Phospholipid-based Immobilized Artificial Membrane (IAM) Chromatography: A Powerful Tool to Model Drug Distribution Processes

Immobilized Artificial Membrane (IAM) chromatography constitutes a valuable tool for medicinal chemists to prioritize drug candidates in early drug development. The retention on IAM stationary phases encodes lipophilicity, electrostatic and other secondary interactions contrary to traditional octanol-water partitioning. An increasing number of publications in recent years have suggested that IAM indices, including isocratic log k(IAM) or extrapolated log kw(IAM) retention factors, chromatographic hydrophobicity index CHI(IAM) or the polarity parameter Δlog kw(IAM) can successfully model the passage of xeniobiotics through biological membranes and barriers and predict pharmacokinetic properties, often in combination with additional descriptors. Examples referring to the modeling of human oral absorption, blood-brain penetration and skin partition are described. More recently, IAM chromatography has been applied to estimate toxicological endpoints in regard to drug safety, such as phospholipidosis potential, or in regard to chemical risk hazards including the bioconcentration factor and aquatic organisms’ toxicity. The promising results in both medicinal chemistry and in environmental science in combination with the speed, reproducibility and low analyte consumption suggest that a broader application of IAM chromatography in the early drug discovery process and in ecotoxicity may save time and money in initial drug candidate selection and will contribute to a reduced risk hazard of chemicals.

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Immobilized artificial membrane (IAM) liquid chromatography as a model for antimicrobial peptide partitioning into cell membranes: An evaluation

Eureka ◽

10.29173/eureka8021 ◽

2010 ◽

Vol 1 (1) ◽

pp. 20-33

Author(s):

Matthew Benesch ◽

Ruthvnen Lewis ◽

Ronald McElhaney

Keyword(s):

Liquid Chromatography ◽

Antimicrobial Peptides ◽

Lipid Bilayers ◽

Screening Method ◽

Interfacial Region ◽

Artificial Membrane ◽

Lipid Packing ◽

Immobilized Artificial Membrane ◽

Fast Screening ◽

Packing Densities

Non-covalent immobilized artificial membrane reverse-phase high performance liquid chromatography was previously evaluated as a means whereby elution times for antimicrobial peptides from columns mimicking the lipid bilayers of different membrane systems might be used as a fast-screening method to compare relative binding effectiveness. Such a system would aid in the development of antimicrobial peptides that bind preferentially to model pathogenic systems and leave the host’s membranes reasonably unaffected. A non-covalent approach allows for flexibility in membrane composition but was found to be inadequate for analysis of most peptides due to significant lipid loss at high acetonitrile concentrations. A covalent approach where phosphatidylcholine was amide-linked to the silica surface was examined to evaluate its use as a fast-screening method and compare its data to that collected from the non-covalent columns. Initial work with a 1-cm column proved ineffective due to problems with balancing flow rates with retention times, and work was shifted to a longer 10-cm column. Results suggested that peptides bind much more strongly to covalent columns than non-covalent ones, with the binding especially enhanced by the presence of cationic residues. These columns had lipid packing densities much lower than true membranes, indicating that the peptides were partitioning deep into the bonded phase of the columns rather than into the interfacial region of the phosphate head groups, as expected in situations of biologically-relevant lipid packing densities.

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