PARTIALLY UNFOLDED PROTEINS EFFICIENTLY PENETRATE CELL-MEMBRANES - IMPLICATIONS FOR ORAL-DRUG DELIVERY

We have previously reported on the biological activity of members of a library of low molecular weight compounds (carriers) that enable the oral delivery of proteins (Milstein, Proceedings of the 1995 Miami Bio /Technology Winter Symposium on Protein Engineering and Structural Bio logy, IRL Press at Oxford Vniversity Press, 1995, p. 13; Leone-Bay et al., J. Med. Chem. 38 (1995) 4263-4269; Leone-Bay et al., J. Med. Chem . 39 (1996) 2571-2578; [1-3]). When rats or primates are orally admini stered a solution of carrier and either recombinant human alpha-interf eron (rhIFN), insulin or recombinant human growth hormone (rhGH) signi ficant serum concentrations of the proteins are detectable. The transp ort activity of these compounds is positively correlated with their st ructural effects on the protein molecules. Direct measurement of the i nteraction of these carrier molecules with the proteins indicates that they reversibly destabilize the native state of the molecule favoring a partially unfolded conformation. Apparently these intermediate prot ein conformations are transport competent and are able to be absorbed through the intestinal tissue and into the bloodstream. Since the meas ured binding of the carriers to the partially unfolded proteins is rel atively weak (K-b=100 M-1) and the systemic activity of the proteins a ppears to be unaffected, the changes in the structure of the proteins are manifestly reversible. (C) 1998 Elsevier Science B.V.