Drug Development with the DynaPro Plate Reader III

Dynamic Light Scattering (DLS) is regarded as an indispensable tool in the research and development of nanoparticles, proteins, macromolecules, and colloids with sizes ranging from less than one nanometer up to a few micrometers. When it comes to high-throughput analysis and screening of biologics,

DynaPro Plate Reader line of in-plate dynamic light scattering instruments from Wyatt Technology has become the gold standard. Drug product development researchers across the globe rely on these instruments for assessing pre-formulation, developability, aggregation, and stability.

The latest generation of the instrument series, DynaPro Plate Reader III (PRIII) provides new capabilities that further extend its value as the leading screening tool for stability and size. The PRIII measures multiple essential biophysical properties, robustly, simultaneously, and conveniently for development of monoclonal antibodies, therapeutic proteins, antibody-drug conjugates (ADCs), vaccines, virus-like particles, and biosimilars.

  • Molar mass
  • Size and size distributions
  • % large aggregates
  • Polydispersity
  • Thermal stability: Tm/Tonset (unfolding) and Tagg (aggregation)
  • Colloidal stability: kD, A2 and their temperature dependence
  • Viscosity
  • Solubility

The DynaPro Plate Reader III, beyond biophysical characterization, also gives a bigger picture: it captures a photo of each well to help detect macroscopic instabilities and offer measurement diagnostics. In other words, it gives a detailed profile of behavior and properties of proteins.

One instrument, so much information...

The DynaPro Plate Reader III measures dynamic and static light scattering in situ in standard microwell plates.

Figure 1. The DynaPro Plate Reader III measures dynamic and static light scattering in situ in standard microwell plates.

Who Needs a DLS Plate Reader?

DLS measurements are performed in suspension or solution, rapidly and with a tiny amount of material, to help evaluate various properties such as aggregation, size, purity, and stability. However, traditional DLS instruments have one major disadvantage: “one-at-a-time” measurements and manual sample loading.

Using either quartz or disposable cuvettes, conventional DLS needs significant operator time just to make a few measurements, even when the real data acquisition merely takes a few minutes. Due to this reason, researchers are deterred from full and proper utilization of DLS, which should comprise of replicate samples, acquisition of multiple repeats, controls and a range of different conditions. The scientist—and the science—get bogged down. Fortunately, a suitable solution is at hand.

The automated DLS instrument, DynaPro Plate Reader carries out measurements on samples in standard 96, 384, or 1536 well plates. Users do not have to manually replace each cuvette; they can simply load the plate, place it in the PRIII instrument, click ‘Go’, and walk away. Previous generations of this instrument—the DynaPro Plate Reader Plus and its successor, the DynaPro Plate Reader II—have been used by many protein, pharmaceutical, and nanoparticle development scientists to boost productivity by an order of magnitude or more. These scientists implemented high-content DLS workflows that had been considered unfeasible until the introduction of the DLS plate reader. The DynaPro DLS Plate Reader proved useful in nanoparticle process development, biotherapeutic formulation and stability screens, and optimization of crystallization buffers.

The latest generation in the DynaPro product line is the DynaPro Plate Reader III (DynaPro PRIII). This instrument integrates multiple technological advances to provide more valuable functionality. Maybe the new and most important feature is in-plate measurement of solution weight-averaged molar mass (Mw) and second virial coefficient (A2 or B22) through static light scattering.

Imagine a Quantum Leap

Apparently, science experiences quantum leaps when the automation of previously slow and tedious processes translates to qualitatively new research. From screening of compound libraries in drug discovery, to massively parallel computing, to genome-sequencing and PCR, high-throughput automation provides more benefits than simply saving time. With high throughput, users can imagine—and perform—new studies that were previously inaccessible to most laboratories (unless they happened to have bench after bench of “one-at-a-time” instruments attended by legions of technicians).

The DynaPro PRIII provides the opportunity to dream big dreams for DLS measurements. Users can obtain the data in one day that might otherwise take weeks. Hundreds of samples and thousands of excipient/buffer /temperature conditions can be tested with no more effort than that required to load one microwell plate. Using SpectralView™, the heat-map generator in DYNAMICS® software, users can analyze and view the whole dataset in one fell swoop and then zoom in for a comprehensive analysis of the most promising conditions.

Loading and unloading can be automated, as shown here with a Hudson Plate Crane. The DYNAMICS API provides tools for controlling the instrument and transferring results to external software.

Figure 2. Loading and unloading can be automated, as shown here with a Hudson Plate Crane. The DYNAMICS API provides tools for controlling the instrument and transferring results to external software.

For even larger-scale automation, the DynaPro PRIII can be integrated with robotic liquid handling. The DYNAMICS API offers tools to incorporate temperature control, data acquisition, plate handling, and additional PRIII features into the plate-based, fully-automated workflow that integrates sample preparation and loading, liquid handling, and other analytical techniques.

Quantity without Sacrificing Quality

In the DynaPro Plate Reader III, industry-standard microwell plates from Greiner, Corning, and other vendors are used to make all the measurements in situ. Since there is no sample handling (beyond pipetting into the plates), there is no issue of cross-contamination, and immense time savings are realized. For additional analyses, the plates can be easily transferred to chromatographic well-Δplate samplers or spectroscopic plate readers.

Luckily, high-throughput and automation do not come at the cost of data quality. Even with disposable, inexpensive plates, the robustness and sensitivity designed into the instrument by Wyatt’s dedicated R&D team are similar to those acquired by other DLS instruments with precision-fabricated (i.e., expensive) quartz cuvettes, and definitely better by far than measurements in costly capillary arrays.

More data can be can be collected in less time, with less labor, and with greater accuracy; with the ability to integrate multiple replicates easily into each experiment, users can also achieve robust statistical analyses.

Under the Hood

Dynamic vs. Static Light Scattering

The technical terms ‘static’ and ‘dynamic’ are loaded with cultural significance. All humans want to be perceived as ‘dynamic’, agile, and forward-looking individuals; nobody wants to be seen as ‘static’, sedentary, and stuck in place. However, the negative or positive connotations of these words do not hold up in the milieu of light scattering; both static and dynamic light scattering are robust analytical techniques. Both these forms of light scattering measure different properties of particles and macromolecules, and integrate synergistically to build a better understanding of the quality of the sample and the viability for therapeutic use or research.

Weighing Molecules with Light

Static light scattering (SLS) offers two main pieces of information about nanoparticles and macromolecules – molar size and mass. Remarkably, SLS does so from first principles and hence it is a sound and powerful technique.

In SLS measurements, a solution is first illuminated with a laser beam and the intensity of light scattered from the solution corresponding to the illumination intensity is measured. The analysis is quite simple as long as the particles are relatively smaller than the wavelength of the illuminating laser (radius less than ~12-15 nm for the PRIII) – the molar mass is acquired from the ratio of scattered intensity to analyte concentration. If the solution contains more than one species, the calculation offers the weight-averaged molar mass Mw.

For both static and dynamic light scattering in a well plate, laser illumination and detection take place from below.

Figure 3. For both static and dynamic light scattering in a well plate, laser illumination and detection take place from below.

In the case of larger particles, the light scattering signals differ with angle and therefore a correction to the SLS is required; DYNAMICS reliably executes this second-order correction to the molar mass value for particles up to 50 nm in radius by assuming a molecular conformation. A multi-angle light scattering (MALS) detector is needed for greater precision or even larger particles.

The analysis gives both molar size and mass in terms of the rms radius rg. The DAWN® HELEOS® II is a MALS detector that is traditionally coupled to a separation system such as field-flow fractionation (FFF-MALS) or size-exclusion chromatography (SEC-MALS) in order to acquire true size distributions. The PRIII is not suited for determining the molar mass of these larger particles by SLS, but it can nevertheless determine size from DLS and estimate molar mass by assuming a particular conformation.

Information from Noise

Dynamic light scattering leverages the Brownian motion of particles in suspension or solution to measure their size. A narrow laser beam is used to illuminate the fluid, and each particle in the beam scatters light waves in all directions. When the particles undergo diffusion, they create fluctuations in the intensity of light scattered into any specific direction. A detector subjected to the scattered light will produce signals that change over time correspondingly. Since the Brownian motion of the particles is random, the signal changes, appearing as uncorrelated intensity fluctuations on time scales of microseconds to milliseconds, more generally referred to as ‘noise’. Figure 4 shows DLS raw data that truly look like detector noise.

Figure 4. Brownian motion of particles produces dynamic light scattering signals that look like noise. However, these fluctuations do contain useful information: diffusion coefficients that can be converted to size.

On the other hand, as the rate of diffusion relies on particle size (besides solution viscosity and temperature), the fluctuations in the optical signal obviously contain some critical information. The fluctuation rate directly corresponds to the diffusion rate of the scattering particles. While larger particles diffuse more slowly resulting in slow optical fluctuations, smaller particles diffuse more rapidly, resulting in fast optical fluctuations. The particles’ diffusion coefficient Dt can be established by conducting a mathematical algorithm called “autocorrelation analysis” on the raw optical signals and accommodating the resulting autocorrelation function (acf). From the diffusion coefficient, the particle size is determined using the Stokes-Einstein equation.

Yet More Information

Onboard camera is an interesting feature included in the DynaPro Plate Reader III. This camera takes an image of each well. Scientists who have made DLS measurements have, at some point, run into unusual data that resulted from precipitation, dust, or a bubble in the sample. The only means to find the source of the poor data was to hold the cuvette up to the light and inspect the sample with a jeweller’s loupe... assuming, of course, that the cuvette has not been discarded or emptied. Now, thanks to the PRIII’s camera, when odd results show up, users can simply pull up the image that was taken automatically and check if there was crystallization, precipitation, a bubble, or debris. This eliminates guesswork, or squinting—just plenty of information on the sample’s behavior.

Figure 5. Well-bottom images captured with the DynaPro Plate Reader's onboard camera show sample behavior beyond nanoparticle size distributions.

So, What’s New?

Weigh the Plate

A general misconception is that proteins’ molar mass can be determined using DLS, but physics does not support this. DLS determines size and diffusion coefficient; molecular weight can then be estimated by assuming a specific molecular conformation such as random coil for polymers or globular for proteins. However, Nature does not cooperate in these assumptions, and creates non-conforming species such as branched polymers and non-globular proteins which invalidate the assumptions.

The DynaPro PRIII adds a number of new features, the first of which is true molecular weight measurements of macromolecules, including proteins, in the plate, using SLS. SLS does not need assumptions of conformation, and hence is suitable even when Nature does not cooperate. All that is required for a proper measurement of molar mass is knowledge of the refractive increment dn/dc and the sample concentration, as well as a highly linear detector (often a well-known constant for standard buffers and proteins, dn/dc can also be measured, if required, for modified proteins and/or non-standard buffers).

While this sounds easy enough to pull off, it turns out that there is a trade-off between sensitivity, speed, and linearity of detector modules. Normal p-i-n photodiodes (like those employed in a MALS detector) are highly linear over many orders of magnitude of signal, but when operated at high gain, exhibit a slow response — too slow for DLS. Generally used in DLS instruments (such as the DynaPro), avalanche photodiodes have high speed and high gain with sub-microsecond response times, but are generally quite nonlinear.

In the DynaPro PRIII instrument, the standard APD was substituted with a new module that preserves linearity over a sizeable range of signals. This range is appropriate for studying common polymers proteins, at concentrations typical of SLS and DLS measurements. For pure and monodisperse sample, SLS measurement in the plate will offer an exact molecular weight value; when the sample is a mixture of species, SLS will establish the weight-average molar mass. The DynaPro PRIII is the first (and only) plate reader to measure molecular weights in a low-volume, highly automated format, making this quite an exciting development.

B22 and A2, too

Non-specific interactions between proteins, occurring from surface moieties such as hydrophobic or charged residues depicted in Figure 6, affect the propensity and colloidal stability for aggregation of biotherapeutics. One of the main thermodynamic parameters that describe these interactions is the second virial coefficient A2, a.k.a B22; SLS is a primary, first-principles method for measuring A2.

However, traditional SLS needs relatively large amounts of protein, which are usually unavailable in early stages of biotherapeutic development. Recently, DLS was used by researchers working on early-stage biologics to measure the diffusion interaction parameter kD as a reasonably reliable proxy for A2. While kD is not a purely thermodynamic quality, it incorporates both thermodynamic and hydrodynamic properties and may be measured by DLS using much smaller quantities of sample than SLS. Even better, the DynaPro Plate Reader can be used to measure kD in a highly automated fashion; it has been shown that kD correlates reasonably well to aggregation propensity and the viscosity of high-concentration monoclonal antibodies.

Non-specific protein-protein interactions arise from hard-core repulsion, net charge, charge homogeneities, local dipoles, hydrophobic residues and another source. To first order they are quantified by the second virial coefficient, A2 (measured by SLS), or its proxy, kD (measured by DLS).

Figure 6. Non-specific protein-protein interactions arise from hard-core repulsion, net charge, charge homogeneities, local dipoles, hydrophobic residues and another source. To first order they are quantified by the second virial coefficient, A2 (measured by SLS), or its proxy, kD (measured by DLS).

This latest capability of the DynaPro PRIII extends high-throughput, automated screening of multiple candidates or formulations to include A2, satisfactorily complementing kD measurements. Combined with conformational and thermal stability screening using denaturant series, temperature ramps or accelerated stability tests at high temperatures, A2 analysis provides the DynaPro PRIII comprehensive stability screening and prediction of the viability of biotherapeutic drug products.

Evaporation, Begone

The DynaPro PRIII is an extremely versatile platform meant for process development and stability testing. These assays often need long-term storage at room or elevated temperatures or extended temperature ramps, all of which subject the solutions in the plate to evaporation. With just microliters per sample, it does not take much evaporation to considerably increase sample concentration and potentially induce aggregation or precipitation.

Capping the wells with silicone or mineral oil is the preferred way of preventing evaporation in the DynaPro Plate Reader. Being less hydrophobic than air, oil produces a milder interface for proteins with regards to denaturation. Also, it is beneficial to the optical system as it produces a perfectly smooth and clean surface, far from the detection volume, that does not scatter the laser light projected from beneath the well. Conversely, oil can be messy and additional fluid handling is required to cap the wells. Surfactants may change the formulation by drawing some of the oil into the solution.

Another effective method for preventing evaporation is to use transparent sealing tape – which is less messy than oil and easier to use (foil cannot be used as it blocks the camera lighting). The challenge with transparent sealing tape in earlier models of the DynaPro Plate Reader has been condensation of vapors on the tape; the resultant droplets scatter abundant amounts of light and degrade the DLS signals.

This condensation issue has been fully resolved in the DynaPro PRIII. When specified in the method, the device turns on a gentle heating element that increases tape’s temperature by 2-3 °C above that of the plate. This is more than enough to prevent condensation and ameliorate any unfavorable optical effects without affecting the temperature of the plate contents.

Therefore, in the DynaPro PRIII, transparent sealing tape or oil capping can be utilized to prevent evaporation, without adversely affecting the optical performance. Users are free to select their desired method.

Looks Count for Something, Too

Like all Wyatt detectors, the DynaPro PRIII features a graphic touch screen display on the front panel which is handy for manual operation of the instrument, rapidly assessing the history of temperature and signals, and diagnosing faults or alarms. All it requires is a quick look to establish what is going on.

A new feature in the DynaPro PRIII is the improved front panel display that makes it much simpler to identify key operation details and system parameters at a glance. Need more? By simply tapping the screen, users can navigate the charts and other displays for a deeper look.

Front panel display on the DynaPro Plate Reader III.

Figure 7. Front panel display on the DynaPro Plate Reader III.

Building Experiments, from Novice to Expert

DYNAMICS is a robust software package developed for detailed data analysis, and its Event Schedule scripting language helps construct complicate methods for scanning wells in plates over various temperature profiles. It has been useful for experts who require multiple options. However, what about novices?

DYNAMICS has been certainly made more complex than necessary, especially for novices who just want to carry out basic temperature profiles and partial-plate scans. Wyatt apologizes to those users and has now fixed this issue.

Initially implemented in DYNAMICS version 7.7, the Experiment Builder makes it easy to produce a basic method in a few simple steps:

  1. Choose a temperature profile (fixed, discrete, or ramped steps) and specify the preferred temperature(s)
  2. Graphically choose the wells to be measured and detect their contents
  3. Specify additional data such as time to wait between measurements, the number of repeat measurements, and whether to take camera images.
  4. Press Go, and bring the DynaPro Plate Reader to life!

 The Experiment Builder in DYNAMICS 7.7 and above allows novices and experts alike to painlessly create methods for the DynaPro Plate Reader.

Figure 8. The Experiment Builder in DYNAMICS 7.7 and above allows novices and experts alike to painlessly create methods for the DynaPro Plate Reader.

If this sounds too easy, users need not worry. The Event Schedule feature is still available if users require more complicated methods, for example temperature cycling. Wyatt believes that ease of use need not come at the cost of versatility.

Applications, Old and New

The Basics

Protein and particle sizing

Size and aggregation of proteins, sub-micron particles, liposomes, viruses, and other macromolecules are bread and butter for DLS. Easily running dozens or hundreds of samples is more like pralines and caviar, a rare luxury. Unless, users have to stand there day in and day out, spoon-feeding a cuvette-based DLS instrument, then automated measurements using a DynaPro Plate Reader are absolutely important.

Shown in Figure 9 are the results of a 45-minute, hands-off experiment, measuring 96 samples in a single well plate. According to user-specified criteria, SpectralView color-codes the plate representation, for example polydispersity, average molecular weight, average size, %mass above Rh=10 nm—and these are only the more common options. Each well can be subsequently checked in more detail to observe the size distribution of its contents, and the entire result set exported in spreadsheet format.

Automated screening of size and aggregation in a 96-well plate takes just 45 minutes. The results are displayed in a SpectralView heat map as well as individual size distributions. (Courtesy Sabin Inst.)

Figure 9. Automated screening of size and aggregation in a 96-well plate takes just 45 minutes. The results are displayed in a SpectralView heat map as well as individual size distributions. (Courtesy Sabin Inst.)

Protein crystallization

The right buffer has to be selected for protein crystallization but finding one can be frustrating as well as time- and material-consuming. Users may try hundreds or thousands of conditions, and either a crystal forms, or it does not (mostly the latter).

Usually, the process can be rationalized and made to converge much more rapidly using DLS to map out the level of polydispersity and aggregation for each condition. The sweet spot for crystallization can be found by interpolation, even if users do not nail exactly the right condition the first time. Obviously, this only makes sense in the context of high-throughput DLS because users would not dream of making all those measurements manually!

Protein Stability Characterization

Automated, high-throughput aggregation screening for formulations and developability

Design of Experiment (DoE) is a smart method to set up formulation screens for implementing Quality by Design. With DoE, formulations can be optimized over a large design space, but in the end users are still limited, by the statistical validity of the measurements and number of samples, in the total parameter set they can explore.

Using a 1536-well plate, the DynaPro PRIII only needs 4 μL of solution per well. This presents an extended DLS/SLS aggregation screen over various therapeutic candidates, excipients, buffers, and conditions, with multiple replicates, whilst consuming reasonable amounts of protein. Users will have sufficient data to be confident that they have made the right choice for their product.

Figure 10. Formulation screening: average size (top) and apparent molecular weight (bottom) of 2 monoclonal antibodies in 6 buffers, measured in a 384 well plate. The apparent molecular weight differs from the true molecular weight as a result of concentration-dependent protein-protein interactions. Each well can be further examined to determine the size and distribution of large aggregates as well as polydispersity index for small aggregates. Some invalid data, due to precipitation, not shown.

Accelerated stress and aggregation rate

The DynaPro PRIII is particularly suitable for accelerated stress studies:

  • Samples can be incubated at elevated or reduced temperatures directly in the instrument
  • Plates can be transferred to shaking/stirring devices, freeze-thaw chambers or temperature chambers and subsequently returned for analysis
  • The plates can be transferred to plate samplers or other plate-based analytical instruments for orthogonal/additional study

Time course at 40 °C showing a highly stable mAb reference standard provided by NIST. Both weight-average solution molar mass and size are unchanged under these accelerated stress conditions.

Figure 11. Time course at 40 °C showing a highly stable mAb reference standard provided by NIST. Both weight-average solution molar mass and size are unchanged under these accelerated stress conditions.

Colloidal stability: A2 and kD

Data utilized to calculate A2 and kD of multiple conditions in each well plate include apparent molecular weight (top) and diffusion co-efficient (bottom) vs. concentration. Data shown correspond to the measurements of Figure 10.

Figure 12. Data utilized to calculate A2 and kD of multiple conditions in each well plate include apparent molecular weight (top) and diffusion co-efficient (bottom) vs. concentration. Data shown correspond to the measurements of Figure 10.

A single 384-well plate is sufficient to determine the diffusion interaction parameter kD and the second virial coefficient A2 through a protein concentration series, for a dozen formulation conditions, in triplicate. As soon as the DynaPro PRIII instrument has scanned the plate and obtained the data (in as little as 1.5 hours), DYNAMICS will automatically overlay the graphs and examine the results to establish these indicators of colloidal stability, for each condition.

Thermal stability: temperatures of unfolding and aggregation

Another stability-indicating measurement is thermal denaturation, which is often employed to assess formulations for optimal stability and candidate biologics for developability. Many ways are available to determine thermal stability, each of which examines a different physical property of the molecule. Most of these methods depend on indirect signals such as intrinsic fluorescence (IF) and differential scanning calorimetry (DSC) or extrinsic probes such as fluorescent dyes.

Only light scattering gives direct biophysical proof of thermally-induced changes:

  • Size by DLS is direct evidence of unfolding and/or aggregation
  • Molar mass by SLS is direct evidence of aggregation

Simultaneous determination of two transition temperatures of an IgG for aggregation (from SLS) and unfolding (from Rh). Since aggregation occurs, a true melting temperature cannot be determined for this protein.

Figure 13. Simultaneous determination of two transition temperatures of an IgG for aggregation (from SLS) and unfolding (from Rh). Since aggregation occurs, a true melting temperature cannot be determined for this protein.

The DynaPro PRIII can establish, in a single temperature ramp, multiple transition temperatures for multiple formulations or candidates:

  • Tonset is the onset temperature for unfolding, determined by DLS
  • Tagg is the onset temperature for onset of aggregation, determined by SLS
  • Tm is the melting temperature, or the midpoint in a transition between denatured and folded and denatured states, determined by DLS with confirmation from SLS that aggregation has not occurred.

The presence of appropriate fluorophores, usually tyrosine or tryptophan, is required for intrinsic fluorescence (IF). IF may not report the unfolding of domains that lack these amino acids. It also demands the use of short-wavelength UV excitation which is well known to promote aggregation in many biotherapeutics, particularly antibody-drug conjugates (ADCs). Hence, an instrument depending on

UV scattering to measure aggregation may actually be the culprit in inducing aggregation. The infrared wavelength employed in the DynaPro Plate Reader, 830 nm, is safe and does not induce aggregation.

Temperature onset of interaction

Something DSC and IF cannot do is indicate that nature of changes that take place in protein-protein interactions in the course of thermal transitions, even if users have valid reason to believe that their signals indicate structural instability and unfolding. Although, light scattering can.

Simultaneous determination of three transition temperatures of an IgG for aggregation (from SLS), unfolding (from Rh) and interactions (from kD). The increasingly negative value of kD indicates strong colloidal attraction, well before the onset of unfolding or aggregation.

Figure 14. Simultaneous determination of three transition temperatures of an IgG for aggregation (from SLS), unfolding (from Rh) and interactions (from kD). The increasingly negative value of kD indicates strong colloidal attraction, well before the onset of unfolding or aggregation.

A2 and kD are direct proof of protein-protein interactions. By determining their dependence on temperature, users will know at what temperature the structure of the protein structure has changed and also know if the change leads to increasingly repulsive interactions (and hence stability), increasingly attractive interactions (and hence instability), or neither.

In certain cases, it has been noted that the transition temperature for protein-protein interactions is fairly clear from the onset temperatures for aggregation or unfolding. Probably, these three temperatures correlate to different aspects of protein stability, and therefore their measurement gives more insight into the properties of each protein formulation or candidate.

Viscosity

Whether for ocular delivery or subcutaneous injection, formulation of monoclonal antibodies and other biologics is increasingly happening at high concentrations. Considering that solution viscosity under these conditions can be unfavorable to injectability, production, processing and storage, high viscosity should be identified and mitigated as early as possible in the development pipeline.

DLS in microwell plates is perfectly suited to low-volume, high-throughput viscosity screening. All that is needed is suspension of a small amount of sub-micron particles of known size, such as 100 nm PEG-coated gold nanoparticles or polystyrene latex spheres, into each well.

As the particle’s diffusion coefficient is inversely related to the solution viscosity η, DYNAMICS can compare the quantified diffusion coefficient against the coefficient measured in water (or measured from the known size) to instantly give the value of η. Values determined by DLS closely correlate with those measured by traditional, high-volume/low-throughput methods.

Comparison of viscosity measurement by DLS with conventional measurements. R refers to the size of the polystyrene latex bead used in the DLS viscosity determination.

Figure 15. Comparison of viscosity measurement by DLS with conventional measurements. R refers to the size of the polystyrene latex bead used in the DLS viscosity determination.

Solubility by turbidity

Generally, turbidity is measured to assay solubility, either as an increase in scattering or a reduction in transmission. The DynaPro PRIII provides a means of low-volume, high-throughput solubility measurements in plates through static light scattering, which can be calibrated in terms of nephelometric units if so required, or presented merely as normalized scattering intensity.

One more common stability assay is PEG-induced precipitation, which can be implemented in the DynaPro PRIII, to evaluate the solubility of a range of formulations. Besides nephelometry by scattering, precipitation can also be visualized with the help of camera images.

Formulation Phase Diagrams

With so many formulation variables such as ionic strength, pH, type of salt used and so many properties to characterize for biologics, as well as additional excipients including different types of surfactants and sugars, it is no wonder that scientists have looked for ways to organize all the data in a digestible manner. One method is phase diagrams like those shown in Figure 17.

SLS measurements can be calibrated in terms of NTUs

Figure 16. SLS measurements can be calibrated in terms of NTUs

The phase diagram integrates two formulation variables (such as pH, protein concentration or salt concentration), with a set of experiments that determine two or more solution properties (such as viscosity, Tagg or kD). Formulation variable ranges, separated by boundary lines, create acceptable versus unacceptable ranges for each property, with the intersection of acceptable ranges emphasized in white. This multivariate analysis helps establish the optimal formulation design space.

The true power of the DynaPro Plate Reader III is that it can, in a single run, map out various essential biophysical properties in an easy and robust way.

  • Average molar mass
  • Average size
  • Polydispersity Index
  • Presence and quantity of large aggregates
  • Second virial coefficient A2
  • Diffusion interaction parameter kD
  • Onset temperature of aggregation Tagg
  • Onset temperature of unfolding Tonset
  • Onset temperature of interactions
  • Solution viscosity
  • Solubility

The DynaPro Plate Reader also does so in standard plates, across a large set of conditions, to create phase diagrams and even more complicated multivariate analyses. One instrument, so much information.

Phase diagrams used to map out optimal formulation space. Top: white space corresponds to kD values above 6 mL/g for colloidal stability and Tagg values above 65 °C for conformational stability and % large aggregates at 25 °C below 2%. Bottom: White space corresponds to viscosity η below 20 cP for injectability and Tagg above 70 °C for thermal stability.

Figure 17. Phase diagrams used to map out optimal formulation space. Top: white space corresponds to kD values above 6 mL/g for colloidal stability and Tagg values above 65 °C for conformational stability and % large aggregates at 25 °C below 2%. Bottom: White space corresponds to viscosity η below 20 cP for injectability and Tagg above 70 °C for thermal stability.

Epilogue: Be Productive

If the goal is to get biologics faster to market, then productivity is the name of the game. Users need additional protein stability and quality analyses, faster, covering more indicators. This dream can be realized with DynaPro Plate Reader III, which gives the confidence that can only be achieved by robust, detailed measurements of static and dynamic light scattering, over many replicates, samples, and conditions. It does all this easily and automatically in standard microwell plates, with high throughput, allowing users to be productive in other activities while SLS and DLS measurements are taking place.

This information has been sourced, reviewed and adapted from materials provided by Wyatt Technology.

For more information on this source, please visit Wyatt Technology.

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