Our understanding of the mechanisms behind inter-and intra-patient variability in drug response is inadequate. Advances in the cytochrome P450 drug metabolizing enzyme field have been remarkable, but those in the drug transporter field have trailed behind. Currently, however, interest in carrier-mediated disposition of pharmacotherapeutics is on a substantial uprise. This is exemplified by the 2006 FDA guidance statement directed to the pharmaceutical industry. The guidance recommended that industry ascertain whether novel drug entities interact with transporters. This suggestion likely stems from the observation that several novel cloned transporters contribute significantly to the disposition of various approved drugs. Many drugs bear anionic functional groups, and thus interact with organic anion transporters (OATs). Collectively, these transporters are nearly ubiquitously expressed in barrier epithelia. Moreover, several reports indicate that OATs are subject to diverse forms of regulation, much like drug metabolizing enzymes and receptors. Thus, critical to furthering our understanding of patient-and condition-specific responses to pharmacotherapy is the complete characterization of OAT interactions with drugs and regulatory factors. This review provides the reader with a comprehensive account of the function and substrate profile of cloned OATs. In addition, a major focus of this review is on the regulation of OATs including the impact of transcriptional and epigenetic factors, phosphorylation, hormones and gender.

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Carboxyfluoroquinolones, such as ciprofloxacin, are used for the treatment of numerous infectious diseases. Renal secretion is a major determinant of their systemic and urinary concentration, but the specific transporters involved are virtually unknown. In vivo studies implicate the organic anion transporter (OAT) family as a pivotal component of carboxyfluoroquinolone renal secretion. Therefore, this study identified the specific renal basolateral OAT(s) involved, thereby highlighting potential sources of carboxyfluoroquinolone-drug interactions and variable efficacy. Two heterologous expression systems, Xenopus laevis oocytes and cell monolayers, were used to determine the roles of murine and human renal basolateral mOat1/hOAT1 and mOat3/hOAT3. Ciprofloxacin was transported by mOat3 in both systems (K m value, 70 Ϯ 6 M) and demonstrated no interaction with mOat1 or hOAT1. Furthermore, ciprofloxacin, norfloxacin, ofloxacin, and gatifloxacin exhibited concentration-dependent inhibition of transport on mOat3 in cells with inhibition constants of 198 Ϯ 39, 558 Ϯ 75, 745 Ϯ 165, and 941 Ϯ 232 M, respectively. Ciprofloxacin and gatifloxacin also inhibited hOAT3. Thereafter, in vivo elimination of ciprofloxacin was assessed in wild-type and Oat3 null mice [Oat3(Ϫ/Ϫ)]. Oat3(Ϫ/Ϫ) mice exhibited significantly elevated plasma levels of ciprofloxacin at clinically relevant concentrations (P Ͻ 0.05, male mice; P Ͻ 0.01, female mice). Oat3(Ϫ/Ϫ) mice also demonstrated a reduced volume of distribution (27%, P Ͻ 0.01, male mice; 14%, P Ͻ 0.01, female mice) and increased area under the concentration-time curve (25%, P Ͻ 0.05, male mice; 33%, P Ͻ 0.01, female mice). Female Oat3(Ϫ/Ϫ) mice had a 35% (P Ͻ 0.01) reduction in total clearance of ciprofloxacin relative to wild type. In addition, putative ciprofloxacin metabolites were significantly elevated in Oat3(Ϫ/Ϫ) mice. The present findings indicate that polymorphisms of and drug interactions on hOAT3 may influence carboxyfluoroquinolone efficacy, especially in urinary tract infections.Ciprofloxacin is a broad-spectrum antimicrobial that is used in the treatment of numerous infectious diseases, including those afflicting the skin (Lipsky et al., 1999) (Gogos et al., 1991). It is also a preferred agent for the prevention and treatment of anthrax (Meyerhoff et al., 2004). Its mechanism of action is through the effective inhibition of DNA gyrase, thus preventing DNA replication in susceptible bacteria (Gellert et al., 1977;Sugino et al., 1977). Ciprofloxacin is a carboxylic acidcontaining fluoroquinolone (carboxyfluoroquinolone) that undergoes renal and hepatic elimination, with ϳ50% (oral) or ϳ80% (intravenous) appearing in the urine as parent compound and metabolites 24 h after administration in humans (Höffken et al., 1985). Approximately 20 to 40% of circulating Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org. doi:10.1124/mol.107.042853.ABBREVIATIONS: LLC-PK 1 , porcine kidney cells; AUC, area under the concentration-t...

The interaction of renal basolateral organic anion transporter 3 (Oat3) with commonly used pharmacotherapeutics (e.g., NSAIDs, beta-lactams, and methotrexate) has been studied extensively in vitro. However, the in vivo role of Oat3 in drug disposition, in the context of other transporters, glomerular filtration, and metabolism, has not been established. Moreover, recent investigations have identified inactive human OAT3 polymorphisms. Therefore, this investigation was designed to elucidate the in vivo role of Oat3 in the disposition of penicillin G and prototypical substrates using an Oat3 knockout mouse model. Oat3 deletion resulted in a doubling of penicillin's half-life (P < 0.05) and a reduced volume of distribution (P < 0.01), together yielding a plasma clearance that was one-half (P < 0.05, males) to one-third (P < 0.001, females) of that in wild-type mice. Inhibition of Oat3 abolished the differences in penicillin G elimination between genotypes. Hepatic accumulation of penicillin was 2.3 times higher in male knockouts (P < 0.05) and 3.7 times higher in female knockouts (P < 0.001). Female knockouts also exhibited impaired estrone-3-sulfate clearance. Oat3 deletion did not impact p-aminohippurate elimination, providing correlative evidence to studies in Oat1 knockout mice that suggest Oat1 governs tubular uptake of p-aminohippurate. Collectively, these findings are the first to indicate that functional Oat3 is necessary for proper elimination of xenobiotic and endogenous compounds in vivo. Thus Oat3 plays a distinct role in determining the efficacy and toxicity of drugs. Dysfunctional human OAT3 polymorphisms or instances of polypharmacy involving OAT3 substrates may result in altered systemic accumulation of beta-lactams and other clinically relevant compounds.

Ethanol elevates methylphenidate (1) plasma concentrations and yields the metabolite ethylphenidate (2). The therapeutic implications are under investigation. The IC(50) for dopamine reuptake inhibition by (+)-2 was 27 nM compared to 367 nM for cocaine and 1730 nM for (-)-2. Binding selectivity for dopamine versus norepinephrine transporters was greater for (+)-2 than for cocaine. Intraperitoneal (+)-2 was approximately half as active as (+)-1 in stimulating mouse motor activity at 5 mg/kg, but (+)-2 was as active as (+)-1 at 10 mg/kg.