Optimal design of clinical trials for drugs designed to slow the course of Alzheimer's disease

Study partners should be required in preclinical Alzheimer's disease trials

Background

In an effort to intervene earlier in Alzheimer’s disease (AD), clinical trials are testing promising candidate therapies in preclinical disease. Preclinical AD trial participants are cognitively normal, functionally independent, and autonomous decision-makers. Yet, like AD dementia trials, preclinical trials require dual enrollment of a participant and a knowledgeable informant, or study partner.

Main text

The requirement of dyadic enrollment is a barrier to recruitment and may present unique ethical challenges. Despite these limitations, the requirement should continue. Study partners may be essential to ensure participant safety and wellbeing, including overcoming distress related to biomarker disclosure and minimizing risk for catastrophic reactions and suicide. The requirement may maximize participant retention and ensure data integrity, including that study partners are the source of data that will ultimately instruct whether a new treatment has a clinical benefit and meaningful impact on the population health burden associated with AD. Finally, study partners are needed to ensure the scientific and clinical value of trials.

Conclusions

Preclinical AD will represent a new model of care, in which persons with no symptoms are informed of probable cognitive decline and eventual dementia. The rationale for early diagnosis in symptomatic AD is equally applicable in preclinical AD—to minimize risk, maximize quality of life, and ensure optimal planning and communication. Family members and other sources of support will likely be essential to the goals of this new model of care for preclinical AD patients and trials must instruct this clinical practice.

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Frequency and impact of informant replacement in Alzheimer disease research

Informants serve an essential role in Alzheimer disease research. Were an informant to be replaced during a longitudinal study, this could have negative implications. We used data from the National Alzheimer's Coordinating Center Uniform Data Set to examine the frequency of informant replacement among Alzheimer disease dementia participants, whether patient and informant characteristics were associated with replacement, and how replacement affected research outcome measures. Informant replacement was common (15.5%) and typically occurred after the first or the second research visit. Adult child (24%) and other (38%) informants were more frequently replaced than spouse informants (10%). Older spouse informant age and younger adult child informant age were associated with replacement. The between-visit change in Functional Assessment Questionnaire scores was greater in patients who replaced informants than in those with stable informants. Clinical Dementia Rating-Sum of Boxes, Functional Assessment Questionnaire, and Neuropsychiatric Inventory scores showed greater variability in between-visit change in patients who replaced informants compared with those with stable informants. These findings suggest that informant replacement is relatively common, may have implications to study analyses, and warrant further examination in the setting of clinical trials.

Why are spousal caregivers more prevalent than nonspousal caregivers as study partners in AD dementia clinical trials?

OBJECTIVES

Most Alzheimer disease (AD) caregivers are not spouses and yet most AD dementia trials enroll spousal study partners. This study examines the association between caregiver relationship to the patient and willingness to enroll in an AD clinical trial and how caregiver burden and research attitudes modify willingness.

DESIGN

Interviews with 103 AD caregivers who met criteria for ability to serve as a study partner.

RESULTS

A total of 54% of caregivers were spouses or domestic partners and the remaining were adult children. Willingness to enroll a patient in a clinical trial was associated with being a spouse [odds ratio (OR)=2.53, P=0.01], increasing age (OR=1.39, P=0.01), and increasing scores on the Research Attitudes Questionnaire (OR=1.39, P<0.001). No measures of caregiver burden or patient health were significant predictors of willingness. In multivariate models both research attitudes (OR=1.37, P<0.001) and being a spouse, as opposed to an adult child, (OR=2.06, P=0.048) were independently associated with willingness to participate.

CONCLUSIONS

Spousal caregivers had both a higher willingness to participate and a more positive attitude toward research. Caregiver burden had no association with willingness to participate. The strongest predictor of willingness was research attitudes.

Exploring the effects of coexisting amyloid in subcortical vascular cognitive impairment

Background

Mixed pathology, particularly Alzheimer’s disease with cerebrovascular lesions, is reported as the second most common cause of dementia. Research on mixed dementia typically includes people with a primary AD diagnosis and hence, little is known about the effects of co-existing amyloid pathology in people with vascular cognitive impairment (VCI). The purpose of this study was to understand whether individual differences in amyloid pathology might explain variations in cognitive impairment among individuals with clinical subcortical VCI (SVCI).

Methods

Twenty-two participants with SVCI completed an ¹¹C Pittsburgh compound B (PIB) position emission tomography (PET) scan to quantify global amyloid deposition. Cognitive function was measured using: 1) MOCA; 2) ADAS-Cog; 3) EXIT-25; and 4) specific executive processes including a) Digits Forward and Backwards Test, b) Stroop-Colour Word Test, and c) Trail Making Test. To assess the effect of amyloid deposition on cognitive function we conducted Pearson bivariate correlations to determine which cognitive measures to include in our regression models. Cognitive variables that were significantly correlated with PIB retention values were entered in a hierarchical multiple linear regression analysis to determine the unique effect of amyloid on cognitive function. We controlled for age, education, and ApoE ε4 status.

Results

Bivariate correlation results showed that PIB binding was significantly correlated with ADAS-Cog (p < 0.01) and MOCA (p < 0.01); increased PIB binding was associated with worse cognitive function on both cognitive measures. PIB binding was not significantly correlated with the EXIT-25 or with specific executive processes (p > 0.05).

Regression analyses controlling for age, education, and ApoE ε4 status indicated an independent association between PIB retention and the ADAS-Cog (adjusted R-square change of 15.0 %, Sig F Change = 0.03). PIB retention was also independently associated with MOCA scores (adjusted R-Square Change of 27.0 %, Sig F Change = 0.02).

Conclusion

We found that increased global amyloid deposition was significantly associated with greater memory and executive dysfunctions as measured by the ADAS-Cog and MOCA. Our findings point to the important role of co-existing amyloid deposition for cognitive function in those with a primary SVCI diagnosis. As such, therapeutic approaches targeting SVCI must consider the potential role of amyloid for the optimal care of those with mixed dementia.

Trial registration

NCT01027858

Reasons that prevent the inclusion of Alzheimer's disease patients in clinical trials

AIM

To assess reasons that prevent Alzheimer's disease (AD) patients from being included in clinical trials.

METHODS

In 2009, we reviewed the Lille Memory Clinic's case database to identify patients suitable for inclusion in four AD clinical trials. An initial selection was made on the basis of four criteria: (i) a diagnosis of AD (with or without white matter lesions [WML]), (ii) age, (iii) mini mental state examination (MMSE) score and (iv) symptomatic treatment of AD (cholinesterase inhibitors/memantine). Next, data on patients fulfilling these criteria were reviewed against all the inclusion/exclusion criteria for four clinical trials performed in 2009 at the Memory Clinic. Reasons for non-inclusion were analyzed.

RESULTS

Two hundred and five patients were selected according to the four initial criteria. Reasons for subsequently not including some of patients in clinical trials were abnormalities on MRI (56.9%, 88.9% of which were WML), unauthorized medication (37.3%), the lack of a study partner/informant (37.1%), the presence of a non-authorized disease (24.4%), contraindication to MRI (9%), a change in diagnosis over time (3.9%), visual/auditory impairments (2.9%), alcohol abuse (2%) and an insufficient educational level (1%).

CONCLUSION

A high proportion of AD patients presented with vascular abnormalities on MRI. This was not unexpected, since the patients were selected from the database and, as shown in epidemiologic studies, cerebrovascular diseases are frequently associated with AD. The presence of a study partner is essential for enabling a patient to participate in clinical trials because of the need to record reliably primary and secondary outcomes.

Combination therapy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive, degenerative brain disease. The mainstay of current management of patients with AD involves drugs that provide symptomatic therapy. Two classes of medications have been approved by the US FDA for the treatment of AD: the cholinesterase inhibitors (ChEIs), which include galantamine and rivastigmine (both approved for use in mild to moderate AD) and donepezil (approved for use in mild to severe AD); and the non-competitive NMDA receptor antagonist memantine (approved for use in moderate to severe AD). The European and Asian regulatory bodies have also approved ChEIs as monotherapy in mild to moderate AD. Future research directions are mostly focusing on disease modification and prevention. This review covers key studies of the efficacy, safety and tolerability of combination therapy in AD, defined as a combination of the NMDA receptor antagonist memantine with any of the ChEIs (donepezil, galantamine or rivastigmine) for the treatment of AD. Relevant studies were identified via a PubMed search. This review shows that combination therapy for AD seems to be safe, well tolerated and may represent the current gold standard for treatment of moderate to severe AD and possibly mild to moderate AD as well.

Power Calculations for Two-Wave, Change from Baseline to Follow-up Study Designs

Change in a quantitative trait is commonly employed as an endpoint in two-wave longitudinal studies. For example, early phase clinical trials often use two-wave designs with biomarker endpoints to confirm that a treatment affects the putative target treatment pathway before proceeding to larger scale clinical efficacy trials. Power calculations for such designs are straightforward if pilot data from longitudinal investigations of similar duration to the proposed study are available. Often longitudinal pilot data of similar duration are not available, and simplifying assumptions are used to calculate sample size from cross-sectional data, one standard approach being to use a formula based on variance estimated from cross sectional data and correlation estimates abstracted from the literature or inferred from experience with similar endpoints. An implicit assumption of this standard approach is that the variance of the quantitative trait is the same at baseline and follow-up. In practice, this assumption rarely holds, and sample size estimates by this standard formula can be dramatically anti-conservative. Even when longitudinal pilot data for estimating parameters required in sample size calculations are available, sample size calculations will be biased if the interval from baseline to follow-up is not of similar duration to that proposed for the study being designed. In this paper we characterize the magnitude of bias in sample size estimates when formula assumptions do not hold and derive alternative conservative formulas for sample size required to achieve nominal power.

Role of biochemical Alzheimer's disease biomarkers as end points in clinical trials

Amyloid-beta (Abeta) peptides, and total and phosphorylated tau are potential biomarkers for use in the development of treatments for Alzheimer's disease. Abeta(1-41) forms extracellular amyloid plaques, while tau and phospho-tau form intracellular neurofibrillary tangles in the brains of Alzheimer's disease patients. Plasma and cerebrospinal fluid concentrations of Abeta decreased following the clinical administration of gamma-secretase inhibitors and increased following the clinical administration of an anti-Abeta antibody. Therapies targeting Abeta decreased tau and phospho-tau concentrations in the cerebrospinal fluid. These biochemical biomarkers appear to be useful to establish therapeutic dosing for Phase III trials. Pivotal registration trials that rely on clinical measures as primary end points can utilize biochemical biomarkers as secondary outcomes indirectly measuring Alzheimer's disease pathology.

Current Alzheimer's disease clinical trials: methods and placebo outcomes

BACKGROUND

Eighteen-month-long randomized, placebo-controlled clinical trials are common for phase II and phase III drug development for Alzheimer's disease (AD). Yet, no 18-month trial has shown statistically significant outcomes favoring the test drug. We examined characteristics and underlying assumptions of these trials by assessing the placebo groups.

METHODS

We searched the clinicaltrials.gov registry for randomized, placebo-controlled clinical trials for AD of at least 18-month duration and extracted demographic, clinical, and trials characteristics, and change in main outcomes from the placebo groups. We obtained additional information from presentations, abstracts, publications, and sponsors.

RESULTS

Of 23 trials identified, 11 were completed and had baseline data available; nine had follow-up data available; 17 were phase III. General inclusion criteria were very similar except that minimum Mini-Mental State Examination (MMSE) scores varied from 12 to 20. Sample sizes ranged from 402 to 1,684 for phase III trials and 80 to 400 for phase II. Cholinesterase inhibitor use was from 53% to 100%, and memantine use was from 13.5% to 78%. The AD Assessment Scale-cognitive (ADAS-cog) was the co-primary outcome in all trials; and activities of daily living, global severity, or global change ratings were the other co-primaries. APOE epsilon4 genotype carriers ranged from 58% to 67%; mean baseline ADAS-cog was 17.8 to 24.2. ADAS-cog worsening in the placebo groups during 18 months ranged from 4.34 to 9.10, with standard deviations from 8.17 to 9.39, increasing during 18 months.

CONCLUSIONS

Inclusion criteria are essentially similar to earlier 6-month and 12-month trials in which cholinesterase inhibitors were not allowed, as were mean ADAS-cog rates of change. Yet increasing variability and relatively little change overall in the ADAS-cog placebo groups, eg, about 25% of patients do not worsen by more than 1 point, might make it more unlikely than previously assumed that a modestly effective drug can be reliably recognized, especially when the drug might work only to attenuate decline in function and not to improve function. These observations would be strengthened by pooling individual trials data, and pharmaceutical sponsors should participate in such efforts.

Long-term course and effectiveness of combination therapy in Alzheimer disease

OBJECTIVE

To compare the real-world clinical effectiveness and long-term clinical trajectory in patients with Alzheimer disease (AD) treated with combination (COMBO) therapy consisting of cholinesterase-inhibitor (CI) plus memantine (MEM) versus CI alone versus no treatment with either.

METHODS

Three hundred eighty-two subjects with probable AD underwent serial clinical evaluations at a memory disorders unit. Cognition was assessed by the Information-Memory-Concentration subscale of the Blessed Dementia Scale (BDS) and function was assessed by the Weintraub Activities of Daily Living Scale (ADL) at 6-month intervals. One hundred forty-four subjects received standard care without CI or MEM (NO-RX), 122 received CI monotherapy, and 116 received COMBO therapy with CI plus MEM. Mean follow-up was 30 months (4.1 visits) and mean cumulative medication treatment time was 22.5 months. Rates of decline were analyzed using mixed-effects regression models, and Cohen's d effect sizes were calculated annually for years 1 to 4.

RESULTS

Covarying for baseline scores, age, education, and duration of illness, the COMBO group had significantly lower mean annualized rates of deterioration in BDS and ADL scores compared with the CI (P<0.001; Cohen's dBDS=0.10-0.34 and dADL=0.23-0.46 at 1 to 2 y) and NO-RX groups (P<0.001; Cohen's dBDS=0.56-0.73 and dADL=0.32-0.48 at 1 to 2 y). For the COMBO group, Cohen's d effect sizes increased with treatment duration. Similar comparisons significantly favored the CI over the NO-RX group on the BDS.

CONCLUSIONS

COMBO therapy slows cognitive and functional decline in AD compared with CI monotherapy and no treatment. These benefits had small-to-medium effect sizes that increased with time on treatment and were sustained for years.

Partnership between academia and industry for drug discovery in Alzheimer's disease

Drug discovery has traditionally been almost exclusively the purview of pharmaceutical and biotechnology companies, whereas universities have focused on basic research. However, given the challenges involved in discovering and developing truly effective, symptomatic treatments and disease-modifying drugs for Alzheimer's disease, there is a need to reassess this simple division of labor. Whereas each sector is likely to retain a core interest and expertise at either end of the drug discovery spectrum, there is room for closer cooperation at the intersection of the for-profit and not-for-profit sectors. The Alzheimer's Association Research Roundtable convened a meeting of senior industry researchers and academic investigators to discuss this intersection and to assess the opportunity for closer partnership on Alzheimer's disease drug discovery and development.

Controversies in Alzheimer's disease drug development

Understanding of the pathophysiological basis of Alzheimer's disease (AD) is increasing rapidly and a variety of potential treatment modalities have emerged based on these improved mechanistic insights. The optimal way of proceeding with disease-modifying drug development remains to be clarified and controversies have emerged regarding the definition of Alzheimer's disease, the participation of mild cognitive impairment patients in clinical trials, the definition of disease modification, the potential impediments to satisfaction from patients receiving disease-modifying therapy, the importance of add-on therapy with symptomatic agents, the optimal clinical trial design to demonstrate disease modification, the best means of minimizing time spent in Phase II of drug development, the potential role of adaptive designs in clinical trials, the use of enrichment designs in clinical trials, the role of biomarkers in clinical trials, the treatment of advanced patients with disease-modifying agents, and distinctions between disease modification and disease prevention. The questions surrounding these issues must be resolved as disease-modifying therapies for AD are advanced. These controversies are framed and potential directions towards resolution described.

Current and future uses of neuroimaging for cognitively impaired patients

Technological advances have led to greater use of both structural and functional brain imaging to assist with the diagnosis of dementia for the increasing numbers of people with cognitive decline as they age. In current clinical practice, structural imaging (CT or MRI) is used to identify space-occupying lesions and stroke. Functional methods, such as PET scanning of glucose metabolism, could be used to differentiate Alzheimer's disease from frontotemporal dementia, which helps to guide clinicians in symptomatic treatment strategies. New neuroimaging methods that are currently being developed can measure specific neurotransmitter systems, amyloid plaque and tau tangle concentrations, and neuronal integrity and connectivity. Successful co-development of neuroimaging surrogate markers and preventive treatments might eventually lead to so-called brain-check scans for determining risk of cognitive decline, so that physicians can administer disease-modifying medications, vaccines, or other interventions to avoid future cognitive losses and to delay onset of disease.

A perspective on risks that impede development of drugs to modify the course of Alzheimer's disease: can they be reduced?

Discovery, development, and testing of new drugs with novel mechanisms and new indications are extremely risky. The number of new drugs introduced into clinical practice with new mechanisms and novel indications has not increased during recent years in spite of advances in biologic science. The sources of uncertainty leading to failure in drug development are discussed in three categories: biologic or target risk, clinical development uncertainty, and market uncertainty. Efforts to develop drugs that modify the course of Alzheimer's disease and/or delay the initial clinical manifestations of disease are subject to all three types of risk. Opportunities for government, academic researchers, advocacy groups, and the pharmaceutical industry to mitigate some of these risks and possibly speed the introduction of new therapies are mentioned.

New pathways in drug discovery for alzheimer’s disease

Specific treatments for Alzheimer's disease (AD) were first introduced in the 1990s using the acetyl-cholinesterase inhibitors. More recently, the N-methyl-D-aspartate (NMDA) antagonist memantine has become available. Although these treatments do provide a modest improvement in the cognitive abnormalities present in AD, their pharmacology is based on manipulation of neurotransmitter systems, and there is no compelling evidence that they interfere with the underlying pathogenic process. Pathologic and genetic data have led to the hypothesis that a peptide called amyloid ss(Abeta) plays a primary role in the pathophysiology of AD. Several investigational therapies targeting Abeta are now undergoing clinical trials. This paper reviews the available data regarding Abeta-directed therapies that are in the clinic and summarizes the approach to biomarkers and clinical trial designs that can provide evidence of modification of the underlying disease process.