Resumen de Impact of membrane transporters polymorphisms on nucleoside-derived drug bioavailability and action = Impacte dels polimorfismes en transportadors de membrana en la biodisponibilitat i acció de fàrmacs anàlegs de nucleòsids
Cristina Arimany Nardi
Nucleoside-derived drugs are used for the treatment of haematological malignancies, viral infections and autoimmune or inflammatory diseases. These drugs require membrane transporters to be internalised and be active. Transporters implicated in nucleoside and nucleoside derivatives internalisation are concentrative nucleoside transporters (CNTs) encoded by SLC28 and equilibrative nucleoside transporters (ENTs) encoded by SLC29. Other transporters such as organic cation transporters (OCTs) encoded by SLC22 have been implicated in the transport of some antiviral nucleoside derivatives, too. Nucleoside transporters as well as hOCT1 have been detected in immune cells, as well as in polarised epithelia where they are asymmetrically distributed mediating a net flux of the natural nucleoside or the derivative. Membrane transporters can present polymorphic variants which can alter its ability to interact with the substrate. Of all studied transporters, hOCT1 is the most polymorphic, being its polymorphic variants implicated in pharmacokinetics and pharmacodynamics of some drugs used in clinics such as metformine among others. In this thesis we show the importance polymorphic variants of hOCT1 have not only in lamivudine uptake but also in drug-drug interactions with other drugs co-administrated with lamivudine. Infected PBMCs showed an up-regulation of hOCT1 expression which would made it a better lamivudine target. We also discard the possibility that polymorphisms located at the extracellular loop might affect oligomerization. hOCT1 has been also identified as a bendamustine transporter and hOCT1 polymorphic variants modulated bendamustine sensitivity. Bendamustine sensitivity in CLL cells ex vivo can partially be explained by the hOCT1 polymorphic variants they are carrying. In case of DNMT inhibitors, nucleoside transporters are responsible for zebularine internalisation but not decitabine and mediate a apical-basolateral flux in polarised epithelia. hOCT1 can mediate zebularine efflux which is impaired by the presence of polymorphic variants. In this case polymorphic variants would confer sensitivity to zebularine treatment. In order to better understand the transporter-substrates interaction a hCNT3 model has been generated based on the recent crystallised V.cholerae nucleoside transporter. This model has been preliminary proved experimentally showing, so far, to be a good model. In summary, this thesis highlights the importance drug transporters and their polymorphic variants play in drug bioavailability and action
