Involvement of microsomal NADPH-cytochrome P450 reductase in metabolic reduction of drug ketones

Synthesis, activity and metabolic stability of propan-2-one substituted tetrazolylalkanoic acids as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase

The serine hydrolases cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are interesting targets for the development of new anti-inflammatory and analgesic drugs. Structural modifications of a potent dual inhibitor with a propan-2-one substituted tetrazolylpropionic acid moiety led to compounds with also nanomolar activity against both enzymes but better physicochemical properties. The structure-activity relationships showed that the variations had partially divergent effects on the inhibitory activity of the compounds towards cPLA2α and FAAH reflecting differences in the binding mode to the enzymes. Furthermore, the metabolic stability of the target structures was investigated in vitro.

Synthesis, activity, metabolic stability and cell permeability of new cytosolic phospholipase A2α inhibitors with 1-indolyl-3-phenoxypropan-2-one structure

Cytosolic phospholipase A2α (cPLA2α), the key enzyme of the arachidonic acid cascade, is considered to be an interesting target for the development of new anti-inflammatory drugs. Potent inhibitors of the enzyme include indole-5-carboxylic acids with propan-2-one residues in position 1 of the indole. Previously, it was found that central pharmacophoric elements of these compounds are their ketone and carboxylic acid groups, which unfortunately are subject to pronounced metabolism by carbonyl reductases and glucuronosyltransferases, respectively. Here we show that the metabolic stability of these inhibitors can be improved by introducing alkyl substituents in the vicinity of the ketone group or by increasing their rigidity. Furthermore, permeability tests with Caco-2 cells revealed that the indole derivatives have only low permeability, which can be attributed to their affinity to efflux transporters. Among other things, the polar ketone group in the center of the molecules seems to be a decisive factor for their reverse transport. After its removal, the permeability increased significantly. The enhancement in metabolic stability and permeability achieved by the structural variations carried out was accompanied by a more or less pronounced decrease in the inhibitory potency of the compounds against cPLA2α.

Synthesis and pharmacokinetic properties of novel cPLA2α inhibitors with 1-(carboxyalkylpyrrolyl)-3-aryloxypropan-2-one structure

Indole-5-carboxylic acids with 3-aryloxy-2‑oxopropyl residues in position 1 have been shown to be potent inhibitors of cytosolic phospholipase A₂α (cPLA₂α), an enzyme involved in the formation of pro-inflammatory lipid mediators. Unfortunately, in animal experiments, only very low plasma concentrations could be achieved after peroral administration of this type of compound. Since insufficient metabolic stability was suspected as the cause, structural modifications were made to optimize this property. These included the conversion of the aromatic into an aliphatic carboxylic acid function as well as the rigidification of the lipophilic structural elements. A selected pyrrole-3-propionic acid was tested for its peroral in vivo bioavailability in mice. However, higher plasma concentrations could not be achieved also with this compound. Using the Caco2 cell permeation assay, substances investigated were found to be very good substrates for gastrointestinal efflux transporters, which explains their poor peroral absorption.

Metabolism of F18, a Derivative of Calanolide A, in Human Liver Microsomes and Cytosol

10-Chloromethyl-11-demethyl-12-oxo-calanolide (F18), an analog of calanolide A, is a novel potent nonnucleoside reverse transcriptase inhibitor against HIV-1. Here, we report the metabolic profile and the results of associated biochemical studies of F18 in vitro and in vivo. The metabolites of F18 were identified based on liquid chromatography-electrospray ionization mass spectrometry and/or nuclear magnetic resonance. Twenty-three metabolites of F18 were observed in liver microsomes in vitro. The metabolism of F18 involved 4-propyl chain oxidation, 10-chloromethyl oxidative dechlorination and 12-carbonyl reduction. Three metabolites (M1, M3-1, and M3-2) were also found in rat blood after oral administration of F18 and the reduction metabolites M3-1 and M3-2 were found to exhibit high potency for the inhibition of HIV-1 in vitro. The oxidative metabolism of F18 was mainly catalyzed by cytochrome P450 3A4 in human microsomes, whereas flavin-containing monooxygenases and 11β-hydroxysteroid dehydrogenase were found to be involved in its carbonyl reduction. In human cytosol, multiple carbonyl reductases, including aldo-keto reductase 1C, short-chain dehydrogenases/reductases and quinone oxidoreductase 1, were demonstrated to be responsible for F18 carbonyl reduction. In conclusion, the in vitro metabolism of F18 involves multiple drug metabolizing enzymes, and several metabolites exhibited anti-HIV-1 activities. Notably, the described results provide the first demonstration of the capability of FMOs for carbonyl reduction.

Structure-activity relationship studies on 1-(2-oxopropyl)indole-5-carboxylic acids acting as inhibitors of cytosolic phospholipase A2α: Effect of substituents at the indole 3-position on activity, solubility, and metabolic stability

Cytosolic phospholipase A₂α (cPLA₂α) is a key enzyme in the biosynthesis of pro-inflammatory lipid mediators and therefore represents an attractive target for the development of new anti-inflammatory drugs. Recently, we have found that 1-[3-(4-octylphenoxy)-2-oxopropyl]indole-5-carboxylic acid (4) is a potent inhibitor of the enzyme. In this work, we evaluate the effect of butanoyl- and hexanoyl-substituents in position 3 of the indole scaffold of this compound bearing terminal groups of varying polarity. As a result, inhibitory potency was not affected considerably in most cases, while metabolic phase I and phase II in vitro stability and aqueous solubility could be influenced and modulated by the structural modifications performed.