Targeting the cGAS-STING Pathway Using a Homogenous, HTS Compatible Transcreener cGAS Assay

Transcreener cGAMP cGAS Assay

Transcreener cGAMP cGAS Assay directly measures cyclic GMP-AMP (cGAMP) produced by cyclic GMP-AMP synthetase (cGAS, C6orf150, 2'3'-cGAMP Synthetase). These cGAMP measurements allow researchers to effectively determine the enzyme's activity. The assay provides a powerful tool to screen compound libraries for cGAS modulators to help find new therapies for disease.

The kit comes complete with the detection reagents required to measure activity. cGAS enzyme is not included in the inhibitor screening assay kit. Recombinant cGAS enzyme is available for separate purchase through BellBrook labs. 

This assay is designed to be used with purified enzyme preparations. Transcreener assays are not validated with cell lysates, blood, serum, or other biological samples.

Important Messenger in the STING Pathway

DNA in the cytosol of eukaryotic cells indicates infection or cellular damage, and it elicits a robust immune response, driven by type I interferon (IFN) induction. 

cGAS is an exquisitely sensitive sensor for double-stranded DNA in the cytoplasm.  Binding of DNA activates the enzyme to produce a unique cyclic dinucleotide second messenger, cGAMP, which acts as an agonist for the STING (stimulator of interferon genes) receptor, leading to induction of a type I interferon response.

cGAS STING Pathway

How Does This cGAS Assay Work?

The Transcreener cGAMP cGAS Assay determines cGAS enzyme activity by directly measuring the cGAMP formed by the enzyme using the Transcreener cGAMP Assay. By detecting cGAMP output, the assay provides a universal method to assess the activity of any cGAMP-producing enzyme in real-time.

Transcreener cGAMP Assay technology uses a simple but highly effective method that consists of an antibody selective to cGAMP and a far-red fluorescent tracer. cGAMP produced in the reaction competes with the tracer changing the fluorescent properties and providing fluorescent readout. 

The cGAS assay is available with FP and TR-FRET. It is a simple mix-and-read format. Perform your enzyme reaction, add the detection reagent, and measure. The simplicity of the system yields robust results that also makes it extremely amiable to HTS. 

Direct Detection of cGAMP to Measure cGAS Enzymatic Activity

Fluorescent Polarization (FP)

cGAS Assay Schematic FP

Time-Resolved Förster Resonance Energy Transfer (TR-FRET)

cGAS Assay Schematic TR-FRET


  • Measure Enzymatic Activity of cGAS
  • Screen Compound Libraries for cGAS inhibitors
  • Quantify Inhibitor Potency
  • Determine Inhibitor-cGAS Residence Time


  • Direct detection of unlabeled cGAMP
  • Easy to use, homogenous, one step format
  • Robust Assay Z’ > 0.7 under initial velocity conditions
  • Far-red fluorescent readouts minimize compound interference
  • A safe, non-radioactive method
  • Available in FP or TR-FRET readouts

Easy-to-Use, Mix-and-Read, HTS-Ready Assay

Run your enzyme reaction, add Transcreener reagents, and read your plates. The cGAS assay is compatible with 96, 384, and 1536-well formats.

Transcreener Mix and Read Assay

Outstanding Signal Stability

The assay exhibits 24 hours+ signal stability. Plate stability like this is vital for sizeable high throughput screens that take significant time to complete due to massive sample quantity.


Standard curves include ATP, GTP, dsDNA, and titration of cGAMP. The same plate was read at each time point.

Detection of cGAMP Under cGAS Initial Velocity

The assay demonstrates linearity when raw data is converted to cGAMP using a standard curve. cGAS is activated by double-stranded DNA and requires ATP and GTP substrates for the production of cGAMP.

Full-Length Human cGAS Titration

Full-length human enzyme titration

Linear Response

Screen for Inhibitors & Perform SAR

The Transcreener cGAS Assay is designed for screening compound libraries in a high throughput format. Follow up SAR can also be performed using the assay to determine inhibitor potency with ease.

1600 Compound Pilot Screen

cGAS Assay Pilot Screen

Dose Response Measurements

cGAS Dose Response Curve

Yields Accurate Dose Response Results with Known cGAS Inhibitor, G150

Example dose response curves using known cGAS inhibitor, G150. Assay conditions include 100 μM ATP, 100 μM GTP, 100 nM ISDNA, 20 mM Tris (pH 7.5), 5 mM MgCl2, 0.01% Brij-35 (pH 7.5). The enzyme reaction took place for 60 minutes at room temperature. The FP Detection Mix included 1X Stop & Detect Buffer B, 8 nM cGAMP 633 Tracer, and 2.0 μg/mL cGAMP antibody. The TR-FRET Detection Mix included 1X Stop & Detect Buffer C, 16 nM cGAMP ATTO 647 Tracer, and 8 nM cGAMP Antibody-Terbium. The Detection Mix was incubated for 1 hour at room temperature. 

FP Readout

cGAS Assay DRC with G150 inhibitor in FP Readout

IC50 = 0.04 μM

TR-FRET Readout

cGAS Assay DRC with G150 inhibitor in TR-FRET Readout

IC50 = 0.05 μM

Illustrates DNA & Substrate Dependance of the cGAS Enzyme

The assay accurately demonstrates the characteristics of the cGAS enzyme. Double-stranded DNA activates the enzyme which generates cGAMP in the presence of both GTP and ATP. A 45 base pair ISD (interferon stimulatory DNA) and a 60 base pair HSV (herpes simplex virus) DNA  both activate the enzyme. The assay has a high affinity to cGAMP and can detect even in the presence of other nucleotides.

cGAS Enzyme Activation by dsDNA

cGAS DNA Titration

Dependence on ATP and GTP

BellBrook Lab's Recombinant cGAS Enzyme

Active, full-length Human Cyclic GMP-AMP synthase enzyme, His-tagged protein expressed and purified from E.coli. The enzyme has been thoroughly validated with Transcreener cGAS Activity Assays. For specific activity, please refer to the Certificate of Analysis for each individual enzyme lot. Purity is >90% in a 20 mM Tris 7.5, 200 mM NaCl, 1mM DTT, 10% glycerol buffer composition. The enzyme is currently used in the Transcreener cGAS Activity Assay at 30 nM, which is 1.75 μg/mL (17.5 ng in 10 µL enzyme reaction volume in a 384-well format). Please adjust the enzyme concentration based on your requirements.

Recombinant cGAS Enzyme

cGAS Assay Services

Interested in moving your program forward, but don't want to bring an assay in-house? Our scientists can help! BellBrook scientists will use their extensive biochemistry and enzymology expertise to work with you and accelerate your cGAS program.

Assay Development Services

Lead Discovery Services Include:

  • Inhibitor Screening – To identify or confirm activity with the target.
  • Inhibitor Potency Profiling – Dose-response with target and/or related proteins. Fast IC50 results.
  • Residence Time Measurements – Determination of koff using ‘jump dilution’ enzymatic assay method.
  • Mechanism of Action Studies – Kinetic analysis to define the mode of inhibition.

Contact Us to Learn More

Please fill out the form below. We will respond quickly to get the conversation moving and learn how we can help. We keep things discrete, confidential, and professional.

Far-Red FP & TR-FRET Readouts Validated on Major Multimode Readers

SupplierInstrumentFP AssaysTR-FRET Assays
TriStar2S LB 942In ReviewClick Me ArrowValidated
Tristar 5In ReviewIn Review
Mithras2 LB 943In ReviewClick Me ArrowValidated
CytationTM 5ValidatedValidated
CytationTM 3ValidatedValidated
CytationTM 1ValidatedValidated
SynergyTM H1ValidatedValidated
SynergyTM 2/H4/4Click Me ArrowValidatedClick Me ArrowValidated
SynergyTM HTXNot CapableNot Capable
SynergyTM Neo 2ValidatedValidated
POLARstar® OmegaClick Me ArrowValidatedClick Me ArrowValidated
FLUOstar® OmegaNot CapableClick Me ArrowValidated
PHERAstar® FSXClick Me ArrowValidatedClick Me ArrowValidated
PHERAstar® Plus/FSClick Me ArrowValidatedClick Me ArrowValidated
CLARIOstar® /PlusClick Me ArrowValidatedClick Me ArrowValidated
VANTAstarTMClick Me ArrowValidatedClick Me ArrowValidated
SenseIn ReviewIn Review
Analyst® GT/HTClick Me ArrowValidatedClick Me ArrowValidated
Gemini® XPS/EMNot CapableNot Capable
SpectraMax® M2/M2eNot CapableNot Capable
SpectraMax® M5/M5e/FlexStation® 3Not CapableClick Me ArrowValidated
SpectraMax® ParadigmClick Me ArrowValidatedClick Me ArrowContact Us
SpectraMax® iD3/iD5Click Me ArrowValidatedClick Me ArrowValidated
SpectraMax® i3xClick Me ArrowValidatedClick Me ArrowValidated
EnVision®/EnVision® XciteClick Me ArrowValidatedClick Me ArrowValidated
Infinite® M1000/M1000Pro/Safire2TMClick Me ArrowValidatedClick Me ArrowValidated
Infinite® M200Not CapableNot Capable
Infinite® F500Click Me ArrowValidatedClick Me ArrowValidated
Infinite® F200/UltraevolutionClick Me ArrowContact UsClick Me ArrowContact Us
SparkTM 10MClick Me ArrowValidatedClick Me ArrowValidated

What's Included

What You Will Need

Transcreener cGAMP cGAS Assay Kits

* For custom or bulk orders (over 100,000 wells) please contact us (info@bellbrooklabs.com) for a quote.

cGAS Enzyme Ordering Information

* For custom or bulk orders (over 100 μg) please contact us (info@bellbrooklabs.com) for a quote.

Related Resources

Interconnections Between the DNA Damage Response and Innate Immunity

There is extensive crosstalk between the DNA damage response (DDR) pathways and innate immune pathways. Both the individual pathways and the interconnections between them are a focus for exciting new small molecule drug therapeutics that target cancers and debilitating autoimmune disorders. The Transcreener HTS Assay platform accelerates these efforts by providing a robust and easy-to-use biochemical assay to measure activity of key enzymes in the innate immune and DDR pathway.

In this guide, we provide an overview of the DDR and innate immune pathway, and describe Transcreener Assays and Assay Systems for key therapeutic targets. The enzyme targets discussed include:


  • POLQ
  • WRN
  • PARP1
  • PARG
  • DNA PK

Innate Immunity

  • cGAS
  • TREX1
  • TBK1
  • IKKβ
  • IRAK4
  • ENPP1
  • CD38
  • OAS-1
  • RIG-1/MDA5
  • DDX3
  • CD39
  • CD73
DNA Damage Response and Innate Immunity Preview

The Role of cGAS As a Therapeutic Target

cGAS recognizes foreign double-stranded DNA and initiates an innate immune response, called the cGAS-STING pathway. cGAS can cause tissue or autoimmune diseases if overactivated by the body's abnormal DNA. Examples of diseases caused by this include Aicardi-Goutières syndrome, systemic lupus erythematosus, and primary biliary liver disease (Li et al, 2021).

The cGAS-STING pathway is an attractive target for autoimmune diseases and cancers. Transcreener's cGAMP cGAS Assay is an excellent tool for researchers examining the therapeutic effects of cGAS.