Characterization of ritonavir-mediated inactivation of cytochrome P450 3A4.

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Rock BM, Hengel SM, Rock DA, Wienkers LC, Kunze KL

Characterization of ritonavir-mediated inactivation of cytochrome P450 3A4.

Mol Pharmacol. 2014 Dec;86(6):665-74. doi: 10.1124/mol.114.094862. Epub 2014 Oct 1.

PubMed ID

25274602 [ View in PubMed

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Abstract

Ritonavir is a human immunodeficiency virus (HIV) protease inhibitor and an inhibitor of cytochrome P450 3A4, the major human hepatic drug-metabolizing enzyme. Given the potent inhibition of CYP3A4 by ritonavir, subtherapeutic doses of ritonavir are used to increase plasma concentrations of other HIV drugs oxidized by CYP3A4, thereby extending their clinical efficacy. However, the mechanism of inhibition of CYP3A4 by ritonavir remains unclear. To date, data suggests multiple types of inhibition by ritonavir, including mechanism-based inactivation by metabolic-intermediate complex formation, competitive inhibition, irreversible type II coordination to the heme iron, and more recently heme destruction. The results presented here demonstrate that inhibition of CYP3A4 by ritonavir occurs by CYP3A4-mediated activation and subsequent formation of a covalent bond to the apoprotein. Incubations of [(3)H]ritonavir with reconstituted CYP3A4 and human liver microsomes resulted in a covalent binding stoichiometry equal to 0.93 +/- 0.04 moles of ritonavir bound per mole of inactivated CYP3A4. The metabolism of [(3)H]ritonavir by CYP3A4 leads to the formation of a covalent adduct specifically to CYP3A4, confirmed by radiometric liquid chromatography-trace and whole-protein mass spectrometry. Tryptic digestion of the CYP3A4-[(3)H]ritonavir incubations exhibited an adducted peptide (255-RM K: ESRLEDTQKHR-268) associated with a radiochromatic peak and a mass consistent with ritonavir plus 16 Da, in agreement with the whole-protein mass spectrometry. Additionally, nucleophilic trapping agents and scavengers of free oxygen species did not prevent inactivation of CYP3A4 by ritonavir. In conclusion, ritonavir exhibited potent time-dependent inactivation of CYP3A, with the mechanism of inactivation occurring though a covalent bond to Lys257 of the CYP3A4 apoprotein.

DrugBank Data that Cites this Article

Drugs

Ritonavir

Drug Interactions

Drugs	Interaction
Integrate drug-drug interactions in your software
Amiodarone Tipranavir	The metabolism of Amiodarone can be decreased when combined with Tipranavir.
Bepridil Tipranavir	The risk or severity of QTc prolongation, torsade de pointes, and Cardiac Arrhythmia can be increased when Tipranavir is combined with Bepridil.
Bosentan Saquinavir	The serum concentration of Bosentan can be increased when it is combined with Saquinavir.
Fosphenytoin Fosamprenavir	The serum concentration of Fosphenytoin can be decreased when it is combined with Fosamprenavir.
Phenytoin Fosamprenavir	The serum concentration of Phenytoin can be decreased when it is combined with Fosamprenavir.