Acoustic Droplet Ejection and Open Port Interface for Rapid Analysis of Metabolic Stability Assays

In vitro absorption, distribution, metabolism and elimination (ADME) assays are widely used for profiling compounds in pharmaceutical drug discovery programs. Many compounds are screened in metabolic stability assays, using liver microsomes as a model of intrinsic hepatic clearance. Analysis of metabolic stability assays has relied on high throughput LC-MS/MS techniques to keep up with automated assays and compound profiling needs. An experimental alternative to sample analysis via fast chromatography employs an open port interface (OPI) which dilutes and directs acoustically-ejected droplets from microtiter plates to a conventional electrospray ion source for ionization and introduction into a mass spectrometer. Metabolic stability assays of 37 commercial drug compounds using in human, dog, rat and mouse liver microsomes (LMs), were analyzed by LC-MS/MS and an experimental breadboard version of an ADE-OPI-MS/MS system. Results from the experiments comparing intrinsic clearance (CL_int) generated with ADE-OPI-MS/MS vs fast LC-MS/MS for all compounds showed ≥86% of CL_int values were within a factor of two with R² ≥ 0.86 using 25 nL and 5 nL sample ejection volumes on the ADE-OPI-MS/MS instrument. Throughput with the experimental ADE-OPI-MS/MS system used in this study was more than ten-fold faster than analysis by the fast LC-MS/MS at 1.3 s/sample versus 17.2 s/sample, respectively.