Model analysis of the concentration-dependent permeability of P-gp substrates.
OBJECTIVE
Recently, it was reported that the apparent Michaelis-Menten constant (Km(app)) of a P-glycoprotein (P-gp) substrate, defined for the extracellular substrate concentration, increases as the P-gp expression level in the cell increases. By its nature, the Km value should not depend on the level of P-gp expression. The purpose of this study is to establish a model which can estimate the Km value independent of the P-gp expression level in cells.


METHODS
The previously reported concentration-dependent permeability of verapamil, quinidine, and vinblastine in MDR1-MDCKII, P-gp-highly induced Caco-2, P-gp-induced Caco-2, normal Caco-2, and MDR1-knockdown Caco-2 cells data were analyzed using a model in which the Km value was defined for the intracellular substrate concentration.


RESULTS
The estimated Km values defined for the substrate concentration inside the cells were almost the same among various cells with different levels of P-gp expression. The estimated Vmax values were approximately proportional to the P-gp expression level.


CONCLUSIONS
The established kinetic model was found to be rational based on the results that the Km values of P-gp substrates were about the same for cells expressing various levels of P-gp, while the Vmax values were proportional to the expression levels of P-gp.
Tachibana
Tatsuhiko
T
Pre-clinical Research Department, Chugai Pharmaceutical Co., Ltd., 1-135 Komakado, Gotemba, Shizuoka, 412-8513, Japan. tachibanatth@chugai-pharm.co.jp
Kitamura
Satoshi
S
Kato
Motohiro
M
Mitsui
Tetsuya
T
Shirasaka
Yoshiyuki
Y
Yamashita
Shinji
S
Sugiyama
Yuichi
Y
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D018938:Caco-2 Cells; D015870:Gene Expression; D006801:Humans; D008954:Models, Biological; D011802:Quinidine / Q000493:pharmacokinetics*; D014700:Verapamil / Q000493:pharmacokinetics*; D014747:Vinblastine / Q000493:pharmacokinetics*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D014747:Vinblastine; D014700:Verapamil; D011802:Quinidine