Microsomal Binding

Microsomal binding test is an important part of in vitro drug metabolism studies and can predict in vivo pharmacokinetics (PK). BOC Sciences is a leading CRO in drug development with a focus on formulation development. We offer microsomal binding services as part of our in vitro ADME (absorption, distribution, metabolism, and excretion) service program or as a stand-alone study.

What is Microsomal Binding?

Microsomes are nearly spherical vesicle-like structures formed by the self-fusion of the broken endoplasmic reticulum (ER) obtained during cell homogenization and differential centrifugation, and contain two basic components: the endoplasmic reticulum membrane and ribosomes. In in vitro experiments, it has the basic functions of endoplasmic reticulum such as protein synthesis, protein glycosylation and lipid synthesis. Microsomes can be obtained after homogenization of liver or other tissues. Microsomes contain cytochrome P450 oxidase, which is associated with oxidative metabolism.

In vitro techniques are increasingly being used in the development of new drugs to predict drug metabolism and disposition in humans. Microsomal binding in in vitro metabolism assays can significantly affect the observed metabolic kinetics and impede accurate prediction of metabolic intrinsic clearance. In vitro PK studies, most commonly with human liver microsomes, have been performed. Quantitative prediction of in vivo drug intrinsic clearance and the extent of potential drug interactions through in vitro microsomal binding assays is important for the development of drugs with optimal PK properties.

Our Methods

In the study of drug microsome binding, equilibrium dialysis, ultracentrifugation, and ultrafiltration methods can be applied. The principle of these methods is to physically separate and measure unbound and bound drugs in order to calculate their relative fractions. Our microsomal binding experiments carefully consider the lipophilicity, charge and degree of ionization of the drug under test at pH 7.4.

1. The unbound fraction of drug in the microsomal mixture is determined by equilibrium dialysis in phosphate buffer (pH 7.4).
2. The data are fitted to a standard binding model defined by binding affinity and maximum binding capacity.
3. The derived binding parameters can be used to model the effect of microsomal binding on in vitro enzyme kinetics.

Why Microsomal Binding Test?

• Microsome is a type of hepatic in vitro testing system used to assess the potential for drug-drug interactions (DDI) of investigational drugs.
• Microsomes are test systems used in drug inhibition and drug metabolism studies. According to FDA guidelines, drug inhibition studies require measurement of microsomal protein binding (MPB).
• Microsomes contain CYP and UGT enzymes, among others. Drugs sequestered in microsomes in vitro are unable to interact directly with metabolic enzymes.
• In addition to binding to plasma proteins, the drug to be tested can also bind to microsomes. Since only the free unbound portion of the drug can interact with metabolizing enzymes, microsomal binding can influence the prediction of in vivo PK from in vitro data.

Why Choose BOC Sciences?

• Development of a model for the effect of microsomal binding on the in vitro kinetics of drug metabolizing enzymes
• Characterization of binding of drugs with different physicochemical properties to microsomes
• Compliance with good laboratory practices (GLP)
• Report on the physicochemical properties and binding parameters of the studied drugs
• Advanced pharmacokinetic data collection and analysis techniques
• Extensive ADME expertise and a team of experienced experts