Chemical Synthesis of Interleukin-6 for Mirror-Image Screening.

Interleukin-6 (IL-6), a multifunctional cytokine, is an attractive therapeutic target for immunological and inflammatory diseases. We investigated the chemical synthesis of IL-6 and its enantiomer (d-IL-6) using a sequential N-to-C native chemical ligation strategy from six peptide segments. Solubilizing Trt-K10 tags improved the intermediate solubility and served as protecting groups during the metal-free desulfurization to facilitate the synthesis of full-length IL-6 protein. Synthetic l-IL-6 and recombinant IL-6 exhibited nearly identical structural and binding properties. The symmetrical binding property of d-IL-6 was also demonstrated by functional analysis using IL-6-binding peptides. The resulting functional d-IL-6 was employed to screen a phage-displayed antibody fragment library, leading to the identification of several d-IL-6-binding single-domain antibodies. This work will contribute to the development of novel, potent IL-6 inhibitors without the adverse effects of undesired immune activation.

Engineering a Low-Immunogenic Mirror-Image VHH against Vascular Endothelial Growth Factor.

Immunogenicity is a major caveat of protein therapeutics. In particular, the long-term administration of protein therapeutic agents leads to the generation of antidrug antibodies (ADAs), which reduce drug efficacy while eliciting adverse events. One promising solution to this issue is the use of mirror-image proteins consisting of d-amino acids, which are resistant to proteolytic degradation in immune cells. We have recently reported the chemical synthesis of the enantiomeric form of the variable domain of the antibody heavy chain (d-VHH). However, identifying mirror-image antibodies capable of binding to natural ligands remains challenging. In this study, we developed a novel screening platform to identify a d-VHH specific for vascular endothelial growth factor A (VEGF-A). We performed mirror-image screening of two newly constructed synthetic VHH libraries displayed on T7 phage and identified VHH sequences that effectively bound to the mirror-image VEGF-A target (d-VEGF-A). We subsequently synthesized a d-VHH candidate that preferentially bound the native VEGF-A (l-VEGF-A) with submicromolar affinity. Furthermore, immunization studies in mice demonstrated that this d-VHH elicited no ADAs, unlike its corresponding l-VHH. Our findings highlight the utility of this novel d-VHH screening platform in the development of protein therapeutics exhibiting both reduced immunogenicity and improved efficacy.