A platform of ADAPTive scaffolds: development of CDR-H3 β-hairpin mimics into covalent inhibitors of the PD1/PDL1 immune checkpoint.

Aberrant and dysregulated protein-protein interactions (PPIs) drive a significant number of human diseases, which is why they represent a major class of targets in drug discovery. Although a number of high-affinity antibody-based drugs have emerged in this therapeutic space, the discovery of smaller PPI inhibitors is lagging far behind, underscoring the need for novel scaffold modalities. To bridge this gap, we introduce a biomimetic platform technology - adaptive design of antibody paratopes into therapeutics (ADAPT) - that enables the paratope-forming binding loops of antibodies to be crafted into large β-hairpin scaffolds (ADAPTins). In this study, we describe a novel strategy for engineering native CDR-H3 "hot loops" with varying sequences, lengths, and rigidity into ADAPTins, ultimately transforming these compounds into irreversible covalent inhibitors. A proof-of-concept was established by creating a series of ADAPTin blockers of the PD1:PDL1 immune checkpoint PPI (blocking activity EC₅₀ < 0.3 μM) which were subsequently modified into potent covalent PD1 inhibitors. The compelling rate of stable and folded ADAPTins above physiological temperature (21 out of 29) obtained across six different scaffolds suggests that the platform technology could provide a novel opportunity for high-quality peptide display and biological screening.