Is the door closed? : In vitro studies on the pharmacokinetic effects of OATP1B1 gene-drug and drug-drug interactions.

Organic Anion Transporting Polypeptide 1B1 (OATP1B1) is a membrane protein that acts in a door-like manner, facilitating the uptake of compounds that otherwise have difficulties passing biological membranes. The transported compounds include several structurally diverse endogenous substances as well as drugs and other xenobiotics. OATP1B1 is located in the sinusoidal (blood-facing) membrane of hepatocytes and is an integral part of hepatic distribution and elimination of many of its substrates. OATP1B1 function can be impaired (the door get closed), leading to increase in plasma exposure of these substrate drugs. Increased plasma exposure, in turn, can increase the risk of adverse drug effects. This impairment can result from SLCO1B1 pharmacogenetics (e.g. non-synonymous single-nucleotide variants (SNVs), so-called gene-drug interaction) or inhibition of transport activity by another drug (drug-drug interaction). While the clinical consequences of common variants such as SLCO1B1 c.521T>C are well-known, the effects of rare variants remain understudied. However, implementation of clinical pharmacogenetics and genotype-guided dosing requires information on the predicted phenotype, yet this is lacking on rare variants. In this thesis, baculovirus expression system in HEK293 cells was used to assess the possible changes 19 naturally occurring rare SNVs cause in OATP1B1 function and expression. Quantitative targeted absolute proteomics analysis measured the changes in membrane protein expression caused by the SNVs and pharmacokinetic modelling evaluated the degree of change in plasma exposure of rosuvastatin and the need for dosing adjustments according to the changes in the observed in vitro OATP1B1 activity. Indeed, 9 out of the 19 variants showed impaired (<50% of reference) OATP1B1 activity. The membrane protein expression, however, does not fully explain these changes. Pharmacokinetic modelling estimated that doses of 30 mg (with 50% OATP1B1 function) and 20 mg (with 0% OATP1B1 function) result in plasma exposure similar to 40 mg dose (the maximum approved dose, with 100% OATP1B1 function), while liver exposure remained proportionate to the dose. The possible mechanism behind rhabdomyolysis cases in patients receiving ticagrelor and rosuvastatin concomitantly was also investigated. Ticagrelor (an antithrombotic drug) and rosuvastatin (a cholesterol-lowering drug) are both commonly prescribed as secondary prevention after cardiovascular events. The in vitro inhibition assays using the same expression method and ticagrelor and rosuvastatin revealed that ticagrelor inhibits OATP1B1, OATP2B1 and OATP1B3 with IC50 values in the low micro molar range. However, when taking into account the unbound concentration at the hepatic inlet, clinical interaction is unlikely and the primary cause was accredited to inhibition of intestinal breast cancer resistance protein. Additionally, SLCO1B1 c.521T>C was observed to affect the plasma exposure of fluvastatin enantiospecifically in a clinical trial. To elucidate the mechanism behind this observation, transport of 3R,5S- and 3S,5R-fluvastatin was examined in reference and c.521T>C OATP1B1 with the same expression system. No significant differences were observed in the uptake activity in reference OATP1B1 and the c.521T>C variant impaired the transport of both enantiomer equally. Further research is needed to clarify whether another mechanism are involved in fluvastatin pharmacokinetics enantiospecifically. In conclusion, this thesis examined several situations when the door of OATP1B1 transport gets closed. Rare variants of SLCO1B1 were observed to be able to impair OATP1B1 function and membrane expression and this might lead to increased plasma exposure of rosuvastatin. Dose reductions might be considered to avoid increased plasma exposure and reduce risk of rosuvastatin-induced muscle symptoms. The effect of SLCO1B1 c.521T>C on fluvastatin transport is not enantiospecific in vitro. Ticagrelor inhibits OATP1B1, 1B3, 2B1 and BCRP and concomitant use with high-dose rosuvastatin should be avoided.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2023

Author dc:creator

• Kiander, Wilma

• farmasia

Statement dc:rights

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Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/352683

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F352683