Chromatographic retention measurement in immobilized artificial membranes (IAMs) is considered a fast and reliable method to predict biological properties (drug distribution) because of the IAM structure, which consists of phospholipid analogues bonded covalently to silica particles. A new parameter (d) is proposed to estimate the similarity between IAM columns, conventional HPLC columns, and drug distribution systems, and thus the performance of chromatographic systems to predict drug distribution. An IAM.PC.DD2 column has been used for this study, together with two XTerra columns (MSC18 and RP18), at several acetonitrile-water mobile phases. According to the d parameter, good correlations should be obtained between chromatographic systems (both IAM and C18) and octanol-water partition coefficient (log P), and thus both types of columns could be used to obtain log P values. The IAM.PC.DD2 system shows a close similarity to human skin partition, tadpole narcosis, and blood-brain permeability processes, showing that it can be useful as a model for these biological processes. Controversially, it is shown that human skin permeation is more similar to C18 partition than to IAM partition. Other biological processes such as blood-brain distribution and tissue-blood partition show a poor similarity to IAM and C18 systems, demonstrating that estimation of these drug distribution processes by chromatographic measurements may not be adequate.
We report here a new, label-free approach to measure serum protein binding constants. The assay is able to measure HSA K d values in the milli-molar to micromolar range. The protein is not immobilized on any surface and the assay self-corrects for nonspecific adsorption. No mass balance is required to get accurate binding constants and it is not necessary to wait for equilibrium to extract the binding constant. The assay runs in a 96-well format using commercially available parts and is, therefore, relatively easy to implement and automate. As the chemical membranes used are not water permeable, there is no volume change due to the osmotic pressure and pretreatment (soaking) is not necessary. The concept can potentially be extended to other proteins and could thus serve as a label-free technique for general binding constant measurements.
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