Structure-activity relationship of carbacephalosporins and cephalosporins: antibacterial activity and interaction with the intestinal proton-dependent dipeptide transport carrier of Caco-2 cells

Abstract

An intestinal proton-dependent peptide transporter located on the lumenal surface of the enterocyte is responsible for the uptake of many orally absorbed beta-lactam antibiotics. Both cephalexin and loracarbef are transported by this mechanism into the human intestinal Caco-2 cell line. Forty-seven analogs of the carbacephalosporin loracarbef and the cephalosporin cephalexin were prepared to evaluate the structural features necessary for uptake by this transport carrier. Compounds were evaluated for their antibacterial activities and for their ability to inhibit 1 mM cephalexin uptake and, subsequently, uptake into Caco-2 cells. Three clinically evaluated orally absorbed carbacephems were taken up by Caco-2 cells, consistent with their excellent bioavailability in humans. Although the carrier preferred the L stereoisomer, these compounds lacked antibacterial activity and were hydrolyzed intracellularly in Caco-2 cells. Compounds modified at the 3 position of cephalexin and loracarbef with a cyclopropyl or a trifluoromethyl group inhibited cephalexin uptake. Analogs with lipophilic groups on the primary amine of the side chain inhibited cephalexin uptake, retained activity against gram-positive bacteria but lost activity against gram-negative bacteria. Substitution of the phenylglycl side chain with phenylacetyl side chains gave similar results. Compounds which lacked an aromatic ring in the side chain inhibited cephalexin uptake but lost all antibacterial activity. Thus, the phenylglycl side chain is not absolutely required for uptake. Different structural features are required for antibacterial activity and for being a substrate of the transporter. Competition studies with cephalexin indicate that human intestinal Caco-2 cells may be a useful model system for initially guiding structure-activity relationships for the rational design of new oral agents.

Structural Biology and Function of Solute Transporters: Implications for Identifying and Designing Substrates

“…In addition to transporting its natural substrates, di-and tri-peptides occurring in food products, [52 -56] it shows affinity toward a broad range of peptidelike pharmaceutically relevant compounds, such as b-lactam antibiotics [57,58] and "angiotensin converting enzyme" (ACE)-inhibitors. [59 -69] In fact, these molecules can oftentimes be viewed as "peptide-like" in their molecule composition (Fig.…”

Functional Expression of Stereoselective Metabolism of Cephalexin by Exogenous Transfection of Oligopeptide Transporter PEPT1

“…However, it was shown that L-CEX binds to the peptide transporter with high affinity and L-CEX is transported by assessing substrate-induced intracellular acidification caused by H ϩ cotransported with the substrate in Caco-2 cells (Wenzel et al, 1995). Regarding affinity of CEX to the H ϩ -coupled peptide transporter, L-CEX competitively inhibited D-CEX uptake more strongly than did D-CEX itself in a rat intestinal everted sac and human intestinal model cell line Caco-2 cells (Tamai et al, 1988;Wenzel et al, 1995;Snyder et al, 1997). Thus, although L-CEX seems to be transported via the same carrier system as D-CEX and the affinity of the transporter for L-CEX is higher than that for D-CEX, L-CEX is not detected inside the cells because it is metabolized very rapidly.…”

“…L-CEX is not used as a medicine because it is rapidly metabolized after administration p.o. (Tamai et al, 1988), and it lacks antibacterial activity (Snyder et al, 1997). D-CEX is a highly hydrophilic compound, and it mainly exists in an ionized form in the vicinity of the brush-border membrane of intestinal epithelial cells, where the microclimate pH is 6.5 to 7.5 in the rat jejunum (Iwatsubo et al, 1986) and the pK a values of D-CEX are 2.56 and 6.88 (Yamana and Tsuji 1976).…”

In Vitro and Pharmacophore-Based Discovery of Novel hPEPT1 Inhibitors

“…In addition to transporting its natural substrates, di-and tri-peptides occurring in food products (5), it shows affinity toward a broad range of peptide-like pharmaceutically relevant compounds, such as ␤-lactam antibiotics (6) and angiotensin converting enzyme (ACE)-inhibitors (7). For this reason, hPEPT1 has been recognized as an important intermediate in the oral bioavailability of peptidomimetic compounds (8).…”