## Endpoint to Predict
- Endpoint scope: assay
- Measurement type: Kd
- Label type: continuous
- Binary semantics: pchembl
- Assay description: Surface Plasmon Resonance (SPR): Binding interactions of ligands with STING proteins were quantified using Surface Plasmon Resonance (SPR) with a minimally biotinylated STING protein immobilized on Streptavidin chip surface. In this manner highly active STING protein surfaces were obtained that were not compromised by a low pH required for amine coupling methods. Minimal biotinylation of purified huSTING protein was performed using a previously described methodology (Chabbra 2012). Briefly, approximately 20 nmol of recombinant STING protein in 1×TBS buffer (25 mM Tris-HCl, 150 mM NaCl, 5 mM DTT) was mixed with of EZ-LinkH Sulfo-NHS-LC-LC-Biotin (Thermofisher Scientific, cat #21338) at a molar ratio of 1 to 0.6 and then incubated on ice for 2 hours. To remove any unreacted biotin reagent, protein/biotin mixture was passed through a Superdex 75 (10/300 GL) column equilibrated with 10 mM HEPES pH 7.4, 150 mM NaCl, 5 mM DTT, 5% (v/v) glycerol. A protein peak containing biotinylated huSTING protein was collected and stored in aliquots at −80° C. Streptavidin was simultaneously immobilized in all four channels of a CM5 sensor chip docked in a Biacore instrument (either Biacore S200 or Biacore T200, GE Healthcare) as described previously (Zender 2013). Minimally biotinylated STING protein was captured onto Streptavidin coated chip surface at 25° C. in SPR binding buffer (50 mM HEPES pH 7.4, 150 mM NaCl, 2.5 mM TCEP, 2% (v/v) DMSO) gradually injected in a single channel at a constant flow-rate of 2 μL/min until SPR response increases were no longer observed resulting in typical capture levels of 5000 to 7000 RU (1 RU=1 μg/mm2). To determine binding affinity, compound interaction with immobilized STING protein was analysed using dose-response experiments. All binding experiments were performed at 25° C. in SPR binding buffer. Fresh 10 mM DMSO solutions of compound were diluted directly into SPR binding buffer to a final concentration of 10 μM and then further diluted either 2-fold or 3-fold aiming for either a 5- or 7-point concentration series range. Each ligand concentration series was injected at a constant flow rate of 60 μL/min with a 90 second association and a 180 second dissociation time. Scrubber 2 (www.biologic.com.au) was utilized for data processing and analysis. Thus, SPR signals were referenced against the blank surface (streptavidin+D-biotin) and further corrected for DMSO refractive index change and then double-referenced using a buffer-blank injection (Papalia 2006). To determine binding affinities (KD values) from dose-response experiments, binding responses at equilibrium were fit to either a 1:1 steady state affinity or to 1:1 binding kinetic models (both available within Scrubber software).
- Target name: Unchecked
- Target type: UNCHECKED

## Reference Molecule A
- Canonical SMILES: NC(=O)c1ccc(OCc2c(C(=O)O)sc3cccc(Cl)c23)cn1
- Properties:
- ChEMBL ID: CHEMBL5797012
- Molecular weight: 362.79
- Heavy atoms: 24
- Hydrogen bond donors: 2
- Hydrogen bond acceptors: 5
- TPSA: 102.51
- LogP: 3.33
- Rotatable bonds: 5
- Ring count: 3
- Aromatic rings: 3
- Formal charge: 0
- Fraction Csp3: 0.06
- QED: 0.72

## Known Reference Result on This Endpoint
- Molecule A clean result: median pChEMBL = 5.01
- This result is provided as context for predicting Molecule B on the same endpoint.

## Reference Molecule A Other ChEMBL Evidence
- type Kd; relation =; value 9700; units nM; pChEMBL 5.01; comment 1267678

## Query Molecule B
- Canonical SMILES: NC(=O)c1cc(Cl)c(OCc2c(C(=O)O)sc3cccc(Cl)c23)c(Cl)c1
- Properties:
- ChEMBL ID: CHEMBL5940177
- Molecular weight: 430.7
- Heavy atoms: 26
- Hydrogen bond donors: 2
- Hydrogen bond acceptors: 4
- TPSA: 89.62
- LogP: 5.24
- Rotatable bonds: 5
- Ring count: 3
- Aromatic rings: 3
- Formal charge: 0
- Fraction Csp3: 0.06
- QED: 0.58

## Molecule Similarity
- Weighted Tanimoto: 0.65

Answer: 5.55