Identification of the Significant Involvement and Mechanistic Role of CYP3A4/5 in Clopidogrel Bioactivation

Pharmacokinetic/Pharmacodynamic Assessment of the Structural Refinement of Clopidogrel Focusing on the Balance between Bioactivation and Deactivation

The delicate balance between ischemic and bleeding risks is a critical factor in antiplatelet therapy administration. Clopidogrel and prasugrel, belonging to the thienopyridine class of antiplatelet drugs, are known for their variability in individual responsiveness and high incidence of bleeding events, respectively. The present study is centered on the development and assessment of a range of deuterated thienopyridine derivatives, leveraging insights from structure-pharmacokinetic relationships of clopidogrel and prasugrel. Our approaches were grounded in the molecular framework of clopidogrel and incorporated the C2-pharmacophore design from prasugrel. The selection of ester or carbamate substituents at the C2-position facilitated the generation of the 2-oxointermediate through hydrolysis, akin to prasugrel, thereby bypassing the issue of CYP2C19 dependency. The bulky C2-pharmacophore in our approach distinguishes itself from prasugrel's acetyloxy substituent by exhibiting a moderated hydrolysis rate, resulting in a more gradual formation of the active metabolite. Excessive and rapid release of the active metabolite, believed to be linked with an elevated risk of bleeding, is thus mitigated. Our proposed structural modification retains the hydrolysis-sensitive methyl ester of clopidogrel but substitutes it with a deuterated methyl group, shown to effectively reduce metabolic deactivation. Three promising compounds demonstrated a pharmacokinetic profile similar to that of clopidogrel at four times the dose, while also augmenting its antiplatelet activity. SIGNIFICANCE STATEMENT: Inspired by the structure-pharmacokinetic relationship of clopidogrel and prasugrel, a range of clopidogrel derivatives were designed, synthesized, and assessed. Among them, three promising compounds have been identified, striking a delicate balance between efficacy and safety for antiplatelet therapy. Additionally, the ozagrel prodrug conjugate was discovered to exert a synergistic therapeutic effect alongside clopidogrel.

Pleiotropic effects of clopidogrel

Clopidogrel is a widely prescribed prodrug with anti-thrombotic activity through irreversible inhibition of the P2Y₁₂ receptor on platelets. It is FDA-approved for the clinical management of thrombotic diseases like unstable angina, myocardial infarction, stroke, and during percutaneous coronary interventions. Hepatic clopidogrel metabolism generates several distinct metabolites. Only one of these metabolites is responsible for inhibiting the platelet P2Y₁₂ receptor. Importantly, various non-hemostatic effects of clopidogrel therapy have been described. These non-hemostatic effects are perhaps unsurprising, as P2Y₁₂ receptor expression has been reported in multiple tissues, including osteoblasts, leukocytes, as well as vascular endothelium and smooth muscle. While the "inactive" metabolites have been commonly thought to be biologically inert, recent findings have uncovered P2Y₁₂ receptor-independent effects of clopidogrel treatment that may be mediated by understudied metabolites. In this review, we summarize both the P2Y₁₂ receptor-mediated and non-P2Y₁₂ receptor-mediated effects of clopidogrel and its metabolites in various tissues.

Ball milling - a new concept for predicting degradation profiles in active pharmaceutical ingredients

A method for forced oxidative mechanochemical degradation of active pharmaceutical ingredients (APIs) using clopidogrel hydrogensulfate as a model compound is presented. Considerable and selective formation of degradants occurs already after very short reaction times of less than 15 minutes and the nature of the products is strongly dependent on the used oxidant.

Cytochrome P450 enzyme-mediated auto-enhanced photodynamic cancer therapy of co-nanoassembly between clopidogrel and photosensitizer

Reactive oxygen species (ROS)-based photodynamic therapy (PDT) has a widespread application in cancer therapy. Nevertheless, the efficiency of PDT is far from satisfactory. One major impediment is the overexpression of glutathione (GSH) in tumor cells, which could deplete the level of PDT-generated ROS. Herein, we develop a novel type of cytochrome P450 enzyme-mediated auto-enhanced photodynamic co-nanoassembly between clopidogrel (CPG) and photosensitizer pyropheophorbide a (PPa).

Methods: In this work, we prepare the co-assembled nanoparticles of CPG and PPa (CPG/PPa NPs) by using one-step precipitation method. The assembly mechanism, drug release behavior, GSH consumption, ROS generation, cellular uptake, cytotoxicity of CPG/PPa NPs are investigated in vitro. The mice bearing 4T1 tumor are employed to evaluate in vivo biodistribution and anti-tumor effect of CPG/PPa NPs.

Results: Such CPG/PPa NPs could disrupt the intracellular redox homeostasis, resulting from the elimination of GSH by CPG active metabolite mediated by cytochrome P450 enzyme (CYP2C19). The in vivo assays reveal that CPG/PPa NPs not only increase the drug accumulation in tumor sites but also significantly suppress tumor growth in BALB/c mice bearing 4T1 tumor. With CPG-mediated GSH consumption and PPa-triggered ROS generation, CPG/PPa NPs show the enhanced PDT treatment effect by breaking intracellular redox balance.

Conclusion: Our findings provide a valuable knowledge for the rational design of the PDT-based combinational cancer therapy.

DT-678 inhibits platelet activation with lower tendency for bleeding compared to existing P2Y12 antagonists

The novel clopidogrel conjugate, DT-678, is an effective inhibitor of platelets and thrombosis in preclinical studies. However, a comparison of the bleeding risk with DT-678 and currently approved P2Y12 antagonists has yet to be determined. The objective of this study was to evaluate the bleeding tendency of animals treated with clopidogrel, ticagrelor, and DT-678. Ninety-one New Zealand white rabbits were randomized to one of 13 treatment groups (n = 7). Platelet activation was assessed by flow cytometry and light transmission aggregometry before and after the administration of various doses of DT-678, clopidogrel, and ticagrelor. Tongue template bleeding times were also measured before and after drug treatment. Treatment with P2Y12 receptor antagonists caused a dose-dependent reduction in markers of platelet activation (P-selectin and integrin αIIbβ3) and aggregation in response to adenosine diphosphate stimulation. At the same doses required for platelet inhibition, clopidogrel and ticagrelor significantly prolonged bleeding times, while DT-678 did not. DT-678 and the FDA-approved P2Y12 antagonists clopidogrel and ticagrelor are effective inhibitors of platelet activation and aggregation. However, unlike clopidogrel and ticagrelor, DT-678 did not prolong bleeding times at equally effective antiplatelet doses. The results suggest a more favorable benefit/risk ratio for DT-678 and potential utility as part of a dual antiplatelet therapy regimen.

CYP-independent inhibition of platelet aggregation in rabbits by a mixed disulfide conjugate of clopidogrel

Dual antiplatelet therapy with clopidogrel and aspirin has been the standard of care in the United States for patients with acute coronary syndromes (ACS) and/or undergoing percutaneous coronary interventions (PCI). However, the effectiveness of clopidogrel varies significantly among different sub-populations due to inter-individual variability. In this study we examined the antiplatelet potential of a novel mixed disulfide conjugate of clopidogrel with the aim to overcome the inter-individual variability. In the metabolic studies using human liver microsomes and cDNA-expressed P450s, we confirmed that multiple P450s are involved in the bioactivation of 2-oxoclopidogrel to H4, one of the diastereomers of the pharmacologically active metabolite (AM) possessing antiplatelet activity. Results from kinetic studies demonstrated that 2C19 is the most active in converting 2-oxoclopidogrel to H4 with a catalytic efficiency of 0.027 µM-1min-1 in the reconstituted system. On the basis of this finding, we were able to biosynthesise the conjugate of clopidogrel with 3-nitropyridine-2-thiol, referred to as clopNPT, and examined its antiplatelet activity in male New Zealand white rabbits. After administration as intravenous bolus at 2 mg/kg, the clopNPT conjugate was rapidly converted to the AM leading to the inhibition of platelet aggregation (IPA). Analyses of the blood samples drawn at various time points showed that intravenous administration of clopNPT led to ~70% IPA within 1 hour and the IPA persisted for more than 3 hours. Since the antiplatelet activity of clopNPT does not require bioactivation by P450s, the mixed disulfide conjugate of clopidogrel has the potential to overcome the inter-individual variability in clopidogrel therapy.

Significant Improvement of Antithrombotic Responses to Clopidogrel by Use of a Novel Conjugate as Revealed in an Arterial Model of Thrombosis

Clopidogrel is a prodrug that requires bioactivation by cytochrome P450 (P450) enzymes to a pharmacologically active metabolite for antiplatelet action. The clinical limitations of clopidogrel are in large part due to its poor pharmacokinetics resulting from inefficient bioactivation by P450s. In this study, we determined the pharmacokinetics and pharmacodynamics of a novel conjugate of clopidogrel, referred to as ClopNPT, in animal models and we evaluated its potential to overcome the limitations of clopidogrel. Results from pharmacokinetic (PK) studies showed that ClopNPT released the active metabolite with a time to maximal plasma concentration of <5 minutes in C57BL/6 mice after either oral or intravenous administration, and plasma concentrations of the active metabolite reached Cmax values of 1242 and 1100 ng/ml after a 10-mg/kg oral dose and a 5-mg/kg intravenous dose, respectively. Furthermore, ClopNPT was highly effective in preventing arterial thrombosis in rabbits and mice after vascular injuries. Formation of occlusive thrombi was prevented by ClopNPT at the 1-mg/kg dose with no significant increase in tongue bleeding time, whereas clopidogrel was ineffective at the same dose. These results suggest that ClopNPT has favorable PK/pharmacodynamic properties that can potentially overcome the attenuated PK properties of clopidogrel and thus significantly improve the efficacy of antiplatelet therapy.

Dosing Recommendations for Concomitant Medications During 3D Anti-HCV Therapy

The development of direct-acting antiviral (DAA) agents has reinvigorated the treatment of hepatitis C virus infection. The availability of multiple DAA agents and drug combinations has enabled the transition to interferon-free therapy that is applicable to a broad range of patients. However, these DAA combinations are not without drug-drug interactions (DDIs). As every possible DDI permutation cannot be evaluated in a clinical study, guidance is needed for healthcare providers to avoid or minimize drug interaction risk. In this review, we evaluated the DDI potential of the novel three-DAA combination of ombitasvir, paritaprevir, ritonavir, and dasabuvir (the 3D regimen) with more than 200 drugs representing 19 therapeutic drug classes. Outcomes of these DDI studies were compared with the metabolism and elimination routes of prospective concomitant medications to develop mechanism-based and drug-specific guidance on interaction potential. This analysis revealed that the 3D regimen is compatible with many of the drugs that are commonly prescribed to patients with hepatitis C virus infection. Where interaction is possible, risk can be mitigated by paying careful attention to concomitant medications, adjusting drug dosage as needed, and monitoring patient response and/or clinical parameters.

The mechanism and risk factors of clopidogrel-induced liver injury

CONTEXT AND OBJECTIVE

Clopidogrel (CLP) is a prodrug which is widely used as a platelet aggregation inhibitor. Hepatotoxicity is rare but a potentially serious adverse reaction that is associated with CLP. Thiophene in CLP (the thienopyridine derivative) is a group that is easily oxidated by cytochrome P450 enzymes (CYP450s) to generate reactive metabolites (RMs), it may be implicated in the mechanism of CLP-induced hepatotoxicity. CYP2C19 and CYP2B6 are important CYP450s involved in the metabolism and activation of CLP, and the aim of this study is to investigate whether the metabolites of CYP2C19 and CYP2B6 are associated with the CLP-induced liver injury.

METHOD

Primary rat hepatocytes are applied to evaluate the hepatotoxicity of CLP. Glutathione-depleted mouse model is used to evaluate whether this toxicity of CLP is metabolized by CYP450s. We also used HepG2 cells co-incubated with recombinant CYP2B6 and CYP2C19 enzymes to further assess whether the metabolites of CYP2C19 and CYP2B6 are associated with the CLP-induced hepatocellular toxicity.

RESULT

CLP in high dose (100 μM and 300 μM) showed cytotoxicity in primary rat hepatocytes assay. Administration of CLP with l-buthionine-S, R-sulfoxinine (BSO) for seven days enhanced the liver injury of CLP. The level of ALT, AST and TBIL in plasma increased significantly, and the histopathological results showed the obvious liver injury; Pretreatment of 1-aminobenzotriazole, a nonspecific inhibitor of CYP450s, suppressed CLP-induced hepatotoxicity; CLP showed a dose-dependent toxicity in HepG2/CYP2C19 enzyme and HepG2/CYP2B6 enzyme models.

CONCLUSION

High activities of CYP2C19 and CYP2B6 are the risk factors for hepatocellular toxicity of CLP.

Harnessing C-H Borylation/Deborylation for Selective Deuteration, Synthesis of Boronate Esters, and Late Stage Functionalization

Ir-catalyzed deborylation can be used to selectively deuterate aromatic and heteroaromatic substrates. Combined with the selectivities of Ir-catalyzed C-H borylations, uniquely labeled compounds can be prepared. In addition, diborylation/deborylation reactions provide monoborylated regioisomers that complement those prepared by C-H borylation. Comparisons between Ir-catalyzed deborylations and Pd-catalyzed deborylations of diborylated indoles described by Movassaghi are made. The Ir-catalyzed process is more effective for deborylating aromatics and is generally more effective in the monodeborylation of diborylated thiophenes. These processes can be applied to complex molecules such as clopidogrel.

Comparative risk of ischemic stroke among users of clopidogrel together with individual proton pump inhibitors

BACKGROUND AND PURPOSE

There is controversy and little information about whether individual proton pump inhibitors (PPIs) differentially alter the effectiveness of clopidogrel in reducing ischemic stroke risk. We, therefore, aimed to elucidate the risk of ischemic stroke among concomitant users of clopidogrel and individual PPIs.

METHODS

We conducted a propensity score-adjusted cohort study of adult new users of clopidogrel, using 1999 to 2009 Medicaid claims from 5 large states. Exposures were defined by prescriptions for esomeprazole, lansoprazole, omeprazole, rabeprazole, and pantoprazole-with pantoprazole serving as the referent. The end point was hospitalization for acute ischemic stroke, defined by International Classification of Diseases Ninth Revision Clinical Modification codes in the principal position on inpatient claims, within 180 days of concomitant therapy initiation.

RESULTS

Among 325 559 concomitant users of clopidogrel and a PPI, we identified 1667 ischemic strokes for an annual incidence of 2.4% (95% confidence interval, 2.3-2.5). Adjusted hazard ratios for ischemic stroke versus pantoprazole were 0.98 (0.82-1.17) for esomeprazole; 1.06 (0.92-1.21) for lansoprazole; 0.98 (0.85-1.15) for omeprazole; and 0.85 (0.63-1.13) for rabeprazole.

CONCLUSIONS

PPIs of interest did not increase the rate of ischemic stroke among clopidogrel users when compared with pantoprazole, a PPI thought to be devoid of the potential to interact with clopidogrel.

Oxidovanadium(v) complexes of aroylhydrazones incorporating heterocycles: synthesis, characterization and study of DNA binding, photo-induced DNA cleavage and cytotoxic activities

The interaction of four neutral oxidovanadium(v) complexes with DNA and their cytotoxic activities have been reported.

In vitro interaction of clopidogrel and its hydrolysate with OCT1, OCT2 and OAT1

Clopidogrel (CP) is metabolized by CYPs to the active metabolite, or hydrolyzed by esterase to clopidogrel carboxylate (CPC) in liver, and CPC is partly excreted from urine. Therefore, the objective of the present study was to evaluate the interactions of CP and CPC with organic cation transporter 1 (OCT1) (in liver), and CPC with organic cation transporter 2 (OCT2) and organic anion transporter 1 (OAT1) (in kidney). Both CP and CPC inhibited the uptake of 1-methyl-4-phenylpyridinium (MPP(+)) and metformin, typical substrates of OCT1, in MDCK-hOCT1 cells with low IC₅₀ (0.307-14.0 μM). CPC (100 μM) reduced the uptake of MPP(+) and metformin mediated by OCT2 in MDCK-hOCT2 cells to 60.8% and 33.6% of the control, CPC (500 μM) decreased the uptake of 6-carboxyfluorescein (6-CFL) and para-aminohippuric acid (PAH), substrates of OAT1, in MDCK-hOAT1 cells to 64.6% and 79.4% of the control. CP and CPC were also found to inhibit other drugs of OCT1 substrates, such as lamivudine and amantadine, in MDCK-hOCT1 cells with the IC₅₀ of 1.97-4.15μM, except CPC on amantadine (IC₅₀>100 μM). The inhibition of CP and CPC on lamivudine uptake in primary rat hepatocytes was also confirmed with the IC₅₀ of 2.91 and 1.25μM, respectively. Additionally, CP and CPC were not substrates of OCT1 and OCT2, whereas CPC was a substrate of OAT1 with the Km of 5.61 μM. In conclusion, CP and CPC are strong inhibitors of OCT1, but weak inhibitors of OCT2 and OAT1, and CPC is a high affinity substrate of OAT1.

Hepatocellular toxicity of clopidogrel: mechanisms and risk factors

Clopidogrel is a prodrug used widely as a platelet aggregation inhibitor. After intestinal absorption, approximately 90% is converted to inactive clopidogrel carboxylate and 10% via a two-step procedure to the active metabolite containing a mercapto group. Hepatotoxicity is a rare but potentially serious adverse reaction associated with clopidogrel. The aim of this study was to find out the mechanisms and susceptibility factors for clopidogrel-associated hepatotoxicity. In primary human hepatocytes, clopidogrel (10 and 100 μM) was cytotoxic only after cytochrome P450 (CYP) induction by rifampicin. Clopidogrel (10 and 100 μM) was also toxic for HepG2 cells expressing human CYP3A4 (HepG2/CYP3A4) and HepG2 cells co-incubated with CYP3A4 supersomes (HepG2/CYP3A4 supersome), but not for wild-type HepG2 cells (HepG2/wt). Clopidogrel (100 μM) decreased the cellular glutathione content in HepG2/CYP3A4 supersome and triggered an oxidative stress reaction (10 and 100 µM) in HepG2/CYP3A4, but not in HepG2/wt. Glutathione depletion significantly increased the cytotoxicity of clopidogrel (10 and 100 µM) in HepG2/CYP3A4 supersome. Co-incubation with 1 μM ketoconazole or 10mM glutathione almost completely prevented the cytotoxic effect of clopidogrel in HepG2/CYP3A4 and HepG2/CYP3A4 supersome. HepG2/CYP3A4 incubated with 100 μM clopidogrel showed mitochondrial damage and cytochrome c release, eventually promoting apoptosis and/or necrosis. In contrast to clopidogrel, clopidogrel carboxylate was not toxic for HepG2/wt or HepG2/CYP3A4 up to 100 µM. In conclusion, clopidogrel incubated with CYP3A4 is associated with the formation of metabolites that are toxic for hepatocytes and can be trapped by glutathione. High CYP3A4 activity and low cellular glutathione stores may be risk factors for clopidogrel-associated hepatocellular toxicity.

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 targeted metabolism shift 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.