Time matters – in vitro cellular disposition kinetics help rationalizing cellular potency disconnects

Abstract

Loss in potency is commonly observed in early drug discovery when moving from biochemical to more complex cellular systems. Among other factors, low permeability is often considered to cause such potency disconnects. We developed a novel cellular disposition assay in MDCK cells to determine passive uptake clearance (PSinf), cell-to-medium ratios at steady-state (K p) and the time to reach 90% steady-state (TTSS90) from a single experiment in a high-throughput format. The assay was validated using 40 marketed drugs, showing a wide distribution of PSinf and K p values. The parameters generally correlated with transcellular permeability and lipophilicity, while PSinf data revealed better resolution in the high and low permeability ranges compared to traditional permeability data. A linear relationship between the K p/PSinf ratio and TTSS90 was mathematically derived and experimentally validated, demonstrating the dependency of TTSS90 on the rate and extent of cellular accumulation. Cellular disposition parameters could explain potency (IC50) disconnects noted for seven Bruton’s tyrosine kinase degrader compounds in a cellular potency assay. In contrast to transcellular permeability, PSinf data enabled identification of the compounds with IC50 disconnects based on their time to reach equilibrium. Overall, the novel assay offers the possibility to address potency disconnects in early drug discovery.