Development and Analysis of a Polymer Protecting from Luminal Enzymatic Degradation Caused by α-Chymotrypsin

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Abstract
We have been developing a modified polymer which protects inserted peptide and protein drugs from chymotrypsinic degradation. A trypsin-chymotiypsin-inhibitor was covalently bound to a bioadhesive polymer (poly (acrylic acid)) by a condensation reaction of the available amino groups of the inhibitor with the carboxyl groups of the polymer. The inhibition of α-chymotrypsin by the isolated conjugate was determined by an enzyme assay using N-benzoyl-L-tyrosine ethyl ester as substrate. It had an inhibitory effect of 2.4 CIU (= chymotrypsin inhibiting units) per mg. The protective effect was also evaluated in a drug delivery system containing 5% of this modified polymer. Under physiological α-chymotrypsin concentrations it demonstrated, in lateral parts of the carrier matrix, the remaining of 71.4% ± 14.3% (means of three experiments; ± S.D.) of undigested inserted test-protein (β-galactosidase) afer 7 hr of incubation at 37 ± 0.5°C. Samples from the center of the matrix did not show any digestion of the protein. On the other hand a complete digestion in lateral parts and the remaining of only 67% ± 14.4% of undigested test-protein in the center, could be observed by the same delivery system without the conjugate. Because of this verified protective effect and the possibility to exclude toxic side effects of the inhibitor by immobilization, the system described here seems to be an important step towards a successful peroral (poly)peptide drug administration.