Controversies in Alzheimer's disease drug development

Complement as a powerful "influencer" in the brain during development, adulthood and neurological disorders

The complement system was long considered as only a powerful effector arm of the immune system that, while critically protective, could lead to inflammation and cell death if overactivated, even in the central nervous system (CNS). However, in the past decade it has been recognized as playing critical roles in key physiological processes in the CNS, including neurogenesis and synaptic remodeling in the developing and adult brain. Inherent in these processes are the interactions with cells in the brain, and the cascade of interactions and functional consequences that ensue. As a result, investigations of therapeutic approaches for both suppressing excessive complement driven neurotoxicity and aberrant sculpting of neuronal circuits, require broad (and deep) knowledge of the functional activities of multiple components of this highly evolved and regulated system to avoid unintended negative consequences in the clinic. Advances in basic science are beginning to provide a roadmap for translation to therapeutics, with both small molecule and biologics. Here, we present examples of the critical roles of proper complement function in the development and sculpting of the nervous system, and in enabling rapid protection from infection and clearance of dying cells. Microglia are highlighted as important command centers that integrate signals from the complement system and other innate sensors that are programed to provide support and protection, but that direct detrimental responses to aberrant activation and/or regulation of the system. Finally, we present promising research areas that may lead to effective and precision strategies for complement targeted interventions to promote neurological health.

Evaluation of the efficacy, safety and tolerability of orally administered BI 409306, a novel phosphodiesterase type 9 inhibitor, in two randomised controlled phase II studies in patients with prodromal and mild Alzheimer's disease

Background

There are currently no approved treatments for the prodromal stage of Alzheimer’s disease (AD). Approved symptomatic treatments for mild-to-moderate AD include acetylcholinesterase inhibitors and memantine, but more efficacious treatments are needed. BI 409306 is a potent and selective phosphodiesterase 9 inhibitor assessed for the symptomatic treatment of AD. Efficacy and safety of BI 409306 was analysed in two phase II proof-of-concept clinical trials in cognitive impairment associated with prodromal AD (study 1) and mild AD (study 2).

Methods

Two multicentre, double-blind, parallel-group, randomised controlled phase II studies were conducted (North America/Europe). Following study run-in, eligible subjects were randomised to one of four oral doses of BI 409306 (10–50 mg daily) or placebo (1:1:1:1:2 ratio) for 12 weeks. The primary efficacy endpoint was the change from baseline in Neuropsychological Test Battery (NTB) total z-score after 12 weeks’ treatment. Secondary efficacy assessments included change from baseline in Clinical Dementia Rating scale-Sum of Boxes (CDR-SB), Alzheimer’s Disease Assessment Scale-cognitive subscale (ADAS-Cog11) and Alzheimer’s Disease Cooperative Study-Activities of Daily Living scale (ADCS-ADL; mild cognitive impairment [MCI] version for prodromal patients) after 12 weeks’ treatment. Safety and tolerability assessments included adverse event reporting and vital sign monitoring. Change from baseline in NTB total z-score (primary endpoint) and CDR-SB were analysed using the restricted maximum likelihood-based mixed-effects model with repeated measurement. An analysis of covariance model was used to assess other secondary endpoints.

Results

Four hundred fifty-seven patients were randomised (study 1 for prodromal AD, N = 128; study 2 for mild AD, N = 329); 427 (93.4%) completed.

A prespecified pooled analysis of the primary endpoint revealed no significant changes in NTB total composite z-score at week 12 in the BI 409306 treatment groups compared with placebo, with similar findings observed in the individual studies. The analysis of all secondary endpoints, including pooled analysis of CDR-SB and ADAS-Cog11, ADCS-MCI-ADL (study 1), ADCS-ADL (study 2), also gave no indication of a treatment benefit for BI 409306, compared with placebo. BI 409306 was well tolerated.

Conclusions

Overall, the data do not demonstrate efficacy of BI 409306 in improving cognition in patients with prodromal and mild AD. BI 409306 is well tolerated.

Trial registration

ClinicalTrials.gov, NCT02240693 and NCT02337907. Registered 15 September 2014 and 09 January 2015, respectively.

Static and Dynamic Cognitive Reserve Proxy Measures: Interactions with Alzheimer's Disease Neuropathology and Cognition

OBJECTIVE

Years of education are the most common proxy for measuring cognitive reserve (CR) when assessing the relationship between Alzheimer's disease (AD) neuropathology and cognition. However, years of education may be limited as a CR proxy given that it represents a specific timeframe in early life and is static. Studies suggest that measures of intellectual function provide a dynamic estimate of CR that is superior to years of education since it captures the effect of continued learning over time. The present study determined whether dynamic measures of CR were better predictors of episodic memory and executive function in the presence of AD pathology than a static measure of CR.

METHODS

Subjects examined died with a pre-mortem clinical diagnosis of no cognitive impaired, mild cognitive impairment and mild to moderate AD. CERAD and Braak stage were used to stratify the sample by AD pathology severity. Linear regression analyses using CR by CERAD and CR by Braak stage interaction terms were used to determine whether Extended Range Vocabulary Test (ERVT) scores or years of education were significantly associated with episodic memory composite (EMC) and executive function composite (EFC) performance. All models were adjusted for clinical diagnosis, age at death, gender, APOE e4 carrier status and Braak stage.

RESULTS

For episodic memory, years of education by CERAD interaction were not statistically significant (β=-0.01, SE=0.01, p=0.53). By contrast, ERVT interaction with CERAD diagnosis was statistically significant (β=-0.03, SE=0.01, p=0.004). Among the models using Braak stages, none of the CR by pathology interactions were associated with EMC or EFC.

CONCLUSION

Results suggest that a dynamic rather than a static measure is a better indicator of CR and that the relationship between CR and cognition is dependent upon the severity of select AD criteria.

Post Hoc Analyses of ApoE Genotype-Defined Subgroups in Clinical Trials

BACKGROUND

Many post hoc analyses of clinical trials in Alzheimer's disease (AD) and mild cognitive impairment (MCI) are in small Phase 2 trials. Subject heterogeneity may lead to statistically significant post hoc results that cannot be replicated in larger follow-up studies.

OBJECTIVE

We investigated the extent of this problem using simulation studies mimicking current trial methods with post hoc analyses based on ApoE4 carrier status.

METHODS

We used a meta-database of 24 studies, including 3,574 subjects with mild AD and 1,171 subjects with MCI/prodromal AD, to simulate clinical trial scenarios. Post hoc analyses examined if rates of progression on the Alzheimer's Disease Assessment Scale-cognitive (ADAS-cog) differed between ApoE4 carriers and non-carriers.

RESULTS

Across studies, ApoE4 carriers were younger and had lower baseline scores, greater rates of progression, and greater variability on the ADAS-cog. Up to 18% of post hoc analyses for 18-month trials in AD showed greater rates of progression for ApoE4 non-carriers that were statistically significant but unlikely to be confirmed in follow-up studies. The frequency of erroneous conclusions dropped below 3% with trials of 100 subjects per arm. In MCI, rates of statistically significant differences with greater progression in ApoE4 non-carriers remained below 3% unless sample sizes were below 25 subjects per arm.

CONCLUSIONS

Statistically significant differences for ApoE4 in post hoc analyses often reflect heterogeneity among small samples rather than true differential effect among ApoE4 subtypes. Such analyses must be viewed cautiously. ApoE genotype should be incorporated into the design stage to minimize erroneous conclusions.

Alzheimer's drug-development pipeline: 2016

Background

Alzheimer's disease (AD) is growing in frequency and new therapies are urgently needed.

Methods

We assessed clinicaltrials.gov (accessed 1-4-2016) to determine the number and characteristics of trials in phase I, phase II, and phase III for treatment of AD.

Results

There are currently 24 agents in 36 trials in phase III of AD drug development. Seven of these 24 agents are symptomatic cognitive-enhancing compounds, and 17 are disease-modifying treatments (DMTs). Most DMTs address amyloid-related targets (76%). There are 45 agents in phase II being assessed in 52 clinical trials. Phase II trials include 30 DMTs, with 26 small molecules and 4 immunotherapies. There are 24 agents in the first phase of AD drug development.

Discussion

Amyloid is the principal target of late-stage development programs. There are relatively few agents in clinical trials for AD suggesting a need to amplify the drug discovery ecosystem.

The M1 Muscarinic Positive Allosteric Modulator PQCA Improves Performance on Translatable Tests of Memory and Attention in Rhesus Monkeys

Improved treatment of Alzheimer disease (AD) is a significant unmet medical need that is becoming even more critical given the rise in the number of patients and the substantial economic burden. The current standards of care, acetylcholinesterase inhibitors (AChEIs), are hindered by gastrointestinal side effects owing to their nonselective activation of muscarinic and nicotinic receptors. Recently, the highly selective M1 positive allosteric modulator PQCA (1-((4-cyano-4-(pyridine-2-yl)piperidin-1-yl)methyl-4-oxo-4 H-quinolizine-3-carboxylic acid) has been demonstrated to improve cognition in a variety of rodent and nonhuman primate cognition models without producing significant gastrointestinal side effects. Here we describe the effect of PQCA and the AChEI donepezil on two clinically relevant and highly translatable touchscreen cognition tasks in nonhuman primates: paired-associates learning (PAL) and the continuous-performance task (CPT). Blockade of muscarinic signaling by scopolamine produced significant impairments in both PAL and CPT. PQCA and donepezil attenuated the scopolamine deficits in both tasks, and the action of these two compounds was similar in magnitude. In addition, the combination of subeffective doses of PQCA and donepezil enhanced PAL performance. These results further suggest that M1-positive allosteric modulators, either as monotherapy or as an add-on to current standards of care, have potential to reduce the cognitive deficits associated with AD.

Using baseline cognitive severity for enriching Alzheimer's disease clinical trials: How does Mini-Mental State Examination predict rate of change?

Background

Post hoc analyses from clinical trials in Alzheimer's disease (AD) suggest that more cognitively impaired participants respond differently from less impaired on cognitive outcomes. We examined pooled clinical trials data to assess the utility of enriching trials using baseline cognition.

Methods

We included 2882 participants with mild to moderate AD in seven studies from a meta-database. We used mixed effects models to estimate the rate of decline in Alzheimer's disease Assessment Scale-cognitive (ADAS-Cog) scores among Mini-Mental State Examination (MMSE) groups.

Findings

Baseline MMSE category was associated with baseline scores and rate of decline on the ADAS-Cog, adjusting for age and education (both P < .001). Greater baseline cognitive impairment was associated with more rapid progression.

Interpretations

Although we found significant differences in rate of decline, most differences between individuals were from baseline ADAS-Cog values. Since enrichment based on MMSE would reduce the recruitment pool while adding only slightly to detecting differences in rate of progression, it is not advised.

Sensitivity to change and prediction of global change for the Alzheimer's Questionnaire

INTRODUCTION

Longitudinal assessment of cognitive decline in amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD) often involves the use of both informant-based and objective cognitive assessments. As efforts have focused on identifying individuals in pre-clinical stages, instruments that are sensitive to subtle cognitive changes are needed. The Alzheimer's Questionnaire (AQ) has demonstrated high sensitivity and specificity in identifying aMCI and AD; however its ability to measure longitudinal change has not been assessed. The aims of this study are to assess the sensitivity to change of the AQ and to determine whether the AQ predicts change in global cognition and function in cognitively normal (CN), aMCI, and AD subjects.

METHODS

Data from 202 individuals participating in a brain and body donation program were utilized for this study (101 CN, 62 aMCI, 39 AD). AD and aMCI individuals were matched on age, education, and gender to CN individuals. Sensitivity to change of the AQ was assessed in addition to the AQ's ability to predict change in global cognition and function. The Mini Mental State Exam (MMSE) and Functional Activities Questionnaire (FAQ) were used as gold standard comparisons of cognition and function. Sample size calculations for a 25% treatment effect were also carried out for all three groups.

RESULTS

The AQ demonstrated small sensitivity to change in the aMCI and CN groups (d = 0.33, d = 0.23, respectively) and moderate sensitivity to change in the AD group (d = 0.43). The AQ was associated with increases in the Clinical Dementia Rating Global Score (OR = 1.20 (1.09, 1.32), P <0.001). Sample size calculations found that the AQ would require substantially fewer subjects than the MMSE given a 25% treatment effect.

CONCLUSIONS

Although the AQ demonstrated small sensitivity to change in aMCI and CN individuals in terms of effect size, the AQ may be superior to objective cognitive tests in terms of required sample size for a clinical trial. As clinicians and researchers continue to identify and treat individuals in earlier stages of AD, there is a need for instruments that are sensitive to cognitive changes in these earlier stages.

Neuropathologic correlates of trial-related instruments for Alzheimer's disease

To advance disease-modifying therapies, it is critical to understand the relationship between the neuropathological changes of Alzheimer's Disease (AD) and the clinical measures used in therapeutic trials. We reviewed neuropathologically proven cases of AD from the National Alzheimer's Coordinating Center (NACC) and examined correlations between neuropathological changes and clinical-trial related instruments collected as part of the Uniform Dataset (UDS). We explored the relationships between neurofibrillary tangles, neuritic plaques, and total pathology burden with immediate and delayed recall, Clinical Dementia Rating-Sum of Boxes, Functional Activity Questionnaire, Neuropsychiatric Inventory Questionnaire, and Mini-Mental State Examination scores. 169 patients in NACC database had appropriate neuropathological and clinical data. All instruments correlated highly with neuritic plaques, Braak staging, and total pathology. Correlation coefficients for the relationships were relatively modest, suggesting that the pathologic burden examined accounts for between 13 and 40% of the variance of each of the instruments assessed. We conclude that there is a strong correlation between clinical trial-related measures and neuropathology identified at autopsy in AD. The amount of variance explained by the pathology is limited and other factors, both disease- and measurement-related, contribute to the variability observed in clinical measurements.

Economic analysis of opportunities to accelerate Alzheimer's disease research and development

The development of disease-modifying treatments for Alzheimer's disease (AD) faces a number of barriers. Among these are the lack of surrogate biomarkers, the exceptional size and duration of clinical trials, difficulties in identifying appropriate populations for clinical trials, and the limitations of monotherapies in addressing such a complex multifactorial disease. This study sets out to first estimate the consequent impact on the expected cost of developing disease-modifying treatments for AD and then to estimate the potential benefits of bringing together industry, academic, and government stakeholders to co-invest in, for example, developing better biomarkers and cognitive assessment tools, building out advanced registries and clinical trial-readiness cohorts, and establishing clinical trial platforms to investigate combinations of candidate drugs and biomarkers from the portfolios of multiple companies. Estimates based on interviews with experts on AD research and development suggest that the cost of one new drug is now $5.7 billion (95% confidence interval (CI) $3.7-9.5 billion) and could be reduced to $2.0 billion (95% CI $1.5-2.9 billion). The associated acceleration in the arrival of disease-modifying treatments could reduce the number of case years of dementia by 7.0 million (95% CI 4.4-9.4 million) in the United States from 2025 through 2040.

Is AD a homogeneous nosologic entity? Yes

Alzheimer's disease (AD), the most prevalent disorder causing dementia, is considered a neurodegenerative disease. The cause is unknown for over 95% of the cases who do not have a genetic disease and the pathogenetic mechanisms are incompletely known. The main hypotheses to explain the lesions and the decline in brain functioning are the amyloid cascade and the abnormal phosphorylation of tau protein, which are the grounds for the typical AD lesions: senile plaques and neurofibrillary tangles. Some observations, however, indicate that the relationship between those mechanisms, structural changes, and cognitive state is not univocal or specific. On the other hand, age at onset and clinical presentation are quite variable, as is the duration of the disease. As a matter of fact, a wide differential diagnosis may be necessary and, in the absence of a reliable diagnostic marker, the adscription to widely accepted criteria is compulsory. Nonetheless, the accuracy of the usually applied diagnostic criteria is around 80-90%. From a nosologic perspective, the current clinicopathological concept of AD, with unknown etiology, hypothetically variable pathogenesis, and wide clinical variability, justifies considering AD in a comprehensive manner. Therefore, a disorder primarily affecting structures in medial temporal lobe, with accumulation of amyloid β and abnormal tau, neuritic plaques and tangles, progressive loss of memory and/or other cognitive deficits, ultimately resulting in dementia should be classified as AD. Hopefully, scientific advances (in genetics, proteomics, metabolomics, etc.) will allow a more precise definition of the disease in the future.

Novel approaches to incorporating pharmacoeconomic studies into phase III clinical trials for Alzheimer's disease

The societal and individual costs of Alzheimer's disease are significant, worldwide. As the world ages, these costs are increasing rapidly, while health systems face finite budgets. As a result, many regulators and payers will require or at least consider phase III cost-effectiveness data (in addition to safety and efficacy data) for drug approval and reimbursement, increasing the risks and costs of drug development. Incorporating pharmacoeconomic studies in phase III clinical trials for Alzheimer's disease presents a number of challenges. We propose several specific suggestions to improve the design of pharmacoeconomic studies in phase III clinical trials. We propose that acute episodes of care are key outcome measures for pharmacoeconomic studies. To improve the possibility of detecting a pharmacoeconomic impact in phase III, we suggest several strategies including; study designs for enrichment of pharmacoeconomic outcomes that include co-morbidity of patients; reducing variability of care that can affect pharmacoeconomic outcomes through standardized care management; employing administrative claims data to better capture meaningful pharmacoeconomic data; and extending clinical trials in open label follow-up periods in which pharmacoeconomic data are captured electronically by administrative claims. Specific aspects of power analysis for pharmacoeconomic studies are presented. The particular pharmacoeconomic challenges caused by the use of biomarkers in clinical trials, the increasing use of multinational studies, and the pharmacoeconomic challenges presented by biologicals in development for Alzheimer's disease are discussed. In summary, since we are entering an era in which pharmacoeconomic studies will be essential in drug development for supporting regulatory approval, payor reimbursement and integration of new therapies into clinical care, we must consider the design and incorporation of pharmacoeconomic studies in phase III clinical trials more seriously and more creatively.