Bernard Faller

Coexistence of passive and carrier-mediated processes in drug transport.

The permeability of biological membranes is one of the most important determinants of the pharmacokinetic processes of a drug. Although it is often accepted that many drug substances are transported across biological membranes by passive transcellular diffusion, a recent hypothesis speculated that carrier-mediated mechanisms might account for the majority of membrane drug transport processes in biological systems. Based on evidence of the physicochemical characteristics and of in vitro and in vivo findings for marketed drugs, as well as results from real-life discovery and development projects, we present the view that both passive transcellular processes and carrier-mediated processes coexist and contribute to drug transport activities across biological membranes.

Alkylamides from Echinacea Are a New Class of Cannabinomimetics CANNABINOID TYPE 2 RECEPTOR-DEPENDENT AND -INDEPENDENT IMMUNOMODULATORY EFFECTS

Alkylamides (alkamides) from Echinacea modulate tumor necrosis factor α mRNA expression in human monocytes/macrophages via the cannabinoid type 2 (CB2) receptor (Gertsch, J., Schoop, R., Kuenzle, U., and Suter, A. (2004) FEBS Lett. 577, 563–569). Here we show that the alkylamides dodeca-2E,4E,8Z,10Z-tetraenoic acid isobutylamide (A1) and dodeca-2E,4E-dienoic acid isobutylamide (A2) bind to the CB2 receptor more strongly than the endogenous cannabinoids. The Ki values of A1 and A2 (CB2 ∼60 nm;CB1 >1500 nm) were determined by displacement of the synthetic high affinity cannabinoid ligand [3H]CP-55,940. Molecular modeling suggests that alkylamides bind in the solvent-accessible cavity in CB2, directed by H-bonding and π -π interactions. In a screen with 49 other pharmacologically relevant receptors, it could be shown that A1 and A2 specifically bind to CB2 and CB1. A1 and A2 elevated total intracellular Ca2+ in CB2-positive but not in CB2-negative promyelocytic HL60 cells, an effect that was inhibited by the CB2 antagonist SR144528. At 50 nm, A1, A2, and the endogenous cannabinoid anandamide (CB2 Ki >200 nm) up-regulated constitutive interleukin (IL)-6 expression in human whole blood in a seemingly CB2-dependent manner. A1, A2, anandamide, the CB2 antagonist SR144528 (Ki <10 nm), and also the non-CB2-binding alkylamide undeca-2E-ene,8,10-diynoic acid isobutylamide all significantly inhibited lipopolysaccharide-induced tumor necrosis factor α, IL-1β, and IL-12p70 expression (5–500 nm) in a CB2-independent manner. Alkylamides and anandamide also showed weak differential effects on anti-CD3-versus anti-CD28-stimulated cytokine expression in human whole blood. Overall, alkylamides, anandamide, and SR144528 potently inhibited lipopolysaccharide-induced inflammation in human whole blood and exerted modulatory effects on cytokine expression, but these effects are not exclusively related to CB2 binding.

Modeling Promiscuity Based on in vitro Safety Pharmacology Profiling Data

This study describes a method for mining and modeling binding data obtained from a large panel of targets (in vitro safety pharmacology) to distinguish differences between promiscuous and selective compounds. Two naïve Bayes models for promiscuity and selectivity were generated and validated on a test set as well as publicly available drug databases. The model shows a higher score (lower promiscuity) for marketed drugs than for compounds in early development or compounds that failed during clinical development. Such models can be used in triaging high‐throughput screening data or for lead optimization.

4‐[3,5‐Bis(2‐hydroxyphenyl)‐1,2,4‐triazol‐1‐yl]‐ benzoic Acid: A Novel Efficient and Selective Iron(III) Complexing Agent

An exceptionally stable 1:2 complex [FeL2]3− is formed from the ligand H3L and FeIII. In contrast, the affinity of this ligand for other biometals is relatively small. These properties make H3L a highly promising candidate for medical applications (e.g. for the treatment of iron overload).

Metabolic soft spot identification and compound optimization in early discovery phases using MetaSite and LC-MS/MS validation.

Metabolic stability is a key property to enable drugs to reach therapeutic concentrations. Microsomal clearance assays are used to dial out labile compounds in early discovery phases. However, because they do not provide any information on soft spots, the rational design of more stable compounds remains challenging. A robust soft spot identification procedure combining in silico prediction ranking using MetaSite and mass-spectrometric confirmation is described. MetaSites first rank order predictions were experimentally confirmed for only about 55% of the compounds. For another 29% of the compounds, the second (20%) or the third (9%) rank order predictions were detected. This automatic and high-throughput reprioritization of a likely soft-spot increases the likelihood of working on the right soft spot from about 50% to more than 80%. With this information, the structure-metabolism relationships are likely to be understood faster and earlier in drug discovery.

The Identification of Indacaterol as an Ultralong-Acting Inhaled β2-Adrenoceptor Agonist

Following a lipophilicity-based hypothesis, an 8-hydroxyquinolinone 2-aminoindan derived series of beta(2)-adrenoceptor agonists have been prepared and evaluated for their potential as inhaled ultralong-acting bronchodilators. Determination of their activities at the human beta(2)-adrenoceptor receptor showed symmetrical substitution of the 2-aminoindan moiety at the 5- and 6-positions delivered the targeted intermediate potency and intrinsic-efficacy profiles relative to a series of clinical reference beta(2)-adrenoceptor agonists. Further assessment with an in vitro superfused electrically stimulated guinea-pig tracheal-strip assay established the onset and duration of action time courses, which could be rationalized by considering the lipophilicity, potency, and intrinsic efficacy of the compounds. From these studies the 5,6-diethylindan analogue indacaterol 1c was shown to possess a unique profile of combining a rapid onset of action with a long duration of action. Further in vivo profiling of 1c supported the long duration of action and a wide therapeutic index following administration to the lung, which led to the compound being selected as a development candidate.

ICL670A: Preclinical Profile

Man is unable to actively eliminate iron from the body, once it has been acquired. Toxic and eventually lethal levels of iron accumulate as a result of repeated transfusions, e.g. in s-thalassemia major, or due to excessive dietary iron uptake in anemias and hereditary hemochromatosis. Excess iron is deposited in the form of hemosiderins (insoluble “iron cores” of ferritin) mainly in the liver, spleen, many endocrine organs and in the myocardium. The exact mechanism of iron damage to these tissues is unknown, but it is established that organ failure correlates with iron burden in these tissues. Except for infectious diseases, cardiac complications are the major cause of death in s-thalassemia major patients.

Evidence-based approach to assess passive diffusion and carrier-mediated drug transport.

Evidence supporting the action of passive diffusion and carrier-mediated (CM) transport in drug bioavailability and disposition is discussed to refute the recently proposed theory that drug transport is CM-only and that new transporters will be discovered that possess transport characteristics ascribed to passive diffusion. Misconceptions and faulty speculations are addressed to provide reliable guidance on choosing appropriate tools for drug design and optimization.

Passive lipoidal diffusion and carrier-mediated cell uptake are both important mechanisms of membrane permeation in drug disposition

Recently, it has been proposed that drug permeation is essentially carrier-mediated only and that passive lipoidal diffusion is negligible. This opposes the prevailing hypothesis of drug permeation through biological membranes, which integrates the contribution of multiple permeation mechanisms, including both carrier-mediated and passive lipoidal diffusion, depending on the compounds properties, membrane properties, and solution properties. The prevailing hypothesis of drug permeation continues to be successful for application and prediction in drug development. Proponents of the carrier-mediated only concept argue against passive lipoidal diffusion. However, the arguments are not supported by broad pharmaceutics literature. The carrier-mediated only concept lacks substantial supporting evidence and successful applications in drug development.

Evolution of the physicochemical properties of marketed drugs: can history foretell the future?

A set of diverse bioactive molecules, relevant from a medicinal chemistry viewpoint, was assembled and used to navigate the physicochemical property space of new and old, or traditional drugs against a larger set of 12,000 diverse bioactive small molecules. Most drugs on the market only occupy a fraction of the property space of the bioactive molecules, whereas new molecular entities (NMEs) approved since 2002 are moving away from this traditional drug space. In this new territory, semi-empirical rules derived from knowledge accumulated from historic, older molecules are not necessarily valid and different liabilities become more prominent.