Evaluation of N-(2-hydroxypropyl)methacrylamide copolymer-peptide conjugates as potential oral vaccines. Studies on their degradation by isolated rat small intestinal peptidases and their uptake by adult rat small intestinal tissue in vitro

Oral administration therapeutic peptides and peptide antigens has achieved limited success owing to their degradation and poor transport across the gastrointestinal tract. In this study covalent coupling of peptides to the water soluble polymer N-(2-hydroxypropyl)methacrylamide (HPMA) is explored as a means to overcome these problems. A model peptide, b-chain of insulin (b-chain), and the human rhinovirus antigenic determinant, peptide VP2, were covalently bound to HPMA copolymers of molecular weight; 23 200 to give a peptide content of approximately 25% (w/w). Conjugation resulted in a marked reduction in the rate of degradation of both peptides during in vitro incubation with small intestinal brush border (BBM) and luminal enzymes. In the case of b-chain, reductions of up to 80% and 60% were observed with BBM and luminal peptidases, respectively. For peptide VP2, reductions up to a maximum of 80% and 55% were observed with BBM and luminal peptidases, respectively. Incubation of I-125-labelled b-chain with everted rat jejunal sacs in vitro showed no serosal transfer of intact free I-125-labelled b-chain as a result of peptide degradation. In contrast, the I-125-labelled HPMA copolymer-peptide conjugate displayed transfer of intact b-chain into the serosal fluid, and sacs with or without Peyer's Patches (PP) displayed transfer of 66 and 58 ng of conjugated b-chain per mg tissue protein. As polymer conjugation both protects against peptide degradation and promotes peptide uptake, HPMA copolymer conjugation has the potential to improve oral vaccination using peptide antigens.