In vitro metabolic stability is an important early ADME test for predicting in vivo half-life and clearance of the test compounds. Although the metabolism of drugs generally occurs in a variety of tissues such as the intestinal wall, kidneys, lung, skin and blood, the liver is considered to be the major site of drug metabolism. Hepatocytes or liver microsomes are, therefore, the fast and cost-effective way to determine the intrinsic clearance (CLint) of a drug candidate. These CLint assays, along with other parameters including plasma protein binding and blood-to-plasma ratio, often allow a good prediction of in vivo hepatic clearance.
Whether the drug is designed to be administered orally, intravenously, or topically will affect the type of in vitro testing required. Creative Bioarray offers a wide range of biological systems to determine in vitro metabolic stability including primary hepatocytes, tissue homogenates and tissue fractions (e.g. microsomes, mitochondrial preparations, S9 fractions and intestinal fluid) from a variety of preclinical species.
Liver microsomes are a recognized source of drug metabolizing enzymes. They contain cytochrome P450, FMO carboxylesterases, epoxide hydrolase and UGT. Liver microsomes are widely used to determine in vitro intrinsic clearance (CLint), which can then be scaled to predict in vivo hepatic clearance.
S9 fractions can be used to evaluate phase I metabolism and some phase II (conjugation) reactions, including sulfation and glucuronidation, depending on the co-factors added. It is highly enriched in cytoplasm and microsomes.
Intact hepatocytes are often referred to as the "gold standard" for in vitro evaluation of metabolism, as they allow for measurement of phase I and II metabolism under conditions where compound movement is restricted by membranes as it is in vivo and in the presence of similar co-factor concentration.
The intestinal fluid are comprised of bile salts, phospholipids, cholesterol and bicarbonate as well as a series of digestive enzymes such as proteases, peptidases, lipases, carbohydrases and nucleases. However, their value to assess drug stability is limited, as they do not contain digestive enzymes.
The small intestinal mucosa consists mainly of mucus and enterocytes. These cells are rich in phase I and phase II enzymes and can significantly lower oral bioavailability. Small intestinal mucosal homogenate is a powerful and cost-effective tool for assessing drug metabolic stability in the presence of relevant co-factors.
Creative Bioarray has a leading portfolio of compound stability services designed to help you understand the metabolic profile of your compounds. All our assays can be ordered individually or in combination to provide cost savings.