Challenges in detecting disease modification in Parkinson's disease clinical trials

Despite the wealth of encouraging data from numerous compounds that demonstrate “neuroprotection” in pre-clinical studies of Parkinson's disease, and despite numerous clinical trials, to date, no intervention has been demonstrated to able to modify the course of disease progression. While this “failure to translate” is likely due to numerous factors including our incomplete understanding of the pathogenic mechanisms underlying PD together with excessive reliance on data from the toxin-based animal models of PD, here we will discuss the “structural issues” pertaining to inadequate clinical trial design, selection of inappropriate endpoints and poor patient selection which are often not addressed following failed disease modification trials. Future directions to overcome these challenges such as reducing the heterogeneity of patient cohorts, identifying and utilising a pre-diagnostic population, embracing a personalised medicine approach and utilising novel trial designs may be required to ultimately fulfil the goal of conclusively demonstrating evidence of disease modification.     

Sham neurosurgical procedures in clinical trials for neurodegenerative diseases: scientific and ethical considerations

There have been several recent scientific advances in gene-based and cell-based therapies that might translate into novel therapeutic approaches for neurodegenerative disorders. Such therapies might need to be directly delivered into the CNS, and complex scientific and ethical assessment will be needed to determine whether a sham neurosurgical arm should be included in clinical trials assessing these agents. We have developed a framework of points for investigators to consider when designing trials that involve direct delivery of a therapeutic agent to the CNS. The inclusion of a sham neurosurgical arm will be guided in part by the objectives of the clinical study (preliminary safety, optimisation, and feasibility vs preliminary efficacy vs confirmatory efficacy) and the need to minimise bias and confounds. Throughout the clinical development process, the perspectives of researchers, ethicists, and patients must be considered, and risks should be minimised whenever possible in a manner that is consistent with good trial design.     

Research to improve the quality of care for depression: alternatives to the simple randomized clinical trial

Recognition of gaps between evidence gained from mental health research and clinical practice in the community together with changes in treatment patterns and patient/provider preferences for care have led to interest in enhancements in the designs and analyses of clinical and community trials of mental health interventions. Gaps between clinical trials and community care include differences in populations and treatment strategies. To bridge these gaps, we propose enhancing the simple randomized trial with several different designs with the immediate aims of improving patient recruitment and adherence in psychiatric intervention studies thus bringing study designs more in line with clinical practice. The goals are to estimate treatment efficacy and effectiveness so that both internal and external validity are optimized. In this discussion, we address design and analytic issues with respect to a number of enhancements of the randomized trial design, including partial patient-provider preference designs, randomized encouragement and consent designs, fixed adaptive design, and random between- and within-patient adaptive designs. Each has advantages and disadvantages depending on the effect under investigation. Some of these enhancements, such as the fixed adaptive design, have begun to be implemented in effectiveness trials in mental health services research, but all are worthy of more attention.     

Methodological aspects of clinical trials in tinnitus: a proposal for an international standard

Chronic tinnitus is a common condition with a high burden of disease. While many different treatments are used in clinical practice, the evidence for the efficacy of these treatments is low and the variance of treatment response between individuals is high. This is most likely due to the great heterogeneity of tinnitus with respect to clinical features as well as underlying pathophysiological mechanisms. There is a clear need to find effective treatment options in tinnitus, however, clinical trials differ substantially with respect to methodological quality and design. Consequently, the conclusions that can be derived from these studies are limited and jeopardize comparison between studies. Here, we discuss our view of the most important aspects of trial design in clinical studies in tinnitus and make suggestions for an international methodological standard in tinnitus trials. We hope that the proposed methodological standard will stimulate scientific discussion and will help to improve the quality of trials in tinnitus.     

Anti-epileptogenic Clinical Trial Designs in Epilepsy: Issues and Options

Although trials with anti-seizure drugs have not shown anti-epileptogenic or disease-modifying activity in humans, new compounds are on the horizon that may require novel trial designs. We briefly discuss the unique challenges and the available options to identify innovative clinical trial designs that differentiate novel anti-epileptogenic and disease-modifying compounds, preferably early in phase II, from current anti-seizure drugs. The most important challenges of clinical testing of agents for epilepsy prevention include having sufficient preclinical evidence for a suitable agent to proceed with a human trial of an anti-epileptogenic drug, and to demonstrate the feasibility of doing such a trial. Major challenges in trial design to assess agents for disease modification include the choice of suitable study parameters, the identification of a high-risk study population, the type of control, the time and duration of treatment, and a feasible follow-up period.     

Strengthening clinical effectiveness trials: equipoise-stratified randomization.

As psychiatric practice patterns evolve to take advantage of the growing list of treatments with proven efficacy, research studies with broader aims will become increasingly important. Randomized trials may need to accommodate multiple treatment options. In completely randomized designs, patients are assigned at random to one of the options, requiring that patients and clinicians find each of the options acceptable. In "clinician's choice" designs, patients are randomized to a small number of broad strategies and the choice of specific option within the broad strategy is left up to the clinician. The clinician's choice design permits some scope to patient and clinician preferences, but sacrifices the ability to make randomization-based comparisons of specific options. We describe a new approach, which we call the "equipoise stratified" design, that merges the advantages and avoids the disadvantages of the other two designs for clinical trials. The three designs are contrasted, using the National Institute of Mental Health Sequenced Treatment Alternatives to Relieve Depression trial as an example.     

Prototype Antiepileptic Drug Clinical Development Plan

Antiepileptic drug (AED) development has been generally difficult owing to many factors: regulatory requirements for demonstration of efficacy and safety, subject availability, traditional trial designs, and physicians' beliefs about epilepsy and its treatment. The U.S. Food and Drug Administration (FDA) regulations require a new drug to be shown safe and effective for its intended use before it can be marketed. The unambiguous proof required is a formidable hurdle for AED development. We report a recent clinical development plan highlighting innovations in clinical trial design that have addressed these requirements, discuss alternative endpoints, and compare the results of various trial designs at various stages of development. This model clinical development plan includes trials relevant to all three clinically relevant contexts in which an AED might be used: as an adjunct to an existing regimen, as a substitution for much of an existing AED regimen, and as monotherapy.     

Apathy as a Treatment Target in Alzheimer's Disease: Implications for Clinical Trials

Apathy is one of the most prevalent, stable and persistent neuropsychiatric symptom across the neurocognitive disorders spectrum. Recent advances in understanding of phenomenology, neurobiology and intervention trials highlight apathy as an important target for clinical intervention. We conducted a comprehensive review and critical evaluation of recent advances to determine the evidence-based suggestions for future trial designs. This review focused on 4 key areas: 1) pre-dementia states; 2) assessment; 3) mechanisms/biomarkers and 4) treatment/intervention efficacy. Considerable progress has been made in understanding apathy as a treatment target and appreciating pharmacological and non-pharmacological apathy treatment interventions. Areas requiring greater investigation include: diagnostic procedures, symptom measurement, understanding the biological mechanisms/biomarkers of apathy, and a well-formed approach to the development of treatment strategies. A better understanding of the subdomains and biological mechanisms of apathy will advance apathy as a treatment target for clinical trials.     

Why do neuroprotective drugs work in animals but not humans?

Many neuroprotective agents that seemed promising in animal studies of ischemic brain injury prove to have no effect when tested in clinical trials, suggesting that fundamental elements of translational research require better definition. A number of modifications have led to improvements in preclinical and human studies since the earliest controlled trials failed to confirm hypotheses suggested by animal data. Continued re-evaluation and sharing of information derived from the laboratory bench or the patient's bedside should eventually lead to effective neuroprotection in acute stroke. Experimental data should be carefully studied to improve the quality of agents coming to clinical trials and to design trial phasing that effectively determines drug safety and efficacy. This article will examine preclinical modeling and its translation to prospective studies of acute stroke therapy and will focus on some potential solutions directed at clinical trial design.     

Comparative bioethics in bipolar and epilepsy research.

RATIONALE: AEDs are increasingly evaluated for efficacy in bipolar disorders utilizing double-blind, placebo-controlled, randomized clinical trials (RCTs) as required by the FDA. However, the risk to patients is under-estimated in trial design. Bipolar depression has a significant risk for suicide; bipolar episodes can lead to kindling with increased long-term morbidity; rapid regression may occur during the placebo phase or during dose ranging trials with resultant active suicide status. The associated risks mandate that the ethics of FDA-required protocols are addressed. METHOD: Comparative analysis and literature review of bipolar and epilepsy research designs. RESULTS: In psychiatry, all INDs require RCTs for approval. In epilepsy, AEDs are initially approved as add-on agents only. Once AEDs have demonstrated add-on efficacy, cross-over studies comparing active AEDs, sub-optimal dosing paradigms, new-onset, and pre-surgical inpatient placebo trials are utilized to prove efficacy of the new AED in monotherapy. Ethical considerations to avoid seizures and to minimize risks to subjects have led to newer clinical trial designs. CONCLUSIONS: The FDA initially requires add-on studies with new AEDs due to the risk of seizures during the placebo phase. The author argues that bipolar research warrants similar add-on studies to prove efficacy because the risk of suicide and increased long-term morbidity in the bipolar population is as significant as the risk of seizures in the epilepsy population. Although the number of patients needed to prove statistical efficacy would increase, the safety of such research would also markedly increase. The author further concludes that with the risk of suicide during bipolar research, ethical considerations require increased frequency of patient contact with a significant other co-signing the informed consent for research and serving as a contact for the coordinator.     

Measuring the efficacy of antiepileptic drugs.

Clinical trials of new antiepileptic drugs (AEDs) include regulatory studies aimed at demonstrating efficacy and reasonable safety, post-marketing open-open label studies and longer term outcome studies. Regulatory trials involve a carefully selected population of patients and are conducted under rigorously standardised conditions. Data from such studies cannot often be translated into clinical practice. Pragmatic post-marketing studies using flexible dosing schedules allow clinicians to better judge the utility of the new drug in a wider population of patients with epilepsy and decide the most appropriate dosing schedules. This paper discusses some of the issues surrounding the measurement of efficacy of new AEDs in both pre- and post-marketing phases of their development. All of the newer AEDs are initially used in patients with refractory partial seizures as adjunctive treatment. These trials are generally parallel-group studies although cross-over designs have been employed. The use of placebo-control is uncontroversial in this type of study. Efficacy endpoints are generally manipulations of seizure frequency on study drug compared to control. Global outcome measures and health related quality of life scores can also be used to measure efficacy. As the standard AEDs are associated with a high rate of seizure remission in patients who receive them as monotherapy, demonstration of superior efficacy of a new agent in a comparative trial will require large numbers of patients in a design that takes into account the natural history of treated epilepsy. Comparing investigational agents to a standard AED in an 'active-control' study with demonstration of equivalent efficacy would seem to be an acceptable way of assessing efficacy of new AEDs in this population. Some regulators, however, do not accept equivalence as proof of efficacy and insist on demonstration of superiority compared to a control. The use of placebo alone in the control group is ethically dubious. Several innovative study designs have, therefore, been used to satisfy regulatory requirements, while maintaining patient safety including withdrawal to monotherapy using high versus low dose comparators. Observational outcome studies provide the best opportunity of exploring the long-term utility of individual AEDs. Such studies largely follow standard clinical practice and need considerable time and resources. They can, however, yield valuable information about the effectiveness of AEDs in everyday clinical practice. Data from regulatory trials should be complemented by postmarketing studies and longer term studies of outcome to help clinicians decide the best way of utilising new AEDs and establishing their role in the therapeutic armamentarium.     

Alzheimer's therapeutics: translation of preclinical science to clinical drug development

Over the past three decades, significant progress has been made in understanding the neurobiology of Alzheimer's disease. In recent years, the first attempts to implement novel mechanism-based treatments brought rather disappointing results, with low, if any, drug efficacy and significant side effects. A discrepancy between our expectations based on preclinical models and the results of clinical trials calls for a revision of our theoretical views and questions every stage of translation-from how we model the disease to how we run clinical trials. In the following sections, we will use some specific examples of the therapeutics from acetylcholinesterase inhibitors to recent anti-Aβ immunization and γ-secretase inhibition to discuss whether preclinical studies could predict the limitations in efficacy and side effects that we were so disappointed to observe in recent clinical trials. We discuss ways to improve both the predictive validity of mouse models and the translation of knowledge between preclinical and clinical stages of drug development.     

The natural history of multiple sclerosis: implications for trial design.

The understanding of the natural history of multiple sclerosis has many implications for the design and interpretation of randomized controlled trials. Selection criteria, patient stratification, outcome measurements, and definitions of treatment failure can influence randomized controlled trial results and limit comparisons among trials. The focus of future studies should shift from short-term determinations of efficacy to definitive evaluations of long-term effectiveness. This will require novel investigative strategies such as the use of historic controls derived from natural history studies.     

Translational research in stroke: Taking advances in the pathophysiology and treatment of stroke from the experimental setting to clinical trials

Many advances have occurred regarding an increased understanding of the basic pathophysiology of ischemic brain injury that could lead to enhanced therapy for this disorder. Among the more important basic science advances are enhanced knowledge of the components of the ischemic cascade, the phenomenon of ischemic preconditioning, the potential relevance of hibernation, studies on gene expression in ischemic tissue, and imaging identification of the ischemic penumbra. The large number of unsuccessful prior clinical trials with a wide range of purported acute stroke therapies has provided many insights and lessons regarding how to perform better trials in the future. Translating these basic science and clinical trial design advances into effective and safe therapies will require increased interaction and cooperation between basic scientists and clinical researchers.     

Statistical approaches to effectiveness measurement and outcome-driven re-randomizations in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) studies

The design of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) schizophrenia and Alzheimer's disease studies pose several statistical challenges, including issues related to performing multiple comparisons, defining effectiveness outcomes, and collecting and analyzing data from a design with multiple outcome-driven re-randomizations. We discuss the CATIE strategy for addressing many hypotheses within the context of one clinical trial while controlling the overall type I error rate. We provide motivation for the use of two effectiveness outcomes: time to all-cause discontinuation and composite endpoints that combine outcomes from multiple domains, such as efficacy, safety, cost-effectiveness, and quality of life. Methods for statistical analysis of an outcome-driven re-randomization trial are compared and evaluated. We describe analysis within each phase, analysis based on the first randomization or treatment algorithms, and repeated measures modeling. Finally, strategies are described for designing an electronic data collection system for trials with repeated outcome-driven re-randomizations.     

Clinical Trials of Investigational Antiepileptic Drugs: Monotherapy Designs

The standard designs for safety and efficacy trials of investigational antiepileptic drugs are placebo-controlled, add-on trials and active control equivalence studies. These designs, motivated by medical ethics, have serious evidential limitations. Add-on trials are frequently criticized as insensitive and difficult to interpret in the presence of drug interactions; active control equivalence studies are not probative of test drug activity. As an alternative, we describe two trial designs: a placebo-control design with inpatients who in undergoing a presurgery seizure evaluation have had all antiepileptic drugs discontinued; and an active-control design aimed at showing the test drug superior to the control treatment, thus avoiding the interpretational difficulties of no-difference outcomes. A critical feature of these new designs is the limitation of subject exposure to unacceptable treatments. This is accomplished through protocol criteria--corresponding to therapeutic failure--which both terminate a subject's trial participation and form the basis of efficacy comparisons.     

Accelerating the development of improved analgesic treatments: the ACTION public-private partnership

There has been considerable progress identifying pathophysiologic mechanisms of neuropathic pain, but analgesic medications with improved efficacy, safety, and tolerability still represent an unmet public health need. Numerous treatments examined in recent randomized clinical trials (RCTs) have failed to show efficacy for neuropathic pain, including treatments that had previously demonstrated efficacy. This suggests that at least some negative results reflect limited assay sensitivity of RCTs to distinguish efficacious treatments from placebo. Patient characteristics, clinical trial research designs and methods, outcome measures, approaches to data analysis, and statistical power may all play a role in accounting for difficulties in demonstrating the benefits of efficacious analgesic treatments vs placebo. The identification of specific clinical trial characteristics associated with assay sensitivity in existing data has the potential to provide an evidence-based approach to the design of analgesic clinical trials. The US Food and Drug Administration recently launched the Analgesic Clinical Trial Innovations, Opportunities, and Networks (ACTION) public-private partnership, which is designed to facilitate the discovery and development of analgesics with improved efficacy, safety, and tolerability for acute and chronic pain conditions. ACTION will establish a collaborative effort to prioritize research objectives, develop a standardized analgesic database platform, and conduct methodologically focused studies to increase the assay sensitivity and efficiency of analgesic clinical trials. The results of these activities have the potential to inform and accelerate the development of improved pain management interventions of all types, not just pharmacologic treatments.     

Methodological issues in developing new acute treatments for patients with bipolar illness.

One important aim of the recent reorganization of the National Institute of Mental Health (NIMH) is to streamline the development of new treatments for patients with severe mental illnesses, such as bipolar disorder. Researching new treatments for patients with bipolar disorder presents specific problems not readily addressed by traditional efficacy trial methodologies that aim to maximize internal validity. This article reexamines several assumptions that have guided the design of these efficacy trials but that also create obstacles for studies of bipolar disorder and suggests potential solutions. This article draws on literature from neurology and psychiatry and discussions at a MacArthur Foundation-sponsored Conference on Longitudinal Methodology in 1992 (David J. Kupfer, M.D., Chair), which brought together investigators to consider alternative designs for patients with severe and persistent mental illness. In addition, we benefited from discussions at two NIMH-sponsored conferences, one held in 1989 (Prien and Potter 1990) and the other in 1994 (Prien and Rush 1996), at which investigators and methodologists discussed issues surrounding the development and conduct of informative efficacy trials for patients with bipolar disorder. Based on these discussions and recent literature reviews, we 1) outline common problems in the development and evaluation of effective acute treatments for bipolar disorder and 2) suggest possible solutions to these impediments. We also discuss alternative designs by which to build a sequence of acute treatment studies from which efficacy, safety, and the comparative value of different treatments can be established.     

Perspectives on molecular targeted therapies and clinical trials for neurodegenerative diseases

Recent advancements in neurobiology have provided increasing insights into the pathophysiology of neurodegenerative diseases, and opened doors to the development of molecular targeted therapies. Although many compounds showed positive results in animal studies, there is almost no drug for which the efficacy has been confirmed in clinical trials. This failure reflects a number of unsolved problems: limited knowledge of the exact pathways of neuron loss; safety and delivery issues of compounds; lack of established animal models that faithfully recapitulate human pathology; lack of validated, sensitive outcome measures; and limited tools to diagnose pre-symptomatic patients. To investigate the efficacy of potential disease modifying agents with limited financial and patient resources, the efficiency of both basic and clinical studies should be improved by integrated approaches. The reproduction of positive results from animal experiments that analyse the efficacy of compounds at symptomatic stages is needed to improve the credibility of preclinical studies. To effectuate proof of concept processes, novel designs of phase 2 clinical trials, such as the futility study, are being developed. Given the modest effects of molecular targeted therapies in human, it is necessary to explore clinical outcome measures that are resistant to variability, subjectivity and placebo. Furthermore, there is an increasing need for testing interventions before the onset of symptoms. Analyses of natural histories of biological and neurophysiological markers may provide indispensable information for designing such preventive trials. As it is now clear that conventional approaches are not necessarily appropriate for the development of molecular targeted therapies, both basic and clinical studies require conceptual innovation.