Predictive, non-GLP models of secondary pharmacodynamics: putting the best compounds forward

Toxicology Strategies for Drug Discovery: Present and Future

Attrition due to nonclinical safety represents a major issue for the productivity of pharmaceutical research and development (R&D) organizations, especially during the compound optimization stages of drug discovery and the early stages of clinical development. Focusing on decreasing nonclinical safety-related attrition is not a new concept, and various approaches have been experimented with over the last two decades. Front-loading testing funnels in Discovery with in vitro toxicity assays designed to rapidly identify unfavorable molecules was the approach adopted by most pharmaceutical R&D organizations a few years ago. However, this approach has also a non-negligible opportunity cost. Hence, significant refinements to the "fail early, fail often" paradigm have been proposed recently to reflect the complexity of accurately categorizing compounds with early data points without taking into account other important contextual aspects, in particular efficacious systemic and tissue exposures. This review provides an overview of toxicology approaches and models that can be used in pharmaceutical Discovery at the series/lead identification and lead optimization stages to guide and inform chemistry efforts, as well as a personal view on how to best use them to meet nonclinical safety-related attrition objectives consistent with a sustainable pharmaceutical R&D model. The scope of this review is limited to small molecules, as large molecules are associated with challenges that are quite different. Finally, a perspective on how several emerging technologies may impact toxicity evaluation is also provided.

Application of data mining and visualization techniques for the prediction of drug-induced nausea in man

The therapeutic value of many drugs can be limited by gastrointestinal (GI) adverse effects such as nausea and vomiting. Nausea is a subjective human sensation, hence little is known about preclinical biomarkers that may accurately and effectively predict its presence in man. The aim of this analysis was to use informatics and data-mining tools to identify plausible preclinical GI effects that may be associated with nausea and that could be of potential use in its prediction. A total of 86 marketed drugs were used in this analysis, and the main outcome was a confirmation that nausogenic and non-nausogenic drugs can be clearly separated based on their preclinical GI observations. Specifically, combinations of common preclinical GI effects (vomiting, diarrhea, and salivary hypersecretion) proved to be strong predictors. The model was subsequently validated with a subset of 20 blinded proprietary small molecules and successfully predicted clinical outcome in 90% of cases. This investigation demonstrated the feasibility of data-mining approaches to facilitate discovery of novel, plausible associations that can be used to understand drug-induced adverse effects.

Cardiovascular Function in Nonclinical Drug Safety Assessment

There are several recent examples where clinically significant, safety-related, drug effects on hemodynamics or cardiac function were not apparent until large clinical trials were completed or the drugs entered the consumer market. Such late-stage safety issues can have significant impact on patient health and consumer confidence, as well as ramifications for the regulatory, pharmaceutical, and financial communities. This manuscript provides recommendations that evolved from a 2009 HESI workshop on the need for improved translation of nonclinical cardiovascular effects to the clinical arena. The authors conclude that expanded and improved efforts to perform sensitive yet specific evaluations of functional cardiovascular parameters in nonclinical studies will allow pharmaceutical companies to identify suspect drugs early in the discovery and development process while allowing promising drugs to proceed into clinical development.

Preclinical characterization of A-582941: a novel alpha7 neuronal nicotinic receptor agonist with broad spectrum cognition-enhancing properties

Among the diverse sets of nicotinic acetylcholine receptors (nAChRs), the alpha7 subtype is highly expressed in the hippocampus and cortex and is thought to play important roles in a variety of cognitive processes. In this review, we describe the properties of a novel biaryl diamine alpha7 nAChR agonist, A-582941. A-582941 was found to exhibit high-affinity binding and partial agonism at alpha7 nAChRs, with acceptable pharmacokinetic properties and excellent distribution to the central nervous system (CNS). In vitro and in vivo studies indicated that A-582941 activates signaling pathways known to be involved in cognitive function such as ERK1/2 and CREB phosphorylation. A-582941 enhanced cognitive performance in behavioral models that capture domains of working memory, short-term recognition memory, memory consolidation, and sensory gating deficit. A-582941 exhibited a benign secondary pharmacodynamic and tolerability profile as assessed in a battery of assays of cardiovascular, gastrointestinal, and CNS function. The studies summarized in this review collectively provide preclinical validation that alpha7 nAChR agonism offers a mechanism with potential to improve cognitive deficits associated with various neurodegenerative and psychiatric disorders.

N-{3-[2-(4-Alkoxyphenoxy)thiazol-5-yl]-1-methylprop-2-ynyl}carboxy Derivatives as Acetyl-CoA Carboxylase InhibitorsImprovement of Cardiovascular and Neurological Liabilities via Structural Modifications

A preliminary safety evaluation of ACC2 inhibitor 1-(S) revealed serious neurological and cardiovascular liabilities of this chemotype. A systematic structure-toxicity relationship study identified the alkyne linker as the key motif responsible for these adverse effects. Toxicogenomic studies in rats showed that 1-(R) and 1-(S) induced gene expression patterns similar to that seen with several known cardiotoxic agents such as doxorubicin. Replacement of the alkyne with alternative linker groups led to a new series of ACC inhibitors with drastically improved cardiovascular and neurological profiles.

Hemodynamic effects of potent and selective JNK inhibitors in anesthetized rats: Implication for targeting protein kinases in metabolic diseases

The hemodynamic effects of a series of potent and selective 4-aminopyridine carboxamide-based pan-JNK inhibitors were assessed in an anesthetized rat model. The effects of these agents on mean arterial pressure, heart rate, cardiac contractility, and peripheral vascular resistance are described, and the implication for targeting protein kinases in metabolic diseases is discussed.

Screening for cardiovascular safety: a structure-activity approach for guiding lead selection of melanin concentrating hormone receptor 1 antagonists

An inactin-anesthetized rat cardiovascular (CV) assay was employed in a screening mode to triage multiple classes of melanin-concentrating hormone receptor 1 (MCHr1) antagonists. Lead identification was based on a compound profile producing high drug concentration in both plasma (>40 microM) and brain (>20 microg/g) with <15% change in cardiovascular endpoints. As a result of these stringent requirements, lead optimization activities on multiple classes of MCHr1 antagonists were terminated. After providing evidence that the cardiovascular liabilities were not a function of MCHr1 antagonism, continued screening identified the chromone-substituted aminopiperidine amides as a class of MCHr1 antagonists that demonstrated a safe cardiovascular profile at high drug concentrations in both plasma and brain. The high incidence of adverse cardiovascular effects associated with an array of MCHr1 antagonists of significant chemical diversity, combined with the stringent safety requirements for antiobesity drugs, highlight the importance of incorporating cardiovascular safety assessment early in the lead selection process.

Differentiation of Arrhythmia Risk of the Antibacterials Moxifloxacin, Erythromycin, and Telithromycin Based on Analysis of Monophasic Action Potential Duration Alternans and Cardiac Instability

Antibacterial drugs are known to have varying degrees of cardiovascular liability associated with QT prolongation that can lead to the ventricular arrhythmia torsade de pointes. The purpose of these studies was to compare the assessment for the arrhythmogenic risk of moxifloxacin, erythromycin, and telithromycin. Each drug caused dose-dependent inhibition of the rapidly activating delayed rectifier potassium current encoded by the human ether-á-go-go-related gene (hERG) with IC20 concentrations of 31 microM (moxifloxacin), 21 microM (erythromycin), and 11 microM (telithromycin). These drugs were also evaluated in an anesthetized guinea pig model to measure changes in monophasic action potential duration (MAPD) and to quantify beat-to-beat alternations in MAPD during rapid ventricular pacing. Moxifloxacin dose dependently increased MAPD and caused a rate-dependent increase in alternans at the highest achieved free drug concentration (41 microM). Erythromycin also increased MAPD at its highest free drug concentration (58 microM), but alternans occurred at a relatively lower therapeutic multiple (13.9 microM), and the magnitude of alternans at higher concentrations was independent of pacing rate. Further analysis of the data showed that the beat-to-beat pattern of alternans with erythromycin was less stable than that with moxifloxacin and suggestive of greater arrhythmogenic liability. In contrast to erythromycin and moxifloxacin, telithromycin decreased both MAPD and alternans at the highest achievable drug concentration (7.9 microM). The relative risk at therapeutic concentrations is erythromycin>moxifloxacin>telithromycin and appears to be consistent with clinical observations of torsade de pointes in patients.