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Starting from the approval of two oral cyclic peptides, this article analyzes R&D opportunities for cyclic peptide therapeutics in antibody replacement, targeted radiopharmaceuticals, chronic diseases, intracellular protein–protein interactions, and targeted protein degradation.
Compare the targets, discovery technologies, molecular optimization, and oral delivery strategies of the two oral cyclic peptide drugs Icotrokinra and Enlicitide to understand how they are turning the drug space between traditional small molecules and antibodies into an actively developable direction.
From first-in-human exposure to FRONTIER and ICONIC, icotrokinra ultimately demonstrated that an oral cyclic peptide of nearly 1900 Da can translate limited absorption into clinical efficacy for patients and become an FDA-approved drug.
icotrokinra still has difficulty crossing the intestinal epithelium, but its gastrointestinal stability, 200 mg dose, and picomolar-level potency allow even limited absorption to generate effective systemic exposure.
Starting from oral proof-of-concept lead Compound 1a, the team addressed oxidation, solubility, process-safety, and isomer liabilities through a five-module platform and selected Compound 18—MK-0616/Enlicitide.
Peptide 1185 is already stable and highly engineered, so why continue to modify a small number of residues? This article uses real patent SAR to distinguish experimental results from structural interpretation.
The oral development of ICOTYDE first addresses not substantial systemic absorption, but gastrointestinal stability. Peptide 1185 demonstrates how cyclization, terminal capping, and engineered residues such as Pen, 2-Nal, F(4-2ae), and Lys(Ac) can jointly expand the chemical space of natural peptides.
From the established bicyclic platform to tricyclic Compound 35 and property-engineered Compound 44, the program combined potency, stability, PK, and an enabled formulation to demonstrate oral PCSK9 target engagement in primates.
Compound 30 had a clear PCSK9 binding mode, but stability, PK, safety, and solubility remained unresolved. Structure-guided D-amino-acid substitution, bicyclization, and N-methylation advanced the series while revealing new developability liabilities.
Compound 30 enabled the first co-crystal structure for this PCSK9 macrocycle series, making its binding mode visible and turning empirical SAR into testable structure-based design hypotheses.
PCSK9 was a validated yet difficult protein–protein interaction target. mRNA display found two cyclic-peptide hit series in a vast chemical space, but a binder was only the beginning of the drug-discovery journey.
mRNA display discovers signals across large molecular spaces, AI helps prioritize candidates and guide the next design round, and experiments determine which ideas should move forward.