RT Journal Article
SR Electronic
T1 Derivation of a system-independent Ki for Pgp-mediated digoxin transport from system-dependent IC50 data by accounting for the contribution of additional digoxin transporters.
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP dmd.117.075606
DO 10.1124/dmd.117.075606
A1 Aqsaa Chaudhry
A1 Git Chung
A1 Adam Lynn
A1 Akshata Yalvigi
A1 Colin Brown
A1 Harma Ellens
A1 Michael O'Connor
A1 Caroline Lee
A1 Joe Bentz
YR 2018
UL http://dmd.aspetjournals.org/content/early/2018/01/09/dmd.117.075606.abstract
AB It has been previously demonstrated that IC50 values for inhibition of digoxin transport across confluent cell monolayers are system-dependent. We have applied the structural mass action kinetics model for P-glycoprotein mediated transport of digoxin across confluent cell monolayers to fit IC50 curves for inhibition of digoxin transport. The model fit digoxin IC50 data from a subset of labs participating in the P-gp IC50 Initiative (2 Caco-2 labs, 1 LLC-PK1-hMDR1-NKI lab and 2 MDCKII-hMDR1-NKI labs), as well as IC50 data for inhibition of digoxin transport through monolayers of primary human proximal tubule cells (HPTC) using eight of the same inhibitors. The data fitting demonstrated that all cells kinetically required a basolateral uptake transporter for digoxin. The range of the efflux active P-gp surface densities and basolateral uptake clearances in the Caco-2, MDCKII-hMDR1 and LLC-PK1-hMDR1 cells was about an order of magnitude. The HPTCs had a 10-100-fold lower efflux active P-gp surface density than the cell lines. Taken together, the lab-to-lab variability of these ranges, for the Caco-2, LLC-PK1-hMDR1-NKI and MDCKII-hMDR1-NKI cells, can explain 60-70% of the IC50 variability found in Bentz et al. (2013). This kinetic analysis of IC50 data from multiple inhibitors and cell systems has demonstrated that the lab-to-lab variability in IC50 values is primarily a consequence of differences in expression levels of P-gp and the basolateral digoxin uptake transporter. Moreover, it was demonstrated for all cell systems studied (including the HPTC) that the off-rate of the inhibitor, and hence the Ki, from P-gp was system-independent.