Incubation Time Influences Organic Anion Transporter 1 Kinetics and Renal Clearance Predictions

Accurate predictions of drug uptake transporter involvement in renal excretion of xenobiotics requires determination of in vitro transport kinetic parameters under initial rate conditions. The purpose of the present study was to determine how changing incubation time from initial rate to steady state influences ligand interactions with renal organic anion transporter 1 (OAT1), and the impact of the different experimental conditions on pharmacokinetic predictions.   Transport studies were performed with Chinese hamster ovary cells expressing OAT1 (CHO-OAT1) and the Simcyp Simulator was used for physiologically based pharmacokinetic predictions.  Maximal transport rate and intrinsic uptake clearance (CLint) for PAH decreased with increasing incubation time. The CLint values ranged 11-fold with incubation times spanning from 15 sec (CLint,15s, initial-rate) to 45 min (CLint,45min, steady-state).  The Michaelis constant (Km) was also influenced by incubation time with an apparent increase in Km value at longer incubation times.  Inhibition potency of five drugs against PAH transport was tested using incubation times of either 15 sec or 10 min.  There was no effect of time on inhibition potency for omeprazole or furosemide, whereas indomethacin was less potent, and probenecid (~2-fold) and telmisartan (~7-fold) more potent with the longer incubation time.  Notably, the inhibitory effect of telmisartan was reversible, albeit slowly. A pharmacokinetic model was developed for PAH using the CLint,15s value.  The simulated plasma concentration-time profile, renal clearance and cumulative urinary excretion-time profile of PAH agreed well with reported clinical data, and the PK parameters were sensitive to the time-associated CLint value used in the model.