(T1430-05-31) Analysis of Pharmacogenetic Polymorphism Effect of ABCB1 2677G >T/A Through Molecular Modeling Approach

Purpose: P-glycoprotein (P-gp) is widely expressed in the body and is known to be a membrane transporter of multi-drugs with multi-specific recognition properties. Whether or not the pharmacokinetic diversity of drugs that are substrates of P-gp according to the polymorphisms of the ABCB1 gene encoding P-gp has been continuously raised in the past. The aim of this study was to approach the resolution of the pharmacokinetic difference controversy according to the ABCB1 genetic polymorphism (with a focus on the frequently reported missense polymorphism according to 2677G >T/A) through the mechanical function analysis of P-gp using in-silico molecular modeling.

Methods: Based on the human P-gp amino-acid sequence and structural information, P-gp's structures could be modeled. And polymorphic P-gp was created through amino-acid substitution and prepare-protein approach according to base sequence change.

Results: The genetic polymorphism of ABCB1 2677G >T/A (Ala893Ser/Thr) does not correspond to the nucleotide-binding-domain (NBD) or drug-binding-pocket (DBP) of P-gp and does not involve changes in the mechanical conformational of P-gp. Although the amino-acid substitution by c.2677G >T/A caused approximately 30% increased strain in one α-helix hinge between the NBD and DBP of P-gp internal tunnel, no overall structural change was identified (compared to wild-type). This suggested that c.2677G >T/A might have a minor effect on the rate of P-gp inward-to-outward conformational change by increasing the torsional energy, but would not have a significant effect on the general functioning and maintenance of P-gp.

Conclusion: Our findings provide useful insight into resolving the debate about whether ABCB1 genetic polymorphisms are effective covariates and their significance in relation to population pharmacokinetic variability of multiple drugs of P-gp substrates.

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Acknowledgements:This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2022R1A2C1010245).

Figure 1. Molecular structures of P-glycoprotein (P-gp) in apo-state (A), ligand-docked state (B), and outward-facing state (C). Arrows indicate major conformational sites in the ligand-docked state compared to the apo-state. For easy comparison of steric changes in each conformational state of P-gp, cassette 1 is labeled in yellow. In the ligand-docked state, red-labeled region represents drug binding pocket.

Figure 2. Comparison (alignment and superimpose with wild-type structures) of point polymorphism structures of Ala893Ser (A; ABCB1 2677G>T) and Ala893Thr (B ; ABCB1 2677G>A) in the ligand-docked state of P-glycoprotein. Point polymorphism structures by Ala893Ser/Thr are labeled in yellow.

Figure 3. Comparison graph of –CDOCKER interaction energy values according to docking simulation with P-glycoprotein (P-gp) ligand-docked state of drugs corresponding to substrate (digoxin, imatinib, and verapamil) or non-substrate (antipyrine, nifedipine, and tolbutamide) of P-gp. The red dotted line in the graph represents the energy value (30) that approximates the degree of effective substrate interaction with P-gp.