Abstract
ATP-binding cassette (ABC) proteins, including the breast cancer resistance protein (BCRP) and the multidrug resistance proteins (MDRs), actively transport structurally diverse chemicals from a number of tissues. Moreover, transporters are being increasingly cited as mediators of clinically relevant drug-drug interactions. The potential outcomes of concomitantly administering two drugs that interact at the same transporter include altered disposition and toxicity and/or efficacy of one or both of the drugs. Research demonstrating the role of transporters in clinical pharmacokinetics has shed light on the need for
in vitro
screening methods that detect drug-transporter interactions during preclinical development. This paper describes a cell-based model for the detection of functional inhibitors of BCRP and MDR1 by measuring fluorescent substrate accumulation in suspended cells that overexpress or endogenously express these proteins using an automated cell counter. An alternate protocol is provided describing the use of a spectrophotometer with fluorescence detection capabilities to identify functional inhibitors of BCRP and MDR1 in transporter overexpressing cells. While a spectrophotometer is available in most laboratories, an automatic cell counter offers convenience, sensitivity, and speed in measuring the cellular accumulation of fluorescent substrates and identification of novel inhibitors.