Kinetic analysis of P-glycoprotein-mediated doxorubicin efflux.
P-glycoprotein lowers the intracellular concentration of a variety of unrelated compounds including doxorubicin by actively removing them from the cell. Mathematical modeling techniques have been applied to the transmembrane transport of doxorubicin in a nonresistant HL-60 cell line and in a P-glycoprotein-containing resistant subclone, HL-60R, to obtain clearances for inward and outward transport. Distribution of [14C]doxorubicin from extracellular fluid into the cell pellet was analyzed with a closed two-compartment system that fitted experimental measurements of drug concentrations in the extracellular fluid and in the cell pellet, represented by a third compartment that includes trapped extracellular doxorubicin along with the intact cells. Transmembrane diffusion clearance was similar for the two cell lines (1.00 vs. 1.06 microliters sec-1), yielding an apparent doxorubicin permeability coefficient of 7.4 x 10(-5) cm sec-1. However, the total efflux clearance averaged 0.99 +/- 0.05 microliters sec-1 in HL-60 and 2.29 +/- 0.62 microliters sec-1 in HL-60R. The estimated P-glycoprotein-mediated efflux clearance in HL-60R averaged 1.23 +/- 0.51 microliters sec-1. This experimental approach provides direct estimates of transport parameters in intact cells and should be useful in studying the mechanism of action and interactions of inhibitors of P-glycoprotein.
Dordal
M S
MS
Robert H. Lurie Cancer Center, Department of Medicine, Northwestern University Medical School, Northwestern Memorial Hospital, Chicago, Illinois.
Winter
J N
JN
Atkinson
A J
AJ
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001692:Biological Transport / Q000187:drug effects; D002452:Cell Count; D002463:Cell Membrane Permeability; D004317:Doxorubicin / Q000493:pharmacokinetics*; D004351:Drug Resistance; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D008433:Mathematics; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008562:Membrane Glycoproteins; D004317:Doxorubicin