In Vitro Metabolism

The liver represents the major organ for drug metabolism and contains the cytochrome P450 (CYP) enzymes, the major enzyme system for xenobiotic metabolism. The identification of human CYP enzymes involved in drug metabolism allows the prediction of potential drug-drug interactions resulting from co-administration of drugs with CYP inhibitors or inducers and of interpatient variability in drug exposure. Various approaches have been applied to identify human enzymes involved in drug metabolism, including inhibition studies with specific chemical inhibitors and inhibitory antibodies, correlation studies, and studies using heterologously expressed CYP isoforms. Typically, xenobiotics are eliminated from the body by two mechanisms: metabolism to active or inactive metabolites; and excretion.

An understanding of the metabolism of the drug is extremely important in the drug discovery and development continuum primarily because these studies help to identify potentially toxic metabolites. As such, it is frequently desirable to elucidate the structure of the metabolites at an early stage to preclude costly failures. In vitro screening of potential drug candidates in early drug discovery has been successfully utilized to identify compounds with unfavorable ADME characteristics. These drug metabolism assays can include: CYP inhibition; CYP induction; intestinal permeability in Caco-2 cells; metabolite profiling and identification in hepatocytes and microsomes; metabolic stability in hepatoctyes and microsomes; protein binding (equilibrium dialysis); CYP reaction phenotyping; and species comparisons of in vitro metabolism in microsomes and hepatocytes.

Analytical Capabilities for Drug Metabolism Studies

The Southern Research bioanalytical program provides comprehensive analytical services to assist clients with their drug discovery and development programs for in vitro drug metabolism. Using state-of-the-art analytical instrumentation, our experienced analytical scientists can develop analytical methods using triple quadrupole and linear ion trap for metabolic profiling across multiple species as well as structural elucidation in hepatocytes, microsomes, or supersomes. The MS³ capability on the linear ion trap enables us to provide additional complementary information for structural elucidation of metabolites. In addition, Analyst® and Light Sight^® software enables scientists to conduct both known and de novo metabolite identification by control subtraction and isotope pattern filtering. Knowledge of the structure of the metabolites enables enhancement in finding a lead candidate and synthesis of the metabolites for use as a reference standard.

Additionally, we offer expertise in developing LC/MS/MS-based assays for quantitation of the test article or substrate in other in vitro metabolism assays such as metabolic stability, CYP inhibition, CYP induction, and protein binding.