Preparation of μSPOT Lactam-Cyclized Peptides for Ligand Optimization

Cyclic peptides have emerged as promising therapeutic agents for targeting challenging protein-protein interactions (PPIs), combining high affinity, specificity, stability, and potential for improved drug-like properties. The outlined protocol describes a streamlined method for side chain-to-side chain lactam cyclization in a peptide array format based on the μSPOT method. The approach enables efficient synthesis and screening of cyclic peptide libraries with minimal synthetic effort, focusing on exploring cyclization positions and linker topology. The method is exemplified by developing cyclic peptide modulators of the APP/Mint2 PPI, a target implicated in Alzheimer's disease. The workflow integrates orthogonal protection strategies, analytical controls, and array-based binding assays, enabling the identification of binding-optimized cyclic peptides. Follow-up validation through fluorescence polarization assays demonstrated a strong correlation with array-based relative binding data (r² = 0.88). The described approach is versatile and scalable, offering a robust platform for discovering novel cyclic peptides with enhanced stability, affinity, and permeability, paving the way for advanced therapeutic applications in PPI modulation.