Interrogating direct NLRP3 engagement and functional inflammasome inhibition using cellular assays

As a key regulator of the innate immune system, the NLRP3 inflammasome responds to a variety of environmental insults through activation of caspase-1 and release of the proinflammatory cytokines IL-1β and IL-18. Aberrant NLRP3 inflammasome function is implicated in numerous inflammatory diseases, spurring drug discovery efforts at NLRP3 as a therapeutic target. A diverse array of small molecules is undergoing preclinical/clinical evaluation with a reported mode of action involving direct modulation of the NLRP3 pathway. However, for a subset of these ligands the functional link between live-cell target engagement and pathway inhibition has yet to be fully established. Herein we present a cohort of mechanistic assays to both query direct NLRP3 engagement in cells, and functionally interrogate different nodes of NLRP3 pathway activity. This system enabled the stratification of potency for five confirmed NLRP3 inhibitors, and identification of two reported NLRP3 inhibitors that failed to demonstrate direct pathway antagonism.

Monitoring phosphorylation and acetylation of CRISPR-mediated HiBiT-tagged endogenous proteins

Intracellular pathways transduce signals through changes in post-translational modifications (PTMs) of effector proteins. Among the approaches used to monitor PTM changes are immunoassays and overexpression of recombinant reporter genes. Genome editing by CRISPR/Cas9 provides a new means to monitor PTM changes by inserting reporters onto target endogenous genes while preserving native biology. Ideally, the reporter should be small in order not to interfere with the processes mediated by the target while sensitive enough to detect tightly expressed proteins. HiBiT is a 1.3 kDa reporter peptide capable of generating bioluminescence through complementation with LgBiT, an 18 kDa subunit derived from NanoLuc. Using HiBiT CRISPR/Cas9-modified cell lines in combination with fluorescent antibodies, we developed a HiBiT-BRET immunoassay (a.k.a. Immuno-BRET). This is a homogeneous immunoassay capable of monitoring post-translational modifications on diverse protein targets. Its usefulness was demonstrated for the detection of phosphorylation of multiple signaling pathway targets (EGFR, STAT3, MAPK8 and c-MET), as well as chromatin containing histone H3 acetylation on lysine 9 and 27. These results demonstrate the ability to efficiently monitor endogenous biological processes modulated by post-translational modifications using a small bioluminescent peptide tag and fluorescent antibodies, providing sensitive quantitation of the response dynamics to multiple stimuli.

Abstract 1428: Luminescent immunoassays for homogeneous determination of cell proliferation and senescence

We have developed homogeneous, luminescent immunoassays for simple and rapid determination of Ki-67 and uPAR levels in 96-well format, thereby enabling efficient and quantitative assessment of proliferation and senescence in mammalian cell culture. Assessment of proliferative capacity is of key importance in numerous research areas, including cancer and various proliferative disorders, assessment of cell fitness (e.g., T cell fitness, stem cell characterization), and evaluation of test compound or drug effects. Cell senescence, characterized in part by loss of proliferative capacity, is an altered, proinflammatory state of cells induced in response to developmental ques, aging, disease, or acute stressors typically involving DNA damage. Ki-67 is a nuclear protein widely used as a marker of proliferation due to its pervasive expression in cycling cells but absence from non-dividing (G0) cells, whether quiescent, senescent, or terminally differentiated. In contrast, urokinase plasminogen activator receptor (uPAR) is a cell-surface protein whose expression was recently reported to increase significantly with the induction of senescence. Of note, commonly used assays of Ki-67 and uPAR levels typically rely upon non-homogeneous methods, including imaging, flow cytometry, or western blotting. Application of Lumit™ technology enabled our development of no-transfer, no-wash immunoassays for Ki-67 (lytic) and uPAR (nonlytic) determinations directly in cell wells. Treatment of human CD8+ T cells with CD3/CD28 T cell activator produced more than a 10-fold upregulation of Ki-67 levels, consistent with induction of T cell proliferation. In contrast, treatment of HCT116 colorectal cancer cells for 48 h with the antiproliferative compounds doxorubicin (100 nM) and nutlin-3A (10 μM) produced 65% and 90% reductions, respectively, in Ki-67 levels normalized to a measure of viable cell number, consistent with their relative antiproliferative activities. Dose-dependent treatment of HCT116 cells with nutlin-3A for 24 and 48 h produced 69% and 93% reduction, respectively, in normalized Ki-67 levels with a potency of ~2.5 μM. Treatment of HCT116 and A549 cancer cell lines for 72 h with 10-20 μM nutlin-3A, in addition to causing profound reduction in Ki-67 levels and loss of proliferative capacity, produced 2.3- to 4-fold increases in cell-surface uPAR levels, reflective of the emergence of the senescence phenotype. These luminescent, homogeneous Ki-67 and uPAR immunoassays provide an efficient means to quantitatively assess changes in cell proliferation and senescence in cell culture models for basic research and drug discovery applications.

Citation Format: Dan F. Lazar, Kevin R. Kupcho, Andrew L. Niles, James J. Cali. Luminescent immunoassays for homogeneous determination of cell proliferation and senescence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1428.

A direct capture method for purification and detection of viral nucleic acid enables epidemiological surveillance of SARS-CoV-2

Studies have demonstrated that SARS-CoV-2 RNA can be detected in the feces of infected individuals. This finding spurred investigation into using wastewater-based epidemiology (WBE) to monitor SARS-CoV-2 RNA and track the appearance and spread of COVID-19 in communities. SARS-CoV-2 is present at low levels in wastewater, making sample concentration a prerequisite for sensitive detection and utility in WBE. Whereas common methods for isolating viral genetic material are biased toward intact virus isolation, it is likely that a relatively low percentage of the total SARS-CoV-2 RNA genome in wastewater is contained within intact virions. Therefore, we hypothesized that a direct unbiased total nucleic acid(TNA) extraction method could overcome the cumbersome protocols, variability and low recovery rates associated with the former methods. This led to development of a simple, rapid, and modular alternative to existing purification methods. In an initial concentration step, chaotropic agents are added to raw sewage allowing binding of nucleic acid from free nucleoprotein complexes, partially intact, and intact virions to a silica matrix. The eluted nucleic acid is then purified using manual or semi-automated methods. RT-qPCR enzyme mixes were formulated that demonstrate substantial inhibitor resistance. In addition, multiplexed probe-based RT-qPCR assays detecting the N1, N2 (nucleocapsid) and E (envelope) gene fragments of SARS-CoV-2 were developed. The RT-qPCR assays also contain primers and probes to detect Pepper Mild Mottle Virus (PMMoV), a fecal indicator RNA virus present in wastewater, and an exogenous control RNA to measure effects of RT-qPCR inhibitors. Using this workflow, we monitored wastewater samples from three wastewater treatment plants (WWTP) in Dane County, Wisconsin. We also successfully sequenced a subset of samples to ensure compatibility with a SARS-CoV-2 amplicon panel and demonstrated the potential for SARS-CoV-2 variant detection. Data obtained here underscore the potential for wastewater surveillance of SARS-CoV-2 and other infectious agents in communities.

A direct capture method for purification and detection of viral nucleic acid enables epidemiological surveillance of SARS-CoV-2

Studies have demonstrated that SARS-CoV-2 RNA can be detected in the feces of infected individuals. This finding spurred investigation into using wastewater-based epidemiology (WBE) to monitor SARS-CoV-2 RNA and track the appearance and spread of COVID-19 in communities. SARS-CoV-2 is present at low levels in wastewater, making sample concentration a prerequisite for sensitive detection and utility in WBE. Whereas common methods for isolating viral genetic material are biased toward intact virus isolation, it is likely that a relatively low percentage of the total SARS-CoV-2 RNA genome in wastewater is contained within intact virions. Therefore, we hypothesized that a direct unbiased total nucleic acid(TNA) extraction method could overcome the cumbersome protocols, variability and low recovery rates associated with the former methods. This led to development of a simple, rapid, and modular alternative to existing purification methods. In an initial concentration step, chaotropic agents are added to raw sewage allowing binding of nucleic acid from free nucleoprotein complexes, partially intact, and intact virions to a silica matrix. The eluted nucleic acid is then purified using manual or semi-automated methods. RT-qPCR enzyme mixes were formulated that demonstrate substantial inhibitor resistance. In addition, multiplexed probe-based RT-qPCR assays detecting the N1, N2 (nucleocapsid) and E (envelope) gene fragments of SARS-CoV-2 were developed. The RT-qPCR assays also contain primers and probes to detect Pepper Mild Mottle Virus (PMMoV), a fecal indicator RNA virus present in wastewater, and an exogenous control RNA to measure effects of RT-qPCR inhibitors. Using this workflow, we monitored wastewater samples from three wastewater treatment plants (WWTP) in Dane County, Wisconsin. We also successfully sequenced a subset of samples to ensure compatibility with a SARS-CoV-2 amplicon panel and demonstrated the potential for SARS-CoV-2 variant detection. Data obtained here underscore the potential for wastewater surveillance of SARS-CoV-2 and other infectious agents in communities.

Abstract 1933: Improved DAMP assays for the in vitro assessment of immunogenic cell death

The extracellular levels of damage-associated molecular patterns (DAMPs) released during immunogenic cell death (ICD) are positively correlated with the magnitude and efficacy of the resulting in vivo immune response. Therefore, extracellular ATP (eATP) and high mobility group box 1 (HMGB1) have been identified as key biomarkers for their predictive capacity during in vitro ICD screening activities. Current methods for identifying eATP and HMGB1 inducers are laborious, costly, and hampered by poor throughput. To overcome these challenges, we developed easy-to-use, homogeneous, bioluminescent assays that measure dose-dependent release of these immunostimulatory agents directly in cell culture. The eATP assay utilizes an optimized ATP detection chemistry that can be employed directly to assess live-cell kinetic responses for up to 24 h, with even longer exposures supported by a staggered reagent addition approach. The HMGB1 assay measures the protein's concentration at exposure endpoint in the same sample well using complementary luciferase fragment-labelled monoclonal antibodies. We tested the utility of the assays using U20S, Jurkat and U937 cells dosed with serial dilutions of known ICD inducers (doxorubicin, idarubicin, mitoxantrone, and bortezomib). The resulting data suggest the potency of eATP and HMGB1 release is dependent upon cell model and agent but can be reproducibly and robustly measured in 96 and 384 well environments. Further, the eATP assay produced remarkable early dose-dependent response resolution whereas the HMGB1 data provided a confirmatory post-mortem ICD parameter. This new ICD biomarker detection workflow may help to efficiently define and rank-order the capacity of new chemical entities to induce apoptosis and immunogenic cell death.

Citation Format: Andrew L. Niles, Kevin R. Kupcho, Dan F. Lazar, James J. Cali. Improved DAMP assays for the in vitro assessment of immunogenic cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1933.

A live-cell assay for the real-time assessment of extracellular ATP levels

Extracellular ATP (eATP) is a potent damage associated molecular pattern (DAMP) molecule known to exert profound effects on the innate and adaptive immune responses. As such, it has become an important biomarker for studying means to pro-actively modulate inflammatory processes. Unfortunately, traditional methodologies employed for measuring eATP require cumbersome supernatant sampling, onerous time courses, or unnecessary duplication of effort. Here we describe a new reagent that is tolerable to test cells in extended exposures and enables a fully homogeneous assay method for real-time determinations of extracellular ATP levels. The reagent is introduced into assay plates containing cells at the time of stimulus introduction. The real-time feature of the format allows for sensitive, continuous accounting of eATP levels in the test model over at least 24 h. This work details our efforts to create and characterize this new reagent and to validate utility by demonstrating its use with multiple cell lines and chemically diverse eATP induction stimuli.

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 Luminescence Assay to Quantify Cell Viability in Real Time

Comprehensive understanding of cellular responses to changes in the cellular environment or by drug treatment requires time-dependent analysis ranging from hours to several days. Here, we describe a sensitive, nonlytic live-cell assay that allows continuous or 'real-time' monitoring of cell viability, growth, and cytotoxicity over an extended period of time. We illustrate the use of the assay for small drug molecule and antibody-dependent cytotoxicity studies using cancer cells in 384-well plates. We show that the ability to measure changes in live cells over time provides instantaneous information on the biological status of the cells, information about the mode of action of the drug, and offers an added advantage of preserving the cells for multiplexing with downstream applications.

Abstract 1832: A real-time extracellular ATP assay to identify modulators of the innate immune response

Damage-associated molecular patterns (DAMPs) liberated or exposed by dying cells after chemotherapeutic treatment augment innate immune responses and improve clinical outcomes as a result of the immunogenic cell death (ICD) phenotype. Extracellular ATP (eATP) is a potent DAMP that acts as a chemotactic agent for dendritic cells and as an immunomodulator for fine-tuning the inflammatory response. Current in vitro methods for identifying eATP inducers are procedurally difficult and laborious and are hampered by the instability of eATP in cell culture environments. To overcome these challenges, we have developed an easy-to-use, homogeneous, bioluminescent chemistry that can be introduced with test articles to measure dose-dependent ATP release kinetics and magnitudes of response in real time. We tested the assay using U20S and U937 cells dosed with serial dilutions of doxorubicin, idarubicin, mitoxantrone, and romidepsin. Luminescent data were continuously collected throughout the 24h exposure in 5- or 10- minute increments using a conventional multimode plate reader with CO2-independent medium, or with readers equipped with atmospheric control. When coupled with parallel cell health assays designed to measure either viability or loss of membrane integrity, the data can reveal agents that potentiate ATP release during early or late apoptosis. Our real-time data suggest the potency of eATP release is dependent upon cell model and agent and can be reproducibly and robustly measured in 96 and 384 well environments with kinetic resolution not possible by other methods. This new eATP measurement workflow may help define the capacity of new chemical entities to induce apoptosis and immunogenic cell death.

Citation Format: Andrew L. Niles, Kevin R. Kupcho, Dan F. Lazar, James J. Cali. A real-time extracellular ATP assay to identify modulators of the innate immune response [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1832.

Abstract 5595: Rapid and sensitive determination of cytokine release from cells without the need for sample transfer

Cytokines play a major role in cancer biology as inflammatory and immunomodulatory agents and are frequently measured in cell culture models and other biological samples. Various methods are available for in vitro measurement of cytokines, but they typically require sample transfer, sample dilutions, multiple wash steps, time-consuming protocols, and/or specialized instrumentation. We have utilized NanoLuc® Binary Technology (NanoBiT®) to develop a completely homogeneous and rapid assay method (< 70 min completion time) to measure cytokines released from cells in culture without the need for sample transfer and requiring only a standard, plate-reading luminometer for signal acquisition. In this approach, separate antibodies to a specific cytokine are individually labeled with either the small, 11-amino acid subunit of NanoBiT luciferase (SmBiT) or its 17.6 kDa complementary subunit (LgBiT). When SmBiT- and LgBiT-labeled antibodies converge on the target cytokine, the resultant proximity of SmBiT and LgBiT subunits reconstitutes a bright luciferase that produces light proportional to analyte levels when the substrate furimazine is present. Utilizing this technology, homogeneous bioluminescent immunoassays have been developed for several cytokines, including IL-1β, IL-2, IL-6 and IFN-γ. These assays share excellent sensitivities (LODs typically < 10 pg/ml) and broad linear ranges extending over three or more logs of analyte concentration, significantly mitigating the need for sample dilutions. Following 24-hour treatment of human PBMCs in 96-well plate format with vehicle, LPS, R848, or a combination of PMA and ionomycin, cytokine detection reagents were added directly to the culture wells containing cells and medium. Depending on cell stimulus, maximal signal to background ratios (S/B) achieved for the various cytokines assayed were 347-, 450-, 580- and 655-fold for IL-1β, IL-2, IL-6 and IFN-γ, respectively. In a separate cell model comprised of activated T cells and target Raji B cells induced for 20 hours with increasing concentrations of the bispecific T-cell engager Blincyto®, dose-dependent release of IL-2 and IFN-γ were observed with an EC50 of ~0.2 ng/ml and maximal S/B for IL-2 and IFN-γ release of 82- and 168-fold, respectively. In all cases, a calibration curve of recombinant cytokine enabled straightforward conversion of relative light units (RLU) to concentration of released cytokines. The implementation of this novel detection chemistry will enable rapid “add-and-read” assays for cytokine detection amenable for both low- and high-throughput screening applications.

Citation Format: Dan F. Lazar, Kevin R. Kupcho, Casey A. Sondgeroth, David V. Thompson, Martha A. O'Brien, Julia K. Gilden, Kevin Hsiao, James J. Cali. Rapid and sensitive determination of cytokine release from cells without the need for sample transfer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5595.

Rapid and sensitive determination of cytokine release from cells without the need for sample transfer

We have utilized NanoLuc® Binary Technology (NanoBiT®) to develop a homogeneous and rapid assay method (≤ 70 min completion time) to measure cytokines released from cells in culture without the need for sample transfer and requiring only a standard, plate-reading luminometer for signal acquisition. Separate antibodies to a specific cytokine are labeled with the small, 11-amino acid subunit of NanoBiT luciferase (SmBiT) or its 17.6 kDa complementary subunit (LgBiT). When SmBiT- and LgBiT-labeled antibodies converge on the target cytokine, the resultant proximity of SmBiT and LgBiT reconstitutes a bright luciferase that produces light proportional to analyte levels. In this manner, immunoassays have been developed for several cytokines, including IL-1β, IL-2, IL-6 and IFN-γ. In general, these assays share LLODs < 10 pg/ml and linearity over three logs of analyte concentration, mitigating the need for sample dilution. Following 24 h treatment of human PBMCs in 96-well plates with vehicle, LPS, R848, or a combination of PMA and ionomycin, cytokine detection reagents were added directly to the culture wells containing cells and medium. Depending on stimulus, maximal signal to background ratios (S/B) achieved for the cytokines were 347-, 450-, 580- and 655-fold for IL-1β, IL-2, IL-6 and IFN-γ, respectively. In a cell model comprised of activated T cells and target Raji B cells induced for 20 h with increasing bispecific T-cell engager Blincyto®, release of IL-2 and IFN-γ were observed with an EC50 of ~0.2 ng/ml and maximal S/B for IL-2 and IFN-γ of 82- and 168-fold, respectively. The implementation of this novel detection chemistry will enable rapid “add-and-read” assays for cytokine detection for both low- and high-throughput applications.

Abstract 710: Real-time apoptosis and necrosis detection in 3D spheroid cellmodels

The structural and biological complexity of cancer spheroids make them uniquely suited to address or approximate the pharmacodynamics of new chemical entities directed at chemotherapeutic reduction of tumor masses. Unfortunately, this same complexity represents a substantial technical challenge for measuring apoptosis and necrosis using conventional methods in real time. To address this challenge, we explored the use of a multiplexed bioluminescent and fluorescent, real-time assay reagent which utilizes annexin V fusion proteins containing binary elements of a complementing luciferase, a time-released luciferase substrate and an excludable DNA membrane integrity dye. The assay reagent was added to HCT-116 and HepG2 spheroids dosed with serial dilutions of panobinostat, bortezomib, or paclitaxel to examine the magnitude, potency and kinetics of the responses. Luminescent and fluorescent data were continuously collected throughout the 48h exposure using a conventional multimode plate reader equipped with atmospheric control. After the exposure period, the treated spheroids were imaged by fluorescence microscopy to assess necrotic burden as well as analyzed for remaining cellular viability using ATP content compared to untreated control. Consistent with their known modes of cytotoxic action, bortezomib produced the first measurable phoshatidylserine (PS) exposure (~8h), followed by panobinostat (~12h) and paclitaxel (18-22h). The apoptotic potencies and magnitudes of response matured thereafter as a function of time until 48h. Secondary necrosis resulting from completion of the apoptotic program lagged PS exposure in both time and magnitude. Imaging results for necrosis and ATP determinations provided orthogonal and inversely complementary verification of data values obtained with the apoptosis assay reagent. Taken together, this workflow may help define the in vitro pharmacological disposition of new chemical entities with respect to their capability to penetrate and induce apoptosis in spheroids and/or other more complex multicellular models.

Citation Format: Andrew L. Niles, Kevin R. Kupcho, Terry L. Riss, Dan F. Lazar, James J. Cali. Real-time apoptosis and necrosis detection in 3D spheroid cellmodels [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 710.

Evaluation of Luminogenic Substrates as Probe Substrates for Bacterial Cytochrome P450 Enzymes: Application to Mycobacterium tuberculosis

Several cytochrome P450 enzymes (CYPs) encoded in the genome of Mycobacterium tuberculosis (Mtb) are considered potential new drug targets due to the essential roles they play in bacterial viability and in the establishment of chronic intracellular infection. Identification of inhibitors of Mtb CYPs at present is conducted by ultraviolet-visible (UV-vis) optical titration experiments or by metabolism studies using endogenous substrates, such as cholesterol and lanosterol. The first technique requires high enzyme concentrations and volumes, while analysis of steroid hydroxylation is dependent on low-throughput analytical methods. Luciferin-based luminogenic substrates have proven to be very sensitive substrates for the high-throughput profiling of inhibitors of human CYPs. In the present study, 17 pro-luciferins were evaluated as substrates for Mtb CYP121A1, CYP124A1, CYP125A1, CYP130A1, and CYP142A1. Luciferin-BE was identified as an excellent probe substrate for CYP130A1, resulting in a high luminescence yield after addition of luciferase and adenosine triphosphate (ATP). Its applicability for high-throughput screening was supported by a high Z'-factor and high signal-to-background ratio. Using this substrate, the inhibitory properties of a selection of known inhibitors could be characterized using significantly less protein concentration when compared to UV-vis optical titration experiments. Although several luminogenic substrates were also identified for CYP121A1, CYP124A1, CYP125A1, and CYP142A1, their relatively low yield of luminescence and low signal-to-background ratios make them less suitable for high-throughput screening since high enzyme concentrations will be needed. Further structural optimization of luminogenic substrates will be necessary to obtain more sensitive probe substrates for these Mtb CYPs.

Abstract 373: Bioluminescent non-lytic metabolite and cytotoxicity assays for cancer and immunotherapy research

The growing interest in understanding metabolic adaptations that occur in cancer and immune cells in the tumor microenvironment and the advances made towards developing effective immunotherapies have increased the need for sensitive and efficient methods for studying cell metabolism and viability. We have developed bioluminescent assays for monitoring cell metabolism and cytotoxicity during cell growth and in response to environmental conditions and treatments. The plate-based assays employ coupled enzyme reactions and bioluminescent NADH detection chemistry to detect metabolites and enzymes. We used the assays in a non-lytic format, analyzing samples of cell culture medium and leaving the cells intact for additional measurements or multiplexing with other assays. In this way, changes occurring in a single well of cells were followed over time by collecting medium at multiple time points. We used assays for glucose, lactate, glutamine and glutamate detection to obtain information about the key metabolic pathways, glycolysis and glutaminolysis, and metabolically profile cancer cell lines. When we compared the metabolism of two ovarian cancer cell lines, OVCAR-3 and SKOV-3, the rates for glucose consumption and lactate secretion were similar, but the SKOV-3 cells consumed more glutamine and secreted 20-fold more glutamate. Glutamate secretion by the OVCAR-3 cells was low, only 5-fold higher than background controls. Analysis of the metabolites in cell lysates further supported the conclusion that the two cell lines differed in glutamine metabolism. The metabolite detection assays were also used to monitor metabolic pathway reprogramming in response to the environment. The induction of glycolysis is an early, critical step in the activation of T cells, and results in increased lactate production. We investigated the requirements for T-cell activation by measuring lactate levels over time and observed robust activation only in the presence of glutamine and anti-CD3/anti-CD28 costimulatory signals. In addition to metabolite levels, cell culture medium was used to assess cytotoxicity by following lactate dehydrogenase enzyme (LDH) release into cell culture medium. We used this assay to study cancer cell cytotoxicity induced by immunotherapeutic treatments, including antibody-drug conjugates (ADC) and antibody-dependent cell-mediated cytotoxicity (ADCC). The high sensitivity of the assay permitted the use of fewer cells, in 2D and 3D cultures, and the earlier detection of small changes (10 lysed cells in medium lacking serum). These sensitive bioluminescent assays require small amounts of sample and minimal sample processing to facilitate (1) identification of unique cancer cell metabolic signatures and potential therapeutic targets, (2) studies of connections between metabolism and effective immune cell function, and (3) the evaluation of cytotoxic immunotherapies.

Citation Format: Donna M. Leippe, Natasha Karassina, Michael P. Valley, James J. Cali, Jolanta Vidugiriene. Bioluminescent non-lytic metabolite and cytotoxicity assays for cancer and immunotherapy research [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 373.

Abstract 3312: A novel plate-based assay for screening autophagic activity in 2D and 3D cell culture models

The critical importance of autophagy in cell health and its proposed role in disease-relevant biology, including cancer, inflammation, and immunology, has increased the need for more effective assays to screen for agents that modulate autophagic activity. Here we utilize NanoLuc Binary Technology (NanoBiT) to develop a homogeneous plate-based assay to measure autophagic flux in cell culture models. In this approach, an exogenous LC3B (Atg8) fusion protein was tagged on its N-terminus with an 11 amino acid peptide (HiBiT) and stably expressed in mammalian cells, including U2OS and HEK293. After exposure to various treatment conditions, cellular levels of this novel autophagy reporter were determined by addition of a lytic detection reagent containing Large BiT (LgBiT). LgBiT rapidly associates with HiBiT in the cell lysate, producing a bright, luminescent enzyme in the presence of the furimazine substrate. The bright signal allows low levels of expression of the reporter, maximizing the assay response, and the signal is stable, allowing assay of multiple 96- or 384-well plates in the same experiment. In response to autophagic stimuli, including nutrient deprivation and various mTORC inhibitors (e.g., PP242 and rapamycin), autophagic degradation of expressed LC3 reporter was evident by reduced assay signal. In contrast, in response to both upstream (e.g., 3-MA and wortmannin) and downstream (e.g., bafilomycin A1 and chloroquine) inhibitors of the autophagy pathway, degradation of the autophagic reporter was effectively blocked and assay signal was consistently increased as predicted. Compound effects were time dependent and stratified according to expected potency and efficacy of the test agents employed. The use of a mutant reporter based on LC3G120A further demonstrated the specificity of the wild-type LC3 reporter for the detection of autophagic activity. When assayed in 384-well plates with automation, HEK293 autophagy reporter cells produced Z’ values of ~0.7 in response to autophagy induction with PP242, while subsequent blockade of autophagy with bafilomycin A1 resulted in Z’ values of ~0.8. This data, and subsequent LOPAC library screening, indicates the potential utility of this assay method for HTS applications. In addition, the HEK293 autophagy reporter cells can be induced to form 3D cell spheroids, thus allowing investigation of assay performance in this more complex model. Autophagy reporter levels increased with increasing spheroid size (up to 650 μm diameter tested) in a manner proportional to a surrogate measure of viable cell number. Importantly, both induction and inhibition of autophagic activity was easily detected following PP242 and bafilomycin A1 treatment, respectively. Using this novel plate-based assay system for the determination of autophagic flux, it is possible to screen test agents and quantitatively determine both the potency and efficacy of autophagy modulation.

Citation Format: Dan F. Lazar, Amani A. Gillette, Braeden L. Butler, Christopher T. Eggers, Brock F. Binkowski, Gediminas Vidugiris, Michael R. Slater, Dongping Ma, James J. Cali. A novel plate-based assay for screening autophagic activity in 2D and 3D cell culture models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3312. doi:10.1158/1538-7445.AM2017-3312

Cell-based, bioluminescent assay for monitoring the interaction between PCSK9 and the LDL receptor

Monitoring the expression of cell-surface receptors, their interaction with extracellular ligands, and their fate upon ligand binding is important for understanding receptor function and developing new therapies. We describe a cell-based method that utilizes bioluminescent protein complementation technology to interrogate binding of a cellular receptor with its extracellular protein ligand, specifically LDL receptor (LDLR) and proprotein convertase subtilisin/kexin type 9 (PCSK9). Purified, full-length tagged PCSK9 is added to assay wells containing cells that stably express LDLR with an extracellular complementary tag. When the tagged PCSK9 binds the receptor, a bright luminescence signal is generated. The interaction is detected at the cell membrane with add-and-read simplicity, no wash steps, and flexibility, allowing data to be collected in endpoint format, kinetically, or with bioluminescent imaging. The assay is flexible, is rapid, and reports accurate biology. It is amenable to 96-well and 384-well formats, and the robustness allows for screening of new drug candidates (Z′ = 0.83). The assay reports correct potencies for antibody titrations across a 50%–150% potency range and detects potency changes due to heat stress, suggesting that it may be useful during drug development. This assay technology can be broadly applied when studying other receptors with their extracellular ligands, whether protein or small-molecule binding partners.

Bioluminescent Assays for Glucose and Glutamine Metabolism: High-Throughput Screening for Changes in Extracellular and Intracellular Metabolites

Cancer cell metabolism is a complex, dynamic network of regulated pathways. Interrogation of this network would benefit from rapid, sensitive techniques that are adaptable to high-throughput formats, facilitating novel compound screening. This requires assays that have minimal sample preparation and are adaptable to lower-volume 384-well formats and automation. Here we describe bioluminescent glucose, lactate, glutamine, and glutamate detection assays that are well suited for high-throughput analysis of two major metabolic pathways in cancer cells: glycolysis and glutaminolysis. The sensitivity (1–5 pmol/sample), broad linear range (0.1–100 µM), and wide dynamic range (>100-fold) are advantageous for measuring both extracellular and intracellular metabolites. Importantly, the assays incorporate rapid inactivation of endogenous enzymes, eliminating deproteinization steps required by other methods. Using ovarian cancer cell lines as a model system, the assays were used to monitor changes in glucose and glutamine consumption and lactate and glutamate secretion over time. Homogeneous formats of the lactate and glutamate assays were robust (Z′ = 0.6–0.9) and could be multiplexed with a real-time viability assay to generate internally controlled data. Screening a small-compound library with these assays resulted in the identification of both inhibitors and activators of lactate and glutamate production.

Bioluminescent, Nonlytic, Real-Time Cell Viability Assay and Use in Inhibitor Screening

Real-time continuous monitoring of cellular processes offers distinct advantages over traditional endpoint assays. A comprehensive representation of the changes occurring in live cells over the entire length of an experiment provides information about the biological status of the cell and informs decisions about the timing of treatments or the use of other functional endpoint assays. We describe a homogeneous, nonlytic, bioluminescent assay that measures cell viability in real time. This time-dependent measurement allowed us to monitor cell health for 72 h from the same test samples, distinguish differential cell growth, and investigate drug mechanism of action by analyzing time- and dose-dependent drug effects. The real-time measurements also allowed us to detect cell death immediately (>75% signal decrease within 15 min of digitonin addition), analyze drug potency versus efficacy, and identify cytostatic versus toxic drug effects. We screened an oncology compound library (Z′ = 0.7) and identified compounds with varying activity at different time points (1.6% of the library showed activity within 3 h, whereas 35.4% showed a response by 47 h). The assay compared well with orthogonal endpoint cell viability assays and additionally provided data at multiple time points and the opportunity to multiplex assays on the same cells. To test the advantage of time-dependent measurements to direct optimal timing of downstream applications, we used the real-time cell viability assay to determine the ideal time to measure caspase activity by monitoring the onset of cell death and multiplexing a luminescent caspase activation assay on the same test samples.

Bioluminescent cell-based NAD(P)/NAD(P)H assays for rapid dinucleotide measurement and inhibitor screening

Abstract The central role of nicotinamide adenine dinucleotides in cellular energy metabolism and signaling makes them important nodes that link the metabolic state of cells with energy homeostasis and gene regulation. In this study, we describe the implementation of cell-based bioluminescence assays for rapid and sensitive measurement of those important redox cofactors. We show that the sensitivity of the assays (limit of detection ∼0.5 nM) enables the selective detection of total amounts of nonphosphorylated or phosphorylated dinucleotides directly in cell lysates. The total amount of NAD+NADH or NADP+NADPH levels can be detected in as low as 300 or 600 cells/well, respectively. The signal remains linear up to 5,000 cells/well with the maximum signal-to-background ratios ranging from 100 to 200 for NAD+NADH and from 50 to 100 for NADP+NADPH detection. The assays are robust (Z' value >0.7) and the inhibitor response curves generated using a known NAD biosynthetic pathway inhibitor FK866 correlate well with the reported data. More importantly, by multiplexing the dinucleotide detection assays with a fluorescent nonmetabolic cell viability assay, we show that dinucleotide levels can be decreased dramatically (>80%) by FK866 treatment before changes in cell viability are detected. The utility of the assays to identify modulators of intracellular nicotinamide adenine dinucleotide levels was further confirmed using an oncology active compound library, where novel dinucleotide regulating compounds were identified. For example, the histone deacetylase inhibitor entinostat was a potent inhibitor of cellular nicotinamide adenine dinucleotides, whereas the selective estrogen receptor modulator raloxifene unexpectedly caused a twofold increase in cellular nicotinamide adenine dinucleotide levels.

Abstract 5446: Continuous real-time measurement of live and dead cells in culture over multiple days

Recently developed assay technologies have made it possible to use a multi-well plate reader to estimate the number of live or dead cells in culture in real time over a period of days to monitor the effects of long term exposure to test substances. An advantage of the real time assay chemistries is that the cells remain viable and available for other measurements. The purpose of this study was to determine if the real time assay methods could be multiplexed with other assay endpoints and applied to three dimensional (3D) culture models. The measurement of the number of live cells in real time is accomplished by providing a pro-substrate that viable cells (but not dead cells) can convert into a substrate for a luciferase derived from a marine shrimp. The pro-substrate and luciferase can be added with a single reagent addition step and because they are not toxic, they can be incubated with cells in culture for up to three days. Live cell conversion of the pro-substrate into a substrate for luciferase results in a luminescent signal that is proportional to the number of live cells. The signal diminishes immediately upon cell death. Detection of dead cells in real time is accomplished by using a fluorogenic DNA binding dye that is non-permeant and thus non-toxic to live cells. The dye enters dead cells that have a compromised membrane, binds to DNA, and becomes fluorescent. We have demonstrated that the real time assays can be multiplexed to measure both live and dead cells in the same sample. We further demonstrate the use of these assays to measure viability of cells in 3D spheroids formed using the hanging drop culture technique. We also demonstrate multiplexing of real time assays with subsequent measurement of apoptosis or extraction of RNA for expression studies. Utilization of real time assay chemistries that are non-toxic enabled repeated recording of data in a kinetic mode from the same sample of cells which eliminated the need for duplicate cultures and provided flexibility during assay protocol development. The ability to multiplex real time assays improved overall lab efficiency by eliminating the need for duplicate cultures for each experiment.

Citation Format: Terry Riss, Jolanta Vidugiriene, Sarah Duellman, Wenhui Zhou, Gediminas Vidugiris, Mike Valley, Jean Osterman, Ruslan Arbit, Laurent Bernad, Poncho Meisenheimer, James J. Cali. Continuous real-time measurement of live and dead cells in culture over multiple days. [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 5446. doi:10.1158/1538-7445.AM2015-5446

Abstract 5435: A bioluminescent assay for measuring glucose uptake

Glucose management is a key biological process. In adipose tissue and skeletal muscle, decreased rates of glucose uptake commonly associated with diabetes mellitus lead to chronic hyperglycemia and a wide array of physiological damage. In contrast, the overexpression of glucose transporters in cancer cells results in increased rates of glucose uptake to support their high rates of proliferation. Thus, activators and inhibitors of glucose uptake are useful for both diabetes management and anticancer therapies. The standard method of assaying glucose uptake involves addition of a radioactive glucose analog (2-deoxyglucose) and measurement of the accumulation of the stable and impermeable phosphorylated derivative, 2-deoxyglucose-6-phosphate (2DG6P). However, radioactive assays are laborious, costly, and require special handling of radioactive materials and waste. A simpler assay can be made by measuring the production of NADPH through the oxidation of 2DG6P by glucose-6-phosphate dehydrogenase. We have developed a bioluminescent glucose uptake assay that is both rapid and convenient and exhibits a larger signal window than comparable fluorescent or colorimetric approaches. The utility of this assay will be demonstrated with both cancer cells and insulin-sensitive 3T3L1 adipocytes and L6 myotubes.

Citation Format: Michael P. Valley, Mary Sobol, Jolanta Vidugiriene, James J. Cali. A bioluminescent assay for measuring glucose uptake. [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 5435. doi:10.1158/1538-7445.AM2015-5435

Altered cytotoxicity of ROS-inducing compounds by sodium pyruvate in cell culture medium depends on the location of ROS generation

Induction of oxidative stress by drugs and other xenobiotics is an important mechanism of cytotoxicity. However, in vitro studies on the relationship between oxidative stress and cytotoxicity in cultured cells is frequently complicated by the fact that cell culture medium components affect reactive oxygen species (ROS) exposures in ways that vary with the mode of ROS production. The objectives of this study were to first determine the mode of ROS induction by certain model compounds when they are applied to cultured cells, and then to determine how ROS induction and cytotoxicity were affected by the ROS-quenching medium component pyruvate. Three compounds, eseroline, benserazide, and pyrogallol induced H₂O₂ in cell culture media independent of cells. However, another compound, menadione, induced H₂O₂ in a manner largely dependent on the MDA-MB-231 breast cancer cells used in this study, which is consistent with its known mechanism of inducing ROS through intracellular redox cycling. 1 mM pyruvate, as well as catalase, reduced the H₂O₂ in culture wells with each ROS inducer tested but it only reduced the cytotoxicity of cell-independent inducers. It reduced the cytotoxicity of benserazide and pyrogallol >10-fold and of eseroline about 2.5-fold, but had no effect on menadione cytotoxicity. From this data, it was concluded that depending on the mechanism of ROS induction, whether intra- or extracellular, a ROS-quenching medium component such as pyruvate will differentially affect the net ROS-induction and cytotoxicity of a test compound.

Abstract 3743: Bioluminescent, non-lytic, real-time cell viability assay

Cell-based assay development for cancer drug discovery continues to advance toward more innovative methods that provide efficient workflow and meaningful data. Rapid, sensitive techniques that are non-lytic and therefore facilitate multiplexing with a wide range of assays allow more data to be gained per well and conserve precious samples. Real time measurement of cell viability also allows numerous measurements over time without the need for separate plates at each time point. Real time measurements allow unique analyses including interrogation of the timing of drug killing, identification of static vs toxic drug effects, and determination of the ideal time to multiplex an additional assay. Cancer drug discovery would benefit from novel assay technologies that allow real time measurements with multiplexing capability.

We have developed a homogeneous, non-lytic, and bioluminescent method to analyze cell viability in real time through measurement of the reducing potential of the cell. The signal correlates with the number of viable cells making it well-suited for cytotoxicity studies. This Real Time Cell Viability Assay utilizes the NanoLuc luciferase enzyme, which is 100-fold brighter than either firefly (Photinus pyralis) or Renilla reniformis luciferase, and the novel substrate, furimazine. Together these reagents produce high intensity luminescence through an ATP-independent reaction.

The assay can be performed in two formats, live cell endpoint or continuous read. The live cell endpoint method is sensitive, rapid, and enables extensive multiplexing opportunities due to the non-lytic measurement and signal depletion upon cell lysis. When the assay is set up in the continuous read format, the cell viability reagents can be added at the same time as cell plating, drug dosing, or at whatever point in the assay the researcher would like to start obtaining viability readings. The luminescent signal can be continually monitored from the same wells over an extended period of time to analyze cell viability in real time.

This real time cell viability assay enables non-lytic cell viability measurements, extensive multiplexing options including both fluorescent and luminescent assays with no special filter requirements, straightforward normalization studies, conservation of precious samples and reagents, and a sensitive, real time measurement of cell viability.

Citation Format: Sarah J. Duellman, Jolanta Vidugiriene, Wenhui Zhou, Jean Osterman, Ruslan Arbit, Laurent Bernad, Poncho Meisenheimer, James J. Cali. Bioluminescent, non-lytic, real-time cell viability assay. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3743. doi:10.1158/1538-7445.AM2014-3743

Abstract 5531: A bioluminescent cell viability assay optimized for 3D microtissues

It has been well demonstrated that the morphology, gene expression, and overall biological response of cells assessed in 3-dimensional (3D) culture models are frequently more physiologically relevant than that of cells studied in standard 2D culture formats. In spite of rapidly growing interest, one hindrance to the use of 3D models for drug discovery and other research efforts is the lack of convenient and effective assays explicitly validated for application to 3D microtissues. Here we report on a bioluminescent ATP-detection assay comprised of both an improved formulation and an optimized protocol specifically designed to measure the viability of cells grown in 3D culture. The ability of the 3D-optimized reagent to effectively lyse cells from throughout the full thickness of 3D microtissues, including cancer cell spheroids, was clearly demonstrated by use of confocal laser fluorescent microscopy in conjunction with a fluorogenic, membrane-impermeant DNA-binding dye. Importantly, the assay's ability to accurately report the ATP content, and therefore viability, of various 3D microtissues (including a range of cancer cell line spheroids) was demonstrated by comparison to a trichloroacetic acid ATP extraction method. In scaffold-free as well as scaffold-dependent 3D models, recovery and detection of greater than 80% of ATP present was routinely observed. In contrast, another frequently used ATP-detection assay was found to have greatly reduced lytic and ATP detection properties (<50% recovery). This new, homogeneous 3D-assay format requires minimal sample manipulation, a brief incubation period (generally less than 30 min), and exhibits excellent sensitivity. It should be amenable to both low- and high-throughput applications and accurately report drug sensitivities of cells assayed in both 2D and 3D culture models.

Citation Format: Michael P. Valley, Chad Zimprich, James J. Cali, Dan F. Lazar. A bioluminescent cell viability assay optimized for 3D microtissues. [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 5531. doi:10.1158/1538-7445.AM2013-5531

Bioluminescent assays for cytochrome P450 enzymes

The cytochrome P450 (CYP) family contains 57 enzymes in humans. The activity of CYPs against xenobiotics is a primary consideration in drug optimization efforts. Here we describe a series of bioluminescent assays that enable the rapid profiling of CYP activity against compound collections. The assays employ a coupled-enzyme format where firefly luciferase is used to measure CYP enzyme activity through metabolism of pro-luciferase substrates.

Molecular imaging of cytochrome P450 activity in mice

Detailed knowledge of drug metabolism is relevant information provided by preclinical drug development research. Oxidative enzymes such as those belonging to P450 family of cytochromes (CYP) play a prominent role in drug metabolism. Here, we propose an innovative method based on bioluminescence in vivo imaging which has the potential to simplify the in vivo measurement of CYP activity also providing a dynamic measure of the effects of a drug on a specific P450 enzyme complex in a living mouse. The method is based on a pro-luciferin which can be converted into the active luciferase substrate by a specific P450 activity. The pro-luciferin is administered to a luciferase reporter mouse which produces luminescent signals in relation to the cytochrome activity present in each tissue. The photon emission generated can be easily localized and quantified by optical imaging. To demonstrate the validity of the system, we pharmacologically induced hepatic Cyp3a in the reporter mouse and proved that pro-luciferin administration generates a Cyp3a selective signal in the chest area that can be efficiently detected by optical imaging. The kind of tool generated has the potential to be exploited for the study of additional CYPs.

Proluciferin acetals as bioluminogenic substrates for cytochrome P450 activity and probes for CYP3A inhibition

Cytochrome P450 (P450) assays use probe substrates to interrogate the influence of new chemical entities toward P450 enzymes. We report the synthesis and study of a family of bioluminogenic luciferin acetal substrates that are oxidized by P450 enzymes to form luciferase substrates. The luciferin acetals were screened against a panel of purified P450 enzymes. In particular, one proluciferin acetal has demonstrated sensitive and selective CYP3A4-catalyzed oxidation to a luciferin ester-K(m) and k(cat) are 2.88 μM and 5.87 pmol metabolite · min(-1) · pmol enzyme(-1), respectively. The proluciferin acetal was used as a probe substrate to measure IC(50) values of known inhibitors against recombinant CYP3A4 or human liver microsomes. IC(50) values for the known inhibitors correlate strongly with IC(50) values calculated from the traditional high-performance liquid chromatography-based probe substrate testosterone. Luciferin acetals are rapidly oxidized to unstable hemi-orthoesters by CYP3A resulting in luciferin esters and, therefore, are conducive to simple rapid CYP3A bioluminescent assays.

Automated Triplexed Hepatocyte-Based Viability and CYP1A and -3A Induction Assays

Cytochrome P450 (CYP) enzymes are key players in drug metabolism. Therefore, it is essential to understand how these enzymes can be affected by xenobiotics with regards to induction and toxicity to avoid potential drug–drug interactions. Typically, information has been gathered by combining data from multiple experiments, which is time-consuming and labor intensive, and interassay variability may lead to misinterpretation. Monitoring CYP induction and cytotoxicity by xenobiotics using an automated, multiplexed format can decrease workload and increase data confidence. Here the authors demonstrate the ability to monitor CYP1A and CYP3A4 induction, combined with a cytotoxicity measurement, from a single microplate well using cryopreserved human hepatocytes. The assay procedure was automated in a 384-well format, including cell manipulations, compound titration and transfer, and reagent dispensing, using simple robotic instrumentation. EC50 and Emax values were derived for multiple known CYP1A and -3A4 inducers. Induction and toxicological responses in the triplex system were validated based on literature values from conventional single-parameter assays. Validation and pharmacology data confirm that multiplexed cell-based CYP assays can simplify workload, save time and effort, and generate biologically relevant data.

Automated luminescence-based cytochrome P450 profiling using a simple, elegant robotic platform

The determination of inhibitory effects that lead compounds have on cytochrome P450 (CYP) enzymes is an important part of today's drug discovery process. Assays can be performed early in the discovery process to predict adverse drug-drug interactions caused by CYP inhibition and to minimize the costs associated with terminating candidates in late stage development or worse, removing a drug from the market after launch. For early discovery work, testing substantial numbers of compounds is desirable, thus automated "mix and read" assays are beneficial. Here, we demonstrate the automation of the CYP profiling process using a simple, yet robust robotic platform. Compound titration, as well as transfer of compounds and assay components was performed by the same automated pipetting system. IC(50)s of small molecule drugs were determined using recombinant CYP enzymes, CYP3A4, -2C9, and -2D6 and luminogenic substrates specific to each. Compounds were profiled against all three enzymes on the same 384-well assay plate.

N-Alkylated 6'-aminoluciferins are bioluminescent substrates for Ultra-Glo and QuantiLum luciferase: new potential scaffolds for bioluminescent assays

A set of 6'-alkylated aminoluciferins are shown to be bioluminescent substrates for Ultra-Glo and QuantiLum luciferases. These studies demonstrate that both the engineered and wild-type firefly luciferases tolerate much greater steric bulk at the 6' position of luciferin than has been previously reported. The nature of the alkyl substituent strongly affects the strength of the bioluminescent signal, which varies widely based on size, shape, and charge. Several compounds were observed to generate more light than the corresponding unsubstituted 6'-aminoluciferin. Determination of Michaelis-Menten constants for the substrates with Ultra-Glo indicated that the variation arises primarily from differences in V max, ranging from 1.33 x 10 (4) to 332 x 10 (4) relative light units, but in some cases K m (0.73-10.8 microM) also plays a role. Molecular modeling results suggest that interactions of the side chain with a hydrogen-bonding network at the base of the luciferin binding pocket may influence substrate-enzyme binding.

Bioluminescent assays for ADMET

Bioluminescent assays couple a limiting component of a luciferase-catalyzed photon-emitting reaction to a variable parameter of interest, while holding the other components constant or non-limiting. In this way light output varies with the parameter of interest. This review describes three bioluminescent assay types that use firefly luciferase to measure properties of drugs and other xenobiotics which affect their absorption, distribution, metabolism, elimination and toxicity. First, levels of the luciferase enzyme itself are measured in gene reporter assays that place a luciferase cDNA under the control of regulatory sequences from ADMET-related genes. This approach identifies activators of nuclear receptors that regulate expression of genes encoding drug-metabolizing enzymes and drug transporters. Second, drug effects on enzyme activities are monitored with luminogenic probe substrates that are inactive derivatives of the luciferase substrate luciferin. The enzymes of interest convert the substrates to free luciferin, which is detected in a second reaction with luciferase. This approach is used with the drug-metabolizing CYP and monoamine oxidase enzymes, apoptosis-associated caspase proteases, a marker protease for non-viable cells and with glutathione-S-transferase to measure glutathione levels in cell lysates. Third, ATP concentration is monitored as a marker of cell viability or cell death and as a way of identifying substrates for the ATP-dependent drug transporter, P-glycoprotein. Luciferase activity is measured in the presence of a sample that supplies the requisite luciferase substrate, ATP, so that light output varies with ATP concentration. The bioluminescent ADMET assays are rapid and sensitive, amenable to automated high-throughput applications and offer significant advantages over alternative methods.

A bioluminescent assay for monoamine oxidase activity

This article describes a novel two-step homogeneous bioluminescent assay for monoamine oxidase (MAO) that is simple, sensitive, and amenable to high-throughput screening. In the first step, MAO reacts with an aminopropylether analog of methyl ester luciferin. In the second step, a luciferin detection reagent inactivates MAO and converts the product of the first step into a luminescent signal. The amount of light produced is proportional to the amount of MAO and the time of incubation in the first step, but the luminescent signal is stable in the second step with a half-life greater than 5h. The assay has high precision, is more sensitive than current fluorescent methods, and can accurately measure the binding constants of known substrates and inhibitors. An automated screen of the Sigma-RBI Library of Pharmacologically Active Compounds (LOPAC(1280)) revealed a surprisingly high percentage of MAO inhibitors (16%) with a low false hit rate (0.9%). This implies that a significant number of compounds interact with the MAO enzymes and suggests that it is important to include MAO assays in drug metabolism studies. Other advantages of this bioluminescent assay over comparable fluorescent assays are discussed.

Luminogenic cytochrome P450 assays

Luminogenic cytochrome P450 (CYP) assays couple CYP enzyme activity to firefly luciferase luminescence in a technology called P450-Glo(TM) (Promega). Luminogenic substrates are used in assays of human CYP1A1, -1A2, -1B1, -2C8, -2C9, -2C19, -2D6, -2J2, -3A4, -3A7, -4A11, -4F3B, -4F12 and -19. The assays detect dose-dependent CYP inhibition by test compounds against recombinant CYP enzymes or liver microsomes. Induction or inhibition of CYP activities in cultured hepatocytes is measured in a nonlytic approach that leaves cells intact for additional analysis. Luminogenic CYP assays offer advantages of speed and safety over HPLC and radiochemical-based methods. Compared with fluorogenic methods the approach offers advantages of improved sensitivity and decreased interference between optical properties of test compound and CYP substrate. These homogenous assays are sensitive and robust tools for high-throughput CYP screening in early drug discovery.

Type VIII adenylyl cyclase in rat beta cells: coincidence signal detector/generator for glucose and GLP-1

AIMS/HYPOTHESIS

The secretory function of pancreatic beta cells is synergistically stimulated by two signalling pathways which mediate the effects of nutrients and hormones such as glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) or glucagon. These hormones are known to activate adenylyl cyclase in beta cells. We examined the type of adenylyl cyclase that is associated with this synergistic interaction.

METHODS

Insulin release, cAMP production, adenylyl cyclase activity, mRNA and protein expression were measured in fluorescence-activated cell sorter-purified rat beta cells and in the rat beta-cell lines RINm5F, INS-1 832/13 and INS-1 832/2.

RESULTS

In primary beta cells, glucagon and GLP-1 synergistically potentiate the stimulatory effect of 20 mmol/l glucose on insulin release and cAMP production. Both effects are abrogated in the presence of the L-type Ca(2+)-channel blocker verapamil. The cAMP-producing activity of adenylyl cyclase in membranes from RINm5F cells is synergistically increased by Ca(2+)-calmodulin and recombinant GTP(gamma)S-activated G(s alpha)-protein subunits. This type of regulation is characteristic for type I and type VIII AC isoforms. Consistent with this functional data, AC mRNA analysis shows abundant expression of type VI AC, four splice variants of type VIII AC and low expression level of type I AC in beta cells. Type VIII AC expression at the protein level was observed using immunoblots of RINm5F cell extracts.

CONCLUSION/INTERPRETATION

This study identifies type VIII AC in insulin-secreting cells as one of the potential molecular targets for synergism between GLP-1 receptor mediated and glucose-mediated signalling.

Dimerization of mammalian adenylate cyclases

Mammalian adenylate cyclases are predicted to possess complex topologies, comprising two cassettes of six transmembrane-spanning motifs followed by a cytosolic, catalytic ATP-binding domain. Recent studies have begun to provide insights on the tertiary assembly of these proteins; crystallographic analysis has revealed that the two cytosolic domains dimerize to form a catalytic core, while more recent biochemical and cell biological analysis shows that the two transmembrane cassettes also associate to facilitate the functional assembly and trafficking of the enzyme. The older literature had suggested that adenylate cyclases might form higher order aggregates, although the methods used did not necessarily provide convincing evidence of biologically relevant events. In the present study, we have pursued this question by a variety of approaches, including rescue or suppression of function by variously modified molecules, coimmunoprecipitation and fluorescence resonance energy transfer (FRET) analysis between molecules in living cells. The results strongly suggest that adenylate cyclases dimerize (or oligomerize) via their hydrophobic domains. It is speculated that this divalent property may allow adenylate cyclases to participate in multimeric signaling assemblies.

Isozyme-dependent sensitivity of adenylyl cyclases to P-site-mediated inhibition by adenine nucleosides and nucleoside 3'-polyphosphates

Recombinant adenylyl cyclase isozyme Types I, II, VI, VII, and three splice variants of Type VIII were compared for their sensitivity to P-site-mediated inhibition by several adenine nucleoside derivatives and by the family of recently synthesized adenine nucleoside 3'-polyphosphates (Désaubry, L., Shoshani, I., and Johnson, R. A. (1996) J. Biol. Chem. 271, 14028-14034). Inhibitory potencies were dependent on isozyme type, the mode of activation of the respective isozymes, and on P-site ligand. For the nucleoside derivatives potency typically followed the order 2',5'-dideoxyadenosine (2',5'-ddAdo) > beta-adenosine > 9-(cyclopentyl)-adenine (9-CP-Ade) >/= 9-(tetrahydrofuryl)-adenine (9-THF-Ade; SQ 22,536), with the exception of Type II adenylyl cyclase, which was essentially insensitive to inhibition by 9-CP-Ade. For the adenine nucleoside 3'-polyphosphates inhibitory potency followed the order Ado < 2'-dAdo < 2',5'-ddAdo and 3'-mono- < 3'-di- < 3'-triphosphate. Differences in potency of these ligands were noted between isozymes. The most potent ligand was 2',5'-dd-3'-ATP with IC50 values of 40-300 nM. The data demonstrate isozyme selectivity for some ligands, suggesting the possibility of isozyme-selective inhibitors to take advantage of differences in P-site domains among adenylyl cyclase isozymes. Differential expression of adenylyl cyclase isozymes may dictate the physiological sensitivity and hence importance of this regulatory mechanism in different cells or tissues.

Splice variants of type VIII adenylyl cyclase. Differences in glycosylation and regulation by Ca2+/calmodulin

Three alternatively spliced type VIII adenylyl cyclase messages have been identified by cDNA cloning and amplification from rat brain cDNA. Type VIII-A was previously referred to simply as type VIII (Cali, J. J., Zwaagstra, J. C., Mons, N., Cooper, D. M. F., and Krupinski, J. (1994) J. Biol. Chem. 269, 12190-12195). The types VIII-B and -C cDNAs differ from that of type VIII-A by deletion of 90 and 198 base pair exons, respectively, which encode a 30-amino acid extracellular domain with two consensus sites for N-linked glycosylation and a 66-amino acid cytoplasmic domain. Stable expression of types VIII-A, -B, and -C cDNAs in human embryonal kidney 293 (HEK-293) cells leads to the appearance of novel proteins, which are recognized by type VIII-specific antibodies and which co-migrate with immunoreactive species detected on immunoblots of rat brain membranes. Types VIII-A and -C are modified by N-linked glycosylation, while type VIII-B is insensitive to treatment with N-glycosidase F. An influx of extracellular Ca2+ stimulates cAMP accumulation in HEK-293 cells stably expressing type VIII-A, -B, or -C, but not in control cells. Adenylyl cyclase activity of each of the variants is stimulated by Ca2+/calmodulin and the EC50 for activation of type VIII-C is one fourth of that for either type VIII-A or -B. Type VIII-C also has a distinct Km for substrate, which is approximately 4-12-fold higher than that for types VIII-A or -B depending on whether Mn2+ or Mg2+ is the counterion for ATP. The differences in the structural and enzymatic properties of these three variants are discussed.

Type VIII adenylyl cyclase. A Ca2+/calmodulin-stimulated enzyme expressed in discrete regions of rat brain

A cDNA that encodes type VIII adenylyl cyclase has been isolated from two rat brain libraries. The open reading frame encodes a 1248-amino acid protein predicted to have two sets of six transmembrane spans and two putative nucleotide binding domains as is characteristic of other mammalian adenylyl cyclases. Two type VIII messages are detected in rat brain with estimated sizes of 5.5 and 4.4 kilobases. In situ hybridization indicates that the type VIII messages are most abundantly expressed in the granule cells of the dentate gyrus, the pyramidal cells of hippocampal fields CA1-CA3, the entorhinal cortex, and the piriform cortex. Hybridization is also detected in the neocortex, the amygdaloid complex, and regions of the thalamus and hypothalamus. Stable expression of the type VIII cDNA in human embryonal kidney cells leads to the appearance of a novel 165-kDa glycoprotein in the membrane fraction. Stimulation of these cells with agents that increase intracellular Ca2+ results in up to 43-fold increases in cAMP accumulation over that of control cells transfected with the expression vector. Addition of isoproterenol alone does not lead to type VIII-specific effects in intact cells. Adenylyl cyclase activity in membranes prepared from type VIII-transformed cells is stimulated up to 40-fold by the addition of Ca2+/calmodulin (EC50 = 53 nM calmodulin). The addition of activated recombinant alpha subunit of Gs synergistically increases the Ca2+/calmodulin-stimulated activity. A possible role for type VIII adenylyl cyclase in long-term potentiation is discussed.

Frameshift and splice-junction mutations in the sterol 27-hydroxylase gene cause cerebrotendinous xanthomatosis in Jews or Moroccan origin

The sterol 27-hydroxylase (EC 1.14.13.15) catalyzes steps in the oxidation of sterol intermediates that form bile acids. Mutations in this gene give rise to the autosomal recessive disease cerebrotendinous xanthomatosis (CTX). CTX is characterized by tendon xanthomas, cataracts, a multitude of neurological manifestations, and premature atherosclerosis. A relatively high prevalence of the disease has been noted in Jews originating from Morocco. The major objectives of the present investigation were to determine the gene structure and characterize the common mutant alleles that cause CTX in Moroccan Jews. The gene contains nine exons and eight introns and encompasses at least 18.6 kb of DNA. The putative promoter region is rich in guanidine and cytosine residues and contains potential binding sites for the transcription factor Sp1 and the liver transcription factor, LF-B1. Blotting analysis revealed that the mutant alleles do not produce any detectable sterol 27-hydroxylase mRNA. No major gene rearrangements were found and single-strand conformational polymorphism followed by sequence analysis identified two underlying mutations: deletion of thymidine in exon 4 and a guanosine to adenosine substitution at the 3' splice acceptor site of intron 4 of the gene. The molecular characterization of CTX in Jews of Moroccan origin provides a definitive diagnosis of this treatable disease.

Cloning of the human cholesterol 7 alpha-hydroxylase gene (CYP7) and localization to chromosome 8q11-q12

Cholesterol 7 alpha-hydroxylase (7 alpha-hydroxylase) is a microsomal cytochrome P450 that catalyzes the first step in bile acid synthesis. In this paper, we describe the cloning, characterization, and chromosomal mapping of the human 7 alpha-hydroxylase gene (CYP7). The gene spans 10 kb and contains six exons and five introns. The exon-intron boundaries are completely conserved between the human and rat genes. Sequencing of the 5' flanking region revealed consensus recognition sequences for a number of liver-specific transcription factors. The human CYP7 gene was mapped to chromosome 8q11-q12 using both mouse-human somatic cell hybrids and in situ chromosomal hybridization studies. A total of four single-stranded conformation-dependent DNA polymorphisms and an Alu sequence-related polymorphism were identified. Of the individuals analyzed, 80% were heterozygous for at least one of these five polymorphisms. The localization and characterization of the human 7 alpha-hydroxylase gene, as well as the identification of polymorphisms, provide the molecular tools necessary to investigate the role of this gene in disorders of cholesterol and bile acid metabolism.

Selective tissue distribution of G protein gamma subunits, including a new form of the gamma subunits identified by cDNA cloning

The GTP-binding regulatory proteins (G proteins) that transduce signals from receptors to effectors are composed of alpha, beta, and gamma subunits. Whereas the role of alpha subunits in directly regulating effector activity is widely accepted, it has recently been demonstrated that beta gamma subunits may also directly regulate effector activity. This has made clear the importance of identifying and characterizing beta and gamma subunits. We have isolated a cDNA clone encoding a new gamma subunit, referred to here as the gamma 7 subunit, using probes based on peptide sequences of a gamma subunit previously purified from bovine brain. The clone contains a 1.47-kilobase cDNA insert, which includes an open reading frame of 204 base pairs that predicts a 68-amino acid polypeptide with a calculated M(r) of 7553. The predicted protein shares amino acid identities with the other known gamma subunits, ranging from 38 to 68%. Also characteristic of gamma subunits is a carboxyl-terminal CAAX motif. The expression of the gamma 7 subunit as well as the gamma 2, gamma 3, and gamma 5 subunits was examined in several bovine tissues at both the mRNA and protein levels. Whereas the gamma 2 and gamma 3 subunits were selectively expressed in brain, the gamma 5 and gamma 7 subunits were expressed in a variety of tissues. Thus, the gamma 5 and gamma 7 subunits are the first G protein gamma subunits known that could participate in the regulation of widely distributed signal transduction pathways.

Characterization of human sterol 27-hydroxylase. A mitochondrial cytochrome P-450 that catalyzes multiple oxidation reaction in bile acid biosynthesis

The enzyme sterol 27-hydroxylase catalyzes the first step in the oxidation of the side chain of sterol intermediates in the bile acid synthesis pathway. Human sterol 27-hydroxylase cDNAs were isolated from a liver cDNA library by cross-hybridization with a previously cloned rabbit cDNA probe. DNA sequence analysis of hybridization-positive clones predicted a human sterol 27-hydroxylase consisting of a 33-amino-acid mitochondrial signal sequence followed by a mature protein of 498 amino acids. RNA blotting experiments demonstrated sterol 27-hydroxylase mRNAs of approximately 1.8 to 2.2 kilobases in liver and fibroblast cells. The steady state levels of the mRNA did not change when cultured cells were grown in the presence or absence of sterols. Introduction of the sterol 27-hydroxylase cDNA into Simian COS cells resulted in the expression of active enzyme capable of catalyzing multiple oxidation reactions (R-CH3----R-CH2OH----R-COOH) at carbon 27 of sterol intermediates of the bile acid synthesis pathway.