Beyond Overton’s Rule: Quantitative Modeling of Passive Permeation through Tight Cell Monolayers

Abstract

One of the great challenges in pharmacokinetics is to find a means to optimize the transport across cell barriers. In this work, permeation across a cell monolayer, such as the tight endothelia in the blood-brain barrier, was modeled using a homologous series of amphipatic molecules, 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)-labeled alkyl chain amphiphiles (NBD-Cn, n = 2 to 16), to obtain rules that relate permeant structure to permeability. The amphiphile enters the system from the serum, equilibrated with serum albumin and lipoproteins, and its sequestration by serum components, interaction with the endothelium, and accumulation in the tissue is followed over time. The dependence of the permeability coefficient on the number of carbons of the amphiphile's alkyl chain has a parabolic-like shape. After a threshold value, an increase in the hydrophobicity of the amphiphile, along the homologous series, results in a decrease in the characteristic rate of permeation to the tissue. A sensitivity analysis was performed, and the rate limiting steps for permeation of each amphiphile were identified. Sequestration in the serum and rate of interaction with the endothelium, particularly the rate of desorption, were found to be the determinant processes for some amphiphiles, while for others translocation was the rate limiting step. Additionally, for some amphiphiles a single rate limiting step could not be identified, with several steps contributing significantly to the overall permeation. Finally, we derived analytical equations that adequately describe the rate of amphiphile accumulation in the tissue for the cases where permeation is controlled by a single rate limiting step.

Demonstrating In-Cell Target Engagement Using a Pirin Protein Degradation Probe (CCT367766)

“…Large lipophilic heterobifunctional molecules are particularly susceptible to aggregation, 46 and this decreases the free concentration that drives cell membrane flux. 47 To balance the lipophilicity, we removed the tertiary amide bond to the piperazine, introducing a cationic amine, which would be substantially charged at pH 7.4 (MoKa, version 2.5.2, p K a = 8.0). 48 The second amide in the linker was also removed, reducing the HBD count further and increasing the overall flexibility of the ligand, consistent with the formation of the crucial PDP ternary protein complex.…”

Nonclassical Size Dependence of Permeation Defines Bounds for Passive Adsorption of Large Drug Molecules

“…6 Additionally, increased resolvation penalties associated with departitioning from the membrane may cause membrane exit to become an additional rate limiting step. 32 …”

Interaction of NBD-labelled fatty amines with liquid-ordered membranes: a combined molecular dynamics simulation and fluorescence spectroscopy study

“…1 In the last few years, our research group has been characterising in detail the interaction of amphiphiles with serum proteins and lipid bilayers regarding both the equilibrium and the kinetic parameters. Moreover, the interaction of amphiphilic molecules with lipid bilayers determines their location inside the cells.…”