Exploration of Catalytic Properties of CYP2D6 and CYP3A4 Through Metabolic Studies of Levorphanol and Levallorphan

Abstract

ABSTRACT:CYP2D6 and CYP3A4, two members of the cytochrome P450 superfamily of monooxygenases, mediate the biotransformation of a variety of xenobiotics. The two enzymes differ in substrate specificity and size and characteristics of the active site cavity. The aim of this study was to determine whether the catalytic properties of these isoforms, reflected by the differences observed from crystal structures and homology models, could be confirmed with experimental data. Detailed metabolite identification, reversible inhibition, and time-dependent inhibition were examined for levorphanol and levallorphan with CYP2D6 and CYP3A4. The studies were designed to provide a comparison of the orientations of substrates, the catalytic sites of the two enzymes, and the subsequent outcomes on metabolism and inhibition. The metabolite identification revealed that CYP3A4 catalyzed the formation of a variety of metabolites as a result of presenting different parts of the substrates to the heme. CYP2D6 was a poorer catalyst that led to a more limited number of metabolites that were interpreted in terms to two orientations of the substrates. The inhibition studies showed evidence for strong reversible inhibition of CYP2D6 but not for CYP3A4. Levallorphan acted as a time-dependent inhibitor on CYP3A4, indicating a productive binding mode with this enzyme not observed with CYP2D6 that presumably resulted from close interactions of the N-allyl moiety oriented toward the heme. All the results are in agreement with the large and flexible active site of CYP3A4 and the more restricted active site of CYP2D6.

Spirocycle MmpL3 Inhibitors with Improved hERG and Cytotoxicity Profiles as Inhibitors of Mycobacterium tuberculosis Growth

“…Pyrazole 4 was more rapidly cleared by CYP2D6 bactosomes (0.34 min –1 ) than CYP3A4 bactosomes (0.07 min –1 ). As the CYP2D6-active site is known to be smaller in comparison to CYP3A4, it was proposed that increasing the size of substituents on either the 5-methyl pyrazole or the phenyl in 4 could potentially lead to a decrease in CYP2D6 metabolism and thereby improve the metabolic stability to be more in line with the larger compound 3 .…”

Regioselective oxidation of phospho‐NSAIDs by human cytochrome P450 and flavin monooxygenase isoforms: implications for their pharmacokinetic properties and safety

“…Substrate binding to CYP3A4 induces large increase in the volume of its active site (Ekroos and Sjogren, 2006), which could account for its preference for bulky substrates such as phospho‐ibuprofen. In addition, the structure of CYP3A4–ligand complex is remarkably flexible (Ekroos and Sjogren, 2006; Bonn et al ., 2010), which may lead to its broad regioselectivity in phospho‐ibuprofen oxidation.…”

In vitro metabolic fate of alizapride: evidence for the formation of reactive metabolites based on liquid chromatography‐tandem mass spectrometry

“…It has been reported in the literature that acrolein, which shares carbonylating and alkylating properties, was generated through the CYP‐mediated oxidation of cyclophosphamide, being also responsible for the serious bladder toxicity associated with this drug treatment. Differently, it has not so far been reported the formation of acrolein during the metabolic biotransformation of drugs containing the N ‐allyl moiety such as naloxone and levallorphan …”

“…Differently, it has not so far been reported the formation of acrolein during the metabolic biotransformation of drugs containing the N-allyl moiety such as naloxone and levallorphan. [9,10] Alizapride (AL) (AE)-6-methoxy-N-{[1-(prop-2-en-1-yl)-pyrrolidin-2-yl]methyl}-1H-benzotriazole-5-carboxamide (Table 1) is a dopamine antagonist with prokinetic and antiemetic effects administered as a racemic mixture in the treatment of cancer chemotherapy-induced nausea and vomiting, including postoperative nausea and vomiting. [11] Although pharmacodynamic studies of AL in mice and rats demonstrated little toxicity (particularly after parenteral administration), [12] only few data are available about AL toxicity in man.…”