We previously reported a quantitative time-lapse imaging (QTLI)-based analysis method to assess drug-drug interactions (DDI) at multidrug resistance-associated protein 2 (Mrp2) in rat sandwich-cultured hepatocyte (SCH) system, utilizing the fluorescent Mrp2 substrate, 5-(and 6)-carboxy-2',7'-dichlorofluorescein (CDF). Here, we aimed to examine the feasibility of using QTLI to evaluate DDI involving drug metabolite(s) generated in hepatocytes. We used estradiol (E2) and bilirubin as model compounds; both are not substrates of MRP2, whereas their hepatic metabolites, estradiol-17β-glucuronide (E17G) or bilirubin glucuronides, are known to be its substrates as well as inhibitors. When rat SCHs were pre-exposed with E2, fluorescence of CDF accumulated in bile canaliculi decreased depending upon both the duration of pre-exposure and the concentration of extracellular E2. The decrease corresponded with the increase in intracellular concentration of E17G in hepatocytes. Furthermore, cytotoxicity of vinblastine, a substrate of MRP2, was enhanced in SCHs treated with E2. Similarly, CDF accumulated in bile canaliculi was significantly reduced in rat SCHs pre-exposed with bilirubin. In conclusion, these results suggest that phase II biotransformation of a competitor is reflected in alteration of MRP2-mediated CDF transport detected in QTLI. The QTLI might provide a convenient platform to evaluate transporter-based DDIs involving hepatic metabolites of drug candidates without the need to identify the metabolites.
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