Metabolic soft-spot identification

Trunzer M, Faller B, Zimmerlin A. Metabolic soft spot identification and compound optimization in early discovery phases using MetaSite and LC-MS/MS validation. / Med Chem. 2009 52(2) 329-335. 

Metabolism Metabolic stability (see Section 6.3.2.1) Metabolic soft-spot identification (see Table 6.10) Reactive metabolites (see Table 6.10) Assessing in vitro metabolic liabilities by drug-metabohsm enzymes such as CYP Predicting in vivo clearance Assay ° Liver microsomes from various species ° NADPH as co-factor ° 0.5-5 i,M incubation concentration Analysis ° PPT followed by LC-MS/MS or onhne SPE-MS/MS... 

In silico approaches to predict drug metabolism are of particular interest to the pharmaceutical industry as having the potential to impact the early drug discovery process as well as in the candidate selection phase. The identification of metabolic soft spots in a new chemical entity could help improve the hepatic... 

For metabolic stability screens to be most effective, the screens must be tightly linked to some means of gathering information on metabolite structure. Methods for rapidly determining metabolite molecular weight and limited structural information have improved dramatically and allow this approach to be routinely employed (Anari and Baillie, 2005 Watt et al., 2003). The goal of this type of approach is to allow the identification of metabolic soft spots which can then be altered to produce compounds with improved metabolic stability. The literature of successful structural modification to increase stability has recently been reviewed (Thompson, 2001). 

At the early stage of compound selection and optimization for deciding a clinical candidate, drug metabolism studies are often conducted in vitro with liver fractions and in vivo with rats using nonlabeled compounds to define metabolic stability, soft-spot identification, CYP inhibition/induction potential, bioactivation or toxic metabolite formation, major in vitro metabolic pathways, and the limited in vitro interspecies comparison. Mass balance (or ADME) studies with collection of plasma in animals and humans using a... 

This LC-MS experimental approaches used in NEF metabolite identification are also routinely employed for in vitro metabolism comparisons across species, in which liver microsomes or hepatocytes from humans and animal species are used. In addition, liver microsomal incubations followed by metabolite identification and quantitative estimation using liquid chromatography-ultraviolet/ mass spectrometry (LC-UV/MS) is an approach commonly taken to determine metabolic soft spots, where a major metabolic reaction takes place (Table 6.10). Use of UV detection allows for quantitative analysis of major metabolites in the absence of chemical standards, with the assumption that the metabolic reaction did not disturb the molecule s UV chromophore. 

The rapid structure identification of metabolites provides an early perspective on the metabolically labile sites or soft spots of a drug candidate [86], This information is useful during lead optimization and can serve to initiate research efforts that deal with metabolism-guided structural modification and toxicity. 

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