Chemical fate in vitro: A physiological biokinetic (PBK) model for cell-based assays

In vitro toxicology assays are widely used in the context of toxicology to study in vivo outcomes and to improve mechanistic understanding of toxic responses. For this purpose, a better characterization of actual exposure and the fate of chemicals within the cellular test system is required. The present study aimed to develop a novel model, INSIGHT (In Silico Guide for Harmonized in vitro Testing), that integrates physiological and physicochemical parameters to better describe chemical fate in vitro and to guide assay design. The newly developed model, integrating the dynamic features of the Virtual Cell Based Assay model with the partitioning framework of the Virtual In Vitro Distribution model, was calibrated using both a large literature dataset and original experimental data, com­prising a total of 42 chemicals and 7 commonly used cell lines: HepaRG, HepG2, 3T3 Balb/c, PC12, MCF-7, RTgill-W1, and HEK293. These cell lines were selected for their diverse tissue and species origins, metabolic capacities, and potential for functional transport mechanisms, which are known to influence chemical kinetics. The INSIGHT model demonstrated flexibility and robustness across a range of cell lines when the parameters driving their metabolic activity or functional transport were informed. The present study underscores the pivotal function of logPow determination and the necessity for accurate calibration of partition coefficients, permeability, and metabolic pro­cesses to account for variability across cell lines and tested chemicals. This approach supports and facilitates enhanced experimental design and advancing quantitative in-vitro-to-in-vivo extrapo­lation (qIVIVE) in toxicology and strengthens next generation risk assessment (NGRA) workflows.