Acetylenes: cytochrome P450 oxidation and mechanism-based enzyme inactivation

Abstract

The oxidation of carbon-carbon triple bonds by cytochrome P450 produces ketene metabolites that are hydrolyzed to acetic acid derivatives or are trapped by nucleophiles. In the special case of 17αethynyl sterols, D-ring expansion and de-ethynylation have been observed as competing pathways. The oxidation of acetylenic groups is also associated with mechanism-based inactivation of cytochrome P450 enzymes. One mechanism for this inactivation is reaction of the ketene metabolite with cytochrome P450 residues essential for substrate binding or catalysis. However, in the case of monosubstituted acetylenes, inactivation can also occur by addition of the oxidized acetylenic function to a nitrogen of the heme prosthetic group. This addition reaction is not mediated by the ketene metabolite, but rather occurs during oxygen transfer to the triple bond. In some instances, a detectable intermediate is formed that is most consistent with a ketocarbene-iron heme complex. This complex can progress to the N-alkylated heme or revert back to the unmodified enzyme. The ketocarbene complex may intervene in the formation of all the N-alkyl heme adducts, but is normally too unstable to be detected.

Bioactivation and reactivity research advances – 2021 year in review

“…The authors utilized various in vitro tools to determine the irreversible inhibition mechanism of ICT with CYP3A. It has been reported that oxidation of acetylenic groups can lead to inactivation of CYPs ( Ortiz de Montellano 2019 ). From their mechanistic studies, the authors proposed that the acetylene moiety of ICT was metabolically activated, and the resulting ketene intermediate was responsible for heme destruction and the observed CYP3A enzyme inactivation.…”

Time-dependent enzyme inactivation: Numerical analyses of in vitro data and prediction of drug-drug interactions

“…The acetylenes are initially oxidized either to a ketene intermediate (for terminal acetylenes) (Sridar, et al, 2012;Zhao, et al, 2018) or an oxirene intermediate (for internal acetylenes). Both these intermediates can either alkylate heme or the apoprotein depending upon the overall structure of the inactivator (Ortiz De Montellano, 2019;Roberts, et al, 1998;Roberts, et al, 1993;Roberts, et al, 1994). More recently, sulfenylation of the heme thiolate has been observed for CYP4A11 and may be involved in the modification of catalytic activity (Albertolle, et al, 2017).…”

“…TDI drugs have different mechanisms of CYP inactivation depending on the functional group present on the drug (Fontana, et al, 2005;Hollenberg, 2002;Kamel & Harriman, 2013;Orr, et al, 2012;Ortiz De Montellano, 2019). Some of the notable functional groups that inactivate CYPs are methylenedioxy aromatic groups, acetylenes, alkyl and aryl olefins, thiophenes, amines, furans, and phenols (Kalgutkar, et al, 2007;Kalgutkar & Soglia, 2005;Zhou, et al, 2004).…”

The Functions of Cytochrome P450 ω-hydroxylases and the Associated Eicosanoids in Inflammation-Related Diseases

“…About 300,000 CYP sequences have been collected from public and private sources ( Nelson, 2018 ). The common reactions catalyzed by CYPs include hydroxylation, heteroatom oxygenation and release, epoxidation, and oxidation of double, triple, or aromatic π-bonds ( Guengerich, 2001 ; McIntosh et al, 2014 ; Ortiz de Montellano, 2019 ). Mammalian CYP enzymes are distributed in a variety of tissues and organs of organisms, and play a core role in cell metabolism to maintain cell homeostasis mainly by mediating the metabolism of a large number of xenobiotic and endobiotic molecules, including but not limited to drugs, industrial toxins, steroids, cholic acid, and fatty acids through regio-, chemo- and stereospecific oxidation, peroxidation and reduction ( Urlacher and Girhard, 2012 ; Manikandan and Nagini, 2018 ).…”