Human studies metabolic stability

When assayed in HEK293 cells transfected with the cloned human, rat and guinea pig TRPVl, (23a) showed similar potencies. Not unexpeetedly, (23a) showed poor metabolic stability and a structure-activity study to optimize potency and drug-like properties was initiated. Modification on the left-handed A -aryl section showed that ... 

Metabolic stability in human liver preparations may represent a suitable experimental tool to obtain relevant pharmacokinetic information in an early phase of drug discovery. Compounds which are metabolized principally by the liver can be identified and studied in more detail to determine the principal sites of biotransformation. 

Several kinetic parameters can be measured on different experimental systems to account for the interaction of a compound with CYPs. For example when studying the metabolic stability of a compound, it could be measured in a recombinant CYP system, in human liver microsomes, in hepatocytes and so on. Each system increases in biological complexity. Although in the recombinant CYP system only the cytochrome under consideration is studied, in the case of the human liver microsomes, there is a pool of enzyme present that includes several CYPs, and finally in the hepatocyte cell system, metabolizing enzymes play an important role in the metabolic compound stability. In addition, transport systems are also present that could involve recirculation or other transport phenomena. The more complex the experimental system, the more difficult it is to extract information on the protein/ligand interaction, albeit it is closer to the in vivo real situation and therefore to the mechanism that is actually working in the body. 

In addition, compound 15 also had good metabolic stability in human liver microsome in vitro assay (hLM ti/2 = 39min) and in rat in vivo pharmacokinetic studies (ty2 = 3.3 h, po), with a rat oral bioavailability of 15%, showing a significant improvement in these PK parameters over the lead compound 1. The observed improvement in PK during the optimization was another validation of the strategy discussed above. This part of the optimization process is summarized in Scheme 19.2. 

Linget JM, du Vignaud P (1999) Automation of metabolic stability studies in microsomes, cytosol and plasma using a 215 Gilson liquid handler. J Pharm Biomed Anal 19 893-901 Long L, Dolan RC, Dolan ME (2001) Debenzylation of 06-benzyl-8-oxoguanine in human liver implications for 06-benzylguanine metabolism. Biochem Pharmacol 61 721-726... 

The availability of human tissues has allowed several human DMPK parameters to be evaluated in drug discovery before the compound enters into clinical studies. One such assay is the determination of human hepatocyte clearance. Since liver is the major site of metabolism for most drugs, screening compounds for metabolic stability in liver preparations is usually one of the primary screenings employed in drug... 

The studies described in this section demonstrate both success and challenges, and reflect the current understanding of prediction of hepatic clearance using in vitro human metabolic data. In contrast to the well-defined concepts, readily applicable biochemical methods, and sensitive analytical techniques available to studies of metabolic stability and enzyme kinetics, efforts to accurately predict in vivo, using in vitro data, require further refinement. 

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 chapter follows the large-scale MMP analysis paradigm and studies the relationship between molecular transformations and the resulting changes in experimental property, particularly human liver microsomal metabolic stability. More specifically, the ultimate aim has been the identification of metabolic stability isosteres, that is, transformations and replacements with zero or positive effect on metabolic stability. Furthermore, in line with the recent study of Papadatos et al. [18], the possibility of context-dependent isosteric replacements is explored. 

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