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Surface Plasmon Resonance: Driving Better & Faster Decision-making in Drug Discovery

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Developing small molecule drugs is expensive, extremely time consuming – and not always successful. Low success-rates have created the need to find and adopt novel ways to quickly and accurately measure their activity and binding characteristics throughput the entire discovery and development process.

We recently spoke to Bruker’s JoAnne Bruno, Director Sales and Marketing and Sven Malik, Senior Application Specialist, to learn how surface plasmon resonance (SPR) can be used to investigate the binding properties of small molecules, and how it can help researchers make better decisions about drug candidates and support efforts to design new molecules for future programs.

Q: What is surface plasmon resonance (SPR), what are the basic principles of this technology?

A: Surface plasmon resonance is a biophysical approach used to investigate biomolecular interactions between two or more molecules. The types of molecules that can be characterized are diverse, from ions and fragments to proteins and viruses. One interacting partner is attached to the sensor surface (ligand) and the sample is delivered to the sensor surface (analyte) to enable binding. Sample delivery via a continuous flow microfluidic device yields the most accurate binding measurements. The change in refractive index is measured as a function of time. The refractive index change is directly proportional to the mass accumulating on the surface during a binding event. During the association phase, the flowing buffer is replaced with sample and the analyte molecule binds to the ligand on the sensor surface. In the dissociation phase, buffer replaces sample at the sensor surface and the complex dissociation is observed.

A typical sensorgram, which is the output from an SPR experiment, is shown below. The shape of the curve gives information about binding specificity, kinetics and affinity. Depending on the interaction, a change in buffer properties (e.g. pH, ionic strength) can be used to remove bound material during the regeneration step, which prepares the surface for another analyte binding cycle.

Q: How can SPR technology be used to aid drug discovery efforts?

A: The high cost, lengthy time and low success rate for small molecule drugs has created the need to quickly and accurately measure their activity and binding characteristics throughput the entire discovery and development cycle. Investigating the binding properties of small molecules using SPR technology, enables researchers to make better and faster decisions about compounds in development and to design new molecules for future programs. For example, binding specificity of a small molecule for its target protein, control or serum proteins (e.g. HSA or AGP) creates a profile of binding behavior. Kinetic characterization reveals the speed and stability of complex formation. Compounds can have the same binding affinity but different kinetics, which affects their behavior as a drug.

Q: What are some of the benefits of using SPR, compared to other detection technologies?

A: SPR allows the detection of molecular interactions in real-time and without the use of any labels. Whereas traditional techniques requiring labels for detection can answer questions on the binding specificity and possibly the affinity, SPR provides information on the specificity, affinity, kinetics, thermodynamics and concentration of an interaction for a wide range of molecules. In many cases, SPR measurements are completed in minutes and reagent consumption is low, since active and control data can be collected from a single injection of sample. Samples do not need to be purified; binding can be measured for crude or purified samples in complex matrices, such as serum, cell culture supernatants or organic solvents.

Q: Can you explain more about the ‘frame-inject’ feature on Bruker’s SierraTM SPR-32 system?

A: Frame inject can be used to investigate the impact of co-factors (mechanistic studies) on molecular interactions.

The traditional method of adding the co-factors into the running buffer increases analysis time, reagent consumption and cost.

Frame inject uses a portion of the co-factor containing buffer to pre-stabilize the surface before the specific compound is injected. During the dissociation phase the co-factor containing buffer is used so that the dissociation kinetics of the complex are measured in the presence of the critical co-factor. By limiting the use of the co-factor containing buffer to the pre-injection and dissociation phases of the assay, Frame inject saves on time and consumable costs.

Q: Do you envisage researchers using the SierraTM SPR-32 system alongside their mass spectrometry systems? If so, what benefits does this provide?

A: Yes, definitely! The combination of the two technologies is a powerful option for high-throughput screening programs. Whether MALDI or SPR is used as the primary tool depends on workflow. In one approach, the specificity of an interaction is measured using MALDI and then the hits are confirmed and the affinity and/or kinetics are characterized by SPR. At present, this scenario describes the standard workflow: primary screening using MALDI followed by secondary and tertiary screening and characterization using SPR.

Initial screening by SPR with a secondary, confirming experiment using MALDI would also be interesting and beneficial for researchers in drug discovery and development programs.

JoAnne Bruno and Sven Malik were speaking to Laura Elizabeth Mason, Science Writer for Technology Networks.