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Ready-to-use assay systems for DMPK and ADMET studies

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Microsomal Binding

A fast high throughput assay for liver microsomal binding. Available as a kit, the assay is based on the affinity to human liver microsomal membranes.

  • Ready-to-use 96-well microtiter plates carrying TRANSIL beads with a single lipid bilayer reconstituted from synthetic lipids matching the microsomal membrane composition, designed to conveniently measure microsomal binding.
  • Kit includes spreadsheet, facilitating manipulation of statistical parameters and calculation of final results.
  • Designed for automated liquid handlers or manual pipetting.
  • TRANSIL beads are integrated into 96-well microtiter plates to enable easy handling.
  • One plate can be used for measuring microsomal binding of up to 12 compounds.
  • Only 12 minutes assay incubation time.
  • Rapid compound quantification due to immobilized plasma proteins (e.g. injection via RapidFire™).
  • Highly reproducible results and robust correlation with conventional dialysis technique.
Background and Technical Information

In early drug research projects, much emphasis is placed on being able to predict the pharmacokinetics of a drug in humans to help identify candidates with appropriate characteristics. Metabolic clearance is a key parameter that must be estimated. In general, this is achieved either via extrapolation using allometry or through translating an understanding of metabolic stability in preclinical non-human species, liver microsomes and hepatocytes to those in human. In the latter case, there has often been the assumption that the concentration added to the microsome or hepatocyte incubation is the same as the unbound concentration in the incubation. More recently, it has been shown that binding to microsomes and hepatocytes can be significant, and hence the unbound concentration is lower than the total concentration added, often resulting in a dramatic effect on the estimate of clearance. Consequently, it is important to estimate microsomal binding in these in vitro incubations. Often, the binding to microsomal membranes is estimated as the free fraction of drug in incubations of microsomes (without cofactor) in dialysis rigs. As the equilibration of microsomal binding in dialysis systems tends to require overnight incubations, it often suffers more than other experiments from compound instability through hydrolysis and precipitation of poorly soluble drugs. Moreover, the free fraction which is determined experimentally relates to the experimental concentration of microsomes which will in many cases differ from the incubations that have occurred with the metabolic stability experiments. To adjust the free fractions in the microsomal binding experiment to the free fractions in the metabolic stability experiment an equation developed by Austin and coworkers is used. However, this equation is limited in the range concentration changes of microsomal incubations.

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