Modulation of trabectedin (ET-743) hepatobiliary disposition by multidrug resistance-associated proteins (Mrps) may prevent hepatotoxicity

Trabectedin is a promising anticancer agent, but dose-limiting hepatotoxicity was observed during phase I/II clinical trials. Dexamethasone (DEX) has been shown to significantly reduce trabectedin-mediated hepatotoxicity. The current study was designed to assess the capability of sandwich-cultured primary rat hepatocytes (SCRH) to predict the hepato-protective effect of DEX against trabectedin-mediated cytotoxicity. The role of multidrug resistance-associated protein 2 (Mrp2; Abcc2) in trabectedin hepatic disposition also was examined. In SCRH from wild-type Wistar rats, cytotoxicity was observed after 24-hr continuous exposure to trabectedin. SCRH pretreated with additional DEX (1 µM) exhibited a 2–3-fold decrease in toxicity at 100 nM and 1000 nM trabectedin. Unexpectedly, toxicity in SCRH from Mrp2-deficient (TR−) compared to wild-type Wistar rats was markedly reduced. Depletion of glutathione from SCRH using buthionine sulfoximine (BSO) mitigated trabectedin toxicity associated with 100 nM and 1000 nM trabectedin. Western blot analysis demonstrated increased levels of CYP3A1/2 and Mrp2 in SCRH pretreated with DEX; interestingly, Mrp4 expression was increased in SCRH after BSO exposure. Trabectedin biliary recovery in isolated perfused livers from TR− rats was decreased by ~75% compared to wild-type livers. In conclusion, SCRH represent a useful in vitro model to predict the hepatotoxicity of trabectedin observed in vivo. The protection by DEX against trabectedin-mediated cytotoxicity may be attributed, in part, to enhanced Mrp2 biliary excretion and increased metabolism by CYP3A1/2. Decreased trabectedin toxicity in SCRH from TR− rats, and in SCRH pretreated with BSO, may be due to increased basolateral excretion of trabectedin by Mrp3 and/or Mrp4

Impact of Basolateral Multidrug Resistance-Associated Protein (Mrp) 3 and Mrp4 on the Hepatobiliary Disposition of Fexofenadine in Perfused Mouse Livers

The disposition of fexofenadine, a commonly-used antihistamine drug, is governed primarily by active transport. Biliary excretion of the parent compound is the major route of systemic clearance. Previous studies demonstrated that fexofenadine hepatic uptake is mediated by organic anion transporting polypeptides. Recently, we showed that in mice fexofenadine is excreted into bile primarily by Mrp2 (Abcc2). In the present study, the role of Mrp3 (Abcc3) and Mrp4 (Abcc4) in the hepatobiliary disposition of fexofenadine was examined in knockout mice using in situ liver perfusion. Compared to wild-type mice, basolateral excretion of fexofenadine was impaired resulting in a ~50% decrease in perfusate recovery in Abcc3 ( − / − ) mice; in contrast, fexofenadine hepatobiliary disposition was unaltered in Abcc4 ( − / − ) mice. As expected, in Abcc2 ( − / − ) mice, fexofenadine was redirected from the canalicular to the basolateral membrane for excretion. In Abcc2 ( − / − )/Abcc3 ( − / − ) double knock-out mice, fexofenadine biliary excretion was impaired, but perfusate recovery was similar to wild-type mice, and more than 2-fold higher than in Abcc3 ( − / − ) mice, presumably due to compensatory basolateral transport mechanism(s). These results demonstrate that multiple transport proteins are involved in the hepatobiliary disposition of fexofenadine. In addition to Mrp2 and Mrp3, other transport proteins play an important role in the biliary and hepatic basolateral excretion of this zwitterionic drug

Transporters in Drug Development: 2018 ITC Recommendations for Transporters of Emerging Clinical Importance

This white paper provides updated International Transporter Consortium (ITC) recommendations on transporters that are important in drug development following the 3rd ITC workshop. New additions include prospective evaluation of organic cation transporter 1 (OCT1) and retrospective evaluation of organic anion transporting polypeptide (OATP)2B1 because of their important roles in drug absorption, disposition, and effects. For the first time, the ITC underscores the importance of transporters involved in drug-induced vitamin deficiency (THTR2) and those involved in the disposition of biomarkers of organ function (OAT2 and bile acid transporters)

Xenobiotics Inhibit Hepatic Uptake and Biliary Excretion of Taurocholate in Rat Hepatocytes

Reports suggest that troglitazone, and to a lesser extent bosentan, may alter bile acid homeostasis by inhibiting the bile salt export pump.Thepresent studies examined the hypothesis that these xeno-biotics may modulate multiple hepatic bile acid transport mechan-isms. In suspended rat hepatocytes, troglitazone (10 mM) decreased the initial rate of taurocholateuptake3-fold; the initial uptake rate of estradiol-17b-D-glucuronide, a substrate of the organic anion transporting polypeptides, also was decreased 4-fold. Bosentan (100 mM) decreased the initial uptake rate of taurocholate and estradiol-17b-D-glucuronide by 12- and 7-fold, respectively. In sandwich-cultured rat hepatocytes, 10-min accumulation of taur-ocholate in cells 1 bile canaliculi (408 6 57 pmol/mg protein) was decreased significantly by troglitazone (1576 17 pmol/mg protein, respectively) only in the presence of Na1, the driving force for the sodiumtaurocholate cotransportingpolypeptide.A similardecreas