Determining compound solubility is essential for the early stages of the drug discovery process and lead optimization. Low solubility can lead to unpredictable and unreliable results during in vitro testing, thereby increasing the development costs. Solubility issues at the later stages of the drug discovery may lead to poor bioavailability, underestimated toxicity, and other obstacles, lowering the chances of a given drug candidate for success. Solubility can be measured either as a kinetic or thermodynamic value. Typically, the kinetic solubility method is used for early-stage drug discovery, as it is fast and well-suited for the HTS format. In this case, solid compounds are first dissolved in DMSO. Then linear serial dilutions of each compound are added to an aqueous buffer and observed for precipitate formation when the compound is not completely soluble. Precipitate appearance can be evaluated by light scattering (laser nephelometry method). For better precision, the solution can be subjected to high-speed centrifugation or filtration using special solubility filter plates. Then the compound concentration is measured in the saturated solution directly by UV or LC-MS using separately built calibration curves. Thermodynamic solubility is important for lead optimization and drug formulation stages. It is usually determined for pure compounds: crystalline powders, amorphous substances, and liquids. In this modification of the solubility assay, long (24 hours or more) incubations are required. Measurements are usually performed by the shake flask method with UV-Vis or LC-MS detection.
Deliverable: Full study report is provided, including solubilities and calibration curves for test and reference compounds (an example report is shown).
Sample Submission: Sample requirements are at least 50 µL of 20 mM stock compound solutions in DMSO for kinetic solubility measurements and 2 x 4 µmol of dry compound for thermodynamic solubility measurements. We do not need to know the structures of the molecules for ADME testing. However, brutto formulas must be provided for all studies involving MS detection.