Mechanistic In Vitro Transporter Modelling: A Path to Consistent Intrinsic Kinetic Inputs Suitable for IVIVE of...

A key aspect of in vitro-to-in vivo extrapolation (IVIVE) linked to physiologically based pharmacokinetic (PBPK) modelling (IVIVE-PBPK) is ensuring that input data derived from in vitro assays intrinsically reflect the compound's true properties, free from the confounding effects of assay design, model structure, or data transformation methods. Having assurance in the model inputs provides an increased confidence in interpreting the model outcomes. Deriving the kinetics of transporter protein activity from in vitro experiments is complex, and the analytical approach applied to the experimental flux data requires careful consideration. Applying different data analysis approaches to the same dataset can yield markedly variable drug parameter estimates illustrating how readily these confounding factors bias the derived values. Mechanistic modelling of the in vitro data addresses this by integrating assay design, structural experimental system components, and statistical fitting to derive intrinsic, physiologically relevant drug parameter estimates that conventional analysis approaches often cannot achieve; this approach typically yields higher, less variable passive permeability estimates and lower, less variable K_i and K_m values. This chapter outlines in vitro assay designs for determining 'intrinsic' drug permeation and active transport kinetics, contrasts the challenges of conventional analysis approaches with the benefits of mechanistic modelling, and provides examples of where the mechanistic approach adds value in practice. Ultimately, deriving intrinsic rather than apparent parameter estimates increases confidence in model conclusions, supporting more reliable IVIVE-PBPK-based predictions of drug disposition and transporter-mediated drug-drug interactions without the broad application of sensitivity analysis to inform dosing and regulatory decision-making.