In vitro and in silico studies of interaction of synthetic 2,6,9-trisubstituted purine kinase inhibitors BPA-302, BP-21 and BP-117 with liver drug-metabolizing cytochromes P450

An evaluation of possible interactions with enzymes of drug metabolism (cytochromes P450, CYP) is an important part of studies on safety and, in general, on the properties of any drug or biologically active compound. The article is focused on the preliminary metabolic study of selected 2,6,9-trisubstituted purine kinase inhibitors with significant anticancer activities which we have developed. The compounds BP-21 and BP-117 represent strong CDK inhibitors and the compound BPA-302 was developed as selective FLT3-ITD kinase inhibitor. Here, emphasis is placed on interactions of these compounds with the nine most important forms of CYP to evaluate the possibility of inhibition of these enzymes. The possibility of their inhibitory effect was studied in vitro on selected human liver microsomal CYP enzymes. The most affected enzyme was CYP2C19. Its activity dropped to 22 % of its original value by BPA 302, to 13 % by BP-21 and to 6 % by BP-117 at the highest concentration tested (250 µmol·l(-1)). The results suggest that the metabolism of concomitantly administered drugs should not be significantly affected at lower doses. Molecular docking of BPA-302 indicated that it can bind to active site of both CYP2C19 and CYP2D6 enzymes above the heme cofactor corroborating the experimental data.

Rosiglitazone Metabolism in Human Liver Microsomes Using a Substrate Depletion Method

Background

Elimination of rosiglitazone in humans is via hepatic metabolism. The existing studies suggest that CYP2C8 is the major enzyme responsible, with a minor contribution from CYP2C9; however, other studies suggest the involvement of additional cytochrome P450 enzymes and metabolic pathways. Thus a full picture of rosiglitazone metabolism is unclear.

Objective

This study aimed to improve the current understanding of potential drug–drug interactions and implications for therapy by evaluating the kinetics of rosiglitazone metabolism and examining the impact of specific inhibitors on its metabolism using the substrate depletion method.

Methods

In vitro oxidative metabolism of rosiglitazone in human liver microsomes obtained from five donors was determined over a 0.5–500 µM substrate range including the contribution of CYP2C8, CYP2C9, CYP3A4, CYP2E1, and CYP2D6.

Results

The maximum reaction velocity was 1.64 ± 0.98 nmol·mg⁻¹·min⁻¹. The CYP2C8 (69 ± 20%), CYP2C9 (42 ± 10%), CYP3A4 (52 ± 23%), and CEP2E1 (41 ± 13%) inhibitors all significantly inhibited rosiglitazone metabolism.

Conclusion

The results suggest that other cytochrome P450 enzymes, including CYP2C9, CYP3A4, and CEP2E1, in addition to CYP28, also play an important role in the metabolism of rosiglitazone. This example demonstrates that understanding the complete metabolism of a drug is important when evaluating the potential for drug–drug interactions and will assist to improve the current therapeutic strategies.

Construction of a CYP2E1-template system for prediction of the metabolism on both site and preference order

We have constructed an in silico system for the prediction of CYP2E1-mediated reaction using a two-dimensional template derived from substrate structures. Although CYP2E1 prefers small-size molecules for the substrates, the enzyme mediates oxidations of large-size molecules, such as benzo[a]pyrene. Overlays of these substrates, to assemble their sites of oxidation into a specific area, suggested a range of regions frequently occupied. The region, having a benzo[a]pyrene-like shape, was thus used as a CYP2E1 template. In this system, atoms in substrates, except for hydrogen atoms, were placed on corners of honeycomb structures of the template after having expanded the structures. Using published data for the metabolism on more than 80 substrates of CYP2E1, the core template was further refined to verify the adjacent area and to define the relative contribution of template positions for the catalysis. The positions on the template were classified into four different point (0-3) groups, depending on relative usage. In addition, we set independent points (-5 to 3) for specific positions to incorporate three-dimensional or functional information. Total scores from both position-occupancy and -function points were calculated for all the orientations of possible conformers of test substrates, and the scores were found to predict the relative abundance (i.e., order) as well as the regioselectivity of human CYP2E1 reactions with high fidelities.

Structure, function, regulation and polymorphism and the clinical significance of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g., benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids). CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances, and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close link between CYP1A1 and 1A2 sharing a common 5'-flanking region. The human CYP1A2 gene spans almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of 1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate binding platforms on either side of the cavity. A large interindividual variability in the expression and activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of them have been associated with altered drug clearance and response and disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.