Pharmaceutical Technology - November 2018

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Pharmaceutical Technology LABORATORY BEST PRACTICES 2018 45 Technique limitations and evolution Despite the range of techniques available, "the short- coming that all techniques have is that you can't get everything in one measurement," says Roberts. With soft-matter physics, you may only need two tech- niques, or you might need different flavors of the same technique, he says. "That does not work with proteins, at least not for the kind of questions we have to answer, so we are always going to need multiple techniques." "Even with all the techniques that anyone can bring to bear, you still are missing some things, you are not getting the full 3-D structural picture you might want and the dynamics of that picture," Roberts explains. "You are always getting a piece of the puzzle. Even if you can double the number of techniques that we have right now, we still would be missing pieces." Roberts is charged with finding new technolo- gies for characterizing protein-protein interactions, protein-environment interactions, structures, and stability, or to find technologies maturing in other fields and adapt them for bioprocessing research. "I am always interested in exploring either truly new techniques using a technology that has not been brought to bear on proteins before, or technologies from other fields that we can adapt and bring to bear on protein-based problems," he says. For example, laser scattering technology was ma- ture in the polymer and colloid sciences fields 20 years ago, he explains, but protein scientists only had x-ray diffraction to get 3-D structures. Now, scattering tech- niques are a standard technique in protein research laboratories. When the scattering instruments first came out, they were limited to a one order-of-mag- nitude range of concentration. Current instruments have a wider range, and the laser can be tuned; sam- ples can be measured in a non-destructive manner. Most spectroscopy techniques are not new; how- ever, instruments have been adapted to be faster, less expensive, able to work with smaller samples, and work with a wider range of conditions. And, what is one technique's weakness is another technique's strength, Roberts says. Concentrating on results Fluorescence spectroscopy and CD spectroscopy were developed to work at very low concentration samples; however, a downfall of the instruments is if you go to 100 mg/mL, you will saturate the detector; so, you have to dilute, Roberts explains. A historic weakness for IR and Raman spectroscopy was that they were reliable only at high concentrations, because the signal inherently is much weaker, Roberts explains. The MMS technology from Redshift Bio has a different instrument design but is still IR spectros- copy. "And now you have a wider dynamic working range, you can work without diluting," he says. Biophysical techniques can be limited in the con- centration ranges they can run. "CD has a narrow linear range you can work in, especially far UV," says Kendrick. "Sometimes you have to dilute your sample quite a bit to get it down to a concentration that is compatible with the measurement; you don't know for sure whether the dilution is tweaking your profile." A technique may require a larger volume and con- centration of the sample, which is not available, forc- ing researchers to use an inferior technique—or no technique at all—which can create a gap in knowledge about the formulation. If sample manipulation is re- quired to perform a technique, interpreting the data to understand how the sample is behaving becomes a challenging, subjective exercise.

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