homogeneous fluorescence assay employing a cAMP-dependent DNA-binding protein (CAP). We demonstrate that the assay is quick and robust compared to traditional methods and is expected to be cost-effective for high-throughput screening of cAMP-PDE inhibitors. The usefulness of the assay is demonstrated by measuring IC50 values of three nonselective PDE inhibitors and by kinetic measurements of cAMP-PDEs from various rat tissues.

Phosphodiesterases in the central nervous system: implications in mood and cognitive disorders

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes that are involved in the regulation of the intracellular second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) by controlling their rates of hydrolysis. There are 11 different PDE families and each family typically has multiple isoforms and splice variants. The PDEs differ in their structures, distribution, modes of regulation, and sensitivity to inhibitors. Since PDEs have been shown to play distinct roles in processes of emotion and related learning and memory processes, selective PDE inhibitors, by preventing the breakdown of cAMP and/or cGMP, modulate mood and related cognitive activity. This review discusses the current state and future development in the burgeoning field of PDEs in the central nervous system. It is becoming increasingly clear that PDE inhibitors have therapeutic potential for the treatment of neuropsychiatric disorders involving disturbances of mood, emotion, and cognition.

High-throughput Giardia lamblia viability assay using bioluminescent ATP content measurements

The human pathogen Giardia lamblia is an anaerobic protozoan parasite that causes giardiasis, one of the most common diarrheal diseases worldwide. Although several drugs are available for the treatment of giardiasis, drug resistance has been reported and is likely to increase, and recurrent infections are common. The search for new drugs that can overcome the drug-resistant strains of Giardia is an unmet medical need. New drug screen methods can facilitate the drug discovery process and aid with the identification of new drug targets. Using a bioluminescent ATP content assay, we have developed a phenotypic drug screen method to identify compounds that act against the actively growing trophozoite stage of the parasite. This assay is homogeneous, robust, and suitable for high-throughput screening of large compound collections. A screen of 4,096 pharmacologically active small molecules and approved drugs revealed 43 compounds with selective anti-Giardia properties, including 32 previously reported and 11 novel anti-Giardia agents. The most potent novel compound was fumagillin, which showed 50% inhibitory concentrations of 10 nM against the WB isolate and 2 nM against the GS isolate.

Toxicity testing in the 21st century: implications for human health risk assessment

At the request of the Environmental Protection Agency, the National Research Council (NRC) recently completed a major report entitled Toxicity Testing in the 21st Century: A Vision and a Strategy. The terms of reference for this report were to develop a long-range vision and strategic plan to advance the practices of toxicity testing and human health assessment of environmental agents. The report describes how current and anticipated scientific advances can be expected to transform toxicity testing to permit broader coverage of the universe of potentially toxic chemicals to which humans may be exposed, using more timely and more cost-effective methods for toxicity testing. The report envisages greatly expanded use of high- and medium-throughput in vitro screening assays, computational toxicology, and systems biology, along with other emerging high-content testing methodologies, such as functional genomics and transcriptomics. When fully implemented, the vision will transform the ways toxicity testing and chemical risk assessment are conducted, moving away from measuring apical health endpoints in experimental animals toward identification of significant perturbations of toxicity pathways using in vitro tests in human cells and cell lines. Population-based studies incorporating relevant biomarkers will also be useful in identifying pathway perturbations directly in humans and in interpreting the results of in vitro tests in the context of human health risk assessment. The present article summarizes and extends the NRC report and examines its implications for risk assessment practice.

Exploration and optimization of substituted triazolothiadiazines and triazolopyridazines as PDE4 inhibitors

An expansion of structure-activity studies on a series of substituted 7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine PDE4 inhibitors and the introduction of a related [1,2,4]triazolo[4,3-b]pyridazine based inhibitor of PDE4 is presented. The development of SAR included strategic incorporation of known substituents on the critical catachol diether moiety of the 6-phenyl appendage on each heterocyclic core. From these studies, (R)-3-(2,5-dimethoxyphenyl)-6-(4-methoxy-3-(tetrahydrofuran-3-yloxy)phenyl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine (10) and (R)-3-(2,5-dimethoxyphenyl)-6-(4-methoxy-3-(tetrahydrofuran-3-yloxy)phenyl)-[1,2,4]triazolo[4,3-b]pyridazine (18) were identified as highly potent PDE4A inhibitors. Each of these analogues was submitted across a panel of 21 PDE family members and was shown to be highly selective for PDE4 isoforms (PDE4A, PDE4B, PDE4C, PDE4D). Both 10 and 18 were then evaluated in divergent cell-based assays to assess their relevant use as probes of PDE4 activity. Finally, docking studies with selective ligands (including 10 and 18) were undertaken to better understand this chemotypes ability to bind and inhibit PDE4 selectively.