Application of lipophilic prodrug charge masking strategy to obtain novel, potential oxytocin prodrugs

A Lipophilic Prodrug Charge Masking (LPCM) strategy involves masking of hydrophilic peptide charges with alkoxycarbonyl groups, which are cleaved by esterases after intestinal absorption. This study investigates the LPCM strategy’s applicability to oxytocin (OT), a peptide with well-defined biological activity. A series of OT prodrugs with varying alkoxycarbonyl chain lengths (2 to 12 carbon atoms) were synthesized, and their permeability was assessed using parallel artificial membrane permeability assay (PAMPA) and Caco-2 cell culture models. The PAMPA results indicated that OT demonstrated poor permeability (Papp = 2.2 × 10−6 cm/s), while its prodrugs Hoc-OT, Oct-OT, and Dec-OT were characterized by significantly better permeability, with Dec-OT achieving a four-fold increase over OT. The prodrug with a 12-carbon chain (Dod-OT) exhibited poor permeability; however, its high mass retention suggests strong membrane affinity. Further evaluation, using the Caco-2 cell model, revealed a 1.8-fold higher Papp of Oct-OT compared to OT, indicating possible higher oral availability. Conversely, Hoc-OT exhibited lower permeability than OT. Our findings indicate that the LPCM strategy can effectively boost the oral bioavailability of certain peptides, paving the way for their transformation into bioavailable drugs.