Enabling Oral and Parenteral Delivery of GLP-1 Peptide from Biophysical and Molecular Investigations

The global market for peptide therapeutics is expanding across various therapeutic domains, underscoring their potential to address unmet medical needs and expanding with rapidly growing pipelines for metabolic, endocrine, and oncology indications. Insulin, glucagon, and GLP-1 receptor agonists—used for type 2 diabetes and obesity—generate a large fraction of peptide revenue, and several GLP 1 drugs are now widely used. Compared with small molecules, peptides’ larger size and conformational flexibility enable potent protein interactions but also cause low physicochemical stability and rapid clearance, complicating development. Therapeutic peptides treating metabolic and autoimmune conditions often require repeated dosing of the same drug over an extended period. As such, these peptides are preferred to be manufactured and delivered in a prefilled syringe autoinjector (use pre-filled syringes (PFS) as primary container) or pen (use pre-filled cartridges as primary container) to facilitate patient self-administration, which also improves dosing accuracy and patient compliance. More recently, the quest for noninvasive, patient-friendly delivery methods has led to intensive research into alternative strategies, with oral delivery standing out as a highly desirable option.

This presentation discusses how to enable oral and parenteral delivery of GLP-1 peptide from biophysical and molecular investigations through three case studies from the drug substance, drug product, and peptide delivery perspectives. The first case study will discuss the molecular mechanism of liraglutide oligomerization. Liraglutide, a fatty acylated GLP-1 analog, displays pH-dependent oligomerization that alters stability and bioactivity. The structural drivers of this assembly remain unclear. To investigate, we used size exclusion chromatography (SEC) and circular dichroism (CD), and applied advanced nuclear magnetic resonance (NMR) to define residue-level interactions and elucidate the structural basis of lipidation-induced oligomerization. These results define how the acyl chain, peptide packing, and dynamics cooperate to drive liraglutide oligomerization. The second case study will discuss the molecular mechanisms of liraglutide aggregation induced by dual air-water and silicone-oil-water interfacial stress. We utilized advanced techniques to probe silicone‑oil-liraglutide interactions and interfacial stress, including high‑resolution label‑free stimulated Raman scattering (SRS) for chemical imaging and nuclear magnetic resonance (NMR) spectroscopy for structural characterization. We observed, for the first time, the peptide adsorption on the silicone oil surface at submicrometer resolution by SRS. Our data suggest that the dual air-water and silicone-oil-water interfacial stress plays a significant role in liraglutide aggregation. These findings emphasize the interactive roles of several stress parameters, including silicone oil concentration, silicone oil interface, headspace, and agitation strength, on the stability of peptide combination drug products, and highlight the critical role of interfacial stress-induced biophysical instability. The third case study will discuss the molecular investigation of SNAC as an oral peptide permeation enhancer in lipid membranes via ssNMR. Our findings indicate an overall increase in the uniaxial motion of phospholipids with SNAC in a PE concentration-dependent manner. This study provides the first quantitative and site-specific ssNMR measurements of membrane mobility influenced by one representative PE as a snapshot of PE lipid interaction in a liposome model, demonstrating how peptide drugs modulate competitive equilibria and PE-induced lipid dynamics.