Improving on nature: making a cyclic heptapeptide orally bioavailable

Area of Science:

• Medicinal Chemistry
• Drug Delivery
• Peptide Therapeutics

Background:

• Peptide drugs face significant limitations in medical applications, including poor membrane permeability, rapid metabolic degradation, high clearance rates, and virtually no oral bioavailability.
• Current methods for predicting oral drug bioavailability, based on physicochemical properties favoring passive permeability and metabolic stability, are often inadequate for peptides.

Purpose of the Study:

• To investigate how structural modifications, specifically heterocyclic constraints, intramolecular hydrogen bonds, and side-chain alterations, influence the oral bioavailability of cyclic heptapeptides.
• To explore strategies for enhancing oral peptide bioavailability without resorting to N-methylation.

Main Methods:

• Utilized Nuclear Magnetic Resonance (NMR) spectroscopy to determine the three-dimensional structures of cyclic heptapeptides.
• Assessed intramolecular hydrogen bond strength using amide H-D exchange rates.
• Analyzed the impact of structural features on bioavailability in rat models.

Main Results:

• The study demonstrated that incorporating heterocyclic constraints significantly rigidifies the peptide structure.
• Stronger intramolecular hydrogen bonds and solvent shielding provided by branched side chains were identified as key factors.
• These combined modifications successfully enhanced the oral bioavailability of cyclic heptapeptides in rats.

Conclusions:

• Structural rigidification, enhanced hydrogen bonding, and strategic side-chain design can overcome the limitations of oral peptide drug delivery.
• This approach improves oral bioavailability of cyclic heptapeptides without requiring N-methylation, presenting a viable strategy for developing oral peptide therapeutics.