Abstract 3505: A bioluminescent, homogeneous annexin V microplate-based method for assessment of apoptosis

The selective elimination of malignant cells via the apoptotic process continues to be the cornerstone of modern anti-cancer therapy regimens. Therefore, in vitro screening approaches aimed at identifying clinically useful apoptosis inducers remain critically important. Recently, phenotypic screening methods have enjoyed a resurgence due to more biologically complex and relevant cell models as well as advances in chemical proteomics which have allowed for more successful target identification. As a consequence, novel probes and tools with enabling attributes are required to fully realize this discovery potential. In an effort to address this unmet need, we have developed a bioluminescent and homogeneous annexin V binding assay for the assessment of apoptosis. Unlike traditional fluorescent annexin V methodology, the “no-wash” reagent employed in this new assay utilizes binary components of a novel luciferase separately fused to annexin V. The annexin V-luciferase subunit fusion pairs have low intrinsic affinity for each other and thus produce no or low luminescence until phosphatidylserine (PtdSer) exposure drives annexin-fusion pair oligimerization. Ultimately, this protein:protein interaction on or near the cell surface reconstitutes full luciferase activity causing an increase in luminescence in the presence of a luciferase substrate. A separate, pro-fluorescent, multiplexed component of the reagent further delineates differences in annexin positivity based on maintenance or loss of membrane integrity corresponding to apoptosis or necrosis, respectively. We validated this method using a panel of diverse cancer cell lines (U2-OS, DLD-1, HeLa, Jurkat, K562, A549, and PC-3), representing both attachment-dependent and -independent morphologies after dose-dependent challenge with intrinsic (bortezomib, panobinostat, staurosporine, and paclitaxel) and extrinsic (rhTRAIL) inducers of apoptosis as well as agents known to produce primary necrosis (ionomycin and digitonin). Caspase activation data was also collected in parallel plates at endpoint as a well-validated and sensitive orthogonal comparator. The bioluminescent annexin V method proved sufficiently robust in 384 well microplate formats to routinely produce Z’ > 0.7 and rank-order potencies in good agreement with caspase activation values. In addition to this microplate functionality, the reagent allowed for sensitive, facile imaging of apoptotic induction in living cells using different imaging platforms. Taken together, the method and reagent should provide unparalleled flexibility with regard to live cell apoptosis detection in both conventional microplate and high content-like imaging formats and advance the pace of new chemical entity discovery.

Citation Format: Kevin Kupcho, John Shultz, Andrew Niles, Wenhui Zhou, Robin Hurst, Jim Hartnett, Thomas Machleidt, Terry Riss, Dan Lazar, Jim Cali. A bioluminescent, homogeneous annexin V microplate-based method for assessment of apoptosis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3505.

Three Efficient Methods for Preparation of Coelenterazine Analogues

The growing popularity of bioluminescent assays has highlighted the need for coelenterazine analogues possessing properties tuned for specific applications. However, the structural diversity of known coelenterazine analogues has been limited by current syntheses. Known routes for the preparation of coelenterazine analogues employ harsh reaction conditions that limit access to many substituents and functional groups. Novel synthetic routes reported here establish simple and robust methods for synthesis and investigation of structurally diverse marine luciferase substrates. Specifically, these new routes allow synthesis of coelenterazine analogues containing various heterocyclic motifs and substituted aromatic groups with diverse electronic substituents at the R(2) position. Interesting analogues described herein were characterized by their physicochemical properties, bioluminescent half-life, light output, polarity and cytotoxicity. Some of the analogues represent leads that can be utilized in the development of improved bioluminescent systems.

NanoLuc Complementation Reporter Optimized for Accurate Measurement of Protein Interactions in Cells

Protein-fragment complementation assays (PCAs) are widely used for investigating protein interactions. However, the fragments used are structurally compromised and have not been optimized nor thoroughly characterized for accurately assessing these interactions. We took advantage of the small size and bright luminescence of NanoLuc to engineer a new complementation reporter (NanoBiT). By design, the NanoBiT subunits (i.e., 1.3 kDa peptide, 18 kDa polypeptide) weakly associate so that their assembly into a luminescent complex is dictated by the interaction characteristics of the target proteins onto which they are appended. To ascertain their general suitability for measuring interaction affinities and kinetics, we determined that their intrinsic affinity (KD = 190 μM) and association constants (kon = 500 M(-1) s(-1), koff = 0.2 s(-1)) are outside of the ranges typical for protein interactions. The accuracy of NanoBiT was verified under defined biochemical conditions using the previously characterized interaction between SME-1 β-lactamase and a set of inhibitor binding proteins. In cells, NanoBiT fusions to FRB/FKBP produced luminescence consistent with the linear characteristics of NanoLuc. Response dynamics, evaluated using both protein kinase A and β-arrestin-2, were rapid, reversible, and robust to temperature (21-37 °C). Finally, NanoBiT provided a means to measure pharmacology of kinase inhibitors known to induce the interaction between BRAF and CRAF. Our results demonstrate that the intrinsic properties of NanoBiT allow accurate representation of protein interactions and that the reporter responds reliably and dynamically in cells.

NanoBRET--A Novel BRET Platform for the Analysis of Protein-Protein Interactions

Dynamic interactions between proteins comprise a key mechanism for temporal control of cellular function and thus hold promise for development of novel drug therapies. It remains technically challenging, however, to quantitatively characterize these interactions within the biologically relevant context of living cells. Although, bioluminescence resonance energy transfer (BRET) has often been used for this purpose, its general applicability has been hindered by limited sensitivity and dynamic range. We have addressed this by combining an extremely bright luciferase (Nanoluc) with a means for tagging intracellular proteins with a long-wavelength fluorophore (HaloTag). The small size (19 kDa), high emission intensity, and relatively narrow spectrum (460 nm peak intensity) make Nanoluc luciferase well suited as an energy donor. By selecting an efficient red-emitting fluorophore (635 nm peak intensity) for attachment onto the HaloTag, an overall spectral separation exceeding 175 nm was achieved. This combination of greater light intensity with improved spectral resolution results in substantially increased detection sensitivity and dynamic range over current BRET technologies. Enhanced performance is demonstrated using several established model systems, as well as the ability to image BRET in individual cells. The capabilities are further exhibited in a novel assay developed for analyzing the interactions of bromodomain proteins with chromatin in living cells.

A luminescent assay for real-time measurements of receptor endocytosis in living cells

Ligand-mediated endocytosis is a key autoregulatory mechanism governing the duration and intensity of signals emanating from cell surface receptors. Due to the mechanistic complexity of endocytosis and its emerging relevance in disease, simple methods capable of tracking this dynamic process in cells have become increasingly desirable. We have developed a bioluminescent reporter technology for real-time analysis of ligand-mediated receptor endocytosis using genetic fusions of NanoLuc luciferase with various G-protein-coupled receptors (GPCRs). This method is compatible with standard microplate formats, which should decrease work flows for high-throughput screens. This article also describes the application of this technology to endocytosis of epidermal growth factor receptor (EGFR), demonstrating potential applicability of the method beyond GPCRs.

Abstract 3512: Measuring intracellular target engagement and drug residence time with nanoBRET

We present a biophysical method to directly measure target engagement within intact mammalian cells using bioluminescence energy transfer (BRET). Compound interactions with intracellular targets can be detected with complete specificity by their ability to compete with energy transfer complexes introduced into the cells. These complexes can be detected at physiologically relevant levels by exploiting an extraordinarily bright luciferase (NanoLuc), together with fluorescent tracers optimized for cell-permeability and spectral resolution from the luciferase. We demonstrate applications of the technology for target engagement among key drug target classes, including; kinases, histone deacetylases (HDACs), bromodomains, and the methyltransferase EZH2. Intracellular selectivity and affinity profiles of various reference compounds and approved drugs will be presented. For a panel of HDAC inhibitors, affinity profiles for specific HDAC isozymes strongly correlate with phenotypic potencies (e.g. cell viability). Furthermore, the luminescent output of the energy transfer complex enables a technique to monitor ligand occupancy in real-time. Association and dissociation rates can be derived from the kinetic measurements, providing a means to quantify drug residence time on select targets within intact cell populations. This novel application of intracellular BRET should significantly advance target engagement work flows, and allow for intracellular target affinities to be coupled to phenotypic outcomes.

Citation Format: Matthew B. Robers, Melanie Dart, Chad Zimprich, Thomas Kirkland, Sergiy Levin, Thomas Machleidt, Jim Hartnett, Kris Zimmerman, Rachel Ohana, Danette Daniels, Mei Cong, Frank Fan, Keith Wood. Measuring intracellular target engagement and drug residence time with nanoBRET. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3512. doi:10.1158/1538-7445.AM2015-3512

Application of BRET to monitor ligand binding to GPCRs

Bioluminescence resonance energy transfer (BRET) is a well-established method for investigating protein-protein interactions. Here we present a novel BRET approach to monitor ligand binding to G protein-coupled receptors (GPCRs) on the surface of living cells made possible by the use of fluorescent ligands in combination with a novel bioluminescent protein (NanoLuc) that can be readily expressed on the N-terminus of GPCRs.

Abstract 4272: NanoLucTM as an improved BRET donor to monitor EGFR interactions within living cells

As a small, versatile protein fusion reporter, NanoLuc™ luciferase offers superior brightness and sensitivity compared to any luciferase described to date. The small size and enhanced brightness of NanoLuc™ makes it ideally suited as an energy donor for Bioluminescence Resonance Energy Transfer (BRET) to a variety of fluorescent acceptors within living cells. By combining genetic reporters such as NanoLuc™ luciferase and HaloTag™ fluorescent labelling technology, it is possible to monitor the interactions of cell surface receptors such as EGFR with adapter proteins in response to growth factor stimulation. In addition to demonstrating inducible protein interactions, it may also be possible to apply this foundational BRET system to the measurement of ligand or small molecule binding events within living cells.

Citation Format: Matthew B. Robers, Thomas Machleidt, Thomas Kirkland, Carolyn Woodroofe, Frank Fan, Mei Cong, Keith Wood. NanoLucTM as an improved BRET donor to monitor EGFR interactions within living cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4272. doi:10.1158/1538-7445.AM2013-4272

Engineered luciferase reporter from a deep sea shrimp utilizing a novel imidazopyrazinone substrate

Bioluminescence methodologies have been extraordinarily useful due to their high sensitivity, broad dynamic range, and operational simplicity. These capabilities have been realized largely through incremental adaptations of native enzymes and substrates, originating from luminous organisms of diverse evolutionary lineages. We engineered both an enzyme and substrate in combination to create a novel bioluminescence system capable of more efficient light emission with superior biochemical and physical characteristics. Using a small luciferase subunit (19 kDa) from the deep sea shrimp Oplophorus gracilirostris, we have improved luminescence expression in mammalian cells ∼2.5 million-fold by merging optimization of protein structure with development of a novel imidazopyrazinone substrate (furimazine). The new luciferase, NanoLuc, produces glow-type luminescence (signal half-life >2 h) with a specific activity ∼150-fold greater than that of either firefly (Photinus pyralis) or Renilla luciferases similarly configured for glow-type assays. In mammalian cells, NanoLuc shows no evidence of post-translational modifications or subcellular partitioning. The enzyme exhibits high physical stability, retaining activity with incubation up to 55 °C or in culture medium for >15 h at 37 °C. As a genetic reporter, NanoLuc may be configured for high sensitivity or for response dynamics by appending a degradation sequence to reduce intracellular accumulation. Appending a signal sequence allows NanoLuc to be exported to the culture medium, where reporter expression can be measured without cell lysis. Fusion onto other proteins allows luminescent assays of their metabolism or localization within cells. Reporter quantitation is achievable even at very low expression levels to facilitate more reliable coupling with endogenous cellular processes.

Discovery of potent and selective covalent inhibitors of JNK

The mitogen-activated kinases JNK1/2/3 are key enzymes in signaling modules that transduce and integrate extracellular stimuli into coordinated cellular response. Here, we report the discovery of irreversible inhibitors of JNK1/2/3. We describe two JNK3 cocrystal structures at 2.60 and 2.97 Å resolution that show the compounds form covalent bonds with a conserved cysteine residue. JNK-IN-8 is a selective JNK inhibitor that inhibits phosphorylation of c-Jun, a direct substrate of JNK, in cells exposed to submicromolar drug in a manner that depends on covalent modification of the conserved cysteine residue. Extensive biochemical, cellular, and pathway-based profiling establish the selectivity of JNK-IN-8 for JNK and suggests that the compound will be broadly useful as a pharmacological probe of JNK-dependent signal transduction. Potential lead compounds have also been identified for kinases, including IRAK1, PIK3C3, PIP4K2C, and PIP5K3.

TR-FRET cellular assays for interrogating posttranslational modifications of histone H3

Posttranslational modifications such as phosphorylation, acetylation, and methylation play important roles in regulating the structures and functions of histones, which in turn regulate gene expression and DNA repair and replication. Histone-modifying enzymes, such as deacetylases, methyltransferases and demethylases, have been pursued as therapeutic targets for various diseases. However, detection of the activities of these enzymes in high-throughput cell-based formats has remained challenging. The authors have developed high-throughput LanthaScreen cellular assays for Histone H3 site-specific modifications. These assays use cells expressing green fluorescence protein-tagged Histone H3 transiently delivered via BacMam and terbium-labeled anti-Histone H3 modification-specific antibodies. Robust time-resolved Förster resonance energy transfer signals were detected for H3 lysine-9 acetylation and dimethylation (H3K9me2), serine-10 phosphorylation, K4 di- and trimethylation, and K27 trimethylation. Consistent with previous reports, hypoxic stress increased K4 methylation levels, and methyltransferase G9a inhibitor UNC-0638 decreased K9me2 levels significantly, with little effects on other modifications. To demonstrate the utility of this assay platform in screening, the K9 acetylation assay was used to profile the Enzo Epigenetics Library. Twelve known HDAC inhibitors were identified as hits and followed up in a dose-response format. In conclusion, this assay platform enables high-throughput cell-based analysis of diverse types of posttranslational modifications of Histone H3.

Design and characterization of a potent and selective dual ATP- and substrate-competitive subnanomolar bidentate c-Jun N-terminal kinase (JNK) inhibitor

c-Jun N-terminal kinases (JNKs) represent valuable targets in the development of new therapies. Present on the surface of JNK is a binding pocket for substrates and the scaffolding protein JIP1 in close proximity to the ATP binding pocket. We propose that bidentate compounds linking the binding energies of weakly interacting ATP and substrate mimetics could result in potent and selective JNK inhibitors. We describe here a bidentate molecule, 19, designed against JNK. 19 inhibits JNK kinase activity (IC(50) = 18 nM; K(i) = 1.5 nM) and JNK/substrate association in a displacement assay (IC(50) = 46 nM; K(i) = 2 nM). Our data demonstrate that 19 targets for the ATP and substrate-binding sites on JNK concurrently. Finally, compound 19 successfully inhibits JNK in a variety of cell-based experiments, as well as in vivo where it is shown to protect against Jo-2 induced liver damage and improve glucose tolerance in diabetic mice.

Abstract 67: High-throughput cellular assays for interrogating epigenetic histone modifications

Epigenetic histone modifications such as, methylation, acetylation, and phosphorylation play important roles in regulating the structure and functions of histones which in turn regulate essential gene expression. Dysregulation of the enzymes responsible for these modifications has been linked to cancer and many other diseases. In particular, histone deacetylases (HDACs) and histone methyl transferase (HMTs) have been a recent focus for drug discovery. However, detection of these enzymatic activities in an HTS cell-based format has remained challenging, especially since many of these enzymes may require the formation of protein complexes for relevant activity. To help overcome these challenges, we have developed and validated high-throughput compatible LanthaScreen® cellular assays for the analysis of histone methylation, acetylation, and phoshorylation, in cell backgrounds of interest. The acetylation, methylation and phosphorylation of H3 at specific residues can be detected with terbium-labeled antibodies against the specific site and modification. The expression of GFP-H3 substrate allows for detection of antibody binding in cell lysates via TR-FRET between the terbium and GFP. Since the actual modification takes place in the intact cell, native protein complexes that may be important for enzyme function are preserved. Together, these assays enable interrogation of multiple enzymatic activities responsible for epigenetic modifications of challenging histone targets

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 67. doi:10.1158/1538-7445.AM2011-67

Design, synthesis, and structure-activity relationship studies of thiophene-3-carboxamide derivatives as dual inhibitors of the c-Jun N-terminal kinase

We report comprehensive structure-activity relationship studies on a novel series of c-Jun N-terminal kinase (JNK) inhibitors. Intriguingly, the compounds have a dual inhibitory activity by functioning as both ATP and JIP mimetics, possibly by binding to both the ATP binding site and to the docking site of the kinase. Several of such novel compounds display potent JNK inhibitory profiles both in vitro and in cell.

Abstract 4867: High-throughput LanthaScreen® cellular assays for interrogating post-translational modifications of p53 and histones

Post-translational modifications such as phosphorylation, acetylation and ubquitination play important roles in regulating the structure and functions of histones and transcription factors such as p53, which in turn regulate essential gene expression. Dysregulation of these post-translational modifications has been linked to cancer and metabolic diseases. In particular, histone deacetylases (HDACs) have been pursued as valuable targets for various therapeutic interventions. However, detection of these enzymatic activities in a cell-based format has remained intractable using HTS-compatible technologies. To enable the drug discovery for these post-translational modification enzymes, we have developed and validated high-throughput compatible LanthaScreen® cellular assays for the analysis of histone and/or p53-specific acetylation, ubquitination and phoshorylation in cell backgrounds of interest. The cell cycle-dependent acetylation of histone H3 at Lys9 and the phosphorylation of histone H3 at Ser10 can be detected with terbium-labeled anti-Histone H3 acetyl-lys 9 and anti-phospho-Ser10 specific antibodies, respectively. In addition, poly-ubiquitination of Histone H2B can be measured with terbium-labeled anti-poly-ubiquitin antibody. We have also applied this technology and developed cellular assays for measuring DNA-damage induced phosphorylation at Ser15 and acetylation at Lys382 of p53. These assays were further validated with both small molecule inhibitor and siRNA against specific HDAC family members. Our results suggest that the deacetylation of Histone H3 Lys 9 is mediated by type I/II HDACs, whereas the deacetylation of p53 at Lys382 is mediated synergistically by both SIRT1 and type I/II HDAC activities. Together, these assays enable interrogation of multiple enzymatic activities responsible for post-translational modifications of challenging targets such as histones and p53.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4867.

Synthesis and optimization of thiadiazole derivatives as a novel class of substrate competitive c-Jun N-terminal kinase inhibitors

A series of thiadiazole derivatives has been designed as potential allosteric, substrate competitive inhibitors of the protein kinase JNK. We report on the synthesis, characterization and evaluation of a series of compounds that resulted in the identification of potent and selective JNK inhibitors targeting its JIP-1 docking site.

Generation of Site-Specific Retargeting Platform Cell Lines for Drug Discovery Using phiC31 and R4 Integrases

One of the challenges in developing cell lines for high-throughput screening in drug discovery is the labor- and time-intensive process required to create stable clonal cell lines that express specific reporters or drug targets. The authors report here the generation of a site-specific retargeting platform in 3 different cell lines: adherent HEK293, suspension CHO-S, and a human embryonic cell line (BGO1V). These platform cell lines were generated by using a combination of 2 site-specific integrases to develop a system that allows one to efficiently target a gene of interest to a specific locus and generates rapid production of homogeneous cell pools that stably express the gene of interest. The phiC31 integrase was used to create a platform line by placing a target site for the R4 integrase into a pseudo attP site, and then the R4 integrase was used to place a gene of interest into specific R4 target site. The authors demonstrate the successful and rapid retargeting of a G-protein-coupled receptor (cholecystokinin receptor A, CCKAR), an ion channel (the transient receptor potential cation channel, subfamily M, member 8, TRPM8), and a GFP-c-Jun(1-79) fusion protein into the specific loci in these cell lines and show that these retargeted cell lines exhibit functional and pharmacological responses consistent with those reported in the literature.

Fluorescent labeling of proteins in living cells using the FKBP12 (F36V) tag

Over the past decade live cell imaging has become a key technology to monitor and understand the dynamic behavior of proteins in the physiological context of living cells. The visualization of a protein of interest is most commonly achieved by genetically fusing it to green fluorescent protein (GFP) or one of it variants. Considerable effort has been made to develop alternative methods of protein labeling to overcome the intrinsic limitations of fluorescent proteins. In this report we show the optimization of a live cell labeling technology based on the use of a mutant form of FKBP12 (FKBP12(F36V)) in combination with a synthetic high affinity ligand (SLF') that specifically binds to this mutant. It had been previously shown that the use of a fluorescein-conjugated form of SLF' (5'-fluorescein-SLF') allowed the labeling of proteins genetically fused to FKBP-F36V in living cells. Here we describe the identification of novel fluorescent SLF'dye conjugates that allow specific labeling of FKBP12(F36V) fusion proteins in living cells. To further increase the versatility of this technology we developed a number of technical improvements. We implemented the use of pluronics during the labeling process to facilitate the uptake of the SLF'-dye conjugates and the use suppression dyes to reduce background signal. Furthermore, the time and dose dependency of labeling was investigated in order to determine optimal labeling conditions. Finally, the specificity of the FKBP12(F36V) labeling technology was extensively validated by morphological analysis using a diverse set of FKBP12(F36V) fusions proteins. In addition we show a number of different application examples, such as translocation assays, the generation of biosensors, and multiplex labeling in combination with different labeling technologies, such as FlAsH or GFP. In summary we show that the FKBP12(F36V)/SLF' labeling technology has a broad range of applications and should prove useful for the study of protein function in living cells.

Multiplexing of pathway-specific beta-lactamase reporter gene assays by optical coding with Qtracker nanocrystals

Reporter assays are widely used in research and drug discovery for analysis of signaling pathways in a cell-based format. Traditionally, reporter gene assays are run in a single-parameter mode, interrogating only 1 pathway per sample. To enable more complex assay formats for pathway analysis, the authors developed a multiplexed reporter cell-based assay that combines optical encoding with a beta-lactamase reporter gene readout. The optical encoding is achieved by peptide-mediated delivery of quantum dots into reporter cell lines. Using different quantum dots, the authors were able to simultaneously analyze multiple signaling pathways in the same sample using fluorescence microscopy or flow cytometry. They selected 3 beta-lactamase reporter cell lines for the analysis of tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), and interferon gamma (IFN-gamma) induced signaling to perform proof-of-principle experiments. The analysis demonstrates that this multiplexed assay allows the reliable detection of ligand-specific activation patterns as well as pathway-specific inhibitors. This method provides a template for the development of novel assay designs that enable the analysis of complex signaling networks involving multiple signaling pathways as well as cell-specific pathways in heterotypic cell models.

Design, synthesis, and structure-activity relationship of substrate competitive, selective, and in vivo active triazole and thiadiazole inhibitors of the c-Jun N-terminal kinase

We report comprehensive structure-activity relationship studies on a novel series of c-Jun N-terminal kinase (JNK) inhibitors. The compounds are substrate competitive inhibitors that bind to the docking site of the kinase. The reported medicinal chemistry and structure-based optimizations studies resulted in the discovery of selective and potent thiadiazole JNK inhibitors that display promising in vivo activity in mouse models of insulin insensitivity.

Discovery of 2-(5-nitrothiazol-2-ylthio)benzo[d]thiazoles as novel c-Jun N-terminal kinase inhibitors

A new series of 2-thioether-benzothiazoles has been synthesized and evaluated for JNK inhibition. The SAR studies led to the discovery of potent, allosteric JNK inhibitors with selectivity against p38.

Development of LanthaScreen cellular assays for key components within the PI3K/AKT/mTOR pathway

The PI3K/AKT/mTOR pathway is central to cell growth and survival, cell cycle regulation, and programmed cell death. Aberrant activation of this signaling cascade is linked to several disease states, and thus many components of the pathway are attractive targets for therapeutic intervention. However, the considerable degree of complexity, crosstalk, and feedback regulation that exists within the pathway (especially with respect to the regulation of mTOR and its complexes) underscores the need for a comprehensive set of cell-based assays to properly identify and characterize small-molecule modulators. Here, the development and application of time-resolved Förster resonance energy transfer (TR-FRET)-based assays to enable the phosphoprotein analysis of key pathway components in a cellular format are reported. The LanthaScreen cellular assay platform uses FRET between a terbium-labeled phosphorylation site-specific antibody and an expressed green fluorescent protein fusion of particular kinase substrate and provides an assay readout that is ratiometric, robust, and amenable to high-throughput screening applications. Assays specific for 5 different targets within the pathway are highlighted: Ser183 and Thr246 on the proline-rich AKT substrate 40 kDa (PRAS40), Ser457 on programmed cell death protein 4 (PDCD4), and Thr308 and Ser473 on AKT. Each assay was evaluated under various experimental conditions and individually optimized for performance. Known pathway agonists and a small panel of commercially available compounds were also used to complete the assay validation. Taken together, these data demonstrate the utility of a related set of cell-based assays to interrogate PI3K/AKT/mTOR signaling and provide a template for the development of similar assays for other targets.

Cellular LanthaScreen and beta-lactamase reporter assays for high-throughput screening of JAK2 inhibitors

The Janus kinase (JAK) 2/signal transducer and activator of transcription (STAT) 5 pathway is responsible for regulation of cellular responses to a number of cytokines and growth factors. In hematopoietic cells, growth factors such as granulocyte macrophage-colony stimulating factor, interleukin-3, and erythropoietin induce the activation of JAK2, which leads to the phosphorylation, dimerization, and transactivation of STAT5 proteins. Dysregulation of JAK2 by activating mutations such as JAK2V617F results in constitutive phosphorylation of STAT5 and has been linked to numerous myeloproliferative disorders such as polycythemia vera. A cellular LanthaScreen (Invitrogen Corp., Carlsbad, CA) time-resolved Förster resonance energy transfer assay for wild-type JAK2 activity was developed. This assay utilized the growth factor-dependent human erythroleukemia TF1 cell line engineered to express a green fluorescent protein-STAT5 fusion protein. Furthermore, a complementary beta-lactamase reporter gene assay was developed to analyze the transcriptional activity of STAT5 downstream of JAK2 in TF1 cells. The same technologies were applied to the development of cellular assays for the interrogation of the disease-relevant JAK2V617F activating mutant. A small molecule inhibitor and Stealth (Invitrogen Corp.) RNA interference oligonucleotides were used to confirm the involvement of JAK2. Our results suggest that these cellular assays and validation tools represent powerful integrated methods for the analysis of physiological and disease-relevant JAK/STAT pathways within the physiological cellular context.