In Vitro Pharmacokinetic Profiling of Thiourea Derivatives of Naproxen With Anti‐Inflammatory and Anticancer Activity

Pharmacokinetic deficiencies account for nearly 40% of clinical drug candidate failures, emphasising the importance of early in vitro evaluation. Following the 3Rs principle, this study assessed the in vitro pharmacokinetic properties of thiourea derivatives of naproxen (1-14). Permeability assessment using the parallel artificial membrane permeability assay method revealed that derivatives 4 (-logPe = 4.13, p = 0.0859) and 7 (-logPe = 3.94, p = 0.2291) exhibited the highest passive gastrointestinal absorption potential, comparable to naproxen. Evaluation of binding affinity to human serum albumin (HSA) using the high-performance affinity chromatography method identified two groups of compounds: high-binding aromatic amine derivatives (except derivative 5) and low-binding aromatic amino acid ester derivatives. Microsomal stability assays indicated that compound 7 underwent the most extensive metabolic degradation (65.83% decrease). These findings suggest that further structural optimisation of compound 7, such as esterification with higher or branched alcohols, should lead to the improvement of HSA binding and reduction of metabolic susceptibility. Conversely, compound 4 combines favorable biological activity with a pharmacokinetic profile closely resembling that of naproxen. Although limited by the exclusive use of in vitro models and the absence of in vivo validation, this study provides valuable insights for the rational design of naproxen-based thiourea derivatives with enhanced anti-inflammatory and anticancer potential.