A bioluminescent and homogeneous assay for monitoring GPCR-mediated cAMP modulation and PDE activity

3',5'-Cyclic adenosine monophosphate (cAMP), the first identified second messenger, is implicated in diverse cellular processes involving cellular metabolism, cell proliferation and differentiation, apoptosis, and gene expression. cAMP is synthesized by adenylyl cyclase (AC), which converts ATP to cAMP upon activation of Gαs-protein coupled receptors (GPCRs) in most cases and hydrolyzed by cyclic nucleotide phosphodiesterases (PDEs) to 5'-AMP. Dysregulation of cAMP signaling is implicated in a wide range of pathophysiological conditions such as cardiovascular diseases, neurodegenerative and behavioral disorders, cancers, diabetes, obesity, cataracts, and others. Therefore, cAMP targeted therapies have been and are still undergoing intense investigation for the treatment of these and other diseases. This highlights the need for developing assays to detect and monitor cAMP levels. In this study, we show cAMP Lumit assay as a highly specific homogeneous bioluminescent assay suitable for high throughput screenings with a large assay window and a wide dynamic range for cAMP detection. We believe that this assay will aid and simplify drug discovery screening efforts for cAMP signaling targeted therapies.

Luminogenic D-Luciferin Derivatives as OATP1B1 and 1B3 Substrates in No-wash Assays†

The human hepatic organic ion transporting polypeptides OATP1B1 and -1B3 are uptake transporters that influence the disposition of several small molecule drugs and perpetrate certain adverse drug-drug interactions. To predict these in vivo effects, in vitro systems are used to screen new drug entities as potential transporter substrates or inhibitors. To simplify such studies, we synthesized luminogenic derivatives of the OATP1B1 and -1B3 substrate D-luciferin to test as probe substrates in a rapid, no-wash optical approach for substrate and inhibitor identification and characterization. Each derivative is a pro-luciferin containing a self-immolating trimethyl lock quinone linker that is sensitive to intracellular reducing environments that cause the release of free luciferin in proportion to the amount of probe taken up by the transporter. A subsequent luciferin-limited luciferase reaction produces light in proportion to transporter activity. We tested the derivatives in HEK293 cells that overexpress OATP1B1 or OATP1B3 by transient transfection or viral transduction. Derivatives were identified that showed OATP-dependent uptake that was time and concentration dependent, saturable and sensitive to inhibition by known OATP1B1 and -1B3 substrates and inhibitors. These luminogenic transporter probes enabled an add-only multi-well plate protocol suitable for automation and high throughput screening.

A bioluminescent caspase-1 activity assay rapidly monitors inflammasome activation in cells

Inflammasomes are protein complexes induced by diverse inflammatory stimuli that activate caspase-1, resulting in the processing and release of cytokines, IL-1β and IL-18, and pyroptosis, an immunogenic form of cell death. To provide a homogeneous method for detecting caspase-1 activity, we developed a bioluminescent, plate-based assay that combines a substrate, Z-WEHD-aminoluciferin, with a thermostable luciferase in an optimized lytic reagent added directly to cultured cells. Assay specificity for caspase-1 is conferred by inclusion of a proteasome inhibitor in the lytic reagent and by use of a caspase-1 inhibitor to confirm activity. This approach enables a specific and rapid determination of caspase-1 activation. Caspase-1 activity is stable in the reagent thereby providing assay convenience and flexibility. Using this assay system, caspase-1 activation has been determined in THP-1 cells following treatment with α-hemolysin, LPS, nigericin, gramicidin, MSU, R848, Pam3CSK4, and flagellin. Caspase-1 activation has also been demonstrated in treated J774A.1 mouse macrophages, bone marrow-derived macrophages (BMDMs) from mice, as well as in human primary monocytes. Caspase-1 activity was not detected in treated BMDMs derived from Casp1^-/- mice, further confirming the specificity of the assay. Caspase-1 activity can be measured directly in cultured cells using the lytic reagent, or caspase-1 activity released into medium can be monitored by assay of transferred supernatant. The caspase-1 assay can be multiplexed with other assays to monitor additional parameters from the same cells, such as IL-1β release or cell death. The caspase-1 assay in combination with a sensitive real-time monitor of cell death allows one to accurately establish pyroptosis. This assay system provides a rapid, convenient, and flexible method to specifically and quantitatively monitor caspase-1 activation in cells in a plate-based format. This will allow a more efficient and effective assessment of inflammasome activation as well as enable high-throughput screening for inflammasome modulators.

A direct, bioluminescent caspase-1 assay for monitoring inflammasome activation

Caspase-1, an essential component of the inflammasome, is activated in response to inflammatory stimuli, resulting in 1) the processing and release of IL-1b and IL-18, and 2) pyroptosis, an immunogenic form of cell death. To provide a homogeneous method for detecting caspase-1 activity, we developed a bioluminescent assay that combines a substrate, Z-WEHD-aminoluciferin, with a thermostable luciferase in an optimized reagent added directly to cultured cells. The assay can also measure caspase-1 activity released into the medium. Assay specificity for caspase-1 is conferred by inclusion of a proteasome inhibitor, MG-132, in the reagent and by use of a caspase-1 inhibitor, Ac-YVAD-CHO, to confirm activity. Using this assay system, caspase-1 activity has been monitored in THP-1 cells, J774A.1 mouse macrophages, mouse bone marrow-derived macrophages (BMDMs), and human primary monocytes treated with known inflammasome inducers. Caspase-1 activity was not detected in BMDMs derived from Casp 1−/−mice. Measuring caspase-1 activity released into medium enables multiplexing of the sample to monitor additional cell parameters. Multiplexing to monitor caspase-1 activity, cell death, and IL-1b release revealed that unprimed, undifferentiated THP-1 cells stimulated with nigericin or a-hemolysin activate caspase-1 and undergo pyroptosis, but do not release any IL-1b. This suggests that K+ efflux alone can engage the inflammasome and activate caspase-1 in THP-1 cells, providing an interesting system to assess pyroptosis in the absence of IL-1b. This convenient caspase-1 assay will allow a more efficient and effective assessment of inflammasome activation as well as enable high-throughput screening for inflammasome modulators.

Abstract 1319: Monitoring inflammasome activation with a bioluminescent caspase-1 assay

Inflammatory responses and immune modulation play important and complex roles in cancer development and therapy, but methods to monitor caspase-1 activity associated with inflammasome activation have been limited. Inflammasomes are protein complexes induced by diverse inflammatory stimuli. Caspase-1, an essential component of the inflammasome, is activated in response to these stimuli, resulting in the processing and release of cytokines, IL-1β and IL-18, and pyroptosis, an immunogenic form of cell death. Western blots and ELISA are the primary, but indirect, methods for monitoring caspase-1 activity currently in use. To simplify and provide a more direct means of detecting cell-based caspase-1 activity, we developed a sensitive, homogeneous, plate-based assay that eliminates the need for significant sample processing. The assay employs a single-step, bioluminescent format combining a caspase-1 substrate, Z-WEHD-aminoluciferin, with a thermostable luciferase in an optimized reagent subsequently added to treated cells in an assay well. The coupled-enzyme system quickly reaches a steady-state between caspase cleavage of the substrate and luciferase conversion of the aminoluciferin, with light generated proportional to the amount of caspase-1 activity present in the sample. In addition to substrate selection, assay specificity for caspase-1 is conferred by inclusion of a proteasome inhibitor, MG132, in the reagent and by the subsequent use of a caspase-1 inhibitor, Ac-YVAD-CHO, to confirm activity. This approach enables clear determination of caspase-1 activity even in the context of apoptotic cells. Studies with Casp1−/− cells further demonstrate the effectiveness of this assay system to specifically detect cell-based, caspase-1 activity. Using this novel assay system, caspase-1 activation has been quantitatively determined in THP-1 cells following treatment with α-hemolysin, LPS, nigericin, monosodium urate crystals, R-848, Pam3CSK4, and flagellin. Caspase-1 activation has also been demonstrated in treated J774A.1 mouse macrophages, bone marrow-derived macrophages from mice, as well as in human primary monocytes. Of note, caspase-1 activity can be monitored either directly in cells or released into the culture medium following cell treatment with various inflammatory stimuli. Monitoring released caspase-1 activity in supernatants is fast, sensitive, and nondestructive, thereby enabling subsequent multiplexing of the biological sample with other assays to monitor additional cell parameters, such as IL-1β release or cell death. Therefore, this assay system provides a rapid, convenient, and flexible method to specifically and quantitatively monitor caspase-1 activation in cells in a plate-based format. This will allow a more efficient and effective assessment of inflammasome activation as well as enable high-throughput screening for inflammasome modulators.

Citation Format: Martha O'Brien, Danielle Moehring, Raúl Muñoz-Planillo, Gabriel Núñez, Justin Callaway, Jenny Ting, Mike Scurria, Tim Ugo, Laurent Bernad, James Cali, Dan Lazar. Monitoring inflammasome activation with a bioluminescent caspase-1 assay. [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 1319. doi:10.1158/1538-7445.AM2015-1319

Abstract LB-94: A non-lytic, cell-based, bioluminescent HDAC assay

Histone deacetylase (HDAC) class I and II enzymes play a critical role in the normal gene regulation events of development and homeostasis, but their dysregulation has been implicated in a variety of solid tumors and hematological malignancies. Broad spectrum inhibitors of HDAC Class I and II enzymes have been shown to achieve significant biological responses in otherwise refractory cancers. However, the underlying molecular mechanisms of these inhibitors have yet to be fully elucidated. Therefore, more sensitive and efficient tools are needed to rapidly identify and define modulators of HDAC activity. We have recently developed a one-step, homogeneous, luminescent assay for the detection of activity in a high-throughput format from multiple HDAC Class I and II isoforms, in cell culture, enriched or recombinant sources. This luciferase-containing, “glow-type” assay reagent measures HDAC activity in a proportional manner when the pro-luciferin peptide substrate becomes deacetylated and susceptible to lysine-specific cleavage by a developer enzyme contained within the reagent. This substrate is fully cell-permeable and can directly measure HDAC activity in living cells. We will present data demonstrating assay utility with attachment-dependent and suspension cell types using representative inhibitors from the hydroxamate, short-chain fatty acid, benzamide and cyclic peptide classes. Furthermore, we will correlate HDAC inhibition profiles with initiation of caspase activity and/or other cytotoxicity biomarkers.

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 LB-94.