Abstract
Affitins are a novel class of small 7 kDa artificial proteins which can be used as antibody substitutes in therapeutic, diagnostic and biotechnological applications. One challenge for this type of protein agent is their behaviour in the context of oral administration. The digestive system is central, and biorelevant media have fast emerged as relevant and reliable tools for evaluating the bioavailability of drugs. This study describes, for the first time, the stability of Affitins under simulated gastric and intestinal digestion conditions. Affitins appear to be degraded into stable fragments in in vitro gastric medium. We identified cleavage sites generated by pepsin that were silenced by site-directed mutagenesis. This protein engineering allowed us to enhance Affitin properties. We showed that a mutant M1 containing a double mutation of amino acid residues 6 and 7 in H4 and C3 Affitins acquired a resistance against proteolytic digestion. In addition, these mutations were beneficial for target affinity, as well as for production yield. Finally, we found that the mutated residues kept or increased the important pH and temperature stabilities of Affitins. These improvements are particularly sought after in the development of engineered binding proteins for research tools, preclinical studies and clinical applications.
Highlights
Affitins are a novel class of small 7 kDa artificial proteins which can be used as antibody substitutes in therapeutic, diagnostic and biotechnological applications
In the same simulated conditions, similar stable fragments were obtained with all the other Affitins we tested, while a total disappearance of proteins was observed with the other biological binders we examined, such as a nanobody and an antibody
Using our simulated gastric fluid FaSSGF containing pepsin, we investigated whether the substitutions introduced protect Affitins against proteolytic digestion
Summary
Affitins are a novel class of small 7 kDa artificial proteins which can be used as antibody substitutes in therapeutic, diagnostic and biotechnological applications One challenge for this type of protein agent is their behaviour in the context of oral administration. These improvements are sought after in the development of engineered binding proteins for research tools, preclinical studies and clinical applications. In that respect, elaborating in vitro biorelevant media that simulate human digestion has become increasingly important in nutritional and pharmaceutical research and d evelopment[6,7,8,9] Such media should facilitate the prediction of food and drug behaviours in terms of solubility and stability, minimizing the need for animal and human testing. A thermostable Affitin H4 (H4) directed against hen egg white lysozyme was identified[22] and used for different studies as proof of concept[18,19,23]
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