Bioactivation of clopidogrel and prasugrel: factors determining the stereochemistry of the thiol metabolite double bond

Biocatalytic Syntheses of Antiplatelet Metabolites of the Thienopyridines Clopidogrel and Prasugrel Using Fungal Peroxygenases

Antithrombotic thienopyridines, such as clopidogrel and prasugrel, are prodrugs that undergo a metabolic two-step bioactivation for their pharmacological efficacy. In the first step, a thiolactone is formed, which is then converted by cytochrome P450-dependent oxidation via sulfenic acids to the active thiol metabolites. These metabolites are the active compounds that inhibit the platelet P2Y₁₂ receptor and thereby prevent atherothrombotic events. Thus far, described biocatalytic and chemical synthesis approaches to obtain active thienopyridine metabolites are rather complex and suffer from low yields. In the present study, several unspecific peroxygenases (UPOs, EC 1.11.2.1) known to efficiently mimic P450 reactions in vitro—but requiring only hydroperoxide as oxidant—were tested for biocatalytic one-pot syntheses. In the course of the reaction optimization, various parameters such as pH and reductant, as well as organic solvent and amount were varied. The best results for the conversion of 1 mM thienopyridine were achieved using 2 U mL⁻¹ of a UPO from agaric fungus Marasmius rotula (MroUPO) in a phosphate-buffered system (pH 7) containing 5 mM ascorbate, 2 mM h⁻¹ H₂O₂ and 20% acetone. The preparation of the active metabolite of clopidogrel was successful via a two-step oxidation with an overall yield of 25%. In the case of prasugrel, a cascade of porcine liver esterase (PLE) and MroUPO was applied, resulting in a yield of 44%. The two metabolites were isolated with high purity, and their structures were confirmed by MS and MS² spectrometry as well as NMR spectroscopy. The findings broaden the scope of UPO applications again and demonstrate that they can be effectively used for the selective synthesis of metabolites and late-state diversification of organic molecules, circumventing complex multistage chemical syntheses and providing sufficient material for structural elucidation, reference material, or cellular assays.

Update of P2Y receptor pharmacology: IUPHAR Review 27

Eight G protein-coupled P2Y receptor subtypes respond to extracellular adenine and uracil mononucleotides and dinucleotides. P2Y receptors belong to the δ group of rhodopsin-like GPCRs and contain two structurally distinct subfamilies: P2Y₁ , P2Y₂ , P2Y₄ , P2Y₆ , and P2Y₁₁ (principally G_q protein-coupled P2Y₁ -like) and P2Y_12-14 (principally G_i protein-coupled P2Y₁₂ -like) receptors. Brain P2Y receptors occur in neurons, glial cells, and vasculature. Endothelial P2Y₁ , P2Y₂ , P2Y₄ , and P2Y₆ receptors induce vasodilation, while smooth muscle P2Y₂ , P2Y₄ , and P2Y₆ receptor activation leads to vasoconstriction. Pancreatic P2Y₁ and P2Y₆ receptors stimulate while P2Y₁₃ receptors inhibits insulin secretion. Antagonists of P2Y₁₂ receptors, and potentially P2Y₁ receptors, are anti-thrombotic agents, and a P2Y₂ /P2Y₄ receptor agonist treats dry eye syndrome in Asia. P2Y receptor agonists are generally pro-inflammatory, and antagonists may eventually treat inflammatory conditions. This article reviews recent developments in P2Y receptor pharmacology (using synthetic agonists and antagonists), structure and biophysical properties (using X-ray crystallography, mutagenesis and modelling), physiological and pathophysiological roles, and present and potentially future therapeutic targeting.

Inhibitory Effect of Vonoprazan on the Metabolism of [14C]Prasugrel in Human Liver Microsomes

BACKGROUND AND OBJECTIVES

A recent report indicated that the pharmacodynamic interaction between clopidogrel and vonoprazan leading to attenuation of the anti-platelet effect of clopidogrel was unlikely to be caused by the inhibition of cytochrome P450 (CYP) 2B6, CYP2C19, or CYP3A4/5 by vonoprazan, based on in vitro CYP inhibition data. The current report investigates another important antiplatelet inhibitor, prasugrel, that is also activated through metabolism by CYP2B6, CYP2C19 and CYP3A4/5, for its CYP-based DDI potential with vonoprazan. The report describes in vitro metabolic inhibition assessments using radiolabeled prasugrel and human liver microsomes (HLMs).

METHODS

Reversible and time-dependent inhibition studies of vonoprazan as well as esomeprazole on the formation of the active metabolite R-138727 of prasugrel were conducted using HLMs.

RESULTS

Vonoprazan up to 10 μM, a concentration over 100-fold higher than the clinical maximum plasma concentration (C_max) of 75.9 nM after 20 mg once daily for 7 days, did not significantly affect the formation of R-138727 from [¹⁴C]prasugrel via reversible or time-dependent inhibition.

CONCLUSIONS

The in vitro data show that the pharmacodynamic interaction reported in the literature between vonoprazan and prasugrel is unlikely to be caused by CYP inhibition by vonoprazan. The results were similar to those obtained from the study with clopidogrel.

In Vitro Assessment of Potential for CYP-Inhibition-Based Drug-Drug Interaction Between Vonoprazan and Clopidogrel

BACKGROUND AND OBJECTIVES

It was recently proposed that CYP-mediated drug-drug interactions (DDIs) of vonoprazan with clopidogrel and prasugrel can attenuate the antiplatelet actions of the latter two drugs. Clopidogrel is metabolized to the pharmacologically active metabolite H4 and its isomers by multiple CYPs, including CYP2C19 and CYP3A4. Therefore, to investigate the possibility of CYP-based DDIs, in vitro metabolic inhibition studies using CYP probe substrates or radiolabeled clopidogrel and human liver microsomes (HLMs) were conducted in this work.

METHODS

Reversible inhibition studies focusing on the effects of vonoprazan on CYP marker activities and the formation of the [¹⁴C]clopidogrel metabolite H4 were conducted with and without pre-incubation using HLMs. Time-dependent inhibition (TDI) kinetics were also measured.

RESULTS

It was found that vonoprazan is not a significant direct inhibitor of any CYP isoforms (IC₅₀ ≥ 16 μM), but shows the potential for TDI of CYP2B6, CYP2C19, and CYP3A4/5. This TDI was weaker than the inhibition induced by the corresponding reference inhibitors ticlopidine, esomeprazole, and verapamil, based on the measured potencies (k_inact/K_I ratio and the R2 value). In a more direct in vitro experiment, vonoprazan levels of up to 10 µM (a 100-fold higher concentration than the plasma C_max of 75.9 nM after taking 20 mg once daily for 7 days) did not suppress the formation of the active metabolite H4 or other oxidative metabolites of [¹⁴C]clopidogrel in a reversible or time-dependent manner. Additionally, an assessment of clinical trials and post-marketing data suggested no evidence of a DDI between vonoprazan and clopidogrel.

CONCLUSIONS

The body of evidence shows that the pharmacodynamic DDI reported between vonoprazan and clopidogrel is unlikely to be caused by the inhibition of CYP2B6, CYP2C19, or CYP3A4/5 by vonoprazan.

Inhibitory Effects of Trapping Agents of Sulfur Drug Reactive Intermediates against Major Human Cytochrome P450 Isoforms

In some cases, the formation of reactive species from the metabolism of xenobiotics has been linked to toxicity and therefore it is imperative to detect potential bioactivation for candidate drugs during drug discovery. Reactive species can covalently bind to trapping agents in in vitro incubations of compound with human liver microsomes (HLM) fortified with β-nicotinamide adenine dinucleotide phosphate (NADPH), resulting in a stable conjugate of trapping agent and reactive species, thereby facilitating analytical detection and providing evidence of short-lived reactive metabolites. Since reactive metabolites are typically generated by cytochrome P450 (CYP) oxidation, it is important to ensure high concentrations of trapping agents are not inhibiting the activities of CYP isoforms. Here we assessed the inhibitory properties of fourteen trapping agents against the major human CYP isoforms (CYP1A2, 2C9, 2C19, 2D6 and 3A). Based on our findings, eleven trapping agents displayed inhibition, three of which had IC₅₀ values less than 1 mM (2-mercaptoethanol, N-methylmaleimide and N-ethylmaleimide (NEM)). Three trapping agents (dimedone, N-acetyl-lysine and arsenite) did not inhibit CYP isoforms at concentrations tested. To illustrate effects of CYP inhibition by trapping agents on reactive intermediate trapping, an example drug (ticlopidine) and trapping agent (NEM) were chosen for further studies. For the same amount of ticlopidine (1 μM), increasing concentrations of the trapping agent NEM (0.007–40 mM) resulted in a bell-shaped response curve of NEM-trapped ticlopidine S-oxide (TSO-NEM), due to CYP inhibition by NEM. Thus, trapping studies should be designed to include several concentrations of trapping agent to ensure optimal trapping of reactive metabolites.

Why Prodrugs and Propesticides Succeed

What are the advantages of bioactivation in optimizing drugs and pesticides? Why are there so many prodrugs and propesticides? These questions are examined here by considering compounds selected on the basis of economic value or market success in 2015. The 100 major drugs and 90 major pesticides are divided into ones acting directly and those definitely or possibly requiring bioactivation. Established or candidate prodrugs accounted for 19% of the total drug sales, with corresponding values of 20, 37, and 17% for proinsecticides, proherbicides, and profungicides. The 19 prodrugs acting in humans generally had better pharmacodynamic/pharmacokinetic properties for target enzyme, receptor, tissue, or organ specificity due to their physical properties (lipophilicity and stabilization). Bioactivation usually involved hydrolases or cytochrome P450 oxidation or reduction. Prodrugs considered are neuroactive aripiprazole, eletriptan, desvenlafaxin, lisdexamfetamine, quetiapine, and fesoterodine; cholesterol-lowering atorvastatin, ezetimibe, and fenofibrate; various prodrugs activated by esterases or sulfatases, ciclesonide, oseltamivir, dabigatran; omega-3 fatty acid ethyl esters and esterone sulfate; and five others with various targets (sofosbuvir, fingolimod, clopidogrel, dapsone, and sildenafil). The proinsecticides are the neuroactive chlorpyrifos, thiamethoxam, and indoxacarb, two spiro enol ester inhibitors of acetyl CoA carboxylase (ACCase), and the bacterial protein delta-endotoxin. The proherbicides considered are five ACCase inhibitors including pinoxaden and clethodim, three protox inhibitors (saflufenacil, flumioxazin, and canfentrazone-ethyl), and three with various targets (fluroxypyr, isoxaflutole, and clomazone). The profungicides are prothioconazole, mancozeb, thiophanate-methyl, dazomet, and fosetyl-aluminum. The prodrug and propesticide concept is broadly applicable and has created some of the most selective pharmaceutical and pest control agents, illustrated here by major compounds that partially overcome pharmacokinetic limitations of potency and selectivity in the corresponding direct-acting compounds. The challenges of molecular design extend beyond the target site fit to the bioactivatable precursor and the fascinating chemistry and biology matched against the complexity of life processes.

Paraoxonases-1, -2 and -3: What are their functions?

Paraoxonase-1 (PON1), an esterase/lactonase primarily associated with plasma high-density lipoprotein (HDL), was the first member of this family of enzymes to be characterized. Its name was derived from its ability to hydrolyze paraoxon, the toxic metabolite of the insecticide parathion. Related enzymes PON2 and PON3 were named from their evolutionary relationship with PON1. Mice with each PON gene knocked out were generated at UCLA and have been key for elucidating their roles in organophosphorus (OP) metabolism, cardiovascular disease, innate immunity, obesity, and cancer. PON1 status, determined with two-substrate analyses, reveals an individual's functional Q192R genotype and activity levels. The three-dimensional structure for a chimeric PON1 has been useful for understanding the structural properties of PON1 and for engineering PON1 as a catalytic scavenger of OP compounds. All three PONs hydrolyze microbial N-acyl homoserine lactone quorum sensing factors, quenching Pseudomonas aeruginosa's pathogenesis. All three PONs modulate oxidative stress and inflammation. PON2 is localized in the mitochondria and endoplasmic reticulum. PON2 has potent antioxidant properties and is found at 3- to 4-fold higher levels in females than males, providing increased protection against oxidative stress, as observed in primary cultures of neurons and astrocytes from female mice compared with male mice. The higher levels of PON2 in females may explain the lower frequency of neurological and cardiovascular diseases in females and the ability to identify males but not females with Parkinson's disease using a special PON1 status assay. Less is known about PON3; however, recent experiments with PON3 knockout mice show them to be susceptible to obesity, gallstone formation and atherosclerosis. Like PONs 1 and 2, PON3 also appears to modulate oxidative stress. It is localized in the endoplasmic reticulum, mitochondria and on HDL. Both PON2 and PON3 are upregulated in cancer, favoring tumor progression through mitochondrial protection against oxidative stress and apoptosis.

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.