epidermal-growth-factor and pepstatin

The promising strategy of gastric ulcer healing with perorally administered epidermal growth factor (EGF) is so far strongly limited by the pepsinic degradation of this therapeutic polypeptide in the stomach. The incorporation of EGF in a bioadhesive polymer-pepsin inhibitor conjugate used as drug carrier matrix, however, might provide sufficient protection toward pepsinic degradation. The synthesis of appropriate pepsin inhibitors represents a prerequisite for the development of such polymer-inhibitor conjugates. The presented study demonstrates that modifications at the N-terminus of simplified analogues of pepstatin which can be synthesized in a simple and straight way result only in slight variations of the inhibitory activity. These analogues display only 10-fold reduced inhibitory activity, compared to pepstatin A, when bearing a greater N-terminal group like isovaleryl, Boc, or Cbz. Compounds which are substituted at the N-terminus by a shorter N-acyl group like propionyl or cyclopropylcarbonyl show further reduced activity (0.01, compared to pepstatin A). The presence of an amide or a urethane moiety at the N-terminus has no considerable effect on enzyme inhibition. Therefore, the N-terminus of these analogues is able to be modified forming a covalent bond to various bioadhesive polymers via a suitable functionality.

Topics: Anti-Ulcer Agents; Drug Delivery Systems; Epidermal Growth Factor; Pepstatins; Protease Inhibitors

The peroral administration of (poly)peptide drugs requires the development of delivery systems, which provide a protective effect toward a gastrointestinal enzymatic attack. A promising strategy for such systems represents polymer-enzyme inhibitor conjugates in which the embedded therapeutic agent is protected. However, the practical use of polymer-inhibitor conjugates has so far been limited by high production costs of these auxiliary agents. To solve this problem for delivery systems shielding from pepsinic degradation, structurally simplified analogues of the pepsin inhibitor pepstatin A have been synthesized. The synthesis of tripeptide analogues, described by McConnell et al., led us to pursue further modifications varying the C-terminus. Our target to attach a spacer moiety-enabling the free access of pepsin to the inhibitor-should be combined with an attractive synthetic approach providing low production costs in large-scale preparation. Structure modifications comprised either the side chain of the third amino acid which served as starting compound designing the C-terminus (L-leucine, L-isoleucine, L-norvaline) as the length of the spacer link, simulated by a linear alkyl group (n-butyl, n-hexyl, and n-octyl). The inhibitory activities which have been evaluated by an enzyme assay were significantly dependent on the nature of the side chain, whereas the length of the spacer had no influence on the inhibitory effect. Analogues bearing the isobutyl or n-propyl moiety as side chain displayed a strong inhibitory effect which was comparable to that pepstatin A. These congeners represent promising auxiliary agents for the peroral administration of (poly)peptide drugs.

Topics: Administration, Oral; Drug Delivery Systems; Epidermal Growth Factor; Horseradish Peroxidase; Hydrolysis; Pepsin A; Pepstatins; Peptides; Protease Inhibitors; Proteins