Characterization of Inhibition Kinetics of (S)-Warfarin Hydroxylation by Noscapine: Implications in Warfarin Therapy

Abstract

Noscapine is an antitussive and potential anticancer drug. Clinically significant interactions between warfarin and noscapine have been previously reported. In this study, to provide a basis for warfarin dosage adjustment, the inhibition kinetics of noscapine against warfarin metabolism was characterized. Our enzyme kinetics data obtained from human liver microsomes and recombinant CYP2C9 proteins indicate that noscapine is a competitive inhibitor of the (S)-warfarin 7-hydroxylation reaction by CYP2C9. Interestingly, noscapine also inhibited (S)-warfarin metabolism in a NADPHand time-dependent manner, and removal of unbound noscapine and its metabolites by ultrafiltration did not reverse inhibition of (S)-warfarin metabolism by noscapine, suggesting mechanism-based inhibition of CYP2C9 by noscapine. Spectral scanning of the reaction between CYP2C9 and noscapine revealed the formation of an absorption spectrum at 458 nm, indicating the formation of a metabolite-intermediate complex. Surprisingly, noscapine is a 2-to 3-fold more efficient inactivator of CYP2C9.2 and CYP2C9.3 variants than it is of the wild type, by unknown mechanisms. Based on the inhibitory kinetic data, (S)-warfarin exposure is predicted to increase up to 7-fold (depending on CYP2C9 genotypes) upon noscapine coadministration, mainly due to mechanism-based inactivation of CYP2C9 by noscapine. Together, these results indicate that mechanism-based inhibition of CYP2C9 by noscapine may dramatically alter pharmacokinetics of warfarin and provide a basis for warfarin dosage adjustment when noscapine is coadministered.

Inhibition of Cytochrome P450 Enzymes

“…A similar isotope effect encountered in the in vivo insecticide synergizing activity of these compounds firmly confirms the mechanistic association between the formation of CO and the MI complex, with consequent P450 inhibition [165] Three mechanistic pathways are plausible for oxidation of the MDP-dioxymethylene bridge to the iron-coordinated carbene: In the first, hydroxylation of the dioxymethylene bridge followed by elimination of a water molecule results in an acidic oxonium ion that upon deprotonation gives the carbene (Fig 53, path a)In the second, formation of the oxonium species could precede generation of the bridge-hydroxylated metabolite, if the ferryl species were to oxidize the radical formed in the hydroxylation reaction before the oxygen rebound occurs (Fig 53, path b (Fig 54), a selective serotonin reuptake inhibitor (SSRI) [166][167][168][169][170][171][172][173] In vitro studies with purified CYP2D6 indeed reveal the formation of MI complex es with the characteristic spectroscopic signature at 456 nm [172] The intermediacy of a carbene is further supported by the fact that paroxetine is metabolized by CYP2D6 via demethylenation of the MDP group to a catechol and formic acid [169,173] The K I and k inact values of 6.6 ± 2.7 μM and 0.25 ± 0.09 min − 1 , respectively, calculated for the paroxetine-mediated inhibition of human liver microsomal CYP2D6-dependent dextromethorphan O-demethylation [172], are fully consistent with clinical reports of its potent CYP2D6 inhibition [166][167][168][169][170][171][172][173] Another noteworthy example of an MDP-bearing drug is noscap- (Fig 54), a nonaddictive, phthalideisoquinoline alkaloid derived from the opium poppy latex, and widely recognized as a safe and promising cough suppressant as well as a potential cancer chemotherapeutic agent when administered at much higher doses [174][175][176][177] At antitussive doses, significant clinical DDIs of noscapine were repor...…”

Flavonoids and Naphthoflavonoids: Wider Roles in the Modulation of Cytochrome P450 Family 1 Enzymes

“…The biological functions of a-NF have been shown to be involvedi ni nhibiting aromatase, drug transporters and platelet aggregation, as wella si nducing apoptosis, thus contributing to the treatmento fc ancer anda rterial thromboembolism. [79][80][81][82] Additionally,arecent study revealed that a-NF has aclearstimulatory effect on the ovaries, and prevents both systemic and gonadal 3-methylcholanthrene-induced toxicity. [83] In particular, a-NF has attracted considerable interest in modulating cyto-chromeP 450s.…”

The Noscapine Chronicle: A Pharmaco‐Historic Biography of the Opiate Alkaloid Family and its Clinical Applications

“…The time‐dependent inhibition of CYP3A4 and CYP2C9 by noscapine could explain the clinical noscapine–warfarin interaction . Because of noscapine's inhibitory effects, (S)‐warfarin exposure is predicted to increase up to sevenfold when administered alongside noscapine . These pharmacokinetic interactions between warfarin and noscapine indicate that careful monitoring of the international normalized ratio for blood coagulation will be required when noscapine is combined with warfarin.…”