Ligation of Soluble but Unreactive Peptide Segments in the Chemical Synthesis of Haemophilus Influenzae DNA Ligase

A Novel d-Peptide Identified by Mirror-Image Phage Display Blocks TIGIT/PVR for Cancer Immunotherapy

The low response rate and adaptive resistance of PD-1/PD-L1 blockade demands the studies on novel therapeutic targets for cancer immunotherapy. We discovered that a novel immune checkpoint TIGIT expressed higher than PD-1 in many tumors especially anti-PD-1 resistant tumors. Here, mirror-image phage display bio-panning was performed using the d-enantiomer of TIGIT synthesized by hydrazide-based native chemical ligation. d-peptide ^D TBP-3 was identified, which could occupy the binding interface and effectively block the interaction of TIGIT with its ligand PVR. ^D TBP-3 showed proteolytic resistance, tumor tissue penetrating ability, and significant tumor suppressing effects in a CD8⁺ T cell dependent manner. More importantly, ^D TBP-3 could inhibit tumor growth and metastasis in anti-PD-1 resistant tumor model. This is the first d-peptide targeting TIGIT, which could serve as a potential candidate for cancer immunotherapy.

Synthesis of Disulfide Surrogate Peptides Incorporating Large-Span Surrogate Bridges Through a Native-Chemical-Ligation-Assisted Diaminodiacid Strategy

The use of synthetic bridges as surrogates for disulfide bonds has emerged as a practical strategy to obviate the poor stability of some disulfide-containing peptides. However, peptides incorporating large-span synthetic bridges are still beyond the reach of existing methods. Herein, we report a native chemical ligation (NCL)-assisted diaminodiacid (DADA) strategy that enables the robust generation of disulfide surrogate peptides incorporating surrogate bridges up to 50 amino acids in length. This strategy provides access to some highly desirable but otherwise impossible-to-obtain disulfide surrogates of bioactive peptide. The bioactivities and structures of the synthetic disulfide surrogates were verified by voltage clamp assays, NMR, and X-ray crystallography; and stability studies established that the disulfide replacements effectively overcame the problems of disulfide reduction and scrambling that often plague these pharmacologically important peptides.