Optimizing the science of drug development: opportunities for better candidate selection and accelerated evaluation in humans

Absolute Bioavailability, Tissue Distribution, and Excretion of Erinacine S in Hericium erinaceus Mycelia

Erinacine S, so far known to have been produced only in Hericium erinaceus mycelia, has just recently been discovered and is able to reduce amyloid plaque growth and improve neurogenesis in aged brain of rats. However, few investigations have been conducted on the absorption, distribution, and excretion study of Erinacine S. This study aimed to investigate the absolute bioavailability, tissue distribution, and excretion of Erinacine S in H. Erinaceus mycelia in eight-week old Sprague-Dawley rats. After oral administration and intravenous administration of 2.395 g/kg body weight of the H. erinaceus mycelia extract (equivalent to 50 mg/kg body weight Erinacine S) and 5 mg/kg of Erinacine S, respectively, the absolute bioavailability was estimated as 15.13%. In addition, Erinacine S was extensively distributed in organs such as brain, heart, lung, liver, kidney, stomach, small intestine, and large intestine. The maximum concentration of Erinacine S was observed in the stomach, 2 h after the oral administration of H. erinaceus mycelia extract, whereas the maximum amount of Erinacine S found in other tissues were seen after 8 h. Total amount of unconverted Erinacine S eliminated in feces and urine in 24 h was 0.1% of the oral dosage administrated. This study is the first to show that Erinacine S can penetrate the blood–brain barrier of rats and thus support the development of H. erinaceus mycelia, for the treatment of neurological diseases.

Pharmacologic management of Duchenne muscular dystrophy: target identification and preclinical trials

Duchenne muscular dystrophy (DMD) is an X-linked human disorder in which absence of the protein dystrophin causes degeneration of skeletal and cardiac muscle. For the sake of treatment development, over and above definitive genetic and cell-based therapies, there is considerable interest in drugs that target downstream disease mechanisms. Drug candidates have typically been chosen based on the nature of pathologic lesions and presumed underlying mechanisms and then tested in animal models. Mammalian dystrophinopathies have been characterized in mice (mdx mouse) and dogs (golden retriever muscular dystrophy [GRMD]). Despite promising results in the mdx mouse, some therapies have not shown efficacy in DMD. Although the GRMD model offers a higher hurdle for translation, dogs have primarily been used to test genetic and cellular therapies where there is greater risk. Failed translation of animal studies to DMD raises questions about the propriety of methods and models used to identify drug targets and test efficacy of pharmacologic intervention. The mdx mouse and GRMD dog are genetically homologous to DMD but not necessarily analogous. Subcellular species differences are undoubtedly magnified at the whole-body level in clinical trials. This problem is compounded by disparate cultures in clinical trials and preclinical studies, pointing to a need for greater rigor and transparency in animal experiments. Molecular assays such as mRNA arrays and genome-wide association studies allow identification of genetic drug targets more closely tied to disease pathogenesis. Genes in which polymorphisms have been directly linked to DMD disease progression, as with osteopontin, are particularly attractive targets.

Establishment and validation of a rabbit model for in vivo pharmacodynamic screening of tachykinin NK2 antagonists

We attempted to establish and validate an in vivo pharmacodynamic (PD) rabbit model to screen tachykinin NK(2) receptor (NK(2)-R) antagonists using pharmacological and pharmacokinetic (PK)/PD analyses. Under urethane anesthesia, changes in intracolonic pressure associated with intravenous (i.v.) administration of a selective NK(2)-R agonist, βAla(8)-neurokinin A(4-10) (βA-NKA), was monitored as a PD marker. The analgesic effects of NK(2)-R antagonists were evaluated by monitoring visceromotor response (VMR) to colorectal distension in a rabbit model of visceral hypersensitivity induced by intracolonic treatment of acetic acid. Intravenous administration of βA-NKA induced transient colonic contractions dose-dependently, which were inhibited by the selective NK(2)-R antagonists in dose- and/or plasma concentration-dependent manners. The correlation between PD inhibition and plasma concentration normalized with the corresponding in vitro binding affinity was relatively high (r(2) = 0.61). Furthermore, the minimum effective doses on the VMR and ID(50) values calculated in the PD model were highly correlated (r(2) = 0.74). In conclusion, we newly established and validated a rabbit model of agonist-induced colonic contractions as a screening tool for NK(2)-R antagonists. In a drug discovery process, this PD model could enhance the therapeutic candidate selection for irritable bowel syndrome, pharmacologically connecting in vitro affinity for NK(2)-R with in vivo therapeutic efficacy.

A decision-support tool for the formulation of orally active, poorly soluble compounds

Physicochemical data for a set of potentially poorly soluble compounds was analysed in relation to suitable formulations for these compounds. Physical chemistry was found to be a key determinant of formulation class expressed in terms of conventional, solid dispersion, lipidic/surfactant, and crystalline nanoparticle systems. This relationship was used to build a decision-support tool aimed to guide formulation selection for poorly soluble compounds during product development. Tool components included a user interface, a database of compound cases together with known formulations, and predictive modules based on statistics, decision trees, and case-based reasoning. The tool was tested and exhibited significant and consistent predictive ability across testing conditions. This type of tool has the potential to improve the efficiency and predictability of the formulation development process.

Effective integration of systems biology, biomarkers, biosimulation and modelling in streamlining drug development

The European Federation of Pharmaceutical Sciences (EUFEPS) has long established itself as leaders in the field of interdisciplinary meetings to discuss issues that face drug development. It's ever popular and well attended "Optimizing Drug Development" series has tackled numerous issues, most recent of which have been drug interactions, getting the dose right, candidate selection, and biomarkers (Lesko et al., 2000; Rolan et al., 2003; Stanski et al., 2005; Tucker et al., 2001). Over a course of 3 productive days, the meeting on "Effective Integration of Systems Biology, Biomarkers, Biosimulation and Modelling in Streamlining Drug Development", held in Basel, Switzerland was jointly sponsored by EUFEPS, European Biosimulation Network of Excellence (BioSim), American College of Clinical Pharmacology (ACCP), European Centre of Pharmaceutical Medicine (ECPM), and Swiss Society of Pharmaceutical Sciences (SGRW). The meeting was focused on emerging aspects related to the quantitative understanding of underlying pathways in drug discovery and clinical development, i.e. moving from an empirical to a model-based, quantitative drug development process. The objectives of the meeting were: (1) to highlight the current state of the art on biomarkers (as they relate to quantitative fingerprinting of disease), systems biology, modelling and simulation; (2) to illustrate the applications of these emerging tools in increasing the efficiency and productivity of new drug development by case examples; (3) to understand the gaps in the technology and organizational implementations in governance, and (4) allow an opportunity for cross-disciplinary interaction, i.e., scientists with more theoretical and technical modelling and simulation expertise of the BioSim network and researchers experienced in applying modelling and simulation techniques in day-to-day drug development were drawn together. This report summarizes the outcome from this meeting.

Getting the Dose Right: Report From the Tenth European Federation of Pharmaceutical Sciences (EUFEPS) Conference on Optimizing Drug Development

This report highlights the main points emerging from a meeting sponsored on "Getting the Dose Right" in clinical development, jointly sponsored by the European Federation of Pharmaceutical Sciences and the European Center of Pharmaceutical Medicine, as part of the Workshop Series on Frontiers in Drug Development, in Basel, Switzerland on December 9-12, 2002.

Positron emission tomography microdosing: a new concept with application in tracer and early clinical drug development

The realisation that new chemical entities under development as drug candidates fail in three of four cases in clinical trials, together with increased costs and increased demands of reducing preclinical animal experiments, have promoted concepts for improvement of early screening procedures in humans. Positron emission tomography (PET) is a non-invasive imaging technology, which makes it possible to determine drug distribution and concentration in vivo in man with the drug labelled with a positron-emitting radionuclide that does not change the biochemical properties. Recently, developments in the field of rapid synthesis of organic compounds labelled with positron-emitting radionuclides have allowed a substantial number of new drug candidates to be labelled and potentially used as probes in PET studies. Together, these factors led to the logical conclusion that early PET studies, performed with very low drug doses-PET-microdosing-could be included in the drug development process as one means for selection or rejection of compounds based on performance in vivo in man. Another important option of PET, to evaluate drug interaction with a target, utilising a PET tracer specific for this target, necessitates a more rapid development of such PET methodology and validations in humans. Since only very low amounts of drugs are used in PET-microdosing studies, the safety requirements should be reduced relative to the safety requirements needed for therapeutic doses. In the following, a methodological scrutinising of the concept is presented. A complete pre-clinical package including limited toxicity assessment is proposed as a base for the regulatory framework of the PET-microdosing concept.

Clinical biomarkers in drug discovery and development

Biomarkers enable the characterization of patient populations and quantitation of the extent to which new drugs reach intended targets, alter proposed pathophysiological mechanisms and achieve clinical outcomes. In genomics, the biomarker challenge is to identify unique molecular signatures in complex biological mixtures that can be unambiguously correlated to biological events in order to validate novel drug targets and predict drug response. Biomarkers can stratify patient populations or quantify drug benefit in primary prevention or disease-modification studies in poorly served areas such as neurodegeneration and cancer. Clinically useful biomarkers are required to inform regulatory and therapeutic decision making regarding candidate drugs and their indications in order to help bring new medicines to the right patients faster than they are today.

Early microdose drug studies in human volunteers can minimise animal testing: Proceedings of a workshop organised by Volunteers in Research and Testing

Testing the safety and efficacy of a successful human medicine involves many laboratory animals, which can sometimes be subjected to considerable suffering and distress. Also, it is necessary to extrapolate from the test species to humans. UK and European legislation requires that Replacement, Reduction and Refinement of animal procedures (the Three Rs) are implemented wherever possible. Over the last decade, there has been substantial progress with applying in vitro and in silico methods to both drug efficacy and safety testing. This paper is a report of the discussions and recommendations arising from a workshop on the role that might be played by human volunteer studies in the very early stages of drug development. The workshop was organised in November, 2001 by Volunteers in Research and Testing, a group of individuals in the UK which launched an initiative in 1994 to identify where and how human volunteers can participate safely in biomedical studies to replace laboratory animals. It was considered that conducting pre-Phase I very low dose human studies (sub-toxic and below the dose threshold for measurable pharmacological or clinical activity) could enable drug candidates to be assessed earlier for in vivo human pharmacokinetics and metabolism. Moreover, accelerator mass spectrometry (AMS), nuclear magnetic resonance (NMR) spectroscopy and positron emission tomography (PET) are potentially useful spectrometric and imaging methods that can be used in conjunction with such human studies. Some, limited animal tests would still be required before pre-Phase I microdose studies, to take account of the potential risk posed by completely novel chemicals. The workshop recommended that very early volunteer studies using microdoses should be introduced into the drug development process in a way that does not compromise volunteer safety or the scientific quality of the resulting safety data. This should improve the selection of drug candidates and also reduce the likelihood of later candidate failure, by providing in vivo human ADME data, especially for pharmacokinetics and metabolism, at an earlier stage in drug development than is currently the case.

Big physics, small doses: the use of AMS and PET in human microdosing of development drugs

The process of early clinical drug development has changed little over the past 20 years despite an up to 40% failure rate associated with inappropriate drug metabolism and pharmacokinetics of candidate molecules. A new method of obtaining human metabolism data known as microdosing has been developed which will permit smarter candidate selection by taking investigational drugs into humans earlier. Microdosing depends on the availability of two ultrasensitive 'big-physics' techniques: positron emission tomography (PET) can provide pharmacodynamic information, whereas accelerator mass spectrometry (AMS) provides pharmacokinetic information. Microdosing allows safer human studies as well as reducing the use of animals in preclinical toxicology.

Physiologically-based pharmacokinetic simulation modelling

Drug selection is now widely viewed as an important and relatively new, yet largely unsolved, bottleneck in the drug discovery and development process. In order to achieve an efficient selection process, high quality, rapid, predictive and correlative ADME models are required in order for them to be confidently used to support critical financial decisions. Systems that can be relied upon to accurately predict performance in humans have not existed, and decisions have been made using tools whose capabilities could not be verified until candidates went to clinical trial, leading to the high failure rates historically observed. However, with the sequencing of the human genome, advances in proteomics, the anticipation of the identification of a vastly greater number of potential targets for drug discovery, and the potential of pharmacogenomics to require individualized evaluation of drug kinetics as well as drug effects, there is an urgent need for rapid and accurately computed pharmacokinetic properties.

Utilisation of pharmacokinetic-pharmacodynamic modelling and simulation in regulatory decision-making

Modelling and simulation (M&S) play an important role in regulatory decision-making that affects both the public and industry. Technological advances in various fields related to drug development call for more focus on ways to optimise current drug development practices. Recognition of the potential of M&S by regulatory agencies inevitably has a substantial impact on drug development. The objective of the current review is to present the various regulatory initiatives for application of M&S to clinical drug development. The relevant parts of the various recommendations issued by the US Food and Drug Administration (FDA), via guidance documents and advisory committee meeting proceedings, are highlighted. Application of M&S to a variety of activities, such as integrating pharmacokinetic-pharmacodynamic knowledge across a new drug application and designing efficient trials, is discussed. Some of the challenges that pharmaceutical institutions currently face when implementing M&S projects, such as team structure, communication with regulators, training and time constraints, are also presented, and solutions are proposed.

Concentration-controlled or effect-controlled trials: useful alternatives to conventional dose-controlled trials?

Historically, dose-finding trials have been confirmatory in nature despite the fact that these trials represent an important and essential 'learning' phase in the drug development process. About 10 years ago 2 alternatives to the randomised dose-controlled trial (RDCT) were proposed as being more informative trial types. Controlling systemic drug exposure in order to improve efficiency of a trial forms the basis for the suggestion of a randomised concentration-controlled trial (RCCT). For the common instance where pharmacodynamic variability is larger than pharmacokinetic variability, the randomised effect-controlled trial (RECT), where patients are randomised to the effect of interest was suggested as even more informative. A survey of the literature shows that the RCCT has been sparsely applied and RECT not at all. For RCCT, the practical complications of carrying out the study seldom makes it the study type of choice. For RECT, the limited number of suitable situations for its application and the fact that the same effect is used for randomisation and analysis may explain the lack of applications. As a somewhat more favourable trial type, we suggest the randomised biomarker-controlled trial (RBCT), where patients are randomised to a certain value or range of a biomarker whereas the analysis is performed on another, clinically more relevant, effect. Although the RBCT has some attractive features, for example contributing to validation of a biomarker as a surrogate for clinical outcome, it is unlikely to be extensively used. Instead, the main shift from confirming to learning in dose-finding trials is coming from the incorporation of well-known learning components into the RDCT (e.g. sparse concentration measurements combined with population pharmacokinetic-pharmacodynamic, biomarker measurements and analysis of effect measures throughout the entire trial period).

Modeling and stimulation for clinical trial design involving a categorical response: a phase II case study with naratriptan

PURPOSE

The overall aim of the present study was to investigate retrospectively the feasibility and utility of model-based clinical trial simulation as applied to the clinical development of naratriptan with effect measured on a categorical scale.

METHODS

A PK-PD model for naratriptan was developed by using information gathered from previous naratriptan and sumatriptan preclinical and clinical trials. The phase IIa naratriptan data were used to check the PK-PD model in its ability to describe future data. A further PK-PD model was developed by using the phase IIa naratriptan data, and a phase IIb trial was designed by simulation with the use of Matlab. The design resulting from clinical trial simulation was compared with that derived by using D-optimal design.

RESULTS

The PK-PD model showed reasonable agreement with the data observed in the phase IIa naratriptan clinical trial. Clinical trial simulation resulted in a design with four or five arms at 0 mg, 2.5 and/or 5 mg, 10 mg, and 20 mg, PD measurements to be taken at 0, 2, and 4 or 6 h and at least 150 patients per arm. A sub-D-optimal design resulted in two dosing arms at 0 and 10 mg and PD measurements to be taken at 1 and 2 h.

CONCLUSIONS

Clinical trial simulation is a useful tool for the quantitative assessment of the influence of the controllable factors and is the only tool for the quantitative assessment of the uncontrollable factors on the power of a clinical trial.