Numerous studies have demonstrated the impact of organic cation (OCTs; SLC22 family) and anion transporters (OATs; SLC22 family) on the efficacy and safety of clinically important therapeutics. To be specific, OCTs and OATs have been identified as determinants for uptake into and secretion from enterocytes, hepatocytes and renal proximal tubular cells, and are frequent sites of drug-drug interaction (DDI). In addition, OCTs expressed in brain are components of the low-affinity, high capacity clearance pathway (uptake-2) for biogenic monoamine neurotransmitters. As a result, OCTs may represent novel targets for mood disorders. The inhibitory effects of several therapeutic agents, designed drugs and novel compounds were assessed on the function of OCTs/Octs and OATs/Oats. Among these compounds, the anthraquinone rhein showed significant inhibition on hOATs. While the antituberculosis drug ethambutol, the herbal products matrine and oxymatrine, synthetic cathinones, and all quinazoline and guanidine compounds produced significant inhibition on hOCT activity with most IC50 values in the micro- and even nanomolar ranges. Considering the clinically relevant unbound concentrations in biofluids, significant DDI potentials were found for rhein, ethambutol, matrine, oxymatrine and several synthetic cathinones affecting enterocytes, hepatocytes and/or proximal tubules. As hOCT2 and hOCT3 may participate in modulating neurotransmitter homeostasis in the CNS, these findings also suggested that the CNS pharmacological effects of synthetic cathinones, quinazoline and guanidine compounds might be due to their inhibitory effects on OCTs; although their impact may be limited solely to clearance of these compounds. Based upon their in vitro OCT/Oct inhibition profiles, three lead quinazoline and guanidine compounds were chosen for in vivo studies. Potent antidepressant-like effects of one lead hOCT-interacting compound (KEO-099) were re-confirmed in the tail suspension test. While in vivo results of the two newly identified hOCT-interacting lead compounds were somewhat less clear. Finally, homology modeling and docking studies for hOCT3 identified key amino acid residues that might be involved in interaction between hOCT3 and small molecules. Subsequent experiments confirmed a competitive mode of interaction between MPP+ and lead compounds on hOCT3. Thus, preliminary analysis indicates our hOCT3 homology model can be used to support rational drug design and high-throughput screening of novel hOCT substrates/inhibitors.

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Fluoroquinolones (FQ) are broad-spectrum charged antimicrobials exhibiting excellent tissue/fluid permeation. Thus, FQ disposition depends essentially on active transport and facilitative diffusion. Although most early transporter studies investigating renal elimination of FQs have focused on apical efflux of FQs from renal proximal tubule cell (RPTC) into urine, their basolateral uptake mechanism(s) from blood into RPTC (i.e., first step to tubular secretion) has not yet been explored in detail. Renally expressed SLC22 members: organic anion (OATs) and cation (OCTs) transporters are known to transport such small organic ionic substrates (molecular weight ~400 Da). Hence it is of interest to explore the role of these basolateral transporters in renal elimination of FQs, and to further quantitatively assess their impact in clinically observed FQ drug-drug interactions (DDI). An initial systematic review of clinical literature for FQs (n=18) demonstrated substantial differences among their renal clearance (CLren~46-fold) and unbound renal clearance (CLrenu~20-fold), and suggested that tubular secretion and reabsorption could be major determinants of FQ half-life, efficacy, and DDIs. FQs (n=13) identified from the above review were investigated by in-vitro transport studies using stably transfected cell lines, for potential interactions with organic cation [human (h) OCT1, hOCT2 and hOCT3] and anion [mouse (m) and hOAT3, hOAT1; and hOAT4] transporters. Further, kinetic inhibition studies were conducted to determine inhibition potency (Ki/IC50 values) for those FQs exhibiting significant OCT/OAT inhibition in preliminary interaction experiments. Gatifloxacin, moxifloxacin, prulifloxacin, and sparfloxacin were determined to be competitive inhibitors of hOCT1 with Ki = 250±18, 161±19, 136±33, and 94±8 μM, respectively. Moxifloxacin competitively inhibited hOCT3-mediated uptake, Ki = 1,598±146 μM. Enoxacin, fleroxacin, levofloxacin, lomefloxacin, moxifloxacin, prulifloxacin, and sparfloxacin exhibited competitive inhibition for mOat3 with Ki = 396±15, 817±31, 515±22, 539±27, 1356±114, 299±35, 205±12 μM, respectively. Fleroxacin and pefloxacin were found to inhibit hOAT1 with IC50 = 2228±84 and 1819±144 respectively. Despite expression in enterocytes, hepatocytes, and RPTC, hOCT3 does not appear to contribute significantly to FQ disposition. However, due to hepatic and potential RPTC expression, hOCT1 could play an important role in elimination of these antimicrobials. Among renally expressed OATs in humans, hOAT1 and hOAT3 are likely to be involved in FQ elimination.

No description available.

Numerous natural products are widely used as first-line/alternative therapeutics and dietary supplements in both western and eastern society. However, the safety and efficacy profiles for herbal products are still limited. Organic anion transporters (OATs; SLC22 family) are expressed in many barrier organs and mediate in vivo body disposition of a broad array of endogenous substances and clinically important drugs. As some dietary flavonoids and phenolic acids were previously demonstrated to interact with OATs, it is necessary to explore the potential interaction of such components found in natural products in order to avoid potential OAT-mediated drug-drug interactions (DDIs). The inhibitory effects of 23 natural products were assessed on the function of human (h) OATs, hOAT1 (SLC22A6), hOAT3 (SLC22A7), and hOAT4 (SLC22A11) and/or the murine (m) orthologs mOat1 and mOat3. For compounds exhibiting marked inhibition at initial screening, dose-response curves (IC50 values) and DDI indices were determined. At the initial screening concentrations, 14, 19, and 2 test compounds exhibited significant inhibition on hOAT1, hOAT3, and hOAT4, respectively. Additionally, all test Danshen (a Chinese herbal medicine) hydrophilic components significantly reduced mOat1- and mOat3-mediated substrate uptake at 1 mM. For selected compounds, the IC50 and Ki values were estimated to be in the micromolar or even nanomolar range. Considering the clinical plasma concentration and unbound fraction in plasma, DDI indices for gallic acid, gentisic acid, lithospermic acid, protocatechuic acid, rosmarinic acid, salvianolic acid B, and tanshinol indicated DDIs may occur in vivo in situations of co-administration of these compounds and clinical therapeutics known to be OAT substrates. Finally, a new, rapid, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to quantify gallic acid and gentisic acid in cell lysates in order to measure cellular uptake of these compounds in mOat1- or mOat3-expressing cells. Significant cellular uptake of gallic acid was observed in mOat1-expressing cells, compared with background control cells. The absorptive uptake was completely blocked by probenecid (known OAT inhibitor) at 1 mM. These results indicate that gallic acid is a substrate for mOat1 and suggest that human OAT1 might be involved in the active renal secretion of gallic acid.

No description available.