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Browsing by Subject "OATP2B1"

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  • Tikkanen, Alli (2019)
    Organic Anion Transporting Polypeptide 2B1 (OATP2B1) is an influx transporter expressed widely throughout the body in tissues such as intestine, liver, brain, placenta and skeletal muscle. Since many clinically used drugs are transported by OATP2B1, changes in the function of the transporter due to genetic polymorphism could lead to altered pharmacokinetics or -dynamics of OATP2B1 substrate drugs. The aim of this Master’s thesis was to create and optimize a cellular uptake assay to study the function of OATP2B1. Furthermore, the aim was to study the effects of six naturally occurring nonsynonymous single nucleotide variants on OATP2B1 transport function in vitro. With site-directed mutagenesis, single nucleotide changes were introduced into the gene coding for OATP2B1. OATP2B1 variants were expressed in human derived HEK293 cell line using baculovirus expression system. A cellular uptake assay with estrone-3-sulfate and a fluorescent probe 4’, 5’-dibromofluorescein (DBF) as substrates was set up and optimized. With the assay, OATP2B1-mediated uptake of variants was compared to the transport activity of OATP2B1 wild type. Amino acid changes Ser486Phe and Cys520Ser impaired OATP2B1 transport function severely. In addition, variant Thr318Ile transported DBF and estrone-3-sulfate less efficiently compared to OATP2B1 wild type, but Arg312Gln, Thr392Ile and Ser532Arg transport function was not affected. A method to study OATP2B1 function was created successfully. According to the results, single amino acid changes in OATP2B1 can impair OATP2B1 function. The results and method can be utilized to understand findings from pharmacogenetic studies in vivo, and to predict consequences of especially rare variants, which can be difficult to detect in small sample populations in clinical studies. However, further studies on the expression level and cellular localization of OATP2B1 variants are needed to fully characterize the impact of the variants studied.
  • Miinalainen, Annika (2022)
    OATP2B1 is a transmembrane transport protein expressed widely in the human body and transports both endogenous compounds and several drugs from outside the cell into the cytoplasm. The abundant expression of OATP2B1 in pharmacokinetically important tissues such as in the intestine, liver, and kidney suggests an important role in the drug absorption and elimination process, although research data on the clinical significance of OATP2B1 is still limited. Several drugs inhibit the function of OATP2B1, creating a risk for drug-drug interactions. OATP inhibition by some inhibitors is time-dependent, which may lead to more potent in vivo effects than expected. In this study, the time dependence of OATP2B1 inhibition by five different drugs was evaluated using OATP2B1-overexpressing HEK293 cells. IC50 values of inhibitors for OATP2B1-mediated uptake of DBF and E1S were determined with and without preincubation for 20 minutes. In addition, the in vivo interaction potential of the inhibitors in the intestine, liver, and other tissues was evaluated by utilizing the FDA and EMA guidelines. All five drugs showed effective and concentration-dependent OATP2B1 inhibition with IC50 values of 0.12– 8.82 µM. Furthermore, the inhibition of OATP2B1-mediated DBF uptake by ticagrelor and atorvastatin was time-dependent, while the effect of pre-incubation remains below the limit for the other inhibitors. The inhibitory effect of ticagrelor continued even after the inhibitor was removed from the inhibition buffer. All five inhibitors showed the potential to cause in vivo OATP2B1 inhibition in the intestine, which could result in decreased absorption of the co-administered substrate drug. About erlotinib, the risk of interaction also appeared in the liver, which could reduce the transfer of the substrate drug to the liver and thus lower its elimination rate. In this study, pre-incubation did not affect the in vivo interaction potential of the inhibitor drugs. The results indicate that drug-induced inhibition of OATP2B1 may be time-dependent and therefore can lead to interactions at lower concentrations than expected. For this reason, evaluating the time dependence would be appropriate when assessing transport protein-mediated interaction risk. The results of this study can be utilized in designing clinical interaction studies and in understanding the results.