The School of Pharmacy Geneva-Lausanne (EPGL) – The First Ten Years

With the creation of the School of Pharmacy Geneva-Lausanne (EPGL) in 2003, cantons Geneva and Vaud pooled their resources with the objective of reinforcing the research and teaching in the pharmaceutical sciences. Its core research units cover all aspects of fundamental pharmaceutical research and include collaborative research with the University Hospitals of Geneva and Lausanne

Quantitative Structure-Permeation Relationships (QSPeRs) to Predict Skin Permeation: A Critical Evaluation

Purpose. Development of reliable mathematical models to predict skin permeability remains a challenging objective. This article examines some of the existing algorithms and critically evaluates their statistical relevance. Methods. Complete statistics were recalculated for a number of published models using a stepwise multiple regression procedure. The predictivity of the models was obtained by cross-validation using a "leave-one-out” deletion pattern. The relative contribution of each independent variable to the models was calculated by a standardization procedure. Results. The heterogeneity of the data in terms of skin origin and experimental conditions has been shown to contribute to the residual variance in existing models. Furthermore, rigorous statistics demonstrate that some published models are based on nonsignificant parameters. As such, they afford misleading mechanistic insight and will lead to over-interpretation of the data. Conclusions. The large number of published models reflects the need for predictive tools in cutaneous drug delivery and toxicology. However, such models are more reliable when confined within well-defined chemical classes, and their applicability is often limited by the narrow property space of the set of permeants under stud

Water-Oil Partition Profiling of Ionized Drug Molecules Using Cyclic Voltammetry and a 96-Well Microfilter Plate System

Purpose. A new experimental set-up for studying partitioning of ionizable drugs at the interface between two immiscible electrolyte solutions (ITIES) by amperometry is presented. The method is quite general, as it can be applied to any charged drug molecule. Methods. The procedure is based on 96-well microfilter plates with microporous filters to support 96 organic liquid membranes. The new methodology is first validated using a series of tetra-alkylammonium ions and subsequently used to construct the ion partition diagrams of 3,5-N,N-tetramethylaniline and 2,4-dinitrophenol. The lipophilicity of these drugs was examined by potentiometry and cyclic voltammetry in the NPOE/water system. Results. Cyclic voltammetry resulted in potential-pH profiles of the studied drugs. When the aqueous phase pK a is already known, the logP NPOEof lipophilic drugs could be determined using a very little amount of solvents and drugs. The values of the partition coefficients for the neutral forms agree well with those obtained by potentiometry. Conclusions. The procedure based on commercially available 96-well microfilter plates is shown to be useful for determining logP of ionized drugs in a rapid and efficient wa

MLP Tools: a PyMOL plugin for using the molecular lipophilicity potential in computer-aided drug design

The molecular lipophilicity potential (MLP) is a well-established method to calculate and visualize lipophilicity on molecules. We are here introducing a new computational tool named MLP Tools, written in the programming language Python, and conceived as a free plugin for the popular open source molecular viewer PyMOL. The plugin is divided into several sub-programs which allow the visualization of the MLP on molecular surfaces, as well as in three-dimensional space in order to analyze lipophilic properties of binding pockets. The sub-program Log MLP also implements the virtual log P which allows the prediction of the octanol/water partition coefficients on multiple three-dimensional conformations of the same molecule. An implementation on the recently introduced MLP GOLD procedure, improving the GOLD docking performance in hydrophobic pockets, is also part of the plugin. In this article, all functions of the MLP Tools will be described through a few chosen examples

Drug-protein binding: a critical review of analytical tools

The extent of drug binding to plasma proteins, determined by measuring the free active fraction, has a significant effect on the pharmacokinetics and pharmacodynamics of a drug. It is therefore highly important to estimate drug-binding ability to these macromolecules in the early stages of drug discovery and in clinical practice. Traditionally, equilibrium dialysis is used, and is presented as the reference method, but it suffers from many drawbacks. In an attempt to circumvent these, a vast array of different methods has been developed. This review focuses on the most important approaches used to characterize drug-protein binding. A description of the principle of each method with its inherent strengths and weaknesses is outlined. The binding affinity ranges, information accessibility, material consumption, and throughput are compared for each method. Finally, a discussion is included to help users choose the most suitable approach from among the wealth of methods presented. Figure Range of binding constants (log Ka) assessable by the main separative and non-separative analytical tools used to characterize drug-protein interactions. ED: equilibrium dialysis, UF: ultrafiltration, PAMPA: parallel artificial membrane permeability assay, HPAC/ZE: high-performance affinity chromatography/zonal elution approach, HPAC/FA: high-performance affinity chromatography/frontal analysis approach, ACE: affinity capillary electrophoresis (mobility shift assay), CE/FA: capillary electrophoresis/frontal analysis, Spectro.: spectroscopic assays, ITC: isothermal titration calorimetry, comp.: competition studies, titration: titration studies, DSC: differential scanning calorimetry, SPR: surface plasmon resonance-based assay

Fast log P determination by ultra-high-pressure liquid chromatography coupled with UV and mass spectrometry detections

Ultra-high-pressure liquid chromatography (UHPLC) systems able to work with columns packed with sub-2μm particles offer very fast methods to determine the lipophilicity of new chemical entities. The careful development of the most suitable experimental conditions presented here will help medicinal chemists for high-throughput screening (HTS) log P oct measurements. The approach was optimized using a well-balanced set of 38 model compounds and a series of 28 basic compounds such as β-blockers, local anesthetics, piperazines, clonidine, and derivatives. Different organic modifiers and hybrid stationary phases packed with 1.7-μm particles were evaluated in isocratic as well as gradient modes, and the advantages and limitations of tested conditions pointed out. The UHPLC approach offered a significant enhancement over the classical HPLC methods, by a factor 50 in the lipophilicity determination throughput. The hyphenation of UHPLC with MS detection allowed a further increase in the throughput. Data and results reported herein prove that the UHPLC-MS method can represent a progress in the HTS-measurement of lipophilicity due to its speed (at least a factor of 500 with respect to HPLC approaches) and to an extended field of application. Figure The UHPLC approach described here greatly enhanced the time required for log P determination (5' min by compound using UV detection) and, at least, 8 compounds measured in a 5' run when Mass Spectrometry detection in used. These developments offer to medicinal chemists a high-throughput method to estimate the lipophilicity of NCE

Analytical tools for the physicochemical profiling of drug candidates to predict absorption/distribution

The measurement of physicochemical properties at an early phase of drug discovery and development is crucial to reduce attrition rates due to poor biopharmaceutical properties. Among these properties, ionization, lipophilicity, solubility and permeability are mandatory to predict the pharmacokinetic behavior of NCEs (new chemical entities). Due to the high number of NCEs, the analytical tools used to measure these properties are automated and progressively adapted to high-throughput technologies. The present review is dedicated to experimental methods applied in the early drug discovery process for the determination of solubility, ionization constants, lipophilicity and permeability of small molecules. The principles and experimental conditions of the different methods are described, and important enhancements in terms of throughput are highlighted. Figure Scheme of the Drug Research Proces

Rapid determination of p K a values of 20 amino acids by CZE with UV and capacitively coupled contactless conductivity detections

A rapid and universal capillary zone electrophoresis (CZE) method was developed to determine the dissociation constants (pK a) of the 20 standard proteogenic amino acids. Since some amino acids are poorly detected by UV, capacitively coupled contactless conductivity detection (C4D) was used as an additional detection mode. The C4D coupling proved to be very successful on a conventional CE-UV instrument, neither inducing supplementary analyses nor instrument modification. In order to reduce the analysis time for pK a determination, two strategies were applied: (i) a short-end injection to reduce the effective length, and (ii) a dynamic coating procedure to generate a large electroosmotic flow (EOF), even at pH values as low as 1.5. As a result, the analysis time per amino acid was less than 2h, using 22 optimized buffers covering a pH range from 1.5 to 12.0 at a constant ionic strength of 50mM. pK a values were calculated using an appropriate mathematical model describing the relationship between effective mobility and pH. The obtained pK a values were in accordance with the literature. Figure a UV (1) and C4D (2) detectors placed on-line on the CE capillary. b Curve of effective mobility as a function of pH for histidin

How to Increase the Safety and Efficacy of Compounds against Neurodegeneration? A Multifunctional Approach

Successful drug design requires not only the detailed knowledge of the pharmacokinetic and pharmacodynamic profiles of the drug candidate portfolio but also a thorough documentation of the possible toxic effects on humans and the environment. Thus, experimental and computational strategies able to measure or predict specific profiles of designed compounds related to their potential toxicity are highly desired. Moreover, a strategy to avoid toxic effects thus enhancing the potential efficacy of drug candidates is of great interest. To fulfil this aim, the pharmacochemistry research unit at the EPGL has recently developed and improved methodologies that detect the potential human health and environmental hazards of compounds active against neurodegeneration at an early stage. A three-step strategy is presented herein. In particular, i) an alternative index to model the bioconcentration of chemicals in the environment was determined; ii) the antioxidant activity of chemical species against free radicals was evaluated. Moreover, since antioxidants play a key role in both toxicity prevention and neuroprotection, iii) the potential interaction of such compounds with enzymatic targets involved in the neurodegenerative cascade was investigated in silico

Molecular Factors Influencing Retention on Immobilized Artificial Membranes (IAM) Compared to Partitioning in Liposomes and n -Octanol

Purpose. To assess the effect of molecular factors influencing retention on immobilized artificial membrane (IAM) high-performance liquid chromatography columns compared to liposomal partitioning and traditional n-octanol/water partition coefficients. Methods. IAM capacity factors were measured at pH 7.0 on an IAM.PC.DD2 stationary phase. Liposomal partitioning at pH 7.0 and n-octanol/water partition coefficients were measured using the pH metric method. Partitioning in egg-phosphatidylcholine (PhC) liposomes was also measured by equilibrium dialysis for a series of β-blockers. Results. For the ionized β-blockers, potentiometry and equilibrium dialysis yielded consistent partitioning data. For relatively large bases, IAM retention correlated well with PhC liposome partitioning, hydrophobic forces being mainly involved. For more hydrophilic compounds and for heterogeneous solutes, in contrast, the balance between electrostatic and hydrophobic interactions was not the same in the two systems. Hydrogen bonding, an important factor in liposomes partitioning, played only a minor role in IAM retention. Conclusions. Partitioning in immobilized artificial membranes depends on size, hydrophobicity, and charge. When hydrophobic interactions dominate retention, IAM capacity factors are well correlated with liposomal partitioning. On the contary, for hydrophilic solutes, the two systems do not yield the same information and are not interchangeabl