4 research outputs found
In Vitro Biotransformation Studies of 2‑Oxo-clopidogrel: Multiple Thiolactone Ring-Opening Pathways Further Attenuate Prodrug Activation
The biotransformation of clopidogrel has been under extensive
investigation
to address the observed high clinical variability and resistance of
its antithrombotic prodrug therapy. Clopidogrel (M0) is first activated
to its thiolactone intermediate, 2-oxo-clopidogrel (M2), by hepatic
cytochrome P450 (P450) enzymes. Subsequent P450-catalyzed <i>S</i>-oxidation is followed by thioester hydrolysis, which cleaves
the thiolactone ring and yields a sulfenic acid intermediate (M12);
this intermediate is reduced to the final active metabolite (M13).
The aim of the present study is to characterize the metabolic fates
of M2 more comprehensively with focus on the thiolactone ring-opening
pathways. It was found that the bioactivating <i>S</i>-oxidation
confers on the thiolactone moiety not only one electrophilic site
at the carbonyl <i>C</i>-atom (Site A), but also a second
one at the allylic bridge <i>C</i>-atom (Site B). Both sites
can react with H<sub>2</sub>O or other nucleophiles, like glutathione
(GSH), leading to different thiolactone ring-opening pathways. In
addition to the pharmacologically desired A-H<sub>2</sub>O pathway
leading to M13 formation, the A-GSH pathway leads to the formation
of a glutathione conjugate (GS-3), the B-H<sub>2</sub>O pathway leads
to the formation of a desulfurized hydroxyl metabolite (M17), and
the B-GSH pathway leads to the formation of a desulfurized glutathione
conjugate (GS-2). These results demonstrate the reactive nature of
the electrophilic thiolactone <i>S</i>-oxide intermediate
(M11) and suggest that M13 formation from M2 might be accompanied
by more attenuating pathways than previously reported. The research
presented here may facilitate future studies exploring the clinical
antithrombotic response to clopidogrel as well as the susceptibility
to the adverse effect of clopidogrel and its close prodrug analogues
Identification of the Significant Involvement and Mechanistic Role of CYP3A4/5 in Clopidogrel Bioactivation
The clinical response to the antiplatelet prodrug clopidogrel
is
associated with high intersubject variability and a certain level
of therapeutic resistance. Previous studies have suggested that genetic
polymorphism of CYP2C19 might be one determinant of clopidogrel efficacy
and led to the CYP2C19 genotype-tailored antithrombotic therapy. However,
evidence against the role of CYP2C19 from multiple studies implied
the involvement of other factors. Here, we report that prodrug activation
of the thiophene motif in clopidogrel is attenuated by heavy metabolic
attrition of the piperidine motif. CYP3A4/5 was identified to be the
enzyme metabolizing the piperidine motif. Inhibiting CYP3A4/5-mediated
attrition was shown to potentiate active metabolite formation, which
was found to be catalyzed by multiple CYP enzymes. Identifying the
significant involvement of CYP3A4/5 and characterizing its mechanistic
role in clopidogrel bioactivation might assist future pharmacogenomic
studies in exploring the full mechanism underlying clopidogrel efficacy
Deuterated Clopidogrel Analogues as a New Generation of Antiplatelet Agents
Clopidogrel (CPG) is an antithrombotic prodrug that needs
hepatic
cytochrome P450 (CYP) enzymes for its bioactivation. The clinical
effects of CPG have been associated with high intersubject variability
and a certain level of resistance. Recently, comprehensive biotransformation
studies of CPG support that the observed clinical uncertainty stems
from the low bioactivation efficiency, which is attributed to extensive
attritional metabolism (e.g., hydrolysis of the methyl ester functionality
and oxidation of the piperidine moiety). With the goal of potentiating
the desired thiophene 2-oxidation through minimal structural modification,
we have adopted the strategy of <i>targeted metabolism shift</i> and have designed and synthesized deuterated piperidine analogues
of CPG. In vitro studies showed that the prodrug activation percentages
have been significantly increased for the deuterated analogues as
a result of stability enhancement of the piperidine moiety. In a pharmacological
study with a rat model, oral administration of the deuterated analogues
also demonstrated higher inhibitory activity than that of CPG against
adenosine diphosphate (ADP) induced platelet aggregation. These deuterated
analogues represent a new generation of antiplatelet agents with the
potential to overcome the major clinical drawbacks of CPG
Overcoming Clopidogrel Resistance: Discovery of Vicagrel as a Highly Potent and Orally Bioavailable Antiplatelet Agent
A series of optically active 2-hydroxytetrahydrothienopyridine
derivatives were designed and synthesized as prodrugs of clopidogrel
thiolactone in order to overcome clopidogrel resistance. The final
compounds were evaluated for their inhibitory effect on ADP-induced
platelet aggregation in rats. Compound <b>9a</b> was selected
for further in vitro and in vivo metabolism studies, since its potency
was comparable to that of prasugrel and was much higher than that
of clopidogrel. Preliminary pharmacokinetic study results showed that
the bioavailability of clopidogrel thiolactone generated from <b>9a</b> was 6-fold higher than that generated from clopidogrel,
implying a much lower clinically effective dose for <b>9a</b> in comparison with clopidogrel. In summary, <b>9a</b> (vicagrel)
holds great promise as a more potent and a safer antiplatelet agent
that might have the following advantages over clopidogrel: (1) no
drug resistance for CYP2C19 poor metabolizers; (2) lower dose-related
toxicity due to a much lower effective dose; (3) faster onset of action