Back-Scattering Interferometry (BSI) Applications
 Courtesy of Schrödinger, LLCBSI's label-free and tether-free homogeneous assay format enables many small molecule drug candidate binding studies with putative targets where other technologies simply don't work. BSI enables assays with nanomolar levels of target protein to measure picomolar or lower levels of ligand. BSI can measure Kd's over six orders of magnitude.
Isothermal Titration Calorimetry (ITC), one other label-free/tether-free method, typically requires 1000x more protein, often under non-physiological conditions. The time and cost of obtaining so much precious material represents significant savings for BSI. Surface Plasmon Resonance (SPR) and other wave-guide technologies have limited sensitivity as the interaction distance from the measurement surface increases beyond what is normally encountered with a small protein and signals derived from film thickness changes from small molecule binding is poor. Tethering may also produce non-specific binding phenomena that is difficult to remove by reference cell methods. Well-established methods incorporating fluorescent tags or other non-isotopic labels may also produce binding interferences from the bulky labels and are time consuming in methods development.
Given these critical advantages of BSI, we are currently focused on small molecule (inhibitors, agonist, antagonists, etc.) drug development applications in:
- Secondary screening
- Biophysical characterization
- Lead optimization
- Mechanism of action/promiscuous inhibition
- HTS assay development
On going development areas MSI is currently pursuing include: instrumentation automation for HTS, homogenous & heterogeneous kinetic measurements, promiscuous inhibition, cell membrane-bound protein binding, fragment based lead discovery, impure mixture analysis, thermodynamic & stoichiometry measurements, and quantitative assay development.
Ligand Binding Experiment
Small molecule ligand binding with the full head-piece of a large trans-membrane receptor was successfully assayed by BSI. MgCl2 activates the receptor and is absent in the control (-MgCl2).
Antibody Binding Assay in 100% Serum
A low molecular weight hormone antigen was tested against its antibody in buffer, then reconstituted in 100% serum. The measured binding affinity by BSI remained essentially constant.
BACE binding studies -
Results with ELAN and exosite peptides
Sequence: KTEEISEVN(sta)VAEF
MW: 1652 Da
IC50: 30nM
[BACE]: 1.5nM
Signal (Assay-Control): negative
KD= 11.8nM
Comment: Flap-region is closed in the X-ray structure
Sequence: NLTTYPYFIPLP
MW: 1439 Da
KD : 800nM
[BACE]: 8nM
Signal (Assay-Control): positive
KD= 230nM
Comment: Flap-region is flexible/open and Exosite-peptide is binding at an adjacent site in the X-ray structure
BACE binding studies -
Similar effects on signals with small molecules
MW: 472 Da
IC50 : 33nM
[BACE]: 2.5nM
Signal (Assay-Control): positive
KD= 0.4nM
Comment: Flap-region is open in the X-ray structure
MW: 310 Da
IC50 : 5mM KD= 4.3mM
[BACE]: 50nM
Signal (Assay-Control): negative
KD= 0.25mM
Comment: Flap-region is closed in the X-ray structure
Label-free Analysis of Membrane Protein Targets
Additional Applications of BSI
BSI's sensitivity, speed and ease-of-method development provides a wide range of possible end-point and kinetic study applications. The combination of label-free and tether-free, homogeneous assay capability with exquisite sensitivity and dynamic range opens many possibilities.
MSI is expanding BSI applications and has already demonstrated or has under development the following:
- Homogeneous & heterogeneous kinetics capabilities
- Promiscuous inhibitor studies
- Binding studies using impure mixtures as well as membrane preps
- Fragment based lead discovery
- Cell-based assay correlation to target binding
- System automation for HTS
- Thermodynamic & stoichiometry measurements
- Antibody engineering/phage display screening
- Theranostic & diagnostic assay development
- Bioprocess monitoring
|
