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Solubility Assay

 

 

Readout: Compound concentration in mg/mL or uM

Controls: Atenolol, Ketoconazole, Tamoxifen

 

Assay Description – Kinetic Solubility:

A stock solution of compound (50 mM in DMSO) is added to test medium (aqueous buffer, SIF, or SGF). The mixture is shaken at room temperature and then filtered. The liquid is diluted 10x and 30x with DMSO before LC-MS/MS analysis. Standard solutions are prepared as follows: stock solutions are diluted to ten defined concentration points from 60 μM to 0.002 μM with DMSO. Aliquots of samples and standard solutions are filtered and mixed with acetonitrile / H2O, then vortexed and used for LC-MS/MS analysis.

The MS detection is performed by using a Sciex API 4000 Q trap instrument. Each compound is analyzed by reversed phase HPLC using a Kinetex 2.6u C18 100Å column (3.0 mm X 30 mm, Phenomenex). Mobile phase – solvent A: water with 0.1% formic acid,  solvent B: acetonitrile with 0.1% formic acid.

Assay Description – Thermodynamic Solubility:

Test medium (aqueous solvent, SIF, or SGF) is added to solid compound. Excess solid is used and relatively long mixing times are performed to ensure equilibrium is achieved (typically 16-72 h). At the end of the incubation period, the saturated solution is filtered and quantified against a DMSO stock solution.

The MS detection is performed by using a Sciex API 4000 Q trap instrument. Each compound is analyzed by reversed phase HPLC using a Kinetex 2.6u C18 100Å column (3.0 mm X 30 mm, Phenomenex). Mobile phase – solvent A: water with 0.1% formic acid,  solvent B: acetonitrile with 0.1% formic acid.

 

Data Analysis:

The solubility of the test compound is determined based on the calculated concentration. The final DMSO concentration is 1%, and the maximum test concentration is 0.5 mg / mL.

 

Abbreviations:

DMSO                     Dimethylsulfoxide

HPLC                       High-performance liquid chromatography

LC                             Liquid chromatography

MS                           Mass spectrometry

SGF                          Simulated gastric fluid, pH 1.21

SIF                            Simulated intestinal fluid, pH 6.81

 

Literature:

  1. United States Pharmacopeia, USP40-NF35 (2017).
  2. Amidon, G.L.; Lennernäs H.; Shah V.P.; Crison, J.R. “A theoretical basis for a biopharmaceutic drug classification: the correlation of in vitro drug product dissolution and in vivo bioavailability“; Pharm. Res. 12, 413, (1995).
  3. S. Food and Drug Administration: “The Biopharmaceutics Classification System (BCS) Guidance”; 2016.