Structure‐Activity Relationships of Flupirtine Analogues for Liver Esterase‐Mediated Cleavage of the 4‐Fluorobenzylamine Moiety and Its Possible Relevance to Liver Toxicity

Abstract

Flupirtine and retigabine were essential drugs to combat pain and epilepsy. However, the K v 7 potassium channel openers are fraught with hepatotoxicity and tissue discoloration, respectively, limiting their therapeutic value. Both adverse events are likely due to reactive metabolites arising from oxidative metabolism. Designing safer analogues lacking the structural elements leading to described side effects is an active area of current research. One of the main metabolites of flupirtine is the biologically inactive 4-fluorohippuric acid. Hitherto unexplained, the proposed metabolic pathway leading to the formation of 4-fluorohippuric acid from flupirtine is verified here. Through the use of eighteen flupirtine analogues, mechanistic details of this pathway could be elucidated. A possible connection with the in vitro hepatotoxicity of the flupirtine analogues and the levels of 4-fluorobenzoic acid formed in enzyme incubations was examined by correlation analysis. These findings provide important information for the design of new flupirtine analogues as potential drug candidates.

Investigation of TGF‐α‐overexpressing mouse hepatocytes (TAMH) cultured as spheroids for use in hepatotoxicity screening of drug candidates

“…The quinone diimine metabolites tend to polymerize, which was seen in vitro (Methling et al, 2009) and could form protein adducts similar to NAPQI. CYPs do not appear to play an important role in metabolization of flupirtine, but metabolism by carboxylesterases, N-acetylation (metabolite D13223), and glucuronidation does (Beirow et al, 2023;Methling et al, 2009). Several of the abovementioned enzymes showed elevated expression levels in TAMH spheroids compared to monolayer.…”