Prediction of regioselectivity and preferred order of metabolisms on CYP1A2-mediated reactions. Part 1. Focusing on polycyclic arenes and the related chemicals

Construction of a fused grid-based CYP2C8-Template system and the application

A ligand-accessible space in the CYP2C8 active site was reconstituted as a fused grid-based Template∗ with the use of structural data of the ligands. An evaluation system of CYP2C8-mediated metabolism has been developed on Template with the introduction of the idea of Trigger-residue initiated ligand-movement and fastening. Reciprocal comparison of the data of simulation on Template with experimental results suggested a unified way of the interaction of CYP2C8 and its ligands through the simultaneous plural-contact with Rear-wall of Template. CYP2C8 was expected to have a room for ligands between vertically standing parallel walls termed Facial-wall and Rear-wall. Both the walls were separated by a distance corresponding to 1.5-Ring (grid) diameter size, which was termed Width-gauge. The ligand sittings were stabilized through contacts with Facial-wall and the left-side borders of Template including specific Position 29, left-side border of Rings I/J, or Left-end, after Trigger-residue initiated ligand-movement. Trigger-residue movement is suggested to force ligands to stay firmly in the active site and then to initiate CYP2C8 reactions. Simulation experiments for over 350 reactions of CYP2C8 ligands supported the system established.

Construction of a fused grid-based CYP2C18-Template system and its application to drug metabolism

Detailed estimation of cytochrome P450 (CYP)-mediated metabolisms of medicine and other chemicals is necessary for the efficacy and safety assessments. Data on the metabolisms mediated by minor CYP enzymes like CYP2C18 are often not available in metabolisms and safety assessments of chemicals except for medical drugs developed recently. A ligand-accessible space in the active site of human CYP2C18 was thus reconstituted as a fused grid-based Template with the use of structural data of its ligands. An evaluation system of CYP2C18-mediated metabolism was then developed on Template with the introduction of the idea of movement and fastening of ligands after Trigger-residue contact. Reciprocal comparison of the data of simulations on Template with experimental results suggested a unified way of the interaction of CYP2C18, in similar to the CYP2C8 interaction (Drug Metab Pharmacokinet 2023, in press). These experiments also displayed the roles of initial Trigger-residue-localizations on their distinct catalyses among human CYP2C enzymes. Simulation experiments for over 130 reactions of CYP2C18 ligands supported the system established.

Application of fused-grid-based CYP-Template systems for genotoxic substances to understand the metabolisms

Understanding of metabolic processes is a key factor to evaluate biological effects of carcinogen and mutagens. Applicability of fused-grid Template* systems of CYP enzymes (Drug Metab Pharmacokinet 2019, 2020, 2021, and 2022) was tested for three phenomena. (1) Possible causal relationships between CYP-mediated metabolisms of β-naphthoflavone and 3-methylcholanthrene and the high inducibility of CYP enzymes were examined. Selective involvement of non-constitutive CYP1A1, but not constitutive CYP1A2, was suggested on the oxidative metabolisms of efficient inducers, β-naphthoflavone and 3-methylcholanthrene. These results supported the view of the causal link of their high inducibility with their inefficient metabolisms due to the lack of CYP1A1 in livers at early periods after the administration of both inducers. (2) Clear differences exist between human and rodent CYP1A1 enzymes on their catalyses with heterocyclic amines, dioxins and polyaromatic hydrocarbons (PAHs). Reciprocal comparison of simulation results with experimental data suggested the rodent specific site and distinct sitting-preferences of ligands on Template for human and rodent CYP1A1 enzymes. (3) Enhancement of metabolic activation and co-mutagenicity have been known as phenomena associated with Salmonella mutagenesis assay. Both the phenomena were examined on CYP-Templates in ways of simultaneous bi-molecule bindings of distinct ligands as trigger and pro-metabolized molecules. α-Naphthoflavone and norharman served consistently as trigger-molecules to support the oxidations of PAHs and arylamines sitting simultaneously as pro-metabolized molecules on Templates of CYP1A1, CYP1A2 and CYP3A4. These CYP-Template simulation systems with deciphering capabilities are promising tools to understand the mechanism basis of metabolic activations and to support confident judgements in safety assessments.

DruMAP: A Novel Drug Metabolism and Pharmacokinetics Analysis Platform

We developed a novel drug metabolism and pharmacokinetics (DMPK) analysis platform named DruMAP. This platform consists of a database for DMPK parameters and programs that can predict many DMPK parameters based on the chemical structure of a compound. The DruMAP database includes curated DMPK parameters from public sources and in-house experimental data obtained under standardized conditions; it also stores predicted DMPK parameters produced by our prediction programs. Users can predict several DMPK parameters simultaneously for novel compounds not found in the database. Furthermore, the highly flexible search system enables users to search for compounds as they desire. The current version of DruMAP comprises more than 30,000 chemical compounds, about 40,000 activity values (collected from public databases and in-house data), and about 600,000 predicted values. Our platform provides a simple tool for searching and predicting DMPK parameters and is expected to contribute to the acceleration of new drug development. DruMAP can be freely accessed at: https://drumap.nibiohn.go.jp/.

Construction of a fused grid-based CYP2C19-Template system and the application

A ligand-accessible space in the CYP2C19 active site was reconstituted as a fused grid-based Template with the use of structural data of the ligands. An evaluation system of CYP2C19-mediated metabolism has been developed on Template with the introduction of the idea of Trigger-residue initiated ligand-movement and fastening. Reciprocal comparison of the data of simulation on Template with experimental results suggested a unified way of the interaction of CYP2C19 and its ligands through the simultaneous plural-contact with Rear-wall of Template. CYP2C19 was expected to have a room for ligands between vertically standing parallel walls termed Facial-wall and Rear-wall, which were separated by a distance corresponding to 1.5-Ring (grid) diameter size. The ligand sittings were stabilized through contacts with Facial-wall and the left-side borders of Template including specific Position 29 or Left-end after Trigger-residue initiated ligand-movement. Trigger-residue movement is suggested to force ligands to stay firmly in the active site and then to initiate CYP2C19 reactions. Simulation experiments for over 450 reactions of CYP2C19 ligands supported the system established.

Application of CYP1A2-Template System to Understand Metabolic Processes in the Safety Assessment

Cytochrome P450 (CYP)-mediated metabolisms of four chemicals have been investigated to understand their unresolved phenomena of their metabolisms using human CYP-Template systems developed in our previous studies (Drug Metab Pharmacokinet 2019, 2021, 2022). Simulation experiments of a topoisomerase-targeting agent, amonafide, offered a possible new inhibitory-mechanism as Trigger-residue inactivation on human CYP1A2 Template. N-Acetylamonafide as well as amonafide would inactivate CYP1A2 through the interference of Trigger-residue movement with their dimethylaminoethyl parts. The mechanism was also supported on the inhibition/inactivation of two other drugs, DSP-1053 and binimetinib. Both the drugs, after other CYP-mediated slight structural alterations, were expected to interact with Trigger-residue for the intense inhibition on CYP1A2 Template. Possible formation of reactive intermediates of amonafide and 3-methylindole was also examined on CYP1A2 Template. Placements of amonafide suggested the scare N-oxidation of the arylamine part due to the Trigger-residue interaction. Placements of 3-methylindole suggested the formation of a reactive intermediate, 3-methyleneindolenine, rather selectively on rodent CYP1A2 than on human CYP1A2, in consistent with the experimental data. These results suggest that CYP Template systems developed are effective tools to warn an appearance of unstable reactive intermediates. Our CYP-Template systems would support confident judgements in safety assessments through offering the mechanistic understandings of the metabolism.

Refined CYP2E1∗ Template∗∗ system to decipher the ligand-interactions

A Template system for a prediction of human CYP2E1-mediated reactions (Drug Metab Rev 2011) has been refined with the introduction of ideas of Trigger-residue and the residue-initiated movement of ligands in the active site. The refined system also includes ideas of bi-molecule binding and angled-placement, which allow to sit diverse types of ligands on Template. With the use of these ideas in common with other Template systems for human CYP1A1, CYP1A2 and CYP3A4 (Drug Metab Pharmacokinet 2016, 2017, 2019, and 2020), 349 reactions of 192 distinct chemicals published as CYP2E1 ligands were examined in the refined system. Verifications of good and poor substrates, regioselectivity and also inhibitory interaction were available faithfully for these ligands from their placements on the refined Template and rules for interaction modes, accompanied with their deciphering information to lead to the judgements. The refined CYP2E1 Template system will thus offer more reliable estimations of human CYP2E1 catalysis toward ligands of diverse structures.

Deciphering Key Interactions of Ligands with CYP3A4-Template* system

Cytochrome P450 (CYP)-mediated metabolisms are often associated with biological and toxicological events of chemicals. A major hepatic enzyme, CYP3A4, showed clear distinctions on their catalyses even among ligands having resemble structures. To better understand mechanisms of their distinct catalyses, possible associations of ligand interactions at specific parts of CYP3A4 residues were investigated using CYP3A4-Template system developed (DMPK 2019 and 2020). A placement was available selectively for CYP3A4-mediated R-thalidomide 5-oxidation on Template, but not for the 5’-oxidation and the S-isomer oxidations. Similar placements were generated for pomalidomide (4-amino-thalidomide), but not for a poor ligand, lenalidomide (3-deoxy-pomalidomide). The latter ligand took placements lacking IJK-Interaction or sticking the 4-amino part beyond the facial-side wall on Template. A placement was available for the tert-butyl oxidation of terfenadine, but not for an analog, ebastine. Their interactions with upper-Cavity-2 residue were expected to differ at their sites of oxygen substituents. Some phenolic antioxidants behave distinctly toward biological oxidations in vitro and in vivo. Butylated hydroxytoluene is oxidized to the peroxy-derivative in vitro, but solely to the oxidized metabolites at the benzyl and tert-butyl methyl positions in vivo. Involvement of CYP3A4 were suggested for all the three reactions from the placements on Template. Tocopherols were also applied on Template for the oxidations for chroman and side-chain terminals. The primary placement was suggested to undergo the futile-recycling through formation of the peroxide intermediate subsequently to lead the substantial lack of the CYP3A4-mediated oxidation. These data suggest the effectiveness of CYP3A4-Template assessment to understand the causal basis of poor oxidations and also to verify the in vivo contribution of CYP3A4-mediated peroxidative reactions.

Development of template systems for ligand interactions of CYP3A5 and CYP3A7 and their distinctions from CYP3A4 template

Starting from established CYP3A4 Template (DMPK. 2019, and 2020), CYP3A5 and CYP3A7 Templates have been constructed to be reliable tools for verification of their distinct catalytic properties. A distinct occupancy was observed on CYP3A4-selective ligands, but not on the non-selective ligands, in simulation experiments. These ligands often invade into Bay-1 region during the migration from Entrance to Site of oxidation in simulation experiments. These results offered an idea of the distinct localization of Bay-1 residue on CYP3A5 Template, in which the Bay-1 residue stayed closely to Template border. The idea also accounted for the higher oxidation rates of CYP3A5, than of CYP3A4, of noscapine and schisantherin E through their enhanced sitting-stabilization. Typical CYP3A7 substrates such as zonisamide and retinoic acids took their placements without occupying a left side region of Template for their metabolisms. In turn, the occupancies of the left-side region were inevitably observed among poor ligands of CYP3A7. Altered extent of IJK-Interaction or localization of a specific residue at the left-side would thus explain distinct catalytic properties of CYP3A7 on Template. These data suggest the alteration of each one of Template region, from CYP3A4 Template, led to the distinct catalytic properties of CYP3A5 and CYP3A7 forms.

Applications of a grid-based CYP3A4 Template system to understand the interacting mechanisms of large-size ligands; part 4 of CYP3A4 Template study

Catalytic interactions of CYP3A4 with large-size ligands have been studied on the Template established in our previous studies using polyaromatic hydrocarbon and steroid ligands (DMPK 34: 113-125 and 351-364 2019 and in press 2020). Typical CYP3A4-substrates including erythromycin, cyclosporin A (ca.1200 Da), ivermectin B1a and taxanes were applied successfully and regioselective metabolisms of these ligands were reconstituted faithfully on Template. These results suggest the applicability of CYP3A4 Template throughout broadened sizes of CYP3A4 ligands. Macrolide antibiotics showed distinct degrees of tight sittings in Width-gauge, a tool for accommodation measure. The observed differences were associated with different inhibitory/inactivation potentials of troleandomycin, erythromycin, clarithromycin and azithromycin, suggesting CYP3A4 Template also as a tool for drug-interaction mechanisms. Slight expansion of Template area was made at near Site of oxidation from simulation results of antitumor agent, rilpivirine, in the present study. Ligand entry from left side of Template is also suggested from macrolide interactions. Broadened applicability of the refined CYP3A4 Template were assured with experiments with various large-size ligands.

Application of cytochrome P450 reactivity on the characterization of chemical compounds and its association with repeated-dose toxicity

Repeated-dose toxicity (RDT) studies are one of the critical studies to assess chemical safety. There have been some studies attempting to predict RDT endpoints based on chemical substructures, but it remains very difficult to establish such a method, and a more detailed characterization of chemical compounds seems necessary. Cytochrome P450s (P450s) comprise multiple forms with different substrate specificities and play important roles in both the detoxification and metabolic activation of xenobiotics. In this study, we investigated possible use of P450 reactivity of chemical compounds to classify the compounds. A total of 148 compounds with available rat RDT test data were used as test compounds and subjected to inhibition assays against 18 human and rat P450s. Among the tested compounds, 82 compounds inhibited at least one P450 form. Hierarchical clustering analyses using the P450 inhibitory profiles divided the 82 compounds into nine groups, some of which showed characteristic chemical and biological properties. Principal component analyses of the P450 inhibition data in combination with the calculated chemical descriptors demonstrated that P450 inhibition data were plotted differently than most chemical descriptors in the loading plots. Finally, association analyses between P450 inhibition and RDT endpoints showed that some endpoints related to the liver, kidney and hematology were significantly associated with the inhibition of some P450s. Our present results suggest that the P450 reactivity profiles can be used as novel descriptors for characterizing chemical compounds for the investigation of the toxicity mechanism and/or the establishment of a toxicity prediction model.

Solving the interactions of steroidal ligands with CYP3A4 using a grid-base template system

Using over fifty steroidal ligands, CYP3A4 Template system established in our previous study (DMPK 34: 113-125, 2019) has been evaluated for the applicability for prediction of regioselective metabolisms of steroids in the present study. Plural regional interactions near Site of Oxidation of CYP3A4 (Slide-down and Adaptation) are newly defined for steroid ligands in addition to previously characterized Trigger- and IJL-interactions on Template. Interaction of steroids at ring-A with CYP3A4 residue (Front-residue), at the facial side of Ring B of Template, determined the availability of ligand sitting at Rings A and B of Template. Steroids having 3-one-4-ene structures, which are not stacked on Front-residue, thus slide down for their 6-oxidations. Some steroids with 3β-ol structures undergo the further right-side movement (Adaptation) for their 7-oxidations. Similar overpassing phenomena are also expected for steroid 15/16-oxidations and 2/1-oxidations. Allowable width on ligand accommodation was also defined as Width-gauge of Template. Reciprocal comparison of sittings of steroids on Template with experimental data offered idea of CYP3A4-mediated oxidations of steroids through seven distinct types of placements on Template and of the relationship with their usage abundance. The present system would offer practical way for structural identification and verification of CYP3A4-mediated metabolisms of various types of steroids.