Human Transporters


MRP3 (multidrug resistance-associated protein 3)

Aliases: ABC31, EST90757, MLP2, MOAT-D, cMOAT2
Gene name: ATP binding cassette subfamily C member 3 (ABCC3)


ABCC3, more commonly referred to as MRP3, is an ATP-dependent, unidirectional efflux transporter that plays a role in xenobiotic absorption, disposition, and distribution, as well as in multidrug resistance. MRP3 was first identified in the liver at the sinusoidal membrane, where it was shown to transport xenobiotics from the liver into the blood [1]; it is also expressed in a number of other tissues including the gastrointestinal tract (GIT). Typical substrates of MRP3 are organic anions such as bile acids and drug-glucuronide conjugates, including morphine-3-glucuronide and acetaminophen-glucuronide. It also facilitates the oral absorption of conjugated forms of some dietary estrogens and antioxidants [2]. It is up-regulated in instances of cholestasis and/or impaired MRP2 function, thus compensating for reduced biliary elimination of bilirubin. MRP3 is not specifically mentioned in the FDA or EMA regulatory guidances, probably because citations on DDIs are lacking. However, investigation may be indicated for some molecules, e.g. where active oral absorption is suspected, circulating glucuronide conjugates are observed, or changes in liver chemistry are noted.


In contrast to MRP2, BCRP, and MDR1, MRP3 is basolaterally expressed in polarized cells, which means that e.g. in the liver it effluxes its substrates into the blood rather than the bile, and it can facilitate absorption from the GIT. It is highly expressed in the liver (cholangiocytes and hepatocytes) and in enterocytes [3, 4], as well as in the adrenal gland, kidney, pancreas, placenta, and gallbladder, with lower expression in the lung, spleen, stomach, brain, and tonsils [5]. In addition, MRP3 is overexpressed in some tumor types, and in the liver under conditions that result in cholestasis [6, 7]. Caco-2 cells, a widely used cell line derived from human colon adenocarcinoma cells, also express the MRP3 transporter at the basolateral membrane [8].

Function, physiology, and clinically significant polymorphisms

MRP3, a 170-kDa protein encoded by the ABCC3 gene (chromosome 17q21.3), consists of 18 transmembrane domains [9]. MRP3 is involved in the physiological regulation of bile salt enterohepatic circulation and in the disposition of some plant derived compounds (e.g. phytoestrogens, resveratrol) [2]. MRP3 expression is induced under cholestatic conditions, and/or where MRP2 function is impaired (e.g. Dubin-Johnson syndrome), functioning as an alternative hepatocellular protection pathway when normal canalicular bile salt transport is compromised [10, 11]. Although associated with chemotherapy resistance, MRP3 only impacts on methotrexate, vincristine, and epipodophyllotoxin (e.g. teniposide and etoposide) therapies [12], which is in marked contrast with the other ABCC members MRP1 and MRP2.
Substrates of MRP3 include endogenous compounds (estradiol-17β-glucuronide, leukotriene C4, monovalent bile salts such as cholate and glycocholate), chemotherapeutic agents, and other drugs, such as acetaminophen-glucuronide, morphine-3-glucuronide, and fexofenadine [13, 14]. As opposed to MRP1 and MRP2, MRP3 has a higher affinity for glucuronide conjugates than for glutathione conjugates, and, unlike MRP1 and MRP2, MRP3 does not require glutathione to transport substrates [15].
Inhibitors of MRP3 include tenofovir, indomethacin, furosemide, and probenecid, as well as non-nucleoside reverse transcriptase inhibitors (delavirdine, efavirenz, and nevirapine), and nucleoside reverse transcriptase inhibitors (emtricitabine and lamivudine). In in vitro studies, the highly potent and MRP-specific inhibitor MK571 is often used [16, 17].
There is limited information on the clinical consequences of MRP3 genetic variants in humans. Sasaki et al. identified 61 genetic variants of MRP3 [18]; a few years later Bruhn and Cascorbi reported a somewhat higher figure, little over 100 [19]. Some polymorphisms showed high inter-ethnic variability, but none of the 27 non-synonymous coding SNPs had an allele frequency greater than 5% in any ethnic population. A PK study in 50 healthy individuals showed no association between genetic variants in the promoter region and changes in the PK of 4-methylumbelliferone glucuronide (4-MUG), an MRP3 substrate [18]. Nonetheless, the A-189 allele of the AT regulatory polymorphism is associated with poor treatment responses in childhood acute lymphoblastic leukemia [20], and in another study small cell lung cancer patients carrying the ABCC3 -211T allele showed significantly worse progression-free survival. Finally, a transfected cell-based in vitro assessment of the functional consequences of several non-synonymous polymorphisms (R1381S, S346F, and S607N) in MRP3 indicated that these may be risk factors in the development of hepatotoxicity [21], but this has not been explored in vivo.

Clinical significance

To date, no clinically relevant DDIs involving MRP3 have been reported, and there is limited information on its role in the clinical ADME of drugs. This is perhaps not surprising, given that MRP3 often transports conjugated metabolites of drugs (e.g. morphine-3-glucuronide and acetaminophen-glucuronide), which are not generally monitored clinically. However, Mrp3 (-/-) mice show decreased AUC of conjugates of resveratrol, phytoestrogens, of gemfibrozil-glucuronide, methotrexate, and 4-MUG. At least some of this decrease may be attributed to altered oral absorption profiles; hence, MRP3 modulation may be possible in the GIT in humans. MRP3 appears to play a compensatory role for MRP2 in bile acid transport, especially in cholestasis, as evidenced by its up-regulation in Dubin-Johnson sufferers, as well as TR- and EHBR (transport-deficient and Eisai hyperbilirubinemic) rats, all of whom are genetically deficient in MRP2. MRP3 also transports bilirubin glucuronides into the blood under conditions of impaired biliary bilirubin excretion.
Genetic polymorphisms of MRP3 may be important in the long-term outcomes for some chemotherapy patient groups. For example, the MRP3 189A>T regulatory polymorphism is associated with reduced survival outcomes in childhood acute lymphoblastic leukemia. Carriers of this allele had higher plasma levels of methotrexate, and gene reporter assays indicated enhanced promoter activity for the A-189 allele, indicating increased efflux activity of MRP3 [20]. MRP3 was overexpressed in HER2-positive breast cancers [7], but its involvement in chemotherapy resistance is very limited compared to that of MRP1 or MRP2.

Regulatory requirements

Currently, neither the FDA nor the EMA guidance specifically recommends the study of MRP3 interactions for NCEs. This is probably due to the lack of clear clinical citations of MRP3-mediated DDIs. However, this transporter may be relevant to NCEs where active oral absorption is suspected, where conjugated (particularly glucuronide) metabolites circulate systemically, or changes in circulating levels of bile salts or bilirubin are observed.

Location Endogenous substrates In vitro substrates used experimentally Substrate drugs Inhibitors
liver (cholangiocytes and hepatocytes) enterocytes, adrenal glands, kidney, small intestine, colon, pancreas, placenta, gallbladder, lungs, spleen, stomach, brain, tonsils bile salts, estradiol-17β-glucuronide, leukotriene C4 estradiol-17β-glucuronide, fexofenadine, methotrexate, vincristine, teniposide, etoposide

fexofenadine, methotrexate, vincristine, teniposide, etoposide, ethenyl estradiol, clopidogrel metabolites, acetaminophen-glucuronide,
resveratrol conjugates,
phytoestrogen conjugates


delavirdine, efavirenz, nevirapine, emtricitabine, lamivudine, tenofovir, indomethacin, furosemide, probenecid,


1.    Borst, P., et al., A family of drug transporters: the multidrug resistance-associated proteins. J Natl Cancer Inst., 2000. 92(16): p. 1295-302.
2.    van de Wetering, K., et al., Targeted metabolomics identifies glucuronides of dietary phytoestrogens as a major class of MRP3 substrates in vivo. Gastroenterology., 2009. 137(5): p. 1725-35. Epub 2009 Jul 3.
3.    Ortiz, D.F., et al., MRP3, a new ATP-binding cassette protein localized to the canalicular domain of the hepatocyte. Am J Physiol., 1999. 276(6 Pt 1): p. G1493-500.
4.    van de Wetering, K., et al., Intestinal breast cancer resistance protein (BCRP)/Bcrp1 and multidrug resistance protein 3 (MRP3)/Mrp3 are involved in the pharmacokinetics of resveratrol. Mol Pharmacol., 2009. 75(4): p. 876-85. Epub 2008 Dec 29.
5.    Scheffer, G.L., et al., Tissue distribution and induction of human multidrug resistant protein 3. Lab Invest., 2002. 82(2): p. 193-201.
6.    Rau, S., et al., Expression of the multidrug resistance proteins MRP2 and MRP3 in human cholangiocellular carcinomas. Eur J Clin Invest., 2008. 38(2): p. 134-42.
7.    Partanen, L., et al., Amplification and overexpression of the ABCC3 (MRP3) gene in primary breast cancer. Genes Chromosomes Cancer., 2012. 51(9): p. 832-40. doi: 10.1002/gcc.21967. Epub 2012 May 14.
8.    Hirohashi, T., et al., Function and expression of multidrug resistance-associated protein family in human colon adenocarcinoma cells (Caco-2). J Pharmacol Exp Ther., 2000. 292(1): p. 265-70.
9.    Van Aubel, R.A., R. Masereeuw, and F.G. Russel, Molecular pharmacology of renal organic anion transporters. Am J Physiol Renal Physiol., 2000. 279(2): p. F216-32.
10.    Kullak-Ublick, G.A., B. Stieger, and P.J. Meier, Enterohepatic bile salt transporters in normal physiology and liver disease. Gastroenterology., 2004. 126(1): p. 322-42.
11.    Zollner, G., et al., Adaptive changes in hepatobiliary transporter expression in primary biliary cirrhosis. J Hepatol., 2003. 38(6): p. 717-27.
12.    Kool, M., et al., MRP3, an organic anion transporter able to transport anti-cancer drugs. Proc Natl Acad Sci U S A., 1999. 96(12): p. 6914-9.
13.    Zhou, S.F., et al., Substrates and inhibitors of human multidrug resistance associated proteins and the implications in drug development. Curr Med Chem., 2008. 15(20): p. 1981-2039.
14.    Patel, M., K.S. Taskar, and M.J. Zamek-Gliszczynski, Importance of Hepatic Transporters in Clinical Disposition of Drugs and Their Metabolites. J Clin Pharmacol, 2016. 56 Suppl 7: p. S23-39.
15.    Zelcer, N., et al., Characterization of drug transport by the human multidrug resistance protein 3 (ABCC3). J Biol Chem., 2001. 276(49): p. 46400-7.
16.    Weiss, J., et al., Inhibition of MRP1/ABCC1, MRP2/ABCC2, and MRP3/ABCC3 by nucleoside, nucleotide, and non-nucleoside reverse transcriptase inhibitors. Drug Metab Dispos., 2007. 35(3): p. 340-4. Epub 2006 Dec 15.
17.    Bodo, A., et al., Differential modulation of the human liver conjugate transporters MRP2 and MRP3 by bile acids and organic anions. J Biol Chem., 2003. 278(26): p. 23529-37. Epub 2003 Apr 19.
18.    Sasaki, T., et al., Systematic screening of human ABCC3 polymorphisms and their effects on MRP3 expression and function. Drug Metab Pharmacokinet., 2011. 26(4): p. 374-86. Epub 2011 Apr 22.
19.    Bruhn, O. and I. Cascorbi, Polymorphisms of the drug transporters ABCB1, ABCG2, ABCC2 and ABCC3 and their impact on drug bioavailability and clinical relevance. Expert Opin Drug Metab Toxicol, 2014. 10(10): p. 1337-54.
20.    Ansari, M., et al., Polymorphism in multidrug resistance-associated protein gene 3 is associated with outcomes in childhood acute lymphoblastic leukemia. Pharmacogenomics J., 2012. 12(5): p. 386-94. doi: 10.1038/tpj.2011.17. Epub 2011 May 24.
21.    Kobayashi, K., et al., Functional analysis of nonsynonymous single nucleotide polymorphism type ATP-binding cassette transmembrane transporter subfamily C member 3. Pharmacogenet Genomics., 2008. 18(9): p. 823-33.


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