(M1130-02-07) The Significance of Biotransformation in Discovery Research of NCEs (New Chemical Entity): Examples of Unique Case Studies

Purpose: Biotransformation is defined as chemical reactions that occur in the organism which are generally mediated by enzymes. Drug metabolism is the term used to describe the biotransformation of pharmaceutical substances in the body so that they can be eliminated more easily. The majority of metabolic processes that involve drugs occur in the liver, as the enzymes that facilitate the reactions are concentrated there. Biotransformation plays a major role in drug discovery. Determination of metabolic pathways of NCEs (new chemical entity) can contribute towards the decision-making process as this information provides suggestions on structural modification of drug candidates in various cases like enhancing metabolic stability and avoiding formation of reactive metabolites which can cause toxicity. In this poster presentation we are going to demonstrate overall biotransformation process and some unique case studies which will illustrate the role of biotransformation in drug discovery. First case study: EXT-XXXX was lead molecule. To understand the metabolic profile of EXT-XXXX biotransformation study of EXT-XXXX was conducted in human liver microsomes.

Methods: EXT-XXXX was incubated in human liver microsomes supplemented with NADPH and GSH for 60 minutes. Then at both 0 and 60 minutes time points some aliquot was withdrawn from the reaction mixture and precipitated by equal volume of Acetonitrile to stop the reaction. The negative control was without NADPH and GSH. Then it was vortexed, centrifuged at 14000 rpm and then samples were analyzed by HRMS Q-exactive. Metabolites were detected by both PDA and by HRMS analysis. Structure elucidation, metabolite profiling was done by using Xcalibar and chemdraw software.

Results: EXT-XXXX was metabolized only thorough reactive metabolic pathway which raised red alert for progression of this lead molecule as this reactive metabolic pathway/GSH adduct pathway can lead to off target toxicity which can invite toxicity related issues later on for the development of this molecule (Figure 1). Hence it was important to mitigate the propensity of formation of GSH adduct and switch the reactive metabolic pathway to non-toxic metabolic pathway. The putative mechanism of formation of GSH adduct was given in Figure 2. The driving force for formation of GSH adduct could be through epoxide formation due to CYP mediated Bio-activation which was a reactive metabolite. The reactive metabolite was trapped by nucleophile GSH. Additionally –Br/Cl could have served as better leaving group during aromatization process resulting formation of GSH adduct. SAR studies were done by conducting metabolite profiling of different molecules with substitutions of different functional group in the benzene ring which was shown in Figure 3.

Conclusion: SAR studies demonstrated that substitution of Methyl at the adjacent position of –Br/Cl/F has mitigated propensity of formation of reactive metabolic pathway and metabolism was shifted towards non-reactive oxidative pathway. Hence instead of EXT-XXXX the other molecule where –Br was substituted by –Me was pursued further for development.