Cross-species translational modelling of targeted therapeutic oligonucleotides using physiologically based...

Oligonucleotide therapeutics hold promise for targeted gene silencing, yet achieving optimal tissue-specific delivery remains challenging. This study introduces a mechanistic whole-body physiologically based pharmacokinetic (PBPK) model to predict tissue uptake dynamics of both conjugated (targeted) and unconjugated oligonucleotides across species. The model incorporates two uptake pathways: a non-saturable nonspecific pathway for all oligonucleotides and receptor-mediated endocytosis (RME) specific to conjugated molecules. Parameters for nonspecific uptake were derived from plasma and tissue concentration data of unconjugated antisense oligonucleotides (ASOs) in rats, while RME parameters for N-acetylgalactosamine (GalNAc)-conjugated oligonucleotides targeting the asialoglycoprotein receptor (ASGPR) were obtained from literature. Model validation against experimental data for conjugated and unconjugated ASOs and small interfering RNAs (siRNAs) in rats and mice demonstrated good predictive performance, with median predicted-to-observed AUC ratios of 0.84 (Interquartile range [IQR] 0.434-1.22) in rats and 0.629 (IQR 0.3-1.6) in mice. Local sensitivity analyses identified key parameters and processes influencing organ uptake, including the unbound plasma fraction and receptor-mediated uptake efficiency. Simulations highlighted the potential of sustained-release formulations to improve targeting specificity by mitigating receptor saturation. This is the first whole-body PBPK model to describe oligonucleotide pharmacokinetics across species and modalities. The model provides critical mechanistic insights to optimize tissue-specific delivery, guide formulation strategies, and enhance therapeutic outcomes for targeted oligonucleotide therapeutics.