Candidate selection is the third phase of the drug development process.¹ The main purpose of candidate selection is to continue screening and filtering down to the most promising antibodies, ideally having one or two progress forward. During this phase, researchers are looking to evaluate the developability of a pool of less than five antibodies. One important parameter to evaluate developability is the antibody’s conformational stability, measured by T_onset and T_M, with differential scanning calorimetry (DSC) being the tool of choice. The candidates with the highest conformational stability have the highest potential for future drug usage. Traditionally, DSCs require a large amount of protein sample to accurately measure T_onset and T_M, but it is critical to get an accurate value for both the T_onset and T_M which is why DSC is still the gold standard for this measurement. At this stage it is also important to start testing on higher concentrations that will mimic dosage concentrations, as conformational stability can be affected by the concentration of the antibody formulation.

As mentioned above, proteins with the highest conformation stability are the most promising for drug use. Ideally a candidate will have a T_onset >55°C, T_M of the Fab domain >65°C. Microcalorimetry techniques, such as the Nano DSC, are designed to measure conformational stability through a controlled temperature ramp. As researchers utilize this technology, they can prioritize which antibodies are most stable and therefore have a higher probability for successful drug development. It is important to note that the thermogram obtained for an antibody under certain conditions is like a fingerprint, unique. This thermogram gives insights into the antibody’s structure, which is important because there is a strong correlation between structure and function for antibodies. The thermograms obtained during candidate selection can serve as a baseline as the antibody progresses to the formulation stage of drug development, where further screening of buffers is performed.

During the formulation phase of drug development, researchers transition from solely screening antibodies to screening both antibodies and different additives, such as excipients, buffers, salts, etc. In this stage, they are typically evaluating the final one or two antibodies to develop the first in human (FIH) formulation for trials. Conformational stability still plays an important role in this phase because it is necessary to evaluate the effects of stability as a function of these different buffer formulations. If the antibody formulation is lyophilized for storage, excipients play a huge role in protecting the structure of the antibody to ensure that it remains intact upon reconstitution.² Therefore, it is crucial that the final excipient chosen exhibits superior stability properties.

It is important to consider efficiency, and more specifically the time it takes, when testing different excipients. Different variations of each of the formulation components can result in hundreds of individual samples that need to be tested. Tools such as the autosampler for Nano DSC enable higher throughput and less hands-on time. High throughput experimentation is the future of developability testing, as it enables rapid optimization of antibody formulations.

Overall, it is crucial to begin optimizing formulations after the candidate selection process. Specifically, conformational stability is a key parameter for determining the likelihood of antibodies to act as a successful drug. When developing an antibody, it is important to also consider the structural stability of the excipient, as this will influence the biophysical properties of the drug to interactions between the two compounds. Therefore, it is important to be able to quickly screen large quantities of formulations, highlighting the value of automation. The future of drug development lies in high throughput experimentation, where researchers can rapidly optimize and screen different antibodies and formulations, allowing for more efficient evaluation of different drug candidates.