Specificity of doxorubicin versus rhodamine-123 in assessing P-glycoprotein functionality in the LLC-PK1, LLC-PK1 : MDR1 and Caco-2 cell lines

The LLC-PK1:MDR1, LLC-PK1 and Caco-2 cell lines were used to investigate wh ether rhodamine-123 or doxorubicin would be the preferred substrate to stud y P-glycoprotein (P-gp) functionality in vitro. Both rhodamine-123 and doxo rubicin showed highly polarised transport in the Caco-2 cell Line and the L LC-PK1:MDR1 cell line, indicating that P-gp is actively transporting these drugs. However, for rhodamine-123 polarised transport was also seen in the monolayers of the wild-type LLC-PK1 cell line, indicating the presence of a nother active transporter for this compound. Polarised transport of doxorub icin in the Caco-2 and the LLC-PK1:MDR1 cell lines could be inhibited by th e P-gp inhibitors SDZ-PSC 833 (PSC 833), cyclosporin A (CsA), verapamil and quinine, but not by the inhibitors for the organic cation carrier systems cimetidine and tetraethylammonium (TEA). Polarised transport of rhodamine-1 23 in the Caco-2 cell line could only be inhibited by P-gp inhibitors. In t he LLC-PK1:MDR1 and LLC-PK1 cell Lines transport was also inhibited by inhi bitors for the organic cation transport systems. In conclusion, rhodamine-1 23 is a substrate for both P-gp and the organic cation carrier systems in t he kidney cell line. This indicates that rhodamine-123 is not selective eno ugh to study P-gp functionality in cell systems were organic cation carrier systems are also present. Doxorubicin appears to be a more selective P-gp substrate and therefore more useful in studying P-gp functionality in vitro . (C) 2000 Elsevier Science B.V. All rights reserved.