Abstract
Purpose. To evaluate the cellular permeation characteristics and the chemical and enzymatic stability of coumarinic acid-based cyclic prodrugs 1 and 2 of the opioid peptides [Leu5]-enkephalin (H-Tyr-Gly-Gly-Phe-Leu-OH) and DADLE (H-Tyr-D-Ala-Gly-Phe-D-Leu-OH), respectively. Methods. The rates of conversion of the cyclic prodrugs 1 and 2 to [Leu5]-enkephalin and DADLE, respectively, in HBSS, pH 7.4 (Caco-2 cell transport buffer) and in various biological media having measurable esterase activity were determined by HPLC. The cell permeation characteristics of [Leu5]-enkephalin, DADLE and cyclic prodrugs 1 and 2 were measured using Caco-2 cell monolayers grown onto micropores membranes and monitored by HPLC. Results. In HBSS, pH 7.4, cyclic prodrugs 1 and 2 degraded chemically to intermediates that further degraded to [Leu5]-enkephalin and DADLE, respectively, in stoichiometric amounts. In 90% human plasma and rat liver homogenate, the disappearance of cyclic prodrugs 1 and 2 was significantly faster than in HBSS, pH 7.4. The half- lives in 90% human plasma and in rat liver homogenate were substantially longer after pretreatment with paraoxon, a known inhibitor of serine- dependent esterases. When applied to the AP side of a Caco-2 cell monolayer, cyclic prodrug 1 exhibited significantly greater stability against peptidase metabolism than did [Leu5]-enkephalin. Cyclic prodrug 2 and DADLE exhibited similar stability when applied to the AP side of the Caco-2 cell monolayer. Prodrug 1 was 665-fold more able to permeate the Caco-2 cell monolayers than was [Leu5]-enkephalin, in part because of its increased enzymatic stability. Prodrug 2 was shown to be approximately 31 fold more able to permeate a Caco- 2 cell monolayer than was DADLE. Conclusions. Cyclic prodrugs 1 and 2, prepared with the coumarinic acid promoiety, were substantially more able to permeate Caco-2 cell monolayers than were the corresponding opioid peptides. Prodrug 1 exhibited increased stability to peptidase metabolism compared to [Leu5]-enkephalin. In various biological media, the opioid peptides were released from the prodrugs by an esterase-catalyzed reaction, which is sensitive to paraoxon inhibition.
Original language | English (US) |
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Pages (from-to) | 7-15 |
Number of pages | 9 |
Journal | Pharmaceutical Research |
Volume | 16 |
Issue number | 1 |
DOIs | |
State | Published - 1999 |
Externally published | Yes |
Keywords
- Caco-2 cells
- Chemical and enzymatic stability
- Esterase-sensitive prodrugs
- Membrane permeability
- Opioid peptides
- Peptide delivery
ASJC Scopus subject areas
- Biotechnology
- Molecular Medicine
- Pharmacology
- Pharmaceutical Science
- Organic Chemistry
- Pharmacology (medical)