ADME/Tox profiling is the systematic evaluation of the absorption, distribution, metabolism, excretion, and toxicity properties of drug candidates. It is integrated early in drug discovery to identify compounds with favorable pharmacokinetic and safety profiles before committing to expensive development.
Absorption studies assess how a compound moves from the administration site into the bloodstream. Caco-2 cell monolayers model intestinal permeability. The apparent permeability coefficient predicts the fraction absorbed in humans. Parallel artificial membrane permeability assays provide rapid permeability estimates. Aqueous solubility at physiological pH is measured by shake-flask or nephelometric methods.
Distribution studies evaluate the extent and pattern of compound distribution throughout the body. Plasma protein binding is measured by equilibrium dialysis or ultrafiltration. The unbound fraction determines the concentration available at the target site. Volume of distribution is estimated from in vitro data and in vivo PK studies. Tissue distribution studies using quantitative whole-body autoradiography or LC-MS/MS map compound localization.
Metabolism studies characterize the biotransformation of compounds. Hepatic microsomal stability assays measure intrinsic clearance. Metabolic half-life and intrinsic clearance are scaled to predict in vivo clearance. Cytochrome P450 inhibition and induction assays identify potential drug-drug interactions. Reactive metabolite screening detects compounds that form protein-reactive intermediates. Metabolite identification using LC-MS/MS determines the sites of metabolism and guides structural modification.
Excretion studies assess elimination pathways. Biliary excretion is measured using sandwich-cultured hepatocytes. Renal clearance is predicted from plasma protein binding and glomerular filtration rate. Transporter-mediated elimination is evaluated using cell lines expressing uptake and efflux transporters.
Toxicity screening identifies safety liabilities early. Cytotoxicity assays (MTT, ATP content) measure general cell health. Hepatotoxicity is evaluated using primary hepatocytes and hepatic cell lines. hERG channel inhibition predicts cardiac QT prolongation risk. Ames test detects mutagenicity. Phototoxicity, phospholipidosis, and genotoxicity are assessed in specialized assays.
The integration of ADME/Tox data uses multi-parameter optimization to balance potency with drug-like properties during lead optimization. Lipinski’s rule-of-five, ligand efficiency, and lipophilic efficiency guide compound selection. In silico prediction models estimate properties from chemical structure and prioritize compounds for experimental testing.
