Abstract
Purpose
Tissue partitioning is an important component of drug distribution and half-life. Protein binding and lipid partitioning together determine drug distribution.
Methods
Two structure-based models to predict partitioning into microsomal membranes are presented. An orientation-based model was developed using a membrane template and atom-based relative free energy functions to select drug conformations and orientations for neutral and basic drugs.
Results
The resulting model predicts the correct membrane positions for nine compounds tested, and predicts the membrane partitioning for n = 67 drugs with an average fold-error of 2.4. Next, a more facile descriptor-based model was developed for acids, neutrals and bases. This model considers the partitioning of neutral and ionized species at equilibrium, and can predict membrane partitioning with an average fold-error of 2.0 (n = 92 drugs).
Conclusions
Together these models suggest that drug orientation is important for membrane partitioning and that membrane partitioning can be well predicted from physicochemical properties.
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Abbreviations
- acc:
-
Number of acceptors
- don:
-
Number of donors
- fum :
-
Fraction unbound in microsomal incubation
- fup :
-
Unbound fraction in plasma
- KL :
-
Association constant for drug binding to the lipid
- Kp :
-
Tissue partition constant
- L:
-
Amount of lipid in the tissue
- NO2:
-
Number of NO2 groups
- PBPK:
-
Physiologically based pharmacokinetic models
- pKa,a and pKa,b:
-
pKa values for acids and bases are respectively
- PLS:
-
Partial least squares
- SO:
-
Number of S=O groups
- Vss :
-
Steady-state volume of distribution of a drug
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ACKNOWLEDGMENTS AND DISCLOSURES
This work was partially funded by NIH/NIGMS grants 1R01GM104178 and 1R01GM114369 to KK and SN.
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Nagar, S., Korzekwa, K. Drug Distribution. Part 1. Models to Predict Membrane Partitioning. Pharm Res 34, 535–543 (2017). https://doi.org/10.1007/s11095-016-2085-z
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DOI: https://doi.org/10.1007/s11095-016-2085-z