Modeling and Simulation Identifies Endocytosis Uptake Rate and Fraction Unbound as Important Predictors of Oligonucleotide Pharmacokinetics

Therapeutic oligonucleotides (TOs) represent an emerging modality, which offers a promising alternative treatment option, particularly for intracellular targets. The two types of TOs, antisense oligonucleotides (ASO) and small interfering RNAs (siRNAs), distribute highly into tissues, especially into the liver and the kidneys. However, molecular processes at the cellular level such as the uptake into the cell, endosomal escape, binding to the target mRNA, and redistribution back to the systemic circulation are not well characterized because experimental data and assays are lacking. We developed a whole-body PBPK model for TOs and verified the predictive performance against clinically observed data for three ASOs and five siRNAs. The predicted concentration-time profiles were in accordance with the clinically observed data for all investigated TOs, and all pharmacokinetic parameters were predicted within twofold. Sensitivity analysis with the evaluated PBPK model revealed that the endocytosis uptake rate and the fraction unbound in plasma impact the peak concentration (C_max), time to C_max (t_max), and the area under the curve (AUC) of a subcutaneously administered ASO, whereas the redistribution rate and the nuclease clearance had minor to no impact. The mathematical model can guide the development of required in vitro assays for key parameters to better understand the pharmacokinetics of TOs. PBPK models, parameterized with reliable in vitro data, could be used in the future to predict the pharmacokinetics in special populations with limited clinical data to ensure a safe and effective therapy.