Novel oral drug formulations. Their potential in modulating adverse effects

Biologically erodable microspheres as potential oral drug delivery systems

Biologically adhesive delivery systems offer important advantages over conventional drug delivery systems. Here we show that engineered polymer microspheres made of biologically erodable polymers, which display strong adhesive interactions with gastrointestinal mucus and cellular linings, can traverse both the mucosal absorptive epithelium and the follicle-associated epithelium covering the lymphoid tissue of Peyer's patches. The polymers maintain contact with intestinal epithelium for extended periods of time and actually penetrate it, through and between cells. Thus, once loaded with compounds of pharmacological interest, the microspheres could be developed as delivery systems to transfer biologically active molecules to the circulation. We show that these microspheres increase the absorption of three model substances of widely different molecular size: dicumarol, insulin and plasmid DNA.

Design and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion

Site-directed mutagenesis was used to construct pepsin-resistant, single-point mutations of the N-terminal extended IGF-I analogue, long-R3-IGF-I. In order to identify the most susceptible sites, the kinetics of long-R3-IGF-I digestion by purified porcine pepsin were determined. Pepsin initially cleaved the Leu10-Phe11 bond in the N-terminal extension peptide to generate FVN-R3-IGF-I, followed in rapid succession by cleavage at Gln15-Phe16, Tyr24-Phe25, Leu10-Val11 and Met59-Tyr60 in the IGF-I moiety. Single-point mutations at these sites were designed on the basis of the preferred cleavage bonds for pepsin, as well as amino acid substitutions less likely to disturb protein structure. These included Leu10Val, Phe16Ala, Phe25Leu, Asp53Glu and Met59Gln. All five muteins retained growth-promoting activity equivalent to or higher than that of IGF-I. In terms of pepsin susceptibility, Leu10Val and Asp53Glu were degraded as rapidly as the parent long-R3-IGF-I, Met59Gln and Phe25Leu were partially stabilised, and Phe16Ala showed a marked improvement in stability over a wide range of pepsin:substrate ratios. Accordingly, the Phe16Ala mutein, long-R3A16-IGF-I, has potential for oral applications to enhance gastric growth and repair.