EFFECT OF STEREOCHEMISTRY ON THE TRANSPORT OF ACA-LINKED BETA-TURN PEPTIDOMIMETICS ACROSS A HUMAN INTESTINAL-CELL LINE

Transcellular transport is one of the most important barriers facing t he development of new therapeutic agents. However, little is known abo ut the specific effects of structure and particularly stereochemistry on cell permeability. An attractive in vitro model has been developed for the direct assessment of cell transport, using the immortalized hu man epithelial cell line, Caco-2. The present study assesses the effec ts of stereochemistry on transport in a commonly used beta-turn model system. Thus, L,L- and L,D-Ala-Ala were cyclized with aminocaproic aci d, resulting in macrocycles in which the dipeptides correspond to the i + 1 and i + 2 positions of a beta-turn. The transport of these dipep tides across a Caco-2 cell monolayer was determined, along with corres ponding acyclic models (L,L- and L,D-CH3CH2C(0)-Ala-Ala-n-Pr). The tra nsport studies were carried out in the presence and absence of verapam il, a known inhibitor of the apically polarized efflux system present in Caco-2 cells. Both apical-->basolateral and basolateral-->apical tr ansport were measured. Measurements made in the presence of verapamil showed that the cyclic peptides experienced a ca. 4-5-fold difference in intrinsic flux depending on stereochemistry, with the L,D isomer be ing transported at a higher rate. These differences disappeared in the acyclic cases examined (permeability coefficient ratios of the L,D/L, L isomers were 1.04-1.13). These observations are discussed in terms o f the conformations and hydrogen-bonding characteristics of the compou nds as determined by NMR spectroscopy. (C) 1997 Elsevier Science Ltd.