This is a high-throughput and affordable option for rapid evaluation of kinetic solubility for a large number of compounds in any aqueous buffer. Linear serial dilutions of each compound to be analyzed are prepared from DMSO stock solutions in an aqueous buffer of the specified composition and pH and the precipitation points for each compound are determined from the light scatter graphs (typical working solubility range is from 50-100 µM up to 1-2 mM). This assay is typically performed in duplicates.
For a rough estimate of aqueous solubility (“solubility not lower than…”), this method can be even more simplified: instead of linear serial dilutions, light scattering can be measured in two concentrations of compounds (high-throughput solubility threshold method). Those compounds yielding light scattering signal values higher than that of the highly soluble compound 2′-Deoxy-5-fluorouridine, are considered insoluble at tested concentrations. As a control, reference compound poorly soluble at the same concentrations is used.
BMG Labtech Nephelostar laser microplate nephelometer is used in our lab for the light scattering measurements. 96 or 384 well plates can be used.
We typically perform high-throughput solubility threshold assay in singletons, at up to 2mM compound concentrations, with ondansetron as a poorly soluble reference and deoxyfluorouridine as a well soluble one. This method can be modified upon request.
Compound’s solubility normalized to deoxyfluorouridine (100% soluble) and ondansetron (0% solubility) is calculated. Selected ranges of Relative Solubility (>0.8, 0.6-0.8 and <0.6) allow dividing compounds in clearly distinguishable groups (good solubility, intermediate solubility and poor solubility) at the chosen solubility threshold. Full study report is provided.
Typically, a minimal accurately weighable quantity of dry compound (~1 mg or 2 µmol) or 100 µL of 20 mM stock DMSO solution, is required for this assay. However, the exact required amount would depend upon the solubility range of interest.
List of references:
1. T.A. Fligge, A. Schuler, Integration of a rapid automated solubility classification into early validation of hits obtained by high throughput screening. Journal of Pharmaceutical and Biomedical Analysis, 2006, Vol. 42, P. 449–454.
2. M.E. Stevens, P.J. Bouchard, I. Kariv, T.D.Y. Chung, K.R. Oldenburg, Comparison of automation Equipment in high throughput screening. Journal of Biomolecular Screening, 1998, V.3, #4, P 305-311
3. C.D. Bevan, R.S. Lloyd, A High-Throughput Screening Method for the Determination of Aqueous Drug Solubility Using Laser Nephelometry in Microtiter Plates. Anal. Chem. 2000, V. 72, P. 1781-1787.