Substrate- and pH-Specific Antifolate Transport Mediated by Organic Anion-Transporting Polypeptide 2B1 (OATP2B1-SLCO2B1)

Abstract

Human organic anion-transporting polypeptide (OATP) 2B1 (OATP-B; SLCO2B1) is expressed in the apical membrane of the small intestine and the hepatocyte basolateral membrane and transports structurally diverse organic anions with a wide spectrum of pH sensitivities. This article describes highly pHdependent OATP2B1-mediated antifolate transport and compares this property with that of sulfobromophthalein (BSP), a preferred OATP2B1 substrate. At pH 5.5 and low substrate concentrations (ϳ2.5 M), only [3 H]pemetrexed influx [in contrast to methotrexate (MTX), folic acid, and reduced folates] could be detected in OATP2B1-transfected HeLa R1-11 cells that lack endogenous folate-specific transporters. Influx was optimal at pH 4.5 to 5.5, falling precipitously with an increase in pH Ͼ6.0; BSP influx was independent of pH. Influx of both substrates at low pH was markedly inhibited by the proton ionophore 4-(trifluoromethoxy)phenylhydrazone; BSP influx was also suppressed at pH 7.4. At 300 M MTX, influx was one-third that of pemetrexed; influx of folic acid, (6S)5-methyltetrahydrofolate, or (6S)5-formyltetrahydrofolate was not detected. There were similar findings in OATP2B1-expressing Xenopus laevis oocytes. The pemetrexed influx K m was ϳ300 M; the raltitrexed influx K i was ϳ70 M at pH 5.5. Stable expression of OAPT2B1 in HeLa R1-11 cells resulted in substantial raltitrexed, but modest pemetrexed, growth inhibition consistent with their affinities for this carrier. Hence, OATP2B1 represents a low-affinity transport route for antifolates (relative affinities: raltitrexed Ͼ pemetrexed Ͼ MTX) at low pH. In contrast, the high affinity of this transporter for BSP relative to antifolates seems to be intrinsic to its binding site and independent of the proton concentration.

Biliary Elimination of Pemetrexed Is Dependent on Mrp2 in Rats: Potential Mechanism of Variable Response in Nonalcoholic Steatohepatitis

“…These instances of induction are probably a result of the same compensatory processes, and thus place the Mrp2 2/2 and MCD experimental groups on a similar plane with respect to Mrp3 expression and function. Another source that may contribute to the disposition changes of pemetrexed in NASH is the hepatic uptake process, which may be mediated by OAT3 and OATP2B1, although more transporters of organic anions may be involved (Visentin et al, 2012;Li et al, 2013). OATP2B1/Oatp2b1 does not exhibit a change in mRNA expression in either human NASH or MCD mice, although MCD does decrease the protein expression of other organic anion-transporting polypeptide isoforms 1b2, 1a1, and 1a4, which is consistent with mRNA expression Clarke et al, 2014).…”

Differential mRNA expression and the uptake of methotrexate in primary MAEC and MLF cells: involvement of the Abc and Slco/Oatp transporters in alveolar epithelial cell toxicity

“…To date, many investigators have revealed that many types of drug transporters and their isoforms (MRP1/3, Mrp2-4, Bcrp, Oatp1a1/1a4/1b2/2b12/4c1) mediate the high affinity transport of MTX (Zeng et al, 2001;Mikkaichi et al, 2004;Borst et al, 2007;Brcakova et al, 2009;Visentin et al, 2012). In addition, other investigators and we have reported that mediate the transport of MTX (Sekine et al, 1997;Kusuhara et al, 1999;Kobayashi et al, 2002a).…”

The Role of Organic Anion Transporters in Diagnosing Liver Diseases by Magnetic Resonance Imaging

“…It is important to note that this stimulation is substrate-dependent (e.g., hOATP2B1-mediated uptake of prostaglandin E 2 is independent from extracellular pH, while transport of thyroxine is stimulated by a low extracellular pH) (Leuthold et al, 2009). hOATP2B1 also transports pemetrexed with a higher rate when the extracellular pH decreases, which does not occur for BSP (Visentin et al, 2012). A detailed analysis of the effect of different transmembrane pH gradients on rOATP1A1 transport activity revealed a complex response of the transporter at different pH gradients (Marin et al, 2003).…”