Whole-body physiologically based pharmacokinetic model for nutlin-3a in mice after intravenous and oral administration

Abstract

Nutlin-3a is an MDM2 inhibitor that is under investigation in preclinical models for a variety of pediatric malignancies, including retinoblastoma, rhabdomyosarcoma, neuroblastoma, and leukemia. We used physiologically based pharmacokinetic (PBPK) modeling to characterize the disposition of nutlin-3a in the mouse. Plasma protein binding and blood partitioning were assessed by in vitro studies. After intravenous (10 and 20 mg/kg) and oral (50, 100, and 200 mg/kg) dosing, tissue concentrations of nutlin-3a were determined in plasma, liver, spleen, intestine, muscle, lung, adipose, bone marrow, adrenal gland, brain, retina, and vitreous fluid. The PBPK model was simultaneously fit to all pharmacokinetic data using NONMEM. Nutlin-3a exhibited nonlinear binding to murine plasma proteins, with the unbound fraction ranging from 0.7 to 11.8%. Nutlin-3a disposition was characterized by rapid absorption with peak plasma concentrations at approximately 2 h and biphasic elimination consistent with a saturable clearance process. The final PBPK model successfully described the plasma and tissue disposition of nutlin-3a. Simulations suggested high bioavailability, rapid attainment of steady state, and little accumulation when administered once or twice daily at dosages up to 400 mg/kg. The final model was used to perform simulations of unbound tissue concentrations to determine which dosing regimens are appropriate for preclinical models of several pediatric malignancies.

Fig. 1.

Schematic diagram of PBPK model for nutlin-3a in mice. C,b, bound drug concentration; C,f, free drug concentration. Arrows connecting compartments represent blood flows from literature values.

Fig. 2.

Analysis of nutlin-3a characteristics in murine blood. A, nutlin-3a blood cell partitioning. Nutlin-3a was spiked into murine whole blood at various concentrations and incubated for 30 min at 37°C. In one aliquot, nutlin-3a was measured in whole blood, and in another aliquot nutlin-3a was measured in the plasma. B, nutlin-3a plasma protein binding. Nutlin-3a was spiked into murine plasma at various concentrations and incubated for 30 min at 37°C. Plasma protein binding was determined by equilibrium microdialysis and is expressed as the percentage of the total nutlin-3a plasma concentration that is unbound. Bars represent the mean, and error bars represent the S.D.

Fig. 3.

Concentration-time plots of nutlin-3a in tissues. Symbols are data points from individual mice, and the lines represent the model-predicted concentrations. Data from the 50 mg/kg oral group are not shown. Data below the lower limit of quantitation are not shown.

Fig. 4.

Simulated concentration-time plot of plasma nutlin-3a after multiple oral doses with once-daily (QD) and twice-daily (BID) dosing. Simulations were based on the final PBPK model.

Fig. 5.

Simulated concentration-time plot of unbound nutlin-3a in the retina and vitreous after multiple oral doses given once daily (QD) or twice daily (BID). The horizontal lines represent the unbound IC₅₀ of nutlin-3a for Weri1 cells.