Early drug metabolism assays

A landmark study reported that 40% of failures in clinical studies were due to PK problems.1-3 This led to the need to develop drug metabolism studies that could be performed on a compound before it was recommended for development. The early drug metabolism and pharmacokinetic (DMPK) studies were used to assess the ADME/PK properties of NCEs. The major pharmaceutical companies were very successful at setting up exploratory drug metabolism departments using various models. This led to an explosion of new higher throughput ADME/PK assays that provided medicinal chemists with the necessary tools to improve the ADME/PK properties of NCEs. 

Quantitative In Vitro ADME Assays Using LC—MS as a Part of Early Drug Metabolism Screening... 

DMDCT is an important parameter because it governs how quickly one can deliver ADME/PK data for certain parameters to a discovery team. The shorter the DMDCT, the more discovery cycles can be completed. For example, if the DMDCT is 1 month, a laboratory could handle 12 discovery studies per year at most. If the DMDCT is 2 weeks, 24 discovery cycles per year are possible. In the early days of exploratory drug metabolism, the DMDCT was typically 4 to 6 weeks, with at least 50% of the time dedicated to assay cycle time. Clearly, a new vision was required for the assay cycle. 

In vitro assays play a very important role in drug discovery. First, these assays provide a simple, convenient, and fast way to test the potency and drug properties of chemical entities to help advance them rapidly. The drug-like properties commonly refer to respectable absorption, adequate distribution, low metabolism, and complete elimination (ADME) from body and minimal toxicological risk. Second, the amount of compound available is often limited in the early drug discovery stage and it is not always feasible for preclinical animal studies. Thus, in vitro assays could be a more rapid alternative to screen compounds. Third, in vitro assays are also designed to answer specific... 

One of the early in vitro assays that is used as part of the new drug discovery paradigm is the metabolic stability assay. This assay is also referred to as the microsomal stability assay or the hepatocyte stability assay or sometimes simply the in vitro stability assay (Thompson, 2000, 2001 Xu et ah, 2002 Jenkins et ah, 2004 Baranczewski et ah, 2006). As these names suggest, there are various ways to perform the in-life part of the assay some departments prefer to screen with liver microsomes, while others find that hepatocytes provide more meaningful data (Lau et ah, 2002). Regardless of the in-life part of the in vitro stability assay, the analytical part represents a significant challenge because the analyst must have compound-specific methods in order to properly analyze the samples. 

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