Browsing by Author "Lähdeniemi, Veera"

Drug metabolism is a series of enzyme catalysed processes that modify foreign compounds into a form that is more easily excreted from the body. Compounds can affect the activity of metabolizing enzymes and this may lead to toxic concentrations of a drug that is metabolized via the enzyme. With prodrugs, on the other hand, the drug might not achieve its biologically active form and therefore the treatment will not be effective. Recognizing and preventing metabolic interactions is important already in the early stages of drug discovery and development. Cytochrome P450 (CYP) enzyme inhibition is one of the major reasons for adverse drug-drug interactions (DDIs). The inhibition can be time-dependent (TDI), which means that the potency of inhibition increases over time. TDI may be reversible or irreversible, latter being more severe as new enzymes need to be produced in the body to restore the enzymatic activity. IC50 shift assay is a method that gives information of new compounds potential to cause TDI. IC50 shift assay does not show whether the TDI is reversible or irreversible, however further studies, e.g. dialysis assay, can be conducted to find it out. If the study compound is irreversibly bound to the enzyme, the enzyme activity should not recover in the dialysis. The aim of this master’s thesis was to develop a dialysis method that could determine the reversibility of the TDI observed in the IC50 shift assay. A dialysis method conducted with microsomes is described in earlier literature. Known inhibitors (both time-dependent and direct) for four CYP isoforms were studied in this work: CYP1A2 (furafylline and fluvoxamine), CYP2C9 (tienilic acid and sulphaphenazole), CYP2D6 (paroxetine and quinidine) and CYP3A4 (verapamil, azamulin and ketoconazole). IC50 shift assays were conducted to each inhibitor before the dialysis experiment. The studied compounds behaved in the dialysis assay mostly as assumed based on the literature. The workflow from IC50 shift assay to dialysis assay worked successfully and the IC50 shift data could be utilized when choosing the test concentrations for dialysis assay. Both the IC50 shift assay and dialysis assay were reproducible and the deviations between replicates and separate studies were relatively low. The method still requires some optimizing, but so far, the results are promising. In the future the dialysis method may be part of in vitro CYP inhibition studies at Orion Pharma.