Sandra A. G. Visser

Model-based drug discovery: implementation and impact.

Model-based drug discovery (MBDDx) aims to build and continuously improve the quantitative understanding of the relation between drug exposure (target engagement) efficacy and safety, to support target validation; to define compound property criteria for lead optimization and safety margins; to set the starting dose; and to predict human dose and scheduling for clinical candidates alone, or in combination with other medicines. AstraZeneca has systematically implemented MBDDx within all drug discovery programs, with a focused investment to build a preclinical modeling and simulation capability and an in vivo information platform and architecture, the implementation, impact and learning of which are discussed here.

Translational pharmacokinetic-pharmacodynamic modeling of QTc effects in dog and human.

INTRODUCTION Preclinical assessment of the heart rate corrected QT interval (QTc) is an important component of the cardiovascular safety evaluation in drug discovery. Here we aimed to quantify the translational relationship between QTc prolongation and shortening in the conscious telemetered dog and humans by a retrospective pharmacokinetic-pharmacodynamic (PKPD) analysis. METHODS QTc effects of 2 proprietary compounds and 2 reference drugs (moxifloxacin and dofetilide) were quantified in conscious dogs and healthy volunteers via a linear and Emax pharmacokinetic-pharmacodynamic models. The translational relationship was quantified by correlating the QTc response from dog and human at matching free drug concentrations. RESULTS A consistent translational relationship was found at low delta-QTc intervals indicating that a QTc change of 2.5-8 ms in dog would correspond to a 10 ms change in human. DISCUSSION The translational relationship developed here can be used to predict the QTc liability in human using preclinical dog data. It could therefore help protect the health of human volunteers, for example by appropriate clinical study design and dose selection, as well as improve future decision-making and help reduce compound attrition due to changes in QT interval.

Has inhibition of Aβ production adequately been tested as therapeutic approach in mild AD? A model-based meta-analysis of γ-secretase inhibitor data.

PurposeTo date, γ-secretase inhibition is the most frequently studied mechanism of reducing Aβ in clinical trials with as yet no therapeutic success for AD patients, as measured by the slowing down of cognitive decline or an improvement in cognitive function. The aims of this investigation were to evaluate whether the amyloid hypothesis has been tested clinically, and to explore whether preclinical data are predictive of clinical Aβ effects.MethodsA model-based-meta analysis on Aβ levels and drug exposure over time was performed on published and in-house (pre-)clinical data with γ-secretase inhibitors (GSIs; semagacestat, avagacestat, begacestat, PF-3074014, and MK0752).ResultsThe clinical data available did not show any significant or robust reduction of CNS Aβ over time at dose levels intended for AD patients. In contrast, these doses resulted in an average increase in plasma Aβ levels over a 24-h interval. A general agreement between preclinical and clinical data was found and allowed for interspecies extrapolations.ConclusionsMore substantially, CNS Aβ-lowering drugs are needed to test whether inhibition of Aβ production is efficacious in mild AD. Predictions based on preclinical data could assist in the selection of drug candidates and trial design.

High-performance liquid chromatography of the neuroactive steroids alphaxalone and pregnanolone in plasma using dansyl hydrazine as fluorescent label : application to a pharmacokinetic-pharmacodynamic study in rats

This report describes a rapid and sensitive analytical method for the quantification of the neuroactive steroids alphaxalone and pregnanolone in rat plasma using derivatization with dansyl hydrazine as fluorescent label. The method involves protein precipitation, alkaline derivatization and extraction of the compounds and internal standard pregnenolone with dichloromethane, followed by isocratic reversed-phase high-performance liquid chromatography on a 3-microm Microsphere C18 column with fluorescence detection at wavelengths 332 nm and 516 nm for excitation and emission, respectively. The mobile phase consists of a mixture of 25 mM acetate buffer (pH 3.7)-acetonitrile (45:55, v/v for alphaxalone and 40:60, v/v for pregnanolone) with a flow-rate of 1 ml/min. The total run time was approximately 35 min. In the concentration range of 0.010-10 microg ml(-1), the intra- and inter-assay coefficients of variation were less than 17% for both methods. In 50 microl plasma samples the corresponding limits of detection were 10 ng ml(-1) (signal-to-noise ratio=3). The utility of the analytical method was established by analyzing plasma samples from rats, which had received an intravenous administration of 5 mg kg(-1) alphaxalone or pregnanolone. Values for clearance, volume of distribution at steady state and terminal half life were 71.9 ml min(-1) kg(-1), 814 mg kg(-1) and 13.5 min for alphaxalone and 69.2 ml min(-1) kg(-1), 1,638 ml kg(-1) and 27.8 min for pregnanolone, respectively. Due to its simplicity and sensitivity this method can be used on a routine basis for pharmacokinetic analysis of neuroactive steroids.

The virtue of translational PKPD modeling in drug discovery: selecting the right clinical candidate while sparing animal lives.

Translational pharmacokinetic-pharmacodynamic (PKPD) modeling has been fully implemented at AstraZenecas drug discovery unit for central nervous system and pain indications to facilitate timely progression of the right compound to clinical studies, simultaneously assuring essential preclinical efficacy and safety knowledge. This review illustrates the impact of a translational PKPD paradigm with examples from drug discovery programs. Paradoxically, laboratory animal use decreased owing to better understanding of in vitro-in vivo relationships, optimized in vivo study designs, meta-analyses and hypothesis testing using simulations. From an ethical and effectivity perspective, we advocate that translational PKPD approaches should be implemented more broadly in drug discovery.

Interplay between α-, β-, and γ-Secretases Determines Biphasic Amyloid-β Protein Level in the Presence of a γ-Secretase Inhibitor

Background: Moderate concentrations of γ-secretase inhibitor increase Aβ production in different scenarios from cell lines to humans. Results: A mathematical model, including α-, β-, and γ-secretases, is proposed describing Aβ rise. Conclusion: The Aβ rise is decided by the interplay between the three secretases and not γ-secretase alone. Significance: This has important implications for the development of drugs targeting Aβ production in Alzheimer disease. Amyloid-β (Aβ) is produced by the consecutive cleavage of amyloid precursor protein (APP) first by β-secretase, generating C99, and then by γ-secretase. APP is also cleaved by α-secretase. It is hypothesized that reducing the production of Aβ in the brain may slow the progression of Alzheimer disease. Therefore, different γ-secretase inhibitors have been developed to reduce Aβ production. Paradoxically, it has been shown that low to moderate inhibitor concentrations cause a rise in Aβ production in different cell lines, in different animal models, and also in humans. A mechanistic understanding of the Aβ rise remains elusive. Here, a minimal mathematical model has been developed that quantitatively describes the Aβ dynamics in cell lines that exhibit the rise as well as in cell lines that do not. The model includes steps of APP processing through both the so-called amyloidogenic pathway and the so-called non-amyloidogenic pathway. It is shown that the cross-talk between these two pathways accounts for the increase in Aβ production in response to inhibitor, i.e. an increase in C99 will inhibit the non-amyloidogenic pathway, redirecting APP to be cleaved by β-secretase, leading to an additional increase in C99 that overcomes the loss in γ-secretase activity. With a minor extension, the model also describes plasma Aβ profiles observed in humans upon dosing with a γ-secretase inhibitor. In conclusion, this mechanistic model rationalizes a series of experimental results that spans from in vitro to in vivo and to humans. This has important implications for the development of drugs targeting Aβ production in Alzheimer disease.

Using pharmacokinetic modeling to determine the effect of drug and food on gastrointestinal transit in dogs

INTRODUCTION The gastrointestinal (GI) tract is one of the target organs of adverse drug effects in different phases of drug development. This study aimed to investigate the feasibility of population pharmacokinetic modeling to quantify the rate of gastric emptying (GE) and small intestinal transit time (SITT) in response to drugs that affect GI motility in fed and fasted dogs. Paracetamol and sulfapyridine (sulfasalazine metabolite) pharmacokinetics were used as markers for GE and SITT, respectively. METHODS In two separate studies, under fed and fasted conditions, six male beagle dogs received a 15min intravenous infusion of vehicle, atropine (0.06mg/kg) or erythromycin (1mg/kg) followed by an intragastric administration of a mixture of paracetamol (24mg/kg) and sulfasalazine (20mg/kg). Food was given just before or at 6h after drug administration in the fed and fasted study, respectively. Blood samples were collected for analysis of paracetamol and sulfapyridine in plasma. Population pharmacokinetic analysis of paracetamol and sulfapyridine in plasma was used to determine the rate of GE and SITT. RESULTS The quantitative parameter estimates demonstrated a detailed and significant influence of atropine, erythromycin and food on GE and SITT. Compared to fasted conditions food intake delayed GE in pharmacologically treated dogs and SITT was shortened after treatment with vehicle or erythromycin. Atropine substantially delayed GE in fed and fasted conditions but the effect on SITT was evident only under fed condition. Erythromycin, in contrast, increased GE only in fasted conditions, and generally delayed SITT. DISCUSSION Population pharmacokinetic modeling of paracetamol and sulfapyridine provides a suitable preclinical non-invasive experimental method for quantification of drug- and food-induced changes in the rate of GE and SITT in conscious beagle dogs for use in safety evaluations to predict changes in GI transit and/or to explain the pharmacokinetic profile of drugs under development.

Decreased axonal transport rates in the Tg2576 APP transgenic mouse: improvement with the gamma-secretase inhibitor MRK-560 as detected by manganese-enhanced MRI.

Neuropil deposition of beta‐amyloid (Aβ) peptides is believed to be a key event in the neurodegenerative process of Alzheimer’s disease (AD). An early and consistent clinical finding in AD is olfactory dysfunction with associated pathology. Interestingly, transgenic amyloid precursor protein (Tg2576) mice also show early amyloid pathology in olfactory regions. Moreover, a recent study indicates that axonal transport is compromised in the olfactory system of Tg2576 mice, as measured by manganese‐enhanced magnetic resonance imaging (MEMRI). Here we tested whether the putative axonal transport deficit in the Tg2576 mouse model improves in response to a selective gamma‐secretase inhibitor, N‐[cis‐4‐[(4‐chlorophenyl)‐sulfonyl]‐4‐(2,5‐difluorophenyl)cyclohexyl]‐1,1,1‐trifluoromethanesulfonamide (MRK‐560). Tg2576 mice or wild‐type (WT) littermates were treated daily with MRK‐560 (30 μmol/kg) or vehicle for 4 (acute) or 29 days (chronic). The subsequent MEMRI analysis revealed a distinct axonal transport dysfunction in the Tg2576 mice compared with its littermate controls. Interestingly, the impairment of axonal transport could be fully reversed by chronic administration of MRK‐560, in line with the significantly lowered levels of both soluble and insoluble forms of Aβ found in the brain and olfactory bulbs (OBs) following treatment. However, no improvement of axonal transport was observed after acute treatment with MRK‐560, where soluble but not insoluble forms of Aβ were reduced in the brain and OBs. The present results show that axonal transport is impaired in Tg2576 mice compared with WT controls, as measured by MEMRI. Chronic treatment in vivo with a gamma‐secretase inhibitor, MRK‐560, significantly reduces soluble and insoluble forms of Aβ, and fully reverses the axonal transport dysfunction.

Correct assessment of new compounds using in vivo screening models can reduce false positives.

During early drug discovery the initial in vivo efficacy testing is often performed in rodent models optimized to screen and select lead compounds rapidly, before progressing them to in vivo models that reflect the human form of the disease more closely. The way such models are frequently run can risk overestimating the efficacy of new compounds when using pre- and co-administration, as shown in three examples from different central nervous system research areas. This is undesirable for reasons ranging from good decision-making, cost efficiency and time management to the ethics of animal use. Abandoning the use of pre-treatment, monitoring crucial physiological parameters in (satellite) animals and systematically applying simple pharmacokinetic-pharmacodynamic analysis could reduce the number of false positive results.

Optimization of human dose prediction by using quantitative and translational pharmacology in drug discovery

In this perspective article, we explain how quantitative and translational pharmacology, when well-implemented, is believed to lead to improved clinical candidates and drug targets that are differentiated from current treatment options. Quantitative and translational pharmacology aims to build and continuously improve the quantitative relationship between drug exposure, target engagement, efficacy, safety and its interspecies relationship at every phase of drug discovery. Drug hunters should consider and apply these concepts to develop compounds with a higher probability of interrogating the clinical biological hypothesis. We offer different approaches to set an initial effective concentration or pharmacokinetic-pharmacodynamic target in man and to predict human pharmacokinetics that determine together the predicted human dose and dose schedule. All concepts are illustrated with ample literature examples.