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Variability in P-Glycoprotein Inhibitory Potency (IC50) Using Various In Vitro Experimental Systems: Implications for Universal Digoxin DDI Risk Assessment Decision Criteria.

Drug Metab Dispos. 2013 Apr 25;

Authors: Bentz JE, O'Connor M, Bednarczyk D, Coleman J, Lee CA, Palm JE, Pak A, Perloff ES, Reyner EL, Balimane P, Brannstrom M, Chu X, Funk C, Guo A, Hanna IH, Heredi-Szabo K, Hillgren KM, Li L, Hollnack-Pusch E, Jamei M, Lin X, Mason A, Neuhoff S, Patel A, Podila L, Plise E, Rajaraman G, Salphati L, Sands E, Taub ME, Taur J, Weitz D, Wortelboer H, Xia C, Xiao G, Yabut J, Yamagata T, Zhang LK, Ellens H


A P-glycoprotein (P-gp) IC50 working group was established with twenty-three participating pharmaceutical and contract research laboratories and one academic institution to assess inter-laboratory variability in P-gp IC50 determinations. Each lab followed their in-house protocol to determine in vitro IC50 values for sixteen inhibitors using four different test systems: Caco-2 (11 labs), MDCKII-MDR1 (6 labs) and LLC-PK1-MDR1 (4 labs) cells, and membrane vesicles containing human P-gp (5 labs). For cell models, various equations to calculate remaining transport activity (e.g. efflux ratio, unidirectional flux, net secretory flux) were also evaluated. The difference in IC50 values for each of the inhibitors across all test systems and equations ranged from a minimum of 20- and 24-fold between lowest and highest IC50 values for sertraline and isradipine, to a maximum of 407- and 796-fold for telmisartan and verapamil, respectively. For telmisartan and verapamil, variability was greatly influenced by data from one laboratory in each case. Excluding these two data sets brings the range in IC50 values for telmisartan and verapamil down to 69- and 159-fold. The efflux ratio based-equation generally resulted in several fold lower IC50 values compared to unidirectional or net-secretory flux equations. Statistical analysis indicated that variability in IC50 values was mainly due to inter-laboratory variability, rather than an implicit systematic difference between test systems. Potential reasons for variability are discussed and the simplest, most robust experimental design for P-gp IC50 determination proposed. The impact of these findings on drug-drug interaction risk assessment is discussed in the companion paper and recommendations are provided.

PMID: 23620485 [PubMed - as supplied by publisher]