Comparison of nephelometric, UV-spectroscopic, and HPLC methods for high-throughput determination of aqueous drug solubility in microtiter plates.

High-throughput screening (HTS) is an important method in the pharmaceutical industry for discovering hits that will be further developed into leads, clinical candidates, and eventually into medicines. After an HTS campaign, solubility studies of the discovered hits are an important means to judge the validity of the pharmacological result and to prioritize them for further studies. In the present paper, different methods for determination of kinetic solubility were compared that are able to provide sufficient throughput and that consume only small amounts of compound. In particular nephelometric determination, UV-spectroscopic determination, and determination of kinetic solubility by HPLC have been investigated. These three assays have been compared with regard to their detection limit, information content, and speed/throughput. Further on, parameters influencing solubility in the specific HTS assay which may vary for different HTS assays are discussed. These include formation of different salt forms, time used for incubation during the assay, and concentration of cosolvent. Finally a comparison of the results and purpose of kinetic and thermodynamic solubility is given.