Therapeutic antibodies have revolutionized the treatment of numerous diseases, but not every antibody has what it takes to become a licensed medicine. Finding a high-affinity antibody that binds to your target is only the first step. The ideal therapeutic antibody must have good efficacy, safety, pharmacokinetics (PK) and stability, and in addition, be easy to manufacture to ensure commercial viability.
Safety is the first requirement for any medicine, and this is no different for therapeutic antibodies. Perhaps most importantly, a good therapeutic antibody should bind to its target with high specificity. For example, an antibody that is designed to target tumour cells should ignore healthy cells, as off-target binding might lead to unexpected side effects.
It’s also crucial to fine-tune the antibody’s affinity – how tightly it binds to its target. If the affinity is too low and the antibody binds its target only weakly, the therapeutic effect may not be achieved. Conversely, if the affinity is too high, the antibody dose could be “used up” too quickly, and the likelihood of off-target activity might increase.
Another important step is to minimise the risk of the antibody generating an immunogenic reaction. If an antibody is unstable, it can aggregate, misfold or even give rise to potentially dangerous metabolites such as charge variants (which occur when an amino acid has been oxidised or deaminated). These seemingly minor changes can render an antibody immunogenic, as well as reducing its efficacy.
Optimising efficacy and PK
When it comes to optimising the efficacy of an antibody, one of the major challenges is fine-tuning its affinity. The antibody needs to have sufficiently high affinity to ensure that it works as intended, but not high enough that it binds to off-target molecules and causes unintended side effects. In some cases, reducing the antibody’s affinity might actually increase its functionality, particularly in the case of multi-specific antibodies that bind two or more antigens at once (1).
Therapeutic antibodies also need to be delivered efficiently to where they’re needed in the body, and hang around for long enough to have an effect. At the same time, there should be a focus on minimising the number of doses the patient requires. The PK of the antibody can be optimised by careful screening for liabilities in its sequence that could, for example, make it unstable, meaning greater and more frequent doses are required.
Optimising antibody expression and considering the “manufacturability” of antibody sequences is fundamental to developing any therapeutic antibody. A functionally perfect antibody that becomes overly modified or degraded during large scale manufacture will not make it to the clinic. For example, manufacturability can be affected by free cysteines, formation of interchain disulphide bond formation and aggregation. Less dramatic self-interaction may still only be evident at the high concentrations required for a clinical production batch.
Help from a trusted partner
As previously mentioned, finding a high-affinity antibody that binds to your target is only the first step. We guide our clients through the pre-clinical pathway, helping them avoid expensive, lengthy and unnecessary mistakes.
1 Mazor, Y., Sachsenmeier, K., Yang, C. et al. Enhanced tumor-targeting selectivity by modulating bispecific antibody binding affinity and format valence. Sci. Rep. 7, 40098 (2017).