Electronic Thesis and Dissertation Repository


Master of Science


Pharmacology and Toxicology


Dr. Rommel Tirona


P-glycoprotein (P-gp/ABCB1) is an important efflux drug transporter affecting the disposition of 50% of marketed drugs. Cell monolayer permeability assays are the gold standard for assessing P-gp-drug interactions in vitro, but inter-laboratory assay differences produce heterogeneous results. We compared the validity and sensitivity of traditional assay metrics of efflux transport (unidirectional apparent permeability and efflux ratio) with a modeled clearance metric, CLP-gp and hypothesized that CLP-gp would be superior. Cell monolayers heterologously transfected with ABCB1, and 1,25(OH)2D3-modulated ABCB1 in cells served as experimental models. P-gp expression was quantified by western blot and bidirectional [3H]-digoxin transcellular flux was measured. Linear regression analyses were performed for P-gp expression versus each P-gp activity metric. The validity and sensitivity of modeled clearance was comparable to traditional metrics within a cell type, but was superior across different cell types. In conclusion, CLP-gp offers a physiologically-relevant and universally acceptable metric for efflux transport activity.

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