Pitfalls in High Throughput Screening for Drug Absorption Optimization in Drug Discovery

Implementation of combinatorial chemistry and high throughput screening to biological targets has led to produce lipophilic and poorly water soluble lead compounds. Since these compounds show poor absorbability, high throughput methods for improving solubility and membrane permeability have been developed. Kinetic solubility of compounds after dilution of dimethyl sulfoxide solution into aqueous buffer is determined using high throughput methods with turbidimetry, nephelometry or UV assays. The kinetic solubility tends to be overestimated compared with the corresponding thermodynamic solubility obtained using a traditional flask shaking method. A new solid-dissolution method providing thermodynamic solubility similar to that in traditional method has been developed using a 96-well plate for equilibrium dialysis. In conventional Caco-2 assays, the membrane permeability (Papp) of certain lipophilic compounds was underestimated due to insolubility in the apical compartment and adhesion to the device, resulting in a poor relationship between the in vivo absorption fraction and the Papp values. The addition of a solubilizer into the apical compartment and bovine serum albumin in the basolateral compartment improved the relationship, enabling evaluation of widely diverse compounds. The usefulness of these newly-developed methods for compounds with poor physical properties will be discussed, with reviewing currently available high throughput methods for optimizing absorption.