A High-Throughput Cell-Based Method to Predict the Unbound Drug Fraction in the Brain

Optimization of drug efficacy in the brain requires understanding of the local exposure to unbound drug at the site of action. This relies on measurements of the unbound drug fraction (<i>f</i>_u,brain), which currently requires access to brain tissue. Here, we present a novel methodology using homogenates of cultured cells for rapid estimation of <i>f</i>_u,brain. In our setup, drug binding to human embryonic kidney cell (HEK293) homogenate was measured in a small-scale dialysis apparatus. To increase throughput, we combined drugs into cassettes for simultaneous measurement of multiple compounds. Our method estimated <i>f</i>_u,brain with an average error of 1.9-fold. We propose that our simple method can be used as an inexpensive, easily available and high-throughput alternative to brain tissues excised from laboratory animals. Thereby, estimates of unbound drug exposure can now be implemented at a much earlier stage of the drug discovery process, when molecular property changes are easier to make

Rapid Measurement of Intracellular Unbound Drug Concentrations

Intracellular unbound drug concentrations determine affinity to targets in the cell interior. However, due to difficulties in measuring them, they are often overlooked in pharmacology. Here we present a simple experimental technique for the determination of unbound intracellular drug concentrations in cultured cells that is based on parallel measurements of cellular drug binding and steady-state intracellular drug concentrations. Binding in HEK293 cells was highly correlated with binding in liver-derived systems, whereas binding in plasma did not compare well with cellular binding. Compound lipophilicity increased drug binding, while negative charge and aromatic functional groups decreased binding. Intracellular accumulation of unbound drug was consistent with pH-dependent subcellular sequestration, as confirmed by modeling and by inhibition of subcellular pH gradients. The approach developed here can be used to measure intracellular unbound drug concentrations in more complex systems, for example, cell lines with controlled expression of transporters and enzymes or primary cells

Adjusted* S-digoxin means for patients taking zero, one or two Class I P-gp inhibitors

<p><b>Copyright information:</b></p><p>Taken from "Association between the number of coadministered P-glycoprotein inhibitors and serum digoxin levels in patients on therapeutic drug monitoring"</p><p>BMC Medicine 2004;2():8-8.</p><p>Published online 2 Apr 2004</p><p>PMCID:PMC411066.</p><p>Copyright © 2004 Englund et al; licensee BioMed Central Ltd. This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original URL.</p> The numbers of patients were 328, 96 and 17, respectively. The S-digoxin means ± SE (nmol/L) were 1.25 ± 0.04, 1.65 ± 0.07 and 1.83 ± 0.17. *Adjusted for age, sex, digoxin dose and total number of prescribed drugs

An Integrated <i>in Vitro</i> Model for Simultaneous Assessment of Drug Uptake, Metabolism, and Efflux

The absorption, distribution, metabolism, and excretion (ADME) of drugs <i>in vivo</i> are to a large extent dependent on different transport and metabolism routes. Elucidation of this complex transport–metabolism interplay is a major challenge in drug development and at present no <i>in vitro</i> models suitable for this purpose are at hand. The aim of this study was to develop flexible, well-controlled, easy-to-use, integrated cell models, where drug transport and drug metabolism processes could be studied simultaneously. HEK293 cells stably transfected with the organic anion transporting polypeptide 1B1 (OATP1B1) were subjected to either transient transfection or adenoviral infection to introduce the genes expressing cytochrome P450 3A4 (CYP3A4), NADPH cytochrome P450 oxidoreductase (POR), cytochrome <i>b</i>₅ (CYB5A), and multidrug resistance protein 1 (MDR1), in different combinations. Thereafter, the time and concentration-dependent transport and metabolism of two well-characterized statins, atorvastatin (acid and lactone forms) and simvastatin (acid form), were determined in the different models. The results show that CYP3A4-dependent metabolism of the more hydrophilic atorvastatin acid was dependent on OATP1B1 uptake and influenced by MDR1 efflux. In contrast, the metabolism of the more lipophilic atorvastatin lactone was not affected by active transport, whereas the metabolism of simvastatin acid was less influenced by active transport than atorvastatin acid. Our results, together with the models being applicative for any combination of drug transporters and CYP metabolizing enzymes of choice, provide proof-of-concept for the potential of the new integrated cell models presented as valuable screening tools in drug discovery and development

Comparative Proteomic Analysis of Human Liver Tissue and Isolated Hepatocytes with a Focus on Proteins Determining Drug Exposure

Freshly isolated human hepatocytes are considered the gold standard for in vitro studies of liver functions, including drug transport, metabolism, and toxicity. For accurate predictions of the in vivo outcome, the isolated hepatocytes should reflect the phenotype of their in vivo counterpart, i.e., hepatocytes in human liver tissue. Here, we quantified and compared the membrane proteomes of freshly isolated hepatocytes and human liver tissue using a label-free shotgun proteomics approach. A total of 5144 unique proteins were identified, spanning over 6 orders of magnitude in abundance. There was a good global correlation in protein abundance. However, the expression of many plasma membrane proteins was lower in the isolated hepatocytes than in the liver tissue. This included transport proteins that determine hepatocyte exposure to many drugs and endogenous compounds. Pathway analysis of the differentially expressed proteins confirmed that hepatocytes are exposed to oxidative stress during isolation and suggested that plasma membrane proteins were degraded via the protein ubiquitination pathway. Finally, using pitavastatin as an example, we show how protein quantifications can improve in vitro predictions of in vivo liver clearance. We tentatively conclude that our data set will be a useful resource for improved hepatocyte predictions of the in vivo outcome

Optimizing Solubility and Permeability of a Biopharmaceutics Classification System (BCS) Class 4 Antibiotic Drug Using Lipophilic Fragments Disturbing the Crystal Lattice

Esterification was used to simultaneously increase solubility and permeability of ciprofloxacin, a biopharmaceutics classification system (BCS) class 4 drug (low solubility/low permeability) with solid-state limited solubility. Molecular flexibility was increased to disturb the crystal lattice, lower the melting point, and thereby improve the solubility, whereas lipophilicity was increased to enhance the intestinal permeability. These structural changes resulted in BCS class 1 analogues (high solubility/high permeability) emphasizing that simple medicinal chemistry may improve both these properties

Classification of Inhibitors of Hepatic Organic Anion Transporting Polypeptides (OATPs): Influence of Protein Expression on Drug–Drug Interactions

The hepatic organic anion transporting polypeptides (OATPs) influence the pharmacokinetics of several drug classes and are involved in many clinical drug–drug interactions. Predicting potential interactions with OATPs is, therefore, of value. Here, we developed in vitro and in silico models for identification and prediction of specific and general inhibitors of OATP1B1, OATP1B3, and OATP2B1. The maximal transport activity (MTA) of each OATP in human liver was predicted from transport kinetics and protein quantification. We then used MTA to predict the effects of a subset of inhibitors on atorvastatin uptake in vivo. Using a data set of 225 drug-like compounds, 91 OATP inhibitors were identified. In silico models indicated that lipophilicity and polar surface area are key molecular features of OATP inhibition. MTA predictions identified OATP1B1 and OATP1B3 as major determinants of atorvastatin uptake in vivo. The relative contributions to overall hepatic uptake varied with isoform specificities of the inhibitors

Exploration and Pharmacokinetic Profiling of Phenylalanine Based Carbamates as Novel Substance P 1–7 Analogues

The bioactive metabolite of Substance P, the heptapeptide SP_1–7 (H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-OH), has been shown to attenuate signs of hyperalgesia in diabetic mice, which indicate a possible use of compounds targeting the SP_1–7 binding site as analgesics for neuropathic pain. Aiming at the development of drug-like SP_1–7 peptidomimetics we have previously reported on the discovery of H-Phe-Phe-NH₂ as a high affinity lead compound. Unfortunately, the pharmacophore of this compound was accompanied by a poor pharmacokinetic (PK) profile. Herein, further lead optimization of H-Phe-Phe-NH₂ by substituting the N-terminal phenylalanine for a benzylcarbamate group giving a new type of SP_1–7 analogues with good binding affinities is reported. Extensive <i>in vitro</i> as well as <i>in vivo</i> PK characterization is presented for this compound. Evaluation of different C-terminal functional groups, i.e., hydroxamic acid, acyl sulfonamide, acyl cyanamide, acyl hydrazine, and oxadiazole, suggested hydroxamic acid as a bioisosteric replacement for the original primary amide

Achiral Pyrazinone-Based Inhibitors of the Hepatitis C Virus NS3 Protease and Drug-Resistant Variants with Elongated Substituents Directed Toward the S2 Pocket

Herein we describe the design, synthesis, inhibitory potency, and pharmacokinetic properties of a novel class of achiral peptidomimetic HCV NS3 protease inhibitors. The compounds are based on a dipeptidomimetic pyrazinone glycine P3P2 building block in combination with an aromatic acyl sulfonamide in the P1P1′ position. Structure–activity relationship data and molecular modeling support occupancy of the S2 pocket from elongated R⁶ substituents on the 2­(1<i>H</i>)-pyrazinone core and several inhibitors with improved inhibitory potency down to <i>K</i>_i = 0.11 μM were identified. A major goal with the design was to produce inhibitors structurally dissimilar to the di- and tripeptide-based HCV protease inhibitors in advanced stages of development for which cross-resistance might be an issue. Therefore, the retained and improved inhibitory potency against the drug-resistant variants A156T, D168V, and R155K further strengthen the potential of this class of inhibitors. A number of the inhibitors were tested in in vitro preclinical profiling assays to evaluate their apparent pharmacokinetic properties. The various R⁶ substituents were found to have a major influence on solubility, metabolic stability, and cell permeability

Novel Peptidomimetic Hepatitis C Virus NS3/4A Protease Inhibitors Spanning the P2–P1′ Region

Herein, novel hepatitis C virus NS3/4A protease inhibitors based on a P2 pyrimidinyloxyphenylglycine in combination with various regioisomers of an aryl acyl sulfonamide functionality in P1 are presented. The P1′ 4-(trifluoromethyl)­phenyl side chain was shown to be particularly beneficial in terms of inhibitory potency. Several inhibitors with <i>K</i>_i-values in the nanomolar range were developed and included identification of promising P3-truncated inhibitors spanning from P2–P1′. Of several different P2 capping groups that were evaluated, a preference for the sterically congested Boc group was revealed. The inhibitors were found to retain inhibitory potencies for A156T, D168V, and R155K variants of the protease. Furthermore, in vitro pharmacokinetic profiling showed several beneficial effects on metabolic stability as well as on apparent intestinal permeability from both P3 truncation and the use of the P1′ 4-(trifluoromethyl)­phenyl side chain